Handbook of Climate Change Mitigation [1 ed.] 9781441979902, 9781441979919

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Handbook of Climate Change Mitigation

Wei-Yin Chen, John Seiner, Toshio Suzuki and Maximilian Lackner (Eds.)

Handbook of Climate Change Mitigation

With 586 figures and 205 tables

Editors Wei-Yin Chen Department of Chemical Engineering University of Mississippi Mississippi USA John Seiner National Center for Physical Acoustics University of Mississippi Mississippi USA Toshio Suzuki National Institute of Advanced Industrial Science and Technology (AIST) Nagoya Japan Maximilian Lackner The Vienna University of Technology (TU Vienna) Wien Austria

ISBN 978-1-4419-7990-2 e-ISBN 978-1-4419-7991-9 DOI 10.1007/978-1-4419-7991-9 Springer New York Dordrecht Heidelberg London Library of Congress Control Number: 2011938953 © Springer ScienceþBusiness Media, LLC 2012 All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer Science+Business Media, LLC, 233 Spring Street, New York, NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. Printed on acid-free paper Springer is part of Springer ScienceþBusiness Media (www.springer.com)

This Handbook is dedicated to two colleagues of ours, Dr. John M. ‘‘Jack’’ Seiner and Dr. Marie W. Wooten. Both of them were devoted educators and researchers, with special interests in activities surrounding climate change issues, including this Handbook. It is still a great shock to us that they abruptly left us within a tragic six-day period in fall 2010.

Dr. John M. ‘‘Jack’’ Seiner, 66, director of the Jamie Whitten National Center for Physical Acoustics (NCPA) at the University of Mississippi, died October 31, 2010 in Oxford, Mississippi. For over 30 years, he studied jet noise and how to reduce it. Jack spent the first 25 years of his career in jet noise research at the National Aeronautics and Space Administration’s Langley Research Center in Hampton, Va., first as a research engineer in the Noise Control Branch, then as leader of the Jet Noise Team of the Aeroacoustics Branch. While at NASA, he conducted research that not only earned the respect of his colleagues but also more than 20 awards for his achieveJohn M. ‘‘Jack’’ Seiner ments, leadership, and service. After retiring from NASA in 1998, Seiner moved to Oxford to become NCPA’s associate director of applied research. At Ole Miss, he worked to build NCPA’s facilities and a graduate program in aeroacoustics in conjunction with the Department of Mechanical Engineering. His aeroacoustics research group at NCPA conducted a variety of research projects sponsored by the United States Army, Navy and Air Force, and Jack was elevated to NCPA director in 2009. In his 12 years at NCPA, Seiner was responsible for more than $43 million in contracts and grants. ‘‘Jack had an extraordinary ability to use sophisticated science to develop practical solutions to important real-world problems,’’ said Dr. Alice Clark, UM’s vice chancellor for research and sponsored programs. ‘‘He was, throughout his career, a very highly regarded scientist, a committed educator and an enthusiast for innovation and discovery’’. Jack was enthusiastic about the sustainable energy and environmental activities at the University of Mississippi that were initiated in the fall 2007. He constantly offered his advice on the development of new courses, research collaborations, outreach programs, and was an invaluable editor of this handbook. His tireless efforts have no doubt profoundly influenced both faculty and students. When we offered the climate change class for the first time at the University of Mississippi, he not only gave an informative lecture on energy efficiency in transportation systems, but also voluntarily served as a judge for students’ presentations. His lecture slides are posted on the web (see Chapter 54), and his partially finished chapter (see Chapter 37) on this topic was completed by two of us (Maximilian Lackner and Wei-Yin Chen). Jack is survived by his wife of 42 years, Mary Lois Seiner; daughters, Pamela Hart (Jason), Karena Seiner and Sandra Crouse (Matt); son, John M. Seiner Jr. (Jo); brother, George Seiner (Faye); sister, Marie Fleming (Bob); six grandchildren; and many nieces and nephews.

Dr. Marie Wright Wooten, 53, passed away tragically November 5, 2010. She was Dean and Professor of the College of Sciences and Mathematics (COSAM) at Auburn University. Marie grew up in the ‘‘Land Between the Lakes’’ in northwestern Tennessee where she developed a strong interest in nature and science; her childhood heroes were Eleanor Roosevelt, Madame Curie, and Amelia Earhart, which formed the basis for her later passion in advancing opportunities for women in science, technology, engineering, and mathematics. Marie earned a B.S. in microbiology at the University of Memphis in 1979 and a Ph.D. in molecular biology Marie W. Wooten at Texas Woman’s University in 1983. Marie honed her research skills as a post-doctoral associate at the Medical College of Georgia and the Cold Spring Harbor Laboratory in New York, prior to her becoming a COSAM faculty member in biological sciences at Auburn in 1987. She served as Acting Head of the Department of Zoology and Wildlife from 1995-1997, and later became Associate Dean of Research in COSAM in 2000, a position she held until becoming Dean of COSAM in 2010. In addition to her strong commitment to administration at Auburn, Marie was an outstanding leader, role model, and mentor in research, teaching, and service. Marie lived for her research and for her students. She embodied the ideal that to be successful students ‘‘should be life-long learners and individuals who make a difference.’’ Among her many hobbies, Marie was an avid runner, being particularly proud of completing the ‘‘Sprint Triathlon’’ where she finished first in her age group. We got acquainted with Marie during the initial stage of the Handbook project in early 2009. She already had a climate change literacy project sponsored by NASA, and immediately accepted the offer to write a chapter about her NASA project (see Chapter 30). She later agreed to collaborate with the University of Mississippi on other climate change outreach activities. Her proposal for exchanging mutual visits between the UM and Auburn faculties will most likely materialize after this book project is finished. Marie is preceded in death by her parents, James Roy Wright and Lucy Reyes Wright. She is survived by her husband of 31 years, Michael C. Wooten, and cousin Joe Reyes. Wei-Yin Chen Toshio Suzuki Maximilian Lackner

Foreword With scientific evidence mounting that human activities have begun to change global climate, attention is turning to the options available for dealing with that change. Actually only three options are available to us: mitigation, adaptation, and suffering. Mitigating climate change means cutting and sequestering emissions of greenhouse gases to prevent further increases in their atmospheric concentrations and then reducing concentrations to levels deemed less unsafe than the ones to which they have been driven since the start of the industrial revolution. What are safe concentrations is a topic of vigorous debate because we do not yet fully understand the coupled earth system and human system dynamics that will play themselves out in a world of unprecedented greenhouse gas concentrations. How high is too high will be known well after the point of no return has been reached. And so, the extent to which we embrace mitigation, in part, reflects our aversion – or desire – to take risks in matters pertaining not just to the stability of global climate conditions but the global human condition more broadly. It is against this backdrop that contributions from internationally renowned authors from industry and academia have been gathered in this volume to illuminate humanity’s mitigation options by giving broad coverage of climate change and mitigation. There is an urgent need for such work - it is a timely and rich resource. The Handbook of Climate Change Mitigation is the first and only book to collect in a single source information on all technologies related to the reduction of CO2 emission, from utilization of renewable energy and improvement of energy efficiency to establishing a sustainable society and stabilizing the environment. From the handbook’s coverage. it is quite obvious that there is no magic knife with which to cut emissions, because the sources of emissions are varied and intricately woven into the very fabric of our society and economy. Movement from oil, coal, and natural gas, for example, to biological feedstocks for the production of fuels and chemicals is an essential strategy to decarbonize our economies, but the effect of this strategy hinges on the extent to which production of biomass can decouple itself from fossil-based generation of fertilizers and pesticides, minimize land conservation, and prevent the associated release of carbon from soils and impacts on biodiversity. Decarbonization, even when combined with the most aggressive efficiency improvements in the end uses of materials and energy, only translates to net reductions in emissions if other influences do not overwhelm the rates at which these improvements are realized. Among these other influences are economic growth, generating ever larger production of output, population growth, demanding ever more goods and services, and climate change itself, triggering a demand for surplus production to built up our safety nets – from personal insurance to large-scale flood control systems – that can help us weather adverse climate conditions. Despite all efforts to stabilize and perhaps even

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reduce, in the long run, atmospheric greenhouse gas concentrations, humans have already committed themselves to decades of temperature changes and centuries of sea level rise. Since the heat budget of the globe will be disturbed, the frequency and severity of extreme weather events will likely increase. Disruptions in biophysical conditions will trigger, and be triggered by, changes in ecosystems – including changes in the productivity of managed forests and croplands, as wells as changes in the distribution of pests and diseases. The associated tightening of resource constraints will undermine the livelihoods of people, displace populations, and inflict pain and death. There are unlikely to be long-term winners from climate change. None of the places already suffering from shortages in water and food, for example, or flooding and crumbling infrastructures will, in the long run, be better off because of climate change. Climate will not stop changing once optimal conditions are reached, and benefits in one sector will soon be overwhelmed by costs imposed on other parts of the economy and society. This handbook is valuable precisely because it is the first book that discusses climate change mitigation from political, anthropological, educational, technological and journalistic points of view, thus offering variety of possible solutions and challenges Each chapter is written by internationally known experts and contains a section called Future Directions that speculates about the future. The Handbook of Climate Change Mitigation guides students to the direction of considering the climate mitigation when they start working in industry or academia. Understanding the role of mitigation and choosing the proper mitigation strategies is essential, and the Handbook of Climate Change Mitigation is valuable not only because it offers up-to-date knowledge based upon sound science, but also because it suggests specific actions on mitigation of climate change. These techniques run the gamut from proven techniques to novel technologies. The handbook is edited and written in a fashion that ensures that it can be easily followed by students, practitioners, and concerned citizens. The Handbook of Climate Change Mitigation speaks to each of us and will be widely read. Furthermore, the reader will understand the true meaning of climate mitigation; that is not simply reduction of CO2 but also the attitude of each of us towards the issue. Matthias Ruth

Editors-in-Chief Dr. Wei-Yin Chen Department of Chemical Engineering University of Mississippi Mississippi USA

Dr. Toshio Suzuki National Institute of Advanced Industrial Science and Technology (AIST) Nagoya Japan

Dr. John Seiner National Center for Physical Acoustics University of Mississippi Mississippi USA

Dr. Maximilian Lackner The Vienna University of Technology (TU Vienna) Wien Austria

Table of Contents Dedication . . . . . . . Foreword . . . . . . . . Editors-in-Chief . . . List of Contributors

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Volume 1 1 Introduction to Climate Change Mitigation . . . . . . . . . . . . . . . . . . . . . . . . 1 Maximilian Lackner . Wei-Yin Chen . Toshio Suzuki

Section 1 Scientific Evidences of Climate Change and Societal Issues 2 Life Cycle Assessment of Greenhouse Gas Emissions . . . . . . . . . . . . . . . . 13 L. Reijnders

3 Climate Change Legislation: Current Developments and Emerging Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 C. Moore

4 International Efforts to Combat Global Warming . . . . . . . . . . . . . . . . . . 89 Karen Pittel . Dirk Ru¨bbelke . Martin Altemeyer-Bartscher

5 Ethics and Environmental Policy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 David J. Rutherford . Eric Thomas Weber

6 Mass Media Roles in Climate Change Mitigation . . . . . . . . . . . . . . . . . . 161 Kristen Alley Swain

7 Sustainable Development: Ecology and Economic Growth . . . . . . . . . . 197 Arif S. Malik

8 Emissions Trading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235 Roger Raufer . Sudha Iyer

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9 Promotion of Renewables and Energy Efficiency by Politics: Case Study of the European Union . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 Itziar Martı´nez de Alegrı´a Mancisidor . M. Azucena Vicente Molina . Macarena Larrea Basterra

10 Implications of Climate Change for the Petrochemical Industry: Mitigation Measures and Feedstock Transitions . . . . . . . . . . . . . . . . . . 319 Simon J. Bennett

11 Venture Capital Investment and Trend in Clean Technologies . . . . . . . 359 John C. P. Huang

Section 2 Impact of Climate Change 12 Carbon Liability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411 Yoshihiro Fujii

13 Impacts of Climatic Changes on Biogeochemical Cycling in Terrestrial Ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433 Dafeng Hui . Hanqin Tian . Yiqi Luo

14 Sea-Level Rise and Hazardous Storms: Impacts on Coasts and Estuaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471 Yan Ding

15 Impact of Climate Change on Biodiversity . . . . . . . . . . . . . . . . . . . . . . . 505 David H. Reed

16 Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531 Xing Fang . Heinz G. Stefan

17 Climate Change Impacts, Vulnerability, and Adaptation in East Africa (EA) and South America (SA) . . . . . . . . . . . . . . . . . . . . . . . . 571 Anne Nyatichi Omambia . Ceven Shemsanga . Ivonne Andrea Sanchez Hernandez

Volume 2 Section 3 Energy Conservation 18 Energy Efficient Design of Future Transportation Systems . . . . . . . . . . 623 John Seiner . Maximilian Lackner . Wei-Yin Chen

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19 Thermal Insulation for Energy Conservation . . . . . . . . . . . . . . . . . . . . . 649 David W. Yarbrough

20 Thermal Energy Storage and Transport . . . . . . . . . . . . . . . . . . . . . . . . . 669 Satoshi Hirano

21 Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 701 Kailiang Zheng . Helen H. Lou . Yinlun Huang

22 Advanced Real-Time Optimization of Power Plants for Energy Conservation and Efficiency Increase . . . . . . . . . . . . . . . . . . . . . . . . . . . 749 Pal Szentannai

23 Mobile and Area Sources of Greenhouse Gases and Abatement Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 775 Waheed Uddin

24 Energy Efficiency: Comparison of Different Systems and Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 841 Maximilian Lackner

Section 4 Alternative Energies 25 Biomass as Feedstock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 911 Debalina Sengupta . Ralph Pike

26 Biochemical Conversion of Biomass to Fuels . . . . . . . . . . . . . . . . . . . . . 965 Swetha Mahalaxmi . Clint Williford

27 Thermal Conversion of Biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1001 Zhongyang Luo . Jingsong Zhou

28 Chemicals from Biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1043 Debalina Sengupta . Ralph W. Pike

29 Hydrogen Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1091 Qinhui Wang

Volume 3 30 Nuclear Energy and Environmental Impact . . . . . . . . . . . . . . . . . . . . . 1133 K. S. Raja . Batric Pesic . M. Misra

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31 Fusion Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1183 Hiroshi Yamada

32 Harvesting Solar Energy Using Inexpensive and Benign Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1217 Susannah Lee . Melissa Vandiver . Balasubramanian Viswanathan . Vaidyanathan (Ravi) Subramanian

33 Solar Concentrators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1263 Anjaneyulu Krothapalli . Brenton Greska

34 Wind Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1295 Manfred Lenzen . Olivier Baboulet

35 Geothermal Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1325 Hirofumi Muraoka

36 Hydropower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1355 Jingsheng Jia . Petras Punys . Jing Ma

Section 5 Advanced Combustion 37 Reducing Greenhouse Gas Emissions with CO2 Capture and Geological Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1405 J. Marcelo Ketzer . Rodrigo S. Iglesias . Sandra Einloft

38 Chemical Absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1441 Mengxiang Fang . Dechen Zhu

39 Oxy-fuel Firing Technology for Power Generation . . . . . . . . . . . . . . . . 1515 Edward John (Ben) Anthony

40 Integrated Gasification Combined Cycle (IGCC) . . . . . . . . . . . . . . . . . . 1545 Lawrence J. Shadle . Ronald W. Breault

41 Conversion of Syngas to Fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1605 Steven S. C. Chuang

42 Chemical Looping Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1623 Edward John (Ben) Anthony

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Volume 4 Section 6 Advanced Technologies 43 Low-Temperature Fuel Cell Technology for Green Energy . . . . . . . . . . 1657 Scott A. Gold

44 Solid Oxide Fuel Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1703 Nigel M. Sammes . Kevin Galloway . Mustafa F. Serincan . Toshio Suzuki . Toshiaki Yamaguchi . Masanobu Awano . Whitney Colella

45 Molten Carbonate Fuel Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1729 Takao Watanabe

46 Photocatalytic Water Splitting and Carbon Dioxide Reduction . . . . . . 1755 Jacob D. Graham . Nathan I. Hammer

47 Technological Options for Reducing Non-CO2 GHG Emissions . . . . . . . 1781 Jeff Kuo

48 Thermoacoustics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1821 Matthew E. Poese

49 Reduction of Greenhouse Gas Emissions by Catalytic Processes . . . . . 1849 Gabriele Centi . Siglinda Perathoner

50 Integrated Systems to Reduce Global Warming . . . . . . . . . . . . . . . . . . 1891 Preben Maegaard

51 Reducing Personal Mobility for Climate Change Mitigation . . . . . . . . 1945 Patrick Moriarty . Damon Honnery

Section 7 Education and Outreach 52 Bringing Global Climate Change Education to Alabama High-School Classrooms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1983 Ming-Kuo Lee . Marllin Simon . Kevin Fielman . Luke Marzen . Yu Lin . Roger Birkhead . Cathy Miller . Paul Norgaard . Matthew Obley . Jennifer Cox . Laura Steltenpohl . Emily Wheeles . Regina Halpin . Chris Rodger . Marie Wooten

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53 Climate Change: Outreaching to School Students and Teachers . . . . . 2029 Dudley E. Shallcross . Timothy G. Harrison . Alison C. Rivett . Jauyah Tuah

54 An Introductory Course on Climate Change . . . . . . . . . . . . . . . . . . . . . 2077 Wei-Yin Chen

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2111

List of Contributors Martin Altemeyer-Bartscher Department of Economics Chemnitz University of Technology Chemnitz Germany

Roger Birkhead Alabama Science in Motion Program Department of Physics Auburn University Auburn, AL USA

Edward John (Ben) Anthony CanmetENERGY, Natural Resources Canada Ottawa, ON Canada

Ronald W. Breault U.S. Department of Energy National Energy Technology Laboratory Morgantown, WV USA

Masanobu Awano Advanced Manufacturing Research Institute, National Institute of Advanced Industrial Science and Technology Nagoya Japan

Gabriele Centi Dipartimento di Chimica Industriale ed Ingegneria dei Materiali University of Messina and CASPE-INSTM Messina Italy

Olivier Baboulet ISA, School of Physics-A28 The University of Sydney NSW Australia

Wei-Yin Chen Department of Chemical Engineering University of Mississippi Mississippi USA

Simon J. Bennett Imperial Centre for Energy Policy and Technology Imperial College London UK

Steven S. C. Chuang FirstEnergy Advanced Energy Research Center, Department of Chemical and Biomolecular Engineering The University of Akron Akron, OH USA

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Whitney Colella Sandia National Laboratories Albuquerque, NM USA Jennifer Cox Stanhope Elmore High School Millbrook, AL USA Yan Ding National Center for Computational Hydroscience and Engineering The University of Mississippi University, MS USA Sandra Einloft CEPAC – Brazilian Carbon Storage Research Center Pontifical Catholic University of Rio Grande do Sul Porto Alegre, Rio Grande do Sul Brazil and FAQUI – Chemistry Faculty Pontifical Catholic University of Rio Grande do Sul Porto Alegre, Rio Grande do Sul Brazil Mengxiang Fang Institute for Thermal Power Engineering Zhejiang University Hangzhou, Zhejiang China Xing Fang Department of Civil Engineering Auburn University Auburn, AL USA

Kevin Fielman Department of Biological Sciences Auburn University College of Sciences and Mathematics Auburn, AL USA

Yoshihiro Fujii Graduate School of Global Environmental Studies Sophia University Tokyo Japan

Kevin Galloway Department of Metallurgical and Materials Engineering Colorado School of Mines Golden, CO USA

Scott A. Gold Department of Chemical and Materials Engineering University of Dayton Dayton, OH USA

Jacob D. Graham Department of Chemistry and Biochemistry University of Mississippi Oxford, MS USA

Brenton Greska Sustainable Energy Technologies, LLC St. Cloud, FL USA

List of Contributors

Regina Halpin Program Evaluation and Assessment Consultants Auburn, AL USA Nathan I. Hammer Department of Chemistry and Biochemistry University of Mississippi Oxford, MS USA Timothy G. Harrison Bristol ChemLabS School of Chemistry, University of Bristol Bristol UK Satoshi Hirano Thermal and Fluids Systems Group Energy Technology Research Institute National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba Japan Damon Honnery Department of Mechanical and Aerospace Engineering Monash University Melbourne, Victoria Australia Yinlun Huang Lab for Multiscale Complex Systems Science and Engineering, Department of Chemical Engineering and Materials Science Wayne State University Detroit, MI USA

John C. P. Huang Focus Capital Group Cupertino, CA USA

Dafeng Hui Department of Biological Sciences Tennessee State University Nashville, TN USA

Rodrigo S. Iglesias CEPAC – Brazilian Carbon Storage Research Center Pontifical Catholic University of Rio Grande do Sul Porto Alegre, Rio Grande do Sul Brazil and FENG – Engineering Faculty Pontifical Catholic University of Rio Grande do Sul Porto Alegre, Rio Grande do Sul Brazil

Sudha Iyer Cerebronics, LLC Princeton, NJ USA

Jingsheng Jia International Commission on Large Dams (ICOLD) Paris France and China Institute of Water Resources and Hydropower Research Beijing China

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J. Marcelo Ketzer CEPAC – Brazilian Carbon Storage Research Center Pontifical Catholic University of Rio Grande do Sul Porto Alegre, Rio Grande do Sul Brazil Anjaneyulu Krothapalli Department of Mechanical Engineering Florida State University Tallahassee, FL USA Jeff Kuo Department of Civil and Environmental Engineering California State University Fullerton, CA USA Maximilian Lackner The Vienna University of Technology (TU Vienna) Wien Austria Macarena Larrea Basterra Researcher for the Energy Working Group University of the Basque Country Leioa Spain Susannah Lee Department of Chemical and Metallurgical Engineering, Chemical and Materials Engineering Department, LME 310, MS 388 University of Nevada Reno, NV USA

Ming-Kuo Lee Department of Geology and Geography Auburn University Auburn, AL USA Manfred Lenzen ISA, School of Physics-A28 The University of Sydney NSW Australia Yu Lin Department of Physics Auburn University Auburn, AL USA Helen H. Lou Dan F. Smith Department of Chemical Engineering Lamar University Beaumont, TX USA Zhongyang Luo State Key Laboratory of Clean Energy Utilization, Zhejiang University Hangzhou, Zhejiang P. R. of China Yiqi Luo Department of Botany and Microbiology University of Oklahoma Norman, OK USA Jing Ma China Institute of Water Resources and Hydropower Research Beijing China

List of Contributors

Preben Maegaard Nordic Folkecenter for Renewable Energy Hurup Thy Denmark

Swetha Mahalaxmi Department of Chemical Engineering University of Mississippi Oxford, MS USA

Arif S. Malik Department of Electrical and Computer Engineering College of Engineering, Sultan Qaboos University Al-Khod Sultanate of Oman

Itziar Martı´nez de Alegrı´a Mancisidor Engineering School of Bilbao University of the Basque Country Bilbao Spain

M. Misra Center for Materials Reliability, Chemical and Materials Engineering University of Nevada Reno, NV USA

C. Moore Alcoa Inc. Knoxville, TN USA

Patrick Moriarty Department of Design Monash University Melbourne, Victoria Australia

Hirofumi Muraoka North Japan Research Institute for Sustainable Energy (NJRISE) Hirosaki University Aomori Japan

Luke Marzen Department of Geology and Geography Auburn University Auburn, AL USA

Paul Norgaard Alabama Science in Motion Program Department of Physics Auburn University Auburn, AL USA

Cathy Miller Alabama Science in Motion Program Department of Physics Auburn University Auburn, AL USA

Matthew Obley Alabama Science in Motion Program Department of Physics Auburn University Auburn, AL USA

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Anne Nyatichi Omambia National Environment Management Authority Nairobi Kenya Siglinda Perathoner Dipartimento di Chimica Industriale ed Ingegneria dei Materiali University of Messina and CASPE-INSTM Messina Italy Batric Pesic Materials Science and Engineering University of Idaho Moscow, ID Russia Ralph W. Pike Minerals Processing Research Institute Louisiana State University Baton Rouge, LA USA Karen Pittel Ifo Institute for Economic Research and University of Munich Munich Germany Matthew E. Poese Applied Research Laboratory State College, PA USA Petras Punys Water Management Department Water & Land Management Faculty Lithuanian University of Agriculture Kaunas-Akademija Lithuania

K. S. Raja Center for Materials Reliability, Chemical and Materials Engineering University of Nevada Reno, NV USA Roger Raufer Independent Engineer Cinnaminson, NJ USA and Wharton School University of Pennsylvania Philadelphia, PA USA and Institut Franc¸ais du Pe´trole Rueil–Malmaison France Dirk Ru¨bbelke Basque Centre for Climate Change (BC3) Bilbao Spain and IKERBASQUE, Basque Foundation for Science Bilbao Spain David H. Reed Department of Biology University of Louisville Louisville, KY USA L. Reijnders IBED University of Amsterdam Amsterdam The Netherlands

List of Contributors

Alison C. Rivett Bristol ChemLabS School of Chemistry, University of Bristol Bristol UK

Mustafa F. Serincan Department of Mechanical Engineering University of Connecticut Storrs, CT USA

Chris Rodger Department of Mathematics and Statistics Auburn University Auburn, AL USA

Lawrence J. Shadle U.S. Department of Energy National Energy Technology Laboratory Morgantown, WV USA

David J. Rutherford Department of Public Policy Leadership University of Mississippi University, MS USA Nigel M. Sammes Department of Metallurgical and Materials Engineering Colorado School of Mines Golden, CO USA Ivonne Andrea Sanchez Hernandez Dosquebradas, Risaralda Colombia John Seiner National Center for Physical Acoustics The University of Mississippi Mississippi USA Debalina Sengupta Chemical Engineering Department Louisiana State University Baton Rouge, LA USA

Dudley E. Shallcross School of Chemistry University of Bristol Bristol UK Ceven Shemsanga Department of Eco-tourism and Nature Conservation Sebastian Kolowa University College Tumaini University Lushoto-Tanga United Republic of Tanzania Marllin Simon Department of Physics Auburn University Auburn, AL USA Heinz G. Stefan St. Anthony Falls Laboratory Department of Civil Engineering University of Minnesota Minneapolis, MN USA Laura Steltenpohl Auburn High School Auburn, AL USA

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Vaidyanathan (Ravi) Subramanian Department of Chemical and Metallurgical Engineering, Chemical and Materials Engineering Department, LME 310, MS 388 University of Nevada Reno, NV USA

Toshio Suzuki National Institute of Advanced Industrial Science and Technology (AIST) Nagoya Japan

Kristen Alley Swain Meek School of Journalism and New Media University of Mississippi University, MS USA

Pal Szentannai Department of Energy Engineering Budapest University of Technology and Economics Budapest Hungary

Hanqin Tian International Center for Climate and Global Change Research School of Forestry and Wildlife Sciences Auburn University Auburn, AL USA

Jauyah Tuah Secretariat of Brunei Darussalam Technical and Vocational Education Council, Permanent Secretary Office (Higher Education) Ministry of Education Bandar Seri Begawan Brunei Darussalam Waheed Uddin Department of Civil Engineering University of Mississippi University, MS USA Melissa Vandiver Department of Chemical and Metallurgical Engineering, Chemical and Materials Engineering Department, LME 310, MS 388 University of Nevada Reno, NV USA M. Azucena Vicente Molina Economics and Business Administration School University of the Basque Country Bilbao Spain Balasubramanian Viswanathan National Center for Catalysis Research Indian Institute of Technology Madras Chennai India Qinhui Wang Institute for Thermal Power Engineering Zhejiang University Hangzhou Zhejiang China

List of Contributors

Takao Watanabe Energy Engineering Research Laboratory Central Research Institute of Electric Power Industry (CRIEPI) Yokosuka, Kanagawa Japan

Toshiaki Yamaguchi Advanced Manufacturing Research Institute, National Institute of Advanced Industrial Science and Technology Nagoya Japan

Eric Thomas Weber Department of Public Policy Leadership University of Mississippi University, MS USA

David W. Yarbrough R&D Services, Inc. Cookeville, TN USA

Emily Wheeles Benjamin Russell High School Alexander City, AL USA Clint Williford Department of Chemical Engineering University of Mississippi Oxford, MS USA Marie Wooten Department of Biological Sciences Auburn University College of Sciences and Mathematics Auburn, AL USA Hiroshi Yamada Department of Helical Plasma Research National Institute for Fusion Science Toki, Gifu Japan

Kailiang Zheng Dan F. Smith Department of Chemical Engineering Lamar University Beaumont, TX USA

Jingsong Zhou State Key Laboratory of Clean Energy Utilization, Zhejiang University Hangzhou, Zhejiang P. R. of China

Dechen Zhu Institute for Thermal Power Engineering Zhejiang University Hangzhou, Zhejiang China

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1 Introduction to Climate Change Mitigation Maximilian Lackner1 . Wei-Yin Chen2 . Toshio Suzuki3 The Vienna University of Technology (TU Vienna), Wien, Austria 2 Department of Chemical Engineering, University of Mississippi, Mississippi, USA 3 National Institute of Advanced Industrial Science and Technology (AIST), Nagoya, Japan

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Climate Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 The Greenhouse Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Anthropogenic Climate Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Effects of Climate Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Climate Change – What Will change? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Impact of Climate Change Mitigation Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Climate Change Adaption Versus Climate Change Mitigation . . . . . . . . . . . . . . . . . . . . . . . 6 Handbook of Climate Change Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Why This Book Is Needed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Audience of the Handbook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Climate Change There has been a heated discussion on climate change in recent years, with a particular focus on global warming. Instrumental recording of temperatures has been available for less than 200 years. Over the last 100 years, a temperature increase of 0.5 C could be measured [1] with rather different regional patterns and trends [2]. Over the last several million years there have been warmer and colder periods on Earth, and the climate fluctuates for a variety of natural reasons, as data from tree rings, pollen, and ice core samples have shown. However, human activities on Earth have reached an extent that they impact the globe in potentially catastrophic ways. In [3], Bruce D. Smith is quoted as saying: ‘‘The changes brought over the past 10,000 years as agricultural landscapes replaced wild plant and animal communities, while not so abrupt as those caused by the impact of an asteroid as the Cretaceous-Tertiary boundary some 65 million years ago or so massive as those caused by advancing glacial ice in the Pleistocene, are nonetheless comparable to these other forces of global change.’’ At the Earth Summit in Rio de Janeiro in 1992, over 159 countries signed the United Nations Framework Convention on Climate Change (FCCC, also called ‘‘Climate Convention’’), in order to achieve ‘‘stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system’’ [4]. In 2001, the Intergovernmental Panel on Climate Change (IPCC) [30] wrote: ‘‘An increasing body of observations gives a collective picture of a warming world and other changes in the climate system. . . There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.’’ In its fourth assessment report of 2007, the IPCC stated that human actions are ‘‘very likely’’ the cause of global warming. More specifically, there is a 90% probability that the burning of fossil fuels and other anthropogenic factors such as deforestation and the use of certain chemicals have already led to an increase of 0.75 in average global temperatures over the last 100 years, and that the increase in hurricane and tropical cyclone strength since 1970 also results from man-made climate change. The position of the IPCC has been adopted by several renowned scientific societies, and a consensus has emerged on the causes, and partially on the consequences, of climate change. The history of climate change science is reviewed in [5]. There are researchers who oppose the scientific mainstream’s assessment of global warming [6]. However, the public seems to be unaware of the high degree of consensus that has been achieved in the scientific community, as elaborated in a 2009 World Bank report [7]. In [8], there is a treatment of the mass media’s coverage of the climate change discussion with a focus on rhetoric that emphasizes uncertainty, controversy, and climate skepticism.

The Greenhouse Effect A greenhouse, also called a glass house, is a structure enclosed by glass or plastic which allows the penetration of radiation to warm it. Gases capable of absorbing the radiant energy are called the greenhouse gases (GHG). Greenhouses are used to grow flowers,

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vegetables, fruits, and tobacco throughout the year in a warm, agreeable climate. On Earth, there is a phenomenon called the ‘‘natural greenhouse’’ effect, or the Milankovitch cycles. Without the greenhouse gas effect, which is chiefly based on water vapor in the atmosphere (i.e., clouds that trap infrared radiation), the average surface temperature on Earth would be 33 C colder [9]. The natural greenhouse effect renders Earth habitable, since the temperature which would be expected from the thermal equilibrium of the irradiation from sun and radiative losses into space (radiation balance in the blackbody model) is approximately 18 C. On the moon, for instance, where there is hardly any atmosphere, extreme surface temperatures range from 233 C to 133 C [10]. On Venus, by contrast, the greenhouse effect in the dense CO2-laden atmosphere results in an average surface temperature in excess of 450 C [11, 12]. The current discussion about global warming and climate change is centered on the anthropogenic greenhouse effect. This is caused by the emission and accumulation of greenhouse gases in the atmosphere. These gases (water vapor, CO2, CH4, N2O, O3 and others) act by absorbing and emitting infrared radiation. The combustion of fossil fuels (oil, coal and natural gas) has led mainly to an increase in the CO2 concentration in the atmosphere. Preindustrial levels of CO2 (i.e., before the start of the Industrial Revolution) were approximately 280 ppm, whereas today they are above 380 ppm with an annual increase of approximately 2 ppm. According to the IPCC Special Report on Emission Scenarios (SRES) [13], by the end of the twenty-first century, the CO2 concentration could reach levels between 490 and 1,260 ppm, which are between 75 and 350% above the preindustrial levels, respectively. CO2 is the most important anthropogenic greenhouse gas because of its comparatively high concentration in the atmosphere. The effect of other greenhouse-active gases depends on their molecular structure and their lifetime in the atmosphere, which can be expressed by their greenhouse warming potential (GWP). GWP is a relative measure of how much heat a greenhouse gas traps in the atmosphere. It compares the amount of heat trapped by a certain mass of the gas in question to the amount of heat trapped by a similar mass of CO2. With a time horizon of 100 years, the GWP of CH4, N2O, and SF6 with respect to CO2 is 25, 298 and 22,800, respectively [14]. But CO2 has a much higher concentration than other GHGs and it is increasing at a higher rate due to burning of fossil fuels. Thus, while the major mitigating emphasis has mainly been placed on CO2, efforts on mitigating CH4, N2O, and SF6 have also been active.

Anthropogenic Climate Change The climate is governed by natural influences, yet human activities have an impact on it as well. The main impact that humans exert on the climate is via the emission of greenhouse gases. Deforestation is another example of an activity that influences the climate [15]. > Figure 1.1 shows the share of greenhouse gas emissions from various sectors, taken from [16]. The energy sector is the dominant source of GHG emissions.

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Waste 2.5% Agriculture 8%

Energy* 84%

CO2 95%

Industrial processes 5.5% CH4 4% N2O 1%

. Fig. 1.1 Shares of global anthropogenic greenhouse gas emissions (Reprinted with permission from [16])

According to the International Energy Agency (IEA), if no action toward climate change mitigation is taken, global warming could reach an increase of up to 6 in average temperature [17]. This temperature rise could cause devastating consequences on Earth, which will be discussed briefly below.

Effects of Climate Change Paleoclimatological data show that 100–200 million years ago, almost all carbon was in the atmosphere as CO 2, with global temperatures being 10 C warmer and sea levels 50–100 m higher than today. Photosynthesis and CO2 uptake into the oceans took almost 200 million years. Since the Industrial Revolution, i.e., during the last 200 years, this carbon is being put back into the atmosphere to a significant extent. This is a rate which is 107 times faster, so there is a risk of a possible ‘‘runaway’’ reaction greenhouse effect. > Figure 1.2 shows the timescales of several different effects of climate change for the future. Due to the long lifetime of CO2 in the atmosphere, the effects of climate change until a new equilibrium has been reached will prove long term. A global temperature increase of 6 C would be severe, so the IEA has developed a scenario which would limit the temperature increase to 2 C [17] to minimize the effects. Sea level rise will indeed be the most direct impact. Other impacts, including those on weather, flooding, biodiversity, water resources, and diseases are discussed here.

Climate Change – What Will change? An overall higher temperature on Earth, depending on the magnitude of the effect and the rate at which it manifests itself, will change the sea level, local climatic conditions, and the

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Sea-level rise due to ice melting: several millennia Sea-level rise due to thermal expansion: centuries to millennia

CO2 emissions peak: 0 to 100 years

Temperature stabilisation: a few centuries CO2 stabilisation: 100 to 300 years

CO2 emissions Today 100 years

1000 years

. Fig 1.2 Time scales of climate change effects based on a stabilization of CO2 concentration levels between 450 and 1,000 ppm after today’s emissions (Reprinted with permission from [16])

proliferation of animal and plant species, to name but a few of the most obvious examples. The debate on the actual consequences of global warming is the most heated part of the climate change discussion. Apart from changes in the environment, there will be various impacts on human activity. One example is the threats to tourism revenue in winter ski resorts [20] and lowelevation tropical islands [21]. Insurance companies will need to devise completely new business models, to cite just one example of businesses being forced to react to climate change.

Impact of Climate Change Mitigation Actions The purpose of climate change mitigation is to enact measures to limit the extent of climate change. Climate change mitigation can make a difference. In the IEA reference scenario [17], the world is headed for a CO2 concentration in the atmosphere above 1,000 ppm, whereas that level is limited to 450 ppm in the proposed ‘‘mitigation action’’ scenario. In the first case, the global temperature increase will be 6 C, whereas it is limited to 2 C in the latter [17]. The Intergovernmental Panel on Climate Change has projected that the financial effect of compliance through trading within the Kyoto commitment period will be limited at between 0.1 and 1.1% of GDP. By comparison, the Stern report estimated that the cost of mitigating climate change would be 1% of global GDP and the costs of doing nothing would be 5 to 20 times higher [14, 22].

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Climate Change Adaption Versus Climate Change Mitigation Individuals [23], municipalities [24, 25], businesses [20], and nations [26, 27] have started to adapt to the ongoing and expected state of climate change. Climate change adaptation and climate change mitigation face similar barriers [29]. To best deal with the situation, there needs to be a balanced approach between climate change mitigation and climate change adaptation [21, 24, 29]. This will prove to be one of mankind’s largest modern challenges.

Handbook of Climate Change Mitigation Motivation The struggle in mitigating climate change is not only to create a sustainable environment, but also to build a sustainable economy through renewable energy resources. ‘‘Sustainability’’ has turned into a household phrase as people become increasingly aware of the severity and scope of future climate change. A survey of the current literature on climate change suggests that there is an urgent need for a comprehensive handbook introducing the mitigation of climate change to a broad audience. The burning of fossil fuels, such as coal, oil, and gas, and the clearing of forests, has been identified as the major sources of greenhouse gas emissions. Reducing the 24 billion metric tons of carbon dioxide emissions per year generated from stationary and mobile sources is an enormous task that involves both technological challenges and monumental financial and societal costs with benefits that will only surface decades later. The Stern Report (2007) provided a detailed analysis of the economic impacts of climate change and the ethical ground of policy responses for mitigation and adaptation. The decline in the supply of high-quality crude oil has further increased the urgency to identify alternative energy resources and develop energy conversion technologies that are both environmentally sound and economically viable. Various routes for converting renewable energies have emerged – including energy conservation and energy-efficient technologies. The energy industry currently lacks an infrastructure that can completely replace fossil fuels in the near future. At the same time, energy consumption in developing countries like China and India is rapidly increasing as a result of their economic growth. It is generally recognized that the burning of fossil fuels will continue until an infrastructure for sustainable energy is established. Therefore, there is now a high demand for reducing greenhouse gas emissions from fossil fuel–based power plants. The pursuit of sustainable energy resources has become a complex issue across the globe. The Handbook on Climate Change Mitigation is a valuable resource for a wide audience who would like to quickly and comprehensively learn the issues surrounding climate change mitigation.

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Why This Book Is Needed There is a mounting consensus that human behaviors are changing the global climate and that its consequence, if left unchecked, could be catastrophic. The fourth climate change report by the Intergovernmental Panel on Climate Change (IPCC 2007) has provided the most detailed assessment ever on climate change’s causes, impacts, and solutions. A consortium of experts from 13 US government science agencies, universities, and research institutions released the report Global Climate Change Impacts in the United States (2009), which verifies that global warming is primarily human induced, and climate changes are underway in the USA and are only expected to worsen. From its causes and impacts to its solutions, the issues surrounding climate change involve multidisciplinary sciences and technologies. The complexity and scope of these issues warrants a single, comprehensive survey of a broad array of topics, something which the Handbook on Climate Change Mitigation achieves by providing readers with all the necessary background information on the mitigation of climate change. The handbook introduces the fundamental issues of climate change mitigation in independent chapters, rather than directly giving the detailed advanced analysis presented by the IPCC and others. Therefore, the handbook will be an indispensable companion reference to the complex analysis presented in the IPCC reports. For instance, while the IPCC reports give large amounts of data concerning the impacts of different greenhouse gases, they contain little discussion about the science behind the analysis. Similarly, while the IPCC reports present large amounts of information concerning the impacts of different alternative energies, the reports rarely discuss the science behind the technology. There is currently not a single, comprehensive source that enables the readers to learn the science and technology associated with climate change mitigation.

Audience of the Handbook Since the handbook covers a wide range of topics, it will find broad use as a major reference book in environmental, industrial, and analytical chemistry. Scientists, engineers, and technical managers in the energy and environmental fields are expected to be the primary users. They are likely to have an undergraduate degree in science or engineering with an interest in understanding the science and technology used in addressing climate change and its mitigation.

Scope This two-volume handbook offers a comprehensive collection of information on climate change and how to minimize its impact. The chapters in this handbook were written by internationally renowned experts from industry and academia. The purpose of this book

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is to provide the reader with an authoritative reference work toward the goal of understanding climate change, its effects, and the available mitigation strategies with which it may be tackled: ● ● ● ● ● ● ●

Scientific evidence of climate change and related societal issues The impact of climate change Energy conservation Alternative energy sources Advanced combustion techniques Advanced technologies Education and outreach

This handbook presents information on how climate change is intimately involved with two critical issues: available energy resources and environmental policy. Readers will learn that these issues may not be viewed in isolation but are mediated by global economics, politics, and media attention. The focus of these presentations will be current scientific technological development, although societal impacts will not be neglected.

References 1. Le Houe´rou HN (1996) Climate change, drought and desertification. J Arid Environ 34:133–185 2. Folland CK, Karl TR, Nicholls N, Nyenzi BS, Parker DE, Vinnikov KYA (1992) Observed climate variability and change. In: Houghton JT, Callander BA, Varney SDK (eds) Climate change, the supplementary report to the IPCC scientific assessment. Cambridge University Press, Cambridge, pp 135–170 3. Ehrlich PR (2000) Human natures: genes cultures and the human prospect B&T. Island Press, Washington, DC. ISBN 978-1559637794 4. United Nations (UN) (1992) United framework convention on climate change. United Nations, Geneva 5. Miller FP, Vandome AF, McBrewster J (eds) (2009) History of climate change science. Alphascript, Mauritius. ISBN 978-6130229597 6. Linden HR (1993) A dissenting view on global climate change. The Electr J 6(6):62–69 7. Worldbank (2009) Attitudes toward climate change: findings from a multi-country poll. http://siteresources.worldbank.org/INTWDR2010/ Resources/Background-report.pdf 8. Antilla L (2005) Climate of scepticism: US newspaper coverage of the science of climate change. Global Environ Change Part A 15(4):338–352

9. Karl TR, Trenberth KE (2003) Modern global climate change. Science 302(5651):1719–23 10. Winter DF (1967) Transient radiative heat exchange at the surface of the moon. Icarus 6 (1–3):229–235 11. Sonnabend G, Sornig M, Schieder R, Kostiuk T, Delgado J (2008) Temperatures in Venus upper atmosphere from mid-infrared heterodyne spectroscopy of CO2 around 10 mm wavelength. Planet Space Sci 56(10):1407–1413 12. Zasova LV, Ignatiev N, Khatuntsev I, Linkin V (2007) Structure of the Venus atmosphere. Planet Space Sci 55(12):1712–1728 13. IPCC (2010) Special Report on Emission Scenarios (SRES), http://www.grida.no/climate/ipcc/emission/ 14. IPCC (2010) Intergovernmental panel on climate change. http://www.ipcc.ch/ 15. McMichael AJ, Powles JW, Butler CD, Uauy R (2007) Food, livestock production, energy, climate change, and health. Lancet 370:1253–1263 16. Quadrelli R, Peterson S (2007) The energy– climate challenge: recent trends in CO2 emissions from fuel combustion. Energy Pol 35(11): 5938–5952 17. International Energy Association IEA (2009) World energy outlook 2009. International Energy Association (IEA), Paris. ISBN 9789264061309

Introduction to Climate Change Mitigation 18. Kotter JP (1996) Leading change. McGraw-Hill, New York. ISBN 978-0875847474 19. Luecke R (2003) Managing change and transition (Harvard business essentials). McGraw-Hill, New York. ISBN 978-1578518746 20. Hoffmann VH, Sprengel DC, Ziegler A, Kolb M, Abegg B (2009) Determinants of corporate adaptation to climate change in winter tourism: an econometric analysis. Global Environ Change 19(2):256–264 21. Becken S (2005) Harmonising climate change adaptation and mitigation: the case of tourist resorts in Fiji. Global Environmental Change Part A 15(4):381–393 22. Stern N (2007) The economics of climate change: the stern review. Cambridge University Press, Cambridge. ISBN 978-0521700801 23. Grothmann T, Patt A (2005) Adaptive capacity and human cognition: the process of individual adaptation to climate change. Global Environmental Change Part A 15(3):199–213 24. Laukkonen J, Blanco PK, Lenhart J, Keiner M, Cavric B, Kinuthia-Njenga C (2009) Combining climate change adaptation and mitigation measures at the local level. Habitat International 33(3):287–292

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25. van Aalst MK, Cannon T, Burton I (2008) Community level adaptation to climate change: the potential role of participatory community risk assessment. Global Environ Change 18(1):165–179 26. Næss LO, Bang G, Eriksen S, Vevatne J (2005) Institutional adaptation to climate change: flood responses at the municipal level in Norway. Global Environ Change Part A 15(2):125–138 27. Stringer LC, Dyer JC, Reed MS, Dougill AJ, Twyman C, Mkwambisi D (2009) Adaptations to climate change, drought and desertification: local insights to enhance policy in southern Africa. Environ Sci Pol 12(7):748–765 28. Nielsen JO, Reenberg A (2010) Cultural barriers to climate change adaptation: a case study from Northern Burkina Faso. Global Environ Change 20(1):142–152 29. Hamin EM, Gurran N (2009) Urban form and climate change: balancing adaptation and mitigation in the U.S. and Australia. Habitat Int 33(3):238–245 30. Intergovernmental Panel on Climate Change (IPCC), IPCC Fourth Assessment Report: Climate change 2007 (AR4), Vol. 3, Cambridge University Press (2007)

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Section 1

Scientific Evidences of Climate Change and Societal Issues

2 Life Cycle Assessment of Greenhouse Gas Emissions L. Reijnders IBED, University of Amsterdam, Amsterdam, The Netherlands Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 What Is Life Cycle Assessment and How Does It Work? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Goal and Scope Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Inventory Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Impact Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Life Cycle Assessments Focusing on Greenhouse Gas Emissions, or a Part Thereof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Simplified Life Cycle Assessments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Published Life Cycle Assessments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Main Findings from Life Cycle Studies of Greenhouse Gas Emissions . . . . . . . . . . . . . . . 25 Energy Conversion Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Products Consuming Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Conventional and Unconventional Fossil Fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Green Energy Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Biofuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Food . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Crop-Based Lubricants and Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Recycling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Nanotechnology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Reduction of Life Cycle Greenhouse Gas Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Change in Carbon Stocks of Recent Biogenic Origin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Indirect Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

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Comprehensives of Dealing with Climate Warming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Consequential Life Cycle Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

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Abstract: Life cycle assessments of greenhouse gas emissions have been developed for analyzing products ‘‘from cradle to grave’’: from resource extraction to waste disposal. Life cycle assessment methodology has also been applied to economies, trade between countries, aspects of production and to waste management, including CO2 capture and sequestration. Life cycle assessments of greenhouse gas emissions are often part of wider environmental assessments, which also cover other environmental impacts. Such wider ranging assessments allow for considering ‘‘trade-offs’’ between (reduction of) greenhouse gas emissions and other environmental impacts and co-benefits of reduced greenhouse gas emissions. Databases exist which contain estimates of current greenhouse gas emissions linked to fossil fuel use and to many current agricultural and industrial activities. However these data bases do allow for substantial uncertainties in emission estimates. Assessments of greenhouse gas emissions linked to new processes and products are subject to even greater data-linked uncertainty. Variability in outcomes of life cycle assessments of greenhouse gas emissions may furthermore originate in different choices regarding functional units, system boundaries, time horizons, and the allocation of greenhouse gas emissions to outputs in multi-output processes. Life cycle assessments may be useful in the identification of life cycle stages that are major contributors to greenhouse gas emissions and of major reduction options, in the verification of alleged climate benefits and to establish major differences between competing products. They may also be helpful in the analysis and development of options, policies, and innovations aimed at mitigation of climate change. The main findings from available life cycle assessments of greenhouse gas emissions are summarized, offering guidance in mitigating climate change. Future directions in developing life cycle assessment and its application are indicated. These include: better handling of indirect effects, of uncertainty, and of changes in carbon stock of recent biogenic origin; and improved comprehensiveness in dealing with climate warming.

Introduction This handbook is about climate change mitigation. In decision making about climate change mitigation, question marks about proper choices regularly emerge. Is going for electric cars a good thing, when power production is largely coal-based? Do the extra inputs in car production invalidate the energy efficiency gains of hybrid cars? Should a company focus its greenhouse gas management on its own operations or on those of raw material suppliers? Is materials recycling better or worse for climate change mitigation than incineration in the case of milk cartons? And what about biofuels: should their use be encouraged or not? Regarding all these questions assessment of the life cycle emission of greenhouse gases, or more in general the environmental burden, is important for giving proper answers. Life cycle assessments may lead to anti-intuitive results. This can be illustrated by the case of liquid biofuels [1]. It has been argued that biofuels are ‘‘climate neutral’’ (e.g., [2, 3]). The CO2 which emerges from burning biofuels has been recently fixed by photosynthesis, so, it has been argued, there should be no net effect of burning biofuels on the atmospheric

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concentration of CO2. However, if one looks at the ‘‘seed to wheel’’ life cycle of biofuels, a different picture may emerge. Consider, e.g., corn ethanol used as a transport biofuel in the USA. In the actual production thereof there are substantial inputs of fossil fuels [4, 5]. Corn cultivation also leads to emissions of the major greenhouse gas N2O [6]. And corn cultivation is associated with changes in carbon stocks of agro-ecosystems [5]. Considering the life cycle emissions of greenhouse gases leads to the conclusion that bioethanol from US corn is far from ‘‘climate neutral,’’ but is rather associated with larger greenhouse gas emissions than conventional gasoline [5, 7]. This has clearly implications for making good decisions about mitigating climate change linked to fuel choice [1]. Against this background this chapter will consider current life cycle assessment, with a focus on the life cycle emission of greenhouse gases. First, it will be discussed what life cycle assessment is and how it is done. It will appear that such assessment may give rise to substantial uncertainty. Notwithstanding such uncertainty, life cycle assessments can be helpful in making proper choices about climate change mitigation. To illustrate this, main findings from available peer-reviewed life cycle assessments of greenhouse gas emissions will be summarized.

What Is Life Cycle Assessment and How Does It Work? Life cycle assessment has been developed for analyzing current products from resource extraction to final waste disposal, or from cradle to grave. Apart from analyzing the status quo, life cycle assessments may also deal with changes in demand for, and supply of, products and with novel products. The latter type of assessment has been called consequential, as distinguished from the analysis of status quo products, which has been called attributional [8, 9]. The assessment of novel products has also occasionally been called: prospective attributional [10, 11]. Different data may be needed in attributional and consequential life cycle assessment. Whereas in attributional life cycle assessment one, e.g., uses electricity data reflecting current power production, in consequential life one needs data regarding changes in electricity supply. For the short term, assessing a marginal change in capacity of current electricity supply may suffice to deal with changes in electricity supply. When the longer term is at stake, major changes in energy supply, including complex sets of energy supply technologies, should be assessed [12]. When novel products go beyond existing components, materials, and processes, knowledge often partly or fully relates to the research and development stage or to the limited production stage. These stages reflect immature technologies. Comparing these with products of much more mature technologies may be unfair, as maturing technologies are optimized and tend to allow for better resource efficiency and a lower environmental impact [13, 14]. Also, novel products may be subject to currently uncommon environmental improvement options and may have to operate under conditions that diverge from those that are currently common [8, 9]. The latter conditions may, e.g., include constraints on resource availability which currently do not exist, new infrastructures, budget

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constraints, higher resource costs which are conducive to resource efficiency, and strict caps on greenhouse gas emissions. A solution to such divergence from ‘‘business as usual’’ may be found in assuming technological trajectories and/or constructing scenarios which include assumptions about the environmental performance of future mature technologies under particular conditions [9, 14–16]. It should be realized that the assumptions involved lead to considerable uncertainty regarding the outcomes of consequential life cycle assessments, as these assumptions may be at variance with ‘‘real life’’ in the future. Life cycle assessment is generally divided in four stages [17, 18]. – – – –

Goal and scope definition Inventory analysis Impact assessment Interpretation

Goal and Scope Definition In the goal and scope definition stage, the aim and the subject of life cycle assessment are determined. This implies the establishment of ‘‘system boundaries’’ and usually the definition of a ‘‘functional unit.’’ A functional unit is a quantitative description of service performance of the product(s) under investigation. It may for instance be: the production of a Mega Watt hour (MWh) of electricity. This allows for comparing different products having the same output: e.g., photovoltaic cells, a coal-fired power plant, a gas-fired power plant, and a wind turbine. It should be noted though, that the functional unit may cover only a part of the service performance, because products may have special properties. For instance, in the case of power generation the production of a MWh of electricity as a functional unit does not take account of the phenomenon that a coal-fired power plant is most suitable for base load and a gas-fired power plant for peak load. In the goal and scope definition stage, a number of questions have to be answered. For instance, the life cycle of products usually includes a transport stage. As to transport the question arises what to include into the assessment: production of the transport vehicle? road building? building storage facilities for products? Similarly, in the life cycle assessment of fishery products questions arise such as: should one include: the by-catch of fish which is currently discarded? the energy input in shipbuilding and ship maintenance? and/or the energy input in building harbor facilities? In the goal and scope definition stage, one should also consider the matter of significant indirect effects of products. A well known example thereof is the rebound effect in the case of more energy-efficient products with lowered costs of ownership. Such products may for instance increase use of the product and my lead to spending of money saved by the energy-efficient product, which in turn may impact energy consumption, and associated greenhouse gas emissions [19–21]. Another case in point concerns biofuels from crops

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that currently serve as source for food or feed. When carbohydrates or lipids from such crops are diverted to biofuel production, this diversion may give rise to additional food and/or feed production elsewhere, because demand for food and feed is highly inelastic [5]. This, in turn, may have a substantial impact on estimated greenhouse gas emissions. Similarly the use of waste fat for biodiesel production may have the indirect effect of reducing the amount of fat available for feed production, which in turn might lead to an increased use of virgin fat, which will impact land use and may thus change carbon stocks of recent biogenic origin. However, indirect effects of decisions about biofuels do not end with the consideration of indirect effects on land use. It may, for instance, be argued that not expanding biofuel production may increase dependency on mineral oil, and that this may increase military activities to safeguard oil installations and shipping and associated emissions of greenhouse gases [3]. Still another example of indirect effects regards wood products. These may have the indirect effect of substituting for non-wood products, and including such substitution has a significant effect on estimated greenhouse gas emissions [22]. Decision making about significant indirect effects is not straightforward. This has led some to the conclusion that including indirect effects is futile (e.g., [3]), whereas others have argued that including at least some indirect effects is conducive to good decision making (e.g., [5, 22]). System boundaries refer to what is included in life cycle assessment. In general, system boundaries are drawn between technical systems and the environment, between relevant and irrelevant processes, between significant and insignificant processes, and between technological systems. An example of the latter is for instance a boundary between the motorcar life cycle and the life cycle of the building in which the car is produced. The choice of system boundaries may have a substantial effect on the outcomes of life cycle assessments (also: [23, 24]).

Inventory Analysis The inventory analysis gathers the necessary data for all processes involved in the product life cycle. This is a difficult matter when one is very specific about a product: for instance the apples which I bought last Saturday in my local supermarket. However, databases have been developed, such as Ecoinvent [25], the Chinese National Database [26], Spine (www. globalspine.com), JEMAI [27], and the European Reference Life Cycle Data System [28], which give estimates about resource extraction and emissions that are common in Europe, China, the USA, and Japan for specified processes (for instance the production and use of phosphate fertilizer). Also, there are databases which extend to economic input–output analyses and give resource extraction and emissions data at a higher level of aggregation than the process level [29]. A study of de Eicker et al. [30], which also gives a fuller survey of available databases, suggests that among available databases the Ecoinvent database is preferable for relatively demanding LCA studies. If only greenhouse gas emissions are considered, the 2006 Guidelines for national greenhouse gas inventories of the IPCC (Intergovernmental Panel on Climate Change; www.ipcc.ch/) were found to be useful [30].

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Available databases do not always give the same emissions for the same functional units. For instance according to a study of Fruergaard et al. [31], data about the average emission of greenhouse gases linked to 1 kWh electricity production in 25 EU countries varied between databases by up to 20%. For similar estimates in the USA, an even greater between-database uncertainty (on average 40%) was found [32]. Though such uncertainties are substantial, they should not detract from using databases such as Ecoinvent, Spine, and JEMAI, if only because between-process differences often exceed uncertainty. This may be illustrated by the geographical variability in greenhouse gas emissions linked to electricity production. For instance, country-specific average emissions of greenhouse gases per kWh of electricity in such databases vary by a factor 160 [31]. For marginal emissions of greenhouse gases per kWh of electricity (which are used to assess changes in supply or demand as needed for consequential life cycle assessment) variations were even larger: up to 400–750 times [31]. In the inventory stage of life cycle assessments of greenhouse gas emissions, the focus is evidently on the latter emissions. In wider ranging life cycle assessments, the inventory may comprise all extractions of resources and emissions of substances causally linked to the functional unit for each product under consideration, within the system boundaries that were established in the stage of goal and scope definition. Such wider ranging life cycle assessments have a benefit over life cycle assessments, which only focus on greenhouse gas emissions. First, they give a better picture of the overall environmental impact, for which life cycle greenhouse gas emissions may well be a poor indicator [33–35]. Also, such wider ranging LCAs allow for considering ‘‘trade-offs’’ between environmental impacts, and the occurrence of co-benefits linked to reducing greenhouse gas emissions [36–40]. For instance, Walsmsley and Godbold [40] concluded that stump harvesting for bioenergy may not only impact greenhouse gas emissions but may have the co-benefit of reducing fungal infections and may have negative co-impacts linked to erosion, nutrient depletion and loss, increased soil compaction, increased herbicide use, and loss of valuable habitat for a variety of (non-pest) species. Many current transport biofuels have larger life cycle greenhouse gas emissions than the fossil fuel which they replace, but have the benefit that dependence on mineral oil is reduced [7]. A large part of the impacts which go beyond climate change can be covered by standard wider ranging LCAs. Aspects of environmental impact which are, apart from the emission of greenhouse gases, often covered by such wider ranging life cycle assessments are summarized in > Box 2.1. In evaluating buildings, the indoor environment may also be a matter to consider [41, 42]. New operationalizations of some of the aspects of environmental impact mentioned in > Box 2.1 and additions to the list of > Box 2.1 are under development. The latter include: ecosystem services [43, 44] and the impacts of fresh water use [45]. Adding to the aspects often covered in wide ranging LCAs, a proposal has been published for the inclusion into life cycle assessment of change in albedo, characterized in terms of CO2 equivalents [46], which is relevant to climate [47]. As yet, no proposal could be found for the quantitative inclusion of black carbon emissions (characterized in terms of CO2 equivalents), which also impact climate.

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In life cycle assessments, the problem arises that many production systems have more than one output. For instance, rapeseed processing not only leads to the output oil, which may be used for biodiesel production, but also to rapeseed cake, which may be used as feed. Similarly, mineral oil refinery processes may not only generate gasoline, but also kerosene, heavy fuel oil and bitumen, and biorefineries produce a variety of product outputs too [48]. In the case of multi-output processes, extractions of resources and emissions have to be allocated to the different outputs. There are several ways to do so. Major ways to allocate are based on physical units (e.g., energy content or weight of outputs) or on monetary value (price). There may also be allocation on the basis of substitution. In the latter case, the environmental burden of a co-product is established on the basis of another, similar product. Different kinds of allocation may lead to different outcomes of life cycle assessment [7, 23, 31, 49]. The usual outcome of the inventory analysis of a wide ranging life cycle assessment is a list with all extractions of resources and emissions of substances causally linked to the functional unit for the product considered and, apart from the case of nuisance, commonly disregarding place and time of the extractions and emissions. Box 2.1: Aspects of Environmental Impact Which Are Often Considered in Wide Raging Life Cycle Assessments Resource depletion (abiotic, biotic) Effect of land use on ecosystems and landscape Desiccation Impact on the ozone layer Acidification Photo-oxidant formation Eutrophication or nutrification Human toxicity Ecotoxicity Nuisance (odor, noise) Radiation Casualties Waste heat

Impact Assessment The next stage in life cycle assessment is impact assessment. This firstly implies a step called characterization. In this step, extractions of resources and emissions are aggregated for a number of impact categories. When only greenhouse gas emissions are considered, the aggregation aims at establishing the emission of other greenhouse gases in terms of CO2 equivalents (CO2eq), which means that the emission of greenhouse gases like N2O, CH4, and CF4 are recalculated in terms of CO2 emissions. To do so, one needs to choose a time

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. Table 2.1 Estimated global warming potentials (GWP) in CO2eq of CH4 and N2O for time horizons of 20, 100, and 500 years as proposed by the Intergovernmental Panel on Climate Change (IPCC) [50]. Only direct effects are considered Gas/time horizon

20 years

100 years

500 years

CO2

1

1

1

CH4 N2O

72 289

25 298

7.6 153

horizon (e.g., 25 years, 100 years, 104 years), because the greenhouse gas effect of emitted greenhouse gases may be different dependent on the time horizon chosen (see > Table 2.1). The time dependent differences in > Table 2.1 reflect differences in atmospheric fate of greenhouse gases. For instance, the removal of CH4 from the atmosphere is much faster than the removal of CO2 [50]. In practice, often a time horizon of 100 years is chosen and the global warming potentials (GWP) from the corresponding column of > Table 2.1 are commonly used in life cycle assessments. > Table 2.1 considers only direct impacts or effects of the greenhouse gases. There are however also indirect impacts. For instance the emission of CH4 may affect the presence of ozone, which is also a greenhouse gas. There have been proposals for including such indirect effects in global warming potentials. Using a 100 years time horizon and assuming the GWP of CO2 to be 1, Brakkee et al. [51] proposed for instance a GWP for CH4 of 28, and for non-methane volatile organic compounds a GWP of 8. The latter have a direct GWP of 0. A number of estimated examples of global warming potentials calculated with and without indirect effects are in > Table 2.2. One may note that Brakkee et al. [51] give an estimate for the GWP of CH4 (direct effect only), which is different from the value in > Table 2.1. Still another possibility is to calculate GWPs on the basis of a similar percentage of greenhouse gas remaining in, or lost from, the atmosphere. This is exemplified by > Table 2.3, with values as calculated by Sekiya and Okamoto [52]. In the case of life cycle assessment of greenhouse gas emissions, calculating the emission in terms of CO2eq is where the impact assessment stage often ends, though there is also the option to quantify the impact in terms of damage to public health (e.g., [37]), damage to human health and ecosystems [53], and in terms of negative effects on the economy (e.g., [54]). Such damage-based characterizations facilitate weighing of trade-offs and co-benefits, when a variety of environmental impacts (cf. > Box 2.1) are included in life cycle assessment. Having CO2eq emissions as an outcome of life cycle assessment is often sufficient to guide the selection of product life cycle options, policies, and innovations aimed at mitigation of climate change, because the emission of greenhouse gases is in a first approximation directly causally linked with environmental impact (climate change).

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. Table 2.2 Estimated global warming potentials (GWP) with a time horizon of 100 years relative to the GWP of CO2 for a number of gases as calculated by Brakkee et al. [51] Gas/type of GWP

GWP, direct effect only; time horizon 100 years

GWP, including indirect effects; time horizon 100 years

CH4 CO

18 0

28 3

Non-methane volatile organic 0 compounds (NMVOC) Chlorofluorocarbon (CFC) 11 4800 Chlorofluorocarbon (CFC) 12 11000

8 3300 6100

Chlorofluorocarbon (CFC)113 CF4 CO2

4700 6100 1

6200 6100 1

. Table 2.3 Global Warming Potentials in CO2eq for a number of gases Gas/Global Warming Potential CH4 Chlorofluorocarbon (CFC)11 CF4 CO2

GWP assuming only direct effects and GWP assuming 70% removal from atmosphere a time horizon of 100 years as calculated by Brakkee et al. [51] (direct effect only) [52] 10.6 2249

18 4800

1560558 1

6100 1

Still, it should be noted that the temporal pattern of greenhouse emissions may affect the rate of climate change, which in turn is, e.g., a major determinant of impact on ecosystems. When the temporal pattern of the emissions is important, as for instance in the case of land use change or capital investments in production systems, it is possible to adapt life cycle assessment by including the estimated temporal pattern of greenhouse gas emissions linked to the object of life cycle assessment (cf. [55, 56]). Also, one may note that effect of activities on climate may go beyond the emission of greenhouse gases. For instance, agricultural activities may change albedo, evaporation and wind speed, which may in turn affect climate [7]. Also, the greenhouse effect of air traffic may be different than expected solely on the basis of CO2, N2O, and CH4 emissions, because air traffic triggers formation of contrails and cirrus clouds [57]. A direct causal link between emission and impact for greenhouse gas emissions may be at variance with other environmental impact categories. For instance, lead emissions which do not lead to exceeding a no-effect level for exposure of organisms will have no

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direct environmental impact. Also, specificity as to time and place can be very important for other impacts than climate change caused by greenhouse gases, such as the impacts of the emissions of hazardous and acidifying substances [58–61]. It may be noted, however, that in such cases time- and place-specificity may be introduced by adaptation of life cycle assessment or combining life cycle assessment with other tools (e.g., [59, 62, 63]).

Interpretation The interpretation stage connects the outcome of the impact assessment to the real world. Much of the practical usefulness of life cycle assessments of greenhouse gas emissions in this respect depends upon the uncertainty of outcomes, which has a variety of sources (e.g., [23, 64–68]). These can be categorized as uncertainties due to choices, uncertainties due to modeling, and parameter uncertainty [64, 65]. Parameter uncertainty and uncertainty due to choice (e.g., regarding time horizon, type of allocation, system boundaries, and functional unit) would seem to be the most important types of uncertainty in the case of estimating life cycle greenhouse gas emissions. Uncertainty in the outcomes of life cycle assessments of greenhouse gas emissions partly depends on the reliability of input data (categorized as parameter uncertainty). As pointed out above, databases regarding fossil fuel use industrialized countries such as the USA, China, Japan, and EU countries allow for substantial uncertainties in this respect [2, 31]. Similar data regarding other countries tend to be still more uncertain. Greenhouse gas emissions linked to land use, N2O emissions, and animal husbandry are also characterized by a relatively large uncertainty [7, 69]. Additional variability in outcomes of life cycle assessments of greenhouse gas emissions may originate in different choices regarding system boundaries. This has for instance been shown by Christensen et al. [70] and Gaudreault et al. [24], who analyzed life cycle greenhouse gas emissions of forestry products. They found that different assumptions about the boundary to the forestry industry and interactions between the forestry industry on one hand and on the other hand the energy industry and the recycled paper market might lead to substantial differences in outcomes of life cycle assessments. Choices regarding time horizons and the allocation of greenhouse gas emissions to outputs in multi-output processes may also have major consequences for such outcomes [7]. Sensitivity analysis may be part of the interpretation stage and for instance consider the dependence on different assumptions regarding allocation and time horizon. Similarly uncertainty analysis may be part of the interpretation stage. Several approaches to uncertainty analysis have been proposed, using Monte Carlo techniques [65, 71], matrix perturbation [72], or Taylor series expansion [73]. In practice uncertainty analysis has been applied in a limited way. Also in the interpretation stage, conclusions can be drawn. For instance, stages or elements of the product life cycle can be identified, which are linked to relatively high greenhouse gas emissions. These can be prioritized for emission reduction options and policies. Also it may be established that, given a functional unit and specified assumptions,

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one product has lower greenhouse gas emissions (in CO2eq) than another. Examples of conclusions which can be drawn from life cycle assessments are given in > section ‘‘Main Findings from Life Cycle Studies of Greenhouse Gas Emissions.’’ Though life cycle assessment has been developed for products, in practice the methodology has been applied more widely (cf. ‘‘> Published Life Cycle Assessments’’). To the extent that life cycle assessment methodology, which does not focus on products, essentially assess parts of product life cycles (e.g., the nickel industry, waste incineration, and CO2 capture and sequestration), the usefulness of assessment may be similar to the assessment of products: one may find, prioritize, and validate emission reduction options. Some of the applications of life cycle assessments, which go beyond products, give rise to additional problems. For instance, applying life cycle assessments to state economies and trade may give rise to double counting of emissions [74]. On the other hand, e.g., expansion of life cycle assessments to trade between states may give useful insights about the actual environmental impacts of imports and exports. This is a useful addition to climate regimes such as the Kyoto protocol, which focus on greenhouse gas emissions within state borders. Also, economy-wide LCAs may help in prioritizing product categories or economic sectors for policy development [75].

Life Cycle Assessments Focusing on Greenhouse Gas Emissions, or a Part Thereof The emergence of climate change as a major environmental concern has led to a rapid increase in life cycle assessments focusing on the emission of greenhouse gases. However, it should be pointed out that there are also life cycle assessments which cover only a part of the greenhouse gases. In this context, one may note the growing popularity of ‘‘carbon footprinting’’ (e.g., [67, 76–79]). There is no generally agreed upon definition of carbon footprinting. In practice, the focus of carbon footprinting is often on the emission of carbonaceous greenhouse gases, if the footprinting is not being ‘‘slimlined’’ to covering CO2 only (e.g., [79]). Also, there is an increasing interest in life cycle assessments focusing on the cumulative input of fossil fuels, which in turn is closely related to the life cycle emission of the major greenhouse gas CO2 [35, 36]. The focus on carbonaceous greenhouse gases may lead to outcomes which substantially deviate from overall greenhouse gas emissions. As several authors [6, 7, 35, 36] have pointed out, cumulative energy demand may be substantially at variance with overall environmental performance and life cycle emissions of greenhouse gases, in the case of agricultural commodities and in other cases in which life cycles impact land use. The same will hold in the case of a number of compounds, such as adipic acid, caprolactam, and nitric acid, when syntheses are used which generate N2O in a poorly controlled way [80, 81]. Also there can be a major divergence of ‘‘carbon footprinting’’ from overall life cycle greenhouse gas emissions when there are substantial emissions of halogenated greenhouse gases. The latter, e.g., applies to the case of halogenated refrigerant use [82], the use of halogenated blowing agents for the production of insulation [83], to primary aluminum

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production, which is associated with the emission of potent fluorinated greenhouse gases such as CF4 [80, 84], and to circuit breakers using SF6 and magnesium foundries [80, 85]. In the following only assessments will be used which give an estimate of all greenhouse gas emissions, recalculated as CO2eq emissions.

Simplified Life Cycle Assessments Full life cycle assessments require extensive data acquisition, which tends to be laborious and time consuming, and this may well be beyond what practice in industry and policy requires [86]. This has led to the emergence of simplified tools for the life cycle assessment of greenhouse gas emissions, such as screening LCAs. These tend to focus on major causes of life cycle greenhouse gas emissions (‘‘hotspots’’) and are often useful in identifying and prioritizing emission reduction options [87, 88].

Published Life Cycle Assessments A wide variety of products has been the object of life cycle assessments of greenhouse gas emissions. Examples range from teddy bears to power generators, from pesticides to motorcars, from tomato ketchup to buildings, and from a cup of coffee to tablet e-newspapers. Products have not been the only objects of life cycle assessments of greenhouse gas emissions. Life cycle assessment has also been used for state economies, trade between countries, branches of industry, industrial symbiosis, aspects of production and product technologies, networks, soil and groundwater remediation, and waste management options, including CO2 capture and sequestration.

Main Findings from Life Cycle Studies of Greenhouse Gas Emissions Though, as pointed out in > section ‘‘Goal and Scope Definition,’’ there are substantial uncertainties in assessments of life cycle greenhouse gas emissions, some outcomes of such assessments are robust to such an extent that they provide a sufficiently firm basis for conclusions. The latter are summarized here, assuming a time horizon of 100 years, using the values for global warming potentials as given by IPCC [50] (see > Table 2.1), and focusing on direct effects only, unless indicated otherwise. After this summary, options for life cycle greenhouse gas emission reduction which commonly emerge from life cycle assessments will be briefly discussed.

Energy Conversion Efficiency Improvements in efficiency of the conversion of primary energy to energy services, including reduction of heat loss, often lead to lower life cycle greenhouse gas emissions

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for energy services (e.g., [89–93]) when only direct effects are considered. There are some exceptions. Phase change materials, which may be used in buildings to improve energy conversion efficiency, have been shown to not significantly reduce the life cycle greenhouse gas emission of buildings in a Mediterranean climate [94]. Electric heat pumps, though generally giving rise to lower life cycle greenhouse gas emissions for space heating, may increase life cycle greenhouse gas emissions when electricity generation is coal-based [95]. Also the III/V solar cells, which contain, e.g., In (indium) and Ga (gallium) and have higher conversion efficiencies for solar energy into electricity than Si (silicium)-based photovoltaic cells, do not appear to have lower life cycle greenhouse gas emissions per kWh than multicrystalline Si solar cells [14]. Noteworthy is the potential for indirect effects linked to improvements of energy efficiency. As noted before: in the case that improvements in energy conversion lead to lower costs of ownership, there may be a rebound effect on energy use because money linked to such lower costs tends to be spend on increased use of the product or elsewhere, which in turn entails additional energy consumption and emission of greenhouse gases [19–21]. Lower costs may also be conducive to economic growth [20]. When only microeconomic effects of improved energy efficiency are considered, life cycle greenhouse gas emissions tend to be still lowered, though less so than when only the effect of energy efficiency by itself is considered [19, 21]. Including economy-wide rebound effects in life cycle assessments of improved energy conversion efficiency has as yet no firm empirical basis [20].

Products Consuming Energy Life cycle greenhouse gas emissions of products which consume energy are often dominated by emissions during the use stage of the life cycle, when shares of fossil fuels in the production and consumption stages are similar [91, 93, 96–103]. There are exceptions, however, such as for instance a personal computer for limited household use [104], mobile phones [105], and very energy efficient dwellings [92]. The latter illustrates a more general point. To the extent that energy conversion efficiency in the use stage improves, energy embodied in the product (e.g., [106, 107]), and in the case of transport also energy embodied in infrastructure (e.g., [108]), often become a more important factor in life cycle greenhouse gas emissions. It may be noted though, that there are exceptions as to the growing importance of energy embodied in the product, such as CMOS chips for personal computers and other electronics [93, 100].

Transport At continental distances in the order of Box 2.2. Many of these elements mentioned in > Box 2.2 are uncontroversial and often also serve the reduction of other environmental problems, but some may give rise to discussion about the net benefit, including the reduction of life cycle greenhouse gas emissions. Controversies about the use of ‘‘biobased’’ products, such as biofuels, have been referred to earlier in this section. There is also controversy about the net effect of climate compensation. For instance, planting trees has been argued to not properly provide climate compensation for the use of fossil fuels, because the life time of trees is limited, if compared with the 30,000–35,000 years needed for the complete removal of CO2 emitted by burning fossil fuels, because ongoing existence of forests over this period cannot be guaranteed and because tree planting projects often give rise to ‘‘leakage’’: land use changes in which trees are cut [163]. Box 2.2: Elements That Are Often Included in Programs for the Reduction of Product Related Life Cycle Greenhouse Gas Emissions – – – – –

– – –

– –

Reduced life cycle fossil energy use Use of energy supply with low greenhouse gas emissions per Joule Reduction of land use change Lower non-energy inputs in production Lowering non-product outputs (‘‘wastes’’ and emissions) of production processes, especially emissions with a relatively large ‘‘greenhouse effect’’ (e.g., of halogenated compounds, CH4, N2O) Dematerialization of products Increased recycling Reduced ‘‘downstream’’ greenhouse gas emissions linked to improved energy efficiency, e.g., using means of transport that have relatively low greenhouse gas emissions per tonkilometer, by increasing electronic retailing, or improving energy efficiency of products which consume energy Reduction of transport distances, more efficient logistics Increased carbon sequestration and/or ‘‘climate compensation’’

Future Directions There is a growing societal interest in life cycle assessments of greenhouse gas emissions and related assessments, such as life cycle carbon footprinting (e.g., [164]). This seems to

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be paralleled by a trend to simplification (see e.g., > section ‘‘Simplified Life Cycle Assessments’’). However, one should be aware that there are several methodological issues that have substantial relevance to the correspondence of the outcomes of life cycle assessments and impact on climate change in the real world. These issues will be briefly addressed. They are partly in the domain of those involved in methodology development and partly in the domain of those applying life cycle assessment.

Change in Carbon Stocks of Recent Biogenic Origin Changes in carbon stocks of recent biogenic origin have turned out to be very important to life cycle greenhouse gas emissions of food and biofuels. However, their inclusion in life cycle assessments of food and biofuels is so far patchy. Also one might expect such changes to be important in other ‘‘biobased’’ products, such as ‘‘bioplastics’’ and cropbased lubricants, solvents, and other chemicals. However, their inclusion of life cycle assessments of such products is rare. Buildings, roads, hydroelectric dams, and other infrastructural works might also be expected to impact carbon stocks of recent biogenic origin, but again their inclusion in life cycle assessments is very rare. Studies thoroughly evaluating impacts of changes in carbon stocks of recent biogenic origin on life cycle greenhouse emissions would be welcome. These might provide better knowledge regarding the cases that such changes have at least a substantial impact on life cycle greenhouse gas emissions.

Indirect Effects Product life cycles may have indirect effects which are substantial when evaluating their life cycle greenhouse gas emissions. Indirect effects of biofuels on land use change, linked to the inelasticity of demand for food and feed (see > section ‘‘Published Life Cycle Assessments’’), are a case in point. The same holds for the rebound effect linked to lowered costs by improved energy (see > section ‘‘Published Life Cycle Assessments’’). Relations between economic activities as reflected in input–output tables constructed by economists may also be important [165]. A more thorough study and discussion of the question when which indirect effects should be within the system boundaries drawn for life cycle assessment would seem appropriate.

Uncertainty As pointed out in > section ‘‘Interpretation’’, there is substantial uncertainty regarding the outcome of life cycle assessments of greenhouse gas emissions, largely originating in parameter uncertainty and uncertainty due to choices. Transparency about the actual uncertainties regarding the outcome of life cycle assessments of greenhouse gas emissions

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is in practice very limited. Comprehensive uncertainty and sensitivity analyses are rare. However, it is important that societal stakeholders get at least a rough indication of the uncertainties in the outcomes of life cycle assessments presented to them.

Comprehensives of Dealing with Climate Warming As noted in > section ‘‘Inventory Analysis,’’ a proposal has been made to include changes in albedo linked to land use change into life cycle assessment [46]. Also there have been proposals for the quantitative inclusion of the climate effects linked to contrails and cirrus clouds in the climate impact estimates for air traffic [57]. However, there is still some way to go for a comprehensive coverage of climate warming in life cycle assessment. On a timescale of centuries, there are changes in albedo, which will probably contribute to further warming, following from climate change (e.g., due to loss of ice and desertification) [166]. These changes in albedo are as yet not covered by life cycle assessments. A contributor to climate change currently absent from life cycle assessment of climate impact is black carbon or soot [167–170]. Black carbon has a variety of effects which are relevant to climate [167–170]. When emitted, black carbon absorbs and scatters solar radiation, and may affect humidity profiles (cloud formation) and droplet size in clouds. When deposited, black carbon may have an effect on surface albedo. It is currently estimated that the net effect of black carbon emissions on climate is warming [170]. For comprehensiveness in dealing with life cycle impacts on climate, it would seem proper to include both black carbon emissions and long-term changes in albedo in life cycle assessment.

Consequential Life Cycle Assessment In mitigating climate change, changes in products and technologies are much more important than studies of existing products and technologies. Such changes are the object of consequential life cycle assessment. As pointed out in > section ‘‘What is Life Cycle Assessment and How Does It Work?,’’ consequential life cycle assessment is a relatively recent development. The methodological approach, such as constructing scenarios and technological trajectories, deserves substantial attention, if only to provide a more solid basis for more widespread application in the development of new products and technologies.

Concluding Remarks Life cycle assessments of greenhouse gas emissions may be helpful in the analysis and development of options, policies, and innovations aimed at mitigation of climate change. The main findings from available life cycle assessments summarized in > section ‘‘Main

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Findings from Life Cycle Studies of Greenhouse Gas Emissions’’ provide for guidance in that respect. It can be noted that in several cases indirect effects have significant effects on the overall climate impact of products, and including those effects in considering options, policies and innovations aimed at mitigation of climate change would seem important. For any product, or part of the product life cycle, life cycle assessment can be useful in identifying the aspects of production which are main contributors to life cycle greenhouse gas emissions. This can provide a focus for trying to identify or develop options which might reduce such emissions and for life cycle management. Furthermore, life cycle assessments may help in providing guidance for future research and development work, though it should be noted that such guidance may be characterized by relatively large uncertainties.

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3 Climate Change Legislation: Current Developments and Emerging Trends C. Moore Alcoa Inc., Knoxville, TN, USA Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 International Climate Change Mitigation Policy Development . . . . . . . . . . . . . . . . . . . . . . 47 Two Major Steps in International Climate Change Mitigation: Kyoto and Copenhagen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Kyoto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Copenhagen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Measures Available for Climate Change Legislation and Regulation . . . . . . . . . . . . . . . . 55 Potential Legislative Alternatives for Climate Change Mitigation . . . . . . . . . . . . . . . . . . 56 Traditional Command and Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Cap and Trade Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Cap and Dividend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 Carbon Tax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Subsidies and Other Levers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Renewable Energy Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 Major International and Regional GHG Mitigation Programs . . . . . . . . . . . . . . . . . . . . . 63 European Union’s Emission Trading Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 The Northeast Regional Greenhouse Gas Initiative (United States) . . . . . . . . . . . . 65 The Western Climate Initiative (United States and Canada) . . . . . . . . . . . . . . . . . . . 66 Midwestern Regional Greenhouse Gas Reduction Accord (United States and Canada) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 California Climate Change Scoping Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 Florida . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 Australia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 New Zealand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 China . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 India . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 Brazil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_3, # Springer Science+Business Media, LLC 2012

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Indonesia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 South Africa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 Canada . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 United States Environmental Protection Agency Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 Greenhouse Gas Endangerment Finding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 Light-Duty Motor Vehicle Emission Standard for CO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 Greenhouse Gas Tailoring Rule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 Mandatory Greenhouse Gas Reporting Rule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 Summary of Sectors Covered in the GHG Reporting Rule . . . . . . . . . . . . . . . . . . . . . 76 What the Rule Requires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 United States National Environmental Policy Act . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 United States Federal GHG Legislation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 American Energy Security Act (Waxman–Markey: June 2009) . . . . . . . . . . . . . . . . . . . . . 79 Clean Energy Act of 2009 (November 2009) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 Clean Energy Partnerships Act of 2009 (November 4, 2009) . . . . . . . . . . . . . . . . . . . . . . . 80 Carbon Limits and Energy for America’s Renewal (Cantwell–Collins: December 2009) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 American Power Act (Kerry–Lieberman: May 2010) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Compromise Proposals in the United States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 Impact of Federal Legislation on Current GHG Cap and Trade Programs . . . . . . . . . . 82 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

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Abstract: Over the past 3 decades from the 1980s forward, the subject of climate change has progressed from general study and media interest to a daily hot topic discussion in all aspects of society worldwide. In the same way, carbon management programs, climate change legislation, energy legislation, and similar mitigation programs and reduction initiatives have moved from the planning process to reality in many federal, state, and local governments throughout the world. Legislative approaches and carbon management strategies have, thus, become a topic of great interest in businesses, industries, and local communities across the globe that will be impacted by both the effects of climate change and the cost to mitigate carbon emissions. In recent years, various legislative programs and mitigation approaches have been introduced with the intent to reduce the levels of carbon dioxide (CO2) and other greenhouse gas (GHG) pollutants emitted into the atmosphere that have global warming potentials above thresholds of concern. The major driver for legislative approaches to mitigate emissions of these pollutants is the belief that continued increases of the GHG emissions from man-made sources (e.g., industrial emission sources, electricity generation facilities, on-road and off-road mobile transportation sources, etc.) are contributing to increases in global temperatures that could have dramatic climate and, subsequently, environmental impacts. The myriad of legislative approaches and regulatory programs in consideration or already implemented are vast, diverse, ever-changing, and excessively politically charged. The intent of this chapter is to summarize the historical background of climate change policy development and potential legislative strategies, review current climate change legislation proposals and regulatory programs including major regional and international GHG emission reduction programs in place or in development, and discuss emerging trends in worldwide climate change legislation.

Introduction From the 1980s forward, the science of climate and climate change has evolved extensively to the point where climate change legislation, energy legislation, and carbon management have become topics of daily interest and debate in businesses and communities across the globe. Once a distant consideration, legislation of greenhouse gas (GHG) emissions at the local, state, federal, and international levels is moving forward at a brisk pace. The major driver to reduce GHG emissions is the belief that continued increases of these pollutant emissions from man-made sources (e.g., industrial sources, electricity generation facilities, on-road and off-road mobile sources, etc.) are contributing to increases in global temperatures that could have dramatic climate, and subsequently, environmental impacts. In recent years, various local, state, federal, and international programs have been introduced, proposed, and adopted with the intent to implement measures to reduce the

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levels of carbon dioxide (CO2) and other greenhouse gas (GHG) pollutants emitted into the atmosphere. The key GHGs under consideration in the most common legislative strategies are: ● Carbon dioxide (CO2) from fossil fuel burning, wood and other fuel burning, chemical manufacturing, and mobile source fuel combustion ● Methane (CH4) from the production and transport of coal, natural gas, and oil; from livestock and other agricultural practices; and decay of organic waste in municipal solid waste landfills ● Nitrous oxide (N2O) from agricultural and industrial activities and combustion of fossil fuels and solid waste ● Hydrofluorocarbons (HFCs) from industrial processes ● Perfluorocarbons (PFCs) from industrial processes ● Sulfur hexafluoride (SF6) from industrial processes Given the need for consistent international evaluation of GHG emissions and to enable a universal standard of measurement for climate change impacts, GHG emissions are commonly referred to in terms of ‘‘carbon dioxide equivalents’’ or CO2e. A specific global warming potential (GWP) has been developed for each identified GHG. The GWP is a measure of the impact of the emissions of the specific GHG’s climate change influence relative to a similar amount of CO2 over a consistent timeframe. The GWPs for the key GHGs (assuming a 100-year timeframe) are summarized in > Table 3.1 [1]. The type of pollutant and its specific GWP is an important aspect in the planning of legislative and regulatory approaches to mitigate climate change. A myriad of studies have been completed, evaluated, and re-evaluated in the past 3 decades that are now being relied upon heavily to develop and implement sound, reasonable legislative approaches and regulatory programs that are vast, diverse, ever-changing, and excessively politically charged. Debate about the basis of the climate science and the cost to minimize GHG emissions are the key cogs in how climate change policy and legislation is crafted. A representative of the Pew Center on Global Climate Change (a leader in global climate change policy issues and climate change research) recently made the following statement regarding legislative efforts to mitigate climate change, ‘‘Climate change lacks . Table 3.1 Global warming potentials of key greenhouse gases Greenhouse gas

Global warming potential

Carbon dioxide (CO2) Methane (CH4) Nitrous oxide (N2O)

1 21 310

Hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs) Sulfur hexafluoride (SF6)

140–11,700 23,900

For example, in a 100-year timeframe, 1 t of nitrous oxide will impact climate change 310 times more significantly than 1 t of carbon dioxide

Climate Change Legislation: Current Developments and Emerging Trends

3

a silver bullet solution; no single policy, practice, or technology is sufficient to handle the scope of the problem. Instead, climate change requires a ‘silver buckshot’ approach that includes a full suite of solutions pursued by a wide range of actors, including policymakers from all levels of government. Ultimately, an international climate change agreement will be necessary to achieve the GHG emission reduction levels that scientists have determined are required to avoid the most dangerous climate change impacts, but all levels of government can and should play a role in achieving these reductions’’ [2]. The regulatory and legislative landscape has been filled with both traditional and innovative ideas as the world’s policy makers, governments, corporations, nongovernmental organizations, and communities seek to find solid solutions and reasonable compromises to what has been characterized by many organizations and individuals to be the largest global environmental challenge the entire world has ever faced. The intent of this chapter is to summarize the historical background of climate change legislation, review current climate change legislation and regulatory programs including regional and international GHG cap and trade programs, and discuss emerging trends in climate change legislation. With all the science and political debate, the landscape of legislation is fluid, volatile, and ever-changing. The final approaches on all levels are very uncertain as any one legislative approach could derail others in motion depending on the manner in which the governments of the world choose to act.

International Climate Change Mitigation Policy Development In the early 1980s, the United States directed the completion of a study of worldwide environmental challenges that included a detailed study of climate change impacts. Although no specific actions resulted from this early study of climate change and related issues, in 1988, ‘‘because of the need of broad and balanced information about climate change’’ and ‘‘to provide the governments of the world with a clear scientific view of what is happening to the world’s climate,’’ the Intergovernmental Panel on Climate Change (IPCC) was established by the United Nations World Meteorological Organization (WMO) and the United Nations Environment Program (UNEP) [3]. The IPCC was tasked per the UNEP to: ● Prepare a comprehensive review and recommendations with respect to the current state of knowledge of the science of climate change. ● Evaluate the current and projected social and economic impacts of climate change. ● Determine possible response strategies and elements for inclusion in a potential future international convention on climate. The scientific evidence produced in the first IPCC Assessment Report of 1990 revealed the importance of climate change as a future topic of interest for environmental policy and planning. In the years following, the IPCC has produced additional assessment reports as directed and as necessary to update previous conclusions with new or revised climate change data and information. The IPCC’s work has been and continues to be key in developing policies to address climate change mitigation.

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Following development of the IPCC, the United Nations Framework Convention on Climate Change (UNFCCC) was commissioned at the United Nations Conference on Environment and Development (UNCED) in Rio de Janeiro, Brazil, in June of 1992. The United States and 153 other countries signed the UNFCCC that committed all parties to voluntarily reduce GHG emissions to reasonable levels in future years. The UNFCCC was then tasked ‘‘to begin to consider what can be done to reduce global warming and to cope with whatever temperature increases are inevitable’’ [4, 5]. Following ratification of the UNFCCC, annual meetings of all included parties have been conducted in meetings generally referred to as conferences of the parties (COP). Other related meetings have flowed out of the COP meeting process as well. Major COP meetings to date are briefly summarized in > Table 3.2.

Two Major Steps in International Climate Change Mitigation: Kyoto and Copenhagen Kyoto Perhaps the most significant development resulting from all of the COP meetings since the inception of the UNFCCC was the Kyoto Protocol adopted in Kyoto, Japan, on December 11, 1997, and entered into effect on February 16, 2005. The Kyoto Protocol is generally seen as an important first step toward a complete international GHG emission reduction program that will stabilize GHG emissions, provide the essential architecture for any future international agreement on climate change, and enable efficient mitigation and adaptation programs to be developed and implemented. The major achievement of the Kyoto Protocol is that it established binding GHG emission reduction targets for 37 industrialized nations and the European community. These reductions amount to an average of 5% against 1990 emission levels over the 5 year period from 2008 to 2012. The major distinction between the Kyoto Protocol and the Montreal Convention is that while the Montreal Convention ‘‘encouraged’’ countries to stabilize GHG emissions, the Kyoto Protocol ‘‘committed’’ each country to certain levels of GHG emission reductions. The Kyoto Protocol places a larger burden on more developed nations under the principle of ‘‘common but differentiated responsibilities’’ based on the belief that developed countries are ‘‘principally responsible’’ for the levels of GHG emissions in the atmosphere and should assume a greater burden for mitigation of emissions [6]. Under the Kyoto Protocol, countries are required to meet their GHG emission reduction targets primarily through federal and regional measures; however, the Kyoto Protocol offers them an additional means of meeting their reduction targets by way of three market-based mechanisms including: ● GHG emission trading ● The clean development mechanism (CDM) ● Joint implementation (JI)

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. Table 3.2 Summary of major UNFCCC COP meetings [4, 5] COP No. Date

Location of COP meeting

Significant developments and highlights of the meeting

1

1995

Berlin, Germany

2

1996

Geneva, Switzerland

3

1997

Kyoto, Japan

This was the first meeting of UNFCCC COP; established assessment phase known as the Berlin Mandate to develop control options for countries; implemented a 2-year analytical and assessment phase to define specific climate change mitigation options for countries Declaration on scientific basis for climate change by acceptance of IPCC second assessment; defined flexible strategy to mitigate climate change; called for legally binding targets for GHG emission reductions The Kyoto Protocol was adopted during this COP meeting; agreement on legally binding GHG emissions reduction targets by most industrialized countries on an average of 6–8% below 1990 GHG emission levels; the United States signed the protocol, however, US Senate resolutions blocked further action. Note that the Bush administration openly rejected the Kyoto Protocol in 2001 (more detailed summary included below)

4

1998

Buenos Aires, Argentina

5

1998

6

2000

6

2001

7

2001

There was an expectation that unresolved issues from Kyoto would be resolved in Buenos Aires, however, no significant developments; a 2-year plan of action was adopted to move efforts forward on mechanisms for implementing the Kyoto Protocol Bonn, Germany The 1998 Bonn meeting was primarily a technical and administrative meeting with no significant developments or conclusions resulting The Hague, Extensive high-level political negotiations amid major Netherlands controversies (primarily with the United States) such as credit for carbon sinks, consequences for countries not meeting emission reduction targets, and financial assistance obligations. Talks essentially ceased with no significant progress Bonn, Germany The ceased negotiations from The Hague resumed in Bonn. With the United States attending only as observers, agreement was reached on many of the issues of concern identified in The Hague meeting including flexible mechanisms, carbon sinks, compliance, and financing issues Marrakech, Completed work on the Buenos Aires plan of action from Morocco COP-4 setting the stage for ratification of the Kyoto Protocol; the United States continued as observers only and declined to be active in the negotiations amid hope that the United States would reengage the process; continued focus on mitigation mechanisms and global climate mitigation policy issues

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. Table 3.2 (Continued) COP No. Date

Location of COP meeting

8

New Delhi, India

2002

Significant developments and highlights of the meeting

Progress updates on current issues and future planning; no significant developments occurred during the meeting 9 2003 Milan, Italy Progress updates on current issues and future planning; no significant developments occurred during the meeting 10 2004 Buenos Aires, Progress updates on current issues and future planning; Argentina no significant developments occurred during the meeting First ‘‘meeting of the parties’’ (MOP-1) to the Kyoto 11 2005 Montreal, Canada Protocol since initial Kyoto meeting in 1997; one of the largest climate change meetings ever held; discussion of the ratified Kyoto Protocol including discussion of emissions trading systems and other aspects of global emissions policy development; meeting resulted in the Montreal Action Plan that extended the life of the Kyoto Protocol beyond the original 2012 expiration date with deeper GHG emission cuts planned 12 2006 Nairobi, Kenya Combined COP12 and MOP-2; progress updates on current issues and future planning; no significant developments occurred during the meeting 13 2007 Bali, Indonesia Combined COP13 and MOP-3; agreement reached on implementation timelines and structured negotiation on post-Kyoto 2012 timeframe; successful adoption of Bali Action Plan 14 2008 Poznan, Poland Combined COP-14 and MOP-4; agreements reached on financing to help poor nations cope with climate issues through adaptation and financial assistance; approval of forest protection mechanism to combat climate change impacts in heavily impacted forest areas 15 2009 Copenhagen, The original goal of COP-15 and MOP-5 was a global Denmark climate agreement for the period after the Kyoto Protocol expires in 2012; however, worldwide political pressure and the current economic struggles watered down the goal to hopes of less binding agreement; representatives of 192 countries participated (more detailed summary included below) 15-1 June 2010 Bonn, Germany Follow-up meeting to COP-15 in Copenhagen in 2009; continued discussions on long-term climate strategy and preparations for COP-16 meeting in Cancun, Mexico, later in 2010 16 December Cancun, Primary outcome was the incorporation of the elements 2010 Mexico of the COP-15 Copenhagen Accord into the UNFCCC

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These three market-based mechanisms were established to help stimulate significant green investment and technology advancement while also helping all countries meet their GHG emission reduction targets in an efficient and cost-effective manner. Each of the market-based mechanisms is defined in more detail below. GHG Emissions Trading

As noted previously, countries that are party to the Kyoto Protocol have agreed to targets for reducing their GHG emissions during the 2008–2012 initial commitment period [7]. Emissions trading, as established in Article 17 of the Kyoto Protocol, allows countries to sell excess GHG emission credits to other countries that exceed their committed target level of GHG emissions. Beyond actual GHG emission reduction credits, other units are available for trading under the program including: ● A removal unit (RMU) on the basis of land use, land use change, and forestry (LULUCF) activities (e.g., reforestation) ● An emission reduction credit generated by a joint implementation (JI) project ● A certified emission reduction generated from a clean development mechanism (CDM) project Under the Kyoto Protocol, each country’s actual GHG emissions have to be accurately monitored and detailed records maintained of carbon market activity through carbon registries and other means. GHG emission trading schemes may be established in regional or national markets under the guidelines established in the Kyoto Protocol. Clean Development Mechanism

The CDM is essentially a global clearinghouse of acceptable GHG emission offset programs that have been successfully implemented and are thereby certifiable for GHG emissions credits. Designed to stimulate sustainable development and GHG emission reductions, the CDM provides a means of added flexibility for industrialized countries to meet their GHG emission reduction targets and comply with associated limitations. The CDM allows emission reduction projects in developing countries to earn certified emission reduction (CER) credits. Each CER credit is equivalent to 1 t of CO2. These CERs can be traded and sold on the international market and utilized by industrialized nations to meet their GHG emission reduction targets under the Kyoto Protocol [8]. CDM projects must pass a detailed and rigorous qualification process through a public registration and issuance process designed to ensure real, measurable, and verifiable GHG emission reductions. The CDM is overseen by a CDM Executive Board that ultimately answers to the countries that ratified the Kyoto Protocol. In order to be considered for registration, a project must first be approved by the Designated National Authorities (DNA). The CDM has been operational since the beginning of 2006. Since its inception, the CDM has already registered more than 1,000 offset projects and it is anticipated that the CDM will produce CERs amounting to more than 2.7 billion tons of CO2e in the first commitment period of the Kyoto Protocol from 2008 to 2012.

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Joint Implementation

Joint implementation (JI) as defined in Article 6 of the Kyoto Protocol allows a country with a GHG emission reduction or limitation commitment under the Kyoto Protocol to earn emission reduction units from an emission reduction project in another country that is party to the Kyoto Protocol to be counted toward the specific country’s GHG emission reduction target [9]. Joint implementation, thus, allows countries under the Kyoto Protocol the flexibility to invest in other countries through capital projects and technology transfer. A joint implementation project must provide a measurable GHG emission reduction and be approved by all relevant parties under the Kyoto Protocol. Joint implementation projects started as early as 2000 may be considered although the emission reduction credit will be issued for years following 2008. Kyoto Protocol Adaptation Fund

The Kyoto Protocol is also designed to provide assistance to any country in adapting to any adverse effects of climate change through facilitating the development and deployment of strategies that can help a country’s population in an effective response and adaptation to the impacts of climate change that cannot be mitigated. The Adaptation Fund was established to finance adaptation projects and programs in developing countries that are involved with the Kyoto Protocol and that are especially vulnerable to the adverse effects of climate change [10]. The Adaptation Fund is financed from income from CDM projects and other available sources of funding. The share of proceeds amounts to 2% of the certified emission reductions (CERs) issued for a CDM project activity. The Adaptation Fund is supervised and managed by the Adaptation Fund Board (AFB) which is composed of 16 members and 16 alternates that meet twice annually. Country Classifications Under the Kyoto Protocol and UNFCCC

An important aspect of implementation of the Kyoto Protocol and planning under the UNFCCC is how each country is classified. Country classifications determine the level of responsibility under the Kyoto Protocol and are defined as: ● Annex 1 ● Annex 2 ● Developing countries Annex 1 countries that have ratified the Kyoto Protocol have committed to reduce their GHG emissions to targets based on 1990 emission levels. Annex 1 countries are listed in > Table 3.3. Annex 2 countries are essentially a subgroup of the Annex 1 countries and include members of the Organization for Economic Cooperation and Development (OECD) excluding those economies that were in transition as of 1992. These countries, listed in > Table 3.4, are developed countries that will be responsible to pay for mitigation and adaptation costs of developing countries. The final classification is developing countries. These countries are not required to reduce GHG emissions unless developed countries in Annex 1 or 2 provide sufficient

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. Table 3.3 Countries classified as Annex 1 under the UNFCCC Australia Bulgaria

Austria Canada

Belarus Croatia

Belgium Czech Republic

Denmark Germany Ireland Liechtenstein Netherlands

Estonia Greece Italy Lithuania New Zealand

Finland Hungary Japan Luxembourg Norway

France Iceland Latvia Monaco Poland

Portugal Slovenia Turkey

Romania Spain Ukraine

Russian Federation Sweden United Kingdom

Slovakia Switzerland United States

. Table 3.4 Countries classified as Annex 2 under the UNFCCC Australia Denmark Greece

Austria Finland Iceland

Belgium France Ireland

Canada Germany Italy

Ireland Japan Norway Switzerland

Italy Luxembourg Portugal United Kingdom

Japan Netherlands Spain United States

Latvia New Zealand Sweden

funding and technological investment. The basis to not establish short-term reduction goals for developing countries under UNFCCC includes: ● Avoidance of restrictions on development given GHG emissions are a product of industrial capacity ● Ability for these countries to sell emissions credits to Annex 1 or 2 countries who need credits to achieve GHG emission goals ● Enhanced opportunities for financial and technological investment from Annex 1 or 2 countries Developing countries may volunteer to become Annex 1 countries when they are sufficiently developed.

Copenhagen As negotiated in Kyoto, by the end of the first commitment period of the Kyoto Protocol in 2012, an updated international framework was slated to have been developed, negotiated,

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and ratified that would deliver the GHG emission reductions that the IPCC had deemed necessary. The United Nations Climate Change Conference in Copenhagen, Denmark, in December 2009 became the focal point for the development of this new international framework. Copenhagen was an enormous undertaking and included the following sessions: ● Fifteenth session of the Conference of the Parties (COP 15) ● Fifth session of the Conference of the Parties serving as the meeting of the Parties to the Kyoto Protocol (CMP 5) ● Thirty-first session of the Subsidiary Body for Implementation (SBI 31) ● Thirty-first session of the Subsidiary Body for Scientific and Technological Advice (SBSTA 31) ● Tenth session of the Ad Hoc Working Group on Further Commitments for Annex I Parties under the Kyoto Protocol (AWG-KP 10) ● Eighth session of the Ad Hoc Working Group on Long-term Cooperative Action under the Convention (AWG-LCA 8) Although prospects looked dim early in the meeting for any type of agreement, near the conclusion of the COP-15 meetings government leaders negotiated with focused intensity to reach a global agreement on climate change on the last day of the meeting. In describing the newly touted Copenhagen Accord, US President Obama commented that there was ‘‘a meaningful and unprecedented breakthrough here in Copenhagen.’’ President Obama went on to comment that while the international community has come a long way, there is still a long way to go to reach consensus on climate change mitigation policy. The Copenhagen Accord calls for the United States and 185 other nations to reduce GHG emissions levels, invest in clean energy technology, and implement advanced adaption programs in light of the effects of climate change. A key aspect of the Accord is that it acknowledges for the first time in history that staying below 2 C may not be sufficient to mitigate climate impacts and includes a planned technical review in 2015 to determine if there is a need to consider staying below 1½ C or an atmospheric CO2 concentration of 350 parts per million (ppm). Key aspects of the Copenhagen Accord include [11]: ● Countries are required to increase their national and international actions to combat climate change while recognizing the scientific view that an increase in global temperatures should be kept below 2 C. ● All parties to the Copenhagen Accord were required to submit country-specific GHG emission reduction goals by a January 31, 2010, deadline. ● Developing countries agreed to report their climate mitigation actions through a system of ‘‘international consultations and analysis.’’ ● The Copenhagen Accord states that short- and long-term financial support will be provided to developing countries for forest conservation, adaptation, technology development and transfer, and capacity building.

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● Long-term funding will be directed through the ‘‘Copenhagen Green Climate Fund’’ which was formally established by the Copenhagen Accord; however, it still lacks substantial details on funding mechanisms and other aspects. ● The Copenhagen Accord builds in a new scientific assessment of GHG emissions reductions by 2015 that will aid in future considerations on the potential need to strengthen the long-term global goal of limiting the average rise in temperature to 1½ C. ● The Copenhagen Accord affirms the continuing role of the UNFCCC for financial governance, GHG emissions reporting and monitoring, and formal scientific review. Although there has been an incredible amount of effort and many critical steps taken to move forward with an international approach to mitigate climate change, a significant international policy with full cooperation of all parties is still in its infancy. In the midst of continued controversy and debate over climate science and the most effective mechanisms to mitigate and adapt to climate change that may occur, the COP, MOP, and other related conferences and meetings through the UNFCCC continuing annually and more frequently as needed have and will continue to serve an important role in continuing the development of climate change legislation and regulation on the international level.

Measures Available for Climate Change Legislation and Regulation As discussed previously, combating climate change has taken two primary forms [12]: ● Preventative measures ● Adaptive measures Preventative measures are those that lead to reductions or mitigation of GHG emissions and their subsequent impacts. Examples of preventative measures to reduce GHG emissions include: ● Add-on GHG emission controls for industrial facilities, electrical generation facilities, and mobile emission sources ● Reducing activities and energy consumption that drive creation of GHG emissions ● Carbon sequestration and similar techniques for carbon control Many proposed and adopted legislative solutions have focused on the use of preventative measures in a market-based program to combat climate change. From cap and trade to carbon fuel taxes to traditional and innovative GHG emission control technologies, there will be a need to utilize any and all proven technical and political options in crafting reasonable and workable legislative approaches. Many of the potential measures for carbon capture and emissions control are discussed in detail in other chapters within this publication.

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Adaptive measures are those measures that deal with the impacts of climate change including: ● Community and country-specific education and detailed instruction on climate change and its predicted impacts ● Ensuring adequate protections are in place should drought or similar environmental upset conditions occur ● Protecting shoreline living areas through the use of sea walls and barriers ● Implementing local reaction plans as necessary In other words, adaptive measures are those steps taken to help people and nations successfully adapt to a changing climate impacted by GHG emissions. Even with sweeping technical and economic changes, it is anticipated that most areas of the world also need to implement adaptive measures in one form or fashion as part of a comprehensive climate change program.

Potential Legislative Alternatives for Climate Change Mitigation The legislative challenge to regulate GHG emissions and reduce international levels of CO2e is daunting to say the least. As alluded to in the previous section, preventative measures and adaptive measures are both important components in legislative and regulatory strategies on how to mitigate emissions of GHG emissions. A myriad of potential alternatives is available for the planning of future regulation of GHG emissions including: ● Mobile source GHG emission standards and transportation sector controls that reduce GHG emissions at the engine level ● Electrical generation and industrial point source GHG emission controls that reduce GHG emissions at the outlet of the emission source stacks ● Renewable energy standards that enable growth in cleaner forms of energy production ● Use of alternative fuels in transportation, power, and industrial sectors ● Increased use of nuclear energy ● Increased use of solar energy ● Mandatory energy-efficiency audits and incentives for energy-efficiency programs ● Increased mass transit ● Carbon market-based pricing options such as cap and trade, cap and dividend, and carbon taxes As with all political decisions, a major question in the regulation of GHG emissions is how much is it going to cost? To determine the merits of a potential GHG emission control or mitigation measure, the cost to implement and maintain the measure must be fully evaluated. The predominant method utilized to evaluate climate change mitigation methods is the use of marginal abatement cost (MAC) curves. A MAC curve will aid policy

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and decision makers in the evaluation of the costs of certain control measures versus the measures resulting in the reduction of GHG emissions. MAC curves can be used to compare different control technologies as well as different carbon pricing schemes such as a cap and trade program versus a carbon tax. Another use of the MAC curve is comparison of regional, national, and international price structures for overlapping control programs. > Figure 3.1 provides a detailed example of a MAC curve followed by a thorough explanation of how to read MAC in > Fig. 3.2 [13]. As indicated in > Fig. 3.2, the width of the curve for the potential abatement option is the amount of CO2e that can be reduced by this option. The height of the curve is the amount the option would cost to avoid an equivalent 1 t reduction of CO2e as measured against a standard reference case. A negative cost would be represented by a line going below the axis and would imply a cost savings over the life cycle of the option versus a positive cost (as reflected in > Fig. 3.1), where there would be measureable costs to implement the option versus the reference case. Most of the current strategies to mitigate climate change include many of these alternatives in their planning. The application of the abatement options will vary by location depending on economic, social, and other factors. A summary of some potential legislative options is presented with a focus on the specific carbon pricing options (more particularly, cap and trade programs) in a market-based system given their prominence in regional and international carbon mitigation strategy.

Traditional Command and Control One potential mechanism available to policy makers is the use of the concept of traditional command and control. Command and control simply implies that the government establishes a level of emissions that it deems acceptable and then implements regulations accordingly to mandate applicable sources of GHG emissions to lower their emissions to these mandated levels. Command and control has been utilized by governmental agencies in many nations for many years including the United States. The major disadvantage as described in the sections below is that while straightforward, a command and control approach reduces opportunities for innovation and flexibility of the emission sources covered in the program.

Cap and Trade Program While there are many different approaches and options available, the most utilized lever for climate change mitigation and a key component of almost all GHG emission mitigation legislative efforts to date is a basic cap and trade program. A cap and trade program is a market-based approach that is built upon the economic concepts of supply and demand. One reason for the prominence of a cap and trade program in climate mitigation approaches is the successful and efficient use by the United States of a cap and trade program to reduce sulfur dioxide emissions under the Acid Rain provisions of the 1990 Clean Air Act Amendments.

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0

0.6

0.8

1.0

1.2

1.4

1.6

Commercial buildings – new shell improvements

1.8

2.4

2.6

Solar CSP

3.2

Coal-to-gas shift – dispatch of existing plants

Car hybridization

Potential Gigatons/year

3.0

Coal power plants – CCS rebuilds

Coal power plants – CCS new builds

Onshore wind – medium penetration

Coal power plants – CCS new builds with EOR

Reforestation

2.8

Onshore wind – Industry – high penetration CCS new builds on Biomass power – carbonintensive cofiring processes

2.2

Distributed solar PV

Winter cover crops

2.0

Afforestation of Natural gas pastureland and petroleum systems management

Onshore wind – low penetration Industry – combined heat and power Cellulosic Manufacturing – biofuels Existing power HFCs mgmt plant Residential conversion buildings – efficiency new shell improvements improvements Conservation tillage Commercial buildings – CFL lighting

0.4

Fuel economy packages – cars

Commercial buildings – LED lighting

Commercial electronics

0.2

. Fig. 3.1 Example of MAC curve (Adapted from [13])

–230

–120

–90

–60

–30

0

Industrial Residential process Fuel economy Coal mining – buildings – Active forest improvemanagement packages – light methane shell 60 ments trucks mgmt retrofits Residential Commercial Nuclear Commercial electronics Residential buildings – buildings – newwater control combined build 30 Residential heaters systems heat and buildings – power lighting

3

90

Cost Real 2005 dollars per ton CO2e

Abatement cost Fig. 3.3 [15]. Industries would annually be allowed to emit a certain amount of CO2. Plants that emitted less than the cap would be able to sell their letover allowances to industries that exceed caps. The government would gain revenue by auctioning allowances permitting industries to discharge a set amount of greenhouse gases.

Excess CO2

CAP Leftover allowance for sale

CO2 TRADE wances Allo Money

Innovative companies that develop ways to reduce emissions earn income by selling unneeded allowances.

Economic pressure encourages companies that exceed caps to find ways to cut emissions.

. Fig. 3.3 Illustration of how a typical cap and trade program functions

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As indicated in the figure, a key aspect of a cap and trade program is the continual incentive to implement innovative technological solutions that reduce GHG emissions and increase opportunities to gain from those reductions. This financial incentive is not directly present in traditional command and control programs. A company that acts early and can afford the technology investment may benefit if and when a cap and trade program is implemented. Likewise, a company that elects not to implement GHG emissions reduction technology will feel the economic pressure of having to purchase allowances for each and every ton of CO2e emitted. Cost containment mechanisms are extremely important in the design of the cap and trade program. Mechanisms available include: ● ● ● ●

Offsets Borrowing and banking Safety valves Linkage

Offsets refer to projects undertaken outside of the sources involved in the cap and trade programs that enable sources covered in the program to purchase reduction credits from sources not covered in the program. This provides an opportunity to harvest lowcost emission reductions that are quantifiable and defined from a broad range of sources. The CDM established under the Kyoto Protocol established an offset market between developed and developing countries on an international level. Banking and borrowing of allowances are two other mechanisms for cost containment in a cap and trade program. Banking is the process where a source may keep excess or unused allowances for future use or sell. Borrowing is the concept where a source may borrow allowances from the program to cover current year’s emissions with the guarantee that the allowances will be paid back through future emission reductions. Safety valves generally refer to a predetermined allowance cost cap that once reached would trigger other cost containment mechanisms. Choosing a reasonable safety valve is very challenging as setting a trigger too low would diminish economic incentives for innovative technology growth to reduce GHG emissions and setting a cap too high would never realistically impact carbon costs. Finally, as mentioned previously, linkage to other emission trading systems and programs could help to efficiently expand carbon markets without significant changes to programs already in effect. Additional issues with program linkage are addressed in the section below on preemption of current programs.

Cap and Dividend A cap and dividend program starts with a ‘‘upstream’’ economy-wide cap on carbon suppliers as opposed to a downstream cap on carbon emission sources as referred to in the cap and trade discussion above. As noted previously, there are two possible places to implement a cap in a carbon economy:

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● Where CO2 leaves the economy and enters the atmosphere (downstream) ● Where carbon enters the economy in the form of a fossil fuel (upstream) As discussed in detail in the previous section, traditional cap and trade programs place the cap on the downstream end where the emissions actually occur. On the other hand, capping carbon on the upstream as it enters the economy requires the ‘‘first sellers’’ of carbon fuels such as oil, coal, and natural gas to purchase carbon allowances equal to the carbon content of their fuels. Annually, these companies would reconcile their carbon allowances and potentially pay fines if enough allowances have not been purchased to meet their allotted quantity of allowances. When fuel companies purchase carbon emission allowances, these costs will certainly be passed on to consumers of these fuels; thus, the cost of emitting the CO2 is paid by the ultimate consumer of the fuel. In general, the revenues in a cap and dividend program are placed into a trust fund for payment of dividends to consumers and to finance clean energy, energy-efficiency programs, and investment in innovative carbon mitigation strategies.

Carbon Tax Carbon taxes are fairly straightforward and basically the same as the cap and dividend program, without the direct dividend. Basically, a tax would be placed on a per unit basis of any carbon-derived fossil fuels resulting in higher prices for consumption of carbonbased fuels. On paper, the higher prices would drive increased energy conservation and the demand for alternative energy development and implementation into the marketplace. Additionally, a tax may drive increased demand for lower carbon fuels such as natural gas, propane, and other nontraditional fuels in the transportation sector. A carbon-based fuel tax would impact most economic sectors either directly or indirectly given the use of fuels in every aspect of society. Carbon taxes strongly create incentives for consumers and manufacturers to reduce the use of traditional fuels and to consider alternative fuels to help minimize the burden of the carbon tax costs. While several countries in Europe including Sweden, Denmark, Ireland, and Finland have already instituted carbon tax programs, there is general opposition to a European Union-wide carbon tax. France shelved a proposed carbon tax in May of 2010 and other countries are openly opposed to the concept. In the United States, carbon taxes have been discussed in the development of several of the legislative proposals to date; however, cap and trade or cap and dividend programs remain the most prominent option in US GHG emissions mitigation legislation.

Subsidies and Other Levers Government-funded subsidies and other federally funded levers for climate change must obviously have a funding mechanism. Thus, these initiatives will always be coupled with

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programs such as cap and trade or cap and dividend. Governments will carefully study the impacts of economic and control efforts and their impact on the public. Subsidies will be used primarily to help minimize the costs associated with the financial impacts from the primary means of climate change mitigation.

Renewable Energy Standards Many states in the United States have established specific standards requiring electric utilities to generate a certain amount of electricity from renewable or alternative energy sources [16]. These requirements, referred to as a ‘‘renewable portfolio standard’’ (RPS) or ‘‘alternative energy portfolio standard’’ (AEPS), require a certain percentage of an electric utility’s power plant capacity or generation to be derived from renewable or alternative energy sources within a specified timeframe. The standards range from modest to aggressive. Some states also include ‘‘carve-outs’’ (requirements that a certain percentage of the portfolio be generated from a specific energy source, such as solar power) or other incentives to encourage the development of particular resources. While the first RPS was established in 1983, the majority of states passed or strengthened their standards after 2000. Although the strengthened requirements are still new, these efforts are starting to increase the use of renewable energy. Many states allow electric utilities to comply with the RPS or AEPS through emissions trading credits. The success of various state efforts to increase renewable or alternative energy production greatly depends in large measure on emerging federal legislation and policy development to effectively encourage clean energy generation.

Major International and Regional GHG Mitigation Programs As alluded to previously, the major focus of initial legislative and regulatory initiatives has been implementing an effective cap and trade program amid the many pitfalls that exist. Many of the current and developing international, regional, and state-specific (within the United States) GHG programs implemented or being developed to date are summarized in > Table 3.5 and then expanded upon in more detail in the section below.

European Union’s Emission Trading Scheme The European Union’s Emission Trading Scheme (EU ETS) was developed over the past decade and is based on aiding European countries in the quest to meet the GHG emission reduction targets established under the Kyoto Protocol by the year 2012. Formally launched in 2005, the EU ETS remained in a ‘‘trial period’’ through 2007 before formally entering a second phase in 2008 where the EU ETS would be utilized to meet European targets under the Kyoto protocol [17].

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. Table 3.5 International, national, regional, and state-specific greenhouse gas mitigation programs Program or country

Origination date Geographic coverage

European Union’s Emission Trading Scheme (EU ETS) The Northeast Regional Greenhouse Gas Initiative (RGGI) The Western Climate Initiative (WCI)

2005

European Union

2009

Northeastern United States

2007

Midwestern Regional Greenhouse Gas Reduction Accord

2007

Western United States and Canadian Provinces Midwestern United States

California

2008

Florida Australia

2008 2009

California coverage only; linkage to the WCI Florida Australia

New Zealand China India Brazil

2008 2007 2008 2008

New Zealand China India Brazil

Indonesia South America Canada

2008 2008 2008

Indonesia South America Canada (tied closely to United States)

Implementation of the EU ETS is intended to achieve significant reductions in GHG emissions and other goals including: ● Reduction in CO2e emissions of 20% by 2012 ● Increase in renewable energy usage of 20% by 2010 ● Improvements in overall energy efficiency by 20% before 2010 As a traditional cap and trade system, the EU ETS was designed and tailored after the US trading schemes for sulfur dioxide and nitrogen oxides under the Clean Air Act (CAA). Aspects of the EU ETS include: ● An absolute cap on CO2e emissions on many types of facilities ● Free allowance distribution to the covered facilities in the initial implementation phase ● Requirements that facilities in the program must determine CO2e emission levels, report those emissions, and surrender allowances for each ton of CO2 emitted More than 11,000 energy-intensive facilities are included in the program across the 27 European Union member states. The EU ETS presently includes only the power sector,

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specified industries, and large combustion operations. This represents about half of the CO2e emissions in the European Union. Although allocations under the program are currently free allocations, during the third phase (years of 2013–2020) the EU ETS will begin to move toward auctioning of allowances. Also during Phase III, a larger number of facilities will be included in the program as well as adding other GHGs beyond CO2 such as nitrous oxide and perfluorocarbons.

The Northeast Regional Greenhouse Gas Initiative (United States) The Northeast Regional Greenhouse Gas Initiative (RGGI), the first mandatory cap and trade program in the United States for CO2, became effective on January 1, 2009, with a goal of reducing CO2 emissions by 10% from 2009 levels by the year 2018. The program encompasses ten participating Northeast and Mid-Atlantic states including: ● ● ● ● ● ● ● ● ● ●

Connecticut Delaware Massachusetts Maryland Maine New Hampshire New Jersey New York Rhode Island Vermont

RGGI established a cap of 188 million tons of CO2 for the ten states and covers fossil fuel-fired electric power plants that are 25 MW or greater in power generation capacity. This represents about 225 facilities in the ten state regions. Each participating state is provided a CO2 budget based on its share of emissions that is managed accordingly to ensure total capped emissions are not exceeded [18]. Allowances are auctioned under the program on a quarterly basis. Key stated goals to be accomplished by RGGI include: ● Initial stabilization of CO2 emissions in early phase of program ● Reduction of CO2 emissions of approximately 2½% per year as the program matures ● Support of a green economy by using auction revenues for investment in energy efficiency, renewable energy, and accelerating a regional shift to a clean energy economy ● Promotion of energy independence by providing a means for investment in energy efficiency ● Providing a model for national and international programs being designed to reduce CO2 emissions

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The Western Climate Initiative (United States and Canada) The Western Climate Initiative (WCI) kicked off in early 2007 and covers the following US states and Canadian provinces: ● ● ● ● ● ● ● ● ● ● ●

Arizona California Montana New Mexico Oregon Utah Washington British Columbia Manitoba Ontario Quebec Similar to the other established GHG programs, the goals of the WCI include:

● Reduction of GHG emissions ● Spurring the growth of new clean energy technology ● Reducing use and dependence on nondomestic fuel supplies Under the WCI, emissions from 90% of the facilities in the region will be captured in the program including: ● ● ● ● ●

Electricity generation Industrial and commercial fossil fuel combustion Industrial process emissions Gas and diesel consumption for transportation Residential/commercial fuel use

Reporting of emissions will begin in 2011 and will be based on calendar year 2010 emissions with the first phase of a cap and trade beginning in 2012. Beginning in 2015, the program will be expanded to include the remaining 10% of facilities not covered in the initial phase [19]. Once again, cap and trade is the primary driver for the program that includes allowance banking and offsets. The WCI is designed to be fully incorporated into a national GHG trading program, if and when the program is established.

Midwestern Regional Greenhouse Gas Reduction Accord (United States and Canada) The Midwestern Regional Greenhouse Gas Reduction Accord (Midwest Accord) was initiated on November 15, 2007, by the Governors of:

Climate Change Legislation: Current Developments and Emerging Trends

● ● ● ● ● ● ●

3

Illinois Iowa Kansas Michigan Minnesota Wisconsin The Premier of Manitoba

An advisory group was formed including a mix of individuals representing interests from across the region such as governments, business and industry, academia, agriculture, and environmental groups with the intent of developing recommendations for the Midwest Accord. Design principles were utilized to determine the recommendations for reduction targets and the cap and trade program design [20]. The signed Midwest Accord calls for: ● 2020 targets to be established for GHG emission reductions of 20% below 2005 levels and 80% reduction below 2005 levels by 2050 ● Coverage of electricity generation, industrial combustion sources, process emission sources, and fuel use in both commercial and transportation sectors ● Implementation of a stand-alone cap and trade program that also could easily link to the other existing cap and trade programs in the United States and in Europe Members of the Midwest Accord prefer a federal approach to GHG emission limits and a cap and trade program; however, members plan to continue to evaluate the prospects of federal plans and act accordingly within the member states/territories as necessary.

California Climate Change Scoping Plan Adopted in 2009, California’s Climate Change Scoping Plan referred to as the AB32 Scoping Plan (AB32) is the state’s roadmap to achieve GHG emission reductions to reduce impacts of global warming. AB32 includes: ● A cap and trade program covering 85% of the state’s GHG emissions ranging from electricity generation to industrial and transportation sources ● Linkage to WCI program for maximum flexibility and program benefit ● Transportation measures to initially reduce vehicle GHG emissions by 30% by 2016 ● Electricity and energy standards including a goal of 33% renewable energy usage by 2020 ● Identifying pertinent industry standards to reduce GHG emissions ● Focus on the GHG with highest GWP ● Forest and agriculture projects ● Waste gas recycling

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AB32 will be the key cog of California’s development of a green economy by driving efficient growth, increasing venture capital opportunities in the energy sector, producing green jobs, and producing new clean energy technologies [21].

Florida On June 25, 2008, Florida Governor Charlie Crist approved House Bill 7135, which requires the Florida Department of Environmental Protection to create a cap and trade regulatory program to reduce greenhouse gas emissions from major emitters, but sets no specific limits and requires any program to be ratified by the legislature. The Florida Climate Action Team was formed and continues to consider actions that the state can take to develop climate change policy based on other regional and federal programs in the United States [22].

Australia The Government of Australia has been preparing to introduce a comprehensive climate change plan for many years. In announcing its Carbon Pollution Reduction Scheme, the Australian Government believes it ‘‘is acting to reduce carbon pollution, create the jobs of the future and secure Australia’s future prosperity.’’ Through its commitment under the Kyoto Protocol, Australia is on target to slow the growth of the country’s GHG emissions to 108% of 1990 levels by 2012 [23]. The Australian government has established stringent targets to lower the country’s GHG emissions with a goal to reduce emissions to 25% below 2000 levels by 2020. The Australian target is contingent on other industrialized nations agreeing to implement similar long-term commitments for GHG emission reductions. Key aspects of the Australia Carbon Pollution Reduction Scheme include: ● Strengthening efforts to prepare Australia for a low carbon pollution future through the use of renewable energy ● Research and development of clean energy technology ● Measures to help households, businesses, communities, and regions transition and adapt to a low carbon economy

New Zealand New Zealand was party to the Kyoto Protocol and, thus, has agreed to reduce GHG emissions accordingly. Legislative efforts in New Zealand have focused on the development of the New Zealand Emissions Trading Scheme (NZ ETS) similar to the EU ETS. The NZ ETS, which became law in New Zealand in 2008, places the burden of carbon market costs on the producers or carbon emissions. Funds from the NZ ETS will be used to [24]:

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● Reduce GHG emissions through legislative controls ● Invest in clean technology and renewable power operation ● Plant trees for carbon sequestration Sectors included in the NZ ETS include: ● ● ● ● ● ● ●

Forestry Transport fuels Electricity production Industrial processes Synthetic gases Agriculture Waste handling

The NZ ETS began in 2010 with a transition phase through 2012. In the transition phase, emitters of GHG would be required to purchase emission credits from the NZ ETS. Additionally, energy, industrial, and fossil fuel sectors will be required to surrender one credit for every 2 t of GHG emissions produced.

China Although China is a non-Annex 1 country under the UNFCCC and Kyoto Protocol and is not required to reduce GHG emissions, it is included in the CDM established under the Kyoto Protocol and has been a major player in developing CDM credits. While the Chinese government continues to study appropriate levels of GHG emission reductions and believes in ‘‘common but differentiated responsibilities,’’ there are developing policies that show potential for future GHG emissions reductions including [25]: ● Energy efficiency and conservation programs including energy intensity targets, high performer programs, closure of inefficient power plants, and inefficient industrial facilities ● Transportation initiatives primarily in the form of fuel economy standards ● Renewable energy targets and incentives ● Policies including export taxes on energy-intensive products and promotion of advanced clean energy technologies ● Reforestation projects ● Energy diversification in nuclear, natural gas, and hydropower ● Advanced coal initiatives

India India is in the same category as China as a non-Annex 1 country with no binding GHG emission limits under the Kyoto Protocol. Similar to China as well, India is a participant in

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the CDM and is second to China in the number of projects to date. In June 2008, India released a National Action Plan on Climate Change that included programs on climate change mitigation and adaptation [26]. This plan established eight core ‘‘national missions’’ through 2017 focused on: ● ● ● ● ● ●

Renewable energy including solar, wind, and hydropower Clean coal Nuclear power Energy efficiency and conservation Transportation issues including alternative fuels, clean engines, and mass transit Forest and tree cover projectsx

Brazil As part of its stated commitment to sustainable development, the Government of Brazil presented a proposal at the Copenhagen COP-15 meeting that would result in a 36–39% reduction in GHG emissions by the year 2020 [27]. Efforts in Brazil will focus on the reduction of deforestation in the Amazon and initiatives in the agriculture industry. Brazil has developed a National Plan on Climate Change that includes the following primary actions [28]: ● ● ● ● ● ● ●

Stimulate energy efficiency in various economic sectors. Maintain gains in renewable energy growth in the electricity generation matrix. Encourage further growth in the sustainable use of bio-fuels for transportation sector. Seek sustained reduction in deforestation rates. Eliminate net loss of forest coverage in Brazil by 2015. Strengthen inter-sector adaptation actions for vulnerable population groups. Identify potential impacts from climate change to assist in development of an appropriate response strategy.

Brazil passed a National Policy on Climate Change in December 2009 following in step with the National Plan on Climate Change. A National Fund on Climate Change was also instituted to address budgetary aspects of climate change management in Brazil.

Indonesia In September 2009, the Indonesian Minister of National Development Planning and the Minister of Finance launched the Indonesia Climate Change Trust Fund (ICCTF) [29]. The ICCTF focuses on: ● The energy sector including renewable energy and improved energy efficiency ● Sustainable forest management ● Reducing the vulnerability of agriculture, water, and coastal zones

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The goal of the ICCTF is to advance investment in technologies to reduce GHG emissions and adaptation to climate change impacts. The ICCTF is designed to develop grant funding and technological investment from various sources. The United Kingdom, the Netherlands, Australia, Norway, and Sweden have already agreed to participate in the ICCTF.

South Africa The South African Government completed a long-term mitigation scenario (LTMS) in 2006 to study the impact of climate change and to begin to consider strategy options for climate change mitigation and GHG emissions reductions. This effort included input from various stakeholders from the Government, business, communities, and the labor force. Elements of the South African vision for a climate change mitigation strategy include [30]: ● ● ● ● ● ● ●

Energy efficiency and conservation Ambitious targets for GHG emissions reductions Use of a carbon tax or carbon cost scheme Diversifying energy mix away from coal Developing a zero carbon electricity sector Consideration of carbon capture and storage options Transportation elements

Canada The Canadian Government has committed to reduce GHG emissions by approximately 17% from 2005 levels by 2020 and will work closely with US commitments on GHG emission reduction initiatives. As noted above, certain provincial governments within Canada have already engaged with groups in the United States such as the WCI and the Midwest Accord to address GHG emission reductions. Overall, the Government of Canada is committed to [31]: ● ● ● ●

Build a clean energy system and be a leader in clean energy technology Introduce regulations to limit GHG emissions Invest in technology for environmental improvements Support and play an active role in the UN climate change meetings and process

As shown above, the actions by various countries and regions regarding climate change mitigation and legislative actions are different to an extent; however, generally, the mitigation options and GHG emission reduction programs under consideration are consistent in countries around the globe. Although each country is acting somewhat independently, the path to linkage of GHG emission management programs and

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consistency in climate change legislation is fairly straightforward as there are only a limited number of effective options available.

United States Environmental Protection Agency Actions While admitting that the best overall solution to regulation of GHG emissions is federal and international legislation, the United States Environmental Protection Agency (USEPA) believed it could not afford to wait any longer for a legislative mechanism; thus, in 2009, the USEPA initiated a series of actions toward regulation of GHG emissions apart from federal congressional action. Key actions or developments in the USEPA GHG regulatory process include: ● ● ● ● ●

Greenhouse Gas Endangerment Finding Light-Duty Motor Vehicle Emission Standards for CO2 Greenhouse Gas Tailoring Rule Mandatory Greenhouse Gas Reporting Rule National Environmental Policy Act (applicable to US government agencies)

Greenhouse Gas Endangerment Finding The tidal wave of GHG regulatory actions by the USEPA started rolling on April 2, 2007, per Massachusetts v. EPA, 549 US 497 (2007), when the US Supreme Court ruled that GHG emissions are ‘‘air pollutants’’ as defined by and subject to be regulated under the US Clean Air Act (CAA). The Supreme Court said that the USEPA must determine if GHG emissions from new motor vehicles cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare, or whether the science is too uncertain to make a reasoned decision. The USEPA had to follow the specific language of section 202(a) of the CAA. The Supreme Court decision resulted from a petition for rulemaking under section 202(a) filed by more than a dozen environmental, renewable energy, and other organizations [32]. This Supreme Court decision quickly led to a challenge in November of 2008 of a prevention of significant deterioration (PSD) permit on the basis that the permit was issued by USEPA Region 8 but did not include best available control technology (BACT) limits for CO2. The United States Congress established the PSD regulations as part of the new source review (NSR) program in the 1977 Clean Air Act Amendments and modified the regulations in the 1990 Clean Air Act Amendments. NSR is a preconstruction permitting program that: ● Ensures the maintenance of national ambient air quality standards ● Assures that new emissions do not slow progress toward reaching attainment in those areas that do not currently meet the national ambient air quality standards

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● Ensures that appropriate air pollution control technology is installed at new plants or at existing plants that undergo major modifications On December 18, 2008, the USEPA issued a memorandum referred to as ‘‘EPA’s Interpretation of Regulations that Determine Pollutants Covered by Federal Prevention of Significant Deterioration (PSD) Permit Program’’ (known as the ‘‘Johnson Memo’’ or the ‘‘PSD Interpretive Memo’’). Whether a pollutant is ‘‘subject to regulation’’ is important for the purposes of determining whether it is covered under the CAA permitting programs. The PSD Interpretive Memo established that a pollutant is ‘‘subject to regulation’’ only if it is subject to either a provision in the CAA or regulation adopted by EPA under the CAA that requires actual control of emissions of that pollutant. In late December 2008, the USEPA received a petition of reconsideration for the position taken in the Johnson memo from various environmental organizations. The petition questioned the validity of the memo for use in making regulatory determinations. Following the presidential administration change from George W. Bush to Barack Obama in January 2009, the USEPA granted the petition of reconsideration and reopened comment on the endangerment issue in February 2009. Then on December 7, 2009, new USEPA Administrator Lisa Jackson signed two distinct and historic findings regarding GHG under section 202(a) of the CAA: ● GHG Endangerment Finding ● GHG Cause or Contribute Finding The USEPA found that the current and projected atmospheric concentrations of the six key GHGs – CO2, CH4, N2O, HFCs, PFCs, and SF6 – ‘‘threaten the public health and welfare of current and future generations.’’ The USEPA also determined that the combined emissions of the six key GHGs from new motor vehicles and new motor vehicle engines ‘‘contribute to the GHG pollution which threatens public health and welfare.’’ Although this determination, published by the USEPA on December 15, 2009, did not impose any new requirements on industry or other entities, the determination was a prerequisite to finalizing the GHG standards for light-duty vehicles. In this determination, USEPA Administrator, Lisa Jackson commented that, ‘‘After a thorough examination of the scientific evidence and careful consideration of public comments, the U.S. Environmental Protection Agency (EPA) announced today that greenhouse gases (GHGs) threaten the public health and welfare of the American people. EPA also finds that GHG emissions from on-road vehicles contribute to that threat. GHGs are the primary driver of climate change, which can lead to hotter, longer heat waves that threaten the health of the sick, poor or elderly; increases in ground-level ozone pollution linked to asthma and other respiratory illnesses; as well as other threats to the health and welfare of Americans. These long-overdue findings cement 2009’s place in history as the year when the United States Government began addressing the challenge of greenhousegas pollution and seizing the opportunity of clean-energy reform. Business leaders, security experts, government officials, concerned citizens and the United States Supreme Court have called for enduring, pragmatic solutions to reduce the greenhouse gas

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pollution that is causing climate change. This continues our work towards clean energy reform that will cut GHGs and reduce the dependence on foreign oil that threatens our national security and our economy’’ [32]. As expected, on March 29, 2010, the USEPA followed the GHG endangerment finding with a notice conveying the USEPA’s decision to continue applying the PSD Interpretive Memo’s interpretation of ‘‘subject to regulation’’ and concluded that the ‘‘actual control interpretation’’ is the most appropriate interpretation. The USEPA established that CAA permitting requirements apply to a newly regulated pollutant at the time a regulatory requirement to control emissions of that pollutant ‘‘takes effect’’ (rather than upon promulgation or the legal effective date of the regulation containing such a requirement). Based on the anticipated promulgation of the light-duty vehicle rule, the notice stated that the GHG requirements of the vehicle rule would trigger CAA permitting requirements for stationary sources on January 2, 2011.

Light-Duty Motor Vehicle Emission Standard for CO2 Falling in line with the previous decisions, in April 2010, the USEPA and the Department of Transportation’s National Highway Traffic Safety Administration (NHTSA) finalized a joint rule to establish a national program consisting of new standards for model year 2012 through 2016 light-duty vehicles that will reduce GHG emissions and improve fuel economy. ‘‘EPA is finalizing the first-ever national greenhouse gas (GHG) emissions standards under the Clean Air Act, and the NHTSA is finalizing Corporate Average Fuel Economy (CAFE) standards under the Energy Policy and Conservation Act’’ [33]. Based on the regulatory framework now in place, through the setting of the light-duty vehicle standard, GHG emissions would now be formally considered regulated pollutants. Key aspects/considerations of the light-duty motor vehicle rule include: ● Vehicles must meet a combined average emissions level of 250 g of CO2 per mile in model year 2016 equivalent to 35.5 miles per gallon (15 km/l). ● Manufacturers must build a single light-duty national fleet that satisfies requirements of the Federal and State of California standards. ● Provisions for nationwide energy and environmental benefits while maintaining consumer vehicle options.

Greenhouse Gas Tailoring Rule In light of the light-duty motor vehicle rule that established a standard for GHG emissions and, thereby, made GHG a formally regulated pollutant, the USEPA issued a final rule on May 13, 2010, to address GHG emissions from many industrial and electrical generation sources under the traditional CAA permitting programs in place since the 1970s.

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The USEPA rule sets new thresholds for GHG emissions to determine when air permits currently issued under the USEPA NSR PSD and CAA Title V Operating Permit programs are required to include GHG emissions [34]. The USEPA rule is called a tailoring rule because it ‘‘tailors’’ the requirements of these traditional air-permitting programs to clarify the sources required to obtain permits for GHG emissions. The USEPA’s stated goal is to insure that GHG emissions sources in this revised permitting program will include the United States’ largest GHG emitters such as electrical generation plants, chemical plants, refineries, and other production facilities. Emissions from smaller sources with much lower GHG emission levels will be excluded in the initial round of CAA permitting efforts. Although the tailoring rule includes a timeline that initially zeroes in on the largest of GHG emission sources, the rule has future plans built in to evaluate additional GHG emission source coverage in the years ahead. Traditional permitting thresholds for criteria pollutants including sulfur dioxide, nitrogen dioxide, volatile organic compounds, lead, carbon monoxide, etc., have been in the range of 100–250 tons per year (t/year). Permitting GHG emissions at these same levels would result in permits for many very small sources; thus, while ‘‘these thresholds are appropriate for criteria pollutants, they are not feasible for GHGs because GHGs are emitted in much higher volumes.’’ Without this tailoring rule, the lower emissions thresholds would take effect automatically for GHGs on January 2, 2011. PSD and title V requirements at these thresholds would lead to potentially tens of thousands of PSD permits and millions of title V permits. State, local, and tribal permitting authorities would be overwhelmed and the programs’ abilities to manage air quality would be severely impaired. Thus, the USEPA has elected to phase in the CAA permitting requirements for GHGs in two initial steps. Step 1 includes the timeframe from January 2, 2011, to June 30, 2011. Highlights of step 1 include: ● Only emission sources currently subject to the PSD permitting program (i.e., sources that are newly constructed or modified in a way that significantly increases emissions of a pollutant other than GHGs) would be subject to permitting requirements for their GHG emissions under PSD. ● For new projects, only GHG emission increases of at least 75,000 t of GHG per year on a CO2e basis would need to determine the best available control technology (BACT). ● Only sources currently subject to air permitting would be subject to air-permitting requirements for GHG. ● During this phase, no sources would be subject to air-permitting requirements only for GHG emissions. Step 2 is the timeframe from July 1, 2011, to June 30, 2013. Highlights of step 2 include: ● PSD permitting requirements will now cover new construction projects that emit GHG emissions of at least 1,00,000 t/year even if they do not exceed the permitting thresholds for any other pollutant.

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● Modifications at existing facilities that increase GHG emissions by at least 75,000 t/year will be subject to permitting requirements, even if they do not significantly increase emissions of any other pollutant. ● For the first time, air permit requirements will apply to emission sources based on their GHG emissions even if they would not apply based on emissions of any other pollutant. Facilities that emit at least 1,00,000 t/year of CO2e will be subject to title V permitting requirements. In the rule, the USEPA leaves open the possibility of considering additional rulemaking that could begin in 2011 and may include: ● Additional emission sources for GHG permitting ● Provisions for certain smaller sources to be permanently excluded from permitting of GHG emissions ● A range of opportunities for streamlining future GHG permitting that have the potential to significantly reduce permitting burdens

Mandatory Greenhouse Gas Reporting Rule Parallel to the efforts by the USEPA to regulate GHG emissions under the CAA, the USEPA promulgated the mandatory GHG reporting rule under 40 CFR Part 95 on October 30, 2009, and finalized the rule in December 2009. While reporting of GHG emissions has been required in the programs noted previously and many companies have been reporting emissions voluntarily for many years, the new GHG reporting rule is the first national effort to mandate reporting in the United States. The rule requires various electric generation and industrial facilities to report emissions of GHG from plant operations beginning with calendar year 2010 [35]. USEPA’s purpose in promulgating the GHG reporting rule is that the rule will ‘‘provide EPA, other government agencies, and outside stakeholders with economywide data on facility level (and in some cases corporate level) GHG emissions, which should assist in future policy development’’ (Federal Register; October 30, 2009; page 56265). There is great uncertainty regarding what type of policy development and the extent of the impact. However, one thing is certain: Mandatory reporting of GHG emissions begins this year.

Summary of Sectors Covered in the GHG Reporting Rule Applicability is based on industry-type and/or level of emissions. Facilities required to report regardless of emission levels include: ● Electric generation ● Adipic acid production

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● ● ● ● ● ● ● ● ● ● ● ● ● ●

3

Aluminum production Ammonia manufacturing Cement production HCFC-22 production HFC-23 destruction processes Lime manufacturing Nitric acid production Petrochemical production Petroleum refineries Phosphoric acid production Silicon carbide production Titanium dioxide production Municipal solid waste landfills Manure management systems

Additional source categories required to report if combined emissions exceed 25,000 t of CO2e include: ● ● ● ● ● ● ● ● ● ● ●

Ferroalloy production Glass production Hydrogen production Iron and steel production Lead production Pulp and paper manufacturing Zinc production Underground coal mines Industrial wastewater treatment facilities Industrial waste landfills Magnesium production facilities

Finally, facilities that operate stationary combustion units with combined GHG emissions that exceed the 25,000 CO2e level must report.

What the Rule Requires After verifying that reporting is required, a facility must determine if existing monitoring systems are sufficient to provide accurate parameter data needed to complete emission calculations. The applicable subpart and general provisions will dictate the data requirements. In many cases, new or enhanced monitoring systems may need to be installed. Provisions are in place to obtain additional time (through 2010) to use best available data while implementing more robust monitoring systems. One caution is to insure all accuracy requirements such as meter certification and calibrations are met as the GHG reporting rule could be more stringent than current requirements for parameters such as natural gas supply.

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Each facility must maintain a GHG monitoring plan that includes: ● Summaries of methods to monitor, record, and maintain data ● Details of emission calculation procedures ● The organizational structure for GHG data management and review The first GHG emissions reports are due in March 2011 for calendar year 2010 emissions. The details of an individual facility’s report will vary based on facility type and emissions level. Following the initial report in 2011, emission reports will be due to the USEPA annually. With emissions reporting no longer solely a voluntary effort, the bar is being raised for accurate management of GHG emissions including: ● Moving to third-party data verification for the basis of regional emissions reporting rather than internal company-only review ● Satisfying future allowances and emissions trading financial accounting requirements ● Future Securities and Exchange Commission (SEC) reporting ● Federal compliance with the USEPA GHG reporting rule

United States National Environmental Policy Act Following the Supreme Court’s 2007 Massachusetts v. EPA decision, the effort to include GHG emissions evaluation in National Environmental Policy Act (NEPA) evaluations picked up momentum. On February 18, 2010, the White House Council on Environmental Quality (CEQ) issued guidance to federal agencies to consider the following in future NEPA decisions: ● Consider climate change and GHG emissions. ● Implement climate mitigation strategies and monitoring of results. ● Determine if exclusions from including GHG emissions exist for certain projects. This is a highly controversial subject as this guidance will now require policy makers to rely on subjective data to make decisions on public projects. At the time of writing, this guidance was still in a proposed state [36].

United States Federal GHG Legislation With all of the efforts by the USEPA to move forward with GHG emission regulations, there is still a highly probable outcome that the federal government will eventually pass legislation to regulate GHG emissions at a national level and in a consistent manner with other international programs in effect or development as alluded to previously. Some useful definitions related to federal climate legislation include [37]:

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● Allowance – a limited authorization by the government to emit 1 t of pollutant ● Auctions – used in market-based pollution control schemes to raise program revenues and fund various facets of reduction programs ● Banking – the process where allowances can be used or traded in a future year ● Carbon leakage – decreases in GHG emissions or benefits outside the boundaries of a defined regulatory program In 2009 and 2010, there has been a myriad of legislative approaches put forth in the United States including: ● ● ● ● ●

American Energy Security Act (Waxman–Markey: May 2009) Clean Energy Act of 2009 (November 2009) Clean Energy Partnerships Act of 2009 (November 4, 2009) Carbon Limits and Energy for America’s Renewal (Cantwell–Collins: December 2009) American Power Act (Kerry–Lieberman: May 2010) Each of these approaches is summarized briefly below.

American Energy Security Act (Waxman–Markey: June 2009) In June 2009, the 112th Congress of the United States passed the first major climate change bill in US history referred to as the American Energy Security Act or more commonly, the Waxman–Markey bill given that the bill was cosponsored by Representatives Henry Waxman (Democrat from California) and Ed Markey (Democrat from Massachusetts). The Waxman– Markey bill establishes CO2 reduction targets, a federal cap and trade program, a renewable electricity standard (RES), requirements for coal-fired power plants, energy-efficiency standards, worker transition programs, smarter cars, and smarter electricity grids [38]. Emission reduction goals starting in 2012 and based on 2005 emission levels include: ● ● ● ●

A 3% reduction by 2012 A 17% reduction by 2020 A 42% reduction by 2030 More than 80% reduction by 2050

Coverage of the program initially includes approximately 85% of the overall economy including electricity producers, oil refineries, natural gas suppliers, and multiple industry categories. Facilities with CO2 emissions above 25,000 t/year would be required to acquire a permit for their emissions or, in other words, obtain emission allowances for all CO2 emissions on an annual basis. Facilities can trade these allowances to other facilities that need allowances or bank them for future usage. Eighty-five percent of the allowances would be given away under the current plan to major energy users; however, the free allowances will gradually be decreased over the first 20 years of the program. The remaining 15% of the allowances would be auctioned off. Within 20 years from program implementation, essentially all allowances would become part of an auction program. Current projections of CO2 allowances expect the per ton cost in 2012 to be around $20–25 increasing to $50/t by 2025.

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Revenue from the auctioning of allowances under the cap and trade program would be used to: ● ● ● ● ●

Invest in clean energy technology research and deployment Offset increased energy costs for low-moderate income households Prevent international deforestation Fight climate change in other nations Fund worker transition from fossil fuel–dependent industries

Clean Energy Act of 2009 (November 2009) The Clean Energy Act (CEA) of 2009 was introduced on November 16, 2009. The CEA focuses on the creation of incentives and financing programs for nuclear and alternative energy projects under the assumption that broad development will result in GHG reductions. The CEA would amend the current Energy Policy Act of 2005 to expand the flexibility of loan guarantees for various technologies, set aside $10 billion for incentives for innovative technologies, and put into motion the development of further nuclear energy production facilities and associated educational programs to insure a properly trained workforce is available [39].

Clean Energy Partnerships Act of 2009 (November 4, 2009) The Clean Energy Partnerships Act (CEPA) of 2009 addresses various areas of climate change legislation including: ● ● ● ●

Offset Credit Program for Domestic Emission Reductions Carbon Conservation Rural Clean Energy Resources Agricultural and Forestry Research for GHG Mitigation

Under the CEPA, a GHG Reduction and Sequestration Advisory Committee will be established to advise on the establishment and implementation of an offset program. A major focus of the committee would be to establish a program to govern the creation of credits from emission reductions and define eligible projects that generate offset credits [40].

Carbon Limits and Energy for America’s Renewal (Cantwell–Collins: December 2009) The Carbon Limits and Energy for America’s Renewal (CLEAR) Act was proposed on December 11, 2009. The CLEAR Act includes GHG reduction standards as follows: ● Reduction to 80% of 2005 levels by 2020 ● Reduction to 70% of 2005 levels by 2025

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● Reduction to 58% of 2005 levels by 2030 ● Reduction to 17% of 2005 levels by 2050 Other key facets of the CLEAR Act include [41]: ● A fossil carbon limitation program would be moved forward to distribute carbon; shares via monthly auctions develop a market for carbon auctions. ● Carbon share prices would initially be set between $7 and $21 per ton in 2012 and then fluctuate based on inflation rates and other factors. ● Dividend programs are included for US residents to receive distribution of approximately 75% of all revenues. ● Remaining revenues would be invested in the Clean Energy Reinvestment Trust Fund (CERT Fund) and used for program development and incentives related to clean energy and related initiatives.

American Power Act (Kerry–Lieberman: May 2010) On May 12, 2010, another comprehensive climate and clean energy bill was introduced by Senators John Kerry (Democrat from Maryland) and Senator Joe Lieberman (Independent from Connecticut). The Kerry–Lieberman bill, known as the American Power Act (APA) of 2010, is similar in many aspects to the Waxman– Markey Bill put forward in 2009. The APA would go into effect in 2013 for electrical generation facilities and fuel distributors with a 2016 date for industrial sources and natural gas facilities. The APA includes a 15-year transition period that focuses on renewable energy, maximizing energy efficiency, transportation. The APA includes support for nuclear energy and natural gas investment. The APA looks to achieve rapid mitigation of higher intensity GHGs and black carbon and includes adaptation programs [42]. No later than 2025, the APA would look very similar to a refund-based auctionedallowance system promoted by President Obama and advocates of cap and dividend programs. Key aspects include: ● Most regulated sources would be required to purchase emission allowances or offset credits through federal auctions or a regulated market. ● For gasoline and other refined products, fixed allowances would be set quarterly. ● During the period from 2012 to 2025, free allowances would be distributed to sources of GHG emissions to enable a cost-efficient transition for consumers, electrical generation facilities, and fuel suppliers, as well as buffer the impact of carbon economy costs on ‘‘trade-vulnerable’’ industries and petroleum refineries. ● Public facilities may receive some allowances as well during the initial transition period. ● In the years following 2025, an increasing number of allowances would be auctioned and proceeds distributed to US consumers through income tax credits.

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As noted, the APA is heavily based in revenue sharing and sends roughly two-thirds of all revenues not dedicated to US deficit reduction issues back to consumers. The remainder of program income is to help the transition for American businesses and for investment in projects and technologies to reduce GHG emissions and advance energy security. As the program matures, more dividends will go directly back to consumers under the program. The APA: ● Invests in technology to harness domestic power supplies and reduce our dependence on foreign oil ● Invests in innovation across all energy sources by rebuilding our energy infrastructure as we reinvigorate our manufacturing base ● Includes separate, targeted mechanisms for the three major emitting sectors: power plants, heavy industry, and transportation ● Only addresses the largest sources of carbon pollution and provides predictability to businesses and consumers through a hard price collar and the creation of a single, clear set of rules ● Does preempt state and regional GHG cap and trade programs and would formally exclude GHGs from regulation under the CAA as discussed in detail previously. Table 3.6 includes a comparison of reduction targets and allowances in the APA and Waxman–Markey bills. >

Compromise Proposals in the United States In seeking to move forward with a Senate version of a climate change bill that would eventually be merged with the Waxman–Markey bill, there has been significant negotiation and discussion in the US legislative bodies and the presidential administration in 2010. Various proposals would incorporate strategies from the current myriad of legislative approaches summarized above in addition to new concepts and ideas. Limiting the coverage of national program to only electric utilities was one approach that had some initial momentum; however, this approach like many others has not been successful to date.

Impact of Federal Legislation on Current GHG Cap and Trade Programs A key word in the interaction of current regional GHG programs and possible future programs is ‘‘preemption.’’ Preemption refers to the process where a new, broader national or even international legislative effort would supersede current regional programs. In comparing the current GHG cap and trade programs with the program included in the Waxman bill, the general tone of the legislation is consistent with current trading

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. Table 3.6 Comparison of key reduction targets and allowance/offset requirements of APA and Waxman–Markey Bills [43] Provision

APA

Waxman–Markey

GHG emission reduction targets

4.75% by 2013 17% by 2020 42% by 2030

3% by 2012 17% by 2020 42% by 2030

83% by 2050 2013 – Electric power, transportation fuels, heating oil, industrial gas producers, CO2 sequestration sites 2016 – Industrial sources, natural gas distributors

83% by 2050 2012 – Electric power, transportation fuels, heating oil, industrial gas producers, CO2 sequestration sites 2014 – Industrial sources 2016 – Natural gas distributors

Transportation fuels and refined products

Purchase allowances directly from EPA; price set quarterly

Participate in allowance and offset market like other covered sources

Banking of allowances to meet future obligations Borrowing allowances with future effective dates to meet current compliance obligations

Unlimited

Same

No limit on borrowing from next year; limits on amount that can be borrowed from future years and interest payments

Same

Cap and trade phase in

programs. A likely outcome assuming eventual passage of a federal cap and trade bill is that existing US programs will be rolled into a national program (i.e., the existing regional programs are superseded by the federal program). This approach may provide the most flexibility and assurance for industry and utilities. Consistent with the CAA, the Waxman–Markey bill protects the individual states rights to be more stringent than federal requirements. This could be an issue if one of the existing groups of states such as RGGI, WCI, or the Midwest Accord concludes that a federal rule does not go far enough to reduce CO2 emissions or that the rule does not have a strong cap and trade program. If a state or group of states chooses to implement a more stringent program, it could result in more expensive state and regional allowances on a per ton basis depending on the quantity of CO2 emissions and the types of facilities covered by the state and regional program. Depending on the will of the states, as the final federal legislation emerges, there could be an option where regional programs remain intact with linkage to the federal program. This hybrid approach may provide opportunities for those states or regions who believe they will have a more effective program if managed within the state or region and yet have common elements with the federal program.

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In the APA bill from the Senate, the federal program would essentially preempt all regional cap and trade programs while maintaining the State’s rights to regulate mobile source emissions. Regarding how participants in each program may be required to manage, verify, and report GHG reductions and subsequent CO2 allocations, there is still significant uncertainty. Given that the recently proposed USEPA GHG Reporting Rule was designed based on significant review of the existing regional and international programs and other accepted GHG calculation and reporting protocols, this could alleviate many potential problems by not deviating significantly from current efforts.

Future Directions Climate change mitigation and associated legislation has become and will remain a major topic of national and international debate and discussion. While many aspects of state, federal, and international climate change legislation remain very much in flux, there is growing consistency in the GHG emissions reporting requirements and GHG emission mitigation options that will ultimately be included in each nation’s climate legislation strategy and any future international climate agreements that are reached. These consistencies are the outcome of the intense international discussion and negotiation in the UNFCCC and IPCC meetings such as Kyoto and Copenhagen. While these international meetings have grown significantly in scope and attendance since their humble beginnings, the conference of the parties and similar meetings remain the key mechanism to reach international consensus and develop reasonable and acceptable policy that helps steer a course toward workable GHG emission mitigation policies for all entities involved. Continued international cooperation is a key component of moving forward a fair and equitable solution given the overlapping issues associated with a global environmental issue like climate change. ‘‘Common but differentiated responsibilities’’ remains a challenge as the world’s economies grow. COP and MOP meetings along with frequent meetings at local, state, national, and international level will be critical and essential in maintain consistent approaches to the complicated issue of internal climate change mitigation. Various international programs and policies continue to emerge as countries around the globe determine their own course of action for climate change mitigation and adaptation. Many countries and geographical regions have developed plans, programs, and even regulations for emissions of GHG. Even if there are no formal programs or legislative actions in progress, most countries are addressing the issue as a regular course of business within their government. Current federal legislation in the United States has drawn upon the significant work completed both internationally as well as regionally in the United States and also from input from various stakeholder groups in industry, electricity generation, environmental groups, academia, and the public. These efforts should help to minimize the transition to either move from regional programs to a federal program or to enable a regional program

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to be managed within a corresponding federal program. In the same way, programs will continue to evolve to enable global connectivity in climate mitigation legislation. Likewise, consistency in regional, national, and international GHG emission trading programs is imperative for both domestic and international corporations worldwide who need consistency and certainty for managing the interaction of business goals and carbon management requirements into the future. Carbon leakage is also a key concern for many industrialized nations and must be properly addressed for any GHG emission management program to be effective worldwide. Legislative approaches that protect against imbalance in worldwide GHG emissions concentrations are essential. Economic factors such as the recent worldwide economic crisis will certainly influence the path of future climate change legislation. Many efforts that were building momentum were slowed by the difficult business conditions of recent years. Political movement and government administration changes throughout the world are other key variables especially in light of the debate over climate issues. While the regulatory and legislative path to define, develop, and implement sound environmental policy for carbon and GHG emission legislation is still uncertain, it is clear that a carbon-regulated economy is certainly in the international community’s future.

References 1. United States Environmental Protection Agency Greenhouse gas equivalents calculator. http:// www.epa.gov/cleanenergy/energy-resources/calculator.html 2. Anna Motschenbacher, Pew Center on Global Climate Change (2009) Pew Center perspective on state climate programs, Air and waste management’s environmental manager. April 2009, p. 6 3. Intergovernmental Panel on Climate Change (2010) History of intergovernmental panel on climate change. http://www.ipcc.ch/organization/organization_history.htm. June 2010 4. United Nations Framework Convention on Climate Change. In: Wikipedia, The Free Encyclopedia. http://en.wikipedia.org/wiki/United_Nations_ Framework_Convention_on Climate Change. Accessed 18 June 2010 5. Zaikowski L (2007) Global climate change: major scientific and policy issues. eoearth.org. http://www.eoearth.org/article/Global_Climate_ Change:_Major_Scientific_and_Policy_Issues 6. United Nations Framework Convention on Climate Change (2010) Kyoto protocol background. http://unfccc.int/kyoto_protocol/items/2830.php

7. United Nations Framework Convention on Climate Change (2010) Background on the emissions trading. http://unfccc.int/kyoto_ protocol/mechanisms/emissions_trading/items/ 2731.php 8. United Nations Framework Convention on Climate Change (2010) Background on the clean development mechanism. http://cdm.unfccc.int/ about/index.html 9. United Nations Framework Convention on Climate Change (2010) http://unfccc.int/ cooperation_ and_support/financial_mechanism/ adaptation_ fund/items/3659.php 10. United Nations Framework Convention on Climate Change (2010) Background on joint implementation. http://unfccc.int/kyoto_protocol/mechanisms/joint_implementation/items/1674.php 11. United Nations Framework Convention on Climate Change (2010) Copenhagen COP-15 and Copenhagen accord summary. http://unfccc.int/ meetings/cop_15/items/5257.php 12. Harris JM, Codur AM (2008) Policy responses to climate change. eoearth.org. http://www.eoearth. org/article/Policy_responses_to_climate_change

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13. Environmental Health Perspectives (Content Partner); Sidney Draggan (Topic Editor) (2009) ‘‘Climate change abatement strategies’’ In: Cutler J. Cleveland (ed) Encyclopedia of Earth. Environmental Information Coalition, National Council for Science and the Environment, Washington, D.C [First published in the Encyclopedia of Earth July 13, 2009; Last revised July 13, 2009; Retrieved August 6, 2010]. http://www. eoearth.org/article/Climate_change_abatement_ strategies 14. Pew Center on Global Climate Change (2009) Climate change 101: cap and trade. http://www. pewclimate.org/report/climate-change-101-series 15. Washington post, cap and trade: how it would work. http://www.washingtonpost.com/wp-dyn/content/ graphic/2009/02/26/GR2009022600572.html 16. Pew Center on Global Climate Change (2009) Renewable and alternative energy portfolio standards. http://www.pewclimate.org/ what_s_being_done/in_the_states/rps.cfm 17. Ellerman AD, Joskow PL, Massachusetts Institute of Technology (2008) The European union’s emission trading system in perspective, Pew Center on global climate change. May 2008 18. Regional Greenhouse Gas Initiative, Regional Greenhouse Gas Initiative Fact Sheet (2009) http://www.rggi.org/docs/RGGI_Executive%20 Summary_4.22.09.pdf 19. Western Climate Initiative (2009) The western climate initiative cap and trade program. http:// www.westernclimiateinitiative.org/the-wci-capand-trade-program 20. Midwestern Greenhouse Gas Reduction Accord, Advisory Group Draft Final Recommendations. June 2009 21. California Air Resources Board (2010) California’s climate plan fact sheet, http://www.arb.ca.gov/cc/ facts/scoping_plan_fs.pdf 22. State of Florida, Climate Change Action Team (2010) http://www.dep.state.fl.us/ClimateChange/ team/ 23. Australian Government Department of Climate Change and Energy Efficiency, Carbon Pollution Scheme. http://www.climatechange.gov.au/ 24. Government of New Zealand, New Zealand Emissions Trading System. http://www.climatechange. govt.nz/emissions-trading-scheme/about/ 25. Pew Center on Global Climate Change (2007) Climate change mitigation measures in China.

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http://www.pewclimate.org/publications/brief/ climate-change-mitigation-measures-china Pew Center on Global Climate Change (2008) Climate change mitigation measures in India. http:// www.pewclimate.org/publications/brief/climatechange-mitigation-measures-india Government of Brazil Ministerio do Meio Ambiente (2009) Brazil presents its proposal for the UN convention on climate change. http://www.mma.gov. br/sitio/en/index.php?ido=ascom.noticiaMMA&id Estrutura=8&codigo=5329 Government of Brazil, National Plan on Climate Change for Brazil (2008) http://www.mma.gov. br/estruturas/imprensa/_arquivos/96_111220080 40728.pdf Local Government Climate Roadmap (2009) Indonesian Government launches climate change trust fund. http://www.iclei.org/index. php?id=10426 Government of South America, Government Outlines Vision, Strategic Direction and Framework for Climate Policy (2008) http://www.environment.gov.za/HotIssues/2008/LTMS/medStment_ 28072008.html Government of Canada (2010) Canada’s action on climate change. http://www.climatechange.gc. ca/default.asp?lang=En&n=72F16A84-1 United States Environmental Protection Agency, Endangerment and Cause or Contribute Findings for Greenhouse Gases under Section 202(a) of the Clean Air Act Press Release (2009) http://yosemite. epa.gov/opa/admpress.nsf/0/08D11A451131BCA58 5257685005BF252 United States Environmental Protection Agency (2010) EPA and NHTSA to propose greenhouse gas and fuel efficiency standards for heavy-duty trucks; begin process for further light-duty standards fact sheet. http://epa.gov/otaq/climate/regulations.htm United States Environmental Protection Agency (2010) Final rule: prevention of significant deterioration and title V greenhouse gas tailoring rule fact sheet. http://www.epa.gov/NSR/actions. html#may10. May 10, 2010 United States Environmental Protection Agency (2009) Final rule: mandatory reporting of greenhouse gases fact sheet. http://www.epa.gov/ climatechange/emissions/ghgrulemaking.html Dustin Till and Svend Brandt-Erichsen, Marten Law (2010) CEQ Marks 40th anniversary

Climate Change Legislation: Current Developments and Emerging Trends of NEPA with new guidance on greenhouse gas impacts, mitigation and categorical exclusions, Marten Law. https://www.martenlaw. com/newsletter/20100222-nepa-climate-changeguidance 37. McGinley M (2007) Climate change: greenhouse gas reduction bills in the 110th congress. eoearth.org. http://www.eoearth.org/article/Climate _change: _greenhose_gas_reduction_bills_in_the_110th Congress 38. Pew Center on Global Climate Change (2009) Pew Center Waxman-Markey short summary. http:// www.pewclimate.org/federal/analysis/congress/ 111/acesa/waxman-markey-short-summary 39. Pew Center on Global Climate Change (2009) Pew Center summary of the clean energy act of 2009 (Alexander-Webb). http://www. pewclimate.org/federal/congress/111/alexanderwebb-clean-energy-act

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40. Pew Center on Global Climate Change (2010) Pew Center summary of the clean energy partnerships act of 2009 (Stabenow). http://www. pewclimate.org/federal/congress/111/stabenowclean-energy-partnerships-act-2009 41. Pew Center on Global Climate Change (2010) Pew Center summary of the CLEAR act (Cantwell-Collins). http://www.pewclimate.org/ federal/congress/111/clear-act-cantwell-collins 42. Pew Center on Global Climate Change (2010) Summary of the American Power Act (Kerry-Lieberman). http://www.pewclimate. org/federal/analysis/congress/111/pew-center-summary-american-power-act-2010-kerry-lieberman 43. Svend Brandt-Erichsen and Dustin Till, Marten Law (2010) Comparison of Kerry–Lieberman bill to house greenhouse bill, Marten Law. https://www. martenlaw.com/newsletter/20100514-senate-climatebill-comparison

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4 International Efforts to Combat Global Warming Karen Pittel1 . Dirk Ru¨bbelke2,3 . Martin Altemeyer-Bartscher4 Ifo Institute for Economic Research and University of Munich, Munich, Germany 2 Basque Centre for Climate Change (BC3), Bilbao, Spain 3 IKERBASQUE, Basque Foundation for Science, Bilbao, Spain 4 Department of Economics, Chemnitz University of Technology, Chemnitz, Germany

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Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 International Climate Policy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Global Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 The UNFCC and the Kyoto Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 Global Warming Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Concentration in the Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Lifetime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Critique Concerning the Kyoto Protocol and Flexible Mechanisms . . . . . . . . . . . . . . . . 96 Asia-Pacific Partnership on Clean Development and Climate . . . . . . . . . . . . . . . . . . . . . . 97 Why Efficient Climate Protection Is So Difficult to Achieve . . . . . . . . . . . . . . . . . . . . . . . . 100 Welfare Optimum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 International Negotiations in Normal Form Games . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Integration of Ancillary Benefits into the Negotiations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 Price Ducks: An Approach to Break the Deadlock? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 Appendix A.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 Appendix A.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_4, # Springer Science+Business Media, LLC 2012

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Abstract: This chapter sheds some light on the international efforts to curb the global warming threat. The dominant climate agreement to date is the Kyoto Protocol, although competing – or allegedly complement – international climate protection schemes like the Asia-Pacific Partnership on Clean Development and Climate also exist. After describing the main features of these schemes and their failure to establish an efficient global climate protection regime, the disincentives for countries to commit to efficient climate protection efforts in an international agreement are elaborated on. The negotiation situation faced by national governments is depicted in game theoretic settings and private ancillary benefits of climate policy are identified to raise the likelihood for countries joining an international agreement. Yet, it remains quite disputable to which extent ancillary benefits can be an impetus for more action in international climate policy. Finally, after dedicating a large part of the chapter to agreements that, like the Kyoto Protocol, stipulate abatement quantities, alternative schemes are presented which were coined ‘‘price ducks’’ since they influence the effective prices of climate protection. By manipulating prices, e.g., via an international carbon tax, incentives are generated for producing higher climate protection levels. Recently, so-called matching schemes influencing effective prices of climate protection raised much attention in the scientific literature. Such schemes may attenuate free- or easyrider incentives in international climate policy and may even induce a globally efficient climate protection level.

Introduction Global environmental problems have gained much attention in the political as well as the scientific arena during recent decades. Among the most prominent examples of such environmental problems are global warming, the destruction of the ozone layer, the pollution of international waters, and the loss of biodiversity. These problems are likely to have an important impact on the quality of life on earth: ‘‘Traditionally, the next generation’s wellbeing improves compared with that of preceding generations as knowledge, capital, and other assets are passed down. If environmental deterioration continues to destroy the earth’s assets, this tradition will end’’ ([86], Preface). By the time the Brundtland Commission presented its report ‘‘Our Common Future’’ [99] at the latest, the necessity to stop international environmental deterioration had become largely undisputed. Nevertheless, the way to achieve this is subject to an extremely controversial discussion. A main cause of this dispute lies in the fact that, in contrast to local environmental problems, international challenges cannot be counteracted by regulations invented by a coercive central authority. Because of this lack of a coercive authority that can force sovereign nations to take protective actions, international environmental policy crucially depends on the decisions made by the individual countries. These decisions are unlikely to produce a globally efficient level of protection efforts, because countries have incentives to take an easy ride with respect to the protection of global commons like the atmospheric system. International environmental problems have been regularly addressed by international negotiations aiming at agreements on protection efforts. With respect to climate change,

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which will be the central global challenge analyzed in this chapter, a landmark has been the Framework Convention on Climate Change that was signed by more than 150 countries at the Rio ‘‘Earth Summit’’ in 1992. However, this convention only stipulates strategies for protecting the climate, as well as general principles, but it does not specify targets for greenhouse gas emission reductions. The following meetings of the Conference of Parties to the Framework Convention on Climate Change were assigned to make decisions on specific obligations for climate protection. Meanwhile, several of such meetings have already taken place. Outstanding was the third meeting in Kyoto 1997 where the so-called Kyoto Protocol was agreed upon. The Protocol stipulates that the parties included in Annex I to the Framework Convention (industrialized countries and European economies in transition) have to reduce their greenhouse gas emission levels within a specified time frame. Currently there are intense international efforts under way to develop a post-Kyoto agreement on climate change, because the Kyoto Protocol will expire by end of 2012. As Edenhofer et al. [30] point out: ‘‘achieving deep emission reductions requires a comprehensive global effort which includes both a complete change in the energy supply of industrialized countries and the establishment of low-carbon systems in developing countries and emerging markets – in essence, nothing short of a full-scale transformation towards a carbon-free economic system.’’ Hence, international negotiations pursuing an efficient global agreement on climate change present an immense challenge. This chapter will describe past international efforts to curb the global warming threat and it will also outline why the past efforts have failed to yield an efficient global climate protection scheme. Finally, ‘‘price ducks’’ are presented which are international policy regimes targeting the rise in international climate protection efforts by manipulating the effective prices of such efforts. These schemes represent an interesting alternative to ‘‘quantity ducks’’ like the Kyoto scheme which primarily focus on the agreement of greenhouse gas abatement quantities. This chapter is organized as follows. > Section ‘‘International Climate Policy’’ provides an overview of past international agreements on climate change. It does not consider national agreements like the British Climate Change Agreements and largely disregards other national instruments like the British emission trading scheme, although it was launched even before the European Emissions Trading Scheme started. For a discussion of the British Climate Change Agreements, see, e.g., Glachant and de Muizon [40], and for an analysis of the UK Emissions Trading Scheme, see, e.g., Smith and Swierzbinski [91]. Policies like carbon taxes, matching grants, or side-payments are only discussed in an international context. In > section ‘‘Why Efficient Climate Protection Is So Difficult to Achieve’’, the public good properties of climate protection are outlined and the conditions and interplays which lead to a suboptimal low level of climate protection efforts on a global scale are explained. Due to these conditions and interplays and the lack of a global coercive authority, the attainment of an efficient global agreement on climate change is a very difficult task. Alternative negotiation schemes, which differ from the Kyoto concept of negotiating emission reduction quantities, are described. These schemes, so-called price ducks, draw on manipulating prices in such a way that it becomes rational

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for the individual countries to raise their climate protection efforts up to a globally efficient level. > Section ‘‘Conclusions’’ summarizes the chapter and draws some conclusions.

International Climate Policy Global Challenges After the UN Conference on the Human Environment took place in Stockholm in 1972, research gradually found alarming facts about the development of the earth’s state. One among the several hints of the deterioration of the earth’s condition was given by the chemists Mario Molina and Sherwood Rowland from the University of California who published a scientific paper [66] in 1974 which stressed that the emission of chlorofluorocarbons (CFCs) might deplete the stratospheric ozone layer. CFCs are very stable artificially generated gases whose production is rather inexpensive. They were used as, e.g., propellants in spray cans, refrigerants in air-conditioning systems, and solvents in cleaning processes. Stratospheric ozone, which is indeed destroyed by CFCs, absorbs a large part of hostile ultraviolet radiation from the sun and thereby renders possible human life on earth. The depletion of stratospheric ozone causes the so-called ozone holes which are areas in the stratosphere where the concentration of ozone declines below 200 Dobson units and where damaging ultraviolet radiation can advance to a larger extent toward the earth’s surface. Among the negative impacts of the penetration of short wave ultraviolet radiation is the more frequent occurrence of skin cancer and of eye impairments. The problem of the ozone layer depletion had already been addressed in 1987, when the Montreal Protocol was opened for signature. In the Montreal Protocol, which entered into force in 1989, and its amendments, reductions and bans of CFCs were agreed upon on an international level. These international environmental agreements were the first, in whose negotiation process multinational companies (like the globally largest producer of CFCs in 1988, i.e., Du Pont) were involved ([89]: 557). The international efforts to curb CFC emissions have been complemented by a reinforcement of the CFC producing companies’ efforts in researching and developing environmentally friendly substitutes for CFCs. While the problem of ozone layer depletion is largely regarded as solved, there are many other international environmental problems which are still threatening the earth. These threats have been addressed by the United Nations Conference on Environment and Development (UNCED) which took place in Rio de Janeiro, Brazil, from June 2–14, 1992. Five major agreements are associated with this conference: (1) Rio Declaration on Environment and Development, (2) Agenda 21, (3) Statement of principles for the Sustainable Management of Forests, (4) United Nations Convention on Biological Diversity, and (5) United Nations Framework Convention on Climate Change. The Rio Declaration on Environment and Development contains a set of 27 legally nonbinding principles which are designed to commit governments to ensure environmental protection and responsible development. The Agenda 21 is an international plan

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of action for sustainable development which outlines key policies for achieving sustainable development that meets the needs of the poor and recognizes the limits of development to meet global needs. The Statement of Forest Principles is the first global agreement concerning sustainability of forest management and the United Nations Convention on Biological Diversity stipulates the aims of the conservation of biological diversity, the sustainable use of its components, and the fair and equitable sharing of the benefits arising out of the utilization of genetic resources. Since the United Nations Framework Convention on Climate Change (UNFCCC) is the document of the UNCED which is of main importance for the analysis in this chapter, the UNFCCC and its offspring agreement, i.e., the Kyoto Protocol, will be discussed in a separate subsection.

The UNFCC and the Kyoto Protocol The United Nations Framework Convention on Climate Change stipulates general strategies for protecting the climate as well as general principles, but it does not specify concrete targets for greenhouse gas emission reductions. The following meetings of the Conference of Parties to the Framework Convention on Climate Change were assigned to make decisions on specific obligations for climate protection. Meanwhile, several sessions have already taken place. At the third meeting in Kyoto in 1997, the so-called Kyoto Protocol was agreed upon. The Protocol stipulates that the parties included in Annex I to the Framework Convention (industrialized countries and European economies in transition) have to reduce their greenhouse gas emission levels within a specified time frame. The EU-15, e.g., has agreed to cut its emissions by 8% between 1990 and 2008–2012, but reduction obligations vary among individual EU countries as well as among Annex-I parties in general (as stipulated in Annex B to the Protocol). The EU-15 has agreed to share the burden of its overall Kyoto target as depicted in > Fig. 4.1 (so-called Burden Sharing Agreement). If the sub-targets of the individual countries are compared with the GDP per capita in these countries in 1998 (see > Fig. 4.2), when the burden sharing was negotiated, it is conspicuous that the poorest countries (Spain, Portugal, and Greece) have the largest tolerance for emission changes. And indeed the political decision about reduction loads within the EU-15 was made taking into account different country-specific characteristics among which were the economic development circumstances in the individual EU countries: ‘‘The
8% target for the EU as a whole has been shared out amongst Member States so as to allow for different economic development patterns’’ ([28]: 2). Dessai and Michaelowa [23] point out regarding the climate policy process at the EU level that it tends to prefer less stringent emission targets for countries with lower per capita income. The overall emissions of the Annex-I parties should be at least 5.2% below the 1990 levels in the commitment period 2008–2012. However, for the Protocol to come into effect, at least 55 parties had to sign it. Among these, there must be Annex-I countries that together account for at least 55% of the 1990 CO2 emissions of the whole group of Annex-I parties. At the sixth session of the Conference of Parties in Bonn 2001, most

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. Fig. 4.1 Burden sharing in the EU-15

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. Fig. 4.2 GDP per capita in the EU-15 in 1998 (Data from Eurostat 2006)

industrialized countries agreed upon the ratification of an undermined version of the Protocol; the USA has not ratified the Protocol. The Kyoto Protocol, which limits emissions of the greenhouse gases carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6), entered into force on February 16, 2005. These gases have different properties,

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which will be illustrated by considering the examples of carbon dioxide, methane, and nitrous oxides. The gas mainly responsible for the anthropogenic greenhouse effect is CO2. Estimates of its contribution to the anthropogenic greenhouse effect vary widely, predominantly in the range of 50–80%. Other pollutants contributing to the anthropogenic greenhouse effect are CH4, N2O, and CFCs, ([33]: 35, 75; as well as [47]: 22). The contribution of CFCs to the anthropogenic greenhouse effect will decline in the future, since their reduction and phasing out were agreed on in the Montreal Protocol and its amendments. Tropospheric ozone (O3) also plays an important role in aggravating global warming ([32]: 216, [33]: 33–36), yet its importance is difficult to quantify because of the strong variability in its concentration as a consequence of its short lifetime ([8]: 23–24). Dickinson and Cicerone [27] explain that ozone ‘‘is of considerable interest because of its important roles, its complex behavior, and its susceptibility to human-induced global change.’’ The importance of the respective greenhouse gases, i.e., their contribution to the anthropogenic greenhouse effect, depends on the following three ‘‘properties’’:

Global Warming Potential The IPCC [48] defines global warming potential (GWP) ‘‘as the cumulative radiative forcing between the present and some chosen time horizon caused by a unit mass of gas emitted now, expressed relative to that for some reference gas.’’ The radiative forcing is defined as ‘‘the change in average net radiation at the top of the troposphere . . . which occurs because of a change in the concentration of a greenhouse gas’’ ([47]: 22–23). With CO2 representing the reference gas and for a time horizon of 100 years, the GWPs of CH4 and N2O are 21 and 310 respectively ([48]: 22); of course, from the definition it follows that the GWP of CO2 equals unity. Yet, as Smith and Wigley [92] point out, global warming potentials are accurate only for short time horizons.

Concentration in the Atmosphere The atmospheric concentration of CO2 has grown significantly from about 280 ppmv in preindustrial times (about 1750 AD) to 379 ppm in 2005 [50]; ppmv stands for parts per million by volume. The IPCC [50] reports a CH4 concentration of 1.774 ppmv and a N2O concentration 0.319 ppmv in 2005. Preindustrial concentrations of CH4 and N2O were about 0.7 ppmv and 0.275 ppmv respectively [48].

Lifetime CO2 prevails for 50–200 years in the atmosphere, CH4 only for 12  3 years, and N2O for about 120 years ([48]: 15, 19). Thus, the importance of single greenhouse gases varies

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depending on the time horizon of investigations. Short horizons tend to understate the importance of greenhouse gases which prevail for a long time in the atmosphere. Since CO2 represents the most important greenhouse gas, environmental policies that induce reductions of CO2 emissions and concentrations are attractive means for mitigating climate change. Therefore, the main focus in this chapter will be on these policies. Anthropogenic CO2 emissions are – except for emissions by deforestation and to a lower extent by cement production – almost entirely generated by the burning of fossil fuels. With it, many other pollutants like sulfur dioxide (SO2) and nitrogen oxides (NOX) are emitted. In contrast to the local/regional pollutants SO2 and NO2, the emissions of CO2 can still not be removed from post-combustion exhaust in a cost-effective way. Thus, major remaining reasonable approaches to mitigate CO2 concentrations are the reduction of the combustion of substances or the shift to fuels or energies with lower CO2 content. Sequestration of carbon is another option. As Lal [53] explains, soil carbon sequestration is not only an option for mitigating climate change, but it is also a strategy to achieve food security through improvement of soil quality.

Critique Concerning the Kyoto Protocol and Flexible Mechanisms There have been intense disputes about whether the Kyoto Protocol represents a promising approach to global climate protection. Nordhaus [68] criticizes: ‘‘Given the lack of political support, the Kyoto Protocol is a dead duck. Given its inefficiency, it probably deserves to be a dead duck. We need to go back to the duck drawing board.’’ The Kyoto Protocol does not prescribe greenhouse gas (GHG) reductions to developing countries and this fact is employed by opponents to the Kyoto Protocol to stress its inefficiency, since GHG emission mitigation options can regularly be exploited more cheaply in the developing world. The USA which refused to ratify the Protocol demands for participation of developing countries in international GHG emission reduction efforts. This demand is rejected by the developing world because of the economic burden which such efforts would imply. Furthermore, developing countries argue that the industrialized world is mainly responsible for the current dimension of the global warming threat. ‘‘North America and Europe have produced around 70% of CO2 emissions from energy production since 1850, while developing countries – non-Annex 1 parties under the Kyoto Protocol – account for less than one quarter of cumulative emissions’’ ([94], Chap. 7). Therefore, from the developing world’s perspective, it is mainly the industrialized world’s responsibility to combat global warming. Yet, the Kyoto Protocol integrates a mechanism which addresses both opponent views. This mechanism, the Clean Development Mechanism (CDM), allows industrialized countries to fulfill their GHG abatement obligations partly by mitigating GHG emissions in developing countries, where mitigation options can be exploited in a cheaper way. The CDM-associated costs of climate protection are borne by the industrialized world. ‘‘With the already huge and growing amount of greenhouse gas emissions and a great deal of

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low-cost abatement options available, China is widely expected as the world’s number one host country of CDM projects’’ [102]. According to Zhang [101], about 60% of the total CDM flows in 2010 will go to China. As Rive and Ru¨bbelke [80] show for CDM transfers from Europe to China, this mechanism may not only help to improve the efficiency and to raise the level of international climate protection, but it may also support development in poor countries. Yet, as they find out, the level of success of the mechanism in supporting development depends to a large extent on the domestic environmental regulations in the host country of CDM projects. The CDM is only one of three flexible mechanisms scheduled by the Kyoto scheme, the other two being Joint Implementation and Emission Permit Trading (or for short: Emissions Trading). (‘‘The Kyoto mechanisms include international emissions trading, Joint Implementation (JI), the Clean Development Mechanism (CDM), and some would argue joint fulfilment’’ ([24]: 150). Hence, some would also regard the Burden Sharing Agreement within the EU-15 as an application of a flexible Kyoto mechanism (joint fulfillment)). Joint Implementation (JI) allows Annex-I countries to fulfill their GHG abatement obligations partly by mitigating GHG emissions in other Annex-I countries (industrialized countries and European economies in transition). Laroui et al. ([54]: 901) describe the mutual benefits arising for JI investor countries and for host countries of JI projects. For investing countries, JI means a contribution to meeting the emissions reduction targets at lower cost than could be achieved by their own national measures. Furthermore, they argue that it creates new business opportunities for renewables, efficiency technologies, management tools, products, and consultants. According to Laroui et al. ([54]: 901), JI provides opportunities for the host country, e.g., to attract foreign investments, to create incentives for starting new businesses in the sectors for renewable and efficiency technologies and to enhance energy security and independence by lessening demand for energy use. The key idea of Emission Permit Trading is to stipulate an allowed amount of GHG emissions, to partition this amount, and to allocate the parts on tradable emission permits. By allowing transferability of these permits, an emission permit market is constituted. The owners of permits can relinquish their permits and sell them to other agents. Hence, while the total amount of emission permits is preassigned, the permit price is formed in the market. In environmental economics, permit schemes are known as options to cost-efficiently internalize externalities. In the EU, the GHG emissions trading scheme started on January 01, 2005. Despite its flexible mechanisms, the Kyoto Protocol does not generate an efficient global climate protection level. Before the reasons for the difficulties in reaching an efficient international environmental agreement are discussed, an alternative international scheme to protect the environment, i.e., the Asia-Pacific Partnership on Clean Development and Climate, is shortly described.

Asia-Pacific Partnership on Clean Development and Climate The Asia-Pacific Partnership on Clean Development and Climate (APP) was announced in July 2005 and formally launched in January 2006. In fact, Australia and the USA were

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the driving forces behind the APP and convinced China, India, Japan, and South Korea to join the Partnership; Canada joined in 2007. The APP partners have agreed to work together and with private sector partners to meet goals for energy security, national air pollution reduction, and climate change in ways that promote sustainable economic growth and poverty reduction. Hence, according to McGee and Taplin [62]: ‘‘No longer is Kyoto the ‘only game in town’ in terms of national participation in international climate-change initiatives.’’ For a discussion of further non-UN climate change initiatives, see McGee and Taplin [63]. The APP focuses on expanding investment and trade in cleaner energy technologies, goods and services in key market sectors. Projects supported by the APP typically involve small amounts of government funding in conjunction with private investment ([56]: 282). The APP is remarkable not only because it constitutes an additional ‘‘game in town,’’ but also because of the fact that the involved seven partner countries collectively account for more than half of the world’s economy, population, and energy use. They produce about 65% of the world’s coal, 62% of the world’s cement, 52% of world’s aluminum, and more than 60% of the world’s steel (see: http://www.asiapacificpartnership.org/english/ default.aspx). Hence, the APP gathers powerful countries. Without these countries, no solution to the global warming threat is attainable, since their economies cause the threat to a large extent. The Partnership has established eight public–private task forces to develop and implement action plans as depicted in > Fig. 4.3. The Policy and Implementation Committee oversees the APP as a whole, guides the task forces, and reviews their work. The Administrative Support Group coordinates

Policy and implementation committee

Administrative support group

Aluminium task force

Buildings and appliances task force

Cement task force

Cleaner fossil energy task force

Coal mining task force

Power generation and transmission task force

Renewable energy and distributed generation task force

. Fig. 4.3 Organizational structure of the partnership (Figure adopted from [4]: 3)

Steel task force

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the APP’s communications and activities and supports the Policy and Implementation Committee as well as the Partnership more broadly ([4]: 3). In contrast to the Kyoto Protocol, the APP formulates no legally binding commitments on greenhouse gas reduction or the placing of a price upon greenhouse gas emissions. Instead, the individual members of the APP are free to set their own targets based upon individual national circumstances; there are no compulsory contributions to funding climate protection projects. The voluntary national targets aim at reductions of greenhouse gas intensities, rather than commit to emission reductions in absolute terms. As Pezzey et al. ([75]: 107) point out with respect to the APP: ‘‘Unrealistic assumptions were made about how much innovation can be achieved by voluntarism and cooperation supported by only paltry funding, in the absence of either market price incentives or mandatory measures.’’ McGee and Taplin [62] see the real problem posed by the APP in the diversion of attention away from absolute GHG reduction targets. If the Partnership ‘‘takes hold as a fully-fledged alternative climate-change regime, or as a modifier of the future shape of Kyoto, there will be no absolute global emissions reduction and hence a greater risk of dangerous climate change’’ ([62]: 192). The motivation behind launching a scheme – which was described by its founders as a complement to the Kyoto Protocol – has been questioned by many researchers. McGee and Taplin [62] draw the conclusion from their analysis that the regime interaction between APP and Kyoto scheme is most likely to be obstructive and competitive and consequently the claims of complementarity between both regimes are not justified. As Lawrence ([56]: 282) argues, ‘‘Australia’s strong advocacy of the APP in this early period was linked to coal and energy-intensive industry interests.’’ And Karlsson-Vinkhuyzen and van Asselt ([52]: 202) point out that in February 2005, when the world was celebrating the entry of the Kyoto Protocol ‘‘into force in a sort of defiant support of multilateralism after the US rejection, it is quite natural that the US wanted to improve its reputation and show some initiative. It seems logical that the US sought the support of the other Kyoto ‘defector’ in the enterprise’’ (that is Australia, which initially did not ratify the Kyoto Protocol either). Yet, although the initial motivations to launch the APP may have been dubious, this does not mean that the proposed scheme may not have positive effects or may develop into a more effective one. However, given the enormous challenge of global warming, the relatively low number of APP projects set up since its inception ‘‘makes us question the likelihood of the APP significantly contributing to climate change mitigation, even if it could make a contribution to technology transfer’’ ([45]: 314). Furthermore, as Karlsson-Vinkhuyzen and van Asselt ([52]: 206) argue, there are political signs which could be interpreted as unequivocal support for the UN climate regime. Australia has meanwhile ratified the Kyoto Protocol and there are also affirmative signals from the US side concerning the UN climate regime. Yet, despite the softness of the APP arrangement, ‘‘there is considerable inertia in closing down institutionalised activities’’ ([52]: 206) and it is not unlikely that the APP will continue its work, not least because of the lack of a post-Kyoto UN-protocol. Yet, nevertheless one might be tempted to say – in Nordhaus’ terminology – that the APP

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is a dead duck with respect to the objective of launching an international agreement effectively protecting the global climate.

Why Efficient Climate Protection Is So Difficult to Achieve Global climate protection is persisting on a suboptimal low level. This is due to the occurrence of market failures. Climate protection has global public good properties, i.e., climate protection exerts positive externalities which are not compensated via markets. This in turn causes a suboptimal low provision of the public good ‘‘climate protection.’’ In the economics discipline, a pure public good is considered to have two distinguishing properties: (1) non-excludability of consumption and (2) non-rivalry in consumption; in contrast, a private good has none of these two properties (see Cornes and Sandler [20]: 3). Non-excludability with respect to climate protection means that every country in the world benefits from climate protection activities, regardless where these activities have been accomplished. Hence, for a country it does not make a difference whether GHGs are abated in Australia, China, the UK, or the USA, the abatement will positively affect the global climate and no country can be excluded from the respective benefits. Non-rivalry in the consumption of climate protection means that one country enjoying the benefits of the mitigation of global warming does not affect the benefits received by another country from this mitigation.

Welfare Optimum If countries individually decide about the provision of such public goods like climate protection, they will provide – from a global perspective – a suboptimally low amount since they face so-called free-rider incentives. Because non-excludability of benefits from climate protection prevails (a country A cannot force another country B ‘‘not to enjoy’’ the benefits of the climate protection produced by country A), no price can be charged on a market for these benefits. Since production of climate protection is costly, while its consumption is free of charge, countries prefer that others produce more climate protection while they themselves prefer to contribute less. In general, the notion of ‘‘free-riding’’ is employed in the scientific literature in order to characterize such a situation. But in contrast to, e.g., agreements on climate change where countries may take a ‘‘free ride’’ from participation, the problem regarded here is one of degree. As can be shown, it is rational for each single country to provide the public good up to the level where its marginal abatement benefits coincide with its marginal abatement costs. Hence, it might be more appropriate to employ the expression ‘‘easy riding’’, since this is not equivalent to ‘‘not providing anything to the public good.’’ Therefore, Cornes and Sandler ([20]: 30) suggest using the notion ‘‘easy riding’’ in such contexts. In the economics discipline, efficiency or optimality describes a situation where welfare is maximized. In the following, the maximization problem which the government of an individual country i faces is illustrated, or put differently, the case where the national

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government intends to act in the way that maximizes the welfare of the country’s residents is regarded. The national welfare function characterizes the preferences of the residents and the government can enhance the residents’ welfare by allocating the country’s resources in such a way that the respective function is maximized subject to the national income constraint. It is supposed that the income can be spent on two different groups of commodities: The first commodity is a private good yi and the second is the public good climate protection xi. Due to the public good property of climate protection, the total level X of climate protection consumable by country i can be expressed as the sum of all countries’ or regions’ individual contributions to climate protection. In a world of n countries (with i = 1, . . . ,n), the total level of climate protection is X ~i X ¼ xi þ x ¼ xi þ X (4.1) i6¼j j ~i is the sum of climate protection by all countries except for the climate protection where X xi provided by the regarded country i. The preferences of country i concerning both goods are represented by the utility function which is continuous, strictly increasing, strictly quasi-concave, and everywhere twice differentiable. The individual country i maximizes its welfare Ui ~i Þ ¼ Ui ðyi ; XÞ max Ui ðyi ; xi þ X

(4.2)

yi þ xi c ¼ Ii

(4.3)

yi ;xi

s.t.

where Ii is the monetary income of country i. For all countries, the unit price of the private commodity is set equal to unity and the unit price of climate protection is set equal to the constant price c (with c > 0). In the maximization the Nash assumption is employed, i.e., the welfare-maximizing country supposes that its choices do not affect the behavior of the ~i is exogenous. other countries, i.e., X The following first-order condition is obtained @Ui @X @Ui @yi

¼c

(4.4)

Consequently, the individual country will provide climate protection up to the level where the marginal rate of substitution (left-hand side of (> 4.4)) between public good and private good becomes equal to the unit price ratio (right-hand side of (> Eq. 4.4)) between public and private good. This provision level is efficient from an individual country’s point of view, but it is not efficient from a global perspective. Global welfare could be raised by deviating from the provision levels associated with condition (> 4.4). In order to illustrate this, global welfare is maximized in a next step. The respective welfare maximization problem is

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max U ðU1 ðy1 ; XÞ; U2 ðy2 ; XÞ; :::; Un ðyn ; XÞÞ

y1 ;:::;yn ;X

(4.5)

s.t. n X

yi þ cX ¼

i¼1

n X

Ii

(4.6)

i¼1

Let us – for simplicity – assume that each individual country’s welfare has an equal weight with respect to global welfare, i.e., U ðU1 ðy1 ; XÞ; U2 ðy2 ; XÞ; :::; Un ðyn ; XÞÞ ¼ U1 ðy1 ; XÞ þ U2 ðy2 ; XÞ þ ::: þ Un ðyn ; XÞ. Then, optimization yields the Samuelson condition (see [84, 85]) n @Ui X @X @Ui i¼1 @yi

¼c

(4.7)

Therefore, in order to maximize global welfare, an individual country has to provide climate protection up to a level, where the sum of all countries’ marginal rates of substitution between the public and the private good becomes equal to the unit price ratio between the two goods. Such outcomes, where no country can improve its welfare without harming another one, are called Pareto optima. Condition (> 4.7) deviates from condition (> 4.4), since – without international coordination – an individual country would only take its own marginal rate of substitution between public and private good into account when it decides about its climate protection efforts, while Pareto efficiency requires that countries also consider the spillovers exerted on other countries. Therefore, also the other countries’ marginal rates of substitution between the public and private good have to be included in the efficiency condition. On a national level, efficient public good provision can be enforced by the government, but on the global level there is no central coercive authority which can enforce an efficient global climate protection level. Therefore, the only option to approach an efficient global climate protection level is that individual countries voluntarily negotiate a climate protection agreement.

International Negotiations in Normal Form Games Such international negotiations on climate change can be comfortably depicted in a gametheoretical setting. Regularly, such negotiations are described as a Prisoner’s dilemma game which captures the free-rider incentives associated with the provision of public goods. A normal form game in the shape of a Prisoner’s dilemma (PD) situation with two agents or countries is presented in > Fig. 4.4. Both considered countries have the choice between ‘‘participation’’ in an international climate protection agreement (or climate protection efforts) and ‘‘no participation’’ in international climate protection efforts. In the matrix, the numbers in front of the commas represent the payoffs for country A, while

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B’s strategy No participation

Participation

No participation

0, –1

6, –3

Participation

–4, 7

5, 6

A’s strategy

. Fig. 4.4 Prisoner’s dilemma (PD) game

the numbers behind the commas stand for the payoffs received by country B. In the Prisoner’s dilemma case, the dominant strategy for each agent is to choose ‘‘no participation’’ in an international climate protection agreement. A dominant strategy is a strategy which always yields the highest payoff for the agent choosing this strategy, regardless of the choice of the opponents. The Nash equilibrium, the equilibrium where no country has anything to gain by changing only its own strategy unilaterally, is prevailing where both agents do not participate in international climate protection efforts and the payoffs of countries A and B are 0 and
1, respectively. ‘‘From an economic viewpoint an ideal state of cooperation has two features: It is a Pareto-optimum and it is stable’’ ([11]: 82). The Nash equilibrium in the depicted PD situation is of course not Pareto-optimal. Both agents will obtain a higher payoff if they would simultaneously participate in the international agreement. Alternatively, a Chicken game setting can be employed in order to illustrate the negotiation situation. Lipnowski and Maital [59] provide an analysis of voluntary provision of a pure public good in general as the game of Chicken. In fact, a Chicken game tends to describe international negotiations on the provision of the specific public good ‘‘climate protection’’ in a more adequate way than the Prisoner’s dilemma game (see Carraro and Siniscalco [16]). The case of a Chicken game, which belongs to the group of coordination games, is depicted in > Fig. 4.5. In contrast to the PD situation, there exists no dominant strategy. The main difference between both games, i.e., between PD and Chicken games, can be described as follows: While the agents in the PD situation obtain the lowest payoffs when they play unilateral ‘‘participation’’, in the Chicken game, the agents face the lowest payoffs if they mutually play ‘‘no participation.’’ There are a couple of papers investigating the differences associated with the two, PD and Chicken, games. Ecchia and Mariotti [29] investigate coalition formation in international environmental agreements and compare different versions of the two game types

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B’s strategy No participation

Participation

No participation

–6, –6

6, –3

1–p

Participation

–3, 6

3, 3

p

1–q

q

A’s strategy

. Fig. 4.5 Chicken game

using simple three-country examples. In their paper, Rapoport and Chammah [79] stress the difference between both games with respect to the attractiveness of retaliation decisions. Snyder [93] examines differences in the logic and social implications of PD and Chicken games in the context of international politics. Lipman [58] as well as Hauert and Doebeli [44] analyze how the evolution of cooperation differs in the two games. Rabin [78] investigates fairness in these settings. Pittel and Ru¨bbelke [77] depict negotiations on climate change in (3  3)-matrices in which they integrate both Chicken and PD settings simultaneously. Hence, in their study they allow for a broader range of choices for the involved countries. The reason why the Chicken game tends to describe international negotiations in a more proper way is that in case of mutual nonparticipation the whole world is threatened by a global warming catastrophe. This catastrophe can be prevented in the best way by means of mutual cooperation in international climate protection. However, if the other agent refuses to cooperate, then unilateral participation in international climate protection efforts would be the best choice since this is the only remaining way to prevent the global warming catastrophe. Yet, if the other agent provides climate protection (and thus chooses ‘‘participation’’), it would be best to choose ‘‘no participation’’ and thus to take a free ride. Each agent hopes that the other agent provides climate protection, such that he himself can take a free ride in climate protection. As can be observed from > Fig. 4.2, there exist multiple Nash equilibria, which are associated with pure and mixed strategies. The Nash equilibria in connection with pure strategies prevail where the payoffs (
3, 6) and (6,
3) arise. Given possible uncertainties regarding the countries’ behavior, mixed strategies become germane. Agents form probabilities about the other agent’s behavior. Country A assesses the likelihood with which country B will participate (q) or not participate (1
q) – and vice

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versa for country B (p and 1
p). In order to determine the mixed strategies in the Chicken game situation in > Fig. 4.5, the likelihood q∗ (resp. p∗) of participation by country B (country A) has to be calculated, which makes country A (country B) indifferent between playing ‘‘participation’’ and ‘‘no participation’’. Probability q∗ is determined by calculating the level of q, where the expected payoffs of both strategies of A (‘‘participation’’ and ‘‘no participation’’) balance. This is the case if
3ð1
qÞ þ 3q ¼
6ð1
qÞ þ 6q

(4.8)

The left-hand side represents A’s expected payoff from participation and the righthand side reflects A’s expected payoff from defection. Analogously p∗ can be specified
3ð1
pÞ þ 3p ¼
6ð1
pÞ þ 6p

(4.9)

The mixed-strategy equilibrium requires q ¼ p  ¼

1 2

(4.10)

If country A or country B is uncertain whether the other country will participate or defect, then it should cooperate (participate) provided it expects the antagonist to play ‘‘participation’’ with a probability of less than one-half.

Integration of Ancillary Benefits into the Negotiations Climate policies regularly generate side effects. Afforestation and reforestation, e.g., do not only mitigate CO2-induced global warming by sequestering carbon (C), these measures also increase the habitat for endangered species. Furthermore, forests can serve as recreational areas and reduce soil erosion. As Ojea et al. [71] stress, forests’ ‘‘provision of goods and services plays an important role in the overall health of the planet and is of fundamental importance to human economy and welfare.’’ Furthermore, Sandler and Sargent [87] point out that tropical forests provide a bequest value which the current generation derives from passing on the forests to future generations. Concerning the case of Brazil, Fearnside ([36]: 180) stresses: ‘‘The environmental and social impacts of mitigation options such as large hydropower projects, mega-plantations or nuclear energy, contrast with the ‘ancillary’ benefits of forest maintenance.’’ An overview of studies assessing the co-effects of afforestation is provided by Elbakidze and McCarl ([31]: 565). The implementation of more efficient technologies, the reduction of road traffic, and the substitution of carbon-intensive fuels cause a decline in carbon dioxide emissions. Ancillary or secondary benefits induced by activities reducing carbon dioxide emissions accrue from the mitigation of non-CO2 emissions, for example, (see > Fig. 4.6). There are a number of terms which convey the idea of ancillary or secondary benefits. The others are co-benefits and spillover benefits (see IPCC [49]). The main difference is the relative emphasis given to the climate change mitigation benefits versus the other benefits ([61]: 489). Climate change mitigation can be regarded as one of two pillars of climate policy;

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Climate policy (e.g.,Carbon-tax)

GHG abatement measures

Climate protection

Primary (Climateprotection related) benefits

Reduction in local air pollution

Ancillary benefits

. Fig. 4.6 Climate policy generating primary and ancillary benefits, see Ru¨bbelke [81]

adaptation to climate change is the other pillar which will – however – play no role in this chapter. For a discussion of positive co-effects of adaptation policies in the shape of desired distributional effects, see Aakre and Ru¨bbelke [1, 2]. In fuel combustion processes, CO2 emissions are accompanied by emissions of, e.g., NOX, SO2, N2O, and others (for effects of these pollutants, see > Appendix 4.1). Therefore, fuel combustion reductions do not only cause a decrease in CO2 emissions but also diminish the emissions of other pollutants. In general, positive health effects of air pollution reduction that accompany climate protection measures are assessed to represent the most important category of secondary benefits. (However, Aunan et al. ([6]: 289) annotate that ‘‘some particulate air pollution has a cooling effect on the atmosphere, reducing it may exacerbate global warming.’’) Further negative impacts of air pollution, like accelerated surface corrosion, weathering of materials, and impaired visibility are mitigated by fuel combustion reductions too. Road traffic mitigation does not only produce ancillary benefits by reducing the emission of air pollutants but it is also accompanied by lower noise levels and reduced frequency of accidents, less traffic congestion, and less road surface damage. Mostly, ancillary benefits are local or regional ([48]: 217; [72]: 5). They represent domestic public goods for individual countries. (An exception is, for example, the abatement of the greenhouse gases chlorofluorocarbons (CFCs), as the ancillary effect of ozone layer protection and the respective ancillary benefits can be enjoyed globally.) E.g., local air pollution mitigation generated by climate policy can be exclusively enjoyed by the protecting country. Therefore, ancillary effects can be considered to be private to the host country of a climate policy. Consequently, they contrast to climate protection–related primary benefits which exhibit global publicness. Primary benefits accrue from the prevention of climate change–induced damages. Such damages would arise, e.g., from droughts caused by global warming. Ru¨bbelke and Vo¨gele [83] recently analyzed the effects of such droughts on the power sector.

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B’s strategy

No participation

Participation

No participation

–6, –6

6, –3 + ABB

Participation

–3 + ABA, 6

3 +ABA, 3 + ABB

1–q

q

4

A’s strategy

1–p

p

. Fig. 4.7 Chicken game with ancillary benefits

Several studies ascertaining the level of ancillary benefits found that such benefits even represent a multiple of climate protection–related primary benefits, as Pearce [73] illustrates in an overview. In the next stage, ancillary benefits can be explicitly introduced into the normal form game. It will be taken into account that ancillary benefits are enjoyed (mainly) privately by the host country of the climate protection activity. Ancillary benefits arise regardless of the behavior of the antagonist. In > Fig. 4.7, ancillary benefits (ABA, ABB) are explicitly included into the matrix of the Chicken game, where it is assumed that ABA < ABB. Analogously to the procedure concerning the Chicken game situation without ancillary benefits, the mixed strategies can be investigated here. Again, probability q∗ is determined by identifying the level of q, where the expected payoffs of both strategies of A (‘‘participation’’ and ‘‘no participation’’) balance. This is the case if ð
3 þ ABA Þ ð1
qÞ þ ð3 þ ABA Þ q ¼
6 ð1
qÞ þ 6q

(4.11)

∗

Analogously p can be specified ð
3 þ ABB Þ ð1
pÞ þ ð3 þ ABB Þ p ¼
6 ð1
pÞ þ 6p

(4.12)

From (> 4.11) and (> 4.12), q∗ and p∗ can be derived. Scientific studies largely assess that there are especially important co-benefits of local/regional air pollution reduction in developing countries; an overview of a selection of studies investigating ancillary benefits in developing countries can be found in the > Appendix 4.2. Neglecting potential differences in the primary benefits and supposing that A represents the group of industrialized countries, while B represents the developing world, we obtain: 1

1

2

2

q ¼ þ ABA =6 < p ¼ þ ABB =6

(4.13)

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If country A (country B) is uncertain whether the antagonist participates or defects, then it should participate provided it expects the antagonist to play ‘‘participation’’ with a probability of less than ½ + ABA/6 (½ + ABB/6). Comparison of the (> Eqs. 4.10 and > 4.13) yields the result that q∗ and p∗ rise due to the inclusion of ancillary benefits into the analysis. Consequently, for the Chicken game example illustrated above it is found that taking into account ancillary benefits will increase the likelihood of cooperative behavior in international negotiations on climate change. According to (> 4.13), the inclusion of ancillary benefits into the reasoning brings about an increase in the likelihood that developing countries will participate in international climate protection efforts (for a more general analysis of the influence of ancillary benefits in international negotiations on climate change see [76]). Consequently, these results confirm Halsnæs and Olhoff ([43], p. 2324) who stress that ‘‘the inclusion of local benefits in developing countries in GHG emission reduction efforts will [. . .] create stronger incentives for the countries to participate in international climate change policies.’’ Yet, in their analysis of qualitative and strategic implications associated with ancillary benefits, Finus and Ru¨bbelke [37] find a more moderate influence of co-benefits on the participation in international climate agreements and on the success of these treaties in welfare terms. They employ a setting of noncooperative coalition formation in the context of climate change. According to their results, ancillary benefits will not significantly raise the likelihood of an efficient global agreement on climate change to come about although ancillary benefits provide additional incentives to protect the climate. The rationale behind this result is that countries taking the private ancillary benefits to a greater extent into account will undertake more emission reduction, irrespective of an international agreement. However, if we consider the high local/regional pollution levels in developing countries it remains at least highly disputable whether developing countries conduct efficient local/ regional environmental policies. Hence, the commitment in an international climate protection agreement will most likely help to raise the efficiency in local/regional environmental protection in these countries. Consequently, ancillary benefits – although not being the major impetus for immediate action – may take the role of a catalyst to climate policy (rather than that of a direct driver). Joining international climate protection efforts may become politically more feasible for developing countries (like China and India) which face serious local/regional pollution problems, when ancillary benefits are included in the political reasoning.

Price Ducks: An Approach to Break the Deadlock? Due to the inefficiency of the Kyoto Protocol scheme, which is a quantity duck since it stipulates emission reduction quantity targets, there arose an intense discussion about general alternatives to such quantity ducks (and which are more than just

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technology-focused climate policy partnerships like the APP). Nordhaus ([69]: 31) points out: ‘‘Unless there is a dramatic breakthrough or a new design the Protocol threatens to be seen as a monument to institutional overreach.’’ Price-influencing international climate protection schemes have been proposed by Nordhaus [69] as a proper successor of the quantity approach of the Kyoto type. ‘‘This is essentially a dynamic Pigovian pollution tax for a global public good’’ (Nordhaus [69]: 32). An international carbon tax scheme where no international emission limits are dictated is considered to have several significant advantages over the Kyoto mechanism. This scheme could also contain side-payments in order to motivate countries to participate: ‘‘Additionally, poor countries might receive transfers to encourage early participation,’’ ([69]: 32). Such a scheme is a price duck, because via the taxes, the prices of polluting activities are increased, such that there are additional incentives to mitigate the level of such polluting activities. Instead of taxing polluting activities in order to protect the climate, prices can also be influenced by subsidizing climate protecting activities (e.g., energy-efficient appliances or carbon sequestration measures could be subsidized). The subsidy will reduce the effective price of climate protecting activities and hence the agents receiving the subsidy will raise their provision level of climate protection. Recently, Altemeyer-Bartscher et al. [3] elaborated Nordhaus’ proposal of an international carbon tax scheme and analyzed how individual countries or regions could negotiate the design of such a tax scheme in a decentralized way. In the scheme they suggest, countries offer side-payments to their opponents that are conditional on the level of the environmental tax rates implemented in the transfer-receiving opponent country. As can be shown, such a side-payment scheme might yield the first-best optimal tax policy and hence an efficient global climate protection regime. The scheme does not require the coercive power of a central global authority. Instead, the individual countries implement carbon taxes voluntarily. Other price-influencing schemes which work in a similar way and do not require an international coercive authority are matching schemes which were first developed by Guttman [41, 42]. Danziger and Schnytzer [22] provide a general formulation of Guttman’s matching idea which allows for income effects, nonidentical players, and nonsymmetric equilibria. Guttman’s matching approach has been applied to the sphere of international climate agreements by Ru¨bbelke [82]. Guttman’s basic scheme consists of two stages. Each agent i’s contribution xi to the public good can be written as: xi ¼ ai þ bi

n X

aj

(4.14)

j ¼1 j6¼i

where ai is agent’s unconditional or flat contribution to the public good (in our case ‘‘climate protection’’) and bi is his matching rate, which he provides for each unit of flat public good contributions by other agents. Therefore, the agent’s matching contribution is

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aj ðwith j 6¼ iÞ. The unit costs of the goods are supposed to be equal to unity. The

budget constraint of the agent in the shape of the income restriction is: yi þ ai þ bi

n X

aj ¼ Ii

(4.15)

j ¼1 j6¼i

Here, I stands for the monetary income of the considered agent i. In the first stage of the game, each agent makes a decision on the level of matching rates he wants to offer to the other agents. It could be assumed that this decision is stipulated in an international agreement on matching rates, where all negotiating agents or decision makers – as representatives of their nations – agree on the matching rates their countries will provide (see [82]). All the agents’ actions in both stages of the game are guided by welfare maximizing behavior, i.e., the agents aim to maximize their individual countries’ welfare as represented by the function in (> 4.2). In the second stage, all agents will make decisions about their flat contributions. Total public good contribution of all agents then becomes equal to: 0 1 n n X X B C X¼ ðaj ÞA (4.16) @ai þ bi j ¼1 j6¼i

i¼1

Given the matching rates of the other agents, the considered agent will contribute flat contributions to the public good up to the level where the marginal rate of substitution between public and private good is equal to the effective price of the public good, i.e., where MRSi ¼

1þ

1 Pn

j ¼1 j6¼i

bj

(4.17)

The decline in the effective price, from unity to the level specified on the right-hand side of (> Eq. 4.17), induces an increase in the private provision of the public good. Comparison of the right-hand sides of (> Eq. 4.4) (for which it is assumed that c = 1) and (> Eq. 4.17) shows that in the matching scheme the considered agent or country faces a decline in the effective price of the public good ‘‘climate protection’’ as long as at least one other agent provides a positive matching rate bj. As Bergstrom [9] illustrated, there are indeed incentives to announce positive matching rates. Consequently, the matching scheme has a price-influencing effect (similar to that of a subsidy) which the quantity targets stipulated by the Kyoto Protocol do not exert. Due to the decline in the effective price the agent tends to raise the level of his public good provision. Put differently, within the matching scheme, individual countries manipulate (via their matching commitments) the effective price of climate protection from other countries’ point of view in order to influence these opponent countries to raise their public good provision levels. And as Boadway et al. ([10]: 1682) point out, ‘‘the notion that countries might attempt to influence other countries’ contributions by preemptive

International Efforts to Combat Global Warming

4

matching commitments is not far-fetched in light of recent examples of disaster relief or international campaigns to combat the effects of infectious diseases.’’ In the case of identical agents, summing (> 4.17) over all agents, generates n X i¼1

MRSi ¼ n

1þ

1 Pn
1 j ¼1 j6¼i

bj

(4.18)

Hence, a Pareto optimum is attainable if each agent chooses bi = 1. As Buchholz et al. [12] demonstrated, matching may work better if there is a large number of agents/countries (than when there is a small number of agents), which is an important result if it is taken into account that international negotiations involve many countries.

Conclusions The Kyoto Protocol has been an inefficient agreement, although its flexible mechanisms (CDM, Joint Implementation, ETS) helped to mitigate this inefficiency. Efficiency would require that the cheapest GHG abatement options are abated first, which is not generally the case under the Kyoto Protocol. Furthermore, the largest greenhouse gas emitter among the industrialized countries, i.e., the USA, did not commit to emission reduction targets under the Protocol, but sought pretexts for taking an easy ride in climate protection. The immense threat of global warming necessitates an improved global climate protection regime, since otherwise the world might experience dramatic and life-threatening consequences. Among the possible negative effects are the melting of glaciers, a decline in crop yields (especially in Africa), rising sea levels, sudden shifts in regional weather patterns, and an increase in worldwide deaths from malnutrition and heat stress ([94], Chap. 3). An improved future international climate protection regime has to organize climate protection more effectively and it has to stipulate significant GHG emission reductions for all major polluters. Developing countries like China and India belong to the group of major emitter countries. Consequently, if the international climate policy should become capable to succeed in combating global warming, then developing countries will also have to commit to emission reductions under a global agreement. Yet, as the international negotiations on climate change in Copenhagen in 2009 indicated, international policy is stuck in a deadlock. This deadlock has to be broken soon, since the Kyoto Protocol will expire already by the end of 2012 and global GHG emission levels are forecasted to continue to rise in the years to come. Since there is no global coercive authority which could enforce countries to conduct efficient climate protection in future, mutual voluntary negotiations are the only means by which international coordination in climate protection can be accomplished. Put differently, ‘‘international treaties have to rely on voluntary participation and must be designed in a self-enforcing way’’ ([35]: 74). Yet, international easy- or free-rider incentives which are due to the global public good property of climate protection make the agreement on such an international treaty and the breaking of the deadlock in international climate policy a difficult task.

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Another way to protect the global climate, which deviates from the Kyoto concept of stipulating GHG emission reduction quantities, is the negotiation of international priceinfluencing regimes. These regimes manipulate effective prices via taxes, subsidies, or matching grants in order to conduct the behavior of individual countries in such a way that they produce globally efficient climate protection levels. An international carbon tax, as suggested by Nordhaus [69], might indeed yield a more efficient outcome, but due to the lack of will in the political arena to launch such a tax it might be more promising to base the future global climate protection architecture on the already established structures associated with the Kyoto scheme. Yet, the advantages of price ducks like matching schemes are remarkable and international price-influencing concepts like the global carbon tax or matching schemes should not be dismissed with levity. Given the immense threat to our planet which global warming constitutes, a partnership like the Asia-Pacific Partnership on Clean Development and Climate which focuses exclusively on technological aspects of climate protection while ignoring the ‘‘[k]ey inconvenient truths . . . about the economics of climate policy, especially the need to use emission pricing soon to stimulate both cost-effective abatement actions now, and enough technological innovation for the future’’ ([75]: 107), is no real alternative to the Kyoto scheme. Private ancillary benefits may take the role of a catalyst to climate policy rather than a direct driver to international climate negotiations. Joining international climate protection efforts may become politically more feasible for developing countries (like China and India) which face serious local/regional pollution problems, when ancillary benefits are included in the political reasoning. Not only co-effects in terms of reduced local/ regional air pollution are relevant, but also co-benefits in the shape of, e.g., economic development, energy security, and employment.

Appendix Appendix A.1

. Table 4.1 Information taken from Ru¨bbelke [81] Pollutant

Sources

Health effects

Carbon monoxide (CO)

Fuel combustion; industrial processes; natural sources like wildfires

Reduction of oxygen delivery to the body’s organs and tissues; visual impairment; reduced work capacity; reduced manual dexterity; poor learning ability; difficulty in performing complex tasks

Visibility and other effects Acceleration of the greenhouse effect indirectly by reactions with other substances

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4

. Table 4.1 (Continued) Pollutant

Sources

Lead (Pb)

Fuel combustion; Adverse affection of the kidneys, liver, nervous system, metals and other organs; processing neurological impairments such as seizures; mental retardation, and/or behavioral disorders; changes in fundamental enzymatic, energy transfer, and homeostatic mechanism; high blood pressure; and subsequent heart disease Burning of natural gas; coal mining; oil production; decomposition of waste; cultivation of rice; cattle breeding Irrigation of lungs and causing Combustion lower resistance to respiratory processes in automobiles and infections; increased incidence of acute respiratory power plants; diseases in children home heaters and gas stoves also produce substantial amounts

Methane (CH4)

Nitrogen oxide (NOX)

Nitrous oxide (N2O)

Burning of fossil fuels; agricultural soil management

Health effects

Visibility and other effects Deposition on the leaves of plants, and with it, representing a hazard to grazing animals

Acceleration of the greenhouse effect; contributes to increased level of tropospheric ozone

Gaseous NOX absorbs light, reduces the visual range; important precursor to ozone and acidic precipitation; impact on PM concentration; causing severe injury to plants; acceleration of the greenhouse effect by contributing to ozone generation Acceleration of the greenhouse effect; reduces the stratospheric ozone layer

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. Table 4.1 (Continued) Pollutant

Sources

Health effects

Ozone (O3)

No direct emission but formation by the reaction of VOCs and NOX; therefore, ozone is indirectly caused by combustion processes

Increased hospital admissions and emergency room visits for respiratory causes; higher susceptibility to respiratory infection and lung inflammation; aggravation of preexisting respiratory diseases; significant decreases in lung function; increase in respiratory symptoms; irreversible changes in the lungs

Particulate matter (PM)

Emission directly by a source or formation by the transformation of gaseous emissions; combustion processes cause direct emissions

Sulfur dioxide (SO2)

Burning of coal and oil; metal smelting and other industrial processes

Premature death; increased hospital admissions and emergency room visits; increased respiratory symptoms and disease; decreased lung function; alterations in lung tissue and structure and in respiratory tract defense mechanisms; lung cancer Effects on breathing; respiratory illness; alterations in the lungs’ defenses, and aggravation of existing cardiovascular disease

Visibility and other effects Reduction in agricultural and commercial forest yields; reduced growth and decreased survivability of tree seedlings; plants’ higher susceptibility to diseases, insect attack, harsh weather, and other environmental stresses; acceleration of the greenhouse effect Important cause of reduced visibility; airborne particles cause soiling and damage to materials

A major precursor to PM, which is a main pollutant impairing visibility together with NOX, a main precursor to acidic deposition

Appendix A.2 . Table 4.2 Ancillary benefit studies regarding developing countries Study

Country

Pollutants (local/regional) Model/Approach

Aunan et al. [6] China

PM, SO2, TSP

Aunan et al. [7] China

SO2, particles

Comparison of studies that comprise a bottom-up study, a semi-bottom-up study, and a top-down study using a CGE model Analysis and comparison of six different CO2-abating options

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4

. Table 4.2 (Continued) Study

Country

Aunan et al. [5] China [13] India

Cao [14]

China

Cao et al. [15]

China

Pollutants (local/regional) Model/Approach NOX, TSP NOX, particulates, SO2 SO2, TSP NOX, particulates, SO2

Chen et al. [17] China Cifuentes et al. [18] Cifuentes et al. [19]

Chile Brazil, Chile, Mexico

Dadi et al. [21] China Dessus and Chile O’Connor [25] Dhakal [26] Nepal

CO, PM, NOX, SO2 Ozone, particulates

CGE model CGE model

Technology assessment, sensitivity to discount rate Integrated modeling approach combining a top-down recursive dynamic CGE model with a bottom-up electricity sector model Comparison of partial and general equilibrium MARKAL models No economic modeling Development of scenarios that estimate the cumulative public health impacts of reducing GHG emissions

Eskeland and Xie [34]

Chile, Mexico

Garbaccio et al. [38]

China

SO2 CO, lead, NO2, ozone, PM, SO2 CO, HC, NOX, SO2, particles, lead NOX, particulates, SO2, VOCs PM, SO2

Gielen, Chen [39] Ho, Nielsen [46] Kan et al. [51] Larson et al. [55]

China

NOX, SO2

China

SO2, TSP

China China

Particulates SO2

Shanghai MARKAL model MARKAL of energy sector; base vs. advanced technology scenarios for controlling CO2 and SO2

Li [57] Markandya et al. [60]

Thailand China, India

Particulates Particles

Dynamic recursive CGE model Use of the POLES and GAINS models as well as of a model to estimate the effect of PM2.5 on mortality on the basis of the WHO’s Comparative Risk Assessment method Analysis of five pollution control options in Mexico City Project-by-project analysis

McKinley Mexico et al. [64] Mestl et al. [65] China

CO, HC, NOX, particulates, SO2 PM, SO2

Linear programming model CGE model

MARKAL, technology assessment, and alternative policy scenarios CGE model

Analysis of long-range energy system scenarios

Technology and cost-curve assessment

CGE model

115

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. Table 4.2 (Continued) Study

Country

Morgenstern China et al. [67] O’Connor et al. China [70] Peng [74] China Rive, Ru¨bbelke China [80] Shrestha et al. [88]

Thailand

Smith and Haigler [90] Van Vuuren et al. [95]

China China

Pollutants (local/regional) Model/Approach SO2 NOX, SO2, TSP

Survey of recent banning of coal burning in small boilers in downtown area of Taiyuan CGE model

Particulates, SO2 SO2, development benefits

RAINS-Asia for local, and GTAP for economywide effects CGE model

NOX, SO2

Four scenarios, use of end-use-based AsiaPacific Integrated Assessment Model (AIM/ Enduse)

SO2

Sample calculations regarding interventions in the household energy sector Simulation model

Vennemo China et al. [96] Wang and China Smith [97], [98]

SO2, TSP

West et al. [100]

Linear programming model CO, HC, NOX, particulates, SO2

Mexico

particulates, SO2

Synthesis of a significant body of research on co-benefits of climate policy in China No economic modeling

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5 Ethics and Environmental Policy David J. Rutherford . Eric Thomas Weber Department of Public Policy Leadership, University of Mississippi, University, MS, USA Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 Understanding Climate Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 Terminology and Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 Weather and Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 The Climate System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 Climate Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 Climate Variability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 Global Warming and Global Average Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 Climate Forcing and Climate Feedback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 Global Warming Versus Climate Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Thresholds and Tipping Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 Defining and Communicating Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 Adaptation and Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 Perceptions, Communication, and Language of Climate Change . . . . . . . . . . . . . . . . . . . 138 Future Directions: The State of Climate Change Knowledge and Future Predictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 Types of Mitigation Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 Uncertainties and Moral Obligations Despite Them . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 Ethics and Reporting About Climate Science . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 Avoiding the Fallacy of Appealing to Ignorance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 The Limits of Challenges About Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 Traditions and New Developments in Environmental Ethics . . . . . . . . . . . . . . . . . . . . . . . 147 Sources of Value in Environmental Ethics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 Persons Who Experience Benefits and Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 New Developments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

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Abstract: This chapter offers a survey of important factors for the consideration of the moral obligations involved in confronting the challenges of climate change. The first step is to identify as carefully as possible what is known about climate change science, predictions, concerns, models, and both mitigation and adaptation efforts. While the present volume is focused primarily on the mitigation side of reactions to climate change, these mitigation efforts ought to be planned in part with reference to what options and actions are available, likely, and desirable for adaptation. > Section ‘‘Understanding Climate Change,’’ therefore, provides an overview of current understanding of climate change with careful definitions of terminology and concepts along with presentation of the increasingly strong evidence that validates growing concern about climate change and its probable consequences. > Section ‘‘Uncertainties and Moral Obligations Despite Them’’ addresses the kinds of uncertainty at issue when it comes to climate science. The fact that there are uncertainties involved in the understanding of climate change will be shown to be consistent with there being moral obligations to address climate change, obligations that include expanding the knowledge of the subject, developing plans for a variety of possible adaptation needs, and studying further the various options for mitigation and their myriad costs. > Section ‘‘Traditions and New Developments in Environmental Ethics’’ covers a number of moral considerations for climate change mitigation, opening with an examination of the traditional approaches to environmental ethics, then presenting three pressing areas of concern for mitigation efforts: differential levels of responsibility for action that effects the whole globe; the dangers of causing greater harm than is resolved; and the motivating force of diminishing and increasingly expensive fossil fuels that will necessitate and likely speed up innovation in energy production and consumption that will be required for human beings to survive once fossil fuels are exhausted.

Introduction Few subjects are as complex and as frequently oversimplified as climate change. After big snowfalls in winters past, news outlets have featured various observers of these local events, who dismiss the idea of global warming with statements such as, ‘‘So much for the global warming theory’’ [1]. On the other hand, climate scientists note that Earth’s average temperature has risen over time, and as a result, they predict increases in temperature extremes and vaporization of water that, in turn, lead to an expectation of increased snowfall in some years. Problems of understanding and misunderstanding such as these are important causes of confusion in discussions about climate change, and those problems and that confusion combine with the complexity of the issues at stake to add considerable challenge to addressing the topic of focus in this chapter: the ethics of climate change mitigation. This chapter will argue that despite limitations to knowledge about the complexities of the climate system, certain efforts must be undertaken to prepare for and address the developments in climate change. The science on the subject is growing increasingly

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compelling, showing that there is need to work toward mitigating the causal forces that are bringing about climate change along with preparing adaptations to changes in climate, some of which have already begun [2]. Furthermore, the existence of uncertainties with respect to climate science calls for more study of the subject of climate change, with greater collaboration than is already at work. Calling for further study of the subject, however, does not imply the postponement of all or any particular measure of precaution and potential action. This chapter will examine the current knowledge about climate change as well as the moral dimensions at issue in both seeking to minimize those changes and working to prepare for the changes and their effects. When the term ‘‘mitigation’’ arises in this chapter, it is important to keep in mind a consistent meaning. To mitigate something generally means to make it less harsh and less severe, but in relation to climate change, mitigation carries a more precise meaning. The term refers to human actions taken to reduce the forces that are believed responsible for increase of the average temperature of Earth. The primary concern with climate change is the increase of global average temperature, and mitigation is aimed at decreasing the rate of growth of this global temperature and stabilizing it or even decreasing it should it rise too high. Mitigation is sometimes referred to as abatement. Generally, the idea of abatement is to reduce either the rate of growth that is or will likely be problematic, or to actually reverse the trend and reduce global average temperature. In contrast to mitigation, a second category of response to climate change is to find ways of adapting life to new conditions, the method of adaptation. Adaptation refers to adjustments made in response to changing climates that moderate harm or exploit beneficial opportunities [3]. The interesting issue that arises in focusing on climate change mitigation – the efforts to decrease the causal forces of rising global temperatures – is that subtle changes in temperature might be the kind to which some or even many people will be able to adapt relatively easily. For instance, if people live on coastal lands that are increasingly inundated, there are ways of reclaiming land from water or places to which people can move in adaptation to the climate changes. Other adaptations might include systems of planned agricultural crop changes prepared to avoid problems that could arise in growing food for the world’s increasing population. An important consideration about adaptation is that while humans may be able to change and adjust to changing climates, natural ecosystems and habitats may not, a point that will also be addressed in this chapter. There are certainly reasons to worry about sudden, great changes, but more gradual and less severe changes raise a host of ethical issues. For instance, it is reasonable to ask whether a farmer has the moral right to grow a certain crop. If so, then it may be that people have a responsibility to avoid changing the climate. Belief in such a right, however, could be considered highly controversial. What if farmers could reasonably expect some help in adapting the crops that they raise to new conditions? This idea would lessen the moral concern over the ability to grow a certain crop in a particular region, and thus a matter of adaptation would have bearing on the moral dimensions of climate change mitigation. It is likely that the best solution to address the ill effects of climate change will require a combination of mitigation and adaptation strategies. A central claim of this chapter,

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therefore, is that the ethics of climate change mitigation must not be considered in isolation from the options available for adaptation. Of the two, however, the more controversial, morally speaking, are abatement efforts, or mitigation. This is because when climate conditions change, there will be no choice for people but to adapt to new circumstances if presented with serious challenges for survival, at least until humans are able to exert control in a desirable way on the trends in global climate. But abatement efforts, on the other hand, require sacrifices early, before certainty exists about the exact nature and extent of the problems to come and whom the problems, benefits, and mitigating efforts will most affect, and how. Accompanying the problem of complexity that exists in climate change is a necessary challenge of uncertainty. The approach of addressing change through adaptive measures can be started early, and is also possible as some more gradual changes occur, such as in the evacuation of islands that slowly disappear under the rising level of the sea. Other problems, however, are predicted to occur swiftly, such as in the potential disruption of the Ocean Conveyor, a ‘‘major threshold phenomenon’’ that could bring ‘‘significant climatic consequences,’’ such as severe droughts ([4], pp. 562–563). The problem of knowledge, of the limits to human abilities to identify where suffering or benefits will occur, under what form, by which mechanisms, implies that preventive adaptations may be impossible in the face of sudden changes in global climates. Furthermore, if there existed no idea of changes that might occur, this limited knowledge might render the effects of changing conditions less troubling morally speaking. But the fact is that today many scientists have devised models that suggest potential outcomes of climate change and so undercut the option of ignorant dismissal or avoidance of moral obligation. Limited knowledge about climate change first and foremost calls for increasing the knowledge and study of the subject, but it also demands consideration of the kinds of problems that can be expected, weighed against the anticipated costs of alleviating the worst of the threats. This chapter will offer a survey of a number of important factors for the consideration of the moral obligations involved in confronting the challenges of climate change. The first step is to identify as carefully as possible what is known about climate change science, predictions, concerns, models, and both mitigation and adaptation efforts. While the present volume is focused primarily on the mitigation side of reactions to climate change, these mitigation efforts ought to be planned in part with reference to what options and actions are available, likely, and desirable for adaptation. > Section ‘‘Understanding Climate Change,’’ therefore, provides an overview of current understanding of climate change with careful definitions of terminology and concepts along with presentation of the increasingly strong evidence that validates growing concern about climate change and its probable consequences. Next, > section ‘‘Uncertainties and Moral Obligations Despite Them’’ will address the kinds of uncertainty at issue when it comes to climate science. The fact that there are uncertainties involved in human understanding of climate change will be shown to be consistent with there being moral obligations to address climate change. As mentioned above, these are obligations to know more than is currently known, to develop plans for a variety of possible adaptation needs, and to study further the various

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options for mitigation and their myriad costs. Plus, Gardiner [4] presented a convincing case for the weighing of options that concludes in accepting the consequences of a small decrease in GNP from setting limits on global greenhouse gas emissions. Gardiner’s argument is compelling even in the face of uncertainty. After all, the uncertainties involved in climate change resemble uncertainties that motivate moral precaution in so many other spheres of human conduct. Finally, > section ‘‘Traditions and New Developments in Environmental Ethics’’ covers a number of moral considerations for climate change mitigation. This section opens with an examination of the traditional approaches to environmental ethics, then presents three pressing areas of concern for mitigation efforts: differential levels of responsibility for action that effects the whole globe; the dangers of causing greater harm than is resolved (with geoengineering efforts among others); and the motivating forces of diminishing and increasingly expensive fossil fuels that will necessitate and likely speed up innovation in energy production and consumption that will be required for human beings to survive once fossil fuels are exhausted.

Understanding Climate Change Given the complexity of addressing global climate change, it is crucial to clarify the meaning of a number of key terms, forces, and strategies for mitigation, so this first section will begin with a description of central terms and concepts at issue. The section then covers perceptions and methods for describing climate change because ideologies and affective influences on discourse about climate change can be used to mislead the public about the nature and the state of climate science. After that, the section examines the state of scientific knowledge and the predictions that the scientific community has presented about the future of climate change. This is important in order to grasp the extent of concern that world leaders and publics ought to feel about the future of the world’s climates. Finally, this section will close with a brief description of the various proposals that have been considered for mitigating climate change.

Terminology and Concepts Uncertainty, confusion, and misunderstanding result from poorly or ambiguously defined terminology and concepts, and this is especially the case with the topic of climate change. Climate change is complex and often elicits heated and impassioned public discourse. To reduce such problems, this section provides definitions for terms and concepts that are essential for both an explanation of what is known about climate change and for consideration of the broader topic of ethics and climate change mitigation. Some of these definitions are contested, and in such cases, the preferred definitions presented here will be contrasted with other definitions found in the literature, along with provision of an explanation for the selections made.

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Weather and Climate The term ‘‘weather’’ refers to short-term atmospheric conditions occurring in a specific time and place and identified by the sum of selected defining variables that can include temperature, precipitation, humidity, cloudiness, air pressure, wind (velocity and direction), storminess, and more. Weather is measured and reported at the scale of moments, hours, days, and weeks. Climate, on the other hand, is defined (in a narrow sense) as the aggregate of day-to-day weather conditions that have been averaged over longer periods of time such as a month, a season, a year, decades, or thousands to millions of years. Climate is a statistical description that includes not just the average or mean values of the relevant variables but also the variability of those values and the extremes [5, 6].

The Climate System Understanding climate entails more than consideration of just the aggregated day-to-day weather conditions averaged over longer periods of time. Those average atmospheric conditions operate within the wider context of what is called the climate system that includes not just the atmosphere but also the hydrosphere, the cryosphere, the Earth’s land surface, and the biosphere. ● The atmosphere is a mixture of gasses that lie in a relatively thin envelope that surrounds the Earth and is held in place by gravity. The atmosphere also contains suspended liquid and solid particles that ‘‘can vary considerably in type and concentration and from time to time and place to place’’ ([7], p. 37). On average, 50% of the atmospheric mass lies between seal level and 5.6 km (3.48 miles or 18,372 ft) of altitude. To highlight how thin this is, consider that the peak of Mt. McKinley in Alaska is 6.19 km (20,320 ft) above sea level, and as a result, the density of air is less than 50% of that available at sea level, or that the peak of Mt. Everest at 8.85 km (29,029 ft) has less than 32% of the air density that is available at sea level. Commercial jet airliners generally fly at about 10.5 km (35,000 ft) above sea level, and humans would lapse into unconsciousness very quickly if cabin pressure were to decrease suddenly at this altitude [8]. ● The hydrosphere consists of liquid surface water such as the ocean, seas, lakes, and rivers, along with groundwater, soil water, and importantly, water vapor in the atmosphere. ● The cryosphere consists of all snow, ice (glaciers and ice sheets), and frozen ground (including permafrost) that lie on and beneath the surface of the Earth. ● Earth’s land surface consists of the naturally occurring rock and soil along with the structures (buildings, roads, etc.) that humans have constructed. ● The biosphere consists of all living organisms, both plant and animal, on land, in fresh water, and in the ocean, including derived dead organic matter such as litter, soil organic matter, and ocean detritus.

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The climate system functions by means of complex interactions among these five components in which flows and fluxes of energy and matter take place through myriad processes such as radiation, convection, evaporation, transpiration, chemical exchanges, and many more [9]. Given this complexity, climate science is an interdisciplinary endeavor that necessarily involves the interactions and contributions of a wide range of the physical sciences such as physics, chemistry, biology, ecology, oceanography, as well as the atmospheric sciences. Moreover, because human existence involves interactions with climate, the social sciences such as psychology, political science, and sociology also play important roles in human understanding. In addition, climate operates over time and space, so the synthesizing disciplines of history and geography have much to contribute as well. Furthermore, as shown later in this chapter, the humanities contribute to the understanding of the social dimensions of climate systems when it comes to considering the moral implications of various situations and actions in response to climate change.

Climate Change The most recent definition of climate change developed by the Intergovernmental Panel on Climate Change (IPCC) will be used in this chapter: "

Climate change refers to a change in the state of the climate that can be identified (e.g., by using statistical tests) by changes in the mean and/or the variability of its properties, and that persists for an extended period, typically decades or longer ([9], p. 78; see also [10]).

Importantly, this definition is solely descriptive and includes no reference to causation, particularly no indication of the extent to which any changes in climate result from natural or human (anthropogenic) causes. Other definitions of climate change include causation, such as the United Nations Framework Convention on Climate Change: "

‘‘Climate change’’ means a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods ([11], p. 3).

The first definition was selected for use in this chapter because it focuses on identifying and describing observed changes in climate and specifically refrains from assigning causation to either natural or anthropogenic processes. As a result, it draws attention to the distinction between two aspects of inquiry: (1) questions related to the presence, extent, and direction of changes in climate, and (2) questions about causation of any observed changes, especially, determinations of natural or anthropogenic causes. Views about (2) are often disconnected from questions about presence, extent, and direction of change and also tend to generate more contentious debate, especially in public and political discourse. As means to reduce contention, it is helpful to make the clear distinction between these two aspects of inquiry, and such clarity is especially important in this chapter, considering issues of ethics, mitigation, and adaptation. Additionally, and importantly, the selected definition implies no specific type of change(s) but instead fosters recognition that changes can occur in all

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manner of the variables that constitute climate such as temperature, precipitation, humidity, cloud cover, etc. (this point is further elaborated below with respect to the term ‘‘climate change’’ and ‘‘global warming’’). An additional reason to clarify the difference between (1) and (2) is that consideration of (1) generally engenders less controversy, while the task of determining who should act in addressing any needs that arise from climate change will depend in part on how one addresses issue (2). As such, (2) is not to be ignored in addressing the ethics of climate change, but after untangling (1) from (2), the problems to be addressed can be recognized for what they are more easily.

Climate Variability Most definitions of climate variability found in the literature differ little from the above definitions of climate change. For example, as defined in the Synthesis Report for the IPCC Fourth Assessment ([9], pp. 78–79), the two terms actually seem synonymous in that they both refer to changes occurring on time scales of multiple decades or longer and they both allow for natural and anthropogenic causes. Other definitions of climate variability retain the focus on time scales of multiple decades or longer but limit climate variability to only natural causes [12, 13]. In this chapter, however, the term will refer to something different from either of these uses. The term ‘‘climate variability’’ is used in this chapter in recognition that the long-term, statistical averages of the variables that define climates can contain substantial variation around the mean. Droughts, rainy periods, El Nin˜o events, etc., occur in time periods of a year to as much as 3 decades within climates that are considered to be stable as well as within climates that are experiencing changes in the longer term. This variability is different from extreme weather events such as floods and heat waves that occur on time scales of hours, days, and weeks, and it is also different from the long-term climate changes that occur on scales that span multiple decades to millions of years (which have already been defined above as ‘‘climate change’’). The reasons to differentiate climate variability from climate change in this way are twofold. First, climate variability can generate considerable ‘‘noise’’ in the data that can lead to erroneous conclusions about climate change. For example, > Fig. 5.1 shows two levels of variability – interannual and multi-decadal – that are present in the observed global temperature record that extends from 1880 to 2009. Inter-annual variability (variability from year to year) is as much as 0.3 C (0.54 F), a range that could be expressed as 1 year with a very hot summer and a mild winter followed by a second year with a mild summer and a very cold winter. The conditions present in either of these years could lead people to make poor judgments about climate. In particular, the long-term warming trend that the graph shows occurring across the full 119 year period is sometimes dismissed because people generally give greater weight in decision making and opinion formation to immediate affective sensory input over cognitive consideration of statistics [14] (more will be said below about human decision making that is affect-based compared to a basis on statistical description). The

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Global land-ocean temperature index

Temperature anomaly (°C)

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. Fig. 5.1 A line plot of the global land-ocean temperature index from 1880 to 2009, with the base period 1951–1980. The dotted black line is the annual mean and the solid black line is the 5-year mean. The gray bars show uncertainty estimates [16]

variability over several decades is exhibited in > Fig. 5.1 for the time period 1940–1980, which shows a plateau within the longer term, 119-year warming trend. During this shorter time period, media reports and even a few researchers erroneously forecast ‘‘global cooling’’ based on the observational record at the time that included inadequate and uncertain data from years earlier than this time period and, obviously, no data beyond 1980 ([15], p. 85). The second important reason for distinguishing between climate variability and climate change in the way defined in this chapter is related to dynamic equilibrium in ecosystems. Dynamic equilibrium results as ecosystems adapt to dynamic, ongoing forces that are not so extreme as to produce catastrophic changes. This dynamic equilibrium occurs because the change forces are not dramatic enough (or they cancel each other out), so that relative stability in the ecosystem can be perpetuated as the organisms (plants and animals) and the physical environment respond with adjustments that are within their adaptive capacities. In general, ecosystem adaptive capacity is not exceeded (and dynamic equilibrium is maintained) as a result of climate variability as defined here, but climate change, on the other hand, often exceeds this capacity and leads to fundamental alterations of the ecosystems. Such fundamental alterations occurring in natural ecosystems include processes such as species extinction, changes in community compositions, changes in ecological interactions, changes in geographical distributions, etc. Fundamental alterations can also occur within ecosystems upon which humans depend, leading to such changes as increases/ decreases in agricultural productivity and the availability of water, changes in storm patterns, etc. [3]. These effects on both natural and human ecosystems will be discussed in more detail in what follows, but the important point here is that climate variability rarely produces such fundamental alterations whereas climate change frequently can.

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Global Warming and Global Average Temperature Global warming is defined as an increase in the average temperature of Earth’s surface [17]. As > Fig. 5.1 illustrates, this average surface temperature has increased by 0.75 C 0.3 C (1.35 F0.54 F) between 1880 and 2009. While this change might seem small, the paleo-climate record demonstrates that even ‘‘mild heating can have dramatic consequences’’ such as advancing or retreating glaciers, sea level changes, and changes in precipitation patterns that can all force considerable changes in human activity and push natural ecosystems beyond dynamic equilibrium [18]. The graph in > Fig. 5.1 comes from NASA’s Goddard Institute for Space Studies Surface Temperature Analysis (GISTEMP) database which contains temperature observations from land and sea from 1880 to the present [19]. It is one of three such large databases of Earth surface atmospheric observations that all begin in the mid-to-late nineteenth century and extend to the present. The National Oceanic and Atmospheric Administration (NOAA) maintains the second database that is titled the Global Historical Climatology Network (GHCN), and while this database contains observations from land stations only, it includes precipitation and air pressure data as well as temperature [20]. The third database is abbreviated HadCRUT3 which reflects the source of the dataset being a collaborative project of the Met Office Hadley Center of the UK National Weather Service (‘‘Had’’) and the Climate Research Unit (‘‘CRU’’) at the University of East Anglia. The Hadley Center provides marine surface temperature data and the Climate Research Unit provides the land surface temperature data. These three databases are not completely independent because they share some of the same observation stations, but nevertheless, some differences in the raw data exist, and the three centers work independently using different approaches to the compilation and analysis done on the datasets. As such, the comparisons of results from the different databases allow for verification. Considerable consistency is apparent across the databases, especially in the overall trend of global warming since 1880. The different centers "

. . .work independently and use different methods in the way they collect and process data to calculate the global-average temperature. Despite this, the results of each are similar from month to month and year to year, and there is definite agreement on temperature trends from decade to decade. Most importantly, they all agree global-average temperature has increased over the past century and this warming has been particularly rapid since the 1970s [21].

> Figure 5.2 shows the temperature record for each of the three datasets superimposed upon one another, and the consistency among them is clear. In addition, research has been done to identify and quantify uncertainty in the data, and good estimates of the uncertainty indicate that the data are valid. As one such study stated: "

Since the mid twentieth century, the uncertainties in global and hemispheric mean temperatures are small, and the temperature increase greatly exceeds its uncertainty. In earlier periods the uncertainties are larger, but the temperature increase over the twentieth century is still significantly larger than its uncertainty ([22], p. 1).

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Anomoly (°C) relative to 1961–1990

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0 -0.2 -0.4 -0.6 -0.8 1850

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. Fig. 5.2 Correlation between the three global average temperature records. All three datasets show clear correlation and a marked warming trend, particularly over the past 3 decades. The HadCRUT3 graph shows uncertainty bands which tighten up considerably after 1945 [23]

The temperature records shown in > Fig. 5.2 for each of the three centers are developed as each center uses its dataset to calculate a ‘‘global average temperature,’’ both for the past and for monthly updates, and it is these values that are displayed on the graphs in the figure. While these calculations are done differently at the three centers, all three use the following general procedure. First, they expend considerable efforts to obtain the most accurate data possible and define the uncertainty that remains in those data. Then, the monthly average temperature value for each reporting station is converted into what is called an ‘‘anomaly.’’ The anomaly of each reporting station is calculated by subtracting the monthly average value from the average value that the station has maintained over some relatively long-term ‘‘base period’’ (For example, the HadCRUT3 uses the period 1961–1990 as its base period). The reason for using anomalies is stated as follows: "

For example, if the 1961–1990 average September temperature for Edinburg in Scotland is 12 C and the recorded average temperature for that month in 2009 is 13 C, the difference of 1 C is the anomaly and this would be used in the calculation of the global average.

"

One of the main reasons for using anomalies is that they remain fairly constant over large areas. So, for example, an anomaly in Edinburgh is likely to be the same as the

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anomaly further north in Fort William and at the top of Ben Nevis, the UK’s highest mountain. This is even though there may be large differences in absolute temperature at each of these locations. "

The anomaly method also helps to avoid biases. For example, if actual temperatures were used and information from an Arctic observation station was missing for that month, it would mean the global temperature record would seem warmer. Using anomalies means missing data such as this will not bias the temperature record ([21], see [24] for additional explanation of the calculation and use of anomalies as used for the National Climate Data Center’s GHCN system).

Even though using anomalies produces the most accurate record of Earth’s global average temperature, it is still interesting to calculate one single absolute ‘‘global average temperature.’’ Using the GHCN dataset [25], the average value for the last 10 years, the warmest decade on record [16, 26, 27], produces a global average temperature for planet Earth of 14.4 C or 58 F.

Climate Forcing and Climate Feedback Climate forcing refers to the processes that produce changes in the climate. The word force is generally defined as ‘‘strength or energy that is exerted or brought to bear [and that often] causes motion or change’’ [28]. With respect to Earth’s climate system, a variety of forces cause climates to change. These are called ‘‘climate forcings,’’ and they are all related to Earth’s ‘‘energy balance,’’ that is, the balance between incoming energy from the Sun and outgoing energy from the Earth. The forcings can be internal or external. ‘‘Internal forcings’’ occur within the climate system and include processes such as changes in atmospheric composition or changes in ice cover that causes different rates of absorption/reflection of solar radiation. ‘‘External forcings’’ originate from outside the climate system and include processes such as changes in Earth’s orbit around the sun and volcanic eruptions. Forcings can be naturally occurring, such as those resulting from solar activity or volcanic eruptions, or anthropogenic in origin, for example, the emission of greenhouse gases or deforestation ([3], p. 9). A feedback is defined as a change that occurs within the climate system in response to a forcing mechanism. A feedback is called ‘‘positive’’ when it augments or intensifies the effects of the forcing mechanism or ‘‘negative’’ when it diminishes or reduces the effects caused by that original forcing mechanism ([3], p. 875). Forcing and feedback mechanisms often interact in complex ways that make it difficult to decipher the processes and dynamics of climate change. This difficulty also frequently frustrates policymakers, the media, and the public, and it can result in the dissemination of misinformation, both intentional and unintentional, into the public discourse. One example of this relates to the relationship between carbon dioxide (CO2) and temperature. While it is relatively easy to understand that increasing concentrations of atmospheric CO2 can increase the naturally occurring Greenhouse

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Effect thereby causing global warming, confusion and misinformation result when research brings to light a climate record in which changes in the atmospheric CO2 level lag behind changes in temperature by 800–1,000 years. The legitimate question arises as to how it could be possible that CO2 causes global warming if the rise in temperature occurs before the increase in the atmospheric concentration of CO2. While the question is legitimate, unfortunately, some who are disposed to doubt claims of global warming neither seek answers to the question or pursue additional investigation. Instead, they simply assert the premise that because CO2 lags temperature it cannot possibly be the cause of global warming. However, a more objective review of the scientific literature emphasizes the importance of distinguishing between forcings and feedbacks. The initial, external forcing that begins the temperature changes observed in the climate record stems from fluctuations in the orbital relations between the Sun and Earth, and these fluctuations produce rather small changes in the amount of solar radiation reaching Earth [29]. This relatively weak forcing action causes small temperature changes that are then amplified by other processes [30]. One such amplifying process that appears to be quite significant occurs because ocean temperature changes also change the ocean’s capacity to retain soluble CO2. As this capacity changes, it causes CO2 to either be released from the oceans into the atmosphere (during times of warming temperatures) or removed from the atmosphere and dissolved into the oceans (during times of cooling temperatures). Consequently, CO2 operates in these situations as a positive feedback mechanism that augments the temperature change. In other words, it enhances the Greenhouse Effect and amplifies temperature increases during times of warming and reduces the Greenhouse Effect and reinforces temperature decreases during times of cooling [31]. Careful analysis therefore suggests that a climate record which shows CO2 operating as a feedback mechanism neither negates nor renders less likely the potential that CO2 could operate as an initial forcing mechanism as well. Considering that the atmospheric concentration of CO2 has increased by 25% in the last 50 years [32], it is entirely possible that this increasing CO2 concentration is functioning as the forcing agent for contemporary global warming. Simply put, it is a false premise to claim that CO2 could not be causing contemporary global warming because CO2 has been observed to lag behind temperature changes in the past. This false premise has been lampooned by the analogous statement that, ‘‘Chickens do not lay eggs, because they have been observed to hatch from them’’ [33].

Global Warming Versus Climate Change The terms ‘‘global warming’’ and ‘‘climate change’’ have been defined above and those definitions will not be repeated here. But it is important to emphasize the difference between the two terms and the significance of exercising precision in use of them. While ‘‘global warming’’ is a useful way to refer to the increase of global average temperature that strong scientific evidence shows has occurred over the last 130 years (> Fig. 5.2), for some

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people, the term carries the automatic connotation that human activity is the cause of this observed temperature increase. As stated earlier, a clear distinction should be made between questions that, on the one hand, relate to the changes in climate, if any, that are occurring, and on the other hand, the causes of any identified changes, specifically, naturally occurring or anthropogenic. Because the term ‘‘global warming’’ carries the more polemical and politicized connotation, it poses a higher probability of conflating the two questions than does the term ‘‘climate change’’ which has not yet attracted such politicized interpretations. Consequently, in general, the term ‘‘climate change’’ is preferable. A second deficiency with the term ‘‘global warming’’ is the one dimensional and totalizing change that it implies. Although the average temperature of planet Earth is increasing, the temperature change that any particular place on the Earth might experience could be cooling instead of warming, or perhaps, might be experiencing no change in temperature at all. But the term ‘‘global warming’’ is easily, and perhaps most naturally, understood to mean that all places on the Earth will experience warming. Moreover, even if the term is explained, it does not readily lend itself to the broader understanding that although the global average temperature is increasing, it is not necessarily the case that temperature is increasing at any given place on Earth. The term ‘‘climate change,’’ on the other hand, does not imply this uniform nature of change and thus possesses greater capacity to communicate the potential for different changes occurring in different places and regions. In addition, the term ‘‘global warming’’ implies a narrow view of the nature of changes that can occur in the climate system, namely, an exclusive focus on temperature. But the possible changes to climate are not restricted to just the climate variable of temperature, and the observed increase in global average temperature has been associated with changes in a range of other climate variables that include precipitation amounts, timing, and patterns, cloudiness, humidity, wind direction and velocity, storminess, and more. While the term ‘‘global warming’’ places the focus on temperature, the term ‘‘climate change’’ offers a much richer capacity to incorporate these other types of changes as well, and as a result, is generally emerging as the preferred term.

Thresholds and Tipping Points The term ‘‘threshold’’ in ecology and environmental science means ‘‘a fixed value at which an abrupt change in the behavior of a system is observed’’ ([34], p. 450). In climate science, the term ‘‘climate threshold’’ means the point at which some forcing of the climate system ‘‘triggers a significant climatic or environmental event which is considered unalterable, or recoverable only on very long time-scales, such as widespread bleaching of corals or a collapse of oceanic circulation systems’’ ([3], p. 872). Substantial research indicates that climate changes are prone to such thresholds, or ‘‘tipping points,’’ at which climate on a global scale or climates at regional scales can suddenly experience major

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change [35, 36]. A wide number of complex systems exhibit similar threshold events – financial markets, ecosystems, and even epileptic seizures and asthma attacks – in which the system seems stable right up until the time when the sudden change occurs [37]. Research has provided general ideas on where these thresholds or tipping points might operate with respect to climate – the loss of Arctic sea ice or Antarctic ice shelves, the release of methane into the atmosphere from the melting of Siberian permafrost, or the disruption of the ‘‘oceanic conveyor belt’’ – but this knowledge is rudimentary at best. Scheffer and colleagues [37] report tentative efforts to identify ‘‘early warning signs’’ that precede threshold events, and with respect to climate, they state that ‘‘flickering,’’ ‘‘rapid alterations,’’ or increased weather and climate ‘‘variability’’ seem to have preceded sudden changes observed in the climate record. But at present, predicting these climatic thresholds is vague at best. One of the authors explained the idea of thresholds and the uncertainty about them in an interview with Time magazine, ‘‘Managing the environment is like driving [on] a foggy road at night by a cliff.. . .You know it’s there, but you don’t know where exactly’’ [38].

Defining and Communicating Uncertainty Clearly, climate science contains uncertainties that are endemic to the data sources used; to the understanding of processes involved; and to predictions of future trends, impacts, and outcomes. Consequently, it is essential to accompany any study of climate change with careful, explicit, and candid assessments of the levels of certainty or confidence associated with the findings or claims made. Indeed, reports or studies are suspect if they fail to include such information and/or if they make unequivocal statements about ‘‘proving’’ their points. To some extent, the same can be said about commentaries, news reports, or various information sources. While the politicized environment in which climate change is debated might encourage strong and definite affirmations, such statements can prove counterproductive if they are perceived or exposed as exaggerated [14, 39]. Numerous approaches exist for defining and communicating uncertainty, and this brief discussion here does not attempt a comprehensive overview. Instead, it focuses on the approach that the IPCC has developed for its assessment reports. The main function of the IPCC is to ‘‘assess the state of our understanding and to judge the confidence with which we can make projections of climate change, its impacts, and costs and efficacy of options,’’ but in its first and second assessments (1990 and 1995 respectively), the IPCC gave inadequate attention to ‘‘systematizing the process of reaching collective judgments about uncertainties and levels of confidence or standardizing the terms used to convey uncertainties and levels of confidence to the decision-maker audience’’ ([40], p. 5 emphasis added). Consequently, the IPCC conducted a comprehensive project to rectify these inadequacies [41, 42], and the result was the following system for defining and communicating uncertainties in the Fourth Assessment Report published in 2007.

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. Table 5.1 Conceptual framework for assessing the current level of understanding [40, 43] Increasing level of agreement or consensus

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Established but Incomplete High agreement / Limited Evidence

Well Established High agreement / Much evidence

Speculative Low agreement / Limited evidence

Competing Explanations Low agreement / Much evidence

Increasing amounts of evidence (theory, observations, models)

The first step is to present a general summary of the state of knowledge related to the topic being presented. This summary should include (1) the amount of evidence available in support of the findings and (2) the degree of consensus among experts on the interpretation of the evidence [43]. > Table 5.1 illustrates how these two factors form interacting continua that produce qualitative categories. The IPCC guidance notes for addressing uncertainty ([43], p. 3 emphasis in original) state that in cases where the level of knowledge is determined to be ‘‘high agreement, much evidence, or where otherwise appropriate,’’ additional information about uncertainty should be provided through specification of a level of confidence scale and a likelihood scale. The level of confidence scale addresses the degree of certainty that the results are correct, while the likelihood scale specifies a probability that the occurrence or outcome is taking place or will take place. The IPCC guidelines state that the level of confidence scale ‘‘can be used to characterize uncertainty that is based on expert judgment as to the correctness of a model, an analysis or a statement. The last two terms in the scale should be reserved for areas of major concern that need to be considered from a risk or opportunity perspective, and the reason for their use should be carefully explained’’ ([43], p. 4). > Table 5.2 shows the scale. The likelihood scale is used to refer to ‘‘a probabilistic assessment of some well defined outcome having occurred or occurring in the future’’ ([43], p. 4).

Adaptation and Mitigation The terms ‘‘adaptation’’ and ‘‘mitigation’’ were briefly discussed in the introduction to this chapter, but the more detailed definition and explanation in > Table 5.3 outlines important distinctions that will be helpful for the sections of the chapter that follow.

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. Table 5.2 Scales of uncertainty used in the IPCC fourth assessment report, 2007. None of these are statistically significant because no tests are conducted to determine the values. Instead, they are based on expert judgment Qualitatively calibrated levels of confidence [43] Terminology

Degree of confidence in being correct

Very high confidence

At least 9 out of 10 chance in being correct

High confidence Medium confidence Low confidence Very low confidence

About 8 out of 10 chance in being correct About 5 out of 10 chance of being correct About 2 out of 10 chance of being correct Less than 1 out of 10 chance of being correct

Likelihood scale [6] Terminology

Likelihood of the occurrence or outcome (%)

Virtually certain

>99

Extremely likely Very likely Likely More likely than not

>95 >90 >66 >50

About as likely as not Unlikely Very unlikely Extremely unlikely

33–66 section on ‘‘Alternative Economic Approaches to Promote Sustainability’’ seems to be the answer to limit the harmful effects of usury and capitalism. But the struggle should continue to challenge the usurious system in place. Only fair and just economic system can guarantee sustainability. Justice is the key to the future of sustainability. Humanity must devise an economic system: ● ● ● ●

That takes on a holistic view and does not exploit the weak and oppressed In which usury is completely forbidden in all its forms and manifestations Which focuses on distribution of wealth instead of growth In which the distinction is drawn between public property and private property. The basic necessities of life especially water, air, and energy should be under public control (Owning a deep mine of minerals or petroleum fields is not the same as owning a house or a piece of land; neither is owning petrochemical plants or various

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large energy-generating units or a weapons manufacturing facility the same as owning a garment factory or a candy shop; and neither is owning a railway network similar to owning a car. On the recent Deepwater Horizon oil spill in the Gulf of Mexico, Costanza et al. in Solution Journal commented [66]: ‘‘The continuing oil spill from the Deepwater Horizon is causing enormous economic and ecological damage. Estimates of the size and duration continue to escalate, but it is now the largest in U.S. history and clearly among the largest oil spills on record. One major lesson is that our natural capital assets and other public goods are far too valuable to continue to put them at such high risk from private interests.’’ In [15] the author writes: ‘‘Developers, corporations, and ordinary citizens have maximized private benefit at the expense of shared public goods – including the quality of our cities and towns, not to mention the environment. Individualism has triumphed over collective well-being. In a conservative era dominated by free market philosophies, there has been little political interest in recognizing that someone, usually the public sector, must stand up for the common good. Government, which exists in large part to protect and advocate for public interests, is routinely attacked by those who would like to privatize everything. Individualistic attitudes have been institutionalized through law, government policies, corporate practice, advertising, the media, and many other structural elements of our society. These structural forces also reinforce individualistic, consumption-oriented values, types of behavior, and modes of thought within individuals.’’ [emphasis added] In which big corporations do not exploit the world resources in poor and disadvantaged countries (In part it is a problem of a usurious system, having to do with the growing power of global corporations and the decline of smaller-scale businesses that could form a more locally oriented, socially responsible economy) Based on mutual welfare, trust, and partnership in which both the supplier of capital and the user of capital become partners in profit and loss (equity financing instead of debt-financing) In which business dealings are fair, free from speculations, and not tied up to any particular currency In which the medium of exchange is gold and silver coins (Any crisis in the dollar badly affects the currencies of other countries. Also paper currency is a form of exploitation and is part and parcel of the usurious system. To avoid such fiscal crises and be fair and just to all bimetallic coins of gold and silver medium of exchange should be adopted which have their own intrinsic value) In which businesses that exploit society such as gambling casinos, prostitution, etc., are completely forbidden

Is there a model of such a system? Indeed such a system did exist and has worked for centuries until the beginning of twentieth century. The legal framework of the Islamic economic system for a commercial environment totally free of the machinations of usurers is still entirely in place and is just waiting to be re-implemented. It would be utterly unjust if this system were not taken seriously, without looking at its merit, simply because it has the word Islamic in it

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which may have a connotation of an ‘‘old system’’ or as having religious underpinnings. The value system and attitudes that the Islamic system of economics promotes is the belief in the sacredness of the natural world, meaning that all things exist in their own right as creations of their Lord and can be made use of by man provided he treats them with the respect due to them. It encourages simplicity, modesty, charity, mutual help, and cooperation and discourages miserliness, greed, extravagance, and unnecessary waste. It not only strongly prohibits money-lending with interest but also remedies the causes leading to the existence of this evil institution in human society. It acknowledges that man has the right to own property but that right is not absolute or arbitrary or boundless as personal ‘‘wealth’’ cannot be used to produce collective ills or to spread disorder on Earth. It recognizes that livelihood is necessary and indispensable, but that cannot be the true purpose of life and that all true reward lies in the next world (hereafter). There is no isolation of purely economic phenomena from the fabric of life. This is neither a place nor time to discuss the entire conceptual framework of the Islamic economic system but suffice it to say that it has all the attributes of a fair and just system discussed above. A great deal of literature on the Islamic economic system already exists; see for example [67–70]. What is clear from this is that there is a need for a paradigm shift – a complete change in perspective. Awareness of sustainability has opened up discussion on many fronts and that necessarily includes a usurious banking and financial system. There is a need to engage meaningfully in understanding the harmful effects of usury. While the full implications of the quantum change in perspective have yet to filter down to the level of general consciousness the forest has been cleared and the path is open. No doubt, there may be reluctance due to powerful vested interests related to both cognitive belief systems and to the institutional position. But with courage and commitment the harmful effects of untrue economic theory can be challenged. Since collectively the entire social, political, and economic edifice is entrenched in profiting from interest, it is impossible to completely insulate oneself from its poisonous dust particles. However, here are some practical suggestions of what can be considered at the individual and social level [71]: ● Consider avoiding direct involvement in any transaction based on interest. If you are employed in an organization whose business dealings require giving out or taking interest, maybe it is good idea to start looking for another job. ● Think about keeping only interest-free current (Checking) account at the bank. Bank lockers or safes may also be used instead. ● Be concerned about not taking a loan on interest for business, construction, or for buying any item or article of convenience. ● Consider avoiding buying a house with a mortgage, if possible. ● Consider using cash or a debit card for transactions and avoid using a credit card to fall into the debt trap. Total US revolving debt, 98% of which is made up of credit card debt, is $796.5 billion, as of November 2010 [72]. If for some reason, you use a credit card for online shopping then ask the issuer of your credit card to deduct 100% from your bank account whenever the payment is due. (Of the most mischievously ingenious tools created by the banking system is the credit card, whereby people are able

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to buy what they want through an electronic network without carrying any cash.) Credit card companies charge high interest rates for the service they provide. Through this, the banks and financial institutions are able to control the residual liquidity of the depositors. Thus all the cash of consumers is within the financial system for the use of the bank, and thereby, the use of the rich [67]). Think about raising awareness among your family and relatives, colleagues and companions, neighbors and acquaintances about the evils of interest. Consider turning conversations away from idle gossiping and table talk to a serious exchange of ideas about interest, discussing its forms and manifestations, its harmful effects on society, and how it can be avoided. All major world religions condemn usury. Whether you are a Jew or a Christian or a Muslim or a Hindu or a Buddhist, consider distributing the holy verses of your scriptures that condemn usury and usurious practices to your friends and acquaintances (Many of the early Western philosophers including Plato, Aristotle, Cato, Cicero, Seneca, and Plutarch were critics of usury [52]). Think about joining an organized struggle for deconstructing the interest-based system at work. In addition, consider inviting people to join the cause so that the critical mass necessary for an effective public protest is reached. All peaceful forms of agitation and public pressure including demonstrations, protest marches, and civil disobedience demanding the governments to overhaul the system may be used. Consider joining an organized struggle to call for waiving off the international debt of those countries where the principal amount has already been paid back. Remember by eliminating the interest charges in society the world is

● ● ● ● ● ●

Reducing the environmental risk Reducing poverty in the developing world Reducing the gap between rich and poor Reducing the unemployment problem Reducing the problem of inflation Promoting a culture of charity and sacrifice and condemning the culture of greed and selfishness ● Doing justice to nature ● Increasing the economic efficiency ● Safeguarding the interest of future generations and so on

Acknowledgments The author would like to thank Prof. Masudul Alam Choudhury, College of Commerce, Sultan Qaboos University, for reading the draft and providing valuable suggestions. The author would also like to acknowledge Jim Hesson, Director Academic English Solutions (Academicenglishsolutions.com), for editing and proof reading the article and providing valuable comments and feedback.

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8 Emissions Trading Roger Raufer1,2,3 . Sudha Iyer4 1 Independent Engineer, Cinnaminson, NJ, USA 2 Wharton School, University of Pennsylvania, Philadelphia, PA, USA 3 Institut Franc¸ais du Pe´trole, Rueil-Malmaison, France 4 Cerebronics, LLC, Princeton, NJ, USA Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236 The Evolution of Emissions Trading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241 Emissions Trading Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 The US Acid Rain Program (ARP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 Carbon Markets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 Flexible Mechanisms of the Kyoto Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 Clean Development Mechanism (CDM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 Design Concerns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 Joint Implementation (JI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 International Emissions Trading (IET) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 International Cap-and-Trade Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 The European Union Emissions Trading Scheme (EU ETS) . . . . . . . . . . . . . . . . . . . 253 EU ETS Phase I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254 The Linking Directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255 EU ETS Phases II and III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 Other Cap-and-Trade Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 Voluntary Carbon Market . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 The Over-the-Counter (OTC) VER Market . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263 Carbon Financial Derivatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265 Renewable Energy and Energy Efficiency Markets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 Renewable Energy Certificates (RECs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 Energy Efficiency Certificates (EECs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_8, # Springer Science+Business Media, LLC 2012

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Abstract: Climate change is being exacerbated by the emissions of globe-warming greenhouse gases (GHGs) as a consequence of economic activities associated with energy, industry, transportation, and land use. From an economic viewpoint, the Earth’s climate is a public good, and pollution a negative externality; such change therefore constitutes market failure. Controlling air pollution by utilizing economic mechanisms represents an important change in environmental thinking – literally a paradigm shift away from historical command-and-control (CAC) engineering systems. Today, this new approach is being utilized to mitigate the emissions of GHGs, addressing the pollution externality by putting a price on carbon. The international carbon market, largely developed as a result of the Kyoto Protocol, had a total value of $144 billion in 2009. The largest component of that market, the European Union’s Emission Trading Scheme (ETS), was worth $118 billion; it represents a regional market designed to assist Europe in achieving compliance with the Protocol’s requirements, and also has links to the Protocol’s project-based mechanisms, the Clean Development Mechanism (CDM) and Joint Implementation (JI) which help minimize compliance costs. These project-based components themselves were valued at $2.7 billion and $354 million, respectively. Further, other carbon markets created in numerous countries (e.g., the Regional Greenhouse Gas Initiative [RGGI] in the USA and the Greenhouse Gas Abatement Scheme in New South Wales, Australia) were worth $2.3 billion, while the global voluntary market was estimated to be in the $350–$400 million range (a significant drop from the previous year’s $700 million figure). This chapter discusses the structure of these emissions trading carbon markets, the theory behind their development, their historical evolution, ongoing governance challenges, and future prospects.

Introduction The issue of global climate change is as much an economic conundrum as it is one of science and regulatory policy. Climate change is exacerbated by the emissions of globewarming greenhouse gases (GHGs) as a consequence of economic activities associated with energy, industry, transportation, and land use. Historically, polluters have not had to directly bear the social costs of emitting substances into the atmosphere – and therefore they have had no incentive to reduce such emissions. In economics, the Earth’s climate is considered a ‘‘public good,’’ that is, a good that can be consumed by everybody in a society, where those who fail to pay for the good cannot be excluded from enjoying its benefits. An ‘‘externality’’ is the impact of an economic transaction on a party that is not a direct participant of the transaction, and the price therefore does not reflect the full cost of a certain good. Human-induced climate change, then, is a ‘‘negative externality,’’ since the emitter of GHGs does not pay the cost of detrimentally altering a public good (i.e., the Earth’s climate). This means that climate change, from an economic viewpoint, is a market failure; in fact, the British government’s Stern Review, a well-known economic analysis of climate change, called it a ‘‘market failure on the greatest scale the world has seen’’ [38].

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While the fundamental theory of public goods and externalities forms the basis of any economic approach, there are a few facets of global warming that make a market solution to the problem of climate change even more challenging: The climate change externality is global; the impacts are persistent and develop over time because some GHGs remain in the atmosphere for hundreds of years; and, since there is no accurate way of predicting the change in the climate system due to increases in atmospheric GHGs, there are considerable uncertainties and risks in developing a mitigation strategy based upon economic theory. In standard economic theory, the marginal abatement cost (MAC) of pollution control should equal the marginal social benefit (MSB) of such abatement. This means that the goal of the economic control program should be to set a control level such that the next dollar spent on pollution control purchases exactly one dollar’s worth of environmental amenities. > Figure 8.1 illustrates the marginal abatement cost (MAC) and marginal social benefit (MSB) curves. Economists then offer two approaches to arrive at that point: ● A price-based mechanism, also called a Pigouvian tax ● A quantity-based mechanism, commonly referred to as emissions trading The Pigouvian tax approach was first developed by Arthur Cecil Pigou (1877–1959), a British economist who was a professor at Cambridge. Pigou discussed the concept of externalities in his book The Economics of Welfare (1920), and argued that a tax should be imposed on negative externalities such as pollution in order to discourage them. In the case of climate change, a Pigouvian solution would introduce a tax on GHG emissions. If the MAC of a polluter is higher than the tax, the polluter will find it more cost-effective to pay the tax and continue emitting. If the MAC is lower than the tax, then the polluter will try to abate the pollution as opposed to paying the tax (> Fig. 8.2).

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A Pigouvian tax is now considered a well-known and traditional means of bringing a modicum of market forces and therefore better market efficiency to economic situations where externalities exist. Such a tax will make it more expensive to pollute, and will ensure a change in behavior by the polluting entity – forcing the polluter to either pay the tax or implement technologies to reduce pollution, whatever is more cost-effective. Despite being an efficient solution to controlling pollution, taxes introduce a political dynamic that raises questions about wealth transfer from industry to government, the distribution of this revenue, lobbying of the government by special interest groups, polluters, etc. Economists have attempted to address this wealth transfer by linking the tax with subsidies (and utilizing the revenue generated by the tax to fund such efforts); by removing other taxes (so that there is tax neutrality); and similar schemes. The quantity-based market approach, on the other hand, is modeled on the work of John Dales, Professor of Economics at the University of Toronto, in his classic 1968 book Pollution, Property and Prices. In that work, Dales proposed a new market-oriented policy instrument for tackling pollution problems. Dales’ idea was to have an environmental authority issue a limited number of rights (or permits) to emit a specified pollutant, and then leave the determination of the price of these permits to emitters within a market. Today, transactions in such markets are commonly called ‘‘emissions trading.’’ A regulator sets an overall emission limit (‘‘cap’’), which is the total quantity of a pollutant that the participants in the scheme are allowed to emit. That quantity is then divided into a number of ‘‘allowances,’’ and polluters are allowed to trade (i.e., buy and sell) such allowances in a market. Such ‘‘cap-and-trade’’ schemes have become quite popular over recent decades, and their success has led to the development of carbon markets under the Kyoto Protocol. In the figure below, a cap is set at the point where MAC = MSB, which is at the point where 55% of the pollution is controlled. The ‘‘cap’’ of 45 units of pollution could be divided into 45 allowances, which could be bought and sold by polluters. Note

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that those with low marginal costs of control will put on control, rather than purchase such an allowance, and society will ultimately end up at the point where MAC = MSB; the figure also shows that those with higher marginal costs should ultimately end up holding the allowances (> Fig. 8.3). There are several advantages to such ‘‘cap-and-trade’’ programs, the most obvious being that it is an economically efficient way to control pollution without the government having to worry about setting prices. It also has considerable flexibility in addressing the political issues associated with the wealth transfer noted above – allowance allocation schemes can call for 100% auctioning (creating a transfer similar to that of a Pigouvian tax); or distribute the allowances for free to existing polluters (typically called ‘‘grandfathering’’); or utilize any combination in between. This gives the government considerable political leverage in addressing distributional concerns, and politicians can (and have) utilize(d) this to minimize political resistance to the pollution control program. Importantly, such quantity-based systems also limit the total amount of pollution, shifting the burden of dealing with growth on polluters. Under the ‘‘cap,’’ individual emitters participating in the scheme have the flexibility of determining how best and where to deliver emission reductions. A significant cap-and-trade program was introduced in the USA in the early 1990s for acid rain control, but this was not the first Emissions Trading Program (ETP). Earlier, in the 1970s, a baseline-and-credit trading emissions trading system had been established. In baseline-and-credit trading, the regulator defines a specific set of acceptable conditions (the baseline) for an emission source. Depending upon preset rules, improvements to this situation may qualify for ‘‘credits’’ (called Emission Reduction Credits [ERCs] in the US program) which could then be used for various purposes – to either offset new emissions, to reduce the control requirement on other units, or be sold to others who might have

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. Fig. 8.4 Allowances versus credit trading (Adapted from [33])

trouble meeting their own baseline requirements. > Figure 8.4 illustrates the difference between cap-and-trade and baseline-and-credit trading schemes. Later sections will make clear that both of these emissions’ trading approaches play an important role in the international carbon market. The key aim of market-based approaches toward climate change policy is to ensure that those generating GHGs face cost for emissions that reflects the damage they cause (i.e., what economists call ‘‘internalizing the externality’’). In ideal market conditions, both price and quantity-based mechanisms, if designed correctly, can be used to create such a price for carbon, and both approaches have the potential to deliver emission reductions efficiently. This chapter seeks to analyze the role that quantity-based approaches play in mitigating climate change, and the resulting compliance and voluntary carbon markets that have been developed and are in operation around the world. This chapter is organized in such a manner as to provide the reader a historical framework for the development of such

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market approaches – beginning first with traditional engineering approaches to pollution control, and then moving toward implementation of the economists’ ideal, in order to see how carbon markets obtained their current structure. It then profiles the compliance carbon markets and the complementary, but increasingly important, secondary and related markets in operation today.

The Evolution of Emissions Trading The development of markets to address environmental issues represents a strategic shift in the thinking behind environmental management. Pollution control has a long evolutionary history, beginning with traditional engineering approaches and subsequently developing into the economic realm with market-based approaches. Historically, most governments have utilized ‘‘command-and-control’’ (CAC) types of regulations to address pollution problems. As the name suggests, the government would issue some form of ‘‘command’’ – typically a mandate for a pollution source to use some type of technology, or meet some specific pollution level. The government then faced the problem of ensuring that the command was actually followed out – and this required active ‘‘control.’’ ‘‘Control’’ typically includes the monitoring, reporting, and verification (MRV) of emissions, as well as punishment for a failure to meet ‘‘commands.’’ The absolute form of ‘‘command’’ is prohibition, which is used if the potential damage to the environment is severe and difficult to remediate, (e.g., use of polychlorinated biphenyls [PCBs]). More frequently, however, technology-based requirements are employed, typically requiring polluters to meet some emission limit or performance standard for their equipment. Monetary fines, or perhaps imprisonment for egregious cases, are now the norms for ‘‘control.’’ In an 1874 amendment to Britain’s Alkali Act of 1863, polluters faced a requirement to utilize the ‘‘best practicable means’’ (BPM) of pollution control. From an engineer’s perspective, if everyone was utilizing BPM, then whatever happened to the environment simply happened – after all, everyone was doing the best they could with technology. An alternative regulatory approach was adopted in the USA in the 1960s, however. This alternative suggested that the goal of pollution control systems was not simply to use the best technology, but rather, to focus on achieving environmental quality. Technology was just a means of accomplishing such an end, not the goal itself. Environmental goals were thus developed in terms of environmental quality standards, and the technology-oriented requirements became recognized as the means to accomplish such goals. The resulting CAC programs developed in the 1970s therefore adopted the ‘‘traditional’’ (i.e., engineering) approach outlined in the left side of > Fig. 8.5. Economists had a different idea, however, as discussed earlier and as noted on the right side of > Fig. 8.5. From their theoretical perspective, the goal is to develop a program where marginal costs of pollution abatement is equal to the marginal social benefit (i.e., MAC = MSB). All of the information used by the regulators to set environmental quality

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standards in the traditional approach would somehow have to be incorporated into the marginal social benefit curves outlined in the right side of that figure. This obviously would be a very difficult task. > Figure 8.5 suggests that two transitions are occurring today – a shift from an engineering to economic worldview in environmental management, and a secondary shift from price to quantity-based mechanisms. There are important caveats associated with both transitions, however. For the first, the transition is only occurring in the bottom portion of the figure – within the regulatory means, not environmental goal setting. Governments fully recognize the difficulties associated with developing accurate MSB curves, and thus tend to stay with environmental quality standards or depend upon political compromise to set goals. However, they increasingly recognize the strength of using the economic regulatory means (i.e., Pigouvian taxation and emissions trading) as tools to help accomplish such goals. Any portend of a price to quantity shift within economic instruments must similarly be heavily qualified. Economists make choices about the appropriate price or quantity instruments to use based upon the slopes of the MAC and MSB curves, confidence in the data used to estimate them, and similar information. Certainly many governments – and economists – are more comfortable using price-based instruments, and it has frequently been suggested that these are a more appropriate tool for dealing with climate change (see, e.g., [13, 31]). Nonetheless, the political flexibility of quantity-based systems noted above, and the increasing difficulty faced by many governments in imposing taxation schemes, has led to such a longer-term shift over recent decades. Further, many believe

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that it is more appropriate for the government to focus on the physical goal (i.e., the quantity) and have prices respond than the converse. The EU has made cap-and-trade its predominant policy mechanism for dealing with climate change, and prospective US legislation has been following a similar path, as discussed below.

Emissions Trading Programs The US Environmental Protection Agency (EPA) introduced the concept of emission markets in 1976, as a means for new emission sources to locate in areas with unhealthy air quality (i.e., areas that did not meet the National Ambient Air Quality Standards). The new sources were required to use stringent control technology (i.e., Lowest Achievable Emission Rate), but were also required to ‘‘offset’’ the additional pollution they created by a greater than 1:1 ratio. Thus, the new source would help clean up the nonattainment area even though it was adding new pollution. Some economists realized that this created a new asset: Emission reduction ‘‘credits’’ from an existing source were now worth something to a new source hoping to locate within the nonattainment area such as Los Angeles. This emissions trading scheme was expanded in 1979 to include existing sources as well as new ones through the ‘‘bubble’’ policy, which allowed sources to put an imaginary bubble over their facility, and then meet CAC requirements in the most cost-effective manner under the bubble (i.e., based upon their own determination of MAC rather than the government’s embedded within the CAC requirements). It was expanded as well that same year through ‘‘netting,’’ a simplified-permit strategy for replacing old with new equipment; and ‘‘banking,’’ which provided firms the flexibility of storing their emission reductions over time. These four regulatory provisions were collectively brought together in a draft Emissions Trading Program (ETP) in 1982, and finalized in 1986. The US EPA’s ETP did not change the CAC requirements – it merely introduced a new and more flexible means for emission sources to meet them. The time and costs associated with completing a specific ERC transaction have been high, however, and while thousands of ERC trades have occurred, high transaction costs have hobbled this market. The resulting baseline-and-credit ETP is shown in > Fig. 8.6, and remains in effect today.

The US Acid Rain Program (ARP) The ETP laid the groundwork for a pioneering acid rain allowance-trading program that is the predecessor of quantity-based trading programs in operation today. In 1980, rising concern about the extensive environmental impacts of acid rain (i.e., acid deposition) prompted the US Congress to establish the National Acid Precipitation Assessment Program, an interagency organization designed to study its causes, effects, and potential control. With the Clean Air Act amendments in 1990, Congress addressed the control issue and sought to achieve major reductions of the primary components of acid rain:

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. Fig. 8.6 The US EPA’s initial emission trading program

ten million tons of sulfur dioxide (SO2) and two million tons of oxides of nitrogen (NOx) below 1980 levels by the year 2000. In doing so, it established a new paradigm for environmental protection, since it was the first major emissions control program utilizing the economists’ idea of a quantity-based emissions trading mechanism. The centerpiece of the Acid Rain Program (ARP) is a cap-and-trade system for SO2. The NOx reduction program initially took a command-and-control approach, but later a cap-and-trade NOx program was developed in the US Northeast in 1999 (primarily for ozone-control purposes). A two-phased tightening of restrictions on fossil fuel-fired power plants was adopted: Total emissions in 1995 (under Phase I) were 25% below 1990 levels, and more than 35% below 1980 levels [6]. Phase II, which began in 2000 and is currently ongoing, represents a significant 50% cut from 1980 SO2 levels [43]. A recent analysis of the ARP estimates annual benefits of the program in 2010 to be $122 billion, and costs to be only $3 billion (50% of the figure estimated by the EPA in 1990) – a 40-to-1 benefit/cost ratio [42]. Such numbers illustrate why The Economist (July 6, 2002) called it ‘‘probably the greatest green success story of the past decade.’’ A key element of the ARP market design was that it kept the existing ETP (with emission reduction credits) to protect local air quality and public health near the power plants, while superimposing a cap-and-trade scheme (with emission allowances) to deal with total loading of the pollutant. This dual ‘‘baseline-and-credit’’ and ‘‘capand-trade’’ market scheme was a forerunner of the international carbon market, which would similarly use both types of instruments to accomplish desired environmental goals.

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Carbon Markets The foundation for the international carbon market began at the ‘‘Earth Summit,’’ in Rio de Janeiro, Brazil in 1992. The Earth Summit, formally called the UN Conference on Environment and Development, addressed a wide range of environmental and governance issues, including biodiversity, the management of toxic chemicals, and similar issues – but it is perhaps best remembered today for establishing the United Nations Framework Convention on Climate Change (UNFCCC). The UNFCCC committed the signatory governments to a voluntary, nonbinding effort to reduce GHGs with the goal of ‘‘preventing dangerous anthropogenic interference with the earth’s climate system.’’ The UNFCCC came into force in 1994, after 50 countries had ratified it, in accordance with the terms of the treaty. Since the treaty has no end date, there is no set expiry time to the international regime under the treaty. Signatory countries of the UNFCCC agreed to ‘‘common but differentiated responsibilities’’ for addressing emissions, recognizing that the largest share of historical and current emissions was generated from developed countries (i.e., as a result of more than 150 years of industrial activity), and that the share of emissions from developing countries would need to grow to meet their social and developmental needs. This resulted in a division among the signatory countries into two principal groupings: Annex I countries, which are industrialized nations and nations with economies in transition such as Russia and Ukraine, and Non-Annex I countries, which are the remaining (mostly developing) nations. [NB: There is also an Annex II grouping, consisting of OECD members and the European Union, which have a ‘‘special obligation’’ to provide financial resources and facilitate technology transfer to developing countries.] The Kyoto Protocol was adopted in 1997 in Kyoto, Japan, during the third annual meeting of the UNFCCC (called the Conference of Parties [COP]), and, while it opened for signature on March 14, 1998, the Protocol only came into force on February 16, 2005. As of 2010, 189 countries and one regional economic integration organization (the European Community) have ratified the treaty. A major feature of the Kyoto Protocol is that it sets binding GHG emission constraints for the Annex I countries (in Article 3 and Annex B). These are equivalent to an average 5.2% emissions reduction from a 1990 baseline over the first 5-year commitment period (2008–2012). Thus, while the UNFCCC encouraged industrialized nations to reduce GHG emissions, the Kyoto Protocol commits them to doing so. Even though the USA initially introduced the idea of emissions trading and was an ardent proponent of market-based mechanisms to address climate change (based upon its successful experience with the ARP), it never ratified the Kyoto Protocol. As a participant, the USA would have been required to reduce GHG emissions by 7% below 1990 levels. The USA experienced rapid economic growth during the late 1990s, however, and that 7% reduction would have amounted to approximately 30% in real terms for the 2008–2012 commitment period, as growth continued. The USA disagreed with other parties about how the market-based ‘‘flexibility mechanisms’’ should be implemented, as well as other policy issues (e.g., the role of forestry ‘‘sinks’’), and subsequently withdrew from the

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process completely in March 2001. The Australian government similarly decided not to ratify the Protocol in its initial stages, but ultimately did so in December 2007. The USA did pursue domestic initiatives to reduce emissions, however. A number of state/regional cap-and-trade programs to reduce GHGs have been set up or are under development within the country (as described below). In 2005, the USA signed the Asia Pacific Partnership on Clean Development and Climate (APP), with Australia, India, Canada, China, South Korea, and Japan. Together, these countries emit 50% of the world’s GHGs and have agreed to work together with private sector partners to meet goals for energy security, national air pollution reduction, and climate change in ways that promote sustainable economic growth and poverty reduction. Even though the APP describes itself as a partnership, which will ‘‘complement, but not replace the Kyoto Protocol’’ [1], APP critics have tended to see it as an alternative (and thus a threat) to the Kyoto Protocol.

Flexible Mechanisms of the Kyoto Protocol The Kyoto Protocol is a binding agreement to regulate six GHGs: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), perfluorocarbons (PFCs), hexafluorocarbons (HFCs), and sulfur hexafluoride (SF6). The emissions of these GHGs are primarily associated with the generation and use of energy, industrial processes, municipal wastes, and land-use activities such as deforestation. For reporting and tracking purposes, the global warming potential (GWP) in the atmosphere of each gas is expressed in terms of a CO2 equivalent (CO2e). Methane, for example, has a GWP that is 21 times that of CO2. The Protocol sets individual GHG emission reduction targets for Annex I countries under the UNFCCC. These targets are specified in Annex B of the Kyoto Protocol. For the Annex I countries that ratified the Protocol, their assigned GHG emission amounts act as a legally binding cap on emissions between 2008 and 2012, the first commitment period. Annex B countries can meet their emission reduction targets either through national measures (e.g., regulations, taxes or environmental markets), or through the use of three flexible market mechanisms incorporated into the Protocol. Described in Articles 6, 12, and 17 of the Protocol, these flexible mechanisms allow Annex B countries to pursue opportunities to cut emissions or sequester carbon more cheaply in other countries than within their own domestic market. Article 6 of the Protocol defines the mechanism known as Joint Implementation (JI), which allows emission reduction or removal projects in Annex I countries to generate Emission Reduction Units (ERUs), which can then be used to meet the emission reduction or limitation commitments of other Annex B countries. Each ERU is equivalent to 1 t of CO2, and can be counted toward Kyoto target requirements. Article 12 defines the Clean Development Mechanism (CDM), which allows similar carbon credits known as Certified Emission Reductions (CERs) to be generated from projects in developing (i.e., Non-Annex I) countries. The International Emissions Trading (IET) mechanism is outlined in Article 17 of the Protocol, and allows Annex B parties to trade Assigned Amount Units (AAUs) in

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order to meet their commitments. Countries in Annex B that have spare (i.e., permitted but not used) AAUs can thus sell them to countries that exceed their targets. As discussed below, as these flexible mechanisms evolved over time, the CDM was the first to be implemented, since projects under the mechanism could start generating credits relatively quickly (i.e., before the first commitment period began). This was followed by the JI, and thirdly, IET. These latter mechanisms did not fully commence until the start of the first commitment period in 2008. Thus, an Annex B country has several options to reduce emissions in order to comply with its Kyoto Protocol targets: ● Limit emissions through domestic policy, such as implementing direct regulation, Pigouvian taxation, or setting up domestic emissions markets (note: the role of regional markets such as the EU ETS is discussed below). ● Set up eligible projects in Non-Annex I countries under CDM, and use the CER carbon credits generated from these projects. ● Set up eligible projects in Annex I countries under JI, and use the ERU carbon credits from these projects. ● Utilize the IET program to buy/sell AAUs. As an example, Britain, which has a relatively high reduction target of 12.5%, could achieve this target by implementing a portfolio of domestic regulatory policies, such as improving building codes; employing price instruments such as a petrol taxes to reduce emissions from the transportation sector; and using emissions markets (in this case, the EU ETS) to reduce pollution from the power sector. Over and above such domestic efforts, the country could purchase AAUs from Russia or Ukraine, or invest in CDM or JI projects abroad (either through the EU ETS, or separately). The overall market framework for the Kyoto Protocol flexibility mechanisms is shown in > Fig. 8.7. These mechanisms are indeed flexible, and countries are at liberty to employ one or all of these mechanisms, in any combination, depending upon their emissions constraints and economic situation.

Clean Development Mechanism (CDM) Since climate change is a global problem and the physical nature of the pollutant makes the location of emissions reductions irrelevant, CO2 emission reductions can be obtained anywhere – and usually at lower cost in the developing world. Article 12 of the Kyoto Protocol provides for such reductions, and the Clean Development Mechanism outlined in that article has two goals: to reduce GHG emissions and to foster sustainable development. CDM is a project-based mechanism that allows public or private entities to invest in GHG-mitigating activities within developing countries, and to earn abatement credits for those projects. These credits, called CERs and equivalent to 1 t of CO2, can then be applied against their own emissions or sold in the marketplace. Buyers in other Annex I countries, for example, might purchase them to assist in meeting their own GHG reduction goals.

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. Fig. 8.7 The Kyoto Protocol flexibility mechanisms

Prior to the generation of CERs from a CDM project, the developers of the project must go through a formal and rather complex process. They interact with three institutions: the CDM Executive Board (EB), the Designated National Authority (DNA) of the host country, and at least one Designated Operational Entity (DOE), which is an independent private company that serves as an auditor. The CDM EB, which was formed in 2001, is authorized under the Protocol to implement and supervise the CDM. Its ten members are appointed by the COP, and the Board meets no less than three times a year. The DNAs are set up by host countries to review and approve CDM projects, and to provide specific guidance about the operations of CDM (e.g., for sustainable development criteria) within their host country. DOEs are companies which have been certified by the EB to conduct validation and verification of the specific projects undertaken. In order to qualify to receive CERs, projects have to have begun after January 1, 2000, and must submit a Project Design Document (PDD) which includes at least the following information: ● A general description of the project activity. ● The application of an UN-approved baseline methodology for that specific activity. Baseline methodologies have now been approved for many standard renewable energy and energy efficiency applications, but any novel technology or application will first require such an approval. ● The selection of a crediting period. Project developers can select either a fixed 10-year baseline period, or three 7-year baselines with adjustments at the end of the first and second periods (with the exception of afforestation and reforestation sink projects).

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● A monitoring methodology and plan. ● The estimation of GHG emissions and reductions. ● An assessment and demonstration of ‘‘additionality’’ (i.e., that emissions reductions are above and beyond those that would have happened anyway – they are ‘‘additional’’ or ‘‘surplus’’). Additionality is important because developing countries are not required to reduce emissions under the Kyoto Protocol, and Annex I countries utilizing CERs from these countries will take credit for such reductions. This is usually the most difficult criterion for CDM projects to meet and document. ● Documentation that the project meets the DNA’s sustainability criteria for projects within that host country. ● Other relevant data (e.g., contact information for project participants, stakeholder comments, and information on the use of public financing). The CDM project process is outlined in > Fig. 8.8. Note that after the PDD is completed in the design stage, it is validated by the DOE, which will make a recommendation to the EB to register the project. Later, a second DOE will verify that the project has performed as expected, based upon the monitoring plan submitted as part of the PDD – and will recommend that the appropriate number of CERs be issued. Only if all of these criteria are met will the project then be issued CERs, which can be sold in the international carbon market.

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. Fig. 8.8 Carbon credits from the clean development mechanism (CDM) of the Kyoto Protocol (http:// cdm.unfccc.int/CommonImages/ProjectCycleSlide.jpg)

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As of the first quarter 2010, CDM projects in the pipeline are expected to deliver more than 2.7 billion tons of CO2 equivalent in offsets during the first commitment period (2008 to 2012), which makes it the mechanism generating the largest number of emission reductions in the world. There are now more than 4,900 projects included in UNEP Risoe’s CDM Pipeline database [40]. China has accounted for the major share of confirmed transactions in the primary CDM market, with 72% in 2009; all other countries had single digit percentages [45]. With London representing the world’s major center for carbon financing, the UK led transactions on the buyer’s side with 37% of the primary CDM and JI market in 2009. There is an active secondary market associated with CERs, which supports the sale of issued CERs either bilaterally over the counter (OTC), typically through brokers or through exchanges. Since only delivery and counterparty risks are factors in the secondary market when compared with the primary market (where the transaction is directly between the project developer and the buyer), prices of secondary CERs (sCERs) are typically higher. In 2008, there were confirmed transaction volumes of 389 MtCO2e traded (down 30% from 2007) in the primary market, and CER prices averaged at $16.78 for a total value of $6.5 billion. The secondary market, however, continued to grow exponentially, with a total volume of more than one billion sCERs transacted for a value of $26.3 billion. Since the Kyoto Protocol entered into force in 2005, the CDM has developed very rapidly, mobilizing billions of dollars in public and private investment to reduce emissions in developing countries. However, the mechanism has not been without its challenges, and suffers from a number of concerns in its design.

Design Concerns A number of questions about the design of the CDM have been raised, including concerns about the environmental integrity of project transactions, complex governance procedures in the registration of projects, the limited role of technology transfer, an unequal regional distribution of projects, and the CDM’s contribution to sustainable development. A fundamental concern (some consider a flaw) in the market design of the CDM has been the determination of additionality of a project. Defined in paragraph 5c, Article 12 of the UNFCCC, emissions from a CDM project should be ‘‘. . . additional to any that would occur in the absence of such activities.’’ This statement, however, is vague and has been subject to many different interpretations. The idea behind additionality is that the project should owe its existence to the prospective earnings from carbon credits sold in the CDM market, that is, the emission reductions should go beyond what it would be in the absence of the CDM. In general, determining additionality has proven to not only be cumbersome, but has also resulted in increased transaction costs, liability, and risk for investors. Friends of the Earth has estimated, for instance, that 75% of all approved CDM projects were already up and running at the time they were approved by the CDM EB [18]. David Victor, formerly head of Stanford’s Energy and Sustainable Development Program, estimated that between a third and two-thirds of CDM offsets may not represent actual emission cuts [26].

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In mid-2009, the CDM EB ordered an unprecedented review of whether a number of Chinese wind projects satisfied additionality requirements. Now referred to as the ‘‘Chinese wind controversy,’’ ten projects were rejected outright just before COP15 in Copenhagen, sending shockwaves through the CDM investment community. The Chinese government publicly attacked the UN’s oversight of the CDM, and threw doubt on the verification of credits in the world’s largest CDM market [25]. Large hydroelectric power projects in the CDM have also been controversial. Hydro projects constitute a quarter of all CDM projects, and 67% of these are in China. Hydroelectric projects are typically expected to replace power generation that would otherwise have been sourced from fossil fuels. Yet, most of the hydro projects submitted for CDM validation are expected to start generating CERs within 12 months of their validation, when it would normally take several years to build a hydro plant. This points to the likelihood that several of these projects were already underway prior to the commencement of their CDM validation process [39]. The evolution of the CDM market also had its share of challenges in the HFC-23 (trifluoromethane) controversy, which the CDM EB has since attempted to fix. HFC-23 is a highly potent and long-lived greenhouse gas with a global warming potential of 11,700 times that of CO2, which means that every ton of HFC-23 destroyed produces 11,700 CERs for sale in the CDM market. The destruction of HFC-23 (a by-product of HCFC-22 [chlorodifluoromethane] production, which is used as a refrigerant) saw windfall profits created in several projects (especially in China). The NY Times reported that industrialized nations could end up paying $800 million a year to buy CERs, even though the cost of building and operating incinerators would only be approximately $31 million per year [32]. In response to such windfall profits, China imposed a 65% tax on CER revenue generated by HFC-23 projects. Furthermore, the CDM EB has not accepted new projects for HFC-23 destruction in recent years. Moreover, the bulk of CDM projects have been focused on India and China, with only a small percentage (122 out of 4968, or 2.5%) of all projects in the developing world sourced from Africa [40]. With its slow pace of economic development, and poor industrial base, Africa offers fewer investment opportunities compared with China or India. Given the time-consuming project approval process, and delays and conflicting rulings in administration, there are considerable questions about the Mechanism’s future. Ken Newcombe, founding head of the World Bank’s carbon finance unit, questioned whether ‘‘the CDM was capable of delivering emission reductions on the scale necessary in the future when there are large gaps which it fails to address’’ [9]. It can be said without doubt that the CDM market is still evolving, and the challenges outlined above did not get resolved in the COP15 summit in Copenhagen in December 2009.

Joint Implementation (JI) Joint Implementation is a project-based mechanism that assists UNFCCC Annex I countries in meeting their Kyoto commitments by participating in projects in other

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Annex I countries. Entities may partake in JI projects to generate emission credits, known as ERUs, in order to use them for compliance with their emissions targets or to sell in the international carbon market. Similar to the CDM, JI offers parties a flexible and costeffective means of fulfilling part of their Kyoto commitment, while the host party benefits from foreign investment and technology transfer. Unlike CDM, however, projects could only begin generating ERUs in 2008. To be eligible to qualify as a JI activity and to receive ERUs, projects must be undertaken between Annex 1 countries; must provide a reduction that is additional to any that would otherwise occur in the absence of the project; and must be supplemental to domestic actions to reduce greenhouse gas emissions. The lifecycle for projects to be eligible for JI ERUs similarly begins with the preparation of a PDD, following JI guidance established by the JI Supervisory Committee (SC). Then, an Accredited Independent Entity (AIE) determines if the emission reductions were correctly estimated, and if necessary procedures were established to monitor the project performance during its implementation. At this stage, the JI Supervisory Committee will consider the quality of the project and, after 45 days, the project automatically acquires a status of JI project. As with CDM, most countries involved in JI establish their own national Designated Focal Points (DFP) in charge of JI project approval. There are two main tracks by which projects qualify for generating ERUs: Track 1, where a host party meets all eligibility requirements and verifies that emission reductions from the project are additional to a baseline scenario (i.e., the project implementation is largely left up to the participating states); and Track 2, where a host party meets only a limited set of eligibility requirements (verified by an Accredited Independent Entity) and verification of the emission reduction as being additional has to be done by the JI SC. The Netherlands, Denmark, and Austria are currently among the most active buyers in JI projects, mainly through different governmental purchase programs or participation in carbon funds. From the sellers’ side, countries like Bulgaria, Czech Republic, Romania, and Poland moved early in promoting JI projects, while the potential ‘‘big suppliers,’’ Russia and Ukraine, have more recently started to engage in JI initiatives and are rapidly increasing the number of prospective JI projects. As of February 1, 2010, Track 1 has a total of 97 registered projects and Track 2 has 16 projects registered in the JI pipeline [40]. The World Bank reports that the JI market was worth $294 million in 2008, with just 20 MtCO2e confirmed transactions, and equal to just half of the volumes transacted in 2007. Through 2008, the JI market continued to concentrate on Russia, with a 68% market share of transacted volumes and Ukraine, with an 18% market share. However, in early January 2009, the UN suspended Russia from the International Transaction Log (ITL) because it failed to pay the required fees. This made the country unable to transfer emission rights or Emission Reduction Units to a foreign buyer. A prominent carbon market analyst firm, Point Carbon, projects a declining JI market in coming years for several reasons. The global economic slowdown has made investors more risk averse, and the conditions for JI in Russia – especially since the suspension of the nation by the UN from the ITL – have become less attractive. Delivery risk also appears high due to the number of delays most JI projects face.

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International Emissions Trading (IET) The Kyoto Protocol provides for a quantity-based cap-and-trade scheme called International Emissions Trading that is limited to Annex B countries. The national allocations used in the emissions trading are expressed as levels of allowed emissions, or Assigned Amount Units (AAUs). Although these are national allocations and commitments, in practice, individual countries devolve their emissions targets and requirements down to major industrial entities such as power plants and large emitters. Therefore, the ultimate market participants may be individual companies that expect their emissions to exceed their quotas. Russia, Ukraine, and the Central and Eastern European countries have an estimated 8–12 billion tons surplus of AAUs for the 2008–2012 Kyoto commitment period associated with the collapse of the former Soviet Union, which occurred after the Kyoto Protocol’s 1990 base year. This surplus is often pejoratively referred to as ‘‘hot air.’’ Annex I countries could theoretically achieve compliance by purchasing ‘‘hot air,’’ but many buyers are reluctant to do so since that would merely represent payment for economic collapse which occurred nearly 20 years ago, with little ongoing environmental benefits. Green Investment Schemes (GIS) have been introduced to address this ‘‘hot air’’ situation. Under GIS, revenues from the sale of surplus AAUs are invested in environmental improvements (or ‘‘green’’ activities) in the selling nation, even though such activities might not strictly qualify for carbon credits (e.g., training energy auditors). This way, purchased AAUs become linked to GHG mitigation efforts, and many GIS schemes have begun to mirror CDM and JI carbon credit mechanisms, paying detailed attention to additionality, sustainable development criteria, etc. [27]. The World Bank reports that the AAU market in 2008 was valued at approximately $211 million, with about 18 MtCO2e traded [45].

International Cap-and-Trade Programs The Kyoto Protocol enabled Annex I nations to join together to form regional ‘‘bubbles’’ (i.e., which established an overall emission cap, and treated the countries as a single entity for compliance purposes). The states of the European Union formed just such a bubble and created the EU ETS, currently the world’s largest mandatory cap-and-trade scheme, which subsequently became a model for several other national and regional programs around the world.

The European Union Emissions Trading Scheme (EU ETS) Although the EU was initially skeptical about emissions trading, it has become a driving force behind its implementation on a worldwide basis. In January 2005, the EU ETS commenced operation as the largest multicountry, multi-sector GHG trading scheme worldwide. It was thus the first International Emissions Trading scheme, and is many

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times larger than the US Acid Rain Program. There are currently three defined phases in the Scheme: Phase I from 2005 to 2007, also called the trial period; Phase II from 2008 to 2012, coinciding with the first commitment period of the Kyoto Protocol; and Phase III from 2013 to 2020. The EU ETS established a mandatory CO2 cap-and-trade system, which addressed emissions from major sources throughout the EU; it represented about 45% of the CO2e, from more than 11,000 major sources. Sources were allocated a certain number of emission allowances, based on historic performance and other parameters. Specific national targets were established by national governments in what were called National Allocation Plans (NAPs), which specified how many allowances would be awarded to emitters in each regulated industry, and the distribution of such allowances. As is characteristic of a cap-and-trade market, participants who reduced their emissions below their allocation could sell the resulting excess allowances. Those companies who found that reducing their emissions internally was cost-prohibitive could purchase allowances in the open market. Companies were required to provide an independently audited report of their emissions. Those who did not hold sufficient allowances to match their actual emissions at the reconciliation date were fined €40 per ton of CO2 emitted in Phase I, which rose to €100 per ton of CO2 in Phase II. It is important to note that while the EU ETS was designed to meet the goals of the Kyoto Protocol, it is operated by the EU, and is independent of the UN. The EU ETS was enacted before the Kyoto Protocol came into force, and the EU made clear that it would operate the market even if the Kyoto Protocol did not enter into force. Although the Scheme was conceived as a means of ensuring the EU’s compliance with the Protocol during 2008–2012, its first phase fell completely outside the Protocol’s commitment period. Similarly, the EU has announced that it will proceed with Phase III of the ETS, regardless of the actions of other countries in post-2012 climate negotiations.

EU ETS Phase I Phase I of the EU ETS (2005–2007) was established as a ‘‘trial’’ or ‘‘learning’’ phase, before the Kyoto Protocol’s targets came into effect. It was designed to provide companies and governments with experience in developing, operating, and participating in carbon markets. Phase I covered CO2 emissions from more than 11,000 installations in several major emission sectors across the European Union, as well as three non-EU countries (Norway, Iceland, and Lichtenstein). The sectors included energy (combustion installations >20MW, mineral oil refineries, coke ovens); ferrous metals; factories making cement, brick, glass, ceramics; and pulp and paper. Tradable ‘‘European Union Allowances’’ (EUAs) were distributed to these facilities (typically for free), with the sum of distributed allowances equal to the total cap. The amount of emissions allowed by the cap itself was determined through a number of separate decisions made on a country-bycountry basis; each member state proposed a quantity of EUAs, which was reviewed and approved by the EU commission [15].

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The transportation and building sectors were excluded in Phase I. In cases of force majeure, such as exceptionally low winter temperatures, additional emission allowances could be issued by national authorities. Member states also had the flexibility of opting out individual facilities. A notable feature of Phase I of the EU ETS was that there was effectively no restriction on banking or borrowing of allowances within any given multiyear period, but this did not hold between trading periods. While each member state maintained its own registry to record the creation, transfer, and surrender of allowances, a central registry, called the Community Independent Transaction Log (CITL) recorded transfers of EUAs among installations in different member states – in this way, the EU Commission would be able to block transfers from any member state that failed to gain approval of its NAP.

The Linking Directive Another important design feature of the Emissions Trading Scheme is the Linking Directive, which was formally adopted in 2004. Up to a certain limit, it allows entities to comply with emission caps by submitting qualifying credits for emission reductions accomplished outside of the EU through the CDM and JI mechanisms. Credits generated from certain CDM activities such as those from projects associated with nuclear power or CO2 sinks were not allowed. > Figure 8.9 illustrates the role of the Linking Directive. The Linking Directive provided a strong stimulus for the development of CDM projects, and made their use an important means of compliance in the EU ETS. It helped EU Kyoto protocol compliance (i.e., GHG reduction)

Goals

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. Fig. 8.9 The Linking Directive

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to accelerate the carbon marketplace, that is, the EU ETS provided demand in 2005, and the Linking Directive allowed the Kyoto Protocol’s flexible mechanisms to provide supply. Thus, the carbon market was up and running well before the Kyoto Protocol’s first commitment period. As the EU ETS Phase I went into effect on January 1, 2005, a price between €8 and €12 a ton emerged for EUAs in the EU ETS market. Prices then climbed to over €30 a ton for several reasons, including a cold winter spell in early 2005, a dry summer in southern Europe, and high natural gas and oil prices that made coal more attractive. Another reason was that companies with installations that were short allowances and needed to cover their emissions were disproportionately greater in number than those that held long positions [15]. > Figure 8.10 illustrates the price movement of EUAs in Phase I. In April 2006, however, within a span of a week, EUA prices fell sharply from over €30 a ton to €20 for Phase II EUAs and €15 for Phase I EUAs. The precipitating event was the reporting of 2005 emissions by several member states, with emission levels that were significantly less than expected. For the trial period, allowances had been distributed based on an estimate of aggregate emissions, rather than actual emissions. In addition, the restriction on trading between Phases I and II caused prices to decline sharply after September 2006, effectively making trading during the trial period self-contained. OTC markets were the dominant form of trading. However, trading in organized exchanges has gained popularity over time, where it now supports greater than one-third of trades. The European Climate Exchange (ECX) is by far the largest single platform for trading, experiencing tremendous growth – ECX 2009 volumes increased by 82% year-on-year,

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. Fig. 8.10 Evolution of European Union Allowance (EUA) prices 2005–2007 [15]

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equivalent to €62 billion (European Climate Exchange) – and it has now captured 99% of futures trading in EUAs. Ultimately, the ‘‘learning by doing’’ phase did exactly what it was expected to do – it established the necessary infrastructure and created a carbon market for the free trade of emission allowances across the EU. There were several lessons learned from the exercise: The lack of verified emissions data caused difficulties in setting compliance targets; the free distribution of allowances resulted in windfall profits for several power companies, who received allowances for free, yet charged electricity consumers based upon their market price; and the haphazard release of emissions data by individual governments was problematical, since market positions could be affected by such information. The process for setting the cap made it difficult to ensure scarcity in the market, given the uncertainty about the emissions data, as well as the fact that national governments were under considerable pressure from companies not to be too stringent – after all, their competitors in the USA, China, and other major economies were not operating under such constraints. The total EU-wide allocation in Phase I was estimated to be only 1% below projected ‘‘business as usual’’ scenarios. In fact, during 2005, 2,088 million allowances were issued, but actual emissions were only 2,007 million tons resulting in 80 million surplus allowances [2]. These issues were addressed in the design of subsequent phases of the EU ETS.

EU ETS Phases II and III The EU ETS Phase II is currently in operation, lasting 5 years (2008–2012) and coinciding with the Kyoto Protocol’s commitment period. Phase II had a number of changes from Phase I, but most of the significant revisions in the scheme are planned for Phase III. Phase II removed the force majeure provisions, and raised the auctioning limit from 5% to 10%. The penalty for noncompliance increased from €40 to €100. More installations are covered in Phase II, including crackers, carbon black, flaring, furnaces, and integrated steel works. In addition, the aviation sector will be added to the EU ETS in 2012. Importantly, targets specified in the NAPs now reflect actual 2005 reported emissions, as opposed to estimates (i.e., the case in Phase I). Moreover, in order to ensure that a significant portion of the expected emission reductions occurs within each country, the use of CERs and ERUs for meeting compliance requirements is limited within the ETS Phase II as a percentage of the allocation to an installation. Phase III of the EU ETS contains reforms that aim to make it a more efficient, harmonized, and a fairer trading system. Among the major changes in Phase III, NAPs have been abolished in favor of an EU-wide cap that provides a reduction of 11% beyond the Phase II cap [16]. In addition to CO2, nitrous oxide emissions from the production of nitric, adipic, glyoxylic acid, and perfluorocarbons from the aluminum sector will be included in the scheme, and allowances for these sectors will be given free in the same way as the other sectors already covered. Carbon capture and geological storage will also be included. Still another important change is that most of the allowances will be auctioned,

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instead of given away, as in Phases I and II. Eighty-eight percent of the allowances to be auctioned by each member state will be distributed on the basis of the member state’s share of historic emissions under the EU ETS. For purposes of solidarity and growth, 12% of the total quantity will be distributed in a way that takes into account GDP per capita and the achievements under the Kyoto Protocol. The power sector will be subject to full auctioning, but may receive free allowances for district heating and high-efficiency cogeneration activities. The market is also being expanded to include aviation, a sector thus far not covered until 2012. The overall use of CDM and JI credits is capped at 50% of the EU-wide emission reductions over the period 2008–2012, and 50% of the EU-wide reductions below 2005 levels of new sectors and aviation for the period 2013–2020. There are also other proposed provisions on CERs and ERUs in Phase III, including a provision that would require newly registered CDM projects after 2012 to be located in a country included in the UN’s listing of ‘‘least developed countries’’ (unless there was a bilateral agreement between the EU and the other host country). The EU ETS remains the largest carbon market compared to other market segments (such as the CDM and JI), accounting for a full two-thirds of carbon market volume and three-quarters of the value. In the EU ETS market, 6.3 GtCO2e were traded in 2009, with a total value of $118.5 billion [45]. The economic recession in Europe and elsewhere in 2008 and 2009 led to lower demand for housing, cement, automobiles, steel, etc. As demand and commodity prices collapsed, cement and steel companies substantially cut back their production and power consumption. Emissions were therefore lower, as was the need to purchase carbon allowances. Some companies holding substantially more allowances than needed for compliance chose to sell their EUAs on the market to raise cash in a very difficult credit environment. Higher supply and lower demand for allowances brought substantially lower prices for EUAs, and although there has been some rebound in 2010, prices remain well below prerecession ones.

Other Cap-and-Trade Programs Several other cap-and-trade programs are in operation elsewhere in the world. Australia’s New South Wales GHG Abatement Scheme (GGAS) commenced on January 1, 2003 in the province of New South Wales (NSW), Australia. GGAS aims to reduce greenhouse gas emissions associated with the production and use of electricity by establishing annual statewide greenhouse gas reduction targets, and then requiring individual electricity retailers and certain other parties who buy or sell electricity in NSW to meet mandatory benchmarks based on the size of their share of the electricity market. The GGAS program will remain in force until 2012. Another such regional cap-and-trade scheme is the US’ Regional Greenhouse Gas Initiative (RGGI), which is the first mandatory market-based effort in the USA to reduce GHG emissions. Ten Northeastern and Mid-Atlantic states have capped emissions from the power sector, and are expecting reductions of 10% by 2018. Allowances are auctioned and the proceeds are supposed to support low-carbon intensive solutions, such as energy

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efficiency and renewable energies – although individual states have already utilized such proceeds to address state budget shortfalls. The Western Climate Initiative (WCI) is a collaboration of independent jurisdictions in the USA, Canada, and Mexico with a commitment to tackle climate change at the regional level. These jurisdictions participate in the program either as partners (seven US states, four Canadian provinces) or observers (six US states, three Canadian provinces, and six Mexican states). The centerpiece of the WCI is a cap-and-trade program with an aim of reducing GHG emissions by 15% below 2005 levels by 2020. When fully implemented in 2015, this multi-sector program will cover nearly 90% of GHG emissions from electricity, industry, transportation, residential and commercial fuel use in WCI partner states and provinces. However, Arizona and Utah, two founding members of the WCI, announced in early 2010 that they would no longer participate in the WCI cap-andtrade program, and other partner states (i.e., Montana, Washington, and Oregon) have indicated that they might not meet the 2012 start date. An Emissions Trading Scheme in New Zealand has been designed to support efforts to reduce all six GHG emissions by 2015. The program will include all sectors of the economy and can be internationally linked. There will be a ‘‘transition phase’’ from 2010 to 2012 when participants will be able to buy emission units from the government for a price of 25 NZD. The Scheme covers forestry, transport fuels, electricity production, industrial processes, synthetic gases, agriculture, and waste. South Korea, Asia’s fourth largest economy, is hoping to launch a national emissions trading scheme by 2013, and is expected to introduce its carbon trading laws into parliament during the first quarter of 2011. The program is expected to be a threephase cap-and-trade scheme, with the first phase running from 2013 to 2015, with subsequent phases starting from 2016 running for 5 years each. Operators emitting over 25,000 t of CO2 per year, representing approximately 60% of South Korea’s total GHG emissions of just over 600 million tons a year are expected to participate [19]. In addition to these efforts, national, regional, and local carbon market trading schemes have been proposed or are under development in the USA, Australia, Japan, and numerous other countries. Given the difficulties in extending a Kyoto Protocol-type international carbon market evident at the Copenhagen COP, the future might well hold instead a mix of regional, national, and other subnational carbon trading schemes, supplemented by voluntary carbon markets, as well as other structured policy markets designed to accomplish carbon reductions through increased use of renewable energy, energy efficiency, etc. These other market types are discussed in sections below.

Voluntary Carbon Market In addition to the ‘‘compliance’’ markets created by the Kyoto Protocol that were explored in detail in the prior sections, a corollary, voluntary market has been developed that supports carbon trading for companies, individuals, and other entities not subject to mandatory limitations, but still wishing to offset their GHG emissions [3]. As the name

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implies, the voluntary carbon market includes all carbon offset trades that are not required by regulation. Over the past several years, this market has not only provided an opportunity for consumers to alleviate their carbon footprint, but also provided an alternative source of carbon finance. The instrument of trading is called a Voluntary Emission Reduction (VER), although it should be noted that some market participants consider this acronym to mean ‘‘Verified Emission Reduction.’’ While still very much smaller than the Kyoto compliance market ( Table 8.1. Each standard has a slightly different focus in terms of project goals, and addresses each of the above characteristics according to those goals. While the VCS provides a minimum quality-level for VERs and is the most popular, premium carbon verification standards such as the Gold Standard and CCAR attract the highest prices for VERs accredited to them. VERs tend to sell at a discount to CERs or other compliance market project-based carbon credits, and the average carbon credit price on the OTC market in 2009 was $6.5/tCO2e – a figure well below the $12.7/tCO2e for CERs for that same year. There was a very wide price range for VERs, however, from $0.3/ tCO2e to $111.0/tCO2e (BNEF, 2010). Gold Standard VER premium prices averaging $11.1/tCO2e were relatively close to CER pricing. Voluntary carbon credits may be traded bilaterally, OTC, or in organized exchanges. There are several exchanges throughout the world that support voluntary carbon trading, with the most significant (and perhaps most well known) being the Chicago Climate Exchange (CCX). Others include the Tianjin Climate Exchange; the Multi Commodity Exchange of India, Ltd. (MCX); and the China Beijing Environment Exchange. Both the Tianjin Climate Exchange and MCX are affiliated with CCX, and while most of the business for all of these developing country exchanges currently lies within the voluntary

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. Table 8.1 Major certification standards in the voluntary market (Source: Adapted from Making Sense of the Voluntary Carbon Market; A Comparison of Carbon Offset Standards, Stockholm Environmental Institute, 2008) Standard name

Goals

CDM

Part of the Kyoto Protocol and aims to create economic efficiency while also delivering development co-benefits for poorer nations Aims to enhance the quality of carbon offsets and increase their co-benefits by improving and expanding on the CDM process. For large-scale projects, GS requirements are the same as those of the CDM. However, GS also requires the CDM additionality tool for small projects as well The VCS aims to provide a minimum, basic quality threshold for all carbon credits on the voluntary market Very similar approach to CDM for projects types that fall outside the scope of the CDM Sets standards for the listing of credits (including those from offset projects) on their exchange, including the requirement of a CCX approved third-party verifier VOS closely follows CDM requirements and aims to decrease risks for offset buyers in the voluntary market Created to support land management projects that sequester GHG, support sustainable development, and conserve biodiversity Most widely accepted certifier of Renewable Energy Certificates (RECs) Develop and promote credible, accurate, and consistent GHG reporting for organizations to measure and monitor, third-party verify and reduce their GHG emissions consistently across industrial sectors and geographical borders

Gold Standard

Voluntary Carbon Standard (VCS) VER+ CCX

Voluntary Offset Standard (VOS) Climate, Community, and Biodiversity (CCB) Green-e California Climate Action Registry (CCAR)

marketplace (and is therefore discussed within this section), most have plans to play a larger role in future compliance regimes. The CCX claims to be the world’s first legally binding, rules-based GHG emissions trading system. Its holding company Climate Exchange Plc (CLE) has three significant operating businesses: the European Climate Exchange (ECX), which operates an exchange that focuses on compliance certificates for the EU ETS; the Chicago Climate Futures Exchange (CCFE), which is a regulated exchange in the USA with a portfolio of environmental futures contracts; and the CCX. Members voluntarily join the CCX and sign up to its legally binding reductions policy. Since it began operations in 2003, CCX has grown to include some 300 members, including 11% of the Fortune 100 companies in the USA, and 20% of the country’s largest CO2 emitters. The CCX’s unit of trade is the Carbon Financial Instrument (CFI), which represents 100 tCO2e.

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Despite the fact that CCX pioneered the first voluntary cap-and-trade system for GHGs in North America, some criticism has focused on its standards for agricultural offsets and the additionality requirement. In a number of cases, farmers apparently received offset revenues for practicing ‘‘no-till’’ agriculture (which is a means of growing crops on a yearly basis without mechanical agitation of the soil), despite the fact that they had already been utilizing such no-till practices for many years. Other questions have been raised about how CCX calculated emissions reductions, and its relative lack of transparency. CCX responded to this criticism by making its rulebook and many of its methodologies available on its Web site. Climate Exchange Plc was acquired by Intercontinental Exchange Inc. in mid-2010. [7], and announced in October of that year that CCX would conclude its emission reduction program at the end of 2010, but would continue with an offsets registry program. The Tianjin Climate Exchange is a joint venture between the CCX, the municipal government of Tianjin, and PetroChina, and opened on September 2008 in the City of Tianjin, China. Located about 75 miles southeast of Beijing, Tianjin recorded its pilot trades in carbon emissions allowances in February 2010 in a trial program covering heating suppliers serving more than 21.5 million square feet of residential buildings. Citigroup Inc. and Russia’s OAO Gazprom bought energy-intensity credits from three heating utilities that had surpassed efficiency targets. The energy savings were packaged as ‘‘carbon emissions allowances’’ that could be sold to other utilities or to buildings in the city that could not yet meet municipal goals. Also connected with the CCX is the Multi Commodity Exchange of India, Ltd., which entered into a strategic alliance with CCX in September 2005. MCX is a nationwide electronic multi-commodity futures exchange with recognition from the government of India for facilitating online trading, clearing, and settlement operations for futures market across the country. The exchange started operations in November 2003 and is now the top commodity exchange in the country. The China Beijing Environment Exchange (CBEEX) is an environmental equity transaction institution authorized by the Beijing Municipal Government. In 2009, the CBEEX signed a deal with BlueNext to build a trading platform for carbon credits, and at the Copenhagen COP announced the Panda Standard, the first voluntary standard created specifically for the Chinese VER market. The CBEEX also traded the first VER transaction in China in August 2009.

The Over-the-Counter (OTC) VER Market Almost all carbon credits in the voluntary market originate from emissions reduction projects, and thus represent offsets. Since these offsets are not traded in a formal exchange, they are usually termed OTC trades. While VERs are the primary instruments of trade in the voluntary market, OTC buyers may also purchase credits from compliance markets such as the CDM. There are two main types of buyers in the OTC VER market: pure voluntary buyers (i.e., those who simply purchase credits to offset their own emissions,

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and ‘‘retire’’ their credits immediately upon purchase), and ‘‘pre-compliance’’ buyers (i.e., those who hope to obtain credits at a low price that will subsequently be useful in future regulatory regimes). Buyers in the voluntary market have a diverse range of offset project types to choose from. The popularity of project types in the voluntary market has been driven by factors on both the supply and demand sides of the equation. > Figure 8.11 shows the transaction volume of the OTC market in 2008, broken down by project type. On the supply side, renewable energy projects had the biggest market share, with hydropower, landfill gas, and wind capturing 32%, 16%, and 15% of the transaction volume in 2008, respectively. This is because these renewable energy projects are candidates for CDM, often stuck in the bottleneck created by the complicated process of CDM project registration, and would also explain why Asia accounted for 45% of the credits in the OTC market. With 28% of the OTC transactions, the USA was the single largest country supplying offset credits. On the demand side, buying was shaped by entities building portfolios of credits in anticipation of a US regulatory cap-and-trade system, and a general preference by pure voluntary and pre-compliance buyers for noncontroversial credits verified to third-party standards [14]. Interestingly, however, more than half of sold volumes (53%) in the voluntary market went to European buyers, despite the large compliance market in Europe, indicating that the presence of a compliance market does not adversely affect trading in the voluntary market.

Not Specified 2%

RE: Hydro

13%

Landfill Other Types 2%

3% 32%

3% Fugitive Emissions 2% Avoided Deforest 1%

4%

Aff/Ref Conservation Geological Seq

5%

Coal Mine 1% Aff/Ref Plantation 1% Fuel Switching 1% Forest Management 1% Ind. Gas 1% Ag Soil 1%

RE: Wind

Energy efficiency 7%

RE: Biomass Ag Methane 15%

16% Other

Source: Ecosystem Marketplace, BNEF, 2009

. Fig. 8.11 Transaction volume by project type (2008) (Ecosystem Marketplace, BNEF, 2009)

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Carbon Financial Derivatives In anticipation of a price on carbon emissions and the associated market growth created by a cap-and-trade scheme, a number of financial instruments and derivatives based on carbon as a commodity have been developed. These have led to increased carbon trading activity in financial markets. While government officials are responsible for designing effective cap-and-trade systems, and polluters participate in the resulting market to comply with emissions constraints, carbon derivatives trading brings commodities traders, speculators, hedge funds, financial firms, and exchanges into the fray. Derivatives are financial instruments whose cash flow is derived from an underlying instrument. There are several types of derivatives, including future and forward contracts, which are fundamental derivatives that represent an agreement to sell a certain commodity in the future at a fixed price; options, which are slightly more complicated derivatives where the buyer is given the right (but not the obligation) of purchasing the commodity depending on the price of the commodity in the future at a price (agreed upon at the present time); and swaps, in which two counterparties exchange certain benefits of one party’s financial instrument for those of the other party’s instrument. Derivatives can be used for a variety of purposes. They can be used to hedge a transaction, (i.e., reduce risk exposure), and derivatives markets are thus risk transfer mechanisms. They facilitate the transfer of risk from those exposed to it but who do not wish to bear the risk (i.e., hedgers) to others not naturally exposed to it, but willing to bear the risk (i.e., speculators). Derivatives also contribute to price discovery; since individuals with information can buy or sell derivatives, their trades affect prices and these prices reflect their information. Derivatives may be traded bilaterally, or in the OTC market through brokers, or in organized exchanges such as the New York Mercantile Exchange (Nymex). Compliance carbon markets can also support the trading of such derivative products, including futures, options, and swaps. Currently, most carbon is sold in futures or forward contracts. These contracts contain promises to deliver carbon allowances or credits in a certain quantity, at a certain price, by a specified date. In the case of the EU ETS, the forward and futures markets have developed faster than the spot market. Approximately 95% of the total volume in the European carbon market is seen in derivatives trades, with the remaining in spot trades. According to the ECX, this may partly be explained by the initial delay of national registries and final allocations in many of the EU member states, which prevented the execution of instant delivery for spot contracts. Another reason may be that in such a new and volatile market, derivative instruments are crucial tools to optimize the value of an emissions portfolio. There is also a futures market for CERs. CER futures prices traded between €10 and €15 a ton toward the end of 2009. The market for futures, options, and spot transactions for sCERs was valued in excess of $26 billion (€18 billion) in 2008 in various exchanges, representing the largest growth rate of all the segments in carbon markets with more than a 350% increase in traded volumes over 2007 [45]. Carbon derivatives are also traded in the voluntary marketplace, in exchanges such as the Chicago Climate Futures Exchange.

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Carbon derivatives trading was severely affected by several factors in 2009. The economic recession slowed down manufacturing and other industries, causing reduced economic output, and hence lower emissions and a surplus of allowances. A large sell-off of EUAs started in September 2008, as companies realized that the allowances they had received at no charge could help provide liquidity, particularly in the midst of a financial credit crunch. The EUA sell-off, mostly on the spot market, was followed by a discernible increase in trading of EUA options (more calls than puts, on average), showing the intent of some installations to hedge any anticipated 2008–2012 compliance exposure [45]. Failure by governments to achieve a solid agreement on climate change negotiations in Copenhagen in December 2009 added to the downward trend of carbon markets, with carbon prices falling nearly 10% (the biggest decline in 2009) immediately after the summit. The uncertainty about the future of emissions trading after the Kyoto Protocol’s first commitment period expires in 2012, and the continued absence of a national capand-trade program in countries such as the USA and Australia, depressed prices even further. Reuters reported that the global carbon market would have reached $2 trillion by 2020 if nations had agreed to a new climate pact curbing greenhouse gas emissions and if the USA introduced its own federal cap-and-trade scheme [37]. However, because neither case seemed probable in the near term, banks and investors started pulling out of the carbon market and emptying their carbon trading desks in early 2010 [22]. To make matters worse, the EU ETS was hit by two significant controversies in 2009 and 2010. In December 2009, Europol announced that the EU ETS had been the victim of fraudulent traders over a period of 18 months, resulting in losses of approximately €5 billion for several nations [17]. Traders would collect Value Added Tax (VAT) on carbon market transactions, but then not submit the collected revenue to national governments. They would then disappear without a trace, leading to the phrase ‘‘missing trader fraud’’ to describe the crime. In early 2010, there were also market disruptions because of the resale of 2 million surrendered CERs by the Hungarian Government. The Hungarian government first covered the CERs (which had been surrendered by Hungarian companies to comply with the emissions cap under the EU ETS) with AAUs, because the CER price exceeded that of an AAU. They then signed a deal to sell those same CERs to a trading firm, and some of these ‘‘recycled CERs’’ eventually came back into the European market. A number of exchanges were thus forced to shut down, until the integrity of their CERs could be fully established. This loophole is being closed through the establishment of technical barriers that will prevent the entrance of recycled CERs into the EU ETS in the future. The recent financial crisis caused by subprime mortgages and financial derivatives such as credit default swaps based on questionable risk profiles raised other questions about carbon derivatives trading. For example, the potential for ‘‘subprime carbon’’ credits, that is, relatively high-risk contracts to deliver carbon that might not mature to fruition [11], was noted by some analysts. Carbon offset aggregators bundle small offset projects for buyers, and increased demand might give rise to exotic derivatives and structured products, similar to the situation in mortgage-backed securities. In November

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2008, Credit Suisse announced just such a securitized carbon deal in which credits from 25 offset projects were bundled. These were then securitized into three tranches of different risk levels and sold to investors. Of concern here is that the fact that 25 projects were at various stages of UN approval, spread across three different countries and five project developers [11]. Such off-balance sheet products, albeit profitable in the short term, are highly risky and require close regulatory oversight. Needless to say, carbon markets face several challenges en route to becoming mature and effective systems that will ultimately satisfy the environmental objectives they are designed to accomplish.

Renewable Energy and Energy Efficiency Markets While pollution presents policy makers with a negative externality, some energy technologies might be thought of as generating positive externalities because they are easily replenished and nonpolluting in nature, are decentralized, and can increase system resiliency, etc. Consequently, in a mirror image of emissions trading, ‘‘positive externality’’ instruments providing support for renewable energy systems and energy efficiency are growing in popularity.

Renewable Energy Certificates (RECs) The market-based instrument employed in renewable energy markets is the Renewable Energy Certificate (REC), also called a ‘‘green tag.’’ It typically represents 1 MWh of electricity generated from a renewable energy source. A REC is an environmental commodity, and may be sold separately from the underlying electricity generated. Buyers can select RECs based on the generation source (e.g., wind, solar, geothermal), as well as the location of the renewable generator. RECs may be used in both compliance and voluntary markets. In the USA, compliance markets have been established by state Renewable Portfolio Standards (RPS), which require utilities to meet a certain quota of their electricity from renewable sources by a certain date. This quota is often increased over time, the converse of an emissions cap being lowered to reduce GHG emissions. An RPS provides states with a mechanism to increase renewable energy generation using a cost-effective, market-based approach that is administratively and economically efficient. The goal of an RPS is to stimulate market and technology development so that, ultimately, renewable energy will be economically competitive with conventional forms of electric power. Currently, 29 US states plus the District of Columbia, accounting for more than half of the electricity sales in the country, have RPS policies in place (five more have nonbinding goals). California, for instance, requires 33% of its electricity to be generated from eligible renewable sources by the year 2020. Maine has a goal of 40% by 2017 and New York 24% by 2013 [41]. It is important to note that not all states permit REC trading for compliance

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with their RPS. An important feature of the REC compliance market in the USA is that the goals differ from state to state; therefore, prices of RECs also differ. Compliance buyers are generally indifferent to the type of resource that created the REC, but are limited to the geographical area where the REC can be produced. The US Department of Energy’s National Renewable Energy Laboratory (NREL) expects demand in the RPS market for renewable energies to grow from 22,296 GWh in 2008 to 156,527 GWh in 2015 [4]. European Union nations have similar schemes to comply with an EU target of 20% energy from renewable sources by 2020. In the UK, a scheme similar to the RPS has been set up where Renewable Obligation Certificates (ROCs), each representing one MWh, are tradable green certificates issued to an accredited generator for eligible renewable electricity generated and supplied to customers within the country. Late in 2010 the government proposed switching over to a price-based feed-in tariff system, however, which would mark a major shift in Britain’s pro-market regulatory reform [5]. Sweden’s ‘‘Electricity Certificate System’’ aims to increase the production of renewable energy with 17 TWh of new ‘‘green’’ power by 2016. The share of electricity certificates (quota) that the renewable supplier is to submit varies each year. As a result, an increased demand for renewable electricity and RECs are created. There is also an active voluntary REC market, spurred by companies, government agencies, and private consumers who have opted to support ‘‘green power’’ either by buying renewable energy directly, or through a variety of retail programs. In many cases, buyers purchase the ‘‘green attributes’’ of the REC associated with energy generation. Several factors motivate demand in the voluntary renewable energy market, including corporations seeking to differentiate themselves from competitors by environmental means, as well as environmentally minded consumers of electricity. Although much smaller than RPS compliance markets, voluntary REC markets are growing rapidly in the USA and in Europe. The voluntary purchase of RECs accounted for 46% of US consumer green power sales in 2005, and REC markets are growing faster than other segments of green power markets. The advantage of RECs in voluntary markets is that they can be sold unbundled from electricity, and so their market is national, while green power markets tend to be tied to local providers [20]. Data from the NREL and the Department of Energy’s Green Power Network indicate that the number of utilities with green power pricing programs grew from 45 in 2003 to 184 in 2009 [12]. Currently, more than 750 utilities and marketers offer green power products to electricity consumers in most states of the USA. If the voluntary market continues to grow at a rate of 35% annually, it is expected to reach about 40 million MWh by 2010 and represent about one-quarter of the total demand from voluntary and compliance markets [4]. Prices of certificates from eligible renewable facilities under an RPS scheme (compliance RECs, or C-RECS) differ from RECS generated in the voluntary market (V-RECs) because the drivers of demand differ [21]. Prices of RECs in the voluntary market may also vary based on resource type. For instance in 2007, solar RECs commanded between $10 and $20; biomass/low-impact hydro between $1 and $3; wind varied anywhere between $0.75 and $15; and geothermal energy-based RECs were priced between $1 and $10 [28].

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Voluntary market purchases rely on certification programs to verify that the RECs were indeed generated by the renewable resource that is claimed, and that a REC is not sold to more than one buyer. The Green-e program is a nationally recognized standard that helps consumers identify environmentally qualified RECs. The dynamics of linking renewable energy markets with emissions trading schemes brings up interesting questions, and controversies. Because RES emit little-to-no pollutants, they are economically advantaged by any policy that puts a cost on emitting pollutants within the power sector. The issue of converting RECs to carbon offsets has produced heated debates in the voluntary carbon markets, especially in the USA [14]. While the REC market essentially operates independently of the carbon market, RECs are sometimes viewed as tons of carbon dioxide avoided, and are sold into the voluntary carbon market as a carbon offset. The controversy in this practice revolves around the accuracy of carbon calculations, the additionality and ownership terms operating in different markets, and the potential for double counting in two markets with different (but often complementary) policy goals. Voluntary green power and GHG offset markets both lack standardized commodities and regulation, resulting in a great deal of confusion for consumers wishing to offset their emissions associated with energy consumption. Because RECs are typically less expensive (mostly due to differences in additionality requirements) than offset credits, they are generally favored for purchase. The renewable energy market nevertheless grew robustly in 2008, with the USA overtaking Germany as the largest wind-power provider with 25 GW. Investment in renewable energies grew to $120 billion worldwide; double that of the $63 billion investment in 2006 [36]. This increased investment and the improvement in technology performance has resulted in increasing scales of production and use of renewable energies, which in turn, has resulted in lower renewable energy costs.

Energy Efficiency Certificates (EECs) Energy Efficiency Certificates (white tags, or white certificates, as they are sometimes called) are similar to RECs, except that they represent a unit of energy not used. White tags are usually created through energy conservation projects such as equipment upgrades, retrofits, combined heat and power (CHP), or cogeneration and demand-side management. A market for energy efficiency is created by setting an energy-saving obligation on entities in the energy supply chain, with preset rules for trading, monitoring, and verification. EECs are awarded to entities that create more energy savings than the target (typically in terms of electricity or oil equivalent energy units), and these EECs may then be sold or traded in the marketplace to those entities that are unable to meet their obligations. Energy savings are usually cost-effective and efficient ways to reduce GHG emissions, in addition to providing energy security and independence. The process of measuring the energy efficiency savings requires establishing a baseline for energy use and/or demand

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before and after the implementation of an efficiency project. The approach to doing this depends on the specific market design rules, and can include ‘‘deemed savings’’ figures (i.e., standard figures for projects where the expected savings are well understood), engineering calculations, and direct measurement. Many compliance markets require third-party verification using a MRV protocol. The protocol may vary depending on policy decisions about program implementation cost, ease of compliance, and other factors. Currently, EEC markets exist in Italy, the UK, France, and several other nations in Europe. Twenty-one US states have energy efficiency targets either through Energy Efficiency Resource Standards (EERS) or Renewable Energy Standards (RES), and EEC markets are in the process of being implemented at the national level in India. White tags are a type of offset credit instrument because they require the application of projectbased accounting rules, with baseline, additionality, leakage, and ownership constraints. White tags often may be used as part of an RPS scheme (where entities could use energy efficiency investments as a compliance strategy), or may be implemented under a separate portfolio standard. India, the fourth largest polluter in the world, is expected to start a market to trade energy-savings certificates in mid-2010, worth an estimated $16 billion by 2015. The exchange-traded system may help India meet its target of cutting carbon intensity, or the amount of carbon dioxide released per unit of gross domestic product (GDP), by as much as 25% from 2005 levels by 2020 [8]. The proposed ‘‘Perform, Achieve and Trade’’ (or PAT) scheme will cover 714 installations in nine energy-intensive industrial sectors. Under the scheme, the Indian Bureau of Energy Efficiency (BEE) will issue energy-savings certificates (ESCerts) to designated consumers surpassing energy efficiency targets set for them. The targets will be made increasingly stringent over time. The European Action Plan for Energy Efficiency, which aims for a 20% energy saving by 2020 across the European Union, has spurred a number of European countries to introduce market-based mechanisms. In the UK, the Carbon Emissions Reduction Target (CERT) is an ambitious program that is the third 3-year phase of a domestic energy supplier obligation program. This program requires domestic energy suppliers whose customer bases are in excess of 50,000 customers to make savings in the amounts of carbon dioxide emitted by householders. The trading of EE Certificates (called obligations in the UK) also had a strong social focus called the ‘‘fuel poverty strategy,’’ which mandated that at least 50% of energy savings occur in the so-called priority group, which consists of households that receive certain income-related benefits or tax credits [30]. The CERT program, which runs from 2008 to 2011, seeks to double the EEC program commitment. Italy implemented a similar Tradable White Certificate (TWC) energy end-use saving scheme in January 2005, which aimed for a target of 230 PJ in the 5-year period between 2005 and 2009. Electricity savings of 77% and natural gas savings of 19% were achieved, with a total of 3.7 million tons of oil equivalent (toe) saved against a target of 3.3 million tons. Key questions that remain to be answered include how such trading would develop in an EU-wide EEC trading scheme (currently being discussed);

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how the EEC and REC markets would ultimately come together with the EU ETS cap-andtrade emissions program; and how the fungibility and harmonization of instruments in these various markets would work.

Future Directions The year 2008 was pivotal from a climate change perspective, marking the beginning of the Kyoto Protocol’s first commitment period, as well as the start of the EU ETS Phase II (i.e., the non-trial period). President Obama’s election in November 2008 indicated that much-awaited climate change regulation in the USA might actually become reality. The upheaval in financial markets in the latter part of the year also presaged a 2009 that included the global economic recession. This not only depressed carbon prices, but also resulted in fewer emissions due to reduced industrial and production activity, and lower fuel and electricity consumption. December 2009 saw 45,000 persons, including 120 heads of States and Governments, descend on Copenhagen, Denmark for the 15th session of the Conference of the Parties (COP15). Much was expected from COP15, including a comprehensive global treaty to supersede the Kyoto Protocol, whose first commitment period expires in 2012. Things did not play out quite as expected, however. The Copenhagen Accord, drawn up in the meeting’s final hours by the USA, India, China, Brazil, and South Africa, was viewed by many as a repudiation of Europe’s strong, rules-based, global carbon market approach. The Accord ‘‘recognizes’’ the scientific case for keeping temperature rise to no more than 2 C but does not contain specific commitments to emissions reductions to achieve that goal [24]. Instead, countries commit to voluntary ‘‘Nationally Appropriate Mitigation Activities’’ (NAMAs), whose MRV requirements were the subject of considerable (and ongoing) dispute. The Copenhagen Accord does call for spending as much as $100 billion a year to help emerging countries adapt to climate change and develop low-carbon energy systems; to bring energy technology more quickly to the developing world; and to take steps to protect tropical forests from destruction. The USA pledged to reduce greenhouse gas emissions by 17% by 2020 (from a 2005 base), contingent on Congress’s enacting climate change and energy legislation. US officials called the deal a ‘‘meaningful agreement,’’ but even Obama admitted that the ‘‘progress is not enough’’ [23]. India and China formally agreed to the Accord in March 2010, bringing the total number of countries signing the Accord to 107. China agreed to reduce its ‘‘carbon intensity’’ (emissions of carbon dioxide per unit of economic growth) by 40–45% by 2020, compared with 2005 levels. India set a domestic emissions intensity reduction target of 20–25% by 2020, compared with 2005 levels, excluding its agricultural sector. Broadly speaking, the goal of any climate change negotiation is to set policies that will prevent runaway climate change. The motto leading up to COP15 was ‘‘failure is not an option.’’ In the eyes of many, COP15 was a failure for having concluded with no binding

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commitments from countries to reduce emissions. Nevertheless, the Copenhagen Accord did represent a breakthrough, because it is the very first time that major economies (including developing countries) of the world have made commitments (albeit nonbinding) to curb global warming pollution. Since Copenhagen, there has been a lot of uncertainty over how a legally binding treaty to reduce GHG emissions might be reached. Such a deal did not occur at the follow-up COP at Cancun, Mexico in 2010, and the prospects for the next COP’s session in South Africa in 2011 seem no more encouraging. The mood for a US national climate change agreement is no less uncertain. With the financial crisis having wreaked havoc with US banking and financial regulation, and fear of carbon markets evolving into the next ‘‘subprime’’ markets, ‘‘cap-and-trade’’ has become a somewhat disreputable phrase. The weak economy, lingering unemployment, and the financial crisis, linked with real and perceived abuses in the financial markets, caused great suspicion in peoples’ minds about markets in general, and trading in particular. The hostility toward carbon cap-and-trade markets is also exacerbated by a mistrust of the climate change agenda as a whole. Leaked e-mails from climate scientists in late 2009 raised questions in the public mind about scientific objectivity, and a Pew Research Center Poll on Public Priorities for 2010 marked global warming at the bottom of the list. Just 28% of Americans considered it a top priority, down 10% from 2007 [34]. This lack of public enthusiasm for environmental action would explain why there has been so little political support for meaningful climate policy in Washington, and this has been strengthened by the election of many Republican climate change ‘‘doubters’’ in the mid-term elections of 2010. Further, since cap-and-trade systems are the most developed, they tend to act as a ‘‘lightning rod’’ for those who want to see absolutely no regulation at all. Regardless, the nation’s EPA has moved forward on GHG regulations for stricter fuel standards in the transportation sector, and is finalizing rules on further controlling emissions from large stationary sources such as power plants. Climate change is a global problem, however, and the possibility of linking up a diverse, robust mixture of ‘‘bottom-up’’ trading systems has appeal, even if the ‘‘topdown’’ post-Kyoto system sought in Copenhagen cannot be developed in coming years. From an economic perspective, cost savings will be greatest in a situation where participants face very different marginal abatement costs. Linking emissions trading systems will tend to equalize abatement costs faced by companies around the world, thus significantly reducing costs as well as competitiveness concerns. There are numerous difficulties associated with linking up emissions trading programs across the world, of course, including MRV concerns, enforcement, and the potential for fraud already seen in developed economy carbon markets. In emissions trading, the integrity of these factors is magnified because the commodity being traded owes its existence to governmental mandates. Interestingly, two economists who very early propounded the concepts of emissions trading, John Dales and Thomas Crocker (who, at the University of Wyoming, was among the first to discuss markets for air pollution), both expressed skepticism that cap-andtrade is the most effective way to go about reducing carbon. Crocker believes that capand-trade is better suited for discrete, local pollution problems, not for a global problem

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like CO2. The latter has a myriad of sources, it is difficult to enforce an international permit system, and the economic damage from global warming is fraught with uncertainty and nearly impossible to quantify [44]. On the other hand, anyone who has seen how income tax schemes have operated within the USA and Europe will recognize that alternative economic systems are no less subject to abuse and special interests – and the idea of implementing a comprehensive carbon tax across all countries of the world is not likely to be a politically viable strategy either. The efficiency and distributive aspects of quantity-based schemes have some very real appeal – and they have already been successfully implemented to tackle environmental problems. The churning, volatility, self-interest of participants, and seeming chaos of dynamic markets can be uncomfortable, and can pose considerable regulatory challenges – particularly in externality markets specifically constructed by governments. But such markets are ultimately crucial in harnessing entrepreneurial skills for an energy technology revolution, and for delivering the scale of behavioral, technological, and social change sought in Copenhagen. Climate change presents a unique challenge on a global scale to humanity in general, and to economics in particular: The problem is global; it deals with long time horizons, has major risk and uncertainty at its core and requires unprecedented, immediate, collective action. Economics can provide a strong foundation for developing policies to guide action and reducing costs by providing flexibility on how, where, and when emissions are reduced. But pricing the pollution externality and developing robust carbon markets represent only part of the economic task involved in mitigating climate change. Policy frameworks that promote the development and deployment of new, cleaner technologies (i.e., what economists refer to as ‘‘induced technological change’’) and changing behavior in energy consumption (perhaps utilizing new ‘‘behavioral economics’’ and even ‘‘neuro-economic’’ techniques) will be needed as well. One thing is for certain, the costs of reducing emissions enough to limit global warming to 2 C may be high but doing so will provide certain obvious benefits that will clearly outweigh the costs. Indeed, the cost of not acting is likely to be very high.

References 1. Asia-Pacific Partnership on Clean Development and Climate (2010) About the Asia-Pacific partnership on clean development and climate. http://www.asiapacificpartnership.org/english/ about.aspx. Acccessed 21 Mar 2010 2. Baker, McKenzie (2008) Overseas emissions trading experience. http://carbonexpo.com.au/ uploads/file/08/presentation/WED/Katherine% 20 Lake%20wed%20wshop%205%20and%206. pdf. Accessed July 2010 3. Bayon R, Hawn A, Hamilton K (2007) Voluntary Carbon Markets. Earthscan, London, UK

4. Bird L, Hurlbut D, Donohoo P, Cory K, Kreycik C (2009) An examination of the regional supply and demand balance for renewable electricity in the United States through 2015. NREL, U.S. Department of Energy 5. Bird P (2010) Will Britain Abandon Its Quota System in Favor of Feed-in Tariffs? Renewable Energy World, December 6. Burtaw D, Evans D, Krupnick A, Palmer K, Toth R (2005) Economics of pollution trading for SO2 and NOx. RFF Discussion paper 05–05, Resources for the Future, Washington, DC

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7. Business Week (2010, April 30) Sandor exits CO2 trade, sells climate exchange to ICE. http://www.businessweek.com/news/ 2010-04-30/ sandor-exits-co2-trade-sells-climate-exchange-toice-update3-.html. Accessed 7 May 2010 8. Business Week (2010, January 14) India plans $16 billion energy-saving credit market. http://www. businessweek.com/globalbiz/content/jan2010/ gb20100114_100416.htm. Accessed 12 April 2010 9. Carbon Finance (2008, May 7) Carbon finance – news and analysis of market solutions to climate change. Time to rethink CDM additionality – Newcombe. http://www.carbon-financeonline. com/index.cfm?section=lead&action=view&id= 11223. Accessed 2 April 2010 10. CDM Rulebook (2008) Clean development mechanism rules, practice and procedures. http:// cdmrulebook.org/715. Accessed 12 April 2010 11. Chan M (2009) Subprime carbon? Rethinking the world’s largest new derivatives market. http://www.foe.org/pdf/SubprimeCarbonReport. pdf. Accessed July 2010, Friends of the Earth, Washington DC 12. Cook O, Karelas A (2009) Number of utilities with green power pricing programs grew from 45 in 2003 to 184 in 2009. Center for Resource Solutions, San Francisco, CA 13. Cooper R (2008) The case for charges on greenhouse gas emissions. http://belfercenter.ksg.harvard.edu/files/CooperWeb4.pdf. Accessed July 2010. Harvard University, Cambridge MA 14. Ecosystem Marketplace (2009) Fortifying the foundation: state of the voluntary carbon markets 2009. http://www.ecosystemmarketplace.com/documents/cms_documents/StateOfTheVoluntaryCarbonMarkets_2009.pdf. Accessed July 2010 15. Ellerman D, Joskow P (2008) The European Union’s Emissions Trading System in Perspective. Massachusetts Institute of Technology; Pew Center for Global Climate Change, Washington DC 16. European Union (2008, January 23) Questions and answers on the commission’s proposal to revise the EU emissions trading system. http://europa.eu/rapid/pressReleasesAction.do? reference=MEMO/08/35. Accessed 20 April 2010 17. Europol (2009, December 09) Carbon credit fraud causes more than 5 billion euros damage for European taxpayer. http://www.europol.europa. eu/index.asp?page=news&news=pr091209.htm. Accessed 30 Mar 2010

18. Friends of the Earth (2009) Trading in Fake carbon credits: problems with the clean development mechanism (CDM). http://www.foe.org/trading-fake-carbon-credits-problems-clean-development-mechanism-cdm. Accessed Oct 2010 19. FuturesPros.com (2010). http://www.futurespros. com/news/futures-news/factbox-south-korea%27splanned-emissions-trading-scheme-1000005225. Accessed 7 Feb 2011 20. Gillenwater M (2008) Redefining RECs – Part 1: untangling attributes and offsets. Energy Policy 36(6):2109–2119 21. Gillenwater M (2008) Redefining RECs - Part 2: untangling certificates and emissions markets. Energy Policy 36(6):2120–2129 22. Guardian (2010, January 24) Copenhagen dampens banks’ green commitments. http:// www.guardian.co.uk/environment/2010/jan/24/ carbon-emissions-green-copenhagen-banks. Accessed 30 Mar 2010 23. Guardian (2009, December 19) Low targets, goals dropped: Copenhagen ends in failure. http:// www.guardian.co.uk/environment/2009/dec/18/ copenhagen-deal. Accessed 17 Mar 2010 24. Reuters (2010, February 23) U.N. says emissions vows not enough to avoid rise of 2 degrees C. http://www.reuters.com/article/idUSTRE61 M23G20100223. Accessed 17 April 2010 25. He G, Morse R (2010) Making Carbon Offsets Work in the Developing World: Lessons from the Chinese Wind Controversy. Stanford University, Freeman Spogli Institute for International Studies 26. International Rivers (2008) Rip-offsets: the failure of the Kyoto protocol’s clean development mechanism. http://www.internationalrivers.org/ node/3498. Accessed Oct 2010 27. Joanneum Research (2010) Green investment schemes: first experiences and lessons learned. http://www.joanneum.at/climate/Publications/ Solutions/JoanneumResearch_GISWorkingPaper_ April2010.pdf. Accessed Oct 2010 28. Kolchins A (2007) Overview of REC markets and pricing. Evolution Markets Inc. http://apps3.eere. energy.gov/greenpower/resources/pdfs/0907_rec_ kolchins.pdf. Accessed Oct 2010 29. McCombs School of Business (2007, February) University of Texas at Austin. Wal-Mart determined to lead in corporate social responsibility. http://www.mccombs.utexas.edu/news/pressrele ases/Blackwell07.asp. Accessed 2 April 2010

Emissions Trading 30. Mundaca L (2007) Transaction costs of Tradable White Certificate schemes: The Energy Efficiency Commitment as case study. Energy Policy 35(8): 4340–4354 31. Nordhaus W (2009) Economic issues in a designing a global agreement on global warming. http:// nordhaus.econ.yale.edu/documents/Copenhagen_ 052909.pdf. Accessed July 2010 32. NY Times (2006, December 21) Outsize profits, and questions, in effort to cut warming gases. http://www.nytimes.com/2006/12/21/business/ 21pollute.html?pagewanted=2&_r=1. Accessed 20 April 2010 33. OECD (1997) Greenhouse gas emissions trading annex I expert group on the UNFCCC, Working Paper No. 9. OECD/GD(97)76 34. Pew Research Center for the People & the Press (2010, March) Survey reports. Public’s priorities for 2010: economy, jobs, terrorism. http://people-press.org/report/584/policy-priorities2010. Accessed April 2010 35. Raufer R (2008) Carbon markets and emissions trading in Asia. In: Loh C, Stevenson A, Tay S (eds) Climate change negotiations can asia change the game? Civic Exchange, Hong Kong 36. REN21 (2009) Renewables global status report. Renewable energy policy network for the 21st century. http://www.ren21.net/Portals/97/documents/GSR/RE_GSR_2009_Update.pdf 37. Reuters (2009) Carbon trade on brink of boom – or backwater. http://www.reuters.com/article/ idUSTRE5AH2U420091118?sp=true. Accessed 30 Mar 2010

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38. Stern N (2006) The economics of climate change: the stern review. HM Treasury, Office of Climate Change, UK 39. UN NGLS (2009) UN non-governmental liaison service. Climate justice for a changing planet: beyond carbon trading. http://www.un-ngls.org/ spip.php?page=article_s&id_article=1736. Accessed 2 Apr 2010 40. UNEP Risoe Center (2010, February 1) UNEP Risoe CDM/JI pipeline analysis and database. http://www. cdmpipeline.org/overview.htm. Accessed 18 Apr 2010 41. US Department of Energy (2009, June 16) States with renewable portfolio standards. http://apps1. eere.energy.gov/states/maps/renewable_portfolio_ states.cfm. Accessed 9 Apr 2010 42. US EPA (2010) Acid rain program benefits exceeds expectations. http://www.epa.gov/ capandtrade/documents/benefits.pdf. Accessed Oct 2010 43. US EPA (2002) Clearing the air: the facts about capping and trading emissions. http://epa.gov/ airmarkt/presentations/docs/clearingtheair.pdf. Accessed Oct 2010 44. Wall Street Journal (2009, August 13) Capand-trade’s unlikely critics: its creators. http:// online.wsj.com/article/SB125011380094927137. html. Accessed Oct 2010 45. World Bank (2010) State and trends of the carbon market 2010. http://siteresources.worldbank.org/ INTCARBONFINANCE/Resources/State_and_ Trends_of_the_Carbon_Market_2010_low_res. pdf Accessed 28 May 2010, Washington, DC

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9 Promotion of Renewables and Energy Efficiency by Politics: Case Study of the European Union Itziar Martı´nez de Alegrı´a Mancisidor1 . M. Azucena Vicente Molina2 . Macarena Larrea Basterra3 1 Engineering School of Bilbao, University of the Basque Country, Bilbao, Spain 2 Economics and Business Administration School, University of the Basque Country, Bilbao, Spain 3 Researcher for the Energy Working Group, University of the Basque Country, Leioa, Spain Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278 Energy Model and Sustainability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 Conventional Energy Model: Features and Threats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 Basis for a More Sustainable Energy Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 Reasons for the Promotion and Support of Renewable Energy Sources (RES) and Energy efficiency (EE): The European Union (EU) Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 Externalities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 Estimation of External Costs of Energy: Objectives and Instruments . . . . . . . . . 288 Uses and Complexity of External Cost Estimation and Main Critics . . . . . . . . . . 290 Main Barriers for RES and EE Technologies and Instruments to Remove Them . . . . 291 Main Barriers for RES and EE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291 Instruments to Promote RES and EE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291 European Union Policy for a Low Carbon Economy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296 Toward a Stable Regulatory Framework to Promote a Low Carbon Economy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 Instruments for an Integrated Approach to a ‘‘Low Carbon Economy’’ . . . . . . . . . . . 300 Non-technological Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 Technological Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313 Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_9, # Springer Science+Business Media, LLC 2012

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Abstract: Since climate change has become an international concern, most of the developed countries have attempted to adopt energy policies to mitigate global warming and its side effects in the last years. The current energy model, based on fossil fuels and nuclear energy, has been the basis for the functioning and development of modern industrial society. Nevertheless, the threats of this model (environmental problems, exhaustion of fossil sources, possible inflation process and loss of competitiveness, dependency toward energy export countries, etc.) have forced a change in the EU’s traditional energy strategy (which was focused on the security of supply). The present energy model of the European Union, which supports its economic growth and prosperity, is 80% dependent on fossils fuels [1] and it is increasingly dependent on energy imported from Non-EU member countries, creating economic, social, political, and other risks for the Union. From the 1990s, the key objectives of the EU have been security of supply, competitiveness, and environmental protection, making renewable energy sources and energy efficiency the basis for its new energy strategy in the EU. However the lack of a common energy framework seems to have been an obstacle to reach those objectives. Therefore, the European Union has recently adopted new directives and instruments to create a unique energy framework in order to reach the mentioned targets but also to become the world leader in the impulse of renewable energy sources and in the employment of energy efficiency technologies. In this work the main problems of the conventional energy model (CEM) are explained. The basis, obstacles, and challenges for implementing a more sustainable energy model are also analyzed. Likewise, due to the strategic importance of the European Union leadership in developing and implementing new instruments and policies to mitigate climate change, this work is focused in its energy strategy. Thus, the recent energy directives and other measures adopted by the EU are discussed.

Introduction As climate change has become an international concern, a track pursued by the European Union (EU) is the development of low carbon technologies, essential both to the achievement of the goals of reducing greenhouse gas (GHG) emissions and increasing the use of renewable energy, but also as a means to ensuring Europe’s competitiveness. The mitigation of climate change must be based on a new energy model relying on renewable, low carbon, and more efficient energy technologies. Renewable energies, which are derived from natural processes and are replenished constantly, can play an important role in achieving a higher degree of independence as well as developing a more sustainable and secure supply in the foreseeable future. Low carbon and renewable energy technologies, emerging in the European energy market, confront many market and regulatory failures and present structural weaknesses, such as long lead times for these new technologies to mass market, locked-in infrastructure investments, diverse market incentives, and network connection challenges. Furthermore, the market take-up of the new energy technologies is additionally hampered by the nature of the technologies themselves, because they are generally more expensive at the earlier stages than the technologies they replace.

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In short, imperfections and distortions in the market coupled with unfavorable financial, institutional, and regulatory environments imply that governmental intervention is not only desirable but also necessary to promote these new energy technologies [2]. The role of governments includes generic actions such as considering externalities and removing barriers, setting up research and development infrastructure, improving human and institutional capacity, creating an enabling environment for investment, and providing information and mechanisms to promote renewable, low carbon, and more efficient energy technologies. These topics will be deeply analyzed in this chapter, which is organized in three sections, as follows: The first part of the chapter (> section on ‘‘Energy Model and Sustainability’’) gives a short historical description of the current or conventional energy model (CEM), including its main threats. Later, the basis for the development of a more sustainable energy model is established, that is, a model based on the use of renewable energy sources (RES), and EE (energy efficiency) technologies. However, as there is still a long way to the consecution of a sustainable energy model, the second part of the chapter (> section on ‘‘Reasons for the Promotion and Support of Renewable Energy Sources’’) describes the most relevant problems, barriers, and obstacles that use of RES and EE have to face, and also the most important instruments to promote them. The third part of the chapter (> section on ‘‘European Union Policy for a Low Carbon Economy’’) analyzes the current EU’s energy strategy for a low carbon economy, and also describes its main instruments and legislation. Finally, the main conclusions of the chapter and references are included.

Energy Model and Sustainability The conventional energy model, which has contributed to the development and wealth of humankind (mainly in industrialized countries), is considered not to be compatible with sustainable development any longer. This conventional model has encouraged overconsumption of energy from nonrenewable sources through cheaper prices that did not include external costs, such as environmental impacts, depletion, exhaustion of energy sources, etc. Additionally, this energy model has contributed to climate change owing to a massive use of fossil sources (coal, oil, gas) to produce energy. Due to these problems and others that will be treated in next sections, a new model based on renewable energy technologies and energy efficiency is emerging in the EU in order to achieve a sustainable development and, at the same time, to achieve world leadership in the renewable energy sector [3].

Conventional Energy Model: Features and Threats At the end of the eighteenth century, with the Industrial Revolution, starts the development of the current or conventional energy model (CEM). This centralized model is based on a massive use of conventional sources of energy, the fossil resources, starting by coal, later oil (end of nineteenth century), and finally gas and nuclear (twentieth century).

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As explained in Patterson, the ‘‘universal system’’ in the electricity sector (which uses alternating current and direct current converters and transformers) was introduced in 1893, setting the stage for the technical model of centralized thermal power plants. This model was to become the worldwide standard. This central-station electricity system has been a common technical model with many institutional variations as legislation, political processes (with a distinctive and intimate relationship with the relevant government), financial arrangements . . . At the beginning of the twentieth century, all electricity systems were operated under government supervision, called ‘‘regulation.’’ Sometimes, these systems were publicly owned, while others were privately owned. With its different variations, the systems were operated as local or regional monopolies authorized by governments (local, regional, or national), while electricity users were considered ‘‘captive customers.’’ This author also affirms that since electricity has been a fundamental element for the operation and development of the OECD countries, a flow of revenue to the system has been guaranteed, including all building, maintenance and operation costs, whatever timescale might be appropriate. This is why planners and producers could work in decades, because even if they did it wrong someone else would pay the bill. Moreover, electricity has been traditionally considered a ‘‘public service,’’ so anyone wanting a connection to the system had to accept its terms and pay the corresponding tariff [4]. It must be remembered that the questions related to the electricity and energy tariffs and their generation cost are very unclear. According to Patterson [4], in Europe the process of setting tariffs has tended to be opaque, and has involved governments and interested parties in negotiation. Although in the USA this process has been more transparent and accessible, it has also been more legalistic and often adversarial [4]. Regarding energy production cost, two relevant factors make it difficult to estimate. On one hand, there is the problem of calculating the ‘‘external costs,’’ that is, the related environmental costs (see > section on ‘‘Uses and Complexity of External Cost Estimation and Main Critics’’). On the other hand, it is very difficult to take into account both public aid, and the funding or subvention for research given to the CEM through history. In this regard, the European Commission published in 2002 a report of the public aid given to the different energy sources from the 1990s [5]. According to it, the promotion by different European governments of their national energy sources has been very common. The aid for the production of solid fuels deserves special mention, with 5.993 million Euro accounted for 1997 for Germany, France, Spain, and UK. Moreover, the EU itself has supported the research and innovation of conventional sources by different programs, as is described in Martı´nez de Alegrı´a et al. [6]; for example, Thermie (1994–1998) or Energie (1998–2002), received around 30 million Euro for the promotion of research on solid fuels since 1999 to 2001. Also, there is a large amount of funding given by the EU for the research and development in the area of nuclear energy including nuclear fusion, where the great importance of the ITER (International Thermonuclear Experimental Reactor) project must be highlighted [6]. In short, to understand the real success of the CEM, not only must be taken into account the support provided by private investors and companies, but also the continuous support (not only political but also economic and financial) provided by different public

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administrations for its development, which has also contributed to the distortion of energy market prices. According to Patterson, as it was the case in other industries, the ‘‘liberalization process,’’ which started in the mid-1980s, also affected the energy and especially the electricity sector. In the first place, the government of Chile, followed later by the UK, started the privatization process of their electricity systems. In 1986, the European Single Act was adopted to include the objective of the creation of the Internal Market, which became a key element of the European Policy. From then on, the so-called liberalization of European national energy markets has been on the agenda. ‘‘By the early 1990s other governments were ‘liberalizing’ their electricity systems (. . .). Sweden and Finland in the North, Australia and New Zealand in the South, and a lengthening roster of other countries in between, all embarked on various permutations of privatization, restructuring, and introduction of competition’’ [4]. The ‘‘liberalization process’’ means new challenges: – The important element in the process of liberalization is not the privatization, but the introduction of real competition. So, it is fundamental to ensure that public monopolies are not simply replaced by private monopolies or oligopolies. – The liberalized markets ‘‘might not provide sufficient capacity margins to guarantee the reliability of energy systems. Waiting for the inevitable corrections of the market is likely to result in costly disruptions and extreme cost swings as occurred in the deregulation of the electricity market in California. Because reliable electricity is a vital public good, public oversight is needed’’ [7]. – ‘‘Electricity liberalization, by reallocating risk away from users to shareholders and bankers, has altered investment priorities. Traditional generation, based on large-scale and long-term investments, such as major dams, coal-fired and nuclear power generation and long high-voltage transmission lines, becomes very risky in a market context, and all face increasingly severe financial and environmental problems’’ [4]. In fact, the development of the gas-turbine generation is starting a trend toward more and smaller generators closer to users, changing electricity systems away from the traditional centralized configuration to a more decentralized one, where other smallerscale generating technologies, that is, new renewable energy sources, will become increasingly important [4, 7]. There is no doubt that the CEM, and the electricity generation based on central-station generation, has been a real success in providing ‘‘energy services’’ (e.g., electric light, electromotive power, and electronics, but also energy for heating, transport, etc., that can be obtained thanks to the electricity or not), which are a key element of modern industrial society. Moreover, this energy model has been developed under the assumption that a near proportional relationship exists between prosperity or wealth and the increase in energy consumption. Since the oil crisis in the 1970s, the necessity of improving energy efficiency (EE) and the decoupling of the proportionality between energy consumption and gross domestic product (GDP) were especially outlined. Currently, the relation between prosperity and the increase in energy consumption is under challenge [8, 9, 10]. Indeed, with

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a long-term perspective, the CEM could also mean poverty. The CEM is considered not to be compatible with sustainable development in any of its three constituent parts (environmental, social, and economical perspective); this is why more than ever the threats of the CEM have to be taken into account. These threats can be summarized in terms of the following: – Dual energy crisis: while in modern industrial countries there are problems with inefficiency and overconsumption of energy, traditional electricity has failed to reach one-third of humanity. Moreover, 2,400 million people depend on conventional biomass for cooking and heating [7]. – There is a great debate as to whether or not the prospect of exhausting fossil fuel supplies is an immediate concern. However, with a long-term perspective, the increasing reduction of the fossil fuel reserves due to growing energy demand, and the lengthening of the ‘‘energy chain’’ (which includes production or extraction, conversion, transmission, and consumption of energy), will lead to an increase in conventional energy fuel cost, rising problems with the security of supply, inflation, and economic crisis [6, 11, 12]. This problem was specially put in evidence after the ‘‘oil crisis’’ (1973–1974). – The CEM is causing important environmental damage [13, 14], what is threatening human health and quality of life, and is affecting the ecological balance and biodiversity. The negative local, regional, and global impacts such as those caused by oil slicks, nuclear accidents, methane leaks, and, of course, CO2 emissions cannot be forgotten. According to the Intergovernmental Panel on Climate Change (IPCC), there is now clear scientific evidence that emissions from economic activity, particularly the burning of fossil fuels for energy, are causing changes to the Earth’s climate [14]. Presently, about 88% of the global energy mix comes from depleting fuels and, with the exception of nuclear energy (6%), are all carbon-rich fossil fuels such as oil (35%), natural gas (21%), and coal (26%) [15]. – Although energy supply security has been considered adequate for the past 20 years in industrialized countries, more and more risks appear linked to the safety of the energy chain. Taking into account that oil and natural gas are concentrated in ‘‘sensitive or vulnerable areas,’’ potential for geopolitical conflict, sabotage, disruption of trade, and reduction in strategic reserves is high. It is considered that some large-scale energy installations are also considered to be potential targets for acts of terrorism [7].

Basis for a More Sustainable Energy Model Current threats linked to the CEM are clear signs of its exhaustion. Therefore a new and more sustainable energy model is needed. In search of a more sustainable ‘‘economic system,’’ more and more authors refer to ‘‘the low carbon economy’’ or ‘‘the solar economy’’ ([1, 12, 16, 18]), which, regarding the energy sector, may be summarized as: (a) A low energy intensity model: low energy consumption by each unit of GDP generated. Energy intensity gives an indication of the effectiveness with which energy is being

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(b) (c) (d)

(e)

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used to produce added value. It is defined as the ratio of Gross Inland Consumption of Energy to GDP [19]. A low carbon intensity model: low level of CO2 emissions by each unit of GDP generated. A low environmental impact model. That is, a model based on RES (renewable energy sources) and energy efficiency (EE). A socially sustainable model, so it should be designed also for the development of rural and isolated areas and poor nations. Thus RES have been considered as one of the strong contenders to improve the plight of two billion people, mostly in rural areas, without access to modern forms of energy [2, 20]. An economically sustainable, EE is the most economical way to improve competitiveness [21], and RES technologies create more jobs per unit of energy generated [22], however, even if RES technologies are reducing notably their costs, actually there are still important market barriers that difficult a major penetration of these technologies in the market (see next chapter: Reasons for the promotion and Support of RES and EE).

To ensure a lower carbon economy and a sustainable development, some key factors should be taken into account: On one hand, this model should be developed in a decentralized way, where the supply is close to the demand, so reducing the ‘‘energy chain’’ and avoiding as much as possible the energy transport and distribution losses. According to Directive 2009/28/EC [23], on the promotion of the use of energy from RES, the move toward decentralized energy production has many benefits, including the utilization of local energy sources, increased security of energy supply, shorter transport distances, and reduced energy transmission losses. Such decentralization also fosters community development and cohesion by providing income sources and creating jobs locally. Many of the renewable technologies are well-suited for distributed uses. Moreover, the production of energy from renewable sources often depends on local or regional small and medium-sized enterprises (SMEs). Consequently, when favoring the development of the market for renewable energy sources, new regional and local development opportunities are encouraged, and also export prospects, social cohesion, and employment opportunities, in particular as concerns SMEs and independent energy producers. This is why it is so important to support the demonstration and commercialization phase of decentralized renewable energy technologies [23]. However, to obtain major benefits from this model, technological progress and economies of scale must be reached [18]. On the other hand, it should be a model with a lower environmental impact. It is considered that environmental damages caused by energy produced from RES are much lower comparing with those caused by energy produced by fossil sources. ‘‘The need for improving energy efficiency and reducing CO2 emissions and other pollutants, as well as the restructuring of energy markets have favoured the increase of distributed energy sources. The co-ordinated control of these sources comprising RES and distributed generators characterised by higher efficiencies and lower emissions compared to central thermal generation, when based on coal or oil, provide several environmental benefits’’ [24].

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However, it must be remembered that the environmental damage provoked by RET can also be worrying, especially under the following circumstances: (a) If they are not well managed. As an example, the United Nations suggests that problems associated with bio-energy and use of the land (particularly of virgin land, including deforestation, biodiversity loss, soil erosion, and nutrient leaching) will remain the most vexing problem, and will deserve the most attention [25]. According to United Nations and Directive 2009/28/EC on the promotion of RES, more research and evaluations are needed to determine which crops and management practices can best minimize impacts and maximize benefits [23, 25]. Thus, the Brussels European Council, reports that ‘‘it is important to ensure the sustainability of biofuels policies’’ [26]. In this regard, Directive 2009/28/EC includes some ‘‘sustainability criteria’’ for biofuels and bioliquids (art 17; [23]). (b) When they are programmed for large-scale generation and do not take into account the local necessities and impacts. An example is ‘‘The Three Gorges Dam,’’ developed in China, which is the world’s largest hydropower project and most notorious dam. In 2003, a total of six 700 MW units were installed and put into operation, setting a new world record for yearly installation of large-size turbine generators. This large-scale project sets records for the number of people displaced (more than 1.2 million), number of cities and towns flooded (13 cities, 140 towns, and 1,350 villages), and length of reservoir (more than 600 km). The environmental and social impacts of this project have increased Chinese scientists’ and government officials’ concern about local consequences [27]. Traditionally, it has been considered that nonconventional RES (renewable energy sources based on technologies most recently used and developed, such as wind, photovoltaics, etc.), have a scale of production and environmental impact much lower than conventional RES (those renewable energy sources that have been used for long, e.g., hydropower and traditional biomass). However, the scale of production seems not to be clear any more. There exist already wind power and solar thermal plants with a capacity of production of several hundreds of megawatts. As an example, the aim of the ‘‘Desertec’’ project is to pave the way for large-scale production of electricity from sun and wind in the desert, with a long-term goal of satisfying a substantial part of the energy needs of the Middle East and North Africa (MENA) countries and to meet about 15% of Europe’s electricity demand by 2050 (Desertec joint venture [28]). This project is shown as an example of how to solve problems related to climate change, or trends in population growth [29]. Nevertheless, it also could be an example of the ‘‘desire of many governments and big energy companies to continue the maintaining of the classical model of centralised production’’ [16]. Gains in renewable energy have been dramatic over the past few years [30], and there is still a vast potential for obtaining energy from the sun [9, 12], but this potential is also limited. In fact, a sustainable energy model is not compatible with a model of eternally increasing energy and material consumption. In short, the massive use of RES and improvements in EE are not by themselves a guarantee of the sustainability of the model, so changes of current

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consumption patterns are also fundamental. For a real reduction in the energy consumption patterns in the EU, efforts should be specially focused on [31]: (a) The building sector, where the active solar energy (using photovoltaics, solar thermal energy, etc.) and passive solar energy and bioclimatic architecture (i.e., well-orientated or well-located buildings, better wall insulation, etc.) should become key elements. (b) The transport sector, taking into account land planning to improve accessibility, promoting public transport, etc. [1, 21, 31, 32]. Finally, it is important to highlight that the reduction of energy consumption does not necessarily mean a deterioration of the quality of life. On the contrary, better wall insulations and reorientation of buildings, better public transport, etc., could clearly improve it. In this sense, good public management plans linked to innovation seem to be crucial for obtaining best synergies between EE, energy savings, and use of RES while also improving the quality of life.

Reasons for the Promotion and Support of Renewable Energy Sources (RES) and Energy efficiency (EE): The European Union (EU) Case There are different reasons that could explain why the use of RES must receive not only public funding for improving research and innovation, but also public aid for their development: (a) Most of the conventional energy sources are finite and cannot supply the highly increasing demand of energy all over the world. Besides, these traditional energy sources provoke substantial damages on the environment, and consequently on human health, ecosystems, etc., that are not included in market prices and that are known as ‘‘externalities’’ (see > section on ‘‘Externalities’’). So if measures are not taken promptly, by adopting RES and increasing EE, the welfare and development of humankind could be in danger in a near future. The EU, concerned as it is for the promotion of RES and climate change mitigation, has developed aid, programs, and a legislative framework to this aim. However, it is important to clarify that state aid in the EU framework must fulfil certain criteria and be authorized by the European Commission. This institution issues guidelines and frameworks to help Member States (MS) by announcing in advance which measures it will consider compatible with the common market, thus speeding up their authorization. According to the cited guidelines ‘‘environmental protection is a fundamental objective for the EU so, taking into account that, on the one hand, the level of environmental protection is not sufficiently high, and on the other, companies do not fully account for the costs of pollution for societies, the Commission considers that there is a need to do more. In order to address this market failure and promote a higher level of environmental protection, different governments can use regulation to ensure that companies pay for their pollution (e.g., through taxes or emission trading systems) or meet certain environmental standards; give private firms an incentive to invest more in

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environmental protection or to relieve certain firms from a certainly high financial burden in order to enforce a stricter environmental policy’’ [33]. However, these guidelines serve also as a safeguard that it will not be possible to grant badly targeted or excessive state aid which not only distorts competition but also can frustrate the objective of meeting environmental targets [33]. (b) There are social, political, administrative, and economic barriers that impede a wider penetration in the market of the new renewable energy technologies, which means that if RES technologies do not get financial and social support, they will not be able to compete with conventional energy technologies. Moreover, as has been explained before, conventional sources have received important political, economic, and financial support from different governments for a long time, and still receive them. This support has permitted the development of a distorted market based on fossil fuels and nuclear, while it has also allowed the achievement of economies of scale that renewable sources have not achieved yet, and that are still far from this goal. According to the United Nations, large subsidies to conventional energy represent a substantial market distortion, discourage new entrants into the market, and undermine the pursuit of energy efficiency [7]. Although traditional technologies used to have an overwhelming cost advantage over renewable energies a decade ago, things seem to be changing. In > Table 9.1, the estimated generation cost of different electricity generation technologies in 2005 and 2010 are shown. A discount rate of 5% has been considered for all technologies, which allows an objective comparison between them. According to the data, while coal doubles its price for most countries in 2010 compared to 2005, the price is almost triple for the Czech Republic and the Slovak Republic. Cost of nuclear power rises notably, with the exception of Japan. Cost of solar photovoltaic (PV) increases except for the Czech Republic. Regarding onshore wind, its cost rises for most of the countries (with the exception of Netherlands where it has been reduced), but this increase is lower in each country, in relative terms, if they are compared with traditional technologies (coal, gas, nuclear, and hydro). It is also clear that onshore wind becomes the cheapest energy source in 2010 in absolute terms, with US $32.19/MWh in South Africa and US $48.39/MWh in the USA, which suggests that the more is the investment in RES and the more they are deployed, the cheaper the price of renewable energy sources will become. In fact, while traditional energies estimated costs reach the highest relative increase (coal 136.19% and hydro 111.82%) from 2005 to 2010, renewable energies have got the lowest relative increase (48.74% onshore wind), being even negative in the case of solar energy (
44.18%). (c) There is another reason to promote RES and EE in the specific case of EU: Europe wastes at least 20% its energy due to inefficiency, with an estimated direct cost of 100 billion Euro annually by 2020, so realizing the savings potential has been considered the most effective way to improve security of supply, reduce carbon emissions, and foster competitiveness [21]. Consequently, it is important for the EU to encourage research to reach higher levels of EE. In addition in the EU, most traditional energy sources must be imported and there is a trend toward a higher external

79.03 136.19%

72.49 32.19 88.08

73.29 120

49

79.26

53.43

46.7 40.8 52.1 43.6

49.7 60.4 55.9 40

46.4 49.7

2005

Gas

82.32 84.64

2010

Own elaboration (data from [34, 35]). USD/MWh *Data for Switzerland is for small hydro **It is calculated with respect to average cost in 2005

33.46

Average estim. cost % increase**

47.8 31.1

Italy The Netherlands Slovak Republic Canada

27.1 15.7 49.5

29.4 31.9 35.2

Belgium Czech Republic Denmark Germany

United States South Africa Japan Switzerland*

2005

Year discount rate 5 %

Coal

31.45

48 28.8

105.1 94.04 88.75 66.05%

30.1

35.8 31.3 26

28.6

23

2005

76.56

86.85 80.40

85.23

89.71 91.92

2010

Nuclear

. Table 9.1 Estimated generation cost of electricity from different energy sources

60.35 91.89%

49.71 78.24

48.73

62.76 62.59

49.97

61.06 69.74

2010

68.81

31.1

76 94.3

53.4 92.3 50.5 84.1

2005

102.35 48.74%

162.9

48.39 32.19

99.42

145.5 85.52

105.8

95.65 145.8

2010

Onshore wind

603.32

120.6

1520 484.8 287.8

2005

Solar PV

336.78
44.18%

215.4

227.4

410.4 469.9

304.7

392.9

2010

78.05

142.9

39.7

83.2

46.4

2005

Hydro

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energy dependency. It should be emphasized that dependency rates have already negative impacts on the European balance of payments. If unforeseen changes in availability (e.g., because of political instability) and prices of energy sources (e.g., increase of oil prices in 2006–2009) occur, there will be worrying impacts on economic growth. Therefore, the EU has emphasized the importance of energy security and import independence (see > sections on ‘‘European Union Policy for a Low Carbon Economy’’ and > ‘‘Towards a Stable Regulatory Framework to Promote a Low Carbon Economy’’).

Externalities Human activities can cause damages on human beings, ecosystems, and materials. In the 1920s, Pigou had already identified the negative consequences of the economic activity as external costs or externalities. An externality arises ‘‘when the social or economic activities of one group of persons have an impact on another group and when that impact is not fully accounted or compensated for, by the first group’’ [36]. An example of the ‘‘negative externalities’’ regarding the energy sector is the environmental impact (including climate change) caused by the CEM which is not fully accounted for in the energy or electricity tariff. It has to be noted that there could also be positive externalities linked to the energy sector, for example, the development of a mini-hydraulic system to provide electricity to an isolated area could also help to create local employment without a hard negative environmental impact. According to traditional economic theory, externalities are market failures which produce inefficiency. Therefore, the existence of externalities means that market price only reflects private marginal costs (raw materials, labour, etc.) and not the external and social marginal costs. As a consequence, ‘‘including all social, environmental and other costs in energy prices would provide consumers and producers with the appropriate information to decide about energy mix, new investments or research and development’’ [37]. Thus, external costs should be internalized by using the most suitable instruments [36]. However, it cannot be forgotten that conventional energy sources have become a real success also because they have received important support from different governments (not only political but also economic and financial), and that a correct formation of prices is not possible if there is not a cost transparency, which means that fully private marginal costs are not reflected into the consumers tariff, creating a distorted energy market. In short, it may be concluded that current state aid and support to the use of RES and EE is not only justified by the existence of ‘‘externalities,’’ that is, for environmental reasons, but also because the existence of a distorted energy market.

Estimation of External Costs of Energy: Objectives and Instruments The internalization of external costs is intended as a strategy to rebalance the social and environmental dimension with the purely economic one, accordingly leading to greater environmental sustainability. On the whole, the objectives of estimating the

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external costs of energy are to measure the social damages, which are not paid by the energy sector, and transform these damages into a monetary value. Therefore, converting external effects into monetary units would be useful to compare between the different technologies of producing energy. Experts have traditionally used a cost-benefit analysis to estimate these social damages. In such an analysis, the costs to establish measures to reduce a certain environmental burden are compared with the benefits (e.g., the avoided damage due to this reduction). It consists of assessing a decision taking into account its consequences (e.g., economic cost vs. environmental/social benefits). According to Pon et al. [38], environmental impact studies can follow two different paths: bottom-up or top-down. A bottom-up approach tries to establish environmental impacts through a life cycle analysis (LCA) or a ‘‘cradle to grave’’ approach. Top-down studies employ input–output tables in order to value the impact of activities from a macroeconomic perspective [38]. The bottom-up approach is more adequate for microeconomic studies, such as to compare two different technologies or different location options for a single technology, etc. The top-down approach could be used, for example, to calculate CO2 emissions of different regions. LCA has its beginnings in the 1960s, concerning over the limitations of raw materials and energy resources [39]. Currently, the life cycle assessment or analysis is mainly employed to compare the full range of costs, including environmental and social damages of different technologies or products. The LCA is an objective process to evaluate the environmental burden of a product, process, or activity, because, according to Rabl and Spadaro [36], not only there are ‘‘external costs occurring during operation, but also during construction, provision of energy carriers and materials, waste disposal, dismantling, etc.’’ LCA is a ‘‘cradle to grave’’ approach to assess industrial systems. This ‘‘cradle to grave’’ approach ‘‘begins with the gathering of raw materials from the earth to create the product and ends when materials are returned to the earth. LCA enables the estimation of cumulative environmental impacts resulting from all stages in the product’s life cycle, often including impacts not considered in more traditional analyses (e.g., raw material extraction, ultimate product disposal, atmospheric emissions, etc.). By including the impact throughout the product life cycle, LCA provides a comprehensive view of the environmental aspects of the product or process and a more accurate picture of the actual environmental trade-offs in product and process selection’’ [39]. Once research studies have all the information about the inputs and outputs of an activity, they can proceed to an economic assessment of the whole cost of the product or process. Nevertheless, results are usually different from one study to another in this regard, which is mainly due to the complexity involved in the estimation of environmental costs of energy (see > section on ‘‘Uses and Complexity of External Cost Estimation and Main Critics’’). Nevertheless, over the past 20 years, there has been much progress in the analysis of environmental damage costs, particularly through the ‘‘ExternE’’ (External costs of Energy) European Research Network. Since 1991, the ExternE project has involved more than 50 research teams in over 20 countries. The effects of energy conversion are physically, environmentally, and socially complex and difficult to estimate, and involve

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very large, sometimes ultimately irresolvable uncertainties, unforeseen events, and differences of opinion. Despite these difficulties, ExternE has become a well-recognized source for method and results in externalities estimation. To compare technologies or assess policies, it has to be determined whether one composition of impacts and costs is better or worse than another composition. This is not straightforward, as different impacts have different units, so they cannot be added directly. Therefore, before being able to add them, it is necessary to transform them into a common unit. The ExternE methodology provides a framework for doing this [40].

Uses and Complexity of External Cost Estimation and Main Critics Estimation of environmental impacts and other externalities derived from energy production and consumption is not only necessary but also useful. Thus, calculating external costs can have several uses: (a) For investment, consumption, or supporting decisions. Since external costs allow for the consideration of environmental impacts, they should be added to private costs, getting the total cost of kWh production. In this way, organizations and users could make appropriate decisions on what energy technologies to invest in or use. Society and governments should also consider external costs in the decision process about which kind of energy should be promoted. (b) For health and environmental impacts valuation. (c) For choosing the measures to reduce environmental impacts and health risks. (d) For an adequate interpretation of damage. It is generally more useful to have a monetary value; otherwise people could have problems interpreting data that does not have a monetary value. By way of an example: most people do not know whether one gram of CO2 is as harmful as one gram of SO2. However, everybody would understand ‘‘one gram of SO2 costs 5 Euro and one CO2 gram costs 3 Euro.’’ This has the advantage of making it possible to compare costs with benefits, and monetary units are defined independently of the assessment process [36]. Although estimation of the external costs becomes a useful instrument to measure environmental damage and make better decisions regarding energy technologies, it is also quite complex for several reasons. First, because environmental impacts caused by the energy sector do not have a market where a trading price for them can be established. As a consequence, experts are looking for another way to give those impacts a price. For climate change, two approaches are followed: (a) The quantifiable damage is estimated. Because of large uncertainties and possible gaps, an avoidance cost approach is used [36]. (b) At present, the EU emissions’ trading scheme is an attempt to create a market where CO2 emissions have received a price. This market provides economic incentives for achieving reductions in the emissions.

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Second, unanimity cannot be achieved since there is a high level of subjectivity when deciding the variables to consider. These are the principal reasons why researchers show so variable results in their studies about the external cost of different types of energy technologies. And third, because there are many uncertainties calculating external costs. However, ‘‘where there are threats of serious or irreversible damage lack of full scientific certainty should not be used as a reason for postponing such measures’’ [41]. In spite of the difficulties, the external costs estimation is a very useful instrument to determine the weaknesses and strengths of a technology. The results of the different researches are in consequence guidelines, because they are neither completely true nor false [42]. Nevertheless, identifying and assessing energy technologies external costs are necessary for a sustainable development despite the uncertainties.

Main Barriers for RES and EE Technologies and Instruments to Remove Them Main Barriers for RES and EE Regarding EE and RES, two different barriers can be distinguished. On the one hand there are ‘‘artificial barriers,’’ such as the administrative and legislative barriers, or market failures and distortions. On the other hand there are ‘‘natural barriers.’’ These barriers are common to those that the majority of new technologies have to face when penetrating an existing market, as, for example, lack of financing and lack of scale economies. > Table 9.2 presents a brief description of the main barriers and disadvantages of RES. The European Commission [31] describes the main barriers to achieve EE as crosssectorial barriers due to incomplete implementation of EU energy efficiency legislation, insufficient access to financing, and low awareness of the benefits of energy saving. In fact, there are insufficient infrastructures to facilitate EE in transport and a lack of commitment from the sector’s improvement needs. Likewise, a low awareness of the potential benefits and high up-front cost represent clear obstacles for the industry, whereas the current state of financial markets does not help either to improve access to financing in the short term [31]. Policy approaches to achieve the techno-economic potential can either remove the barriers or create conditions where the market is forced to ignore these barriers. The former normally works at the micro level addressing the barriers directly, while the latter acts mostly at macro level to address the barriers indirectly [2]. For example, setting up information centers and establishing codes and standards, address the barriers directly, whereas increasing energy prices through pollution taxation addresses the barriers indirectly.

Instruments to Promote RES and EE There is a vast literature about the instruments that promote RES and EE. There is also a large variety of classifications of these instruments, depending on the perspective

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. Table 9.2 Main types of barriers to RES 1. Market failures and distortions

2. Financial

3. Technological and technical

4. Administrative and legislative

5. Social, cultural, behavioral, and economical

6. Geographical and environmental limits

From own elaboration

! Externalities are not included ! Existence of natural monopolies (electricity logistics) ! Power of great companies linked to conventional energy model: lack of interest for RET and EET (energy efficiency technology) from the firms ! A highly regulated sector ! Aids and subsidies to conventional energy sources and technologies ! High initial investment ! High level of risk (derived from the lack of knowledge and experience of new technologies for users and firms) ! Costs of transaction for existing firms (not only have they to make new investments in RET but they have to recuperate their investments in conventional technologies too) ! Low level of technological development in some RET ! Lack of scale economies ! Lack of professionals facilitate penetration of RET into final markets ! Lack of skills to improve and create new technologies ! Lack of materials (ex. silicon for photovoltaic) ! Lack or difficult access to the electricity grid for some RES ! Different legislatives (energy dumping) ! Lack of an adequate and standard legislation ! Bad application of current legislation ! Lack of juridical stability for projects or technologies ! Excessive bureaucracy and long time periods to obtain permissions for projects ! Lack of coordination between administrations ! Lack/low level of awareness and education of population ! Inadequate information on energy service/process ! Lack of adequate agencies to promote RET and EET ! ‘‘Not in my back yard’’ culture ! Higher prices for users ! Costs of transactions for users (need to adapt or buy new appliances or modify existing facilities, wiring. . .), what implies an even higher price than conventional energy ! Scarcity of specific renewable sources in the geographic area (solar, wind. . .) ! Impact on environment and ecosystems (especially in large-scale energy structures)

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adopted; for example, they can be classified on international, national, and local, or simply by considering if they are conventional or new (nonconventional) instruments, which is the classification followed in this part of the work. Most important traditional instruments to promote RES and EE include: – Financial instruments as subsidies and special tariffs. Tariffs can be used to encourage the adoption of renewable energy sources. It typically includes three main ideas: guaranteed grid access, long-term contracts for the electricity produced, and purchase prices based on the cost of renewable energy generation. Feed-in tariff policies to stimulate renewable technologies have been enacted in 63 jurisdictions [30], such as Australia, Austria, Brazil, Canada, China, Germany, Greece, Hungary, Iran, Israel, Italy, Lithuania, Luxembourg, Portugal, Singapore, South Africa, Spain, Switzerland, and in some states in the USA. – Regulation (see > section on ‘‘Non-technological Instruments’’) – Taxes(see > Table 9.3) – Promotion of information, education, and public awareness . Table 9.3 Traditional instruments to promote renewable energies and energy efficiency Instruments

Description

Advantages

Regulatory approaches Development of regulations
Define the objectives and the instruments to achieve them which establish the way to
Present few uncertainties in relation act in environmental with the objectives efficiency and the subjects or quantitative instruments proposed limits to emissions
They can motivate firms to come up with innovative, productivityimproving responses Financial measures Taxes

Financial incentives

Tariffs

From own elaboration


Incentive to foster energy savings Establish a tax over fossil
Tax over the energy or over the energies, greenhouse gas emissions emissions, and/or electricity
They do not mean a pay out from generation public funds They consist of fostering the development of renewable energies, through lower interest rate, credits, primes, subsidies, etc. To establish a higher price, for the renewable energy producers


They attempt to encourage investments in new technologies that can benefit the environment
They can promote research in new and cleaner projects
They make up for the high costs of renewable electricity
They offer incentives for innovation

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Although these traditional instruments are useful to promote RES and EE, they seem to be not enough by themselves to reach the EU goals on this topic. To this respect, it has to be noted that during the 1990s, the European Commission proposed the adoption of a carbon tax for the EU; however, the proposal failed because of the concern of the European industries about their competitiveness, and the necessity of unanimity between MS for its adoption [6, 43]. > Table 9.4 shows some of the newer instruments created with the objective of promoting sustainability in the energy sector, including their main advantages and disadvantages. They are hybrid approaches, as they try to combine interventionist approaches with the economic efficiency and flexibility of competitive markets. The emission trading system (ETS) is one of the three flexible mechanisms established by the Kyoto Protocol to help developed countries to accomplish their commitments. The other two flexible mechanisms are the clean development mechanisms (CDM) and the joint implementation (JI). A key factor of these last flexible mechanisms is to find the way to evaluate the most interesting projects in order to accomplish the objectives of greenhouse gas (GHG) emission reductions and sustainability. The EU Emission Trading System (EU-ETS) is a cap-and-trade scheme. It started in January 2005 with the adoption of Directive 2003/87/CE [44]. According to the most recent directive on emission trading adopted in 2009 (Directive 2009/29/EC, which amends the previous Directive 2003/87/EC), an auctioning system will be applied to the electricity sector from 2013, while there is a transition period for the rest of the sectors affected by the Directive. This recent directive improves and extends the GHG emission allowance trading scheme of the community and will regulate the emission allowances traded from 1st January 2013. The regime established on this Directive encloses several important novelties with regard to the previous Directive 2003/87/EC. First of all it establishes an objective of a 21% reduction of GHG below 2005 for the affected industries. From 2013, the Commission will establish the overall emission volume to allocate among all Member States, which means that a community view is established opposite to the national approach set by the former directive. Second, it establishes auctions as the allocation method for all the participant sectors (apart from exceptions and transitional provisions). It means that for each tonne of CO2 issued, the issuing entity should present the necessary allowances that have been previously acquired through auction [45]. Auction method established by Directive 2009/29/EC will have two important advantages compared to the previous free allocation method [46]. On one hand, the new directive will remove to a great extent speculative profit introducing a minimal starting price. On the other hand, it treats in an equitable and correct way all companies, giving them the opportunity to purchase emission allowances in a clear way. Therefore, auctions avoid the need to take difficult and politically delicate decisions about the allowances quotas that each country must allocate to each company that is interested in the Emissions Trade System. This mechanism would guarantee equity to new companies that would like to participate in the GHG trading system, because they would have the same opportunities as existing companies to purchase emission permits (except for the permits bought from 2005 to 2012).

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. Table 9.4 Newly created instruments to promote renewable energies and energy efficiency Instruments

Description

Advantages


They encourage the reduction of GHG.
They offer flexibility to achieve the objectives proposed.
They control the total amount of GHG pollution generated by the industry.
They provoke changes in the operating costs as well as in the future production structure.
Users can buy CO2 emission rights improving environment (it can also be a disadvantage for some companies).
Trading platforms are considered to reduce transaction cost and risk of their customers giving fluidity to markets.
They encourage the reduction of ETS: baseline and The ETS based on baseline and CO2. credit credit involve the establishment of (e.g., CDM) a ‘‘baseline level of emissions’’
They offer flexibility to achieve the (usually defined as the business as objectives proposed. usual scenario) for a sector or
Lower level of emissions a project or company. Under this comparing with those emitted by scheme no overall emissions cap is conventional energy-generation set; however actors are encourage projects based on fossil fuels. to reduce their emissions below this
Development of projects in baseline to generate emission renewable technologies. credits that can be traded’’ [43]. An
They are compatible with all the example is the Clean Development instruments to struggle against Mechanism (CDM), which makes emissions. part of the Kyoto Flexible mechanisms. It offers emission credits for an effective emissions reduction thanks to a previous project that looks for a reduction of greenhouse gas emissions. Emission Trade Schemes (ETS): cap-and-trade (e.g., EU-ETS system)

Under the ETS based on ‘‘cap and trade’’ ‘‘the government defines a new set of property rights to use atmosphere based on an emission limit or cap, that is, it establishes the overall level of emissions allowed’’ [43]. Within that limit, participants in the system are allowed to buy or sell allowances as they require. It involves the trading of one metric tonne of CO2 or any other greenhouse gas. An example is the current EU Emission Trading Scheme (EU-ETS).

Green certificates


They encourage the use of This certificate proves the renewable technologies. renewable origin of the energy and
They reduce the burdens that its price will supplement the price governments must withstand. received for the kWh in the market.

Carbon capture and storage

Integrated process in which CO2
Reduction of released CO2 emissions are captured and stocked emissions. in a permanent way.

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. Table 9.4 (Continued) Instruments

Description

Voluntary measures

Taken measures by the supply or the
They involve not only energy companies and industry, but also demand with a volunteer character electricity users. (e.g., Energy Star™). Development of a mechanism that
They can offset the weakness of combines two or more instruments the above mentioned formerly mentioned. instruments.

Combination of techniques

Advantages

From own elaboration

Several countries use green certificates as a mean to support green electricity generation instead of feed-in tariffs. Thus, Poland, Sweden, the UK, Italy, Belgium, and some US states have developed green-certificate markets; however, green certificates cannot be exchanged/ traded between countries unless they accept it. In this sense, Directive 2009/28/EC on the promotion of the use of RES establishes the rules for the certificate of origin of an energy source, reducing administrative and regulatory barriers that impede the growing of RES. The lack of transparent rules and coordination between the different authorization bodies has been shown to hinder the deployment of energy from renewable sources [23]. This is a flexible mechanism that enables statistical transference of this guarantee of origin between MS making it possible to reach their objectives of developing RES out from their territory. To summarize, the previously mentioned flexible mechanisms put a price on carbon emissions in the covered sectors. Thus, a market incentive for higher penetration of low carbon technologies is provided. Consequently, these kind of mechanisms have the objective of internalizing the negative ‘‘externalities’’ of carbon emissions by monetizing them. Other instruments, in particular carbon taxes or, in some cases, standards, can be applied in sectors that are not in the EU-ETS (e.g., in households, transport, and services) (see > section on ‘‘Non-technological Instruments’’) to create similar cost-efficient incentives. The ETS as well as energy or carbon taxes are market instruments. Their intention is to create the incentives to introduce the cheapest and most efficient abatement technologies first, that is, the technologies with lowest costs. In terms of technology development, this is equivalent to the technologies closest to the market. Thus, market-based policy instruments create a powerful stimulus for the introduction of these technologies. At the same time, these instruments also create incentives and accelerate the market uptake of more immature technologies by improving the expected long-term rate of return of new technologies.

European Union Policy for a Low Carbon Economy The present energy model of the European Union, which supports its economic growth and prosperity, is 80% dependent on fossils fuels [1], and it is increasingly dependent on energy imported from Non-EU member countries, creating economic, social, political, and other risks for the Union. As is shown in > Table 9.5, this dependency has been and is still increasing.

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. Table 9.5 Energy dependency for EU-27 [47] EU-27 (%) Energy dependency

2003 49.0

2004 50.3

2005 52.6

2006 53.8

2007 53.1

2008 54.8

Indeed, the security of supply has been the basis of the EU’s energy strategy from its creation, and it must be borne in mind that the EU started from the European Coal and Steel Community (ECSC) in 1951. This is why it seems a paradox that until the Lisbon Treaty [48] ‘‘the previous Treaties did not include any legal basis related to a Common Energy Policy, so actions related to promote RES and EE should be developed under different policies (external relations, internal market, environment, etc.)’’ [6]. Therefore, in the following paragraphs, the strategy of the EU to cope with this target will be analyzed.

Toward a Stable Regulatory Framework to Promote a Low Carbon Economy Energy and transport play a large part in climate change, as they are the two biggest emission sources [19], and energy policy is particularly important in the European Union’s strategy toward sustainability and climate change mitigation. Energy-related emissions represented approximately 80% of total emissions in 2007. The largest emitting source was the energy industry (40% of energy-related emissions), followed by transport (further 24% of energy-related emissions) [19]. The EU also attempts to improve its competitiveness and reduce its energy dependence by improving the security of supply not only by promoting other energy sources but specially by cutting the demand for energy. The necessity of promoting EE was already present in the European energy programs adopted during the 1980s; and in the 1990s, the environmental aspects of energy gained importance. Since 1995, the following three key objectives are pursued by the European Energy Strategy: security of supply, environmental protection, and improvement of competitiveness. In 1997, the European Commission (from now on Commission) published a White Paper on renewable energy [49], which announced a target to double the European Union’s renewable energy share to 12% by 2010. The White Paper also announced a renewable energy strategy and action plan, highlighting the need to develop all renewable energy resources, create stable policy frameworks, and improve planning regimes and electricity grid access for renewable energy. A key element of the action plan was the establishment of European legislation to provide a stable policy framework and clarify the expected development of renewable energy in each Member State (MS). In this regard, Directive 2001/77/EC [50] and Directive 2003/30/EC [51] set indicative targets for 2010 for all MS and require actions to improve the growth, development, and access of renewable energy. A Biomass Action Plan (BAP) was also adopted in 2005 paying attention to the specific need for MS to develop Europe’s biomass resources [52].

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In response to a request formulated by the 2005 Autumn European Council, the Commission worked on the following important tasks: The establishment of the basis for a common energy policy. Their conclusion was that future energy policy should be based on the following ‘‘three pillars’’: sustainable development, increase of competitiveness, and security of supply [53]. They are directly related to RES and EE. Sustainable development has an obvious relation, EE is the basis for competitiveness, and RES are also a key factor because of the great importance that they could gain in the internal energy market. Finally, RES and EE seem to be the only way to reduce increasing energy dependency. The elaboration of the ‘‘European Strategic Plan for Energy Technology’’ or SET-Plan, the objective of which is the consecution of the cited ‘‘three pillars.’’ The final objective was the restructuring of the European full energy system, starting with competitiveness and passing through to technological processes. The Commission also highlighted that to reach this objective, and compared with the current situation, a higher quantity of resources (human and financial) will be needed [21]. In 2007 the reports and the Renewable Energy Roadmap [54, 55] highlighted the slow progress achieved by MS and the likelihood that the EU as a whole would fail to reach its target of reaching a 12% share of RES by 2010. Some possible reasons for this could be the lack of a coherent and effective policy framework throughout the EU with a stable longterm vision, the increase in energy consumption, and the uncertain investment environment provided by the existing legal framework: Action Plan for Energy Efficiency 2000– 2006 [21]. In the Brussels European Council of 8 and 9 March 2007, after debating the Commission work on common energy policy and the SET-Plan, the commonly named ‘‘20/20/20’’ mandate was established, with the following ambitious targets for 2020 [56]: Reduction in GHG emissions by 20% compared to 1990 levels and by 30% when a new global climate change agreement is reached (providing that other developed countries commit themselves to comparable emission reductions and economically more advanced developing countries contribute adequately according to their responsibilities and respective capabilities). Saving 20% of energy consumption compared to projections for 2020. Increasing the level of renewable energy in the EU’s overall mix to 20% (with a minimum target for biofuels of 10% in transport consumption for each MS in the EU). This European Council position was a clear sign of their concern about energy management and climate change; indeed, the first of these targets was a clear sign of engagement and the ‘‘ethic leadership’’ face to the Kyoto Protocol commitment, while the following two were internal objectives and constitute the best complement to reach the first one. The objective of the EU is to change the increasing dependency on fossil fuels and energy import through the promotion of EE and RES. For example, over the 1997–2006 period, annual final energy use has increased by 11%, which represents one-third of all crude oil imports into the EU-27 in 2006 [31]. Nevertheless, the energy intensity ratio

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. Table 9.6 Gross Inland Energy and RES consumption for EU-27 EU-27 (Mtoe/year)

2003

2004

Gross Inland (GI) energy consumption

1802.9 1824.6 1825.3 1825.8 1807.8 1799.3

Annual variation rate (%) GI RES consumption Annual variation rate (%) % of GI RES consumption in GI energy consumption

– 107.8 – 5.98

1.20 116.2 7.81 6.37

2005 0.04 120.1 3.38 6.58

2006 0.03 129.1 7.49 7.07

2007
0.98 143.1 10.82 7.92

2008
0.47 151 5.55 8.39

From own elaboration from [47]

(Gross Inland Consumption (toe)/GDP (M€)) of the EU-27 has decreased, passing from around 215 in 1990 to 177 in 2006 [57], which is a positive sign. In addition, the EU Gross Inland energy consumption has increased very slowly from 1985 until 2001 in EU-15, passing from 1,245 to 1,486.2 Mtoe [58], while a small reduction of consumption has occurred between 2007 and 2008 in EU-27 (see > Table 9.6). However, it has to be noted that in the years when gross energy consumption has decreased (2007 and 2008), RES consumption has increased. However energy dependency of the EU-27 has not decreased (see > Table 9.5). According to the Commission, if the saving objective of 20% is reached, the EU would not only use about 400 Mtoe less primary energy, but it would also avoid the construction of about 1,000 coal power units or half a million wind turbines. CO2 emissions reduction would be around 860 Mt [31]. Biomass is the largest single renewable energy source in absolute terms and is expected to contribute to around two-thirds of the expected renewable energy share in 2020 [59]. Moreover, it is important to note that biomass can be used in the production of heating and electricity as well as in the form of ‘‘biofuels,’’ e.g., the use of biomass in transport. This is why the EU produced the Biomass Action Plan (BAP) in 2005 which highlighted the need for coordination of policy and estimated that biomass could contribute between 130 and 150 Mtoe of EU energy needs by 2010. In 2005, biomass contributed 81 Mtoe to EU-27 energy consumption [60], and 102 Mtoe in 2008 [60] which represents a 25.65% increase from 2005. According to EU Biomass Action Plan [52] this achievement is still a long way from reaching the EU’s biomass potential. It is clear for the EU that the technology and the efficient use of resources lie at the heart of the 20/20/20 Challenge [1]. Indeed the EU aspires to gain world leadership in the RES sector [3]. In fact, as it can be seen in > Table 9.7, several MS of the EU are among the top positions in the world in renewable energies. These top positions are not the fruit of chance, but are the result of efforts and investments in research and development of new technologies focused on an increasing improvement of the efficiency in RES. However, increases in the energy consumption are still the main obstacle to the accomplishment of the EU’s objectives.

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. Table 9.7 Top five countries in renewable energies (Adapted from REN21, 2009) Annual amounts for 2008 1

2

3

4

5

New capacity investment United States Spain

China

Germany

Brazil

Wind power added Solar photovoltaic added (grid-connected)

United States China Spain Germany

Germany

Spain

Solar hot water/heat added

China

India United States South Korea Japan Italy Germany

Brazil

France

Ethanol production Biodiesel production

United States Brazil Germany United States

China France

France Canada Argentina Brazil

Turkey

The European Strategic Energy Technology Plan (SET-Plan) considers that the key factor to reach the mentioned leadership is to accelerate the availability of energy technologies into the market and, at the same time, to engage industry in the process. In other words, these targets are achievable if adequate technological strides are taken, but it is also necessary that these technologies are well introduced into the market. This is why the Council gave to the Commission two new mandates [61]: on the one hand, the elaboration of an ‘‘Energy/Climate-Change package’’ of proposals linking the two areas. On the other hand, to elaborate a specific proposal for the development and execution of the SET-Plan. According to the Commission, ‘‘the achievement of the goals of the European energy and climate change policy necessitates the development and deployment of a diverse portfolio of low carbon energy technologies (. . .) However (. . .) the EU will continue to rely on conventional energy technologies unless there is a radical change in our attitude and investment priorities for the energy system. In response, the EU has endorsed the European Strategic Energy Technology Plan (SET-Plan) as a vehicle to accelerate the development and large scale deployment of low carbon technologies’’ [1]. In the following section, more recent and relevant initiatives adopted by the EU toward the ‘‘low carbon economy’’ are analyzed.

Instruments for an Integrated Approach to a ‘‘Low Carbon Economy’’ Programs (which provide financing) and directives (which establish obligatory mandates for the Member States) are the main instruments managed by the EU to promote RES and EE, in order to face the challenge of a sustainable and ‘‘low carbon economy.’’ These instruments can be classified into two different groups:

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– Non-technological instruments: which are political and legislative tools, such as programs and directives that try to conduct the behavior of citizenry, firms, institutions, etc., of MS – Technological instruments: which are referred to as means to achieve new and/or more efficient technologies, innovative products, etc. Of course, the potential of each kind of instrument differs. For instance, a directive transformed in law in a Member State can be a really worthwhile tool if there are the technological resources to carry out the principles of that legislative norm. Therefore, political and legislative instruments (i.e., programs and directives) are necessary but not enough to solve energy problems in the EU and vice versa, since technological instruments (based on new energy technologies to carry out RES and EE) need to be effective and establish the aid of a legislative framework. In the next sections, both types of instruments will be analyzed more deeply. The SET-Plan can be considered as the fundamental instrument to facilitate the link between technology development and its public acceptance and penetration in the market. The European Commission in collaboration with many other private and public institutions has drawn up the fundamental Technology Roadmap necessary to ‘‘turn Europe into a lowcarbon economy.’’ This indicative Roadmap ‘‘prioritises the different needs of different technologies, depending upon their state of development and maturity, balancing the short term needs against the long term innovation potential’’ [1]. It also analyzes the cost and the potential of various technologies to reduce carbon emissions, or to cover a certain share in electricity or energy consumption. To evaluate this potential, not only technological aspects are considered, but also other socioeconomic and cultural aspects; that is, the time and the challenge for the implementation of each technology. In this approach, EE is by far the cheapest and simplest way to secure CO2 reductions (especially regarding EE in buildings and transport). Later, the cogeneration and wind power technologies are the best placed technologies. Hydrogen cars and fusion technologies are placed last, while other technologies are placed in between [1]. It has to be noted that ‘‘although the presentation of the roadmaps has been harmonized as far as possible, each low carbon technology faces its own challenges, market dynamics, maturity and deployment horizon. Hence, in each case, the activities are tailored to the specific innovation needs, reflecting also non-technological barriers. Similarly, the anticipated impact of the Initiatives varies both in volume, intensity and timing’’ [1]. The implementation of the SET-Plan is based on the European Industrial Initiatives (EII), the Energy Efficiency-Smart Cities Initiative and the European Energy Research Alliance (EERA). Next, the different initiatives of the SET-Plan are described, with their estimated public and private investment needs to make the low carbon technologies affordable and competitive. (It has to be noted that ‘‘there is no directly quantifiable link between research expenditures and the value of the results obtained from research. However, as a pre-requisite for any cost competitive deployment of technologies, each roadmap presents the technology objectives that are critical for making each low carbon technology fully cost-competitive, more efficient and proven at the right scale for market roll-out’’ [1]). In any case, ‘‘this estimated budget includes the cost of research,

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technological development, demonstration and early market take-up, but the cost of deployment and market based incentives are excluded, such as feed-in tariffs’’ [62]. Also, their potential for job creation is offered [62]: (1) the European wind initiative with €6 billion and more than 250,000 skilled jobs; (2) the Solar Europe Initiative, with €16 billion and more than 200,000 skilled jobs; (3) the European electricity grid initiative with €2 billion; (4) the sustainable bio-energy Europe initiative with €9 billion, and more than 200,000 local jobs created; (5) the European CO2 capture, transport, and storage initiative with €13 billion; (6) the sustainable nuclear fission initiative with €7 billion; and (7) the fuel cells and hydrogen initiative with €5 billion for the period 2013–2020. Additionally, as EE in buildings and transport is considered the cheapest and simplest way to secure CO2 reductions, the SET-Plan includes the Energy Efficiency-Smart Cities Initiative, with an estimated budget of €11 billion and the potential of 40% reduction of GHG emissions by 2020 on participant cities and regions. As previously mentioned, the SET-Plan also proposes the European Energy Research Alliance, with the objective of ‘‘elevating cooperation between national research institutes to a new level (from ad-hoc participation in uncoordinated joint projects to collectively devising and implementing joint programmes) (...) taking ideas out of the laboratory and developing them to the point that they can be taken up by industry is a step that needs to be shortened considerably. The involvement of universities in the Alliance through the platform created by the European University Association will help to ensure that the best brains can be mobilised’’ [62].

Non-technological Instruments The European Union, according to Kyoto Protocol, is committed to reducing its GHG emissions, as a whole, by 8% compared to 1990 emissions [63]. However, as it has been mentioned, the European Council of March 2007 made the firm commitment to reduce the overall GHG emissions of the Community by at least 20% below 1990 levels by 2020 [56]. This was not the sole objective of the Council, as it committed to two other objectives: 20% of RES by 2020 and a 20% reduction of energy consumption. These last objectives, however, will make it possible to achieve the 20% reduction of GHG objective, which means that the three targets are closely linked. > Figure 9.1 shows that the EU-25 has obtained a 6% reduction of GHG from 1990 to 2005. Considering the objective of 20% reduction compared to 1990 emissions level by 2020, the EU has to reduce the GHG 14% from 2005 to 2020 [64]. In 2007, EU-27 had already reduced its emissions 9.32%, while the EU-25 had got a reduction of 7.87% compared to the 1990 level [65]. As it is set by Decision 406/2009, each MS must achieve a different objective of emissions reduction ‘‘based on the principle of solidarity between MS and the need for sustainable economic growth across the Community, taking into account the relative per capita GDP of MS.’’ As a consequence, each country has its own reduction objective to 2020 compared to 2005 [66]. The limits between Member States vary from
20% and +20% (e.g.,
20% for Luxembourg, +20% for Bulgaria, and
10% for Spain [66]

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GREEN HOUSE GAS (GHG) EMISSION TARGET –20% below 1990 GHG emission level

–14% below 2005

EU ETS sectors –21% below 2005 Directive 2009/29/EC

EU non ETS Sectors (Transport, buildings, heating...) –10% below 2005 Decision 406/2009/EC

TARGET FOR 27 EU MEMBER STATES from –20% to +20% Source: EU, 2008a.

. Fig. 9.1 Greenhouse gas emission target for European Union in 2010 [64]

(see > Fig. 9.1). It must be pointed out ‘‘The sharing of GHG reduction efforts between MS is determined solely for sectors not covered by the EU ETS’’ [64]. MS are responsible for the fulfilment of this objective through the implementation of national measures, that is, through the promotion of RES and EE. As it is shown in the > Fig. 9.1, in order to perform the 20/20/20 mandate, the EU has established a gradual and foreseeable trajectory of GHG emissions reduction. Directive 2003/87/EC [44] establishes that all sectors of the economy should contribute to emission reductions in order to achieve the objective of a 20% reduction of GHG by 2020 compared to 1990 levels. According to other EU documents [64], the total effort for GHG reduction needs to be divided between the EU-ETS and non-ETS sectors. EU-ETS sectors are the industrial installations included in the European Union Emission Trade System; that is, the sectors included in Directive 2003/87/EC and following directives (for more details about these directives see > section on ‘‘Main Barriers for RES and EE Technologies and Instruments to Remove Them’’), which must reduce their emissions by 21% compared to 2005 [45]. There are few sectors that take part in the EU-ETS (energy activities such as combustion installations, refineries, production and processing of ferrous metals, mineral industry, industrial plants for the production of paper, air transport, etc.), but all together these sectors represented approximately 42.9% of the EU-27 overall emissions in 2007 and 42.68% in EU-25 [65].

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On the other hand, there are the non-ETS sectors or ‘‘diffuse sectors.’’ The ‘‘diffuse sectors’’ are a wide range of sectors that are made up of many small-scale GHG emitters such as transport (cars and trucks), buildings (especially heat consumption), services, small industrial facilities, agriculture, and waste, that together represent large amounts of emissions (57.1% of the EU-27overall emissions and 57.32% in EU-25 in 2007 [65]). Non–EU-ETS sectors should reduce their emissions around 10% compared to 2005 by 2020. Regarding the ‘‘diffuse sectors,’’ it must be taken into account that, while access to energy is not only an important but also a strategic factor to local and/or regional economic development, participation in the decision process regarding buildings and transport and services sectors of local and regional agents (municipalities, citizens, firms, etc.) is necessary for a sustainable progress. Indeed, the EU ambitious objectives to mitigate climate change and become a world leader in renewable energy will only be possible if local and regional authorities take actions to implement locally the national regulations, and if they consider how their actions influence the implicated parts [23]. It must be remembered that the most profitable way for both the EU-ETS sectors and non–EU-ETS sectors to perform their GHG reduction objectives (21% and 10%, respectively) is basically through the promotion of EE and RES [21, 23, 31], indeed, the EU-ETS is considered only as an additional measure applicable to the EU-ETS sectors, that is, the EU-ETS sectors should reach most of their CO2 emissions reductions through improvements in EE and the development of RES, and should purchase as few CO2 permits as possible. > Figure 9.2 (which is not exhaustive) shows the most important legislation for the consecution of EU targets regarding climate change and energy. On the left side all legislation and tools that affects the EU-ETS sectors is shown. The right side of the figure represents all instruments that affects the ‘‘diffuse sectors.’’ Notice that many of the legislations focused on the promotion of RES and EE affect simultaneously the ‘‘diffuse sectors’’ and ‘‘nondiffuse sectors.’’ Those elements with an asterisk constitute the legislation and tools adopted by the EU for the achievement of the ‘‘20/20/20’’ mandate, and comprise part of the ‘‘Energy/ Climate-Change’’ package [53, 61]. The rest of the elements conform to the legislation which existed previously to the cited package, but which is also fundamental for the accomplishment of the established targets. In the following lines, some relevant legislation forming part of the ‘‘Energy/Climate package’’ is described (for more details of some of these directives see > section on ‘‘Main Barriers for RES and EE Technologies and Instruments to Remove Them’’): Directive 2009/29/EC, which amends previous legislation on the matter, is the most recent legislation adopted on the emission trading into the EU. > Figure 9.2 shows that it was through Directive 2003/87/EC [44] and Directive 2004/101/EC [67] that the link between the EU-ETS and the other two ‘‘Kyoto Flexible Mechanisms’’, that is, the CDM and the JI, was established. The EU adopted in 2009 the Directive 2009/28/EC on the promotion of the use of energy from RES [23]. ‘‘Energy from renewable sources means energy from renewable non-fossil sources, namely wind, solar, aero-thermal, geothermal, hydrothermal and ocean energy, hydropower, landfill gas, sewage treatment plant gas, biogases, and biomass.

Promotion of Renewables and Energy Efficiency by Politics

*RENEWABLE ENERGY DIRECTIVE 2009/28/EC

*RENEWABLE ENERGY DIRECTIVE 2009/28/EC ACTION PLAN FOR EE + MS EFFORTS COM/2008/772/final ELECTRICITY FROM RES DIRECTIVE 2001/77/EC CO-GENERATION DIRECTIVE 2004/8/EC ENERGY SERVICES DIRECTIVE 2006/32/EC

9

ACTION PLAN FOR EE + MS EFFORTS COM/2008/772/final

*EMMISIONS TRADING SISTEM DIRECTIVE EU/ETS

DIFUSSE SECTOR: BUILDINGS AND TERTIARY SECTOR

2009/29/EC Reduction target for affected sectors for 2020: –21%

ECOLOGICAL DESIGN DIRECTIVE 2005/32/EC

*CO2 CAPTURE & STORAGE DIRECTIVE 2009/31/EC CONNECTIONS WITH KYOTO PROTOCOL FLEXIBILITY MECHANISMS

EMMISSIONS ALLOCATION PLAN

ENERGY SERVICES DIRECTIVE 2006/32/EC

EE OF BUILDINGS DIRECTIVE 2002/91/EC and *Recast 2010/31/EU *STATE AID IP/08/80

Reduction target for 2020: –10%

*RENEWABLE ENERGY DIRECTIVE 2009/28/EC *NEW PASSENGER CARS REGULATION 443/2009 *FUEL QUALITY DIRECTIVE 2009/30/EC

2003/87/EC EU/ETS 2004/101/EC FLEXIBILITY MECHANISMS

CO-GENERATION DIRECTVE 2004/8/EC

ECOLOGICAL DESIGN DIRECTIVE 2005/32/EC *MEMBER STATES EFFORT DECISSION 406/2009

*STATE AID IP/08/80

ELECTRICITY FROM RES DIRECTIVE 2001/77/EC

*EFFICIENT VECHICLES DIRECTIVE 2009/33/EC

DIFUSSE SECTOR: TRANSPORT

BIOFUELS DIRECTIVE 2003/30/EC ACTION PLAN FOR EE + 2020 OBJECTIVE COM/2008/772/final ENERGY SERVICES DIRECTIVE 2006/32/EC ECOLOGICAL DESIGN DIRECTIVE 2005/32/EC

Source [68]. *STATE AID IP/08/80

. Fig. 9.2 Climate and energy package: interaction with other regulations [68]

Biomass means the biodegradable fraction on products waste and residues (. . .) as well as the biodegradable fraction of industrial and municipal waste’’ [23]. This directive does not distinguish between conventional and nonconventional RES. A novelty of this directive compared to previous directives on the matter is that it establishes different nationally binding objectives for the MS (from 8.5% to 20%), with an overall target of increasing the level of renewable energy in the EU’s energy overall mix to 20% (with a minimum target for biofuels of 10% for all MS). According to the Directive, all MS had to notify the Commission by June 2010 their national renewable energy action plans. These plans must include not only the share of RES, but also the information on what policy measures (including public aid) they will take to fulfil their

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national objectives. The directive also includes some sustainability criteria for biofuels and bioliquids. This is an example of legislation affecting the EU-ETS sectors, and also non–EU-ETS or diffuse sectors simultaneously. According to this directive, the increased use of energy from renewable sources, together with energy savings and increased energy efficiency, constitute important parts to comply with the Kyoto Protocol, promoting at the same time the security of energy supply and the technological development, and providing opportunities for employment and regional development, especially in rural and isolated areas [23]. In > Fig. 9.3 are shown two columns (same color) for the EU-27 and for each Member State, respectively. First column shows the share of electricity generated from renewable sources in 2007. The second column represents the target for 2010, which is unlikely to be achieved considering last years’ trends ([19], p. 76). In 2007, only a few MS (Germany, Hungary, and Denmark) had already achieved their target for 2010, while most of the other countries remaining far away from their targets [19]. Biomass is the predominant renewable energy source across all Member States. In fact, biomass had the fastest growing share and it delivered nearly 70% of the total renewable energy in 2007 [19]. Measures in the Transport Sector

Alongside GHG benefits, security of supply has been a principal reason for adopting the EU targets for renewable energy used in transport.

Austr

ia

80

Swe

den

70

Latvia

60

enia

gdom

Slov

akia Finla nd

d Kin Unite

nd Pola

Lithu

ania Luxe mbo urg Hung ary Malta Neth erlan ds

Italy Cypr

us

Irela nd nia Esto

Slov

ania Rom

Spain ce

ce Gree

any Germ

ublic h Rep

Fran

Denm

0(21 aria Bulg

Czec

10

Belg

ium

20

EU2

30

7201

6%)

%)

40

ark

Portu

gal

50

EU2 7200 7(15 ,

306

0 Source: Own elaboration from EUROSTAT, 2010c [69].

. Fig. 9.3 Electricity generated from renewable sources 2007 and 2010 target (% of gross electricity consumption) [60]

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Directive 2009/28/EC on RES establishes that ‘‘increasing technological improvements, incentives for the use and expansion of public transport, the use of energy efficiency technologies and the use of energy from renewable sources in transport are some of the most effective tools by which the Community can reduce its dependence on imported oil in the transport sector, in which the security of energy supply problem is most acute’’ [23]. In fact, the transport sector grew rapidly between 1995 and 2005 in the EU (goods and passenger transport grew by 31.3% and 17.7%, respectively), and this growth was predicted to continue [70]. Measures to improve fuel quality and a binding target of 10% share of renewable energy sources in transport by 2020 are part of the Climate and Energy package. The Fuel Quality Directive 2009/30/EC was amended to introduce a mandatory target for reducing the GHG intensity of fuel used in road transport, considering that road transportation dominates with 94% of total transport GHG emissions in 2007 [19]. Promotion of biofuels by MS has mainly relied on tax relief and obligations to blend, with important developments having taken place over the last years. These measures have encouraged the supply and demand of biofuels in transport. In 2007, according to MS’ reports, biofuels represented 2.6% of the total fuel consumed in transport in the EU and they accounted for 75% of renewable fuels in transport, of which 26% was imported [71]. From an economic point of view, the increasing use of biofuel has contributed to security of supply by decreasing fossil fuel and diversifying fuel consumption in the EU. Biofuel sectors have also contributed to the EU economy by generating additional jobs [72]. In addition to biofuels policies, important measures have been adopted for the transportation sector by the EU in recent years and some more will be developed in the coming years. More precisely, in 2008, the ‘‘Greening Transport’’ package was launched [73], which was accompanied by a strategy for the internalization of external costs of transport and a proposal on the charging of heavy goods vehicles for infrastructure use. This strategy should encourage the use of cleaner vehicles and improved logistics. In April 2009, Directive 2009/33/EC on the promotion of clean and energy-efficient road transport vehicles was launched to stimulate the development of a market for these vehicles. This directive is addressed to influence the market for standardized vehicles produced in large quantities such as passenger cars, buses, coaches, and trucks. Considering that clean and energy-efficient vehicles initially have a higher price than conventional ones, this directive attempts to create sufficient demand for such vehicles to ensure that economies of scale lead to cost reductions [74]. It also highlights that ensuring a sufficiently substantial level of demand for clean and energy-efficient road transport will encourage manufacturers to invest in and further develop vehicles with low energy consumption, CO2 emissions, and pollutant emissions [74]. Regulation (EC) No 443/2009 was also adopted in April 2009 with the objective to set emission performance standards in order to reduce CO2 emissions from light-duty vehicles while ensuring the adequate functioning of the internal market. It also provides an integrated legislative framework to the Community Strategy, adopted by the Commission in 1995, for reducing CO2 emissions from cars. This strategy was based on three pillars: voluntary commitments from the car industry to cut emissions, improvements in

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consumer information, and the promotion of fuel-efficient cars by means of fiscal measures. In 1998, the European Automobile Manufacturers’ Association (ACEA) adopted a commitment to reduce average emissions from new cars sold to 140 g CO2/km by 2008 and, one year later the Japanese Automobile Manufacturers’ Association (JAMA) and the Korean Automobile Manufacturers’ Association (KAMA) adopted the same commitment to be reached by 2009 [75]. In 2007, two parallel communications were adopted by the Commission, underlining that progress had been made toward the target of 140 g CO2/km by 2008/2009, but that the Community objective of 120 g CO2/km would not be met by 2012 in the absence of additional measures [75]. Therefore, this regulation, consistent with the approach under the voluntary commitments adopted by manufacturers, is aimed to achieve the Community objective by focusing on mandatory reductions of emissions of CO2 to reach an objective of 130 g CO2/km for the average new car fleet by means of improvements in vehicle motor technology. It also establishes fines for those manufacturers whose average specific emissions of CO2 exceed its specific emissions target from 2012 onward [75]. Increasing the share of renewable energy use in transport and the energy efficiency of engine and vehicle technologies will remain key EU priorities to reduce the high oil dependence in the transport sector. Measures aimed at reducing the consumption of the whole stock of cars, such as by increasing car occupancy rates and improving traffic infrastructures, also have a large potential in terms of GHG emission and fuel saving. Nevertheless, these measures require a coordinated effort at local, regional, and central government levels in terms of policies, support, and communication. ‘‘While progress is needed most rapidly in the road transport sector (due to its size and rapid growth rate) developments in other modes, notably aviation, are also important’’ [3]. Renewable Energy Used in Heating and Cooling (Residential Sector)

A complete assessment of the development of renewable energy in Europe requires the evaluation of the heating and cooling sector. According to the Environment Energy Agency [76] heating and cooling is the most significant component of household energy demand, and can vary substantially from year to year depending on climatic variations. Approximately 50% of all final energy consumption and 60% of all renewable final energy consumption is due to the heating and cooling sector [3]. Despite this relatively high share of renewable energy used by this sector, it is far from achieving its potential, partly as a result of the absence of a clear legislative framework and incentives, as well as the existence of nonmarket barriers, such as the lack of information, education, and training of the different agents implicated [3]. The heating and cooling sector depends on different renewable energy sources (biomass, solar and geothermal energy,) but is dominated by the use of biomass [3]. The main legislative instrument dealing with the energy efficiency of buildings is Directive 2002/91/EC, which came into force on 4 January 2003. As buildings are responsible for 40% of energy consumption and 36% of EU CO2 emissions, they are a key factor in the achievement to climate change and energy objectives [77]. Under this

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Directive, ‘‘the MS must apply minimum requirements as regards the energy performance of new and existing buildings, ensure the certification of their energy performance and require the regular inspection of boilers and air conditioning systems in buildings’’ [77]. On 19 May 2010, a recast of this directive on energy performance of buildings was adopted (Directive 2010/31EU) in order to strengthen the energy performance requirements and to clarify and streamline some of its provisions [78]. There is no doubt that the EU legislation and programs related to RES have provided a major boost to the development of these technologies. As stated earlier, EE is considered the cheapest and simplest way to reduce GHG emissions, reduce energy dependency, and increase competitiveness. The five pillars of the EE policy are [31]: 1. The general policy framework and actions under the European Energy Efficiency Action Plan 2. The National Energy efficiency Action Plans based on the Framework Directive on Energy Services 3. The legal framework for the most important consumption sector (buildings) and energy consuming products 4. Flanking policy instruments such as targeted financing, provision of information, and networks like the Covenant of Mayors and Sustainable Energy Europe 5. International collaboration on energy efficiency A large part of the EE legislation is oriented to establish minimum EE requirements or design standards and labeling systems to promote a more efficient consumption, especially in the residential and building sectors. But there are also other legislation measures, such as the Energy Services Directive, or the Ecodesign Directive (see > Table 9.7). According to the Commission, on current implementation trends by MS, it is clear that the 20% saving objective is in danger of not being meet, and even if it is too early to assess the full impacts, the first-hand information on the evolvement and the implementation as well as other indicators suggest that the energy saving potential is not being reached. With the existing EE measures ‘‘should achieve energy savings about 13% by 2010 if properly implemented by MS. Even if this represents a major achievement, this falls far short of what is needed’’ [31]. This is why the Commission proposes an EE package consisting of: ‘‘a proposal for a recast of the Energy Performance of buildings Directive; a proposal for a revision of the Energy Labelling Directive; a proposal for a new Directive containing a labelling scheme for tires; a Commission decision establishing guidelines clarifying the calculation of the amount of electricity from cogeneration; a communication on cogeneration’’ [31]. This new legislation being proposed follows the path of previous legislations and reinforces the existing energy labeling instruments. However, as the Commission explains, a wider application of the measures is proposed, and also some restriction for public purchases taking into account EE levels (e.g., a revised energy labeling directive is foreseen (Directive 92/75/EEC) which will identify which products will not be procured by or receive incentives for public authorities [31], which could be an effective measure. A synthesis of non-technological instruments, to achieve a low carbon economy in EU, is shown in > Table 9.8 (which is not exhaustive). Remember, though that, for the fulfilment

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. Table 9.8 Main non-technological instruments (political and legislative instruments) to promote RES and EE in the European Union Non-technological instruments Promotion of the use of energy from renewable sources Directive 2009/28/EC

Regarding renewable energy sources

It fixes a target of 20% share of energy from renewable sources in the EU gross final consumption of energy in 2020. It also fixes mandatory national targets, establishing rules for a sustainable regime for biofuels and the ‘‘guarantees’’ of origin. It demands improvement for access of RES to the grids and in the access of information and training regarding RES. Intelligent Energy-Europe Intelligent Energy-Europe is the EU’s tool for funding action to IEE (European Parliament and move us toward a more intelligent energy system in Europe, Council 2006) [79] focusing on saving energy and reducing CO2 emissions, and promoting renewable energy sources through the removal of non-technological barriers in the market. Regarding Energy Efficiency It focuses on creating a common framework to promote the Energy performance of improvement of the energy performance of buildings. The Buildings directive requires MS to: (a) apply a methodology of Directive 2002/91/EC; calculation of the energy performance of buildings; (b) Recast: 2010/31/EU establish minimum requirements on the energy performance of new buildings and large existing buildings for renovation; (c) emit an energy performance certificate when buildings are constructed, sold, or rented out; and (d) carry out regular inspection of boilers and of air-conditioning systems in buildings. It attempts to provide a framework for the promotion of this Promotion of cogeneration efficient technique in order to overcome still existing barriers, electricity to advance its penetration in the liberalized energy markets Directive 2004/8/EC and to help mobilizing unused potentials. The main objectives are: (a) the establishment of a harmonized method for calculation of electricity from cogeneration and necessary guidelines for its implementation and (b) to guarantee the origin of electricity produced from high-efficiency cogeneration. Framework for the setting of It establishes that information concerning the product’s ecodesign requirements for environmental performance and EE must be visible, if possible, on the product itself, thus allowing consumers to energy-using products compare before purchasing. Other objectives are to ensure/ Directive 2005/32/EC [80] facilitate the free movement of those products within the internal market. Closely related to this directive are: 2002/40/EC on energy labelling of household electric ovens and 2003/66/EC on energy labelling of household electric refrigerators and freezers.

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. Table 9.8 (Continued) Energy end-use efficiency and To promote the supply side of energy services and create stronger incentives for the demand side. Its purpose is to energy services enhance the cost-effective improvement of energy end-use Directive 2006/32/EC [81] efficiency by means of: (a) providing the necessary indicative targets and mechanisms to remove existing market barriers and imperfections that impede the efficient end use of energy and (b) creating the conditions for the development of a market for energy services and for the delivery of other EE improvement measures to final consumers. Action plan for energy Its purpose is to mobilize society and to transform the internal efficiency energy market in a way that provides EU citizens with the COM (2006) [21] 545 final most energy-efficient infrastructure (including buildings), products (including appliances and cars), and energy systems in the world. It focuses on taking action and controlling consumption and supply in order to save 20% of annual consumption of primary energy by 2020, which corresponds to achieving approximately a 1.5% saving per year up to 2020. Integrating instruments Investing in the development of low carbon technologies (SET-Plan) COM (2009a) [1] 519 final

Renewable energy sources and energy efficiency The SET-Plan is the pillar to turn Europe into a low carbon economy, through the development and deployment of a diverse portfolio of low carbon energy technologies. The SET-Plan is based on the European Industrial Initiatives (EII) including EE-Smart Cities Initiatives and the European Energy research Alliance (EERA). The SET-Plan has analyzed the cost, but also the potential of various technologies in order to reduce carbon emissions, or to cover a certain share in the electricity or energy consumption. To evaluate this potential, not only technological aspects are considered, but also others socioeconomic and cultural aspects; that is, the time and the challenge for the implementation of each technology are considered. Thus, the SET-Plan attempts integrating the technological and non-technological issues and instruments of the EU energy policy.

From own elaboration

of the established objectives, the EU offers specific funding designed to promote education, training, diffusion of information, etc. Actually the Competitiveness and Innovation Framework Programme is in force for the period 2007–2013, with an estimated overall budget of 3,621 million euro. This Framework Programme will be implemented by the following specific programs: (1) Entrepreneurship and Innovation Programme, with 60% of the overall budget; (2) Information and Communications Technologies (ICT) Policy Support Programme, with 20% of the overall budget; and (3) Intelligent Energy-Europe

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Programme (IEE), with 20% of the overall budget. This is the specific program destined to support energy-related actions, especially those that promote RET and EE [79]. The EII program is the most important tool destined to remove the non-technological barriers that RES and EE have to face. This is why it supports projects related to diffusion of information and awareness, improvement of education, etc.

Technological Instruments The Energy Challenge must be based on new renewable and efficient technologies since technology can play an important role in reducing the energy intensity of an economy [82]. Both, energy technology and the innovation processes, have structural weaknesses, such as long lead times for new technologies to penetrate in mass into the market, locked-in infrastructure investments, diverse market incentives, and network connection challenges. Programs supporting ‘‘clean technology’’ development and diffusion are a traditional focus of energy and environmental policies because energy innovations face barriers all along the energy-supply chain, from research and development (R&D), to demonstration projects, to widespread deployment. It is vital that further investments in R&D are made, and direct government support to hasten deployment of new technologies, due to a lack of industry investment and motivation, is often necessary ([83], p. 307). Furthermore, the market take-up of new energy technologies is additionally hampered by the nature of the technologies themselves, because they are generally more expensive than the technologies they replace. There is therefore a need to create a long-term EU framework for energy technology development, and for economic and environmental impacts. In this respect, the European Strategic Energy Technology Plan (SET-Plan) is the technology pillar of the EU energy and climate policy. Similarly, MS are also unlikely on their own to be willing or able to accelerate technology development over a sufficiently broad portfolio of technologies. The European Strategic Energy Technology Plan 2 is the EU’s response to the challenge of accelerating the development of low carbon technologies, leading to their widespread market take-up. It sets out a vision of a Europe with world leadership in a diverse portfolio of clean, efficient, and low carbon energy technologies as a motor for prosperity and a key contributor to growth and jobs. It proposes joint strategic planning and more effective implementation of programs. It now needs to be taken forward to implementation. There are different possible pathways to a low carbon economy. Clearly, no single measure or technology will suffice, and the precise mix in each country will depend on the particular combination of political choices, market forces, resource availability, and public acceptance. The Research and Technological Development (RTD) Framework Programmes are multi-annual programs where the EU scientific objectives and research priorities are established for the following years. These programs also include the specific action lines to be developed and their financial allocation. All actions financed by RTD Framework Programmes have to be focused on the development of new technologies, in precompetitiveness phase. The interest of the EU in promoting the RES and energy clean

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technologies was already highlighted in previous RTD Framework Programmes, as, for example, the VI Framework Programme for the period 2002–2006 was adopted, with a total budget of €16,270 million. The VII RTD Framework Programme was adopted for the period 2007–2013 with a maximum budget of €50,521 million, where €2,751 million are assigned for research on nuclear power (e.g., ITER fusion project) apart from the Euratom Specific Program for nuclear power. ‘‘Energy’’ (included as a thematic area in the ‘‘Co-operation Programme’’) is one of the main areas to be promoted with a budget of €2,350 million. The objective in this area is to adapt the current energy system into a more sustainable one by developing: hydrogen and fuel cells; renewable electricity generation, renewable fuel production, and renewable for heating and cooling; CO2 capture and storage technologies for zero emission power generation; clean coal technologies; smart energy networks; EE and savings; and knowledge for energy policy making. It has to be noted that the mentioned ‘‘Co-operation Programme’’ also includes the ‘‘Environment’’ (including Climate Change) and ‘‘Transport’’ issues, which could be taken into account for financing topics related to the RES and EE [6].

Conclusions The current energy model, based on fossil fuels and nuclear energy, has been the basis for the functioning and development of modern industrial society. The threats of this model (environmental problems, exhaustion of fossil sources, possible inflation process and loss of competitiveness, dependency toward energy export countries, etc.) have forced a change in the EU’s traditional energy strategy (which was focused on the security of supply). From the 1990s, the key objectives are security of supply, competitiveness, and environmental protection, making RES and EE the basis for this strategy. The European Council of March 2007 established the 20/20/20 unilateral mandate, which calls for a reduction of GHG by 20% compared to 1990 levels, increasing the level of renewable energy in the EU’s overall mix to 20% and saving 20% of the energy consumption compared to projections for 2020. In order to achieve the mandate objectives, the ‘‘Energy/Climate-Change Package’’ was adopted in 2009. This package, complementing the previous existing legislation on climate change and RES and EE, constitutes the necessary set of tools for achieving the mandate. In relation with the promotion of RES, an important novelty of Directive 2009/28/EC from previous legislation is the establishment of different nationally binding targets, with an overall target of 20% in the EU’s energy overall mix by 2020. However, the Member States have the responsibility to elaborate their national renewable energy action plans. Currently, biomass is the single largest renewable energy source in absolute terms, and it is expected to contribute to around two-thirds of the estimated renewable energy share in 2020. However, good management of this resource is fundamental. In this sense, LCA evaluation approaches should be taken into account to prevent serious environmental problems. The EE is considered the cheapest and the simplest way to reduce GHG, to reduce energy dependency, and to increase competitiveness. However, bearing in mind current

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implementation trends by Member States, it seems that the 20% saving objective is in danger of not being met. Even if it is too early to assess the full impact of current legislation, the energy saving hoped for is not being reached. With the existing EE measures, 13% of EE could be met, which is still not enough to reach the 20% goal. The Commission has proposed a new EE package. Nevertheless, the proposed new legislation follows the path of previous legislation, reinforcing the existing energy labelling instruments. It can be affirmed that current EU’s low carbon energy strategy is coherent and well developed, combining funding measures with legislation and allowing Member States to offer public aid for RES and EE measures, industries, and products. The EU aspires to gain leadership in the low carbon economy. That is why the EU has established the basis to accelerate a massive penetration of RES in the market. However there are still natural barriers (e.g., technology), and artificial barriers (e.g., market distortion, administrative barriers, etc.) which make the process difficult and delay this penetration. zThese barriers, together with the energy dependency of the EU, make it easy to understand why the EU research funds are focusing on RES and EE technologies, but they also take into account some technologies linked to traditional energy sources (as the CO2 capture and storage technologies, clean coal technologies, smart grids, and research on new nuclear technologies). Regarding energy saving and energy efficiency, structural changes are still needed to be able to change current energy consumption patterns. However, the adoption of a carbon tax for the EU has not been possible to date. Even if some advances have been reached on EE, the EU must still push additional strong measures. Although a certain decrease of energy consumption has been reached in 2007 and 2008, part of these reductions may have their origin in the economic crisis. If the reduction of 20% of energy consumption is not achieved for 2020, reaching the other two objectives (20% of RES and 20% of GHG reduction) will face certain additional difficulties. More efforts and structural changes in favor of energy saving and energy efficiency seem to be still necessary.

Acknowledgments This work has been possible thanks to the collaboration of the Energy Working Group, which belongs to the Chair of International Relations (Social Sciences Faculty) of the University of the Basque Country (UPV-EHU). Special thanks to Gonzalo Molina Igartua and Angela Marı´a Mestizo for their inestimable help and collaboration.

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10 Implications of Climate Change for the Petrochemical Industry: Mitigation Measures and Feedstock Transitions Simon J. Bennett Imperial Centre for Energy Policy and Technology, Imperial College, London, UK Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321 The Chemical Industry Value Chain: From Feedstocks to Final Users . . . . . . . . . . . . . . 323 Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326 Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328 Coal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 Biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331 Twin Concerns: Climate Impact and Resource Sustainability . . . . . . . . . . . . . . . . . . . . . . . 333 Climate Impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333 Primary Sources of Greenhouse Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334 Geographical Variations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336 Future Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336 Resource Sustainability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 Waste Management and Recycling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342 Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_10, # Springer Science+Business Media, LLC 2012

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Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343 Combined Heat and Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344 Carbon Dioxide Capture and Storage (CCS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346 Biorefineries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354

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Abstract: For the past 50 or more years, society has been increasingly reliant on the products of the organic chemical industry to supply the clothes we wear, the food we eat, our health, housing, transportation, security, and other commodities. Approximately 92% of organic chemical products are produced from petroleum, that is, fossil, or mineral, oil, and gas. In addition, these same resources are generally used to provide the large quantities of process heat and power needed by the industry. In the modern petrochemical industry, oil and gas inputs for both raw material and process energy compose around 50% of the operating costs. The result is that not only is the chemical industry (including petrochemicals) the industrial sector with the highest emissions worldwide, it is also very vulnerable to variations in fossil fuel prices and carbon prices. Thus, efficiency has long been a major factor in determining competitiveness in petrochemicals, and the sector has a high success rate in reducing its energy intensity. Despite this, over the past decade, while total use of oil has grown globally at a rate of 1.4% per year over, the use of oil for chemical feedstocks has grown at about 4.0% per year. Reducing greenhouse gas (GHG) emissions in an industry that is so dependent on fossil fuels presents a significant challenge that has begun to receive serious attention from researchers and businesses alike. This chapter introduces the history of the modern chemical industry and the establishment of its close relationship with the oil industry – a relationship that has recently come under strain. It goes on to describe some of the major chemical processes, their GHG emissions, and their geographical variations. The main focus of the chapter is a discussion of the benefits and challenges of three main technological mitigation options: efficiency gains, CO2 capture and storage, and feedstock switching. The interaction of these options with the main climate policy instruments in Europe, and worldwide, is considered. The concept of ‘‘biorefining’’ for bio-based chemicals is given particular prominence for its potential to deliver renewability, low CO2, and energy/feedstock security in the long term. However, establishing new production routes based on biomass in Europe is shown to face considerable social, technical, and economic obstacles to reaching a scale that can contribute valuable emissions reductions.

Introduction Many of the chapters in this book focus on the potential for low-carbon technologies to reduce the rate of emissions of greenhouse gases (GHG) from energy production and use. Combustion of fossil fuels for energy is the major source of GHG worldwide, and, along with energy efficiency and land use, is a primary target for climate change mitigation efforts. Low-carbon energy technologies can be applied in all the key energy-using sectors, including power production, transport, residential applications, and industry. Several of these technologies have the potential to be applied in multiple applications and create linkages between the sectors. This could lead to a new, integrated and sustainable energy landscape in the place of the current fossil fuel-based system. An example of increased integration is the further electrification of transport and the necessary changes to the

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power grid to deliver the ‘‘fuel’’ from both centralized renewable electricity from offshore wind farms and decentralized supply and demand management from the residential sector. This chapter takes a look at climate mitigation from the perspective of an industrial sector that has already for many decades been highly integrated with the prevailing energy system. Because it derives both its energy requirements and raw material from petroleum, the organic chemical industry is both a heavy emitter of GHG and also highly dependent on fossil fuels. In the modern petrochemical industry, oil and gas inputs for both raw material and process energy compose around 50% of the operating costs. For the past 50 or more years, society has been increasingly reliant on the products of the organic chemical industry to supply the clothes we wear, the food we eat, our health, housing, transportation, security, and other commodities [1]. The global organic chemical industry is highly diverse. Derivative products from petrochemical feedstocks are pervasive throughout the economy. They are transferred between firms within the value chain for further processing, such that the industry consumes over one fourth of its own production. Products can be bulk or speciality. Bulk organic chemicals are generally commodity products that compete on price and are produced in large volumes. They include the major platform chemicals such as ethylene, propylene, and benzene, and their immediate derivatives. Methanol, ethanol, commodity polymers, fabrics, and plastics are also included. Speciality chemicals cater to custom markets and generally compete on technological expertise that provides a greater added-value to their products. End products include speciality plastics, fabrics, paints, pigments, and cosmetics. Approximately 92% of chemical products are produced from petroleum, including natural gas. Coal delivers 1.3% of chemical feedstock globally, by energy content [2]. The total use of oil has grown globally at a rate of 1.4% per year over the past decade and the use of oil for chemical feedstocks has grown at about 4.0% per year (> Fig. 10.1). De Vries et al. [3] have highlighted that so far, unlike other materials consumption trends, demand for chemical products such as plastics tends to continually rise with GDP and has not yet reached a saturation point at which consumption stabilizes in the face of increasing wealth. In the USA, approximately 3.4% of a barrel of oil is incorporated into chemical products, while nearly 20 times as much (70.6%) goes to fuel uses [4]. In Europe, the corresponding figure is 9% for chemical feedstocks, as oil (naphtha) dominates natural gas for bulk chemical production [2]. The overall values of the industries are similar, however, with US petrochemicals (excluding pharmaceuticals) returning a pre-tax profit of $375 billion and oil-derived fuels having pre-tax profits of $385 billion [4]. The organic chemical industry is being pressed to revise its energy use for the future, for at least three reasons. Concerns about volatile feedstock costs and potential oil supply constraints have instigated a debate about the sustainability of petroleum-based products [5, 6]. High oil prices at the beginning of the twenty-first century have accelerated the eastward migration of the industry toward low-cost liquefied petroleum gas (LPG) feedstocks. LPG is an associated by-product of oil refining and is thus a cheap resource in the Middle East where oil production costs are low, in comparison to naphtha feedstocks in Europe, or natural gas in the USA, which more closely follow global oil

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10

4

3

2

1 1971

1976

1981

1986

1991

1996

2001

Oil use for chemical feedstock (1 = 60 million tonnes) Oil use for fuel (1 = 2240 million tonnes)

. Fig. 10.1 Global growth in oil use for chemical feedstocks and energy, in % per year [2]

and gas price trends. Thus, energy efficiency and alternative feedstocks have serious economic drivers as well as drivers relating to climate change and security of supply, especially in Europe and North America. This chapter introduces the history of the modern chemical industry and the establishment of its close relationship with the oil industry – a relationship that has recently come under strain. It goes on to describe some of the major chemical processes, their GHG emissions, and their geographical variations. The main focus of the chapter is a discussion of the benefits and challenges of three main technological mitigation options: efficiency gains, CO2 capture and storage, and feedstock switching. The interaction of these options with the main climate policy instruments in Europe, and worldwide, is considered. The concept of ‘‘biorefining’’ for bio-based chemicals is given particular prominence for its potential to deliver renewability, low CO2, and energy/feedstock security in the long term. However, establishing new production routes based on biomass in Europe is shown to face considerable social, technical, and economic obstacles to reaching a scale that can contribute valuable emissions reductions.

The Chemical Industry Value Chain: From Feedstocks to Final Users Organic chemicals are those that contain a structure based on carbon, usually in combination with hydrogen. Although there is no official definition, organic chemicals are widely understood to be the carbon-containing compounds associated with life, such as

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. Table 10.1 Formulae and structures of the main hydrocarbons used in fuel and chemical production (With the exception of methane, only carbon–carbon bonds are shown as lines. Hydrogen atoms are omitted) Group

Example hydrocarbons

Formulae

Natural gas

Methane

CH4

Structures H

H

H H

Olefins

Ethylene, propylene, butadiene

C2H2, C3H6, C4H6

LPG

Ethane, propane, butane

C2H4, C3H8, C4H10

BTX

Benzene, toluene, xylenes C6H6, C7H8, C8H10

Gasoline Octane, plus a variety of saturated and unsaturated hydrocarbons Diesel Cetane, plus a variety of saturated and unsaturated hydrocarbons Coal 60–90% carbon

C8H18, other C4 to C12

C16H18, other C8 to C21

Approximately C135H96O9NS

OH

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sugars, proteins, or the hydrocarbons present in fossil fuels. Coal, oil, and gas contain largely pure hydrocarbons with a carbon backbone and without a high prevalence of heteroatoms such as oxygen, nitrogen, or metals. > Table 10.1 shows some relevant molecular structures. The complex value chain for chemical production from fossil fuels is exemplified by the production of acrylonitrile butadiene styrene (ABS) rubber (> Fig. 10.2). The fundamental building block for this material is butadiene, which is used to make polybutadiene. Hydrocarbon feedstock, such as LPG or naphtha, is first cracked to provide the unsaturated platform chemicals (olefins) ethylene, propylene, and butadiene. These primary bulk chemicals are normally produced at an integrated petrochemical and refining site. Crude butadiene is then separated using solvent extraction and the crude butadiene can be shipped or piped to an extraction unit, although most extraction units are located close to an olefin cracker because butadiene is gaseous and energy is required for its liquefaction and transport. Butadiene monomer is polymerized to polybutadiene, which is subsequently copolymerized with styrene and acrylonitrile to make ABS resin. ABS resin is sold to manufacturers who wish to use the light, rigid, insulating, recyclable thermoplastic in car parts, pipes, and electronics products for sale to end users. ABS is even used in some tattoo inks. The important aspects of this supply chain are, firstly, that downstream users of butadiene, polybutadiene, and ABS are usually very different firms to the major petrochemical companies that produce the primary bulk chemicals [7]. Secondly, styrene and acrylonitrile are also both produced from olefins: styrene from ethylene and acrylonitrile from propylene. This demonstrates the high levels of integration of each step in the value chain and the inherent complexities in influencing changes in any of these steps, which each use large amounts of process energy usually derived from petroleum. One kilogram of ABS requires approximately 2 kg of petroleum in feedstock and energy.

+

Crude oil (distillation products)

CN

Steam cracking

Energy

Energy

Energy n

x CN

. Fig. 10.2 Synthesis of ABS

y

z

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Oil In 2006, 267 million tons (Mt) of oil products were used for chemical feedstock worldwide, representing approximately 7% of all crude oil consumed [8]. A similar amount was used by the petrochemical industry as process energy, although exact figures are unavailable, partly due to the problem of allocating energy balances between the various processes of a refinery and petrochemical site. Crude oil is first distilled to separate the major components, which are further processed to deliver the liquid fuels required to power our transport infrastructure. In terms of tonnage, the primary energy products are diesel (31%), gasoline (25%), jet fuel (6%), plus residual fuel oil used in power generation (15%). The proportions of the different products are determined by the nature of the oil – whether it contains mostly short- or long-chain molecules – but refinery operators have some flexibility to manipulate these values to meet demand. This is evident from a brief consideration of the history of oil demand and supply. In 1850 when Scotsman James ‘‘Paraffin’’ Young first patented oil distillation, it was the illuminating properties of the kerosene product that ensured his technology a bright future [9]. Throughout the supremacy of Standard Oil in the early US oil-refining business it was liquid kerosene lamp fuel that determined how refineries were designed. Kerosene was the only valuable product of otherwise dirty and unpleasant crude. The development of the internal combustion engine had demonstrated a use for one of the other distillates, but when motoring really took off in the 1920s and 1930s there was not enough petrol by-product to meet demand [10]. The story of the oil refinery is one of adjustment to new technologies that maximize output of products for the most attractive markets. Thermal cracking increased the petrol yield and its replacement with catalytic cracking opened the way for selling higher purity coproducts to the chemical and electricity industries, among others [11]. The use of oil for chemical production began in the USA with the manufacture of ethylene derivatives for solvents and, especially, ethylene glycol and tetraethyl lead, whose manufacture for antifreeze and antiknocking went hand in hand with the manufacture of gasoline for the huge expansion in automobile ownership in the 1920s. The feedstock was primarily refinery off-gases, which were in plentiful supply adjacent to oil refineries on the Gulf Coast of the USA [12]. Consequently, the history of petrochemicals is one of close interaction with the oil refining industry. At each turn, innovative chemists found ways of tailoring fuel products to the needs of new engine technologies, such as high octane fuel for military aircraft in the 1930s [13], and found new outlets for unused distillation fractions as chemical products. The early ethylene-based products built on acetylene lighting technology and targeted existing product families like solvents, surfactants, and lubricants. These product families were expanded to integrate other olefin raw materials, for example, isopropyl alcohol from olefinic propylene was Standard Oil’s first petroleum-based product in 1920 [14]. They were predominantly based on small reactive molecular entities. A major revolution in organic chemical production occurred in the mid-1930s with breakthroughs in the field of polymer science. The theory developed by Hermann Staudinger revealed that small reactive chemicals could be joined together purposefully

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to synthesize products with known properties. He suggested that it ‘‘is not improbable, that sooner or later a way will be discovered to prepare artificial fibers from synthetic highmolecular products’’ [15:99]. Confirmation of the theory was delivered by the synthesis of nylon by DuPont shortly afterward. Nylon and polyethylene played highly significant roles in pushing petrochemicals into markets where they could displace natural products such as rubber, wood, and metal. The effectiveness of these materials during World War II opened up the prospect of almost limitless demand for olefins, altering the economics of refining and ensuring that petrochemical complexes would be built alongside refineries in the USA from the 1940s onward. The experience in Europe was markedly different and European petrochemicals production did not catch up with the USA until the 1950s. Before North Sea oil and gas was discovered in the 1960s, Europe did not produce oil to fuel its vehicles. Gasoline was imported from North America and Russia and so a ready supply of olefin by-products was not available. Furthermore, the two major energy using European nations, Germany and the UK, were reluctant to exchange their leadership in coal-based technologies to become reliant on imported fuel and feedstocks [16]. Decisions to support coal-to-oil conversion, alcohol motor fuel, and overseas oil exploration were influenced heavily by governmental attempts to steer technological change toward policy priorities including securing energy supplies, supporting troubled industries, and addressing unemployment. This process was accompanied by the attempts of industrialists to steer policy priorities toward maintaining or developing their preferred technologies [17]. In the UK, ICI’s Chairman Alfred Mond expressed his belief in 1927 that ‘‘not only oil, but the whole field of organic products will be based upon coal as a raw material in the near future’’ [18:84]. Consequently, when ICI decided to invest in petrochemicals after the War, they did so not in collaboration with BP – the major British oil company that was simultaneously moving some refining operations from Iran to Scotland – but as a stand-alone chemicals plant near their existing coal-based operations. As a result, ICI chose to import naphtha for cracking to olefins. Naphtha is a liquid by-product of oil refining that can be transported by ship. This was a novel approach, and reflected the value that ICI and the British government placed on maintaining independent industrial enterprises. The UK continued to lead Europe in petrochemicals, especially as Germany remained committed to its indigenous coal reserves as it rebuilt its economy after the War. The current configuration of European crackers to operate on naphtha is a reflection of this history. In the Middle East, especially Saudi Arabia, exploitation of abundant sources of LPG has been a relatively recent development. This is because petrochemicals production requires heavy investment in local infrastructure; this involves a more complex industrial strategy compared to the rapid returns delivered by investment in oil production and export. The lack of local demand for high-value chemical products also played a part in the delay in investment. However, European naphtha crackers are now relegated to being the marginal suppliers of ethylene and propylene and as oil prices are projected to rise over coming decades, the predominance of LPG is likely to become further entrenched [19]. In summary, the current utilization of petroleum as the major organic chemical feedstock and the options for greater sustainability must be understood in the context

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of the close development of petrochemicals with oil refining for fuels production. The integration of these two industries determines the technologies, product mixes, and economics of organic chemicals production. It has resulted in highly efficient manufacturing complexes that have different designs, often resulting from 5 decades of technical evolution.

Gas Although 5.5% of all natural gas is currently used for chemical feedstock, the strength of the carbon–hydrogen covalent bond in methane is among the strongest in all hydrocarbons, and thus its use as an organic chemical building block is limited [8]. However, natural gas is the primary source of hydrogen worldwide, through a process of steam reforming of methane to hydrogen and carbon dioxide. Hydrogen produced via this method is widely used in the chemical industry, in particular for production of ammonia by the Haber process. Of the 38 Mt of hydrogen produced each year, approximately half is used for ammonia, 80% of which is processed to fertilizers [20, 21]. Because of the production of carbon dioxide as a by-product of steam reforming, and the energy intensity of the Haber process, ammonia production in Europe emits approximately 1.3 t of CO2 per ton of ammonia [22]. Where it is readily available, natural gas is an attractive source of carbon for organic chemical feedstocks. Its use would be likely to be associated with lower CO2 emissions than LPG or naphtha feedstocks and would not be reliant on the markets for other petroleum refinery products. Thus, the economic conversion of methane to useful hydrocarbon building blocks, such as olefins, is an ongoing area of research [23]. Aside from use as a feedstock, natural gas is commonly used to provide the process heat and electricity that powers petrochemical facilities (> Table 10.2). Heat is used in all . Table 10.2 Fossil fuel consumption figures for the OECD in 2007 [52] Energy used by chemical industry (including Total consumption petrochemicals) (million TJ) (million TJ) Oil and oil products Natural gas Coal

95.2

11.2

Used as organic chemical feedstock (million TJ) 10.0

Percentage of total consumption used by chemical industry (including petrochemicals) 11.8

Percentage of total consumption used as organic chemical feedstock 10.5

59.4

3.28

1.59

5.52

2.67

132.9

0.978

0.0328

0.736

0.0247

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10

petrochemical processes and considerable attention has been paid to heat integration in recent years. However, because petrochemical plants and refineries are typically fueled by crude oil, or by waste petroleum products from the conversion processes, the greater efficiency of natural gas combustion is often used to reduce process costs. Petroleum fuel products can be recycled for feedstock or higher-quality energy products. The petrochemical industry is particularly well suited to this ‘‘fuel switch’’ due to its consistent demand for both heat and power for processes requiring a higher energy service quality, such as pumps, instruments, and motors. Heat and power can be provided by cogeneration (or combined heat and power, CHP) plants [24]. Through heat integration, CHP can be 50% more efficient than supplying steam and electricity separately. As a consequence of ever more stringent environmental legislation and higher fuel costs, CHP is being increasingly incorporated on petrochemical sites. Indeed, Europe’s largest CHP plant is a 730 MW facility that provides steam and power to the petrochemical and refining processes at Immingham in the UK. The use of natural gas has been traditionally associated with local availability. As a feedstock and energy source, natural gas (and associated LPG) has been used by the organic chemical industry on the US Gulf Coast, Europe’s North Sea, and, more recently, Saudi Arabia and Brazil among others. The processing of natural gas to higher-value chemical products for export is an economically attractive alternative to gas flaring or investments in pipeline networks for feeding gas to power stations. This has especially been the case in remote locations with abundant gas but little local demand for energy. Following the discovery of natural gas in New Zealand, two plants were established in the early 1980s to convert methane to methanol. The process used steam reforming of methane to carbon monoxide and hydrogen as a first step. Up to 6,700 t per day of crude methanol were produced. These were partly upgraded to gasoline via the Mobil process and partly exported as chemical grade methanol for further processing in the main petrochemical facilities abroad [25, 26]. At the time, this represented the world’s largest methanol production capacity. These days, natural gas in remote locations can be transported to major international ports to feed continental pipelines as liquefied natural gas (LNG). Nevertheless, there remains considerable interest in conversion of natural gas to methanol, dimethyl ether (DME), and, especially, gasoline, for export. Perhaps the most notorious case is that of Qatar, where methanol production is proceeding alongside LNG and gasoline production from natural gas.

Coal Coal was the original feedstock and energy source for the organic chemical industry when it evolved from the early British coal tar pigment industry in the late nineteenth century. It has been remarked that the synthetic dye industry became the ‘‘synthetic-everything-else-industry’’ [27:136]. In addition to the aromatic chromophores (naphthalene, anthracene, and benzene derivatives) that could be obtained from

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coal tar, coal was gasified to yield acetylene and synthesis gas (syngas) that could be upgraded to produce some basic synthetic chemicals. By the end of the 1930s, coal-based chemistry in Germany and the USA had developed to a stage where liquid fuel, rubber, plastics, solvents, lubricants, and many other chemical products were commercially manufactured from coal. Coal-based chemistry laid the foundations for the modern petrochemical industry. In 1938, DuPont claimed that ‘‘in the field of carbon monoxide chemistry’’ they had ‘‘an answer to anything the oil companies can do from hydrocarbon gases’’ [18:321]. By this time, however, coal had already been replaced by petroleum as the primary organic chemical feedstock in the USA, and was about to be overtaken in the UK. > Figure 10.3 shows this transition from coal- to oil-based chemicals in the UK. It mirrors the substitution of coal by oil and gas in primary energy use, but, although starting later, it shows a much more rapid overturn of the raw material base, reaching 50% penetration 20 years earlier. The displacement of coal by oil was completed in the 1960s when technologies for producing aromatic chemicals, such as benzene, from petroleum were commercialized. Aromatics had until then remained the preserve of the coal-based chemical industry. Non-fossil feedstocks are excluded from > Fig. 10.3 due to a lack of reliable data. They are thought to account for a shrinking proportion from a high of up to 15% in the 1930s to less than 3% today.

100 90 80 70 % (GWh basis)

330

60 50 40 30 20 10 0 1924 1929 1934 1939 1944 1949 1954 1959 1964 1969 1974 1979 1984 1989 1994 1999 2004 Year Other primary energy sources (nuclear, hydro etc.) Primary energy from coal Chemical feedstocks from coal Primary energy from oil & gas Chemical feedstocks from petroleum and natural gas

. Fig. 10.3 Transitions from coal to oil and gas in UK primary energy (grey) and chemical feedstocks (black) 1924–2005 (5-year rolling averages from UK official energy statistics)

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10

Since 1940, coal-based chemistry has thrived only under severe resource pressures because it has not been competitive with petroleum-based processes. Without access to reliable oil supplies German chemists during World War II focused their energies on products from syngas, especially gasoline but also synthetic rubber. This technology was applied subsequently by the South African oil and chemicals giant Sasol who had access to large coal deposits but restricted access to international oil markets. By 1974, Sasol was operating its first integrated fuel and chemicals plant based on coal gasification. By 1982, before a significant drop in the global oil price, it was producing 80 different chemicals for about 700 clients and sales of chemicals represented 16% of total sales [28]. Most of these were produced from olefins generated by cracking the naphtha that is a fraction of the so-called Fischer–Tropsch liquid fuel manufactured from syngas. Today, Sasol produces about 2 Mt of olefins from coal per year for the South African chemical industry. Of all the sources of chemical feedstock and process energy, coal gives rise to the largest CO2 emissions. This has been estimated to be 8–11 t of CO2 per ton of high-value chemical produced, in comparison with approximately 4 t for conventional oil-based routes and 4–5 t for those based on natural gas [23]. For natural gas, this result is due to the additional energy requirements of syngas production from methane. Despite these high CO2 emissions and the stringent greenhouse gas regulations introduced in many parts of the world, coal-based chemistry is favored in certain locations. These notably include China where indigenous coal is far more abundant than other fossil fuels. In 2007, about 50% of coal in China was used for production of chemicals, largely using traditional ‘‘low-tech’’ processes such as coking, processing of coke and coal tar, and carbide chemistry. The main growth areas for the future are likely to be coal-to-liquids, coal-tomethanol, and C1 chemistry, that is, based on syngas, as used by Sasol [59]. One such project, a US$7-billion plant to be developed by Sasol and China’s Shenhua Group was given a green light in 2008 and will process 3.2 Mt of coal per year upon completion. Other integrated facilities using coal or coke gasification have been proposed and have gained commercial interest in countries including the USA due to rises and volatility in the prices of oil and gas [29]. These include ammonia plants for fertilizer production based on syngas from coal, which is forecast to be competitive with syngas from methane in the coming years.

Biomass It has been estimated that about 5% of global chemical sales are products from biomass feedstocks. Biomass refers to vegetation or other plant material that can be converted industrially into useful energy, fuel, or materials. Most of the biomass that enters the chemical industry’s value chain is either in traditional bulk processes that have never been fully displaced by petrochemicals or in speciality products that utilize specific natural properties in smaller quantities. The former category includes products such as cellophane, which is produced from cellulose from wood, vegetable oils in soaps, pine

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rosins in paints, and castor oil as a constituent of polyurethane. The latter category includes cosmetics, food additives, dyes, and medical products, for example, those that biodegrade in the body. Croda, a UK-based company founded in 1925 to manufacture lanolin from sheep’s wool, is today a large speciality chemicals firm that obtains 70–80% of its raw materials from ‘‘natural and sustainable sources’’ [30]. The firm focuses on personal care plus crop care, polymers, and coatings, and had a turnover of 0.9 billion GBP in 2007. In many ways, the history of the petrochemicals industry is one of replacement of biomass by synthetic products. Wood, for example, has been replaced in a wide variety of furniture applications by plastic. Cotton has been superseded in certain fabric products by synthetic fibers such as nylon. But, in addition to these ‘‘natural’’ polymers and products there is another class of bio-based chemicals that has a more complex relationship with fossil-based chemicals: synthetic materials from bio-based chemical feedstocks. In Europe and America between World War I and World War II, there was a great deal of interest in industrial use of fermentation ethanol. Support schemes operated in Germany, France, Italy, the UK, and the USA, among others [31]. There were various reasons for these policies, but they mainly related to: the troubled distilling industry under prohibition and temperance; concerns about the security of supply of oil for motor cars; farm support during and after the depression; and, in Europe, a lack of convincing evidence that petrochemistry was truly superior or cheaper. In the UK, the added incentive of adding value to the molasses obtained from sugar plantations in the British Empire led to a significant tax relief for industrial alcohol production (known as the Inconvenience Allowance) [18]. As a result of the Inconvenience Allowance, and the partly related lack of UK refineries, British chemical companies deployed the ethylene-based chemistry that was being developed in the USA by first dehydrating ethanol produced by ex-whisky producers such as the Distiller’s company [32]. The feedstock for the first polyethylene plant in 1938 was, therefore, ethanol. In the USA, a movement based around the Farm ‘‘Chemurgic’’ Council advocated harnessing agricultural production for soybean plastics, corn-based rubber, and agrol (gasoline–ethanol blends) to relieve farm poverty and dependence on powerful oil companies [33, 34]. In 1941, Henry Ford unveiled a car that ran on Agrol and had a soybean plastic body. The notion of separating plastics production from the oil industry was revisited following the oil shocks in the 1970s when ICI began development of Biopol, a polymer made from fermented glucose [35]. As oil prices dropped, the prospect of commercial Biopol production receded, but the development work undertaken by ICI has provided foundations for a new generation of bio-based chemicals. Climate change is one of the concerns that have generated renewed interest in using biomass as a chemical feedstock. Biomass is a renewable resource that sequesters CO2 from the atmosphere as it grows. If the biomass is then used as a chemical feedstock then atmospheric CO2 is incorporated into products. Depending on the end-of-life disposal of the product, the carbon is either locked up indefinitely and kept out of the atmosphere or returned to the atmosphere upon degradation or incineration thereby creating lower net

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emissions than the equivalent fossil-based product. A lower carbon footprint has been calculated for a number of synthetic materials from bio-based feedstocks, most notably polylactic acid (PLA) and Mater-Bi plastics and fibers made from corn starch by NatureWorks in Nebraska, USA and by Novamont in Terni, Italy, respectively [36–38]. At present, the small number of bio-based plastics are more expensive than their petrochemical counterparts, and so are only commercially produced for specific applications where their raw material or biodegradability is able to command a premium. Biomass can be used to meet feedstock and/or energy requirements in organic chemical manufacture in order to provide environmental benefits. A full lifecycle analysis (LCA) of these benefits should account for fossil resource depletion, water use, gaseous emissions, and other pollutants, in addition to CO2 emissions. This type of analysis is useful if, as is the case with renewable raw materials (RRM), the alternative technologies cannot be universally applied due to resource constraints. Because biomass is presently a more limited resource than oil, gas, and coal, in future it may be necessary to allocate it wisely to the applications with the most environmental benefits. This issue is discussed further below.

Twin Concerns: Climate Impact and Resource Sustainability As has been indicated by the previous sections, the heavy dependence of the petrochemical industry on fossil fuels raises two major sustainability concerns: the impact of chemical processes on the climate and the finite and depleting nature of fossil fuel reserves. Through emissions regulations and through real and expected rises in the prices of oil and gas, both of these concerns are impacting on corporate decisions. In the chemical industry, truly sustainable solutions will address both of these problems. However, implementing change requires an appreciation of the entrenched integration in the industry. This integration, as described above, relates to the physical integration of refining and petrochemical infrastructure, the interdependence of the industries on the by-product relationship between oil refining and olefin cracking, and the economic and commercial integration of the main firms involved in the chemical value chain. Technological change in the organic chemical industry is capital-intense and so introducing new lower-carbon processes into such a highly integrated environment presents a significant challenge. The following sections describe the two main concerns and evaluate some mitigation options with regard to their potential for approaching technological change and long-term sustainability.

Climate Impact The chemical and petrochemical industry accounts for more than 30% of the total industrial energy use worldwide. This gives rise to very large levels of CO2 emissions. However, in comparison to other industries the emissions intensity is not high as much of

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the energy is used as feedstock which becomes locked up in products until the end of their lifetime, and in many cases for a long time after disposal. Data on global energy efficiency and GHG emissions from the petrochemical industry are not fully available, due to antitrust issues, limitations to the recorded statistics and difficulties with allocating energy between heavily integrated processes on sites. The International Energy Agency (IEA) has estimated total global CO2 emissions from the chemical and petrochemical industry to be 1141.8 Mt per year [39]. It should be noted that this includes both inorganic and organic chemicals production, and concerns only direct CO2 emissions and excludes emissions from power generation and emissions in energy recovery from petrochemical products during disposal. Discussions of GHG emissions from the production of organic chemical products are more complex than those for other industries. This relates to the nature of the industry as a ‘‘store’’ of fossil carbon in chemical products – carbon that would otherwise have been emitted to the atmosphere. It is estimated that carbon storage in plastics worldwide is 477.3 Mt of CO2 equivalent per year [39]. In comparison, only 30 Mt of plastics are incinerated at the end of their lifetime putting the carbon into the atmosphere as CO2. Furthermore, as is often highlighted by representatives of the chemical industry, a lifecycle approach to calculating climate impact should take into account both end-of-life disposal of carbon-containing products and their contribution to efficiency gains during their lifetime. Many polymers and plastics are used to provide insulation, thus saving considerably more carbon dioxide during their use than was generated during their production [40]. Ultimately, however, such accounting problems could be overcome by applying a price to carbon dioxide emissions throughout the economy.

Primary Sources of Greenhouse Gases The main source of GHGs in the chemical industry is in energy use to power energy intense production processes. Steam cracking to produce olefins is the major energyconsuming process worldwide due to its energy intensity and extensive use. More than 39% of the chemical and petrochemical industry’s final energy use is used for steam cracking. The energy used in steam cracking depends on the technology used and also on the choice of feedstock. Lighter feedstocks such as ethane are cracked at lower temperatures and the ethylene yield decreases as feedstock molecular weight increases. To produce 1 t of ethylene requires 1.25 t of ethane, 2.2 t of propane, or 3.2 t of naphtha (> Table 10.3). To address the problem of lack of data on energy usage in the chemical industry, the IEA has proposed an aggregate product indicator composed of 49 products that represent more than 95% of all energy used in the chemical and petrochemical industry [41]. Of these, the five most energy intense processes are for acetic acid (34 GJ/t), benzene produced by steam cracking (27 GJ/t), xylene by steam cracking (26 GJ/t), toluene by steam cracking (24 GJ/t), and toluene diisocyanate (22 GJ/t). Accounting for production volumes, the three largest energy uses are for the processes that produce ethylene (1.3 million GJ), propylene (0.7 million GJ), and benzene (0.6 million GJ). While there is

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. Table 10.3 Energy requirements for steam cracking for three different feedstocks [39] Feedstock

GJ/t ethylene

Ethane

15–25

Naphtha Gas oil

25–40 40–50

potential for efficiency savings throughout the industry, savings in these processes could yield the greatest climate change mitigation benefits. Carbon dioxide from energy generation is not the only GHG emitted by the organic chemical industry but is the most important by a long way. Mitigation activities should be undertaken to avoid emissions of methane, nitrous oxide, and chlorofluorocarbons (CFCs) wherever they are used. To put the difference in context, however, the EU chemical industry in 2007 reported emissions of 32,307 kt of CO2 but only 118 kt of CO2 equivalents of N2O, 29 kt of CO2 equivalents of NOx, and 21 kt of CO2 equivalents of methane [42]. Emissions also occur in the transport of chemical products for sale or further processing. Often raw materials are processed to final products on one site due to the difficulties of transporting intermediate products (gaseous, unstable, etc.); however, this is not always the case. As with other industries, the greater the proximity of raw material production, manufacture, and sale, the lower the GHG emissions from transport will be. Greater distribution of petrochemical sites to fit raw material and consumption patterns needs to be balanced against significant economies of scale that are gained from large-scale petrochemical sites. On the ‘‘demand side’’ of organic chemicals production, two aspects make important contributions to GHG emissions. Firstly, the scale of demand for chemical products is immense and has been increasing in close connection with GDP for the past 60 years. Reducing consumption is one of the most effective measures to mitigate GHG emissions from the chemical industry. Secondly, it should be recalled that many organic chemical products are used to replace existing materials. Replacing the metal body of a car with a lightweight plastic can reduce fuel consumption and thus reduce GHG emissions from transport. A strong synthetic lightweight polymer such as this could also enable electricpowered vehicles to become commercial as this could help offset the weight of the battery. Carbon fiber in high-performance vehicles is a good example of the weight savings, and therefore emissions reductions, that could be achieved through greater use of organic chemicals. The conclusion is clear: Calculations of the impact on the climate of organic chemicals should be undertaken with an understanding of the lifecycle impact of a particular product or application. There is no space in this chapter to look in depth at particular products. Instead, the sections below on climate change mitigation options consider the potential for improvement of the most polluting petrochemical processes. Production of these basic products

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is likely to continue on a large scale in the next couple of decades even if, as one would hope, serious thought is given to whether demand for the final products should be partly reduced.

Geographical Variations The main petrochemical producing regions are Europe, the Middle East, and the USA. Because these regions rely to a large extent on different raw materials, their GHG emissions vary. > Figure 10.4 shows the percentages of ethylene production capacity in different regions that are based on the six main feedstocks. This demonstrates that ethane dominates in the Middle East and naphtha and heavier fractions dominate in Europe. The USA is mainly reliant on LPG and some naphtha. While the capacities vary between regions, the core technology designs are similar and are based on the steam cracking process developed in the USA in the early 1940s. The biggest plants are currently in the USA and the Middle East. The distribution of CO2 emissions in > Table 10.4 reflects these regional differences and also the emissions intensities of the processes. Thus, the top countries in the table are those with high energy costs and therefore incentives to operate highly efficient, integrated plants, and those that use lighter ‘‘cleaner’’ feedstocks.

Future Trends The main influences on GHG emissions from the organic chemicals industry are feedstock costs and climate change regulation.

100%

80%

60% Others Gas-oil

40%

Naphtha Butane

20%

Propane 0%

Ethane Africa

Asia & Pacific

Europe West

Europe East

. Fig. 10.4 Ethylene plants by feedstock and region [39]

Latin America

North America

Middle East

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. Table 10.4 Total CO2 emissions from national chemical industries, in reverse order of their estimated emissions intensity as an indication of room for improvement [39] Country Netherlands Saudi Arabia Japan United Kingdom France India Germany Italy United States Brazil China Chinese Taipei

Million tons of CO2 per year (Mt CO2/year) 22.7 53.1 120.1 19.4 24.3 51.0 46.8 10.1 275.0 13.6 51.0 13.4

The high oil prices experienced in 2007–2008 gave an indication of how the industry could develop if investment decisions are made in the belief that oil supplies will be tight in the next decades. Middle East producers of olefins from ethane were the most advantaged under these conditions due to the low cost of both feedstock and manufacture from this feedstock. European naphtha-based crackers became the marginal producers and were able to continue operation due to continued integration with local refineries. However, prices of both naphtha feedstock and process energy increased sharply for these producers and caused a delayed downturn in demand. In the event, of course, greater damage was done to demand for petrochemicals by the credit crunch and ensuing global recession. Long-term increases in oil prices would be likely to cause a marked shift in basic petrochemical production to locations where light crude oil is plentiful, especially Saudi Arabia and the Middle East. Although the use of LPG as a basic feedstock is accompanied by lower CO2 emissions, these countries have less-stringent CO2 emission regulations. Nevertheless the nature of the industry is such that minimizing energy costs (for feedstock, heat, steam, and power) is a major factor in plant design worldwide. Under these conditions, European and US companies may find it necessary to return to a level of vertical integration that allows them to absorb price volatility in the value chain. Large plants and multinational companies have always been the status quo in the petrochemical industry and this is not foreseen to change. Another outcome of the oil price spike in 2007–2008 was the growth in interest in coal and biomass feedstocks. The close relationship between oil and gas prices and other geopolitical issues relating to the security of gas supply mean that natural gas has not been considered to be a long-term alternative to oil. However, the impact of unconventional gas has yet to be fully explored. Coal has most interest in China, the USA, Australia,

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and South Africa for reasons of indigenous supplies and technological expertise. Increased use of coal as a feedstock for ammonia and methanol production would lead to higher CO2 emissions. Use of biomass can lead to lower CO2 emissions where it is also used for providing process energy. The concept of a ‘‘biorefinery’’ is discussed further below as a long-term option. An eastward shift in chemical production appears to be an inescapable trend for the near future. Aside from raw materials costs, this relates to lower capital and operating costs in China, India, and Brazil, less costly regulatory environments, and the higher rates of demand growth in these regions. In the developed world, the main markets for bulk chemical products are largely saturated. Investment in new capacity in Europe and America is likely to continue to focus on speciality products and infrastructure considered to be of strategic importance. Chemical plants in regions subject to GHG emissions regulations have a very strong incentive to implement mitigation technologies. Although the timetable is unclear, there is a broad expectation that GHG emissions will be costly for chemical producers in most regions of the world in coming decades. Investments today will therefore consider extensive heat integration and CHP as competitive advantages, as well as the use of biomass to provide a proportion of the heat and power requirements of a chemical site, perhaps through co-firing. Another macroeconomic trend with possible impacts on the petrochemical industry’s emissions intensity is changes to refinery output. Modern refineries are capable of adjusting output to meet demand by cracking and upgrading the different distillation fractions to meet fuel requirements. For example, heavier fractions can be cracked and reformed to produce more high-octane gasoline for instance. Because of the high levels of integration between the fuels and chemicals industries, changes in the – much larger by volume – fuels industry could impact on the fractions of crude oil available for chemical feedstocks. In the near- to medium-term, most of these changes to the current balance of products would most probably lead to a larger amount of processing to supply the existing infrastructure. More processing indicates more CO2. Plausible changes in refinery configurations could result from, among other things, a global trend toward diesel-powered cars; the emergence of a highly competitive market for LPG fuel; a substantial increase in the proportion of electric, hybrid, and biofuel powered cars worldwide; and a trend toward ‘‘heavier’’ crude oils. This last change appears unavoidable. Oil sands, coal to liquids, and other unconventional and difficult-to-access sources of liquid fuels will be needed to replace the depleted supplies of conventional light crude oil. It should be borne in mind, however, that complex industries that have evolved together over many decades will only reorient their supply chains to radically new technologies on the scale of decades; the inertia in the infrastructure is very great. It is worth considering these future trends as they could all impact negatively on the ease with which the organic chemical industry can mitigate its impact on the climate. In the section on mitigation options, the main focus will be on long-term options that offer serious emission cuts. Incremental efficiency improvements may be insufficient to offset trends that lead to higher emissions intensities.

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Resource Sustainability Oil Because of the reliance of the organic chemical industry on fossil fuels, especially oil, for both feedstock and energy, the sustainability of oil supply is of utmost importance. The precise amount of oil left in the ground is a key concern for the petrochemical industry not just because it cannot presently be entirely replaced by alternatives but also because of the link between resource availability and cost. Shortages of oil and gas will lead to high prices as it is not easy to substitute these key economic inputs at low cost. High prices could trigger either lower demand for petrochemicals or feedstock/fuel switching; both of which would have consequences for GHG emissions. It is therefore necessary to say something briefly about ‘‘peak oil.’’ The two men most associated with the ideas behind peak oil concerns are William Stanley Jevons and M. King Hubbert. Both looked at a finite fossil fuel resource and noted that the production rate of that resource, which had risen exponentially initially, would reach a maximum point long before the resource became exhausted. Jevons correctly predicted that UK coal supply would be unable to keep up with demand in the early twentieth century. Hubbert correctly predicted a peak in US oil production in the mid-twentieth century. For both resources, the growth rate of supply was checked at approximately half of the total reserve. Although British coal and American oil could subsequently be replaced by alternative fossil energy sources, mainly through imports, what was recognized by these theorists was that if there is no alternative supply source that can be used as a substitute at similar cost, then the inevitable decline in production will cause intense competition between consumers with entrenched expectations of continuously increasing their demand. Peak oil is therefore a prediction that, in the absence of acceptable and available substitutes, the key date is the extraction of half the ‘‘conventional’’ oil on the planet and not the date of total exhaustion. After the peak (or plateau), very sharp price rises and very dramatic declines in production rates would mean an end to decades of economic growth based on cheap access to oil. In fact, studies suggest that most of the world’s major fields have peaked at between 30% and 40% of their total resource [43]. Conventional oil refers to crude oil, condensate, and natural gas liquids, which are usually relatively easily extracted from subsurface oil fields and require relatively little upgrading to liquid fuels. By contrast, nonconventional oil refers to oil sands, shale oil, and extra-heavy oil, which are not found in a usable form and require more treatment to yield liquid fuels. To nonconventional oil can be added other nonconventional liquids such as coal to liquids, gas to liquids, and biofuels. To date, nonconventional liquids have been more expensive to produce, and have generally only been used in times of scarcity of conventional oil. The date and severity of peak oil is much debated and remains unresolved. It is difficult to draw clear conclusions due to a lack of data. However, the key variables are: the total remaining conventional oil resource, the cost (both economic and environmental) of

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extraction of the remaining conventional oil, the cost and availability of alternatives, the production rate, and the elasticity of oil demand. The first of these is uncertain because of uncertainties associated with national statistics and because the globe has not yet been fully explored. It is also subject to adjustment on the basis of technological improvements or price changes that make previously uneconomic reserves commercially viable. Nevertheless, it is possible to look at the reported annual discoveries of crude oil and equate this with the known depletion rate of oil fields in production. While one must account for possible technological improvements and for economic and political trends that affect the exploration efforts of oil companies, it is reasonable to expect that before the peak cumulative discoveries (plus ‘‘reserve growth’’ of known fields) should significantly outpace production growth. For most parts of the globe, where most social and economic activities are reliant on oil-based transport, diesel for heating or power, or petroleum chemical feedstocks, the elasticity – the responsiveness of the quantity demanded to a change in the oil price – is low. People will therefore find a way to bear the cost of price rises rather than give up or substitute the use of oil. > Figures 10.5 and > 10.6 show the global trends in oil reserves and production. In a review of the evidence for a peak in conventional oil by 2030 by Sorrell et al. [44], it is noted that although there are around 70,000 oil fields in the world, 100 fields account for half of production and up to 500 fields account for two thirds of cumulative discoveries. Most of these giant fields are well past their peak of production or will begin to decline in the next decade. Their analysis indicates that just to maintain production at current levels, 3 million barrels per day of new capacity must be added each year – equivalent to a new Saudi Arabia coming on stream every 3 years. This means that in order to prevent

1,400 Global proved reserves (Gb)

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1,200 1,000 800 600 400 200 0 1975

1980

1985

1990

1995

2000

2005

2010

Year

. Fig. 10.5 Global trends in proved conventional oil reserves [44] (This does not include ‘‘probable’’ or ‘‘possible’’ reserves. Proved reserves are those that are considered to have a 90% chance of economic recovery and are thus subject to changes in technology and oil price)

Implications of Climate Change for the Petrochemical Industry 35

1,200

30

1,000

25 800 20 600 15 400 10 200

5 0 1840

Cumulative production (Gb)

Annual production (Gb)

10

1860

1880

1900

1920

1940

1960

1980

2000

0 2020

Year Annual production

Cumulative annual production

. Fig. 10.6 Global trends in oil production [44] (1 giga barrel=approximately 150 Mt. 2008 production was 82.3 million barrels per day, excluding biofuels)

production from falling, more than two thirds of current crude oil production capacity may need to be replaced by 2030. Yet there is almost no chance that new giant fields will be discovered and discoveries of new smaller fields are not currently at the levels needed. Sorrell et al. [44] conclude that there is a ‘‘significant risk of a peak in conventional oil production before 2020. Given the potentially serious consequences of supply constraints and the lead times to develop alternatives, this risk should be given urgent consideration.’’ Meanwhile, the IEA’s World Energy Outlook 2009 expects a slight increase in conventional oil production by 2030, and a total liquids production of well over 100 million barrels per day. Given that increasing the global ultimately recoverable reserves of conventional oil by 1 billion barrels would delay the date of peak production by only a few days, there is clearly a narrow window to develop substitute fuels and feedstocks. For comparison, the cumulative production from the UK, to date, is approximately 24 billion barrels. Aside from the potentially devastating effect that high oil prices could have on certain petrochemical producers, this message has other important implications for the chemical industry. The substitute fuels are generally considered to be oil sands, shale oil, biofuels, coal to liquids, gas to liquids, and other heavy oils. Each of these is itself a limited resource of differing proportions and none is anticipated to offer a sole solution. Unlike for crude oil, production of liquid fuels from these resources does not produce by-products – such as LPG or naphtha – that are highly suitable for replacing current petrochemical feedstocks. Olefins, aromatics, or syngas can all be produced from nonconventional liquids but they would be competing for the raw material with the fuel users, who may be willing to bid

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high prices if the available resource is constrained. Integrating nonconventional feedstocks into the petrochemical industry could require major changes to the upstream infrastructure and could be very costly. This section has not yet touched upon the climate impact of peak oil. The impact is, however, potentially very significant. Nonconventional feedstocks (with the possible exception of biomass) require energy intense processing methods such as gasification, hydroconversion, or steam injection. If future organic chemical production is going to be sustainable then not only should CO2 emissions be consistently reduced, but the industry must take into account the possibility that it may need to start integrating nonconventional feedstocks in the coming decades. Reconciling these two issues will be extremely challenging. Two ideas are discussed in the sections on climate change mitigation options: CO2 capture and storage, and biorefining.

Waste Management and Recycling Another aspect of resource sustainability that must be considered is that of waste management and recycling. Waste management is important for managing the environmental impact of organic chemical products at the end of their life, including the GHG emissions. As a solution to the waste management problem, recycling also has major benefits in terms of reducing the need for fossil raw materials. Taking plastics as an example, today, only 10 Mt of plastic waste are recycled which is less than 10% of the overall waste generated. In the USA, Japan, and Europe, the proportion is much higher than this. About 30 Mt of plastic waste are incinerated, equating to up to 750,000 GJ of energy, which is 3% of the energy used in plastics production [39]. There is a trend toward less land fill or incineration without energy recovery and more recycling and energy recovery. Most plastics have a relatively high energy content, which is comparable to other hydrocarbon energy sources. Polypropylene, for example, contains 46 MJ per kg, which is equivalent to that of kerosene. Household mixed plastics waste contains approximately 32 MJ per kg, which is favorable compared to coal (approximately 25 MJ per kg). Hence, energy recovery from plastics can substitute fossil fuels in heat or power production. For developed societies, this is a sizable, secure, and competitive energy source. Total plastics consumption worldwide equates to some 235 Mt per year. If one third of this was to be used for energy recovery then it would equate to 2.5 million GJ, five times the global production of renewable energy in 2007. With landfill taxes being employed in many countries for reasons of space constraints and waste management, this resource is increasingly attractive. The climate story of energy recovery is slightly different. As mentioned earlier, the use of fossil fuels as plastics feedstocks effectively locks up the carbon, which breaks down only very slowly in landfills. (It should be noted that where it does break down it is likely to yield methane, a much more potent GHG. However, this can be partially dealt with by landfill gas collection for energy use.) Use of plastics as an energy source creates CO2

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emissions that can be considered as deriving from fossil carbon. If this displaces coal combustion then the climate benefit would be small but useful. If it replaces natural gas combustion then the climate impact would be unfavorable. Therefore, while energy recovery is attractive in terms of conservation of fossil fuels, it is unlikely to be attractive for reduction of GHG emissions. Recycling, on the other hand, offers both energy security and climate benefits. Reducing the amount of fossil (or bio-based) feedstock necessary for chemical production can have a positive effect on the available energy supplies. Perhaps more importantly, recycling can reduce the energy demand, and therefore the GHG emissions, of plastics manufacture by about 0.6 t of CO2(eq) per ton of plastic recycled – compared to landfilling [45]. Maximizing recycling is therefore a vital tool in the pursuit of sustainability in the chemical industry from economic, social, and environmental perspectives. To conclude this short overview of recycling it is necessary to briefly distinguish between thermoplastic recycling and so-called feedstock recycling. Most recycling today is thermoplastic recycling. Thermosplastics are polymers that become liquid when heated and can be reset as plastics when cooled and put to a new use. Feedstock recycling generally refers to the use of plastic waste as a raw material for thermochemical conversion to new feedstocks. This can either be achieved by pyrolysis to liquid fuel, or, as is more usually promoted, by gasification to syngas and then use in similar chemical processes to those fed by natural gas or coal; this could be, for instance, ammonia production, liquid fuel production, methanol, Fischer–Tropsch olefin production, or dimethyl ether. Because feedstock recycling to chemicals requires energy intense conversion of the plastic waste to syngas, it offers a solution primarily to the problem of resource sustainability. It is only likely to yield GHG emissions reductions when compared to coal gasification processes. One main advantage of feedstock recycling is the hydrogen-rich syngas produced in comparison to that from coal. This could be advantageous in a future in which syngas is widely used for production of hydrogen, fuel, or chemicals, suggesting a possible role for ‘‘co-gasification’’ of plastic, coal, and biomass.

Future Directions This section looks at three climate change mitigation options that have the potential to increase the sustainability of the chemical industry from both a resource sustainability and climate perspective. These technologies address the impact of the organic chemical industry that will evolve in the coming decades. It is assumed that the products of this industry will continue to be produced on a massive scale worldwide in order to meet the material demands of a modern society with a growing population. Nevertheless, it should be stressed that alongside these three technologies, thermoplastic recycling and the reduction of consumption should be pursued to the greatest extent practicable. The three following sections focus on combined heat and power, carbon capture and storage, and biorefining.

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Combined Heat and Power This section should perhaps refer to all available efficiency gains that could be achieved in modern organic chemical processes. However, the expansion of cogeneration, or combined heat and power (CHP), represents a unique and expansive opportunity for the chemical industry due to its high demand for heat. Because heat is a low-grade energy product, its production from fossil fuels can be considered to be a low-value use of precious resources unless it can be combined efficiently with the production of electricity or even chemicals. High efficiency is a natural pursuit of any business that is highly exposed to the cost of energy. Consequently, many of the key industrial processes in the chemical industry have been improving their performance year after year. Notable impetuses that gave momentum to this focus on efficiency were the oil price shocks of the 1970s. Early naphtha crackers consumed approximately 38 GJ per ton of ethylene produced, but in the 1970s an extensive redesign lowered the energy requirements by 40–50% [46]. Today, 18–25 GJ is the norm for the furnace and product separation at new plants. The change has been most apparent in Europe, where the energy efficiency of steam crackers improved by 10% between 1999 and 2003, while in North America the improvement was 3%. Among other things, this indicates the impact of using imported naphtha in Europe in comparison to regions with local LPG resources, which require less furnace and separation energy in cracking. In future, the battle for efficiency is likely to be due to the cost of GHG emissions as well as energy costs. There remain improvements that could be made to crackers in developed and developing countries alike. Higher-temperature furnaces, gas–turbine integration, advanced distillation columns, and combined refrigeration plants are possibilities that have been identified as potentially leading to savings of 3 GJ per ton of ethylene. Other options, such as fluidized catalytic crackers (FCC) and new deep catalytic cracking processes, have milder temperature and separation requirements, but are limited either by feedstock availability – FFC generally uses refinery gases – or by the impact on other integrated processes. Deep catalytic cracking yields are at the expense of gasoline yields, for instance. Efficiency improvements of all types are key to the future competitive edge of the major petrochemical firms and will lead to GHG savings. It has been estimated that there is an energy efficiency improvement potential of 30–40% for polyethylene and polypropylene production in total, and 10% for PVC [39]. The message is that such savings will be realized for almost any chemical processes wherever they are profitable, and where there is a shift to lower-cost regions of production the savings may be realized faster than the expected 30-year infrastructure replacement cycle. After all, many of the plants built in the Middle East and Asia are made to cutting-edge European and American designs, for example, the new methyl methacrylate plant commissioned in 2008 by British firm Lucite in Singapore. Lucite was subsequently subject to acquisition by Mitsubishi of Japan. Improvements to the environmental performance of existing processes are encapsulated by the 12 principles of Green Chemistry (> Table 10.5). Green chemistry is an approach to chemical production that stresses the environmental impacts of all process

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. Table 10.5 The 12 principles of green chemistry [53] 1 2

Prevent waste Design safer chemicals and products

3 4 5 6 7

Design less-hazardous chemical syntheses Use renewable feedstocks Use catalysts, not stoichiometric reagents Avoid chemical derivatives Maximize atom economy

8 9 10 11

Use safer solvents and reaction conditions Increase energy efficiency Design chemicals and products to degrade after use Analyze in real time to prevent pollution

12

Minimize the potential for accidents

steps. It encourages industrial producers to use processes that meet as many of the 12 aims as possible. ‘‘Increase energy efficiency’’ is principle 9. The Presidential Green Chemistry Challenge Awards have been awarded annually since 1996 by the American Chemical Society supported by the US Environmental Protection Agency (EPA). In 2009, the Greener Synthetic Pathways Award was won by Eastman Chemical Company for a novel route to the production of esters. The old process used strong acid catalysts at high temperatures; using enzymes eliminates the need for harsh conditions and thus significantly reduces energy use. It reduces the overall requirements for feedstock and solvents. It is also a cheaper process, which was made possible by taking a holistic approach to the industrial process. This section now turns to the energy efficiency technology after which it is named: combined heat and power (CHP). By making use of the ‘‘waste’’ heat produced as steam in electricity production, CHP increases the overall efficiency of a power plant. However, one criticism of CHP use in power plants is that the efficiency of electricity generation is reduced in order to deliver useful heat, and, since heat is a lower-quality energy product than electricity, this does not necessarily constitute a better use of fossil fuel resources. Domestic heating should, it could be argued, be provided by solar heating panels, heat pumps, or even ‘‘micro-CHP’’ instead. A petrochemical facility, on the other hand, has a high demand for both power and high-temperature steam, for processes such as steam cracking. Combining heat and power production is therefore a ‘‘no-brainer’’ – a truth that has not been lost on the industry. The chemical and petrochemical industry is already one of the largest users of CHP. In the USA, 24 GW or 34% of the CHP capacity was in the chemical industry in 2004. ExxonMobil alone has a worldwide installed CHP capacity of 3.7 GW in its facilities in 2006, considered to be equivalent to a reduction of 9 Mt of CO2 per year [39]. Additional

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technical potential in the industry in the USA is estimated to be more than 7.8 GW of power, much of which is at smaller plants as the larger facilities have already made the switch. Between 1999 and 2003, although the average number of CHP units used for powering each steam cracker did not increase, the average number went up by a third. At 730 MW (due to be expanded to 1,180 MW), Europe’s largest CHP plant at Immingham in the UK supplies a refinery and chemicals site and is approximately 70% thermally efficient. CHP is a technology that could be applied at nearly all chemical sites worldwide and could realize considerable GHG emissions savings. It has the advantage of being possible to retrofit without redesigning and investing in new process infrastructure, unlike the huge theoretical energy savings that are actually distributed among many different process improvements. GHG emissions can be reduced still further by using sustainably produced biomass fuel. Two challenges face the expansion of CHP for the organic chemical industry, however. Firstly, the technology needs to become more economically viable at smaller scales than at present (e.g., below 50 MW). Secondly, policies for supporting renewable energy need to be aligned with those for CHP to incentivize the use of biomass with CHP. In the UK, until recently, renewably fuelled CHP plants did not qualify for electricity subsidies. Consequently, the 30 MW biomass power station opened in 2007 at the Wilton chemical site on Teesside site was built without CHP. > Table 10.6 shows the IEA’s estimates of energy savings potential in the chemical industry.

Carbon Dioxide Capture and Storage (CCS) It may have seemed little more than a pipe dream just 10 years ago, but CCS is now widely accepted as a powerful tool in the fight against climate change. Other chapters in this book deal thoroughly with the technical details and the policy context of CCS, especially for the power industry, so only a brief review is necessary here. The main purpose of this section is to describe the applicability of CCS to the chemical industry. The big picture tells us that fossil fuel use continues to grow worldwide, notably in emerging economies such as China. Even in Europe, North America, and Australia, the . Table 10.6 Energy efficiency potential in the chemical and petrochemical industry [39] Estimated savings in EJ (thousand million GJ) Heat Electricity Recycling and energy recovery

4 1 2–4

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challenge of decarbonizing an electricity production system that is so hooked on coal and gas puts even the proudest of achievements in the renewable sector into fairly stark perspective: there is still a long way to go. CCS technologies appear to cut to the heart of these issues. By capturing and permanently storing the CO2 contained in the flue gases of power stations and industrial facilities, emerging economies can continue to nourish themselves on the coal and gas that fattened the Western world. Plus, by retrofitting the technology to existing European facilities, emissions cuts can be achieved much more rapidly than by relying on new renewables or the enigmatic goal of consumer energy efficiency. CCS is really a collection of technologies rather than a single procedure. At each stage of the process there are several technical options, such as the choice of separating the CO2 either before or after combustion of the fuel. Perfecting post-combustion capture would make it possible to retrofit existing power stations, whereas pre-combustion capture could increase the efficiency of the overall process. Similarly, the captured CO2 could be stored on land near the combustion site if a suitable aquifer or depleted hydrocarbon reservoir is nearby, or it could be piped to an offshore platform for injection. Capture could even be improved by using a high oxygen oxyfuel combustion method that reduces the challenges of separation – or the CO2 could be transported by ship rather than pipe. In reality, each of these stages is challenging and is receiving research and industrial attention. If the CO2 is used for enhanced oil or gas recovery (EOR/EGR), then depleting reservoirs are also suitable sites, as long as the CO2 is permanently stored. The extra oil revenues can even help make CCS profitable. It is, however, perhaps debatable whether enhancing the production of oil is consistent with the climate goals that CCS has been conceived to address. In the power sector, CCS is being prioritized by a number of governments as a crucial technology to be enabled in the next 10 years. Utilities and equipment supplier firms have rapidly moved from research to pilot projects and now to demonstration scale projects. Commercial-scale demonstration of the full CCS value chain has been identified as the next major step. If the experience from the first 20 or so plants can be gathered by 2020, then competitive deployment of the technology is anticipated shortly afterward, providing the option of low-carbon fossil fuel use and its attendant climate and energy security benefits. Although CO2 capture has been used by the chemical industry for many years, although CO2 has been transported over many hundreds of kilometers by the American oil industry for enhanced oil recovery (EOR), and although a million tons of CO2 per year has been stored at Sleipner in the North Sea by Norwegian firm Statoil since 1996, the full chain of CCS has never been integrated on a commercial scale. The reason is cost. The inescapable truth is that, in contrast to renewable energy technologies such as photovoltaics, it will never be cheaper to use fossil fuels with CCS than to use fossil fuels without CCS, regardless of the price of coal or oil. As a result, CCS will always be dependent on there being a cost to emitting greenhouse gases, the so-called carbon price that is currently provided to a limited extent by the EU emissions trading scheme (ETS). Furthermore, the cost of a demonstration plant can be up to €1.5 billion, a risk that

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no company is currently willing to take on its own in the absence of a high carbon price and a robust regulatory system for managing the liability issues around CO2 storage. As a result, in 2009, the EU provided €1 billion to assist six demonstration projects to be operational by 2015; it has also earmarked a further €4.5 billion (N.B. This value is heavily dependent on the eventual price of 300 million ETS allowances reserved in the 2009 revision of the EU ETS Directive for CCS and innovative renewables projects) and has established a CCS Project Network to help first-mover projects to share their experiences and advance from pilot to demonstration to deployment. In Canada, the federal and Albertan governments are committing approximately CAN$3 billion to 3–4 CCS demonstration projects, Australia has put $2 billion AUD in the federal budget for demonstration projects and the USA pledged almost US$3 billion to CCS demonstration projects in its American Recovery and Reinvestment Act in 2009, a billion of which could go toward the restarted FutureGen project (a US Government initiative to build a 200 MW coal-fired oxyfuel combustion plant with CO2 storage by the middle of this decade). Aside from the opportunity to sell the solvents that will be used to scrub the CO2 from flue gases, there are a number of reasons why the chemical industry would be well advised to pay close attention to CCS. These include the development of CO2 infrastructure clusters and the integration of CO2 and syngas chemistry through gasification technologies. To transport CO2 from the capture plant to the storage site is generally considered to require pipeline networks. For the first demonstration projects, this is likely to involve a single pipe linking a power station with an onshore or offshore storage site. A couple of these projects are set to be in areas that have a number of heavy emitters in a particular region. In Europe, the new power stations in Rotterdam and Humberside that aim to fit CCS are good examples. These areas have recognized that the next, much larger, tranche of CCS plants are likely to be power plants in these areas that can plug into already existing pipeline networks and utilize the same storage sites. This will greatly reduce costs. In Rotterdam, the discussion has evolved a step further to include chemical producers. Coal power plants have a much lower tolerance to the cost of carbon as electricity is ultimately a low-cost product and competes with other sources of power on the grid. As the cost of carbon rises, CCS could become an option with commercial value for other energy intense industries, such as cement, steel, or chemical production. Rotterdam has a high density of power production, refining, and petrochemicals. The Rotterdam Climate Initiative aims to bring these sources one by one into a linked CO2 network. The common infrastructure, it is proposed, would lower the cost of CCS for each plant and encourage them to be early movers in CO2 capture. In view of rising carbon prices in many parts of the world – despite the continuing absence of an international carbon trading system – petrochemical plants in the West could one day find that CCS is a vital way for them to remain in business. It will be advantageous for them to be located close to pipeline networks and ensure that the networks being developed today are of a sufficient scale to accommodate the facilities that will need to capture their CO2 emissions in 10 or 15 years from now. The Port of Rotterdam intends to capture and store some 20 Mt of CO2 per year from local sources by 2025 to achieve a 50% reduction of emissions compared to 1990 levels. Currently, over 50% of emissions in Rotterdam are from process industry sources.

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In contrast to other energy intensive industries like iron, steel, and cement, CCS could be particularly appropriate for the future petrochemical industry because of the importance of gasification technologies. In pre-combustion CO2 capture, coal is gasified to syngas, whereupon the hydrogen component is separated from the carbon monoxide and dioxide, which is cleaned and pressurized for storage. This is the principle behind IGCC coal power plants. The aforementioned proposed plant at Hatfield, near Humberside, is an example of such a plant. If multifuel turbines can be successfully demonstrated, the hydrogen could be used as a fuel in a gas turbine such that the electricity generation could, in principle, be from natural gas, hydrogen from coal gasification, or syngas. Syngas is already widely used in the chemical industry, primarily for hydrogen production. As was highlighted earlier in this chapter, there is a possibility that marginal organic chemical feedstocks like coal, heavy oil, and natural gas could become sources of petrochemicals via gasification to syngas. Syngas can be used as a starting point for Fischer–Tropsch synthesis of olefins and polymers, but only with higher CO2 emissions than today’s processes. Integration of CCS with industrial syngas ‘‘hubs’’ could enable these alternative feedstocks to be utilized in a manner that is compatible with a low carbon economy. With a strong carbon price, the syngas, the hydrogen and the CO2 could all be tradable commodities between firms (see > Fig. 10.7). Again, realizing such a scheme so that the integration can be optimized requires governments and companies to develop shared visions of how the future chemical industry might look in a carbon-constrained world. The IEA, in its 2010 Technology Roadmap for CCS, charted a course to deployment of CCS to achieve the kinds of capacity that would be required by their scenarios for tackling

Fossil fuels & Biomass Geological CO2 storage

CO2

CO / CO2 Petrochemical, bio-based, oxygenated, nitrogenous reagents etc.

Gasification

CO2

Uncaptured GHGs

CO / CO2 H2

H2 C1 chemical factory, methanol plant, FT-olefin synthesis etc.

Organic chemical value chain

Power & Heat

Power generation

Electricity grid

. Fig. 10.7 Schematic representation of a gasification-based chemical complex with CCS

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climate change. This roadmap shows a requirement for nearly 100 additional commercialscale CCS demonstration projects by 2020. Among these, it is expected that the chemical industry is well placed to make an early contribution to advancing the technology. The IEA considers that 18.5 Mt per year of CO2, or 11% of all captured CO2, could be from the chemical industry in 2020, with projects capturing CO2 from sources such as ammonia and fertilizer production offering near-term, low-cost opportunities. 18.5 Mt equates to approximately 20–40 projects that would need to raise investment funding in the next 5 years. This figure is then projected to fall to 9% of all captured CO2 in 2050, although in real terms it would have risen to a huge 411.3 Mt per year for the chemical industry. The IEA’s analysis is based upon the achievement of a 50% reduction of CO2 emissions levels by 2050, consistent with the aim of stabilizing CO2 levels at 450 ppm. One key point made in this report is that without CCS, the overall costs to halve CO2 emissions levels by 2050 increase by 70%. By 2050, CCS can deliver one fifth of the lowest-cost GHG reduction solution in 2050. This chapter has mentioned numerous technologies that can partly address the fossil fuel dependency and climate impact of the global organic chemical industry. CCS on its own can do very little about the former, but could be a very potent weapon against the latter. The current trends are unmistakable. Although the increasing exploitation of LPG as a chemical feedstock in affluent oil-producing nations means that the carbon intensity of olefin production has decreased, this is more than offset by the rise in production and the use of heavier feedstocks elsewhere in the industry. > Figure 10.8 charts the increase in global chemical feedstock consumption since 1971 and shows that it has largely mirrored the growth in per capita GDP. Without political intervention to reserve the most suitable fractions of conventional oil resources for organic chemical feedstocks, the depletion of these resources will, in the course of the next few decades, increase the energy intensity of chemical manufacture from fossil fuels. If this energy – and this is very likely in the major chemical-producing regions – is itself derived from fossil fuels, then CCS is the only option for substantially reducing CO2 emissions. Efficiency improvements may not even be able to help the industry to stand still in terms of its GHG emissions rate. In its favor, CCS is particularly suited to the chemical industry. GHG emissions from petrochemical manufacture tend to be concentrated upstream in coastal areas of heavy industry, refining, and oil and gas production. These factors offer a strong potential for linking emissions sources together and accessing suitable offshore, or onshore, storage sites.

Biorefineries As was described earlier in this chapter, the ‘‘coevolutionary’’ history of the organic chemical industry and the petroleum fuels industry has led to a highly integrated modern production system. This integration influences the pattern of raw materials use, technological choices, and the institutional organization of the major firms, industry associations, and government departments. Thus, the profitable use of certain fractions

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1 1976

1981

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. Fig. 10.8 Increase of global chemical feedstock consumption and per capita GDP [51, 52]

of each barrel of oil for making chemicals such as plastics contributes to the economic advantage of oil in the energy mix. There are only about 700 oil refineries worldwide, but their products underpin almost every aspect of modern society. The synergies of this ‘‘by-product relationship’’ make it more difficult for each sector – fuels and chemicals – to make the switch to alternative, cleaner resources. One such alternative is to increase the contribution of biomass as a fuel and feedstock. The section introduces the concept of biorefining as a way of maximizing raw material utilization and therefore using integration as a means of improving the competitive position of an alternative to fossil fuels. Peck et al. [47] have noted that there is not yet an agreed definition of a biorefinery, but cite the following: ‘‘The economic conversion, fractionation, or extraction of a spectrum of biomass sources through integrated physical, biological and chemical processing for the production of various commodities and specialities’’ [48]. This is a broad definition, but it indicates the idea of a processing plant that can take in multiple biomass raw materials and produce a range of salable products. These salable products are generally considered to be added-value chemicals, nutraceuticals, and proteins that can improve the economics of large-scale biofuels production by increasing the revenue per ton of biomass converted. By utilizing renewable biomass energy to power its chemical and biochemical processes, a biorefinery can reduce the overall consumption of fossil fuels and GHG emissions in the production of organic chemicals.

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Two strategies toward biomass feedstock substitution are being explored by sections of the industry. Many large chemical firms have taken an interest in the production of platform chemicals. Platform petrochemicals are olefins and BTX (benzene, toluene, xylenes), which form the basic building blocks for most derivative products in all organic chemical market segments. Platform biochemicals could be the same entities, for example ethylene produced from bioethanol, or new entities produced because they are easily accessible from biomass, for example, 1,3-propanediol. The Brazilian firm Braskem is pursuing ethylene from cheap Brazilian cane sugar-based ethanol [49] and DuPont commercially manufactures 1,3-PDO from corn [50]. Other novel platform chemicals could include hydroxymethyl furfural, lactic acid, succinic acid, or phenol. All of these could be produced from sugars with a lower carbon footprint. However, generating new product lines for their derivatives may ultimately be more challenging that finding routes to existing platform chemicals. One reason for this is simply that bio-derived chemicals tend to be more oxygenated and require more processing to yield materials of equal performance to petrochemicals. In contrast, an example of a new route to an existing value chain is the gasification of wood to syngas, followed by chemical or biochemical conversion to fuels and feedstocks. The second strategy to feedstock substitution is to target new products that can easily be accessed from biomass, such as polymers and speciality chemicals. This strategy is more suitable for smaller chemical firms that see an advantage in avoiding existing value chains and marketing their products directly as having novel ‘‘green’’ properties. Biodegradable polymers, such as polylactic acid (PLA), are an example of this. Although PLA is currently manufactured from energy-intense US corn, and only in small quantities, it has been shown to have a lower carbon footprint than the petrochemical alternatives. The challenge for PLA, which has only been produced since 2002, is to develop a broad product slate in areas such as packaging without compromising the biodegradability of the product. After all, one of the things that people find most convenient about plastics is that they do not degrade during the time that people are actively using them. Because of these different strategies, it is clear that unlike the relative homogeneity of oil refineries, individual biorefineries are likely to be very different entities depending on the availability of raw materials and the markets for the different products. Raw materials could include lignocellulosic materials such as wood, oils such as rapeseed, or sugars from cane or beet. Conversion technologies could be thermal (e.g., gasification), chemical catalytic (e.g., Fischer–Tropsch synthesis or dehydration), or biochemical (e.g., fermentation). Of these, it is very likely that biotechnology is going to play a major role in determining the success of biorefining. Enzymatic reactions are often well suited to renewable raw materials and have high specificity and high energy efficiency. Uncertainty prevails over where to find reliable markets for biorefinery products, and this is a hindrance to the raising of capital. Biofuels are currently produced through maximizing the fuel yields for which there are guaranteed outlets. Introducing renewable raw materials into the nonfuels markets will require what have been termed ‘‘lead markets.’’ The European Commission has launched a search for lead markets for biobased products, a process that is already well under way in several sectors, for example, the

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development of niche markets for plant-based cosmetics and biolubricants. Biolubricants could be especially attractive to manufacturers of biofuels as the fuel industry traditionally also sells oil-based lubricants. There is no space here to describe in full the various designs and concepts that have been proposed for biorefineries. As is logical, they differ on the basis of the resources that are geographically available and the product markets that are most attractive to the proponents. Subsidies for biofuels have, for instance, led to most advanced biomass processing facilities in Europe and North America being driven by provision of liquid fuels. Policies that promote bio-based chemicals could encourage firms to seriously consider production of bulk chemicals from biomass. Policies that promote properties, like biodegradability, that can be more easily delivered by using renewable feedstocks could also contribute to this result. For the reduction of GHG emissions, bulk chemicals would be more important targets simply because of the volume of petrochemicals that could be replaced. As a general caveat to this section, it must be borne in mind that biorefineries are currently only at the beginning of a development process. Three critical aspects give reason for caution when advocating biomass as a low carbon raw material for displacing both liquid fuels and organic chemicals. The first is that the biomass resource is more limited than the rate at which mankind has been able to produce petroleum during the last 50 years. Unless yields can be improved dramatically, for example, by intense algae cultivation, then biomass for biorefineries will compete with other uses of agricultural land and forestry. The high food prices in 2007 gave the world a taste the human impact of undersupply of staple foods. If crops are to be produced for industrial products in a world of 9 billion people and water shortages, then it may be difficult for some in developing countries to afford basic foods. Therefore, biorefinery raw material production must be based on policies that ensure that non-food crops are used that do not compete with food production. Aligning the needs of chemical producers with the timescales of agricultural innovation will thus be important. The second critical aspect is the scale at which biorefining can be sustainable. The modern chemical industry operates at vast scales to produce materials that are affordable in many thousands of applications. The biomass resource is relatively diffuse and would need to be transported large distances to feed a very large-scale plant all year round. Biomass generally has a high water content and is more energy intense to transport than petroleum with an equivalent hydrocarbon content. Ultimately, the climate benefits of biorefining will depend on innovations in industrial arrangements. These could range from large-scale ‘‘co-firing’’ of biomass and fossil fuels in gasification processes to localized processing of biomass before shipping the lighter, more valuable components for further processing. Thirdly, and finally, biorefining is a different prospect to oil refining. Oil refineries are based on a fixed set of principles and a relatively fixed set of hydrocarbon distillation products. Biorefineries, because of the diversity of designs, raw materials, products, and scales will not be able to benefit from ‘‘by-product’’ relationships to the same extent. Thus, it may take a lot longer to approach the kind of standardized biorefinery designs that can

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be licensed and propagated worldwide. Given the outlook for GHG emissions and fossil fuel supplies, it appears prudent to consider the biorefinery concept as a long-term objective for addressing looming troubles in the organic chemical industry. This can be helped by recalling the general principles of oil refining rather than the specific processes involved. The best biorefineries will convert all of the raw material to valuable products, and will be highly integrated with the downstream uses of their outputs.

Concluding Remarks This chapter has sought to introduce the organic chemical industry as a highly energy dependent sector of the economy. Presently, the industry is dominated by petrochemicals and a manufacturing system that is almost entirely reliant on fossil fuels, especially oil, for both raw materials and large amounts of process energy. This situation can be understood as the consequence of almost 80 years of ‘‘coevolution’’ of organic chemicals production with liquid fuels production, based around the oil refinery and the platform chemicals that are produced in the refining process. This process of close integration was especially pronounced during the periods of very rapid expansion during the 1950s and 1960s in Europe and North America. It has bequeathed a network of petrochemical clusters that feed the world’s manufacture of plastics, synthetic fibers, solvents, lubricants, medical products, and cosmetics. The efficiency of large-scale, integrated production continues to drive growth and innovation among the small number of multinational firms. As a result, this pattern of fossil fuel use, and thus GHG emissions, can be perceived to be ‘‘locked in,’’ making it very difficult for new low-carbon technologies to break into the chemical value chain. The chemical industry is responsible for 30% of industrial energy use and about 5% of global CO2 emissions. This chapter proposes that to seriously address climate change, GHG emissions from the chemical industry need to be severely reduced and that to do so will require a thorough understanding of the integration between the oil and chemical industries, and the ambiguous nature of fossil carbon storage in chemical products. Truly sustainable solutions will therefore need to address the future trends in petroleum resource availability, and overcome the barriers to market entry raised by the economics of the by-product relationship of olefins production and oil refining. Three options have been introduced that could have the potential to either ‘‘green’’ the existing production paradigm or disrupt it through radical innovation based on biotechnology. These three technology areas – efficiency savings through CHP, carbon capture and storage, and biorefining – could furthermore be combined to enable long-term organic chemical production that is compatible with deep GHG emission cuts. In addition, recycling, demand reduction, and green chemistry are clearly identified as vital complements to the introduction of new technologies. However, as the industry moves closer to a world in which its use of carbon is tightly regulated, new tools that are able to account for the full lifecycle impacts of organic chemicals will need to be developed and established as international standards. For instance, there can be environmental

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benefits to locking up carbon in nondegradable plastics but only if they are not subsequently burned for energy recovery without CCS. Likewise, if biomass resources are limited then they should be directed to where they can have the greatest impact on GHG emissions reductions. This calls for a major role for lifecycle assessment that is accounted for by carbon prices throughout the world economy. The challenge is an immense one that requires committed and enduring action from industry and governments, a fact that has been clearly identified for the two key areas of CCS demonstration and lead markets for bio-based products.

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39. IEA (2007) Tracking industrial energy efficiency and CO2 emissions. In support of the G8 plan of action. International Energy Agency, OECD, Paris 40. Cefic (2006) The chemical industry helps to protect the climate. The European Chemical Industry Council, Brussels 41. Tam C, Gielen DJ (2006) Petrochemical indicators. In: IEA/CEFIC Workshop: feedstock substitutes, energy efficient technology and CO2 reduction for petrochemical products. December 12–13, 2006. Paris, France 42. EC (2009) European community annex I party GHG inventory submission for 2007. UNFCCC, Bonn, DE 43. Ho¨o¨k M, So¨derbergh B, Jakobsson K, Aleklett K (2009) The evolution of giant oil field production behavior. Natural Resources Research 18(1): 39–56 44. Sorrell S, Speirs J, Bentley R, Brandt A, Miller R (2009) Global oil depletion. An assessment of the evidence for a near-term peak in global oil production. UK Energy Research Centre, London 45. Wrap (2006) Environmental benefits of recycling. An international review of lifecycle comparisons for key materials in the UK recycling sector. Wrap, London 46. Gielen D, Bennaceur K, Tam C (2006) IEA petrochemical scenarios for 2030–2050: energy technology perspectives. International Energy Agency, Paris 47. Peck P, Bennett SJ, Lenhart J, Bissett-Amess R, Mozaffarian H (2009) Understanding, acceptance, and support for the biorefinery concept among policy-makers. Biofuels, Bioprod Bioref 3(3):361–383 48. Koutinas AA, Arifeen N, Wang R, Webb C (2007) Cereal-based biorefinery development: Integrated enzyme production for cereal flour hydrolysis. Biotechnol Bioeng 97(1):61–72 49. Braskem (2007) Braskem has the first certified green polyethylene in the world. Press release. http://www.braskem.com.br/site/portal_braskem/ en/sala_de_imprensa/sala_de_imprensa_detalhes_ 6062.aspx, Accessed 27 September 2007 50. DuPont (2006) DuPont tate & lyle bio products begin bio-pdo™ production in tennessee. DuPont News. Accessed 27 September 2007 51. Maddison A (2009) The world economy: historical statistics. OECD, Paris

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11 Venture Capital Investment and Trend in Clean Technologies John C. P. Huang Focus Capital Group, Cupertino, CA, USA Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361 Venture Capital Investment Trend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362 Venture Capital . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362 Venture Capitalist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363 Venture Capital and Cleantech . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363 Venture Capital Investment in Cleantech . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364 Cleantech Venture Investment in 2009 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364 Cleantech Venture Investment in 2010 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365 The Scope of Cleantech . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366 Renewable Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366 Energy Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367 Green Building . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368 Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368 Smart Power, Green Grid, and Energy Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369 Air, Water, and Waste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370 Cleantech Technology Trend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371 Solar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373 Smart Grid and EV Infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377 Green Buildings, Lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381 Biofuels and Biochemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382 Batteries, Fuel Cells, Energy Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384 Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387 Other Energy: Wind, Nuclear, Cleaner Coal, Geothermal . . . . . . . . . . . . . . . . . . . . . . . . . 389 Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393 Green Information Technology (IT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393

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Cleantech Geographic Trend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394 Cleantech in the USA and California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394 Cleantech in China . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396 Cleantech in India . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397 Cleantech in Germany . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397 Solar Energy in Australia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398 Concluding Remark: Globalization and Deployment of Cleantech . . . . . . . . . . . . . . . . . 399 Globalization of Cleantech . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399 Deployment of Cleantech . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401 Venture Capital Firms in USA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401 Venture Capital Firms in Europe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403 Venture Capital Firms in India, China, Japan, and Israel . . . . . . . . . . . . . . . . . . . . . . . . . . 405 How to Secure Venture Capital Money . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405 How is a Business Plan Evaluated? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406

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Abstract: ‘‘Cleantech’’ is being widely used to replace ‘‘Green Technology.’’ It describes a group of emerging technologies and industries, based on principles of physics, chemistry, biology, and resource efficiency, new paradigms in energy, and water conservation. The scope of this field includes large-scale infrastructure projects as well as innovative technologies. The term Cleantech is also often associated with venture capital (VC) investment. The goal of this chapter is to provide readers with an overview of the scope and trends in venture-capital-funded innovation in Cleantech, how to seek VC funding, and Cleantech implications on world climate change. This chapter addresses the basics of venture capital and the dynamic field of Cleantech. Major topics covered include: (1) VC Investment Trend based on the volume of funds invested and the number of projects funded chronologically; (2) The scope of Cleantech encompassing renewable energy, energy efficiency, green building, transportation, smart power, smart grid and energy storage, air, water, and waste; (3) Cleantech Technology Trend through a discussion of the top VC-funded Cleantech start-ups and selected high-profile projects, a total of 61 companies in nine technology categories; (4) Geographic Trend addressing the status in western nations as well as in emerging countries and highlighting the status of Silicon Valley in California, now the heart of Cleantech innovation; (5) Concluding Remark discusses globalization of Cleantech as an infrastructure project and the key to the deployment of Cleantech innovations. The appendix provides a brief introduction of how to apply for VC funding and lists of major venture capital companies in key nations.

Introduction In recent years, the term ‘‘Cleantech’’ is being widely used to replace ‘‘Clean Technologies’’ and ‘‘Green Technology.’’ It describes a group of emerging technologies and industries, based on principles of physics, chemistry, biology, and resource efficiency, new paradigms in energy, and water conservation. The scope of this field includes large-scale infrastructure projects as well as innovative technologies. The term Cleantech is also often associated with venture capital investment. In 2001, the total Cleantech investment in North America, Europe, Israel, China, and India was US $500 million. By 2010, Cleantech investment increased to $7.8 billion, a 15-fold increase in a decade. This private investment is in addition to the very large dollar amounts invested and granted by various government agencies. This chapter addresses the dynamic field of Cleantech in the following five sections: 1. Venture Capital Investment Trend addresses the basics of venture capital and provides an analysis of the historical venture capital investment trend in terms of funds invested and the number of projects funded. 2. The Scope of Cleantech lists the scope of Cleantech that encompasses renewable energy, energy efficiency, green building, transportation, smart power, smart grid and energy storage, air, water, and waste.

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3. Cleantech Technology Trend provides an overview of the key technologies that received venture capital investment. This is accomplished through a discussion of the top 50 VC-funded Cleantech start-ups plus selected eleven high-profile projects. These 61 projects include: renewable energy such as solar thermal systems, solar photovoltaic, wind turbine designs, fuel cells, and biofuels; energy efficiency systems focusing on new conception of battery technology, lighting, and green building; innovative resource management based on software and hardware, such as wireless smart meters and smart grids. 4. Cleantech Geographic Trend provides an overview of nations that allocate funding or establish legislation to support Cleantech, such as China, India, Germany, Australia, and USA. This section will also evaluate the status of Silicon Valley in California (the center of the US venture capital industry), now the heart of Cleantech innovation. 5. Concluding Remark discusses globalization of Cleantech as an infrastructure project and the key to the deployment of Cleantech innovations. The goal of this chapter is to provide readers with an overview of the scope and trends in venture-capital-funded innovation in Cleantech and its implications on world climate change.

Venture Capital Investment Trend Venture Capital Venture capital (also known as VC or Venture) [1] is provided as seed funding to earlystage, high-potential, growth companies and more often after the seed funding round as growth funding round (also referred as series A round) in the interest of generating a return through an eventual realization event such as an IPO (Initial Public Offering) or trade sale of the company. To put it simply, an investment firm will give money to a start-up and growing company. The growing company will then use this money to do research, build infrastructure, develop products, advertise, etc. The investment firm is called a venture capital firm or company, and the money that it gives is called venture capital. The venture capital firm makes money by owning a stake in the firm it invests in. The start-up company that a venture capital firm will invest in usually has a novel technology or creates a business model. Venture capital investments are generally made in cash in exchange for shares in the invested company. It is typical for venture capital investors to identify and back companies in high technology industries such as biotechnology, IT (Information Technology), now Cleantech. The source of funding of Venture capital typically comes from institutional investors, endowment funds, and high net worth individuals and is pooled together by dedicated investment firms. Venture capital firms typically comprise small teams with technology backgrounds (scientists, researchers) or those with business training, financial management, or deep industry experience.

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A core skill within VC is the ability to identify novel technologies or business models that have the potential to generate high commercial returns at an early stage. By definition, VCs also take a role in managing entrepreneurial companies at an early stage, thus adding skills as well as capital (thereby differentiating VC from buyout private equity that typically invest in companies with proven revenue), and thereby potentially realizing much higher rates of returns. Inherent in realizing abnormally high rates of returns is the risk of losing all of one’s investment in a given start-up company. As a consequence, most venture capital investments are done in a pool format where several investors combine their investments into one large fund that invests in many different start-up companies. By investing in the pool format, the investors are spreading out their risk to many different investments versus taking the chance of putting all of their money in one start up firm.

Venture Capitalist A venture capitalist (also known as a VC) [1] is a person or investment firm that makes venture investments, and these venture capitalists are expected to bring managerial and technical expertise as well as capital to their investments. A venture capital fund refers to a pooled investment vehicle, often an LP (Limited Partner) or LLC (Limited Liability Corporation) that primarily invests the financial capital of third-party investors in enterprises that are too risky for the standard capital markets or bank loans. Venture capital is attractive for new companies with limited operating history that are too small to raise capital in the public markets and have not reached the point where they are able to secure a bank loan or government small business loan. In exchange for the high risk that venture capitalists assume by investing in smaller and less mature companies, venture capitalists usually get significant control over company decisions, in addition to a significant portion of the company’s ownership. Young companies wishing to raise venture capital require a combination of extremely rare yet sought after qualities, such as innovative technology, potential for rapid growth, a well-developed business model, and an impressive management team. VCs typically reject 90–98% of opportunities presented to them, reflecting the rarity of this combination. The general rule of thumb for the success rate of VC-invested start-up is: about 60% start-up failed; 30% existed for 5 or more years with little or no profit; only about 10% start-ups go to IPO or are acquired by larger corporations as a separation business unit or merge into an existing operation of a larger corporation.

Venture Capital and Cleantech Traditionally, the venture capital (VC) industry has been focused on information technology, Internet, wireless and broadband communications, and biotechnology. All projects related to innovation of energy generation, energy saving, waste management, and

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environmental impact were grouped into a general industry category and the investment funds were relatively small. In recent years, however, Cleantech investment has become a separate category and played a major role in the VC portfolio.

Venture Capital Investment in Cleantech The following table lists venture capital investment in Cleantech for 2002 to 2010. Cleantech investment in 2010 is the second highest in 2010, but the volume of deals remained strong (North America, Europe, China, Israel, and India. Source: Cleantech Group [2]). Year

Investment (Billions US $)

Deals

2002

$0.9

164

2003

$1.3

301

2004

$1.3

333

2005

$2.0

381

2006

$4.5

409

2007

$6.1

488

2008

$8.5

567

2009

$5.6

557

2010

$7.8

715

Cleantech Venture Investment in 2009 In 2009, 128 venture funds in the USA collected $13.7 billion, down from 205 funds that collected $29.3 billion in 2008, and 204 funds that collected $40 billion in 2007, according to data tracker VentureSource. About US $5.6 billion in venture capital investment went to Cleantech firms in 2009 [3] – including solar, wind, energy efficiency, transportation, and biofuel. The investment flow underscores that: (a) Cleantech became a dominate force. In 2004, the sector accounted for about 3% of venture capital investment. That share expanded to about 25% in 2009. The Cleantech sector in 2009, for the first time, received more private venture capital than any other sector, including software. (b) Energy efficiency and transportation sector became important. The top Cleantech recipient in 2009 was solar, which received 21% of it. However, solar investment declined 64% from the previous year, while the transportation and energy efficiency sectors had record years. The investment decline for solar stems from several factors, including the large investment required to commercialize technologies. Meanwhile, energy efficiency

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firms – those concentrating on a diverse range of technologies ranging from lighting to green building materials – often require less money to bring products or services to market, may rely on more proven technologies, and, consequently, may pose less risk to investors. In 2009, venture capital for transportation – for items such as electric cars and new battery technology – rose 47% to $1.1 billion. Investment in energy efficiency rose 39% to $1 billion. (c) The raise of global interest. Northern America was still dominant for Cleantech venture capital, but its share is declining. In 2009, North America received 62% of Cleantech venture capital dollars, down from 72% in 2008. Europe and Israel received 29% of 2009 dollars, an increase of 22% from 2008. The increased share of venture capital funding in Europe and Israel may reflect the desire for investors to pursue less risky deals in markets where Cleantech is already more widely deployed. Concurrent with the apparent decline in share of Cleantech venture capital in North America, the US Government has invested around $16 billion a year and plans to increase investment to $50 billion annually by 2020. Part of the funding, about $15 billion, will come from tax credits and other fiscal measures. The rest will be derived from rate-payer increases for electricity and other energy. This spending should lead to very large investments in wind, solar, and carbon capture. In addition, the bill would bring into existence the first nationwide system of building codes, which would be further tightened every year through 2030. These codes will lead to considerable demand for green building technologies.

Cleantech Venture Investment in 2010 Cleantech had a second record year in drawing in venture capital in 2010, with $7.8 billion invested globally. The first half of 2010 had an increase in venture capital investing while the second half of 2010 saw two consecutive quarters of declines. Overall, global investing totals saw a 28 percent increase compared to 2009, making it the highest year for investment after 2008 ($8.5 billion). The drawback in the last half of 2010 seems to reflect some skepticism among venture capitalists on capital-intensive investments that are risky and can take years to bear fruit. Instead, investors are looking more towards capital investments like energy efficiency which is less costly to invest. BrightSource Energy is one of the capital-intensive investments and success stories of 2010 received funding sources beyond venture capital. The company behind a massive 392-megawatt Ivanpah solar thermal plant in California’s Mojave Desert received $1.4 billion Department of Energy loan guarantee and was preparing an initial public offering (IPO) in 2011 in a public stock market. Overall, venture capital in North America totaled nearly 70 percent of all the venture capital invested globally in 2010, with dollars invested surging 45 percent to a total $5.28 billion. Big deals included: solar manufacturer Solyndra’s $175 million raised in IPO,

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$350 million raised by electric vehicle infrastructure startup Better Place, $150 million raised by BrightSource Energy, $110 million raised by Abound Solar and $165 million raised by Switzerland’s smart meter company Landis + Gyr. IPOs had a record year as well, with eight of the 10 top IPOs in China worth a combined $10 billion. The country is emerging as a huge energy market with lots of opportunity for Cleantech companies. It has pledged over $7 billion to smart grid alone and continues to subsidize solar panel manufacturers that have undercut global competition in price. The top IPO of the year was the $3.6 billion offering in Madrid by the renewable energy unit of Italian utility Enel Green Power, the renewable energy unit of Italian utility Enel. The most active Cleantech venture capital investors of 2010 were: Chrysalix Energy Venture (16 rounds), Draper Fisher Jurvetson (16 rounds), Carbon Trust Investment Partners (12 rounds), Element Partners (12 rounds), Kleiner Perkins Caufield & Byers (12 rounds). In addition to venture capital funded projects, governments of major nations all invested heavily. According to Bloomberg New Energy Finance (BNEF), global investment in Cleantech reached $243billion in 2010. BNEF indicated that the sector is halfway to achieving the $500 billion a-year investment target that experts believe is required to ensure greenhouse gas emissions peak by 2020. BNEF found that 2010 investment levels surpassed the $186.5 billion spent in 2009, significantly buoyed by an increase in spending in China where BNEF said Cleantech investment in China had expanded 30 per cent year-on-year to US$51.1 billion. The study covered investment in renewable energy, energy efficiency, smart-grid equipment, biofuels, and carbon capture and storage. We can see venture capital investment in Cleantech is only a small portion of the total investments by government, but these VC supported projects are often the most creative and full of scientific innovations.

The Scope of Cleantech The scope of Cleantech encompasses a broad range of technology categories, including renewable energy, energy efficiency, green building, transportation, smart power, smart grid and energy storage, and air, water, and waste. The following lists [4] provide examples of technologies within each of the major categories.

Renewable Energy The Renewable Energy category includes innovations that use, enable, and accelerate the migration to renewable energy. Renewable energy encompasses technologies that use waste streams to directly produce energy.

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Examples include low-emission power sources, such as solar, biofuel, wind, wave and tidal energy, and hydropower. Example technologies include: ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ●

Solar for energy production CIGS Thin-film solar manufacture Concentrating solar PV Coatings for solar panels Polysilicon supply and manufacture Residential scale solar deployment Ethanol Bio-based fuels Tidal energy Wave energy capture Landfill gas to energy systems Agricultural waste to energy systems Hydropower Turbine blade design Advanced fluid flow designs Wind power aerodynamics Wind power conversion efficiency

Energy Efficiency The Energy Efficiency category comprises technology that can significantly reduce wasted energy (including natural gas), driving toward the common goal of saving the equivalent of ‘‘a power plant a year.’’ Examples include advanced light sources and controls, smart/user-friendly energy management systems, energy-efficient water heaters and other appliances, high-efficiency industrial process systems, motors, pumps, and advanced space heating and cooling systems. Example technologies include: ● ● ● ● ● ● ● ● ● ● ●

Pumps for water/material Industrial process improvements Natural gas monitoring and control (industrial or residential) LED lighting Advanced lighting controls Water heating HVAC solutions Heat pumps Waste heat management Efficient heat transfer Utility-scale natural gas controls

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Display systems for energy management Materials used in microelectronics manufacturing Deposition and sputtering processes Alternatives to heat-intensive processes Cooling solutions Glass materials production Pure manufacture techniques for fuel cells

Green Building The Green Building category focuses on reducing the environmental impact of building construction or operation through improved design or construction practices, new or innovative use of building materials, or new hardware or software applications. Technologies are applied directly to the built environment. (Building energy efficiency submissions will be considered in the Energy Efficiency category). Examples include improved site planning, water management systems, reduction of hazardous materials in building construction or operation, use of new environmentally friendly or recycled materials, systems to improve indoor environmental quality, and systems for improved waste reduction or disposal. Example technologies include: ● ● ● ● ● ● ● ● ● ● ● ● ● ●

Insulation materials Cement alternatives Cement production techniques Building integrated PV (BIPV) Indoor air filtration systems Modular housing Disaster relief housing Architectural designs for thermal management Office environment Low VOC carpeting and flooring Water saving toilets, showers, plumbing Residential heat pumps Recycled materials for use in building material Design improvements to commercial environment

Transportation The Transportation category encompasses transportation and mobile technology applications that improve fuel efficiency, reduce air pollution, reduce oil consumption, or reduce vehicle travel (not limited to automobiles). Technologies are applied directly to transportation systems or vehicles. Examples include new vehicles and new types of

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transport services and infrastructure, efficient batteries, fuel cells, bio-based transportation fuels, and use of information technologies. Example technologies include: ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ●

Fleet management hardware and software systems Routing and data solutions for public transportation operators Logistics management Carpooling solutions Hybrid motor systems Storage of energy specifically applied to vehicles Plug-in hybrid vehicles All electric vehicles Fuel cell vehicles Biodiesel applications Intermodal tracking and monitoring NOX/SOX reductions for ocean going vessels Cold-ironing systems Diesel particulate matter filters for locomotives Combustion designs Fuel blends Flex fuel engines and applications Drivetrain conversion kits Route management via GPS networks Exploiting GPS and location information Monitoring and control of driver behavior

Smart Power, Green Grid, and Energy Storage The Smart Power, Green Grid, and Energy Storage category promotes links between information technologies and electricity delivery that give industrial, commercial, and residential consumers greater control over when and how their energy is delivered and used. It includes improvements in all forms of energy storage, from battery technology for consumer-scale products to large chemical, metal, biological, or other approaches to storage of utility-scale energy, as well as methods for controlling or increasing the efficiency of energy storage or energy transmission. Examples include wireless metering and use of real-time pricing information, intelligent sensors, batteries, fuel cells, flywheels, and advanced materials or systems for energy transmission, such as hardware and software controls. Example technologies include: ● ● ● ●

Advanced metering Network architecture for power management Cloud computing, applied to grid Batteries

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Novel battery chemistry Nickel-metal hydride improvements Hydrogen storage Li-ion cells Form factor improvements Improved cycle life for batteries Depth of discharge for batteries Solid oxide fuel cells Novel catalysts in batteries, fuel cells Advanced fuel cell membranes Methanol fuel cells PEM fuel cells Flywheels Grid scale hardware and infrastructure Power storage for intermittent, renewable resources Monitoring and deploying power generated from renewables Transmission efficiency Electrical engineering and controls for power distribution Novel metals and alloys for power transmission Superconducting power transmission Real-time power monitoring

Air, Water, and Waste Entries in the Air, Water, and Waste category focus on improving resource availability, conservation, and pollution control. With respect to waste, the category focuses on cradleto-cradle approaches to reduction, reuse, and recycling technologies, as well as innovative business models and approaches to materials usage. Air examples include services, instruments, and equipment related to emission control, treatment, or reduction technologies. Also included are creative approaches to greenhouse gas reduction, including carbon conversion and sequestration. Water examples include treatment, storage and monitoring, recycling and conservation technologies. Waste examples include waste management equipment; sorting; resource recovery processes; pollution prevention, control, and treatment technology; as well as waste reduction through innovative recycling processes and new recyclable materials, such as bio-based plastics. Example technologies include: ● ● ● ● ●

Water monitoring – on-site in-situ real-time water monitoring for pathogens Cooling solution On-site wastewater recycling – industrial and commercial applications Advanced water metering Storm-water and flood control, rainwater harvesting

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● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ●

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Smart irrigation On-site water disinfection Membranes for water treatment Advanced filtration without membranes Produced water (from oil exploration and drilling) Energy-efficient water pumping Reverse osmosis Advanced filters and filtration (air or water) Emissions controls Scrubber technology Carbon and GHG monitoring and control Carbon sequestration Carbon capture and storage Technology enablers for carbon markets Reduction and remediation of VOCs Waste cleanup and remediation DI water supply Agricultural waste treatment Recycling Microbial water treatment Bio-based packaging solutions Methane capture and storage Soil technology Natural pesticides Clean coal

The scope of Cleantech is extremely broad and involves many scientific and academic disciplines. It is a good field for today’s science and engineering students to pursue as a career for the next decade.

Cleantech Technology Trend Technology Trend provides an overview of the key technologies that received the majority of the venture capital investment. These include: renewable energy such as solar thermal systems, solar photovoltaic, wind turbine designs, fuel cells, and biofuels; energy efficiency systems focus on new conception of battery technology, lighting, and green building; innovative resource management is based on software and hardware, such as wireless smart meters and smart grids. Venture capital firms have invested almost $20 billion into hundreds of Cleantech start-ups since 2005. All of these firms are looking to launch a disruptive force into their target markets, scale rapidly, and grow quickly. Some of these firms will actually make it. Greentech Media [5] announced on March 8, 2010, the top 50 US VC start-ups in

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Greentech (Cleantech) that Greentech Media rated as having a chance of succeeding and making an impact on the energy-intensive lives. The selection criteria are: ● ● ● ● ● ● ● ●

Technological edge Potential to severely disrupt the market Great management team Massive market opportunity Substantial war chest (financial resources) Feasible exit strategy Sheer hype power Only venture-backed private firms

In addition, this section added eleven selected high-profile companies with () added in the following list. These companies generated publicity and general interests; they are either sponsored by VC, or by major corporations. The following information is compiled from sources of green-media.com, linkedin.com, the Web sites of respective companies, Google search, and news stories from Wall Street Journal and Business Week. Most of the companies have employees ranging from 50 to 300 and were founded between 2004 and 2008. These companies received VC funding ranging from $20 million to $100 million; some of them also received additional government agency funding; few have already gone public and their stocks are likely traded in NASDAQ exchange. The combined list of 61 promising companies is grouped in the following nine technologies: 1. Solar – 15 companies: Brightsource Energy, Chromasun, Enphase Energy, eSolar, Innovalight, Nanosolar, Petra Solar, SolarCity, Solyndra, Suniva, SunRun, Ausra, Enel , SolFocus, Stion 2. Smart Grid and EV Infrastructure – 13 companies: Arcadian Networks, Better Place,  CPower, Coulomb Technologies, EcoLogic Analytics, eMeter, OPOWER , Proximetry, Silver Spring Networks, SmartSynch, Tendril Networks, Trilliant 3. Green Buildings, Lighting – seven companies: Adura Technologies, Bridgelux, Optimum Energy, Recurve, Redwood Systems, Serious Materials, Turbine Air Systems 4. Biofuels and Biochemicals – six companies: Amyris, LS9, Sapphire Energy, Solazyme, Synthetic Genomics, Renewable Energy Group 5. Batteries, Fuel Cells, Energy Storage – six companies: Bloom Energy, Deeya Energy, EEStor, General Compression, A123 Systems, Axion Power International  6. Transportation – three companies: Coda Automotive, Fisker Automotive, Tesla Motors 7. Other Energy – Wind, Nuclear, Cleaner Coal, Geothermal – seven companies: Laurus Energy, Nuscale, Nordic Wind Power, Potter Drilling, Ze-Gen, Accio Energy, Carbon Trust  8. Water – three companies: Oasys, Miox, Purfresh 9. Green Information Technology – two companies: Hara, Sandforce

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The following is an undated description of each company. When information is available, each company’s headquarter location is added to illustrate the geographical distribution of Cleantech ventures; the founding year is also included to show the longevity of the company.

Solar Brightsource Energy (BE): located in Oakland, California, and founded in 2006. The original (BE) technology was based on solar thermal parabolic trough technology, which focused sunlight on pipes carrying synthetic oil. In recent years, BE has advanced solar thermal technology by developing new flat mirror reflectors that increase solar-to-thermal conversion efficiency from about 36% (for the older parabolic trough technology) to above 40%. At the same time, the new design significantly reduces overall equipment and project costs. The company is developing more than 4 GW of solar power projects in southwestern USA, enough to power 1.4 million homes. BE now has more than 2.6 GW of power under contract, including the two largest solar power agreements ever – 1,300 MW with Southern California Edison and 1,310 MW with Pacific Gas & Electric Company. The company’s Solar Energy Development Center in Israel’s Negev Desert is now fully operational and demonstrating the effectiveness of its Power Tower technology. Now the challenge is getting past further environmental objections to its first 396-MW power plant in California’s Mojave Desert. Chromasun: located in San Jose, California, developed Micro-Concentrator (MCT) as next-generation high-performance solar collector that uses the same technology as utilityscale solar systems, except now in a much smaller package. It has been designed specifically for rooftop integration. The MCT is low profile, lightweight, and has no external moving parts, so it is simple to mount and easy to maintain. Using a 25 Fresnel reflector optic, the MCT generates temperatures up to 220 C (428 F), something an ordinary flat panel solar collector cannot achieve. Air conditioning accounts for 50% of the demand for power during peak periods in California. Chromasun uses solar thermal collectors to gather solar heat to run a double effect chiller that curbs peak power, broadens the market for solar thermal technology, and fits well within the practices of the building trades. Danish investor VKR Holding led the $3 million investment, along with GoGreen Capital and two unnamed individuals in the USA. Enphase Energy: located in Petaluma, California, and founded in 2006, has new design of solar photovoltaic microinverter, a device that converts direct current (DC) from a single solar module (panel) to alternating current (AC). The contract manufacturing model is working and the company continues to grow. There are a number of microinverter start-ups but Enphase is the only one to reach credibility and volume shipments in

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a high-growth $2 billion market. This well-funded microinverter innovator has shipped more than 120,000 units for residential and commercial deployments. eSolar: founded in 2007 and based in Pasadena, California, engages in the design, development, construction, and deployment of modular and scalable concentrating solar power (CSP) plants for utilities in the USA. Its power plants utilize small mirrors that track the sun with high precision and reflect the sunlight to a tower-mounted receiver, which boils water to create stream that powers a turbine and generator to produce solar electricity. It sought funds to build solar thermal power plants; then switched strategies and decided to license its technology and sell equipment, leaving the actual building of the power plants to others. Since 2009, it has signed deals that will lead to gigawatts worth of its solar technology planted in China, India, Africa, and the Middle East. A 5 MW demo plant went up in 2009 and construction on the first 92 MW begins 2010. ESolar has software that helps improving the efficiency of the overall plant. Google, India’s Acme Group, Oak Investment Partners, and NRG Energy funded the company. Innovalight: based in Sunnyvale, California, and founded in 2002, is dedicated to helping world-class crystalline silicon cell manufacturers improve the performance of their solar cells. Innovalight has developed a portfolio of patented technologies and materials that allow current cell manufacturing companies to cost-effectively produce solar cells with higher conversion efficiencies. Representing over 90% of the solar photovoltaic (PV) market, crystalline silicon solar is the dominant PV technology. Manufacturers of crystalline silicon solar cells have reached the limits in the conversion efficiency of solar cells using current designs. Innovalight’s Cougar™ Platform is a new low-cost cell design enabled by Innovalight Silicon Ink that allows silicon wafer manufacturers to boost their cell efficiency by up to 2% with a low capital outlay. Nanosolar: located in San Jose, California, and founded in 2001, with a facility in the Berlin capital region as its European site. Its solar cell is to deposit a thin film of a semiconductor using a printing process – far faster than conventional high-vacuum deposition – and to create an efficient, durable solar cell. Nanosolar can now apply equipment from the printing industry to produce solar-electric foil at very high speeds, bringing the economics of printing to the world of semiconductor manufacturing. The thin-film pioneer got started in 2002, making it one of the earliest thin-film companies supported by Silicon Valley. Since then, Nanosolar has used every avenue of funding to fund their potentially disruptive solar firm, now at about $500 million in funding to date. Nanosolar is shipping product in the 10–12% efficiency range and has panels in the lab topping 16% efficiency. Nanosolar faces the same challenge as every other solar panel manufacturer – keeping up with silicon and cadmium telluride prices and efficiency. Petra Solar: located in South Plainfield, New Jersey, and founded in 2006. The core technology is a system, which operates as individual power generation stations, combines solar power, smart grid, and power management technologies to enable utilities to

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improve power quality and grid management. Petra Solar’s systems operate on streetlight and utility poles, connecting directly to the grid’s secondary voltage lines at the pole. Petra Solar is also a market channel player; its more than $50 million in VC funds are exploiting an untapped sales channel – solar panels on utility and power poles. Petra has a large contract with Public Service Electric and Gas, New Jersey’s biggest power utility, to install solar panels on streetlights and power poles across the distribution network. PSE&G looks to install 200,000 panels in 2010, according to PSE&G. Petra Solar has potential for high growth in a new application. SolarCity: headquartered in Foster City, California and founded in 2006, is a full-service solar provider for homeowners, businesses and government organizations – the first company to provide solar power system design, financing, installation and monitoring services from a single source. Fast growing SolarCity has emerged as one of the largest residential solar installers in California and has moved into other solar-friendly states. The start-up has innovated in the installation field as well as in the financial field by offering leasing options for homes and small businesses. US Bancorp has set up a $100 million fund to finance SolarCity’s residential and commercial installations. Solyndra: founded in 2005 and headquartered in Fremont, California, with almost a billion dollars in venture capital and half a billion in US Department of Energy loan guarantees, Solyndra is the clear winner in money raising. It designs and manufactures photovoltaic systems, comprised of panels and mounting hardware, for the commercial rooftop market. Using a proprietary cylindrical modules and thin-film technology, Solyndra systems are designed to be able to provide the lowest system installation costs on a per watt basis for the commercial rooftop market. Solyndra operates a state-of-theart 300,000 ft2 highly automated manufacturing complex. When this handbook is about to go to press, the once a star in Cleantech - Solyndra filed for bankruptcy protection on September, 2011. Solyndra’s photovoltaic panels were, as the name implies, a cylindrical design, like a florescent light tube. They were more efficient, as they caught light from not only above, but also reflecting off the roof. But Solyndra’s process technology is more complex and more expensive to produce. Silicon is the primary material used in photovoltaic systems. In 2008, silicon price was $475 per kilogram; by mid 2011 silicon price dropped to $51 per kilogram. Solyndra’s technology needs only a fraction of (one estimate was around 1 to 2%) silicon material in comparison with conventional photovoltaic; as a result, Solyndra lost its competitive advantage. Solyndra’s 1100 employee at Fremont, California lost their jobs. It is possible another Cleantech firm could modify the design, infuse it with cash, and attempt to make a go in the future. Suniva: located in Norcross, Georgia, USA is a well-funded company that produces crystalline silicon solar cells. Investors NEA, Goldman Sachs and Warburg Pincus have invested more than $125 million. Solar cells that Suniva manufactures are made of Polysilicon which is created by refining sand or quartz, one of the most abundant

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materials on earth. After being refined and ‘‘grown’’ into extremely pure monocrystalline ingots, the ingots are carefully sliced into very thin wafers. The monocrystalline wafers then undergo processing steps which apply an electric field to them, a metal grid or pattern of electrodes is affixed, and both an aluminum backing and a surface antireflective layer are applied. Suniva utilizes a number of patents and proprietary knowledge and technologies in these processing steps which yield very high cell efficiency at low cost and when combined with the ability to use thinner wafers results in industry leading cost per watt levels. These Suniva monocrystalline silicon cells are marketed as ARTisun® series which generate more power with fewer panels, resulting in lower costs. SunRun: located in San Francisco, California and founded in 2006, offers residential solar system with Solar power purchase agreements (PPA) – home solar as a monthly service. The company has seen eight to ten times growth in 2009. SunRun has received venture funding from Foundation Capital and Accel Partners, as well as a $105 million tax equity commitment from an affiliate of US Bancorp. Residential PPAs from SunRun might be the disruptive piece that allows solar to better penetrate the residential roof market. Ausra Inc. located in Mountain View, California, provides solar thermal power, steam and energy systems for industrial processes and utility-scale electricity generation. (For detail see ‘‘> Globalization of Cleantech’’). Enel: is located in Viale Regina Margherita, Rome, Italy. The Italian energy company on July 14, 2010, inaugurated an innovative solar thermal plant that stores heat from the sun in molten salts. The Archimede plant of Enel, near Syracuse in southeastern Sicily, is the first to use molten salts as a heat transfer fluid. The 5-MW Archimede plant uses molten salt, rather than an oil called therminol, to transfer heat collected by parabolic mirrors to the boilers for making steam. The plant also sports molten salt storage tanks and a combined cycle gas facility so it can produce power on cloudy days or during the evening. While solar thermal developers have used tanks of molten salt to store excess heat, they have not used molten salt as the transfer fluid that runs in the pipes that sit above the mirrors where heat from the sun is collected. By deploying salt as the heat transfer mechanism inside the pipes of parabolic solar thermal parks as well as a storage medium, the efficiency of solar thermal power plants could inch up incrementally, because molten salt retains heat longer than therminol. Thus, more heat could be ultimately exploited from the mirrors. This approach may potentially help parabolic solar technology, the reigning but aging standard in solar thermal; better compete against heliostats and some of the other new solar thermal architectures. The system involves some 320,000 ft2 of mirrors that concentrate solar rays onto 17,700 ft of pipes containing the molten salts. The plant has a capacity of about 5 MW and is expected to save some 2,100 t of oil equivalent per year and reduce carbon dioxide emissions by about 3,250 t. Italy is Europe’s second largest producer of solar power after Germany.

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SolFocus: founded in 2005 and located in Mountain View, California with European operations in Madrid, Spain, and manufacturing in Mesa, Arizona as well as with manufacturing partners in India and China. SolFocus has developed leading concentrator photovoltaic (CPV) technology which combines high-efficiency solar cells (approaching 40%) and advanced optics to provide solar energy solutions which are scalable, dependable and capable of delivering on the promise of clean, low-cost, renewable energy. Its high-efficiency solar cells with advanced concentrating optics to provide high energy yield using just 1/1,000 the amount of photovoltaic material used in traditional photovoltaic systems. SolFocus, the most heavily funded concentrating solar start-up around, received $70 million in 2009 to a total of $150 million funding. Stion: located in San Jose, California founded in 2006, is a manufacturer of high-efficiency thin-film solar panels. On June 2010, it has raised $50 million from a VC belonging to Taiwanese Semiconductor Manufacturing Company (TSMC) which will take a 21% stake in Stion. The funding brought the total Stion VC investment since 2006 up to $114.6 million. The two companies have reached a series of agreements covering technology licensing, supply, and joint development. Existing investors Khosla Ventures, Braemar Energy Ventures, Lightspeed Venture Partners, and General Catalyst Partners also invested, this latest, series D round, VC investment will be used to expand its current San Jose facility to produce 100 MW worth of solar panels per year, up from the current pace of 10 MWs. TSMC has licensed Stion technology to build a large Copper indium gallium selenide (CIGS) thin-film factory in Taiwan. CIGS is mainly used in photovoltaic cells (CIGS cells); in the form of polycrystalline thin films.

Smart Grid and EV Infrastructure The smart grid of the future is a utility-managed system that orchestrates smart meters, solar panels, batteries, demand response systems and plug-in vehicle chargers to serve as ‘‘virtual power plants’’ scattered throughout a utility service territory. Arcadian Networks: founded in 2006 and headquartered in Valhalla, New York, designs and delivers wireless communication networks to utilities based on the private (licensed), secured 700 MHz spectrum. The 700 MHz appears to be a better choice (than 900 MHz) is rural areas, since the signal can travel farther without relays and can penetrate physical obstacles (such as crops and hilly terrain) that higher frequencies may struggle with. The other major advantage of the 700 MHz spectrum is that because it is licensed there is not any interference from other sources. While 900 MHz mesh networking solutions have dominated the market due in part to their lower costs, as interference continues to create problems for utilities, and as ‘‘intelligent provisioning’’ becomes more common, expect Arcadian Networks to compliment 900 MHz networks in situations where interference is just not acceptable.

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In 2010, Arcadian announced the release of their second generation router/gateway adding the ability to link with WiMax. While this router can also connect to all other major communication networks (3G/4G, 900 MHz, Ethernet, etc.) clearly, Arcadian is doubling down on licensed networks for smart grid. Better Place: founded 2007 and headquartered in Palo Alto, California, is a global company delivering the electric vehicle (EV) networks and services that make an electric car affordable to buy, easy to use, and amazing to own. BetterPlace builds and operates the infrastructure and systems to optimize energy access and use. A $350 million dollar funding round in January 2010 ranks as one of the largest Cleantech deals in history with a pre-money valuation of $900 million. Pre-money means the value of a company before the next VC investment. Commercial launch is targeted for 2011 for the bold electric-vehicle/charging-station/battery-swap/electricityselling start-up with an initial focus on Israel and Denmark. Investors include HSBC, Morgan Stanley Investment Management, Lazard Asset Management, VantagePoint Venture Partners, et al. Better Place is looking to install between 15,000 and 20,000 charging stations in both Israel and Denmark in the near-term. This firm could be a Google or Netscape-type market disruptor. But even a dominant role as an urban vehicle, as a fleet vehicle, as a delivery vehicle, Better Place could win big in a niche market. CPower : founded in 2000 and based in New York, turns commercial buildings into electricity generators by getting its 1,500 commercial customers to cut back on energy during peak periods and selling the saved kilowatts to utilities when the grid is under stress. Cash is the lure for clients: Almost all the money CPower earns goes right back to them. Owners of a 50-story Manhattan tower, for instance, can save up to $30,000 per year. In Texas, customers are getting checks for 15–20% of the totals spent on electricity. With paybacks like that, it is not hard to understand why CPower is booming. In 2010, the company has gone nationwide with some 800 MW of demand response under curtailment management and is no. 3 in the demand response arena behind public companies EnerNOC and Comverge. CPower is looking to quickly move into other energy services, including reserves and frequency regulation, renewable energy credits, and energy efficiency for consumers. The firm, founded in 2000 as ConsumerPowerline and rebranded in 2008 as CPower, has raised $35 million from Mayfield Fund, Expansion Capital, Bessemer Ventures, Schneider Electric Ventures, New York City Investment Fund and Intel Capital. Coulomb Technologies: founded in 2007 and headquartered in Campbell, California, builds a vital piece of the EV infrastructure – charging stations connected to the grid with power and data. Coulomb was founded on two premises – that every charge station should be networked and that Coulomb needed to be a self-sustaining business model – they win revenue from the sale of the charge station and from fee-based charge services. Investors include Voyager Capital, Rho Ventures, Siemens Venture Capital and Hartford Ventures.

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EcoLogic Analytics: founded in 2000 and headquartered in Bloomington, Minnesota, provides meter data management (MDM) software solutions and decision management technologies for utilities. They offer a suite of software solutions that include gateway engines, meter data warehouse, meter read manager, meter reading analytic, navigator graphical user interface, automated validation engine, network performance monitor and reporting engine, real-time outage validation engine, data synchronization engine, calculation engine and residential rate analysis. Their MDM solutions also integrate with other billing systems to business users in the enterprise. EcoLogic Analytics was chosen as the vendor to provide MDM for PG&E, the biggest deployment in North America. In 2009, the company landed its second major contract with Texas utility Oncor and served as the MDM provider for more than three million electric meters. eMeter: founded in 1999 and headquartered in San Mateo, California, makes software that manages the enormous volume of data coming from smart meters, providing both MDM and AMI (Advanced Metering Infrastructure) integration for utility information systems. eMeter’s solutions also allow for demand response and real-time monitoring of resource usage, yielding greater energy efficiency and more reliable service, while minimizing the costs of AMI deployment, data management, and operations. The company competes with AMI companies that can provide their own software AMI and MDM software such as Itron and Sensus, as well as other software companies such as Oracle. In early 2009, eMeter announced a deal with CenterPoint Energy to support the Texas utility’s plan to install two million smart meters in its territory. That follows deals with Alliant Energy, Jacksonville Electric Authority, the Canadian province of Ontario, and European energy company, Vattenfall. The company claims to have more than 24 million meters under contract. eMeter has transitioned from just providing MDM solutions for utilities into consumer services. OPOWER: founded in 2007 and headquartered in Arlington, VA., is an energy efficiency and Smart Grid software company that helps utilities meet their efficiency goals through effective customer engagement. Using cutting edge behavioral science and patent-pending data analytics, the OPOWER platform enables utilities to connect with their customers in a highly targeted fashion, motivating reductions in energy use, increased program participation and overall customer satisfaction. Six of the ten largest utilities in the United States use OPOWER to significantly improve the effectiveness of their energy efficiency portfolios. For utilities with Advanced Metering Infrastructure (AMI), the OPOWER platform represents a cost-effective way to convert hourly data into measureable peak and overall savings, delivering the value of the Smart Grid directly to their customers. In late 2010, OPOWER raised $50 million in a round led by Accel and Kleiner Perkins. Proximetry : founded in 2005 and headquartered in San Diego, California, provides network and performance management solutions for wireless networks to enable network operators to visualize, provision, and actively manage their networks, especially to support mission-critical communications. The company’s software solution, AirSync,

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enables real-time, network-wide visualization, management, and active network control from a single system and location for multivendor, multifrequency, multiprotocol wireless networks. This so-called ‘‘intelligent provisioning’’ which provides ‘‘dynamic bandwidth’’ matching network resource priorities to user and device needs seems like a logical extension of smart-grid networking, and we expect this to be a major new trend going forward. Proximetry is working with San Diego Gas & Electric, widely considered to be one of the most innovative utilities in North America. Silver Spring Networks: founded in 2001 and headquartered in Redwood City, California, has developed standard-based networking for smart meters for close to a decade – building routers and hubs that connect via a wireless mesh protocol. The firm has made announcements of utility contracts with Oklahoma Gas & Electric, Sacramento Municipal Utility District, AEP, and Florida Power & Light and closed a $100 million investment from blue-chip VCs including Kleiner Perkins and Foundation Capital, bringing its VC total to $250 million. Revenues are estimated in the $100 million range a year. It is one of the leading VC-funded smart-grid start-up. SmartSynch: founded in 1999 and headquartered in Jackson, Mississippi, its GridRouter is a modular, standards-based, upgradeable networking device that can handle almost any communications protocol that a utility uses. Four networking card slots allow a single box to handle ZigBee, WiFi, WiMax, or other proprietary communications standards simultaneously. The cards can be removed so utilities can swap out and/or upgrade their networks without replacing the basic piece of installed equipment. It provides communication to any device on the grid over any wireless network. Potentially, that could eliminate some of the fear and uncertainty surrounding smart-grid deployments. The Tennessee Valley Authority selected SmartSynch to serve as the communications backbone in its renewable program. Tendril Networks: founded in 2004 and headquartered in Boulder, Colorado, makes a varied suite of hardware and software solutions for applications such as demand response, energy monitoring, energy management, and load control. It offers an energy management system for consumers and utilities, smart devices (such as smart thermostats, smart plugs, and in-home displays), as well as Web-based and iPhone-enabled displays and energy controls. The company also develops applications for utilities such as network management, direct load control, customer load control. The start-up has deals in place with more than 30 utilities and had a large commercial roll out in 2009, along with a number of field trials. In 2009, the company raised a $30 million third round, bringing its total to more than $50 million and making it one of the better funded private companies competing in the Home Area Network space. General Electric’s Consumer and Industrial division has teamed up with Tendril to develop algorithms and other technology that will allow utilities employing Tendril’s TREE platform to turn GE dryers, refrigerators, washing machines, and other energy-gobbling appliances off or on to curb power consumption. Trilliant: founded in 1985 and headquartered in Redwood City, California, provides utilities with wireless equipment and management software for smart-grid communication

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networks. In 2009, Trilliant acquired SkyPilot Networks, a manufacturer of long-range, high-capacity wireless mesh networks. The acquisition allows them to offer complementary networks, both the neighborhood network and the wide-area network. Trilliant’s largest deployment is a 1.4 million device network spread over 640,000 km2 for Hydro One in Ontario, Canada.

Green Buildings, Lighting Adura Technologies: founded in 2005 and headquartered in San Francisco, California, is an energy management company that provides best in class solutions for existing buildings; a clean energy technology venture applying low-power wireless mesh networking to the lighting controls market. Approximately 85% of commercial office buildings in the USA are illuminated inside with fluorescent tube lights. In the vast majority of cases, these bulbs cannot be dimmed or turned off remotely. Only around 1% of lights in California office buildings are networked. Adura has created a wireless mesh system that effectively flips the lights off when no one is around and dims them when the sun is out. In a recent test conducted by PG&E, Adura managed to cut the power delivered to lights by 72%. Next, the company plans to connect its software to other devices in buildings. VantagePoint is a lead investor. Bridgelux: founded in 2002 and headquartered in Livermore, California, is focused on lowering the cost of LED-based solid-state lighting to a penny per lumen – a disruptive price achieved through clever packaging and innovating in the expitaxial processes of building the phosphor-coated film. Early in 2010, it announced a $50 million funding to finance a new fab, bringing its substantial fund-raising totals to over $150 million from investors including DCM, El Dorado Ventures, VantagePoint Venture Partners, Chrysalix Energy, and Harris & Harris Group. The firm is generating significant revenue. The big question is whether Bridgelux can outrun the big companies like Philips and Osram. Optimum Energy: founded in 2005 and headquartered in Seattle, Washington, addresses the commercial building market’s growing need for more energy-efficient heating, ventilating, and air-conditioning (HVAC) systems. Optimum Energy is the first company to take an enterprise application approach to commercial HVAC systems, and as a result, is changing the way these systems are operated and managed. Optimum makes software that dynamically controls the chillers – the enormous machines that cool water for airconditioning systems in skyscrapers. According to the company, there are more than 150,000 buildings that can use their product and if the software was used in each one, 75 GW could be taken off the grid. Adobe has installed it. Recurve: founded in 2004 and headquartered in San Francisco, California, provides home performance services that help homeowners and contractors create healthy, energyefficient homes through home energy audits and green energy remodeling. It is assembling a dynamic software package that will allow contractors large and small around the world to cut down the time, cost, and errors in conducting retrofits. A lot of the employees

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come from Google that does not happen at other construction companies. A number of large contractors are testing the software. Recurve’s next policy initiative: funding retrofits by getting them classified as carbon credits. Redwood Systems: founded in 2000 and headquartered in Redwood City, California, invented an entirely new, centralized power system capable of individually powering up to 64 LED light fixtures via low voltage network cable. Redwood replaces lighting wires and regular light bulbs with Ethernet cables and LEDs. A building will have a network in your ceiling that every light, smoke detector, and other device can link into, a very creative idea. Serious Materials: founded in 2002 and operating in California and Colorado, received $60 million VC funding in 2009. Their products include: Serious Windows high-performance insulated windows and glass, which can reduce heating and cooling energy costs and emissions by up to 40%. Windows are a $20 billion dollar market in the USA. Serious has won the Empire State Building retrofit project for their thermal windows. The retrofit project will receive the tax credit from the US Government. Turbine Air Systems: founded in 1999 and located in Houston, Texas, received $47 million VC investment in 2009. TAS is a recognized leader in designing, manufacturing, and servicing high-efficiency cooling, heating, and power systems for industry. It claims the industry’s most efficient chilled water and heating systems. TAS helps facility owners and managers reduce energy consumption and operating cost and reduce their facility’s carbon footprint to improve efficiencies by up to 50%, as compared to well-maintained air-cooled systems.

Biofuels and Biochemicals Amyris: founded in 2003 and located in Emeryville, California, has 220 employees, makes second generation biofuel from synthetic microorganisms. This synthetic biology start-up spun out of University of California at Berkeley with more than $200 million in VC funding. Amyris develops microbes that feed on sugars and secrete custom hydrocarbons for conversion into jet fuel, industrial chemicals, or biodiesel. Amyris claims to eventually produce biodiesel that can wholesale for $2 a gallon. In late 2009, the firm paid $82 million to Brazil’s Sa˜o Martinho Group for a 40% stake in an ethanol mill project and entered into agreements with three other Brazilian companies to produce ethanol and high-value chemicals. LS9: founded in 2005 and located in San Carlos, California. LS9 has developed a new means of efficiently converting fatty acid intermediates into petroleum replacement products via fermentation of renewable sugars. LS9 has also discovered and engineered a new class of enzymes and their associated genes to efficiently convert fatty acids into hydrocarbons. LS9 believes this pathway is the most cost, resource, and energy-efficient way to produce petroleum-replacement products and industrial chemicals. This translates

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into efficient land and feedstock use and directly addresses tensions between food versus fuel and chemical production. It plans to reuse a microbe instead of cultivating a new generation that cuts time and costs. Another added bonus: the company is working with Procter & Gamble on green chemicals and with Chevron on fuel. Sapphire Energy: founded in 2006 and headquartered in San Diego, California, plans to produce hydrocarbons from genetically modified algae grown in open ponds. Conceivably, it could be the cheapest and fastest technique for producing algae fuel. But it is also fraught with complications. Growing algae in open ponds for fuel oil at the moment is expensive and complex, and keeping genetically modified organism strains from being outcompeted by natural strains in the open is even more difficult. The company has raised $100 million plus from top-flight VCs, including the firm that invests on behalf of Bill Gates. Solazyme: founded in 2003 and headquartered in South San Francisco, California, is one of the oldest algae companies and the one that is also the furthest along. Solazyme avoids growing algae in ponds or bioreactors through photosynthesis. Instead, it puts algae in beer-brewing kettles, feeds them sugar, and grows them that way. The sugar adds to the raw material costs, but Solazyme makes up that cost because it does not have to extract the algae from water, one of the most vexing problems facing most algae companies. Solazyme says it will be able to show that its processes can be exploited to produce competitively priced fuel from algae in about 2 years. It has produced thousands of gallons already and has a contract to produce 20,000 gallons of fuel for the Navy. The company is already selling algae for revenue to the food industry. Chevron is an investor. Synthetic Genomics: founded in 2005 and located in La Jolla, California, plans to do research and develop next-generation biofuels using photosynthetic algae. Synthetic Genomics’ dynamic founder is J. Craig Venter, a well-known scientist; his vision is to use algae to produce hydrocarbons. In addition to a large funding of $300 million from Exxon, Synthetic Genomics has received funding from Draper Fisher Juvetson, Meteor Group, Biotechonomy, and BP. Renewable Energy Group: located in Ralston, Iowa, has produced and sold biodiesel for more than 10 years through its predecessor companies. It is leading the biodiesel industry by marketing more biodiesel than anyone in the USA. REG is the only fullservice biodiesel company offering plant management, risk management, raw material procurement, plant construction, biodiesel production, and biodiesel sales and marketing services. All planned facilities will utilize patented continuous-flow biodiesel production technology featuring water recycling and methanol recovery. REG serves hundreds of customers including on-highway fleets, original equipment manufacturers, maritime, military, home heating, and agriculture industries. In 2010, it has successful completion of $100 million private financing, one of the largest investments in biodiesel.

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Batteries, Fuel Cells, Energy Storage Bloom Energy: founded in 2001 and headquartered in Sunnyvale, California, after 10 years and close to $400 million VC investment, the fuel cell maker Bloom Energy showed its products on February 24, 2010. The Bloom Energy Server is a solid oxide fuel cell (SOFC) technology that converts air and nearly any fuel source – ranging from natural gas to a wide range of biogases – into electricity via a clean electrochemical process, rather than dirty combustion. Even running on a fossil fuel, the systems are approximately 67% cleaner than a typical coal-fired power plant. When powered by a renewable fuel, they can be 100% cleaner. Each Energy Server consists of thousands of Bloom’s fuel cells – flat, solid ceramic squares made from a common sand-like ‘‘powder.’’ Because of the media publicity and a large amount of VC investment, Bloom Energy technology deserves more discussions. A solid oxide fuel cell (SOFC) is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. Fuel cells are characterized by their electrolyte material; the SOFC has a solid oxide or ceramic, electrolyte. Advantages of this class of fuel cells include high efficiency, long-term stability, fuel flexibility, low emissions, and relatively low cost. The largest disadvantage is the high operating temperature that results in longer start-up times and mechanical and chemical compatibility issues (> Fig. 11.1). A solid oxide fuel cell is made up of four layers (refer to Wikipedia for detail), three of which are ceramics (hence the name). A single cell consisting of these four layers stacked together is typically only a few millimeters thick. Hundreds of these cells are then connected in series to form what most people refer to as an ‘‘SOFC stack.’’

Electric current

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. Fig. 11.1 Solid oxide fuel cell – Diagram from Wikipedia

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. Fig. 11.2 Bloom energy servers fuel cell boxes, photo taken from BloomEnergy.com

The ceramics used in SOFCs do not become electrically and ironically active until they reach a very high temperature and as a consequence the stacks have to run at temperatures ranging from 500 C to 1,000 C. Reduction of oxygen into oxygen ions occurs at the cathode. These ions can then diffuse through the solid oxide electrolyte to the anode where they can electrochemically oxidize the fuel. In this reaction, a water byproduct is given off as well as two electrons. These electrons then flow through an external circuit where they can do work. The cycle then repeats as those electrons enter the cathode material again. Bloom’s fuel cell technology is claimed to differ from others in four primary ways: it uses lower cost materials, provides high efficiency in converting fuel to electricity, has the ability to run on a wide range of renewable or traditional fuels, and is more easily deployed and maintained. Unlike traditional renewable energy technologies, like solar and wind, which are intermittent, Bloom’s technology can provide renewable power 24/7 (> Fig. 11.2). Each Bloom Energy Server provides 100 kW of power in roughly the footprint of a parking space. Each system generates enough power to meet the needs of approximately 100 average US homes or a small office building. For more power, customers simply deploy multiple Energy Servers side by side. Customers who purchase Bloom’s systems can expect 3–5 years of payback on their capital investment from the energy cost savings. Depending on whether they are using a fossil or renewable fuel, they can also achieve a 40–100% reduction in their carbon footprint as compared with the US grid. Fuel cells have been under development by many companies for decades. Any consumer electronics company from Samsung to Sharp, or auto maker, from Hyundai to Toyota, has researchers developing fuel cell technology. The problem is that fuel cells have remained too expensive. We need to see if Bloom can get those costs down. Bloom Energy Compares with Solar and Wind: The Bloom server will produce power for 9–10 cents/kWh after incentives. This price includes service, maintenance, gas, and all of the other costs associated with running it. Commercial solar installations, when incentives and external costs are added, generate power for around 10 cents/kWh. Residential solar generates power for around 19 cents/kWh and utility-scale solar costs around 11 cents/kWh. Cutting-edge wind turbines can generate power for 5 cents/kWh after incentives. On average wind is a little less costly than solar. One of the big hurdles that Bloom will have to leap is the reliability of the ceramic/ zirconium plates inside the fuel cell. These plates, which convert gas to electricity, must

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operate in an 800 C environment without becoming distorted or corrupted. User data will be heavily scrutinized. These plates may have a lifetime of 5 years: replacement at this pace is contemplated at nine to 10 cents/kWh price. If replacement occurs at a faster rate, it will increase cost. For a more detailed discussion, refer to [6]: www.wired.com/epicenter/ 2010/02/bloom-vs-solar-which-one-is-best/ The Bloom’s biggest selling point is availability. The box can produce power 24 hours a day in a completely predictable fashion. Solar panels only produce during the day and wind turbines are only active about 30% of the time. Worse, wind turbines in many areas generate most of their power at night. Fuel cells are by their very nature electricity-storage devices. Power does not get made until gas gets released into the fuel cell stack. General Electric and others are trying to build sodium or lithium battery packs to store power at wind and solar fields but these are in the experimental stage. Deeya Energy: founded in 2006 and headquartered in Fremont, California, develops and manufactures electrical energy storage systems. Deeya Energy’s innovation, the L-Cell, is based on a novel battery technology originally developed by NASA in the early 1970s as a potential energy storage method for long-term space flights. A few years ago, flow batteries were exotic, barely understood pieces of equipment. It has created a battery in which electrolyte flows in and out of the battery so it always stays charged. Utilities and cell phone carriers that need remote power will be the primary customers. In 2009, the company started shipping its first commercial products. The products cost around $4,000 a kW (or about half of what Bloom currently sells its products for). The company hopes to bring the price down to $1,000. EEStor: founded in 2001 and headquartered in Cedar Park, Texas, claims its energy storage technology as a ‘‘multilayered barium titanate ceramic capacitor,’’ and its units are based on ‘‘ultra capacitor architecture.’’ EEStor expects its technology to provide ten times the energy of lead-acid batteries at one tenth the weight and half the price. The firm is attempting to make material advances in ceramic powders used in high energy ultracapacitors. It is a novel idea, but needs more work. General Compression: founded in 2006 and headquartered in Newton, Massachusetts, is developing a system to store large quantities of energy from wind farms and make it available on demand. The cheapest form of energy storage remains compressed air, according to Electric Power Research Institute. To date, however, compressed air has relied upon finding geological formations where one can stuff thousands of cubic meters of air. General Compression, along with SustainX and Isentropic Energy, want to change that with mechanical systems. Both General (which recently raised $17 million) and Isentropic employ pressure and temperature differentials to store and generate heat. Duke Energy is building a 2-MW trial facility for General. A123 Systems: founded in 2001 and located in Waltham, Massachusetts, is a lithium-ion battery maker; plans to develop a nanoscale electrode technology, Nanophosphate™, which is built on a new nanoscale materials initially developed at the Massachusetts Institute of Technology. A123 Systems is now one of the world’s leading suppliers of

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high-power lithium-ion batteries designed to deliver a new combination of power, safety, and life. The company mass produces a variety of battery cells being used in DeWalt power tools, aircraft engine starters, hybrid vehicles, and electric vehicles. In December 2006, the US Advanced Battery Consortium (USABC) in collaboration with the US Department of Energy (DOE) awarded the company a $15 million development contract to optimize A123 Systems’ proprietary doped Nanophosphate battery technology for hybrid electric vehicle applications with a focus on power, abuse tolerance, durability, and cost. USABC is an organization composed of Daimler Chrysler Corporation, Ford Motor Company, and General Motors Corporation. After a series of private and corporate funding, the company on September 23, 2009, raised $380 million going public stock exchange. Axion Power International: founded in 2003 and located in New Castle, Pennsylvania, just outside of Pittsburgh, is developing advanced batteries and an energy storage product based on its patented lead carbon battery PbC Technology™. Conventional lead-acid batteries use negative electrodes made of sponge lead pasted onto a lead grid current collector. In comparison, its technology uses negative electrodes made of microporousactivated carbon with very high surface area. The result is a battery-supercapacitor hybrid that uses less lead. Axion received two grants total $1.1 million from Pennsylvania government agencies in 2010, after $26 million common stock offering in late 2009.

Transportation Coda Automotive: founded in 2009 and located in Santa Monica, California, designs, manufactures, and sells electric vehicles (EV) as well as lithium-ion (iron phosphate) battery systems built for transportation and utility applications. By the end of 2010, Coda will attempt to market an all-electric, mid-priced sedan to American drivers. Car start-ups like Tesla and Fisker have initially aimed at the top end of the market, where price and volume are less important factors. The entire auto market will be watching closely about Coda and BYD. BYD also will represent China’s first major EVentry into the US auto market. Coda’s car is based around a Chinese gas-burning car that has been retrofitted by US engineers – will be assembled in China and will come with a battery made through a joint venture between Coda and Lishen. A Chinese bank has agreed to lend $450 million to the battery venture. Fisker Automotive: founded in 2007 and headquartered in Irvine, California, plans to produce a luxury EV, but unlike the Tesla, the Fisker Karma is a plug-in hybrid, combining a battery and an internal combustion engine. On July 19, 2010, Fisker announced that it has finalized its purchase of a former GM factory where it will build plug-in hybrid electric vehicles that use some composites. Fisker is now in full possession of the 3.2 millionsquare feet/300,000 m2 Wilmington Assembly plant in Wilmington, Del., for which it paid Motors Liquidation Co. (MLC) $20 million. MLC is the holding company formed by General Motors Corp.’s bankruptcy.

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The purchase is supported by a $528.7 million Department of Energy loan for the development of two lines of plug-in hybrids. The Wilmington plant will be home to Project NINA, Fisker’s second line of plug-in hybrid electric vehicles, and where Fisker expects to ultimately create more than 2,000 factory jobs. This firm is another Kleiner Perkins portfolio company and uses batteries from A123. A123 was also an investor in their most recent $115 million funding round. The car sells for $87,900 and already has more than 1,400 people on the waiting list. Hendrik Fisker is a noted car designer who has worked with, among others, Aston Martin. Tesla Motors: founded in 2003 and headquartered in Palo Alto, California, engages in the design, manufacture, and sale of electric vehicles (EV) and electric vehicle power train components. The Tesla Roadster, the company’s first vehicle, is the first production automobile to use lithium-ion battery cells and the first production EV with a range greater than 200 miles (320 km) per charge. The base model accelerates 0–60 mph (97 km/h) in 3.9 seconds and claims twice as energy-efficient as the Toyota Prius. The company had produced its 1,000th Roadster as of January 2010 and has delivered Roadsters in at least 25 countries as of May 2010 (> Fig. 11.3). In May 2010, Tesla had bought the recently closed Toyota Nummi assembly plant in Fremont, California, where it intends to make its Model S luxury electric sedan and other future models. Also Toyota Motor and Tesla Motors will begin developing an electric version of Toyota’s RAV4. The electric vehicle (EV) prototypes will be made using the Toyota RAV4 model with a Tesla electric power train, with the intention of marketing the EV in the USA in 2012. The first prototype has already been built and is currently undergoing testing. Tesla plans to deliver a fleet of prototypes to Toyota for evaluation before the end of 2010. Both

. Fig. 11.3 This Tesla Roadster photo is a file from the Wikimedia Commons. (Commons is a freely licensed media file repository)

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companies will benefit from the mutual arrangement. Tesla wishes to learn and benefit from Toyota’s engineering, manufacturing, and production expertise. Toyota desires to learn more from Tesla’s EV technology. Tesla was founded in 2003 with initial VC investment of $7.5 million, by January 2009; Tesla had raised US $187 million and delivered 147 cars. In June 2009, Tesla was approved to receive US $465 million in interest-bearing loans from the US Department of Energy. The funding, part of an US $8 billion program for advanced vehicle technologies (Advanced Technology Vehicles Manufacturing Loan Program). Tesla went IPO on June 28, 2010.

Other Energy: Wind, Nuclear, Cleaner Coal, Geothermal Laurus Energy: founded in 2007 and located in Houston, Texas, extracts energy from coal in the form of syngas while it is still in the ground using a process known as UCG – underground coal gasification. Laurus then fractionalizes the syngas: carbon dioxide is separated and sent via a pipe to oil fields, where it is injected into other wells to help pull crude out of the ground. The rest of the gases – a combination of hydrogen, methane, and hydrocarbons – are then burnt in a gas-fueled power plant. Power from coal is not going away, so any disruptive technology that lowers the carbon footprint of coal and eliminates mountain top removal can be a new untapped piece of the energy mix. It is currently working with a Native American tribe in Alaska to build a UCG vein with a power plant. The process converts deep, un-mineable coal ‘‘in-situ’’ into multiple gas streams that can be used for low carbon energy production and as feedstocks for chemicals and other products. UCG technology unlocks previously un-mineable coal resources. By some estimates UCG could increase worldwide economically recoverable coal reserves by 600 billion tons, and increase the US reserves alone by up to 300%. Laurus Energy currently controls the rights to 13 billion tons of coal, the third largest coal holding in North America. Nuscale: founded in 2007 and headquartered in Corvallis, Oregon, is formed to construct and sell dedicated design of relatively small (160 MW thermal, 45 MW electric, hence 28% efficient) nuclear reactors, which will be modular, inexpensive, inherently safe, and proliferation-resistant. These reactors could be used for heat generation, production of electricity, and desalinization. NuScale’s modular nuclear reactor design could disruptively shift development away from the large-scale, over-budget, 10-year nuclear power plant projects. Small modular reactors are the ‘‘game-changer’’ in energy technology. NuScale can manufacture modular reactors on a factory assembly line – and cut the time to develop a nuclear plant in half. Nordic Wind Power: founded in 2005 and headquartered in Berkeley, California, is a merger of Swedish, US, and UK teams with decades of success in wind and other renewables. After 20 years of R&D and 10 years of very successful turbine operation in Sweden, Nordic Windpower was formed to commercialize the groundbreaking Nordic

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technology for wind turbines. All of the team members have a longstanding commitment to the renewables industry. With funding from Khosla Ventures, NEA, and Novus Energy Partners, Nordic Wind Power is the only wind turbine company in the USA to get a DOE loan guarantee – $16 million under the innovative renewable energy program. Nordic also received ‘‘significant’’ funding from Goldman Sachs in 2007. Their groundbreaking 1-MW two-blade turbine design challenges the traditional wind turbine design paradigm (> Figs. 11.4–11.6). In 2009, Nordic Windpower was awarded contracts for 19 of its N1000 1-MW wind turbines for public- and private-sector community wind projects in North and South America. The 70 m high N1000 turbine, with blades 59 m in diameter, will provide clean and renewable wind energy for schools, wind farms, a military base, a municipal utility, and a sustainable residential development. The projects span four states in the USA – Arizona, Indiana, Iowa, and Minnesota, and Uruguay in South America. Nordic Wind power will provide a combined total of 19 turbines as follows: 12 MW for community wind projects in Minnesota including a LEED Gold Certified housing development project that is the first of its kind in the USA; 3 MW for a wind turbine installer to add capacity to an existing wind farm in Uruguay; 2 MW for a construction, energy efficiency, and management company, for schools in Indiana; 1 MW for a municipal power company located in Iowa; and, 1 MW to power the grid at a military base in Arizona. Potter Drilling: founded in 2004 and headquartered in Redwood City, California, is focused on developing innovative drilling technology to enable clean energy solutions. It is based on a process known as hydrothermal spallation that has the potential to lower the cost and expand the range of deep hard-rock drilling. Geothermal provided 4.5% of California’s power in 2007 and advocates say that more power could be extracted from underneath the ground, even in non-geothermal hot spots.

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. Fig. 11.4 Wind turbine design – photo credit: NordicWindpower.com

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. Fig. 11.5 Wind turbine farm – photo credit: NordicWindpower.com

The problem has been getting to it economically and safely. Potter, founded by oil industry alums, has come up with a way to drill that is five times as fast and far less costly. Google. org is one of its investors. Ze-Gen: founded in 2004 and headquartered in Boston, is integrating advanced gasification technology to efficiently convert ordinary solid waste streams into synthesis gas and then into different forms of renewable energy. Ze-Gen dips organic landfill waste into molten iron and turns it into biogas. The architecture of the system eliminates many of the inefficiencies associated with biomass. It has a pilot plant and raised $20 million in 2009. The big challenge is in getting a production plant off the ground. The technology detail is described in Wikipedia.org. According to Ze-Gen, a typical 500 t per day waste-to-energy facility would cost about $150 million to build and would generate 13 MW of electricity and 170 t per day of ash waste. A similar size Ze-Gen facility would cost about $40 million to build and would generate 30 MWof electricity and minimal waste. Therefore, the installed cost per kilowatt hour of a Ze-Gen facility should be in the $1,300–$1,400 range, significantly lower than existing waste-to-energy facilities. Accio Energy: founded in 2008 and located in Ann Arbor, Michigan, was funded by private venture and received $250,000 federal contract with the US Defense Advanced

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. Fig. 11.6 The two-bladed design of Nordic‘s wind turbine allows it to be assembled on the ground and lifted in one piece. Most large wind turbines require the turbine housing, or nacelle, to be installed on the tower separately – photo credit: NordicWindpower.com

Research Projects Agency to continue the design and creation of its prototype device. It is developing a stationary ‘‘aerovoltaic’’ device that would be installed on rooftops, harvest wind, and turn it into electricity – without the moving parts associated with wind turbines. It would resemble a wind version of a solar panel. Aerovoltaic technology is an approach to wind energy that does not rely on electromagnetic effects to produce electricity from the wind’s kinetic energy, just as photovoltaic cells exploit photoelectric effects rather than electromagnetic principles. Aerovoltaic technology harvests energy by using the wind to move electrically charged particles against a voltage gradient. The electricity generated is fed directly to the grid or stored locally to provide energy on demand. Aerovoltaic technology plans to have its first external demonstrations in late 2010. Carbon Trust: founded in 2001 and headquartered in London, created a consortium of British businesses to pioneer the development of a world-class, commercially viable process to turn municipal and wood waste into transport biofuel. The consortium will work on the enhancement of a process called pyrolysis to process waste biomass to produce a greener and cheaper alternative to existing biofuels at mass scale, and to blend with fossil fuels. A key advantage of developing a process that will use existing organic waste, rather than plant crops is that it overcomes many of the issues associated with some current biofuels, and can lead to even greater carbon savings by avoiding methane emissions from

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landfill. The carbon footprint of this new pyrolysis biofuel could potentially achieve a carbon saving of 95% when compared to fossil fuels. This is a significantly higher carbon saving than some existing biofuels, which do not currently factor in the impacts of land use change when calculating the carbon saving. The consortium aims to produce its first biofuel from a pilot plant in 2014 and there is potential, using UK biomass alone to scale production to over two million tons per year. This will generate a saving of seven million tons of carbon, which is the equivalent to the annual emissions of three million cars.

Water Oasys: founded in 1999 and headquartered in Bellingham, Washington, is a water start-up to build around research from Yale University with $10 million in venture funds to see if its novel desalination technique, which exploits fundamental chemistry and waste heat, can go commercial. The process is a low-cost, low-energy desalination and purification technology for seawater, wastewater, and industrial waste streams. The company claims its ‘‘forward osmosis’’ process can desalinate water for about half the cost of standard reverse osmosis desalination. Miox: founded in 1994 and headquartered in Albuquerque, New Mexico, has a business plan to distribute water purification instead of the current centralized model. The company makes on-site water purification systems for gray water remediation and water recycling. Distributed water purification could potentially open up a flood of investment into water. Miox’s technology is in making the process cost-effective. The company’s system can purify a given amount of liquid with a volume of salt that is one fourth the amount of liquid chlorine that would be required. Investors include Sierra Venutres, DCM, and Flywheel Ventures. Miox already has some installations in the USA and around the world. Purfresh: founded in 1996 and headquartered in Fremont, California, offers a range of clean technology solutions that purify, protect, and preserve food and water. Purfresh’s innovative crop applications, food wash systems, and cold chain technologies effectively safeguard fresh produce before and after harvest. Its water technologies purify and disinfect bottled, pharmaceutical, and consumer products. The company, backed by Foundation Capital, kills microbes with ozinated water. Growers use it to keep food fresh on the way to store shelves and bottlers use it to sterilize plastic. Orders go up every time an E. coli outbreak occurs. Like Serious Materials, Purfresh is expanding from its base to become a full-service water and food company.

Green Information Technology (IT) Hara: founded in 2008 and headquartered in Redwood city, California, provides ondemand environmental and energy management software solutions that enable

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organizations to grow and profit while optimizing their resource consumed including energy, water, waste, carbon, and other natural resources. Hara enables organizations to comprehensively and securely manage their environmental record and leverage best practices in order to improve efficiency and manage risk. Large enterprise companies are actively looking for software solutions that provide actionable information, metrics, recommendations, and reporting regarding their carbon footprints. Hara has amassed an impressive list of customers, including Coca Cola, News Corp., Akamai, Intuit, Brocade, and Safeway. Sandforce: founded in 2006 and headquartered in Saratoga, California, has created a chip that makes it possible for search companies, banks, and other companies with large datacenters to swap out storage systems made out of hard drives in favor of drives made of flash memory, which only use about 5% of the power. In real terms, it means dropping the power budget for storage systems from $50,000 for 5 years to $250. Storage giant EMC has invested in Sandforce.

Cleantech Geographic Trend Geographic Trend provides an overview of nations that allocate funding or establish legislation to support Cleantech, such as: China, India, Germany, Australia, and USA. This review will also evaluate the status of Silicon Valley in California (the center of the US venture capital industry), now the heart of Cleantech innovation.

Cleantech in the USA and California The USA has been a leader in venture capital financing for Cleantech and has been particularly vibrant in California where strong Cleantech investment continues. Silicon Valley earned its name and first great fortune as the cradle of the computer age. Then it built a launching pad for the Internet age. Now the valley has assumed a leading role in the global competition to develop renewable energy and other clean, green technologies. Cleantech is poised to be the valley’s third great wave of innovation [7] – not just the next big thing, but perhaps the biggest thing ever. Confronting the peril of greenhouse gases and climate change happens to be a multi-trillion-dollar business opportunity. Consider that the sum of America’s yearly utility bills, one component of the nation’s overall energy costs, exceeds $1 trillion – or nearly triple the annual global revenues of the semiconductor industry. The solar and wind energy markets, which totaled about $80 billion in 2008, are projected to nearly triple in size in 10 years, employing 2.6 million people worldwide. Leading venture capitalist suggests that Silicon Valley may someday be called Solar Valley, given that dozens of solar companies have sprung up in recent years. But solar represents just one aspect of the Cleantech revolution. Around the valley, some former ecommerce and software mavens are now busy trying to electrify the automobile industry

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while other technologists are developing energy-efficient glass, drywall, and cement. Still others are introducing cutting-edge information technology to the twentieth-century electricity grid, working on biofuels and fuel cells, and pioneering new methods to recycle waste, protect air and water quality, and enhance agriculture and aquaculture. Most of Silicon Valley start-ups are innovating in new ideas right now, trying new devices. Most of the start-ups will phase out; a few will flourish. Some might come to dominate the energy system and become billion-dollar corporations. Cleantech may seem like a radical departure from Silicon Valley’s semiconductor roots. But solar photovoltaic cells are a simple form of semiconductor, and smart-grid innovators are essentially integrating the twenty-first-century software efficiencies into a wasteful twentieth-century electrical infrastructure. The valley’s expertise in biotechnology is vital to biofuels and its work in nanotechnology is critical to new materials that might find their way into nuclear reactors or a suburban home. However, Silicon Valley does not have a natural advantage in talent – like chemical engineers, fermentation experts, engine designers, and physicists. But Silicon Valley does have a support culture for entrepreneurship and a culture of risk-taking and risk-funding. Google has invested $45 million in a handful of Cleantech firms and other projects concentrating on such things as solar, wind, geothermal, and electric vehicles. Google also recently launched PowerMeter, its online tool to enable consumers to watch their home energy use. Other big-name Silicon Valley firms are also making moves in energy. Cisco Systems unveiled its goal to provide the underlying technology for smart grids – which aim to move electricity more efficiently than do today’s grids – just as Cisco started providing the plumbing for the Internet years ago. A big chunk of what Cisco estimates could be a $20 billion annual smart-grid market within 5 years. Silicon Valley is also home to some of the top companies working on the infrastructure needed to keep electric cars charged up and on the road, including Better Place of Palo Alto and Coulomb Technologies in Campbell, which have established early leads in creating battery-swapping stations and public charging networks. Other companies here are quietly working on creating more powerful batteries for the cars. One is Amprius, a Menlo Park start-up still in ‘‘stealth’’ mode that is developing advanced lithium-ion batteries. Venture capitalists have become willing to enter the transport space, beginning with vehicles and now transitioning into components, batteries, and energy management systems. Silicon Valley has the potential to be a center of the industry. Cypress Semiconductor Corp. declared in July 2010 that Cypress’s headquarters campus in San Jose, California, will be independent from the public utility grid by the year 2015. The announcement was made as the company dedicated three new Bloom Energy fuel cell systems at the site. The Bloom Energy Servers, combined with existing rooftop solar panel installations, supply approximately 75% of Cypress’s electric needs in 2010. In addition to California, many Cleantech start-ups have sprung up in Texas, Massachusetts Colorado, Michigan, New York, New Jersey, Washington, Oregon, Pennsylvania, etc. Private companies, innovative sprits, and venture capital investments are everywhere. It is likely that USA will continue to play a pivotal role in Cleantech arena.

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Cleantech in China China’s Cleantech has primarily been a project of government initiative and funding. The Pew Environment Group has released a report that shows that China’s investments in clean energy have overcome the US figures. According to Pew, China now leads the way with $34.6 billion invested in 2009 across all investment types – nearly double the US figure of $18.6 billion [8]. Top 10 in Clean Energy Investment in 2009 (Source: the Pew Charitable Trusts Research, March 25, 2010). China

$34.6 billion

USA

$18.6 billion

UK

$11.2 billion

Spain

$10.4 billion

Brazil

$7.4 billion

Germany

$4.3 billion

Canada

$3.3 billion

Italy

$2.6 billion

India

$2.3 billion

Rest of EU – 27

$10.8 billion

China is already the largest producer of solar panels and expected to become the world’s biggest producer of wind energy by 2013. One reason China can move so fast is that once its central government decides on a policy, it can execute it quickly through the nation’s handful of state-owned utilities. In the USA, there are thousands of electric utilities and a barrage of regulatory and environmental hurdles to starting new projects. In China, nothing is too fast. They have got the land, the need, and fast decisionmaking. Applied Material is the biggest maker of equipment to make solar panels; in 2010, it opened the world’s largest solar research facility in China. China plans to have ‘‘clean energy’’ account for 15% of its total consumption under a 10-year renewable energy promotion program. The plan would accelerate efforts already under way to help ease reliance on expensive oil imports and heavily polluting coal, which fuels about three quarters of China’s electricity generation. It also is in line with Beijing’s pledges to rein in output of greenhouse gases by reducing China’s carbon intensity – its use of fossil fuels per unit of economic output – by 40–45% by 2020. Renewable energy accounted for 9.9% of China’s total energy consumption in 2009, up from 8.5% the year before. Under the plan, by 2020, the government intends to raise that to 15%. In 2010, Chinese companies raised US $30 million in five disclosed rounds. The largest deal was for Prudent Energy, a developer of flow batteries, which raised $10 million from JAFCO Investment Asia, Mitsui Ventures, and CEL Partners. The largest global Cleantech IPO recorded in 2010 was Origin Water, a China-based developer of membrane filtration systems for municipal and industrial sewage treatment and recycling, which raised

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$370 million from an offering on the Shenzhen Stock Exchange. The company’s share price more than doubled during the first day of trading, valuing the company at about $3.3 billion. Chinese carmakers, such as BYD, are pushing ahead faster than established Japanese and American rivals to mass produce electric vehicles. Its carbon captures technology and high-efficiency ‘‘ultrasupercritical’’ coal plants are close to the global cutting edge. China will be one of the dominant forces in Cleantech investment worldwide in the near future.

Cleantech in India India’s Cleantech industry tends to focus on domestic application and may be more applicable to developing countries. On the outskirts of Bangalore in an industrial area [9], Kotak Solar is churning out solar-powered products of many kinds – to light up streets and gardens with LEDs, heat swimming pools, and provide drinking water. To prove a point that solar can work for every day practical uses, Kotak Solar recently electrified a village in India with solar power. Now 120 families in this remote location pay just five cents per day to get light and drinking water, plus juice for a community-shared mobile phone, plasma TV, and Internet connection. The next step is to take this pilot project to more villages in India, where 80,000 villages or 45% of the total are still not on the grid. It attracted $6 million plus from the US VCs, Kleiner Perkins, and Sherpalo Ventures in 2008. In Delhi, D.Light Energy produces and sells solar-powered LED lanterns to replace kerosene lights in the emerging market villages. In 2 years’ time, the company sold 100,000 lanterns to villagers in India, east Africa, and Latin America. The lights help moms work on handicrafts at night-time to earn some income and get kids to study after sun fall. The potential is huge; about 1.6 billion people worldwide live off the grid. D.Light aims to reach five million people, has funding from US VCs Draper Fisher Jurvetson and Garage Technology Ventures, as well as two social investor groups, and is aiming to generate revenues of $25 million this year.

Cleantech in Germany Germany is positioning itself as the world’s first major renewable energy economy. It is already a Cleantech powerhouse with more than 300,000 people employed in Cleantech industries and is the top exporting country with a 16% share in global Cleantech trade [10]. Let us take a look at the drivers of Cleantech in Germany. Strong government support: As a result of the policy framework, the renewable energy sector in Germany has been characterized by steady growth rates over the past decades, with a significant increase in capital investment across various clean technologies. Germany has saved 57 million tons of carbon dioxide directly through implementation of its Renewable Energy Sources Act of 2000. Sunny Germany: The country has the world’s largest solar power market, despite having extremely cloudy weather. Germany is by far the European leader for photovoltaic

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capacity with a capacity of 8,000 MW, and has the world’s largest solar cell producer, Q-Cells. Cluster of Cleantech companies: Cleantech clusters in Munich and Berlin have a concentration of companies, research institutes, venture capitalists, and infrastructure, and account for a significant amount of employment and research activity in the sector. Stuttgart, in southern Germany, is home to leading automotive companies such as Daimler, Porsche, and Bosch. These companies are seeking advancements in vehicle design and performance, such as new drivetrains and power supplies for hybrid and electric vehicles. German Cleantech exits: Large German multinational corporations such as Siemens and Bosch are creating exit opportunities as they have begun to acquire growing Cleantech companies. In 2009, there were more than $1 billion in Cleantech merger and acquisition transactions in Germany. The German stock exchange has seen many Cleantech initial public offerings and should continue to provide opportunities for future investment exits. Strength in engineering and science: The German word, ‘‘Tu¨ftler,’’ describes the German engineering mentality of a person who tinkers with things. This cultural affinity and Germany’s traditional strengths in machinery, instruments, automobiles, and precision-engineered products are valuable assets for development of its Cleantech economy. Germany boasts some of the world’s leading research institutes, including FraunhoferGesellschaft, Max Planck Society, and the Leibniz Association. An example of the concentration of research institutes is in Berlin. There are more than 30 Cleantech research institutes in Berlin alone, and this has helped develop the Cleantech cluster in the city. German companies have historically been financed by German banks and have had little access to equity capital. Relatively new Cleantech venture capital firms have been formed to focus on the German market, such as Mountain Cleantech, Zouk Ventures, Munich Venture Partners, and Pinvoa Capital. These firms understand the German market and the needs and cultural sensitivities of German owners and managers.

Solar Energy in Australia Australia plans to build the world’s largest solar power station with an output of 1,000 MW in an AU $1.4 billion (US $1.05 billion) investment [11]. The plant would have three times the generating capacity of the current biggest solar-powered electricity plant, which is in California. The project was aimed at exploiting the country’s ample sunshine, which is Australia’s biggest natural resource. The project should eventually lead to a network of solar-powered stations across the country, with locations chosen to fit in with the existing electricity grid and ensure good access to sunshine. The AU $1.4 billion dedicated to this project was part of a wider AU $4.65 clean energy initiative by the government. The innovative spirit of Silicon Valley in California, the master plan of Chinese government in Cleantech, the down to earth of Indian entrepreneurs, the success factors

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of Germany, and the commitment of the Australian government are indicators for other countries to pattern after. Many European, Asian nations, Canada, etc., are also allocating their resource to develop Cleantech.

Concluding Remark: Globalization and Deployment of Cleantech Globalization of Cleantech To be a real successful Cleantech innovation, a project will evolve from: (a) (b) (c) (d)

An academic and concept development A prototype development A small-scale infrastructural project A larger-scale infrastructural implementation

These sequence involved many individual partners, venture capital investments, and multinational corporations. The following is an example to illustrate a real successful Cleantech project. Ausra Inc. is a Silicon Valley company that provides solar thermal power, steam, and energy systems for industrial processes and utility-scale electricity generation. Ausra’s core technology, the Compact Linear Fresnel Reflector (CLFR) solar collector was originally developed by an Australian scientist, Dr. David Mills. Instead of the parabolic troughs or mirrors used in other solar thermal systems, CLFR uses flat reflectors moving on a single axis plus Fresnel lens to concentrate the solar thermal energy in collectors. Flat mirrors are much cheaper to produce than parabolic ones. Another advantage of CLFR is that it allows for a greater density of reflectors in the array. David Mills originally conceived of the approach in the early 1990s while at Sydney University. Mills is known internationally for his academic advancements in non-imaging optics, solar thermal energy, and concentrator systems. Mills is not the only Aussie on the Ausra starting team – a group of solar power scientists, power project developers, and financiers, who want to make reliable, large-scale solar thermal power a reality. Graham Morrison worked with Mills between 1995 and 2001. Morrison ran Australia’s premier solar test facility and is an expert at both solar collector and solar radiation modeling. In 2002, Mills and Morrison founded Solar Heat and Power Pty Ltd. (SHP) in partnership with Ausra CEO Peter Le Lie`vre, and SHP built a successful trial 1 MW system in 2004 for Macquarie Generation in New South Wales. After some nominal sponsorship by several Australian government agencies, in October 2006, the above partnership connected to two Silicon Valley VCs: Khosla Ventures and KPCB. In 2007, the resulting combined entity Ausra moved to Silicon Valley; David Mills became Ausra Chairman. In 2008, Ausra began building large-scale systems and sold projects to a Californian utility company. One solar thermal electric power plant, the 354 MW Solar Energy Generating Systems, which covers 1,000 acres in the Mojave Desert in Southern

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California, produces 90% of the world’s commercially produced solar power. However, a large-scale project like this needed different engineering skills and large infrastructure building experience. Early in 2009, Ausra abandoned plans to build its own solar projects to focus on supplying solar equipment to other developers. In early 2010, Ausra was acquired by French engineering and nuclear giant Areva for around US $400–$500 million (unconfirmed), now renamed Areva Solar [12]. Ausra’s core technology, the Compact Linear Fresnel Reflector (CLFR) solar collector and steam generation system, uses modular flat reflectors to focus the sun’s heat onto elevated receivers, which consist of a system of tubes through which water flows. The concentrated sunlight boils the water in the tubes, generating high-pressure steam for direct use in power generation and industrial steam applications without the need for costly heat exchangers (> Fig. 11.7). Unlike photovoltaic energy resources that immediately shut down during periods of transient cloud coverage, Ausra’s solar steam generators retain heat, allowing for a more seamless integration with the electric grid. For standalone power plants, Ausra can also include a natural gas boiler backup design. These solar-natural gas hybrid plants can provide firm capacity for customers – around the clock. While older solar setups depend on expensive photovoltaic panels, Ausra’s installations boast mass-produced mirror clusters that focus the sun’s rays onto water-filled tubes. When the water begins to boil, it produces enough steam to turn an array of turbines. It is estimated that electricity generated this way will cost 10–12 cents/kWh – on par with power from polluting sources such as coal, and 50% less than photovoltaic power. Photovoltaic is constrained because it uses high-grade silicon; Ausra uses just steel, glass, and water. Paris, France, based AREVA with 75,000 employees, is also a world leader in electricity transmission and distribution, and offers greater grid stability and energy efficiency.

nl ig ht

Water as the working fluid

Su

Receiver pipes

Reflectors

. Fig. 11.7 Figure taken from Ausra website: www.ausra.com/technology/

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Combining Ausra’s proven technology and AREVA’s world leading Engineering, Procurement and Construction skills could build the most cost-effective solar thermal plants for utilities, independent power producers and industrial customers around the world. The market for concentrated solar power plants is expected to grow substantially in the next decade with an average annual growth rate of 20% and should reach an estimated installed capacity of over 20 GW by 2020. The evolution of Ausra illustrates a good globalization of a Cleantech project. From innovation of Australia scientists, added Silicon Valley VC’s funding for a large scale prototype, to the acquisition by a France giant AREVA for large infrastructure enterprise for global implementation.

Deployment of Cleantech Modern society is counting on Cleantech to meet growing energy and other resource demands, while reducing environmental impacts and generating new opportunities for the economy. However, it is important to remember that ultimate success will depend on the coordination of technology development and technology deployment, two separate endeavors, each with requisite incubation characteristics and catalysts. Deployment often depends on the scalability and price parity of new technologies, which often takes years beyond the time of the initial innovation for it to reach the mainstream. New technologies have the potential to continue to improve the world, but also require planning and long-term commitment to its application – indeed, a different skill set than the work of innovation itself. Therefore, it is important that individuals, engineering and science graduates, participating in Cleantech maintain a balanced perspective, based on creativity on one hand and pragmatism on the other, while focusing on the goal of advancement. Through this chapter, readers should gain an overview of the trends in venture-capital-funded innovation in Cleantech, the broad scope of the basic science and technology, and Cleantech implications that affect world climate change.

Appendix Venture Capital Firms in USA USA has more than 1,000 VC firms. The best way for an entrepreneur to seek VC funding is to first look at the local or regional VC firms to begin with. However, in the USA, only 50–100 VC firms could provide larger funding. The following is a list of 50 larger and most popular VC firms in the USA. It is ranked by Web site traffic (based average monthly viewed) in the fourth quarter of 2009. The following are the top 50. The list is prepared by Larry Cheng and Dave Gordon of Volition Capital published on February 2, 2010 on Volition Web site; the original study listed 150 firms [13].

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11 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43.

Venture Capital Investment and Trend in Clean Technologies

First Round Capital (31,632) Sequoia Capital (22,441) Bessemer Venture Partners (14,825) Highland Capital Partners (12,704) Garage Technology Ventures (12,375) Draper Fisher Jurvetson (11,823) New Enterprise Associates (11,762) Kleiner Perkins Caufield Byers (10,924) Polaris Venture Partners (10,217) Benchmark Capital (10,162) Battery Ventures (10,034) Founders Fund (9,654) Accel Partners (9,604) Greylock Partners (9,445) Centennial Ventures (9,224) General Catalyst Partners (9,086) Summit Partners (8,270) Norwest Venture Partners (8,198) Founder Collective (8,189) Spark Capital (7,834) Foundry Group (7,787) Technology Crossover Ventures (7,503) Matrix Partners (7,309) Lightspeed Venture Partners (6,475) Union Square Ventures (6,333) OpenView Venture Partners (6,319) Charles River Ventures (6,316) TA Associates (6,245) Austin Ventures (6,037) Canaan Partners (5,763) Mayfield Fund (5,643) True Ventures (5,627) Atlas Venture (5,462) Alsop Louie Partners (5,346) Maveron (5,164) Mohr Davidow Ventures (5,139) Rustic Canyon Partners (5,006) Redpoint Ventures (4,950) Warburg Pincus (4,863) Highway 12 Ventures (4,821) Shasta Ventures (4,664) Khosla Ventures (4,624) Split Rock Partners (4,613)

Venture Capital Investment and Trend in Clean Technologies

44. 45. 46. 47. 48. 49. 50.

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Trinity Ventures (4,603) Madrone Venture Group (4,593) August Capital (4,521) Venrock (4,298) VantagePoint Venture Partners (4,274) Edison Venture Fund (4,004) US Venture Partners (3,992)

Venture Capital Firms in Europe Europe historically did not have many VC firms. In recent years, the VC industry has flourished. Here is a directory as provide by [14]: 3i – Investment focus: European and Southeast Asian start-ups. Add Partners Limited – Focus: early to late-stage European start-ups in information technology. AltAssets – Focus: news service for global venture capital and private equity professionals. Ariadne Capital – Focus: part of a new European model, helping manage investor exits, drive consolidation, and leverage entrepreneurialism. Athena – Focus: international, for-profit, high technology, business incubator. Baring Communications Equity – Focus: media and communications focused fund for Central and Eastern Europe and the CIS. Business Angels Connect – Focus: global services packaged to young entrepreneurs. CGS Management – Focus: medium-sized technology-based European companies with an emphasis on Switzerland. Cobblestone Private Equity – Focus: venture-oriented direct investments in emerging European technology companies seeking expansion and US market penetration. Copan – Focus: leading European technology executives and investors. Delta Partners – Focus: venture capital and private equity early-stage funding to high technology companies in Europe and Ireland. DeMinds – A pan-European investment group focused on the global Internet market. European Equity Partners – Investment focus: Euro one half to three million initially and up to 5–8 million euros based on meeting key milestones and criteria. Financier Natexis Banques Populaires – Focus: private equity investment holding company active in all segments of the business including venture capital. Hunter Lovec – Focus: consultants helping Central European companies solve their financial problems and achieve their financial goals. IDEA Network – Focus: network of international experts and consultants working under donor-funded projects. Innova Capital – Focus: advises private equity funds with more than 300 million euros for investments into profitable companies in the EU-accession countries of Central Europe.

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Internet Ventures Scandinavia – Focus: adds capital and partner experience to unique Internet ventures. INVEST MEZZANIN – Investment focus: later-stage private equity investing in companies in Austria, Switzerland, and Germany. Investindustrial Holdings Limited – Specializes in medium-sized companies, principally in Italy and Spain. Kildare European Leader Teoranta – Focus: rural development company for County Kildare, Ireland, with funding to distribute to innovative rural projects. Mericom – Focus: venture capital financing and investment services for telecommunication projects, start-up companies, and new businesses in the telecom industry. Michelsen-Partners – Focus: European cross-border mergers and acquisitions advisory services, structured finance advice, and international fund management. Net Partners – Investment focus: European start-up and early-stage initiatives related to the Internet. Northzone Ventures – Offers early-stage venture capital investments and focusing on technology companies. ORAH Investments – Swiss-based venture capital holding financing businesses in Southeast Europe. Permira – Investment focus: formerly known as Schroder Ventures Europe, a leading private equity group and advising funds. Pino Venture Partners – Investment focus: Italian company for operations in information technology, communications, and media. PrivateEquityOnline.com – Focus: tracks private equity activity across Europe, delivering daily news on funds, deals, and exits. PROPHETES – Focus: providing and investing venture capital into innovative companies and projects and providing support to investors who invest capital in the countries of southeastern Europe. Seven Summits Capital – Focus: active in the international private equity market participating in buyouts as an investor, initiator, or catalyst. Startup Avenue – Paris-based B2B incubator funding Internet start-ups that focus on Europe. Stratos Ventures – Investment focus: wireless information and communications technology companies with substantial global growth potential. Triago – Focus: private equity fund raising, limited partnerships, and joint ventures. TustCapital Partners – Focus: Belgian venture capital investment fund. VCG.dk – Focus: lists all Danish venture companies and a profile on them. Venture Capital in Europe – Discussion of the state of venture capital in Europe and its trends. Venture Consulting – Focus: professional business consultancy and services based on extensive international experience. ViewPoint Capital Partners – Specializes in software technology companies in early, expansion, and late-stage situations; offices in Frankfurt, Amsterdam, and Zurich.

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West Private Equity – Focus: provides capital for management buyouts, buy-ins, and the expansion or refinancing of companies headquartered in Western Europe.

Venture Capital Firms in India, China, Japan, and Israel India’s venture capital industry has about 25 VC firms. Wikipedia.com has a listing. China’s venture capital industry has more than 150 VC firms, which altogether manage over US $100 billion in venture capital and private equity funds. China Venture Capital Association (CVCA) provides details of its VC services at www.cvca.com.cn [15]. Japan’s venture capital industry has about 100 active funds. A list could be found at www.irasia.com/venture/jp [16]. Israel’s venture capital industry has about 70 active venture capital funds, of which 14 international VCs are with Israeli offices. For more information, refer to www. investinisrael.gov.il [17]. Australia’s venture capital industry has very limited VC firms. It is mainly supported by the government. For detail see www.avcal.com.au [18].

How to Secure Venture Capital Money Venture capitalists invest money in start-ups in exchange for an equity ownership in the company. VCs receive hundreds of business plans from entrepreneurs each year. There are more than 1,000 venture capital funds around the world. Here are few tips to gain the attention of VC: Step 1 Prepare a comprehensive business plan. VCs will expect you to clearly define the purpose of your business, disclose pertinent financial information (including revenue streams and projections), and provide information on your executive management team. Step 2 Do research on venture funds to find the appropriate fit for your company. Look in Pratt’s Guide to Venture Capital Sources, available in many bookstores and libraries, to see what fields each firm is likely to fund. Some focus on retail and service companies, while others look specifically for technology start-ups. Step 3 Get an introduction to the venture capital firm. You will have a much better chance if you have been personally introduced to the VC rather than blindly sending your business plan. These introductions can be made by executives of companies already being funded by the VC or by lawyers and accountants who work with the firm. Try to contact four to five VCs. Step 4 Arrange a meeting with the VC. Consider bringing key members of the management team to the meeting. Step 5 Follow up your visit with a thank-you note and additional information. Step 6 be persistent and polite; wait for VC evaluations.

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How is a Business Plan Evaluated? When a business plan (BP) arrives at VC office, venture capitalists tend to give a quick review. If they decide a BP deserves a further study, the entrepreneur is invited to VC office for a power point presentation. In the process, one venture capitalist categorized BP into four types [19]: a Home-run, a Struggle, a Joy-ride, or a Time-waster. A Joy-ride project will get many media publicity, but investors would not make much return. The objective of VC is to sponsor a real winner – a Home-run, a project that is not too obvious or too easy to implement, otherwise others will launch the identical or similar one. When great minds think alike, most of them do not make much money. So a good BP needs: – – – –

High market potential – customers will buy it Technology novelty – nonobvious innovation An entrance barrier – a valid patent protection A cohesive and complementary team – technology skill plus management professional – A complementary business alliance – Reasonable funding requirement – Reasonable timing to realize a high return

References 1. Wikipedia, Venture capital & venture capitalist. www.wikipedia.org, 2010 2. Cleantech Group, Clean technology venture investment totaled $5.6 billion in 2009 and Record Number of Clean Technology Venture Investment Deals in 2010. www.cleantech.com 3. Climate Progress, Clean tech gets big piece of venture-capital funding. www.climateprogress.org/ 2010/01/07/clean-energy-and-global-warmingscience-epa-strict-new-health-standards-for-smogclean-tech-funding-vc-sectors-software/. Accessed 7 Jan 2010 4. Cleantech Open, Clean tech open defines clean technology. www.cleantechopen.com/app. cgi/content/competition/category_description, 2010 5. Greentech Media, Top 50 VC-Funded Greentech Startups. www.greentechmedia.com/articles/read/ Top-50-VC-Funded-Greentech-Startups/. Accessed 2 Feb 2010 6. Michael Kanellos, Bloom vs. solar: which one is best? Wired. February 24, 2010

7. Harris SD, Cleantech: silicon Valley’s next great wave of innovation. www.MercuryNews.com. Accessed 11 May 2010 8. Berger E, China’s clean energy investments surpass the United States. www.blogs.chron.com/ sciguy/archives/2010/03/. Accessed 25 Mar 2010 9. Rebecca Fannin, Cleantech startups heat up in India. Forbes. February 21, 2010 10. Lesser S, Enz A, 2010’s top 10 major highlights of Cleantech in Germany. www.cleantech.com/ news/5741. Accessed 30 Mar 2010 11. News Article from Sydney, Australia to build world’s largest solar energy plant: PM. Reuters. May 17, 2009 12. Ausra.com, AREVA completes acquisition of U.S. Solar Company Ausra. www.ausra.com/ technology/ 13. Cheng L, Gordon D, Venture Capital (VC) Firm directory – ranked by Website Traffic. www. ask.volitioncapital.com/ask/venture-capital-vcfirm-directory-ranked-by-website-traffic-q409/. Accessed 2 Feb 2010

Venture Capital Investment and Trend in Clean Technologies 14. Directory Investment, Venture Capital in Europe. www.directoryinvestment.com/Venture-Capital/ Europe.html, 2010 15. China Venture Capital Assoc., China venture capital industry. www.cvca.com.cn, 2010 16. Japan venture capital industry, www.irasia.com/ venture/jp, 2010

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17. Israel venture capital industry, www. investinisrael.gov.il, 2010 18. VC Journal, Australian private equity & venture capital guide 2010. www.vcjournal.com.au, 2010 19. Gaebler.com, How to evaluate a business idea. www.gaebler.com/How-VCs-Look-At-Startups. htm. Accessed 7 Aug 2010

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Section 2

Impact of Climate Change

12 Carbon Liability Yoshihiro Fujii Graduate School of Global Environmental Studies, Sophia University, Tokyo, Japan Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412 Carbon Liability as a Concept in Accounting and in Ecology . . . . . . . . . . . . . . . . . . . . . . . 412 Carbon Liability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412 Similarities and Differences Between the Concepts of Carbon Liability and Environmental Liability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414 Cows’ Belches Can Be Tradable Commodities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415 Different Legal Treatments of Carbon Liability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415 Invisible to Visible . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416 Impact of Potential Carbon Cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416 Quantifying Carbon Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416 Global Carbon Budget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417 Excess Cost of Carbon Imbalance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418 Avoiding Carbon Insolvency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419 The Carbon Break-Even Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420 Measuring the Valuation Materiality of Corporate Carbon . . . . . . . . . . . . . . . . . . . . . . . . . 421 SEC Guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421 Regulation Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422 Physical and Market Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422 Quantitative Carbon Disclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423 The Movement for Quantitative Carbon Disclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424 Putting a Price on Carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425 Difficulties in Monetizing a Price for Carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425 The IFRIC3 Dispute over Accounting Standards for Government Grants of Carbon Allowances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427 Calculating Physical Risk to Price . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429 Applying ARO Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429 Converting a Market Risk to an Opportunity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_12, # Springer Science+Business Media, LLC 2012

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Abstract: By the term ‘carbon liability’, we mean a calculation of value approximating to the economic externalities of carbon emissions in the global economy, in relation to the totality of global economic activity. As a consequence of over two centuries of industrialization, the global carbon budget and its associated global balance sheet of carbon have clearly diverged from a state of natural equilibrium. Three material identifiable, types of carbon risk have emerged; related to regulation, to physical processes and to market-related risk. ‘Cap-andtrade’ schemes are an important economic mechanism aiding both the rectification of these imbalances and the restoration of a natural carbon cycle disrupted by emissions of anthropogenic greenhouse gas (GHG) in both developed and emerging economies. Such schemes establish an economic value to carbon through open market trading. They serve to quantify and to reduce carbon risk, in accordance with appropriate and efficient economic regulation. Monetizing carbon liability through these market mechanisms is a means to place boundaries on, and thus to mitigate, the uncertainties of carbon liability. This process of monetization may also transform market risk into an opportunity for economic exploitation.

Introduction The Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC 2007: ARA4 [1]) concluded that ‘‘warming of the climate system is unequivocal,’’ and that ‘‘most of the observed increase in global average temperatures since the mid-twentieth century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.’’ Although the force of these decisive phrases may have been somewhat diminished by the so-called ‘‘climate-gate scandal,’’ which emerged in late 2009 around the intergovernmental negotiations over the post-Kyoto framework, nevertheless the primary meaning of the ARA4’s conclusions remains robust. The famous words of Galileo Galilei, Italian physicist, mathematician, astronomer and philosopher, are apposite to the current condition of our planet: ‘‘And yet it warms’’.

Carbon Liability as a Concept in Accounting and in Ecology Carbon Liability This chapter focuses on the importance of these findings, in relation to the concept of ‘‘carbon liability’’ and its implications. By this term we refer to a calculation of values related to the economic externalities of carbon emissions in the global economy, and the process of apportioning those values, both in macroeconomic terms within the global economy and microeconomically, to achieve a more true economic value for each individual emitting entity. This process can be referred to as ‘‘carbon management.’’ What is a ‘‘carbon liability?’’ Liability is a concept familiar from accounting and from law. It means an obligation enforceable under contract, whether that contract be explicit

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and operating between individuals, or implicit between individuals and wider agents within society, such as the state. The obligation on a citizen to pay tax is an example of a unilateral liability imposed by a government. From an accounting point of view, a liability means a present obligation arising from past events. Its settlement is expected to result in an outflow of resources. The International Accounting Standards Board (IASB) is currently in the process of changing this definition has proposed a new draft of International Accounting Standards (IAS) 37, defining liabilities to the public. This chapter discusses the current definition. Carbon liability has its roots in this environment of civil obligation. In recent years, governments have introduced regulations to restrict quantified volumes of GHG (greenhouse gas) emissions by incorporated entities, a measure directed toward the public goods of controlling the unequivocal danger – an economic ‘‘bads’’ which includes global warming. Thus ‘‘carbon liability’’ arises from an established tradition of state-initiated regulation. Entities addressed by governments are required to meet the costs of their obligations using their own resources in order to comply with the demands of regulation. Liability in relation to carbon emissions differs in kind, however, from other forms of liability, in that it includes a lot of messy uncertainties about its causality and its composition. The IASB’s International Financial Reporting Standards (IFRS) categorize such instances as a ‘‘contingent liability,’’ in the IFRS’ words, ‘‘a possible obligation depending on whether some uncertain future event occurs’’ and ‘‘a present obligation whose payment is not probable or the amount cannot be measured reliably.’’ These characteristics correspond to the nature of carbon liability, which encompasses the past, present, and future responsibilities for GHG emissions. Carbon liability belongs in addition to a broader definition of Environmental Liability. This field has already been defined legally and in accounting terms in both the USA and the European Union. The US Environmental Protection Agency (EPA) has defined ‘‘environmental liability’’ as an obligation in environmental law to make a future expenditure to remedy the past or ongoing manufacture, use, release, or threatened release of a particular substance, or other activities that adversely affect the environment [2]. This regulatory stance arose from a succession of environmental disasters in the USA during the 1970s and 1980s, which resulted in asbestos exposure and soil contamination and damage to people, property, and the natural environment. To prevent and remedy such damages, US legislators enacted the Comprehensive Environmental Responses, Compensation and Liability Act (CERCLA), otherwise known as the ‘‘Superfund Act.’’ It was enacted in 1980, then was amended as Superfund Amendment and Reauthorization Act (SARA) in 1986, Small Business Liability Relief and Brownfields revitalization Act in 2002, respectively. Drawing on this American legislation, the European Union constructed its own legal framework for the prevention and remediation of damages to the human and natural environment. In 2004, the EU Commission published its Directive on Environmental Liability (ELD), which came into effect in all EU states in 2008. These legal frameworks on either sides of the Atlantic share common characteristics.

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Drawing on these models, the US Federal Accounting Standards Board (FASB) and the IASB have developed an accounting framework on environmental liability. The FASB issued EITF93-5, ‘‘Accounting for Environmental Liabilities,’’ in 1993; in 1996, it was included in the Statement of Position (SOP96-1: Environmental Remediation Liabilities) in the American Institute of Certified Public Accountants (AICPA). As noted earlier, the IASB has referred to environmental liabilities in its IAS 37 standard. What definitions of ‘‘the environment’’ are used in these legal and accounting frameworks? The concept in those frameworks is very broad. For example, the Lugano Convention (Convention on Civil Liability for Damage Resulting from Activities Dangerous to the Environment, June 1993) that laid down fundamental concepts of strict liability for environmental damages caused in EU territories, considers ‘‘the environment’’ to be the realm of all natural resources, both abiotic and biotic, such as air, water, soil, fauna and flora, and the interaction between the same factors. In combination, these properties form part of the cultural heritage and the characteristic aspects of our planet.

Similarities and Differences Between the Concepts of Carbon Liability and Environmental Liability It is clear that any concept of ‘‘carbon liability’’ should be considered in the context of an established corpus of environmental liabilities. Carbon emitted by corporations shares characteristics with other forms of environmental damage including, as already noted, cost of damages attributable to past or present commercial activities, including production of GHGs, and/or their release into the atmosphere. To discharge these obligations, entities must meet the necessary expenses of remediation or reparation from their own resources. In other words, this discharge of legal responsibilities under regulation entails for corporate entities an internalization of a type of cost control of carbon emissions. This has been was previously considered as an economic externality. The similarities in these definitions demonstrate are that they can be constructed in the same kind of legal and accounting framework for carbon liabilities in order to manage resulting marginal costs to the environment and to society as a whole. Similarities notwithstanding, the concept of carbon liability also has several differences from general environmental liability. Most importantly, GHGs are not in themselves toxic. This contrasts directly with the toxic or noxious characteristics of most general pollutants specified or implicated in legislation on environmental liability, such as asbestos, sulphur dioxide, heavy metals, etc. Directly and indirectly, the latter harm human health and the ecosystem. Carbon dioxide, the most common GHG and a primary factor in most cases of carbon liability, is not toxic in itself. It is merely one component in the atmosphere, a natural chemical byproduct of all plant and animal life. (Of course carbon monoxide (CO), which is chemically related to CO2, is clearly toxic. In theory, CO2 itself can be poisonous in high volumes; such a danger is, however, never likely in naturally occurring concentrations. In this context, concentrations of CO2, even in the most dangerous scenario simulated in the IPCC’s ARA4 toward the end of this century, will cause only indirect loss and

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damages, as part of the indirect consequences resulting from climate change. This indirect attenuated chain of causality presents serious difficulties in the calculation of carbon liability in society.

Cows’ Belches Can Be Tradable Commodities The planet is populated with very many agents of GHG emissions, whether animal, corporate, or human. Corporations contribute GHGs by their activities in resource consumption, in production and distribution, and in demand stimulation. Nature’s emission processes include deforestation, volcanic eruptions, swamps and wetlands. Even ruminant livestock in agriculture add to the emissions of animals: the human population, now on the cusp of 6.9 billion, is of course the most highly polluting species of fauna. A belch from a cow or other ruminant emits methane, a GHG with 21 times the warming power of CO2. The Worldwatch Institution, an independent research organization, has estimated that GHG emissions from ruminants contribute between 10% and 15% of the planet’s annual GHG total from all sources. The legal implication is clear: the belch of a cow might be regarded as a carbon liability for its owner. A rancher might compensate by participating in carbon trading, offsetting the wider economic cost of methane from his livestock. If he can find a way to reduce methane from his cows, he can trade a carbon credit on the free market linked to his animals, thereby earning additional income besides selling milk or meat. Idemitsu Kosan, a Japanese petroleum company working in co-operation with Hokkaido University has developed a new food for cattle to reduce output of methane gas bovine eructation in 2007. Besides biology, GHGs are emitted through innumerable economic and industrial processes in manufacturing, power generation, farming, logging, transportation, and so on. These are in addition to the emissions of individual humans. Consequently, it is very difficult to restrict GHG emissions from all sources. This near-universal emission by billions of agents and processes, of gases often essential to life itself, presents a completely different, universally pervasive causality which is more complex than with other recognized pollutants. This difference presents a major obstacle in forming policies to reduce emissions and to manage carbon, both in macroeconomic policy and in the carbon management strategies of individual corporations.

Different Legal Treatments of Carbon Liability As noted above, the concept of carbon liability can be seen as an obligation like others in environmental law. Its treatment and remedies differ from jurisdiction to jurisdiction, however. Developed countries who ratified the Kyoto Protocol recognize a duty to reduce their GHG emissions from 1990 levels. On the other hand, developing countries including even major emitters such as China, India, and Brazil face only a voluntary, non-binding commitment to reduce their own emissions. Some additional differences remain between developed countries. Targets in GHG reductions to be achieved before 2012 under the Kyoto Protocol range from 6% for Japan,

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7% for the EU, and 8% for the USA. After promising quantified reductions, the USA failed to ratify the agreement and left for domestic political reasons. As a result, even in developed countries, there have been different types of legal measures for reducing GHG emissions. These have affected the respective impact of carbon liabilities under different jurisdictions, both in terms of global macroeconomic policy, as well as in relation to the responses and obligations of individual corporations. In consequence, discussions on the post-Kyoto framework have focused as much on the differences between the commitment and stances of developing countries, as on the importance of emerging economies such as China, India, and Brazil.

Invisible to Visible Impact of Potential Carbon Cost What consequences do carbon liabilities carry for carbon-emitting corporations? A recent study by Trucost, a UK-based environmental consulting firm, published under the auspices of the UN’s Principles for Responsible Investment and the United Nations Environment Programme (UNEP), reveals some interesting answers. It calculates that the full cost to the world’s biggest companies of GHG emissions, pollution, and other environmental damage was almost $6.6 trillion in 2008. This figure is 20% larger than the $5.4 trillion decline in the value of pension funds in developed countries caused by the global financial crisis in 2007/ 2008, and equivalent to 11% of world Gross Domestic Product (GDP) [3]. On such analysis as Trucost’s, it is clear that very heavy cost liabilities arising from companies’ impacts on the environment remain to be recognized and accounted for in their market valuations. Almost 70% of the Trucost figure of $6.6 trillion is estimated as being the companies’ own carbon-related obligations to the environment and to civil society. Once properly accounted for, these enormous obligations linked to climate impacts will hugely reduce not only those companies’ market capitalizations, but will also lower their reputations in global public opinion. In calculating carbon impacts over the entire global economy, it must be considered the tasks both of quantifying carbon impacts on the planet’s ecosystem and secondly, of monetizing these carbon liabilities. The first task, an impact assessment of GHG volumes, can be focused on.

Quantifying Carbon Impacts The fast-developing science of climate change obliges all countries on this planet to cut very quickly the GHG concentrations in the atmosphere back toward sustainable levels. Based on the IPCC’s AR4, although it has been already well known in the world that the concentrations of CO2 in the planet’s atmosphere were approximately 380 ppm in 2005, an increase of about 100 ppm – or 36% – from levels before the Industrial Revolution began in Europe in the late eighteenth century. Over the past two centuries, the growth in

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GHG concentrations has averaged 1.9 ppm per year. The long-term rise in GHGs is calculated to have pushed up average global temperatures by 0.74ºC each year, and to have caused sea levels to rise almost 17 cm across all oceans, according to the IPCC’s AR4. Assuming an unchanged global dependency on fossil fuels, the IPCC AR4’s worst-case scenario predicts a 6.4 C rise in average temperatures by 2100, resulting in a 17 cm rise in sea levels. Such a worst-case scenario is anticipated to result in near-cataclysmic damage, affecting all life on the planet. In order to avoid such cataclysm, and to discharge the intergenerational liability to children and to themselves, action is imperative to decrease concentrations of GHGs in the planet’s atmosphere.

Global Carbon Budget The concentrations of GHGs that have built up through human economic activities, due primarily to more than two centuries’ use of fossil fuels, have clearly harmed the earth’s natural ability to sustain life. In non-scientific terms, ‘‘Mother Nature’’ has for billions of years supported plant, animal, and human life through her generosity and tolerance. But now emissions of carbon dioxide have combined with other GHGs and sources of manmade pollution, waste, and other detritus of post-industrial economies. The effect is to exceed the planet’s inherent capacity to absorb the shocks imposed on it by humanity’s weight of life, as much as by its way of life. The IPCC’s ARA4 calculates the planet’s capacity to absorb carbon into its total biosphere of land, air, and oceans as being 3.1 Gt per year (1 carbon tonne = 44/12 equivalent to the CO2). This calculation is based on latest scientific knowledge and on annual averages for the 5 years ending in 2005. Against this sum, current GHG emissions from human activity have reached 7.2 Gt of carbon per year (> Fig. 12.1). This is more than twice the capacity of the ‘‘Pachamama,’’ the mythical ‘‘Mother Earth’’ revered by Bolivia’s native people. The country hosted ‘‘the World People’s Conference on Climate Change and the Rights of Mother Earth’’ in April 2010 at Cochabamba. President Evo Morales advocated concerted Prediction in 2030 445~535ppm

590~710ppm

Current(380 ppm) Natural CO2 concentration(280 ppm)

Natural absorption by the earth(3.1bn carbon tonnes)

. Fig. 12.1 Global carbon budget (Source: AR4)

Accumulation to the earth(4.1bn carbon tonnes) anthropogenic GHG concentrations (7.2 bn carbon tonnes)

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action in defense of the earth of ecosystems. President Morales said ‘‘Human beings cannot survive without Mother Earth, but Mother Earth can survive without us. We have direct accountability to her.’’ He is usually demonized as Bolivia’s anti-USA and antiEuropean dictator. But his words should be heard by western politicians. Excess GHG emissions continue to accumulate in the atmosphere. The resultant rises in global temperatures will not only continue, but will accelerate, following the wellestablished principle of positive and exponential feedback in complex natural systems. In other words, the absorptive, or uptake functions of ‘‘Mother Earth’’ have fallen into environmental near-bankruptcy in terms of their capability to compensate for the changes which humanity has made to the makeup of the atmosphere. The components and causes in this bankrupting of the planet’s ecosystem are obvious. Prime among them stands human activity, especially the overuse of fossil fuels as main sources of energy, in industrial production and in maintaining human life. Annually around 7.2 Gt of carbon are emitted from fossil fuels and cement. The impact of cement production accounts for only 3% of the total. In addition, changes in global land usage over the past two decades have also pushed up GHGs. Among other sources the ARA4 attributes 2.2 Gt of carbon as being due to deforestation in the 1990s and industrialized agriculture brought onto previously virgin woodland. Before the Industrial Revolution, man-made concentrations of GHGs could be contained safely within the earth’s natural capacity to absorb them. This historical fact clearly compels human beings to recover as quickly as they can the earlier successful balance of consumption and of nurture in which humans must coexist with the planet. In economic terms, people must respect the planet’s natural ‘‘uptake capacity.’’ More broadly, they must restore the relationship between the earth and human activities. This means that they have to mitigate and decrease unabsorbed GHG concentrations. (See the right hand part of box in > Fig. 12.1). This number represents only a ‘‘per year’’ imbalance in emissions, of course. It might be referred to as a global ‘‘income statement of emissions,’’ or as a ‘‘profit and loss statement,’’ for anthropogenic GHGs. Any year’s excess of GHG adds to a huge GHG accumulation in the atmosphere, built up over two centuries’ use of fossil fuels. The IPCC’s ARA4 shows these increases in atmospheric CO2 as the contemporary ‘‘carbon budget.’’ Estimates of atmospheric CO2 have shot upwards in successive IPCC reports. In the 1990s, the equivalent of its third report TAR put a figure of 3.2 Gt of carbon on accumulated atmospheric carbon. Less than a decade later over the period from 2000 to 2005, ARA4’s calculation of atmospheric CO2 had risen by 28%, producing a new estimate of 4.1 Gt of carbon.

Excess Cost of Carbon Imbalance How can monetary values be assigned to these quantities of emissions? First, the unit of carbon volume must be reconciled to CO2-equivalent metric tonne. This is because carbon credits are traded in units of ‘‘tonne of CO2-equivalent unit.’’ The molecular weight of CO2 is 44. Therefore, it can be multiplied weights by this factor to calculate gigatons of carbon.

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Thus the figure for CO2-equivalent tons can be derived. Applying this formula to the figures in the previous section, totals can be calculated for annual anthropogenic emissions of 26.4 Gt CO2 equivalent, and 15.0 Gt CO2-equivalent tons for accumulated atmospheric CO2. Next, a monetary value can be derived for these quantities by referring to market prices for carbon in the EU’s Emission Trading Scheme (EU-ETS), the world’s first mandatory GHG emission trading market. As of June 2010, prices in the scheme were running at almost 15 Euro per tonnes. Thus, the total global carbon deficit would monetize to 225.0 billion Euro annually. The annual buildup of CO2 in the atmosphere represents the net increase of carbon liabilities across the planet – or rather, it represents the liabilities of the human race. Huge though these carbon deficits are, they show only one side of the picture. As already mentioned, these trends in accumulation have continued for more than 200 years, since the start of the Industrial Revolution in the eighteenth century. What are the continuing impacts on the earth of those early and long-lasting carbon burdens? They can be considered not only as yearly increments, but also on a fully amortized, ‘‘total cost of ownership’’ basis, as might be used in calculating a ‘‘global carbon balance sheet’’ of the planet. Sadly, these calculations are not easy, due not least to major gaps in current knowledge and in available data sets. For example, the total assets and liabilities of the earth cannot be reconciled in both a monetary sense and in a non-monetary one. It is very difficult to calculate the remaining periods of atmospheric carbon in the earth. Much recent debate in economics has focused on this topic and estimates vary from 15 years to as much as 200 years. Using 15 years as the hypothesis for the remaining period of atmospheric carbon, it must be increased by 15 times AR4’s ‘‘per year’’ assessment of excess liability, and monetized to Euro 3.375 trillion as a total price of carbon liabilities. On any basis of calculation, this number will be huge. In accounting terms, it has to be concluded that, if the mother planet was an enterprise, she should be filing for Chapter 11 insolvency, owing to her children’s persistent ecological trashing of the family home, sustained over a score of decades. Recent studies in the economics of climate change have attempted to set fair value (market value) on centuries of human ecological vandalism. Among the varying estimates produced, the safest conclusion is that the differences between the balance sheets of manmade carbon production of the earth would be huge even in comparison to the previously mentioned annual income statements of carbon. This much is true, not least because account has to be taken of 200 years of anthropogenic CO2 accumulation. Huge liabilities remain, in the form of excess, unabsorbed carbon. That is the reason why it is not sufficient merely to stabilize human consumption of fossil fuels at current levels. Humanity should be aggressively cutting consumption, if we are to stand any chance of achieving 80% cuts in GHG emissions by 2050.

Avoiding Carbon Insolvency Continuing the ‘‘balance sheet’’ analogy, it must be concluded that after two centuries of mass industrialization, human being remain terrible managers of carbon factors of

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production, of carbon assets, and of carbon liabilities. Judged on such universally accepted principles of accounting as ‘‘true and honest valuation’’ and ‘‘prudence,’’ the history of economic activity amounts to a disaster tantamount to ‘‘carbon insolvency’’ or, at the very best, a staggering profligacy with nonrenewable carbon assets. ARA4 presents a simple benchmark for assessing the short- and long-term effects of CO2 increase. This is the ‘‘airborne fraction’’ – in other words, the increase in CO2 concentrations in the atmosphere, as a share of all fossil fuel emissions. From 1959 to the latest, with remarkably little variation, the airborne fraction has averaged 0.55. That means the absorptive capacity of the earth’s biosphere has consistently removed the remaining 45% of fossil-derived CO2 from the atmosphere. So the recent accelerating rate of increase in atmospheric CO2 reflects an increased level of emissions from burning fossil fuels.

The Carbon Break-Even Point Correcting and rewriting the global balance sheet of carbon places us in a series of double binds, in multiple tensions between growth and ecology, between developing and developed countries, between uncertainty and certainty, and between present and future. Reconciling these opposite is far from easy, but it has to be done. The labor of finding balancing points on each continuum depends on how resources distribution can be improved. In short, a range of optimum levels of resource allocation should be identified, appropriate both to achieving cuts in carbon emissions and to securing economic growth. Any honest or prudent management of the planet’s carbon balance sheet would oblige people to allocate to responsible agents Euro 225.0 billion worth of costs of GHG reductions. Given an adequate rise in the market price of carbon – to the level of Euro 30 per tonnes, as reached by the EU-ETS in mid-2008 – the planet’s total carbon liabilities would rise in value to Euro 450.0 billion. That number should be familiar. It is virtually identical to the estimate produced by Sir Nicholas Stern in his 2006 book, ‘‘The Economics of Climate Change (2006).’’ At that time Stern wrote that: "

If a wider range of risks and impacts [of climate change] is taken into account, the estimates of damage could rise to 20% of GDP or more. In contrast, the costs of action can be limited to around 1% of global GDP each year [4].

On the International Monetary Fund (IMF) estimates, world GDP in 2008 amounted to $ 58 trillion. Under this analysis, estimates of damage due to climate change could vary from as high as $11.6 trillion and as low as $0.58 trillion. Comparing Stern’s figures to the carbon balance sheet above, Euro 450.0 billion of excess carbon liabilities is almost the same value as the minimum expenditure estimated by Stern. So it can be safely concluded that securing this value of resources for measures to cut carbon would represent the break-even point. In other words, such a resource base would constitute a ‘‘sweet spot,’’ a point of balance favoring continued economic growth while at the same time preventing further global warming. Besides monetizing and valuing carbon emissions into carbon liabilities, it also has to be accounted for the effects of feedbacks and positive reinforcement in the climate-carbon

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cycle. These feedback effects mean that global warming tends to slow down the absorption of carbon dioxide by the planet’s landmasses and oceans, thus increasing the fraction of emissions remaining in the atmosphere. According to one estimate, the phenomenon of positive feedback will be responsible by itself for a rise in corresponding global average warming of more than 1 C by 2100. This assumption suggests humanity might reach a sustainable point of equilibrium, merely by establishing break-even points of GHG emissions. But this action would be only one step. Governments and supragovernmental agencies need to move very far and very quickly, if we are to achieve meaningful reductions in emissions and stabilize the climate by the middle of this century.

Measuring the Valuation Materiality of Corporate Carbon SEC Guidance The next task is clear. Calculable amounts of values must be allocated and mobilized in the urgent task of reducing global GHG emissions. The most cost-effective way of achieving this allocation would be by considering both macroeconomic and microeconomic issues. The COP 15 in Copenhagen of December 2009 considered macroeconomic issues, as will COP 16 in November 2010, and subsequent Conferences of the Parties. It might be hoped and believed that COP delegates could at last have been able to reach agreement on the post-Kyoto framework. The issues could not affect more closely the future of humanity and that of the earth. Nobody can escape the implications of climate change. The microeconomic agenda, including new obligations of carbon accounting and disclosure for corporations has emerged to apportion sufficient resources to cover climate-related carbon liabilities. The US Securities and Exchange Commission (SEC) published in February 2010 new guidance to companies facing responsibilities to disclose to investors the materiality of their carbon-related activities (‘‘Commission Guidance Regarding Disclosure related to Climate Change’’). The SEC issued its guidance in answer to requests from members of the United States Climate Action Partnership (USCAP) and from the corporate evaluation community. An urgent need is being felt for a policy framework on climate change, in order to make coherent disclosures of material-relevant carbon-related liabilities, for the purposes of valuing companies. The SEC guidelines stress the necessity of carbon disclosure to investors, as defined in new regulations from the US Environmental Protection Agency (EPA), especially as the new rules on GHG data affect reporting by the large emitter entities, as well as the disclosure regulations contained in the EU-ETS. It is estimated that the EPA’s reporting requirements will affect as much 85% of the USA’s GHG generation, emitted by approximately 10,000 plants and facilities. In addition, despite the USA never ratifying the Kyoto Protocol, many registrant companies have operations outside the USA that are subject to SEC standards.

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Regulation Risk The SEC’s guidance examines the materiality of carbon-emitting activities under three categories: 1. Regulatory risk 2. Physical risk 3. Market risk This scheme has been recognized generally by businesses as acceptable and workable. The SEC document begins by explaining the impact of regulatory risk on three types of companies. For some, the regulatory, legislative, and other developments could have a significant effect on operating and financial decisions, chiefly decisions involving capital expenditure needed to reduce GHG emissions. Secondly, for companies subject to ‘‘cap and trade’’ legislation (not yet introduced in Japan or the USA, but promised for implementation soon), the SEC’s guidance sets out the expenses permissible to purchase emissions allowances, where reduction targets cannot be met. Thirdly, the SEC describes how firms not directly affected by emissions regulation, could still be affected indirectly, through higher prices, charged by directly affected companies who need to pass on their own increased costs of compliance. One consequence is that even in jurisdictions still without a mandatory ‘‘cap and trade’’ regime, companies may yet face some regulatory risk, as a consequence of international trade or cross-border procurement and supply chains. These new regulations on emissions reduction may also present new opportunities for investment. This has been the lesson from the EU-ETS and its associated carbon markets. Companies with more allowances than they need, or who are eager to earn offset credits, can raise capital by selling these instruments on the markets. Companies must thus manage both sides of their own carbon balance sheets to balance their carbon assets and liabilities. Just as important in assessing regulatory risk associated with carbon liabilities, is the necessity for companies to understand cycles of trading and regulation. Even in the EUETS, which is based on the current Kyoto Protocol, trading is limited to a defined period. The EU will extend the present trading period to the end of 2020 under the third phase of the ETS. Beyond 2020, no clear commitment exists; as a result companies face uncertainty. The SEC’s guidelines are equally unclear on this point.

Physical and Market Risk Climate change presents corporations with increased physical risk. Extreme weather events such as fiercer storms, hurricanes, more frequent flooding, deeper erosion of coastlines, melting of permafrost and higher temperatures will all affect enterprises’ facilities and operations. Changes in the availability or quality of water and other factors of production are among innumerable physical challenges about to confront to businesses.

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Physical changes associated with climate change may depress consumer demand for products or services. Warmer winters may cut demand for heating fuels, servicing, and equipment. These effects could affect companies’ operations and the value of their assets. Market risk due to climate change may be defined as companies confronting the risk of reductions or eliminations in business opportunities, consequent upon changes in consumer demands and in society’s needs. If companies have not reacted astutely in response to regulatory and physical risks, they could lose the confidence of consumers and investors. This risk is reputational, and can be considered a type of market risk. The SEC’s guidance advises that, depending on a registrant company’s business and its reputation with the public, it may need to consider whether public perception of its published data on GHG emissions could expose it to potential adverse consequences to its business operations or financial condition. The SEC emphasizes the importance of disclosing risk factors linked to climate change in companies’ financial reports, even where the data’s materiality may be hard to assess. The SEC notes fail to give methods for evaluating such data, neither do they provide any criteria to measure the materiality of non-financial factors. The sole quantified threshold shown is the SEC’s explanation on Instruction 5 to Item 103 of Regulation S-K. This recommends citing any current or outstanding environmental litigation related to governmental regulation. Notwithstanding the SEC’s guidance on climate change, familiar questions remain. How can corporations and other carbon-emitting organizations calculate the materiality of their own carbon liability? How should this be measured?

Quantitative Carbon Disclosure Companies are left to their own devices in deciding how to measure the materiality of their carbon exposure and to disclose this in financial reports. With this realization the next problem, namely, measuring a corporation’s carbon liability, must be focused. Research in corporate reporting reveals several different approaches to climate-related risk. Examples include the disclosure of a company’s carbon budget, as described above, and its philosophy for carbon management. Firms in such carbon-intensive sectors as oil exploration, electricity, chemicals, steel and cement have been quick to adopt such approaches. This is because they have hitherto faced the three types of carbon risk already mentioned. Firms can no longer tuck such data away in financial reports. In its latest corporate citizenship report, ExxonMobil explains that it emitted 128 million tonnes of direct GHG in 2009, down by 2.3% on the year before. The US oil giant publishes detailed information on its gas flaring and on its co-generation capacity, two factors with major impacts on carbon liabilities in its sector. Exxon’s peers Shell, Chevron and BP also disclose their quantified data of carbon emissions. BP has faced another hugely expensive environmental liability, stemming from

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the huge Deepwater Horizon oil spill in the Gulf of Mexico in April 2010. In its disclosures of quantified carbon emissions, BP is more precise than Exxon. BP itemizes its direct CO2 emissions of 60.4 million tonnes, direct methane emissions of 0.22 million tonnes, and customer emissions of 554 million tonnes, respectively, in 2009 (> Table 12.1). A huge volume of environmental liabilities, as well as carbon ones, can be expected in BP’s next report, as it meets claims arising from the Gulf Coast accident, which is now rated as America’s worst-ever oil disaster. Japanese companies are strongly competitive in environmental matters. RICOH, a global leader in office automation equipment and very eager to disclose its own environmental data, publishes figures for its CO2 emissions. It quotes its commitment to achieve 30% reductions in 2020 and 87.5% from 2,000 levels (> Table 12.2).

The Movement for Quantitative Carbon Disclosure Years of pressure by environmental movements have given strength to regulators seeking quantitative disclosure of CO2 emissions by companies. Prominent among them are the UK’s Carbon Disclosure Project (CDP) and the Climate Disclosure Standards

. Table 12.1 Quantities of carbon emissions associated with BP’s activities Year 2006

2007

2008

2009

Direct CO2 (Million tonnes) Indirect CO2 (Mt) Direct Methane (Mt)

59.3 10.1 0.24

59.2 10.7 0.20

57.0 9.2 0.21

60.4 9.6 0.22

Direct GHG (Mt) Customer CO2 (Mt) Environmental expenditure ($ million)

64.4 539 4,026

63.5 521 3,293

61.4 530 2,520

65.0 554 2,483

Note: BP sustainability review 2009

. Table 12.2 Quantitative carbon emission in RICOH (ten thousand CO2 tonnes) 2008

2009

2010 (target)

CO2 (in Japan) Accumulated CO2 reduction

17.65 1.15

16.83 1.83

15.58 2.4

CO2 (global other than Japan)

8.97

9.16

7.61

Note: RICOH sustainability report (Environment) 2009

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Board (CDSB). The CDP is a voluntary, non-profit organization which, through force of argument and through a tailored questionnaire, works to persuade global companies to measure and disclose CO2 emissions and strategies in relation to climate change. The CDP co-ordinates research on behalf of 534 institutional investors, with combined holdings worth in the region of $ 64 trillion. CDP reports include statistics on carbon emissions from its respondent companies, plus other analysis. Open to public scrutiny, this information yields important trends and developments in corporate management of carbon emissions. The Climate Disclosure Standards Board is composed of a pro-environment consortium of global companies, accountancy firms and accounting organizations, and nonprofit lobby groups. CDSB’s mission is to develop a global framework for corporate reporting on GHG emissions, with the aim of supporting, strengthening, and harmonizing existing initiatives in climate-related reporting. The board seeks to enhance best practice in the form of a single consistent global framework. Even though both the CDP and the CDSB claim their activities continue to raise standards of corporate accountability toward the environment, neither would claim their work is complete. Information in companies’ financial reports may be useful for investors seeking to select environment-friendly companies for ESG (Environment, Social, Governance). But quantified information in financial reports does not necessarily reflect the precise cash values associated with liabilities in relation to carbon emissions, nor the resources which companies must dedicate to meet them. Quantified disclosure of climate- and carbon-related liabilities is gradually becoming an obligation under company law. Participating companies in the EU-ETS are obliged to provide their emission data on a site-by-site basis to EU national governments. Since 2005, enterprises in Japan consuming 1,500 kl per year in fossil fuels must submit emissions data; the relevant legislation stipulates reporting of all six main greenhouse gases. The Japanese government has made public the names of companies exceeding prescribed levels of quantified CO2 emissions when it recalculates corporates’ declared emissions data on a per-site basis. Companies who fail to quantify and disclose emissions data, face fines. The US EPA has decided to introduce a Japanese-style scheme for compulsory GHG reporting.

Putting a Price on Carbon Difficulties in Monetizing a Price for Carbon Methods are evolving quickly to collect quantified data on carbon emissions from various types and sizes of corporations under various jurisdictions around the world. What are the next steps? Measuring a corporation’s carbon liability means putting a price on it – in other words, monetization. How should this be done? Carbon markets already provide an important tool to measure current prices for carbon in a free market. Emissions trading

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schemes like the EU’s exist to link sellers with buyers, in the process setting a marketclearing price. Two types of environmental trading systems exist, ‘‘cap and trade’’ and ‘‘baseline and credit.’’ In the EU’s cap and trade system, carbon emission credits such as the European Union Allowance (EUA) have been traded. A closing price for this security is reported after every day’s trading. The process is identical to that for trading currencies, stocks commodities, or any other form of financial instrument. As the biggest trading mechanism for corporate carbon credits, the EU-ETS is highly influential in setting a global price for carbon. In consequence, the prices of Certified Emission Reduction (CER) that were issued by Clean Development Mechanism (CDM) projects in developing countries admitted as one of the emission reduction tools in the Kyoto Protocol have settled on arbitrage trading with EUA markets (see > Fig. 12.2). The effect of such price-setting markets has been that, in general, the more emissions a company causes through its activities, the more it must pay to cover its carbon liabilities. Complete understanding of techniques to value carbon liabilities will be lacking, however, if they are considered merely as a mean to the end of trading of carbon credits in the market. Three types of carbon risk exist, each presenting its own valuation issues, namely, regulatory risk, physical risk, and market risk. Regrettably, a market mechanism such as trading cannot monetize all three types of risks. Let’s consider why. Firstly, regulation risks are not shared equally between all types of carbon emitters. Proof of this emerges, when the composition of the current EU-ETS is examined. Now in its second phase of operations, the EU-ETS admits only firms from heavy-emitting industries and eligible sectors including power utilities, energy generation, iron smelting, cement and oil refining. The EU-ETS will expand its targeted eligible sectors gradually.

18 16 14 12 10 8 6 4

2010EUA 2010CER

10/05

10/04

10/03

10/02

10/01

09/12

09/11

09/10

09/09

09/08

0

09/07

2 09/06

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2011EUA 2011CER

. Fig. 12.2 Price differences between EUA and CER (=Euro) (Drawing by the Daiwa Institute of Research based on the data of European climate exchange, June 2010)

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For its third phase running from 2013 to 2020, it will admit firms in chemicals, aluminum, and aviation, but still not expand to include all of CO2-emitting sectors. In a sector-led approach to industrial carbon reduction, national governments thus decide which industries are prioritized. Under the United Nations’ Framework Convention on Climate Change (UNFCCC) and its enforceable Protocol, the job of setting reduction targets is decided at country level. So the UNFCC allows huge political compromises to be made, invariably to the detriment of emissions reduction. If the government of a developing company, for example, judges that a heavy emitter of CO2 – its iron industry, say – is critical to national development and job creation, then the politicians may well exempt that sector from regulation. No penalties follow for the country in terms of its compliance with the treaty, so long as it achieves its overall promised goal for emissions reduction. Methods of limiting national output by sector have been enacted in some trading systems. The RGGI is a mandatory cap and trading system of carbon rights, covering 10 northeastern and Atlantic states in the USA. It targets only the power generation sector, against a goal to cut emissions by 10% by 2018.

The IFRIC3 Dispute over Accounting Standards for Government Grants of Carbon Allowances Any system of public trading of corporate carbon rights will produce a market price at the end of every trading-day. To allocate costs within a company for the resultant carbon price, it is necessary that the company has to include such prices on both the balance sheet and the income statement of companies, in accordance with the prevailing principles of accounting. This necessity is at once very important and very difficult for companies. Regrettably, there is no avoiding it. The International Financial Reporting Interpretations Committee (IFRIC) is the interpretative body of the IASB (International Accounting Standards Board). In December 2004, just as the EU launched its ETS, the IFRIC committee issued IFRIC3, its formal accounting interpretation on Emission Rights, or carbon credits. At that time it was decided that EU-ETS should come into effect from 1 March 2005. In practice the IFRIC3 thus became the new accounting tool of choice for the EU-ETS. But it was withdrawn after only a month, the victim of wrangles between accounting regulators and business leaders. The allowances granted by national governments to the companies participating in the ETS were at issue. According to the IASB, IFRIC 3 specified the following [5]: 1. Rights (allowances) are intangible assets that should be recognized in the financial statements in accordance with IAS 38. 2. When allowances are issued to a participant by government (or government agency) for less than their fair values, the difference between the amount paid (if any) and their fair value is a government grant that is accounted for in accordance with IAS 20.

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3. As a participant produces emissions, it recognizes a provision for its obligation to deliver allowances in accordance with IAS 37. This provision is normally measured at the market value of the allowances needed to settle it. The issue was how to treat such an allowance on the balance sheet. A consensus among businesses held that an allowance is an asset, because it is acquired at a cost, in the same way as any other factors of production such as raw materials and equipments. IFRIC agreed; however, not all business leaders did so. As the IFRC is an interpretative body of the IASB, it is bound by the IASB Framework on the Preparation and Presentation of Financial Statements (‘‘Framework’’). This framework does not assess an asset from the cost evaluation viewpoint. It defines an asset as a ‘‘resource controlled by the entity as a result of past events and from which future economic benefits are expected to flow to the entity’’ [6]. As the EU-ETS began trading, the IFRIC standard recognized as an asset the allocation by EU governments of allowances to companies in their own territory. However, IASs set by IASB require assets to be measured at fair value at each reporting date. In consequence, the IFRIC interpreted allowances in an undifferentiated manner, failing to discriminate between allowances purchased from the market or granted by governments. In contrast at that time, the IASB had a long-standing proposal to amend recognition of governmentallocated granting of rights in the IAS 20 (Accounting for Government Grants and Disclosure of Government Assistance) this stipulated that any grant from a government could no longer be considered as income. The dispute’s implication was that any free emission allowances granted by governments would have to be recognized immediately as income. Business leaders protested that it was impractical for them to recognize fair value at the outset of trading. The IASB withdrew IFRIC3. Further accounting disputes have followed, concerning the structures of the emission trading schemes, and in particular how to establish a scale of values for initial allowances and allocate them among the scheme’s members. At question have been competing methods of rights allocation such as the so-called ‘‘grandfathering approach’’ as used in the first phase of the EU-ETS; alternative methods also considered have included benchmarking approaches, and allocation based on auctions of emissions rights. IFRIC3’s failure was a direct consequence of the ‘‘grandfathering’’ approach favored by the EU. In a statement, the Board of the IASB justified its withdrawal of IFRIC3 claiming that ‘‘the Board decided to take the time to conduct a broader assessment of the nature of the various volatilities resulting from the application of IFRIC 3 to a cap and trade scheme and to consider whether and how it might be appropriate to amend existing standards to reduce or eliminate some of those volatilities.’’ The decision was taken by an overwhelmingly vote of 12 in favor, 1 against, and 1 abstention. After several years, the IASB restarted the debate on limiting free issues in emissions trading schemes. But it chose not to address the controversy surrounding accounting standards for all government grants at December 2007. To date, joint discussions have continued with its US counterpart, the FASB. A new exposure draft proposal will be expected in late 2011 no new version of the IFRIC guideline is anticipated before late 2012.

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Calculating Physical Risk to Price Despite long-standing discussions on setting up comprehensive and intelligible rules in carbon accounting, markets seem to provide the simplest method for setting a carbon price. Companies trading under mandatory emission trading schemes like the EU-ETS can compare carbon prices in the market with their own carbon management on issues such as raw materials purchase, investment in production equipment, identifying a development site, or in deciding about the production of a new product or service. As described above, accounting standards for reporting carbon values have not been decided, and none will be accepted until the new draft of ‘‘IFRICa’’ emerges. Carbon pricing in free markets serves well as one measurement of carbon liability. It is limited, however, in relation to regulatory risk. As described above, the concept of carbon liability comes not only from regulation but also from physical and market risk types. Physical risk may increase carbon damage to the asset side of a company’s balance sheet, as opposed to its liabilities. Some simple examples illustrate the point. Rising sea levels may halt or impede operation of an enterprise’s factories and facilities located along coastlines. Companies face operational interruption or damage, due to fiercer storms, heavier rain, more frequent typhoons, or land erosion caused by drought. Firms will be well advised to introduce climate contingent Business Continuity Plans (BCPs) to prevent deterioration of their fixed assets and operational interruptions caused by climate change. Introducing climate contingent BCPs could serve as a form of environmental insurance against carbon impacts.

Applying ARO Method As companies struggle to calculate climate-related physical risks to their asset base, both now and in future, they have available to them a useful accounting technique. This is the accounting rule for asset retirement obligations (AROs). AROs are legal obligations associated with the retirement of a tangible long-term asset. Such obligations result from the acquisition, construction, development, or normal operation of a long-term tangible asset, as defined in the FAS 143 standard issued in 2002 by the FASB. This accounting rule applies a ‘‘fair value’’ measure of fixed assets, which includes environmental damage or other future obligations. For example, the owner of an asset that is subject to environmental laws such as CERCLA is required to recognize their liability as an ARO on their balance sheet in the period in which it is incurred, based on a reasonable estimate of its fair value. Even if it is not possible to estimate with precision, the liability must be recognized whenever a reasonable estimate of fair value can be made. An ARO is not quite the same as a carbon liability associated with any fixed asset. But it can be said that the nature of the uncertainty surrounding any carbon liability might be

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quite similar to the processing of evaluating an ARO. Companies have to estimate the fair value of a carbon obligation, against the uncertainty of future regulation against the possibility of physical risk. FIN47 is the FASB’s interpretation of FAS 143 issued in March 2005. The US-based environmental accounting consultant C Gregory Rogers [7] specifies that the fair value of an ARO may be determined based on any of the following methods. 1. The amount of the obligation embedded in the acquisition price of the asset 2. A market quote in an active market for transfer of the obligation 3. Application of an expected present value technique to estimate fair value (if neither of the above two situations apply)

Converting a Market Risk to an Opportunity Setting a price on carbon liabilities associated with market risk can be very difficult, not least because this type of risk may be influenced by customers’ changes in taste or in buying behavior. One solution may be to apply marketing methods such as Customer Related Marketing (CRM). If companies use such carbon marketing techniques, they may persuade their customers that their products are differentiated by virtue of low impact on the environment. Perceptions can be altered by careful market positioning. It is not yet clear how many customers will value, or will react to, perceptions of low carbon positioning, rather than to traditional lower prices and higher quality. But more easily than with the other carbon risk types, market risk can be turned from a liability into an asset and a source of competitive advantage. Several global competitors are already attempting to pursue carbon value as a marketable asset. The German chemical giant BASF published its corporate carbon footprint in 2008. The company uses the lifecycle principle to calculate GHG emissions not just at its own controlled facilities, but also at external points in the value chain such as procurement, manufacturing, transport and disposal. BASF emphasize their sound carbon budgeting, based on comparison of emissions and savings. Emissions from procurement, manufacture, transport and disposal come to roughly 90 million tonnes of CO2 equivalent. Almost 30% – or 28 million tonnes – comes from in-house production. By comparison, the use of BASF products saves 287 million tons of CO2, resulting in a ratio of 3:1. Dr. Ulrich von Deessen, BASF’s Climate Protection Officer and head of the Competence Center for Environment, Health & Safety, said in the report that ‘‘Corporate carbon footprints highlight the opportunities and threats that companies face as a result of climate change. This is important both for the company itself, as well as for stakeholders such as investors, customers and employees.’’ Carbon management entails the full realization and declaration of all costs and liabilities arising from man-made carbon, and allocating these costs to appropriate activities both in their production, and to the final retail value of a product. In discharging this management obligation more efficiently, corporations must establish a well-planned

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architecture of mandatory carbon trading which minimizes regulatory risk. Equally desirable and necessary is an agreement on more accurate accounting methods, capable of producing coherent and usable valuations of carbon liabilities, as they materially effect a company’s base of fixed assets and related liabilities. In addition, companies should apply across all its key audiences – customers, investors, and other stakeholders – a comprehensive, appropriately designed strategy of carbon marketing. The goals should be to request and to achieve collective changes in patterns of consumption as well production in order to safeguard the interests of future generations.

References 1. 2.

3. 4.

The Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007 US Environmental Protection Agency (1996) Valuing potential environmental liabilities for managerial decision-making :a review of available techniques UNEP FI & PRI’ Universal Ownership’ October 2010, contributed by Trucost Stern N (2007) The economics of climate change. Cambridge University Press, Cambridge

5. 6.

7.

International Accounting Standards Board (2010) Explanation on emission trading schemes Cook A (2009) Accounting for emissions: from costless activity to market operations. In: Freestone D, Streck C (eds) Legal aspects of carbon trading. Oxford University Press, Oxford Gregory Rogers C (2006) Financial reporting of Environmental liabilities and risks after SarbanesOxley. Wiley, Hoboken

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13 Impacts of Climatic Changes on Biogeochemical Cycling in Terrestrial Ecosystems Dafeng Hui1 . Hanqin Tian2 . Yiqi Luo3 Department of Biological Sciences, Tennessee State University, Nashville, TN, USA 2 International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences, Auburn University, Auburn, AL, USA 3 Department of Botany and Microbiology, University of Oklahoma, Norman, OK, USA

1

Introduction: Global Climate Change and Terrestrial Ecosystems . . . . . . . . . . . . . . . . . 435 Approaches to Evaluate the Impacts of Climate Change on Terrestrial Ecosystems: Observation, Experiment, Model, and Meta-analysis . . . . . . . . . . . . . . . . . . 437 Observation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438 Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440 Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442 Terrestrial Ecosystem (TECO) Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442 Dynamic Land Ecosystem Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444 Model Parameterization and Inverse Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445 Meta-analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446 Impacts of Elevated Atmospheric CO2 Concentration on Carbon Cycling in Terrestrial Ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447 Experimental Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447 Photosynthesis, Respiration, and Stomatal Conductance . . . . . . . . . . . . . . . . . . . . . . 448 Plant Growth, Biomass, Ecosystem Productivity, and Carbon Storage . . . . . . . . 448 Modeling Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449 Meta-analysis Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453 Photosynthesis, Respiration, and Stomatal Conductance . . . . . . . . . . . . . . . . . . . . . . 453 Plant Growth, Biomass, Ecosystem, Productivity, and Carbon Storage . . . . . . . 454

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_13, # Springer Science+Business Media, LLC 2012

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Impacts of Global Warming on Carbon Cycling in Terrestrial Ecosystems . . . . . . . . . . 455 Experimental Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455 Photosynthesis, Respiration, and Soil Respiration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455 Plant Growth, Biomass, Ecosystem Productivity, and Carbon Storage . . . . . . . . 456 Modeling Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457 Meta-analysis Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458 Impacts of Precipitation, Ozone, and Multiple Climatic Factors on Carbon Cycling in Terrestrial Ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460 Experimental Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460 Plant Photosynthesis, Respiration, and Soil Respiration . . . . . . . . . . . . . . . . . . . . . . . 460 Modeling Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462 Meta-analysis Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463 Future Directions: New Experiments, New Models, and New Approaches . . . . . . . . . . 464 Closing Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465

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Abstract: Global climate change has profound effects on biogeochemical cycling in terrestrial ecosystems. This chapter summarizes the existing state of knowledge on how climate change affects biogeochemical cycling, specifically carbon cycling, as the carbon cycling has long been recognized as important for understanding climate change. The review draws largely on knowledge gained from manipulated experiments, modeling, and meta-analysis studies. This chapter starts with a brief description of current changes in several climate factors such as atmospheric carbon dioxide (CO2) concentration, temperature, precipitation, and ozone (O3) and their effects on terrestrial ecosystems. Then approaches commonly applied in global change research such as natural observation, experiment, ecosystem modeling, and meta-analysis are described. The advantages and disadvantages of these approaches and general procedures are also summarized. The impacts of global change such as elevated CO2, global warming, and changes in precipitation and O3 on carbon cycling in different terrestrial ecosystems are further synthesized. In addition, issues related to global climate change such as single factor versus multiple factor studies, graduate versus step increase experiments, and inverse modeling are briefly discussed. At the end of the chapter, some recommendations for future global change research in terrestrial ecosystems are provided.

Introduction: Global Climate Change and Terrestrial Ecosystems The atmospheric carbon dioxide (CO2) concentration has gradually increased from 280 ppm in preindustrial times to 379 ppm in 2005 and is expected to exceed 700 ppm in 2100 [1], mostly due to land use change and fossil fuel combustion. As a consequence of rising CO2 and other greenhouse gases, the Earth’s surface temperature has increased by 0.74 C in the twentieth century and is expected to increase by another 1.8–4.0 C by the end of this century [1]. Precipitation is also anticipated to increase by about 0.5–1% per decade over most of the middle- and high-latitude land areas in the northern hemisphere in this century [1]. The tropospheric ozone (O3) level has been increasing at local, national, continental, and even global scales. Future projections indicate that the trends in greenhouse gases, temperature, and precipitation will continue, resulting in a warmer, wetter, yet drier world in the twenty-first century [1, 2]. Changes in atmospheric CO2 concentration, O3, and other climatic factors have the potential to trigger complex influences on terrestrial ecosystems with feedbacks to climate change [3–5]. Carbon dioxide, for example, is not only one of the main greenhouse gases, but also a substrate of plant photosynthesis. Rising atmospheric CO2 concentration can directly affect photosynthetic rates, plant growth, and ecosystem productivity. Temperature influences all physical, chemical, and biological processes. Global warming can affect ecosystem structure and function, such as ecosystem carbon cycling. Precipitation, O3 concentration, and nitrogen fertilization also regulate plant growth and ecosystem carbon cycling in terrestrial ecosystems [6–9]. The amount of carbon stored in terrestrial ecosystems will feedback and influence future atmospheric CO2 concentrations. Thus, it is very

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important to assess the impacts of global climate change on ecosystem carbon cycling and processes [10]. Ecosystem carbon cycling and fluxes between the atmosphere and terrestrial ecosystems are controlled by the processes of photosynthesis, plant autotrophic respiration, and soil heterotrophic respiration (> Fig. 13.1). The total of plant photosynthesis in terrestrial ecosystems is gross primary productivity (GPP). Soil respiration includes root respiration and heterotrophic respiration (i.e., soil microbial respiration). Ecosystem respiration includes both soil respiration and aboveground autotrophic respiration. The difference between plant photosynthesis and respiration is defined as net primary production (NPP). The difference between NPP and soil heterotrophic respiration, defined as net ecosystem production (NEP), represents the net carbon flux from the atmosphere to ecosystems. Ecosystem carbon processes and productivity are also influenced by plant phenology, nitrogen conditions, land use changes, and disturbances such as fire, drought, and insect outbreaks. Among many factors affecting these processes, the most obvious are elevated CO2 concentration and climate change, which directly and indirectly influence and interact to control the carbon fluxes from ecological and physiological processes [5, 11, 12]. Climate and atmospheric CO2 concentration are key regulators of most terrestrial biogeochemical processes and have the potential to markedly modify the carbon cycling in terrestrial ecosystems [10]. Responses of terrestrial ecosystems to elevated CO2 concentration and global climate change are complex and thus, require different approaches, such as observation, manipulated experiment, ecosystem biogeochemical modeling, and meta-analysis [2]. Long-term observations over large spatial areas provide invaluable insights and background information on ecosystem response to climate changes. Manipulated experiments allow us to seek the different effects and mechanisms of climate change on terrestrial ecosystems. Ecosystem modeling is a very powerful tool to synthesize

Atmospheric CO2

Global warming

Precipitation

O3 and other factors

Soil moisture

Photosynthesis

Plant respiration

Plant growth and productivity

Soil heterotrophic respiration

Soil carbon storage

Net ecosystem carbon storage

. Fig. 13.1 Impacts of climate change on terrestrial ecosystem carbon processes and feedback

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experimental results and assist extrapolation of leaf, plant, and ecosystem-level research results to project changes in ecological processes at regional and global scales [10–12]. Meta-analysis provides a quantitative synthesis and generates a general conclusion of many individual and often inconclusive studies [3, 14, 15]. Many studies have been conducted on the responses of terrestrial ecosystems to elevated CO2 and global climate change during the past several decades using these different approaches. Results from these studies have greatly improved our understanding of the responses of terrestrial ecosystems and the feedback to future climate change. This chapter reviews global climate change studies on the impacts of biogeochemical cycling, specifically carbon cycling, in terrestrial ecosystems, and attempts to provide a comprehensive and up-to-date overview in the field. The complexity of responses is often confounded by other concurrent human-induced global changes such as nitrogen and sulfur deposition, invasive species, and land use changes, but these are not covered in this review. This chapter starts with a description and comparison of different approaches commonly applied in global change studies. Then the impacts of elevated CO2, global warming, precipitation, and other climate change factors on ecosystem carbon cycling are reviewed. Issues related to global climate change such as single factor versus multiple factor studies, graduate versus step increase experiments, and inverse modeling are also briefly discussed. Finally, some recommendations for future global change research in terrestrial ecosystems are provided.

Approaches to Evaluate the Impacts of Climate Change on Terrestrial Ecosystems: Observation, Experiment, Model, and Meta-analysis Several approaches have been used to evaluate the impacts of rising atmospheric CO2 concentrations and climate change on terrestrial ecosystems in the past several decades at different spatial scales. Generally, these approaches can be classified into four categories: observation, experiment, model, and meta-analysis. Among these approaches, experimental study is a powerful tool to evaluate the responses of climate changes on terrestrial ecosystems and to understand the mechanisms underlying these responses. It will continue to be a major tool and has been extensively used, in global change studies. With the advancement of sensor technology, automatic recording, and satellite images, more and more observations and measurements on terrestrial ecosystems under natural conditions can be made over long term and at large spatial scales. Ecosystem modeling becomes more and more important, especially at scaling up from plot-level experiments to large spatial scales and forecasting future responses. As more and more data accumulates, metaanalytic techniques provide another means to quantitatively integrate the individual studies and generate a grand conclusion on a common topic. Recently, Rustad [2] summarized some of these approaches (> Table 13.1), particularly on experimental studies (see also Fig. 1 and Table 1 in [2]). In this section, the four approaches are briefly discussed, with a focus on terrestrial ecosystem carbon cycling.

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. Table 13.1 Advantages and disadvantages of different approaches to evaluating global change impacts on terrestrial ecosystems [2] Approach

Advantage

Disadvantage

Observations

1. Suitable for long-term research 2. Good for model validation

1. No true control, effects of climate are confounded 2. Quality of study depends on data availability 3. Future responses are unknown 1. Can only generate short-term data on short-term response due to costs

Experiments

3. Relative low costs 1. Suitable for evaluating cause–effect relationships

2. Can study past, current, and 2. Step increase is not realistic future climate change 3. Good for model validation 3. Can only realistically alter two to three factors 1. Not possible to validate longer-term Models 1. Integrating existing knowledge effects 2. Extrapolating to long term 2. Need to incorporate heterogeneity, and large scales disturbance, etc. 3. Testing of conceptual and 3. Uncertainty related to model structures, process understanding parameters, and predictions Meta-analyses 1. Integrate multiple individual 1. Only limited levels and single factor experimental results experiments are synthesized 2. Provide quantitative 2. Not provide novel insights conclusions

Observation Observations can provide background information on ecosystem responses to climate changes. To be valuable, these observations/measurements need to be made over long term or at large spatial scales, or both. With long-term observational data, the relationships of ecosystem responses and climatic factors can be developed. For example, using long-term climate data and satellite observations of vegetation activity, Nemani et al. [16] report that the global changes in climate have eased several critical climatic constraints to plant growth, as that as NPP increased by 6%. The largest increase was in tropical ecosystems. They also estimate that water availability most strongly limits vegetation growth over 40% of Earth’s vegetation surface, where temperature limits growth over 33% and radiation over 27% of Earth’s vegetated surface. With observations at large spatial scales, different ecosystem responses to climate change may be derived. Individual observational studies are often made along climate gradients, such as temperature gradient along mountain slopes, precipitation gradient with

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elevations/longitudes, or CO2 gradient near natural CO2 springs. These natural climate gradients provide unique opportunities to study responses of ecosystems to a range of climate factors, and trade space for time. Many observation networks have been built in recent years, due to the advancement of sensor technology and collaborations among scientists. For example, FluxNet is an international network of micrometeorological tower sites that use eddy covariance methods to measure the exchanges of CO2, water vapor, and energy between terrestrial ecosystem and the atmosphere [17]. The goal of FluxNet is to understand the mechanisms controlling the exchanges of carbon, water vapor, and energy across various ecosystem types and over long-term timescales. The network spans a wide cross section of climate zones and ecosystem types. Synthesis of data from EuroFlux, a part of FluxNet network, confirms that many European forests act as carbon sinks, and ecosystem respiration determines net ecosystem carbon exchanges [18]. These data also provide a unique opportunity for researchers to identify the response patterns and the underlying mechanisms of ecosystem carbon fluxes to climate changes. Another example is the Long Term Ecological Research (LTER) network supported by the National Science Foundation (NSF). LTER provides insight on ecosystem responses to global climate change at broad spatial and temporal scales [2]. Other similar networks also demonstrate the value of the collaborative studies. Data from Afritron (African Tropical Rainforest Observatory Network), which includes 79 inventory plots, show that aboveground carbon storage in live trees increased by 0.63  106 g carbon (C) ha 1 year 1 between 1968 and 2007 [19]. Widespread changes in resource availability, such as increasing atmospheric CO2 concentrations, may be the cause of the increase in carbon stocks. In the near future, National Ecological Observatory Network (NEON) will be built with the support from the NSF to make observations across the continental United States [20]. It is a continental-scale research platform for understanding and forecasting the impacts of climate change, land use change, and invasive species on ecological processes. At large spatial scales, satellitebased remote sensing plays an indispensable role in terrestrial ecosystem observations. Satellite-derived land products such as net primary production (NPP), NDVI, and leaf area index are important products toward a global observation capability. NPP derived from Moderate-resolution Imaging Spectroradiometer (MODIS) and NDVI data sets derived from satellite images can be used to derive the relationships of ecosystem carbon fluxes with climate changes. The advantages of observational study include: (1) Data over long term and at large spatial scales can be collected, thus allowing to evaluate long-term effects across different ecosystems (> Table 13.1). (2) For pure observational studies, the costs for experimental site construction are low. Funds are required only for observations and measurements and thus, it is desirable to run for a long time. (3) Regional and international observation networks can be formed to focus on a centered theme to study climate change at large spatial scales across different ecosystems. The disadvantages of the observational study include: (1) There is no true control, thus, the effects of climate changes are often confounded with other environmental factors. (2) Quality of the study depends on the availability of data. The long-term records dating back to more than 100 years (which is

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very long compared to experimental study, but short in terms of climate change) are rarely available [2]. (3) Observational studies mostly lack the ability to predict the future responses.

Experiment Numerous manipulated experiments have been conducted in the laboratories and under field conditions [21–24]. For example, an international research coordination network – Terrestrial Ecosystem Response to Atmospheric and Climatic Change (TERRAC) – includes 135 field experimental sites in 25 countries [2, 24]. These studies include one, two, and multiple climatic factor experiments and consider atmospheric CO2 concentration, temperature, precipitation, and nitrogen addition. Ecosystems include deciduous forest, coniferous forest, grassland, wetland, shrubland, tundra, and desert. In global climate change research, most experimental studies use a perturbation approach that creates treatment levels (i.e., magnitudes in changes of treatment factors) that are large enough to generate detectable ecosystem responses [10]. For example, ecologists usually double CO2 concentration, increase it by 200 ppm, or set a specific level at the onset of experiments conducted in greenhouses, growth chambers, open-top chambers, and Free Air CO2 Enrichment (FACE) facilities (> Fig. 13.2) [21]. In the early years, researchers used closed chambers such as growth chamber to grow plants under control and elevated CO2 levels. These studies were criticized as growth chambers cannot really mimic the real world environment, thus generate responses that are different to those under natural conditions. Open-top chambers provide natural light and precipitation for plants to grow, but often modify air and soil temperature inside the chambers. Open-top chambers have not been used successfully in the studies of ecosystems with large vegetation. They are mostly useful for low-stature systems (e.g., tundra, grassland, tree seedling). FACE is the state-of-the-art facility for studying the effect of elevated CO2 on terrestrial ecosystems, as it creates a high CO2 environment without altering other environmental factors [21]. Scientists measure responses of plants, soil, and ecosystem processes to such a step increase in CO2 concentration through time [10]. Similar to elevated CO2 studies, in order to examine the effects of climate warming on ecosystem processes and community structures, researchers usually raise soil/air temperature instantaneously by 1–4 C in treatment plots than that in the control. The methods used to manipulate temperature include soil warming [25], infrared heaters [26–28], passive heating, and open-top chambers with heated air (> Fig. 13.2) [29]. Most of the experiments with infrared heaters also have constant energy input to the ecosystem, resulting in increases in soil surface temperature being higher at night than during daytime. A comparison and discussion of the warming facilities can be found in Wan et al. [27]. Although other global change factors, such as precipitation and nitrogen deposition, may not evolve gradually in a regular fashion over time and/or uniformly over space as atmospheric CO2 concentration does, experimental studies mostly use the step-change

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. Fig. 13.2 Examples of field facility in global change research. (a). EcoCELLs, Ecologically Controlled Enclosed Lysimeter Laboratories, photo credit: Jay Arnone III; (b). Open-top chambers (OTCs) on a Florida Scrub-oak Ecosystem, photo credit: Bert Drake; (c). FACE (Free Air CO2 Enrichment) experiment in Duke loblolly pine forest, photo credit: Will Owens; (d). The open-top-chamber (OTC) warming facility in the International Tundra Experiment (ITEX) warming study, photo credit: Greg Henry; (e). Global warming experiment in tall grass prairie in Oklahoma, photo credit: Yiqi Luo; (f). Rocky Mountain Biological Laboratory Meadow Warning Experiment, photo credit: John Harte (With kind permission from Springer Science+Business Media: Plant Ecology, Vol. 182, 2006, Rustad, photo); (g). Jasper Ridge multiple factors (CO2, warming, precipitation and nitrogen) Global Change Experiment, California, photo credit: Chris Field; (h). Precipitation shelter in tallgrass prairie at the Konza Prairie Research Natural Area, Kansas, photo credit: Philip A Fay

approach as well [10]. Precipitation amounts were doubled in a grassland experiment in central US Great Plains and reduced by 30%, 55%, and 80% in Argentina [30]. Precipitation amounts were also changed together with timing in some of the studies [6]. Multiple factor experiments are logistically and financially challenging [2]. There are only a small number of experiments that consider more than two climatic factors in the same study. But these studies quantify not only the main effects of climatic factors, but also the interactive effects of these factors. Results from some experimental and modeling

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studies also demonstrate interactive responses to the combinations of treatments and underscore the need for multifactor experiments at different ecosystems and over long term [2, 31–33]. The major advantages of experimental study are: (1) to reveal true ecosystem responses to climate change. As other factors are controlled and kept at relative same levels, the results are considered as the direct effects of climatic change; (2) to help understand the mechanisms of these responses; since only one or a few climatic factors are manipulated, it is relative to track the influences of climatic factors on ecological processes and components; (3) as treatment levels can be set at different levels, the effects of climate change factors in the past, current, and future can be evaluated; and (4) to provide data to parameterize and validate models, and generate mechanisms to be built into models. The disadvantages include: (1) Short terms. Majority of the experiments last less than 5 years. The results from these studies may be transient, and both magnitude and direction of responses may change over time [2, 22]. (2) Using a step increase rather than gradual increase in climatic factors. Many climatic factors such as CO2 concentration, O3, and temperature are increasing gradually over years. But experiments usually expose ecosystems to future high CO2 concentrations, O3, or temperature abruptly. The responses of ecosystems to step increases may be different to those of gradual increases in natural conditions. (3) Climatic factors change simultaneously, but most experiments can only consider one or a few climatic factors, and set two or a few treatment levels. (4) High costs for large global change projects, for example, FACE experiments. The financial costs also limit the number of climate factors that can be considered and the number of years an experiment can take.

Model Process-based ecosystem models provide appropriate tools for integrating the existing knowledge, scaling experimental results up in time and space, and investigating multiple, interacting factors of global change [2, 5, 11, 12, 32–34]. They also represent a key method for testing hypotheses about the response of terrestrial ecosystems to multiple climatic factor changes [34, 35]. Many ecosystem models have been developed with different complex and ecological processes, and applied to assess the impact of climatic change on terrestrial ecosystems [31, 35]. Several model comparison studies also compared model structures, ecological processes, and model performances using one set or sets of experimental/observational data [32, 35]. Here two specific models, one at the stand level and one at large scale, are described to illustrate some common ecological processes included in ecological models.

Terrestrial Ecosystem (TECO) Model TECO is a biochemical and ecophysiological model that uses daily meteorological data to simulate ecosystem carbon dynamics at site level (> Fig. 13.3). It has been applied to

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Canopy photosynthesis CO2 Foliage biomass (X1)

Woody biomass (X2)

Structure litter (X4)

Metabolic litter (X3)

CO2

CO2 Microbes (X5) CO2 CO2

CO2 Slow SOM (X6) CO2

CO2 Passive SOM (X7)

. Fig. 13.3 Diagram of the carbon processes of terrestrial ecosystem (TECO) model ([39]. With permission from AGU). SOM stands for soil organic matter

predict ecosystem responses to rising atmospheric CO2 concentration, climate warming, and altered precipitation frequency and intensity in grasslands and forests [32]. TECO has two major components: a canopy photosynthesis model and an ecosystem carbon dynamic model. The canopy model is a multi-layer, process-based model of an even-aged mono-specific plant stand. The carbon dynamic model considers plant growth, respiration, and soil carbon movement. Allocation of assimilates over the plant components bases on the priority principle and varies with phenology. The effects of climatic factors such as atmospheric CO2 concentration, temperature, and precipitation are built in the model, as these factors will influence most biological processes. For example, precipitation will influence evapotranspiration and soil moisture directly, and then influence leaf photosynthetic rate and soil respiration. Temperature plays an important role in biological processes. It affects photosynthesis, respiration, and transpiration. The main time step of TECO is 1 day. Light penetration, photosynthesis, and transpiration are simulated in half-hourly time steps. Input meteorological driving variables

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(from half-hourly to daily values) are short-wave radiation, rainfall, wind speed, relative air humidity, air temperature, and soil temperature to be collected at the experimental site. The main outputs of the model include ecosystem productivity, ecosystem carbon exchange, soil respiration, and soil carbon pools.

Dynamic Land Ecosystem Model Dynamic Land Ecosystem Model (DLEM) is a highly integrated process-based ecosystem model that simulates the fluxes and storage of carbon, water, and nitrogen among/within the terrestrial ecosystem components with the consideration of multiple natural and anthropogenic perturbations (e.g., climate change, CO2 concentration, atmospheric composition, land use, and management practices), working at multiple scales in time from daily to yearly and space from meters to kilometers, from region to globe. The DLEM includes five core components (> Fig. 13.4): (1) biophysics; (2) plant physiology; (3) soil biogeochemistry; (4) dynamic vegetation; and (5) disturbance, land use, and management. Briefly, the biophysics component simulates the instantaneous fluxes of energy, water, and momentum within land ecosystems and their exchanges with the surrounding environment. The plant physiology component simulates major

Regional climate and atmosphere chemistry (Temperature, precipitation, radiation, wind, pressure, humidity; CO2, Ozone, NO3, NH3) Radiation, humidity, pressure, wind, precipitation, temperature CO2, O3. NO3, NH3

GHG

Ecosystems

Biophysics

GHG

Radiation reflectance/transmission, evaporation, sensible heat flux, water balance

Disturbances, land use and management Disturbances: Diseases, drought, flooding, hurricane, wildfire, etc. Land use: Agriculture, managed forest, pasture, Urban, etc. Management: Fertilization, harvest, irrigation, rotation, tillage, etc.

Land cover, nutrient, PFT, water

Water temperature radiation

Plant physiology

Abbreviations: ET: Evapotranpiration LAI: Leaf Area Index GHG: Green House Gas PFT: Plant Function Type

Litte

Photosynthesis, respiration, allocution, nitragen uptake, ET, turnover, phenology Biomass growth efficiency

Soil moisture temperature

LAI canopy conductance

PFT

Nutrient

Soil biogeochemistry Mineralization, nitrification/denitrification (N2O, NO), decomposition (CO2), fermentation (CH4) Nutrient PFT

Dynamic vegetation Succession, biogeography Carbon, water, nutrient

Water transport Soil Erosion, soil water discharge, River discharge, Nitrogen leaching Carbon, water, nutrient Water, energy, CO2

Water GHG

Water reservoir Lake, Stream, Ocean

. Fig. 13.4 Framework of the Dynamic Land Ecosystem Model (DLEM) (Adapted from [70]. With permission)

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physiological processes, such as plant phenology, C and N assimilation, respiration, allocation, and turnover. The soil biogeochemistry component simulates the dynamics of nutrient compositions and major microbial processes. The biogeochemical processes, including the mineralization/immobilization, nitrification/denitrification, decomposition, and methane production/oxidation are considered in this component. The dynamic vegetation component simulates the structural dynamics of vegetation caused by natural and human disturbances. Two processes are considered: the biogeography redistribution when climate change occurs, and the recovery and succession of vegetation after disturbances. Like most dynamic global vegetation models, the DLEM builds on the concept of plant functional types (PFT) to describe vegetation distributions. The disturbances, land use, and management component simulates cropland conversion, reforestation after cropland abandonment, and forest management practices such as harvest, thinning, fertilization, and prescribed fires. The DLEM has been extensively used to study the terrestrial carbon, water, and nitrogen cycles around the world in response to global change, and the detailed assumptions and processes are well documented in previous work [36–38].

Model Parameterization and Inverse Modeling Traditionally, model parameters need to be derived from individual experimental studies or are based on previous knowledge. The inverse analysis is an approach that fundamentally focuses on data analysis for the estimation of parameters and their variability [10, 39]. It can also be used to evaluate model structure and information content of data. Inverse modeling usually starts with data and asks what the observed responses to a perturbation can tell us about the system in question. By combining prior knowledge about the system, processes underlying the observations can be incorporated into a model for an inverse analysis. The latter is implemented with optimization algorithms to adjust parameter values to the extent that differences between model predictions and observations (i.e., a cost function) are minimized. Those parameter values that satisfy the minimized cost function are considered the optimized parameter estimates, given the observations and model structure [39]. The optimized parameter values can be used in forward analysis, which is usually implemented using simulation models. Generally speaking, the forward analysis asks what a model can tell us about the ecosystems whereas the inverse analysis asks what the data can tell us about the same system. The combination of the two approaches allows us to probe mechanisms underlying ecosystem responses to global change [10]. The major advantages of modeling study are [2] to: (1) integrate existing knowledge into models; (2) provide quantitative estimations and predictions of ecosystem responses; (3) help explain experimental results, formulate predictions, and guide future research; and (4) extrapolate ecosystem responses to large spatial scales over long term. The disadvantages include (1) lack of available data to drive and validate model results; (2) need to incorporate heterogeneity, disturbance, etc., into models; (3) there is usually large uncertainty related to model structures, parameters, and predictions.

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Meta-analysis Meta-analysis is a quantitative method used to compare and synthesize results of multiple independent studies with an attempt to address a common question or to test a common hypothesis [3, 14, 15, 41]. It has been widely applied in the fields of psychology, education, economics, and medical sciences. Since the early 1990s, the use of meta-analysis in the field of ecology and global climate research has increased exponentially [40–43]. As the experimental data accumulates, the number of meta-analysis increases dramatically. Over the last decade, approximately 50 papers using metaanalytical techniques have been published to synthesize the results of the large number of ecological CO2 studies [41]. In 2007, Lei et al. [15] reviewed the application of metaanalysis in global change research. Here a brief overview of the procedure of the method is provided, followed by the discussion of the advantages and disadvantages of meta-analysis. Results from some meta-analysis studies on ecosystem carbon responses to elevated CO2, temperature, and O3 are then summarized. The detailed methods of meta-analysis can be obtained in [3, 14, 40, 42]. In conducting a meta-analysis, formal methods of sampling, partitioning of variance and statistical comparison are applied in order to evaluate the magnitude and distribution of treatment effects across many individual experiments [40]. The general procedure of conducting meta-analysis includes formulating research question, collecting and coding data, analyzing data, and interpreting the results (> Fig. 13.5) [15]. Like an experimental study, the first step in meta-analysis is to generate a research question/hypothesis needed to be addressed. Then collect data from relevant individual studies. Criteria for

Question or hypothesis formulation

Data Collection and evaluation

Data analysis

Conclusions

Type definition of data collection

Literature search

Effect size calculation

Result interpretation

Studies quality assessment

Heterogeneity test and statistical model

Relation with the hypothesis and future research direction

Data extraction and organization

Overall effect

Subgroup analysis, publication bias analysis and sensitivity analysis

. Fig. 13.5 Procedures of meta-analysis (With kind permission from Springer Science+Business Media [15], Fig. 1. © 2007, Science in China Press and Springer-Verlag)

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inclusion of studies should be explicitly documented. After quality control (e.g., delete these with missing data), data should be organized and coded. To analyze data, effective size metrics and analysis models have to be selected. A response ratio (RR, the ratio of means for a measured variable between the treatment group and the control group) is often used as an index of the estimated magnitude of the treatment effect [3, 14]. The significance of RR can be statistically tested to determine whether a response variable of the treatment group is different from that of the control group. The heterogeneity of RR is often calculated to examine whether all studies share a common magnitude of the treatment effect. Finally, the RR is grouped according to independent variables (e.g., vegetation type and time after treatment) for the purpose of detecting the differences in RRs among groups. The major advantages of meta-analysis, compared to traditional narrative reviews, include: (1) It allows a more objective assessment of many individual research results. (2) It provides a more precise, overall estimate of a treatment effect, and increases power to detect true effects. (3) It can explain heterogeneity between the results of individual studies. Meta-analysis often does not provide much novel information. Debates over the meta-analysis include mixing apples and oranges (mixing experiments with different background information or purposes), biased estimates of effects due to publication bias (e.g., negative results are often not published), pooling of heterogeneous studies with different qualities, selection of nonindependence among studies (i.e., multiple entries from one study), and inclusion of unpublished data. Recently, Hungate et al. [43] compared four meta-analysis studies on the effect of elevated CO2 on soil carbon and found that the approach to independence has the largest influence on the results. They recommend that meta-analysts critically assess and report choices about effective size metrics and weighting functions, and criteria for study selection and independence. Overall, when applied adequately, meta-analysis may draw more general and quantitative conclusions on some controversial issues compared to single studies, and provide some new insights and research directions [3, 14].

Impacts of Elevated Atmospheric CO2 Concentration on Carbon Cycling in Terrestrial Ecosystems Experimental Studies Numerous experimental studies have been conducted over the past several decades considering some aspect of the effects of elevated CO2 on plants and ecosystems across different terrestrial ecosystems [40]. These studies generally show that elevated CO2 concentrations stimulate plant and canopy photosynthesis and respiration, reduce transpiration, and increase water use efficiency, leading to increased plant biomass and ecosystem productivity in terrestrial ecosystems. However, the magnitudes, sometimes even the direction of the change, vary among studies with different plant species, functional types, ecosystems, CO2 experimental facilities, pot/plot sizes, and the length of experiments.

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Photosynthesis, Respiration, and Stomatal Conductance The response of plants to elevated CO2 depends on the photosynthetic pathway. For C3 plants (i.e., plants such as wheat, rice and most trees use C3 photosynthetic pathway), photosynthetic CO2 uptake rate are normally increased under high CO2 concentrations. With the C4 photosynthetic pathway, the enhancements of photosynthetic uptake in these C4 plants (e.g., corn and sugarcane) due to elevated CO2 are relatively lower. Experiments under optimal conditions show that doubling the CO2 concentration increases leaf photosynthesis by 30–50% in C3 plant species, but 10–25% in C4 plant species [42, 44]. However, some studies show no difference between C3 and C4 plants, or even instances of effects in the opposite direction. Plants under high CO2 concentrations can partially close their stomata, thereby reduce water loss and increase water use efficiency (WUE, the ratio of the weight of dry matter produced to the amount of water transpired). Acclimation is a non-heritable, reversible change in the physiology or morphology of an organism in response to changing environmental conditions [24]. Photosynthetic downregulation in response to elevated CO2 was initially reported in dozens of CO2 enrichment studies and was generally attributed to decreases in leaf nitrogen and ribulose 1,5-biphosphate carboxylase/oxygenase (Rubisco) that lead to declines in photosynthesis. But the role of photosynthetic downregulation has been questioned, and its prevalence, particularly in earlier pot or chamber studies has been attributed, in part, to root restriction within experimental pots and inadequate N supply. The effect of elevated CO2 on plant respiration is much less clear, and experiments show opposite effects with different species [45]. CO2 stimulation of root exudation can speed up rhizosphere decomposition, causing soil respiration to respond more strongly to photosynthetic rate than to soil temperature. Elevated CO2 can also give rise to litter that has lower nitrogen concentration and is more resistant to microbial breakdown [46]. CO2 effects on litter quality and nutrient availability have proven important in stand- and regional-scale models, but other indirect effects of CO2 have yet to be tested in ecosystemscale models. Results from Duke FACE experiments from 1998 to 2000 showed a significant increase in estimated annual rates of total soil respiration of 0.30 kg C m 2 year 1 in the elevated CO2 plots compared to the controls [13]. However, this initial stimulation of soil respiration declined to 0.12 kg C m 2 year 1 in 2003 after 7 years of manipulations.

Plant Growth, Biomass, Ecosystem Productivity, and Carbon Storage Plant growth, biomass, and aboveground production generally increase with elevated CO2. The enhancement of biomass is lower than photosynthesis responses. For example, on average across several species and under unstressed conditions, compared with current atmospheric CO2 concentrations of 380 ppm, crop yields increase at 550 ppm CO2 in the range of 10–20% for C3 crops and 0–10% for C4 crops. Increases in aboveground biomass

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for trees range from 0% to 30% with the higher values observed in young trees and little to no response observed in the few experiments conducted to date in mature natural forests. Observed increases of aboveground production in C3 pasture grasses and legumes are +10 and +20%, respectively. Atmospheric CO2 increases to 550 ppm have been shown to increase NPP by about 23% across a range of temperate forest sites [47], but the long-term outcome is unclear, especially when interactions with nitrogen availability are considered. Since atmospheric CO2 concentration increases gradually, there are a few studies that tested whether plants and ecosystems respond differently to step versus gradual increase in CO2 concentrations [10]. For example, Hui et al. [23] grew Plantago lanceolata for 80 days before treating plants with ambient CO2 (as the control), gradual CO2 increase, and step CO2 increase for 70 days and found that the step CO2 treatment immediately resulted in an approximate 50% increase in leaf photosynthesis in week 3 after the CO2 treatment. The gradual CO2 increase caused much less stimulation of photosynthesis and less decrease in leaf N concentration than did the step CO2 increase. Klironomos et al. [48] conducted an experiment with Bromus inermis and its associated mycorrhizal community over a period of 6 years during which CO2 concentration increased either abruptly as is typical of most CO2 experiments or gradually over 21 generations. They found that plant photosynthesis did not differentially respond to step versus gradual CO2 increases. Belowground plant production was higher in the step than the gradual CO2 treatments. Experiments using multiple CO2 levels or a CO2 tunnel to create CO2 gradients [49] also demonstrate ecosystem responses to step CO2 changes as, in most, manipulative experiments are different from those in response to a gradual CO2 increase that occurs in the real world. New approaches such as inverse modeling may be needed to improve predictive understanding of ecosystem responses to gradual global change in the real world [10].

Modeling Studies Ecological models have been developed at different scales from leaf, plant canopy, ecosystem, regional to global scales to study climate effects on terrestrial ecosystems. Most of the models simulate the processes of plant photosynthesis and respiration, stomatal conductance, evapotranspiration, nitrogen uptake, carbon allocation among plant organs, litter production, nitrogen mineralization, and soil organic carbon decomposition, and uses these to calculate the carbon fluxes between vegetation, soils, and the atmosphere. At leaf and canopy levels, Farquahar model has been widely used to simulate leaf photosynthesis [10, 35]. This model considers several key processes of CO2 assimilation: diffusion of CO2 into leaf and uptake of CO2 by Rubisco enzyme into carboncontaining molecules. The model has also been built into global models. At regional or global scales, some biogeochemical models use a simplified light use efficient model to simulate photosynthesis and ecosystem productivity [50, 51]. Some ecological models specifically simulate the impacts of elevated CO2 on terrestrial ecosystem carbon processes, while most of the biogeochemical models consider multiple factor impacts and have the capability to simulate the effects of multiple climatic factors

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on terrestrial ecosystem carbon cycling. Several inter-model comparison studies also compared the features, ecological processes built in the models, and model simulation results among some ecosystem models. Several typical modeling results of elevated CO2 impacts on ecosystem carbon processes are summarized below. Similar to experimental results, modeling studies show that elevated CO2 concentrations stimulate plant growth and ecosystem productivity. For example, Luo et al. (2001) simulated gross primary productivity (GPP) in the Duke Forest at both ambient and elevated CO2 (ambient + 200 ppm) concentrations using a physiologically based canopy model (MAESTRA). They found that elevated atmospheric [CO2] resulted in increase of canopy C fixation by 35% in 1996, 39% in 1997, and 43% in 1998. The modeled GPP and its response to elevated [CO2] were sensitive to parameter values of quantum yield of electron transport, leaf area index, and the vertical distribution of LAI within the canopy. Hui and Luo [13] evaluated soil respiration in the same Duke Forest using a process-based modeling approach. Elevated CO2 increased soil respiration by 18–26% (> Fig. 13.6), mainly due to root respiration caused by increased fine root biomass and microbial respiration through increased aboveground litter fall. At large spatial scales, Cao and Woodward [11] used a terrestrial biogeochemical model (CEVSA), forced by simulation of transient climate change with a general circulation model to quantify the dynamic variation in ecosystem carbon fluxes induced by 35 Ambient CO2 Soil CO2 efflux (g CO2 m−2 d−1)

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changes in atmospheric CO2 concentrations (from 288 to 640 ppm) and climate change from 1861 to 2070. They found that NPP, NEP, and carbon stocks are predicted to increase substantially under CO2 increase alone. NPP increases by 45% in tropic ecosystems, 20% in temperate ecosystems, and 36% in northern ecosystems over the period 1861–2070. The CO2 fertilization effect is found to decrease as CO2 increases. The stimulation of photosynthesis by elevated CO2 diminishes at high CO2 concentration, but respiration increases as carbon accumulates in vegetation and soil. As a result, NEP falls rapidly as CO2 exceeds 600 ppm. Tian et al. [12] studied the effect of interannual climate variability on carbon storage in Amazonian ecosystems using a process-based biogeochemical model (Terrestrial Ecosystem Model – TEM) and found that soil moisture appears to be an important control on carbon storage. Climate variability with CO2 fertilization generally resulted in a higher annual NEP than did climate without CO2 fertilization. The strength of CO2 fertilization effect for the Amazon Basin was between 0.1 and 0.4  1015 g C year 1. Field et al. [52] simulated present-day global NPP to be in the range 46.6–49.5  1015 g C year 1, at the low end of the range estimated by others (44.4–66.3  1015 g C year 1; [53]). Over the period 18602100, global NPP increased by 23.3  1015 g C year 1 or 56% in the HadCM2 model–driven simulations and by 17.5  1015 g C year 1 or 43% in the HadCM3-driven simulation. NEP increased after about 1970 to 0.61.8  1015 g C year 1 in the 1990s, to 2.54.5  1015 g C year 1 in the 2030s, and then fell to below zero by 2100. Thus, model Hybrid predicted a growing terrestrial carbon sink, roughly in line with inventory and deconvolution estimates but a collapse and reversal of this sink during the next century. In a multiple model evaluation of the response of climate-carbon cycle models to future CO2 emissions, all 11 models demonstrated a decline through time in the capacity of terrestrial ecosystems to absorb increases in atmospheric CO2 [53]. Terrestrial ecosystem carbon storage increases with higher atmospheric CO2 in all models, driven by a 12– 76% increase in NPP with CO2 doubling (multi-model mean, 48%), offset slightly by enhanced heterotrophic respiration [53]. Using the TECO, Zhou et al. [54] examined the patterns and mechanisms of ecosystem responses to changes in CO2, temperature, and precipitation. Simulated NPP, heterotrophic respiration, and NEP all show parabolic-curve responses to temperature, asymptotic responses to CO2 concentration, and threshold-like curves to precipitation. Ecosystem response to combined temperature, CO2, and precipitation anomalies differed considerably from the responses to individual factors in terms of patterns. Luo et al. [32] used four ecosystem models and simulated NPP in response to treatments of elevated CO2 (C), elevated temperature (T), doubled precipitation (DP), halved precipitation (HP), summer drought (SP), and their combinations at seven ecosystems and found that elevated CO2 enhanced NPP at all sites (> Fig. 13.7). Randerson et al. [55] presented a systematic framework, the Carbon-LAnd Model Intercomparison Project (C-LAMP), for assessing terrestrial biogeochemistry models coupled to climate models using observations that span a wide range of temporal and spatial scales and evaluate two biogeochemistry models that are integrated within the

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. Fig. 13.7 Percent changes relative to control in modeled net primary production (NPP) in response to treatments of doubled precipitation (DP), halved precipitation (HP), summer drought (SP), elevated CO2 (C), elevated temperature (T), and their combinations at Jasper Ridge and Konza (a), Flakaliden and Mols (b), Walker Branch, Tapajo’s and Clocaenog (c). Data indicate the mean 1 SE calculated from simulated values of NPP by the four models (Adapted from [32]. With permission from John Wiley and Sons)

Community Climate System Model (CCSM) – Carnegie-Ames-Stanford Approach (CASA’) and carbon-nitrogen (CN). In response to an instantaneous increase in CO2 mixing ratio to 550 ppm in 1997, both models exhibited a positive step change in NPP, with CASA’ increasing globally by 17% and CN by 10% during the first 5 years after CO2 enrichment. The disproportionately large NEP response in CASA’ (almost threefold larger than CN) can only be partly attributed to the higher sensitivity of NPP to CO2 enrichment; other important factors included a higher baseline NPP and similar turnover times in pools involved with initial carbon storage.

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Recently, Friend [56] conducted sensitivity analysis using Hybrid 6.5, a global scale process-based ecosystem model, and found that leaf phenology has large effects on C3 crop and needle-leaved cold deciduous tree production. An increase in CO2 concentration from current to 720 ppm by the end of this century and climate change increase global NPP by 37.4%. Significant uncertainties concern the extent to which acclimative processes may reduce potential future increase in primary production. These modeling studies and many others demonstrated that NPP and NEP will increase under elevated CO2 conditions, but differ in the magnitudes of the enhancement from stands to global scales. As demonstrated by Hanson et al. [35], which evaluates the efficacy of 13 stand-level forest ecosystem models for predicting the carbon and water budgets of an upland-oak forest in eastern Tennessee, the mean of all model outputs showed better fit than any individual models. While improving individual model capability is still a vital task for ecosystem modelers, ensembles from multiple model simulations might be an adequate approach to reduce model uncertainty.

Meta-analysis Studies Most of the meta-analysis studies in global climate change are performed on the effects of elevated CO2 on terrestrial ecosystems. One reason may be the data availability. During the past decades, numerous individual studies of CO2 effects have been conducted in terrestrial ecosystems. Since most studies consider only two levels of CO2, one is ambient CO2 (350 ppm) and another one is elevated CO2 at a level between 550 ppm and 700 ppm. This data structure is also suitable for meta-analysis, which was originally designed to test treatment effect with a control. The first meta-analysis of CO2 effects was done by Curtis et al. (1996). Since then, there are more than 50 meta-analysis studies conducted [3, 15, 41]. Research using meta-analysis has addressed many ecological processes such as plant photosynthesis and respiration, growth and productivity, soil respiration, and accumulation of soil carbon and nitrogen in terrestrial ecosystems. In 2007, Lei et al. [15] provided a comprehensive study reviewing the applications of metaanalysis in global climate change research. While meta-analysis often provides a general conclusion and a precise effective size, the values also vary among different meta-analysis studies with different sample sizes, effective size metrics, and other issues. Certainty rules may need to be established to facilitate the comparison among different meta-analysis studies. Here the effects of elevated CO2 on ecosystem carbon processes are summarized.

Photosynthesis, Respiration, and Stomatal Conductance Similar to the conclusions from experimental studies, the effects of elevated CO2 on plant photosynthesis and growth based on meta-analysis are generally positive. Facility type and the lengths of CO2 exposure also modify the responses. Both species and size variability in the experimental populations are also a vital factor influencing ecosystem responses.

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In the first meta-analysis of CO2 effects on ecosystems physiology, Curtis and Wang [40] synthesized studies with 41 plant species grown in growth chamber, greenhouse, or open-top chamber, and reported a significant and large increase of net CO2 assimilation (50%). Average light-saturated photosynthesis rate and production increased by 34% and 20%, respectively, in C3 species. Leaf dark respiration under elevated CO2 demonstrates a significant decrease [40, 57]. Similar conclusion was reached in Wang and Curtis [58]. For plant respiration, Wang and Curtis [58] found that mass-based leaf dark respiration was significantly reduced by 18%, while area-based leaf dark respiration marginally increased approximately 8% under elevated CO2. An overall decline in the ratio of heterotrophic component to soil carbon dioxide efflux for increasing annual soil carbon dioxide efflux was also reported. Curtis and Wang [40] reported that stomatal conductance decreased by 11%, not significantly under elevated CO2. Using data collected from 13 long-term (>1 year), fieldbased studies of the effects of elevated CO2 on European tree species, Wang and Curtis [50] reported a significant decrease of 21% in stomatal conductance, but no evidence of acclimation of stomatal conductance was found. Wand and Strain [59] also found a significant decrease in leaf stomatal conductance, and increased water use efficiency and carbon assimilation rate.

Plant Growth, Biomass, Ecosystem, Productivity, and Carbon Storage Curtis and Wang [40] used meta-analytical methods to summarize and interpret more than 500 reports of effects of elevated CO2 on woody plant biomass accumulation. They found total plant biomass significantly increased by 28.8% and the responses to elevated CO2 were strongly affected by environmental stress factors and to a less degree by duration of CO2 exposure and functional groups. Wand and Strain [59] show that total biomass has increased by 33% and 44% in elevated CO2 for both C3 and C4 plants, respectively. Potter et al. [60] evaluated the effects of increased atmospheric CO2 concentrations on vegetation growth and competitive performance using meta-analysis. Responses of fast-growing herbaceous C3 species were much stronger than those of slow-growing C3 herbs and C4 plants. Norby et al. [47] report a meta-analysis of four FACE studies on temperate forests and conclude that the primary productivity of these forests at predicted 2050 CO2 levels is 23% higher than today’s CO2 level. Allocation is increased to leaf and fine root tissues. Ainsworth et al. analyzed 25 variables describing physiology, growth, and yield of soybean. They found the rates of acclimation of photosynthesis were less in nitrogenfixing plants, and stimulation of photosynthesis of nitrogen-fixing plants was significantly higher than that of non-nitrogen-fixing plants. Pot size significantly affected these trends. Biomass allocation was not affected by elevated CO2 when plant size and ontogeny were considered. Ainsworth and Long [42] also synthesized physiology and production data in the 12 large-scale FACE experiments across four continents and found that light-saturated

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carbon uptake, diurnal carbon assimilation, growth and aboveground production increased, while specific leaf area and stomatal conductance decreased in elevated CO2. Different results showed that trees were more responsive than herbaceous species to elevated CO2 and grain crop yield increased far less than anticipated from prior enclosure studies. The results from this analysis may provide the most plausible estimates of how plants growing in native environments and field will respond to elevated CO2 [52]. Jastrow et al. [61] showed a 5.6% increase in soil carbon over 2–9 years, at rising atmospheric CO2 concentrations. Luo et al. [3] synthesized 104 publications and demonstrated that averaged litter and soil carbon pool sizes at elevated CO2 were 20.6% and 5.6% higher than those at ambient CO2. Averaged carbon pool sizes in shoot, root, and whole plant have increased by 22.4%, 31.6%, and 23.0%, respectively [3].

Impacts of Global Warming on Carbon Cycling in Terrestrial Ecosystems Experimental Studies Most of ecosystem carbon processes such as photosynthesis and respiration are regulated by temperature. As a result, ecosystem productivity, carbon sequestration and storage will be influenced by global warming. The responses of terrestrial ecosystem to global warming vary due to differences in ecosystem composition, ecosystem structures, and locations. Difference in experimental designs such as intensity of warming (or temperature level), warming methods and the length of warming, and other environmental factors such as precipitation and nitrogen may also contribute to diverse changes observed in global warming experiments [5].

Photosynthesis, Respiration, and Soil Respiration In a recent synthesis, Luo [5] reviewed field experimental studies and found diverse effects of warming on photosynthesis, including increases, decreases, and no apparent change. Warming air temperature by 3–5 C, for example, increased photosynthesis in four vascular species in arctic tundra [62] and two dominant tree species and a shrub species in a boreal forest [63]. In contrast, a 3.5 C increase in air temperature did not significantly impact the photosynthesis of Polygonum viviparum in arctic polar semi-desert. Zhou et al. [64] also found that leaf photosynthesis increased in spring, decreased in early fall, and did not change in summer and late fall for four species exposed to an air warming of 0.5–2.0 C in the southern Great Plains of the United States. The variable responses are considered as the results of different methods and/or levels of warming, diverse temperature sensitivities and optimal temperatures of photosynthesis among species and ecotypes, and the confounding effects of drought, leaf age, and nutrient availability [5]. Photosynthetic acclimation to increased temperature has long been recognized including both shifts in temperature optima and uniform shifts across all temperatures, due to different thermal

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properties of key photosynthetic enzymes, different temperatures at which membranes are damaged, and differential thermal stability of photochemical reactions [65]. Soil respiration is generally responsive positively to temperature changes. As temperature increases, soil respiration generally increases [25], as warming generally directly increase both autotrophic and heterotrophic soil respiration. For example, with 5 C soil temperature increase above the ambient temperature, Peterjohn et al. [66] reported a dramatic 26–75% increase in soil respiration in the first 4 years. However, 10 years after the initiation of treatments, soil respiration in the warmed plots in 2000 was no longer significantly different from the control, a trend that has continued through the latest period of record [24]. There are a few studies that have also reported decrease in soil respiration under warming. But the decrease at the Rocky Mountain meadow in Colorado [68] was attributed to indirect effect of global warming, as warming induced a decline of soil moisture [24]. Similarly, soil respiration in Norway spruce stands was initially stimulated by experimental warming but then declined, perhaps due to substrate depletion of labile C pools and downregulation of heterotrophic activity [67, 69]. Dorrepaal et al. [70] investigated the climate-change response of ecosystem respiration rates using open-top chambers in a subarctic blanket-bog in Abisko, north Sweden. They show that approximately 1 C warming accelerated total ecosystem respiration rates on average by 60% in spring and by 52% in summer and that this effect was sustained for at least 8 years. Global warming studies also found that soil respiration acclimates to elevated temperature, as soil temperature sensitivity decreases under warming [22, 25]. The acclimation may be caused by warming-induced changes in aboveground and belowground biomass; soil moisture; nitrogen mineralization; substrate quality/quantity; and microbial community activity, biomass, and composition [5, 24]. The warming times of a day may also influence the effects of warming on soil respiration. Xia et al. [71] recently compared the effects of day warming, night warming, and diurnal warming on soil respiration in a temperate steppe and found that day warming showed no effect on soil respiration, while night warming significantly increased soil respiration. Changes in soil respiration and gross ecosystem productivity under diurnal warming are smaller than the summed changes under day and night warming. In the same experiment, Wan et al. [72] found that nocturnal warming increased leaf respiration, stimulated plant photosynthesis, and shifted the steppe ecosystem from a minor carbon source to a carbon sink.

Plant Growth, Biomass, Ecosystem Productivity, and Carbon Storage The effects of warming on plant growth are highly variable [5], similar to photosynthesis responses. Experimental warming increased leaf production by 50% and shoot production by 26% for Colobanthus quitensis but decreased leaf production by 17% for Deschampsia antarctic in Antarctica [73]. By warming a tallgrass prairie 0.5–2 C high using electronic heater, Luo [5] found warming stimulated growth of C4 plants over

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a 6-year experiment. While the growth of C3 plants increased in the first 2 years, the growth decreased in the last 2 years [5]. Field soil-warming experiments showed that herbs and grass were more responsive to elevated temperature than shrubs, whereas tree species were less sensitive in a temperate forest [74]. The individualistic responses to warming reflect differences in optimum growth temperatures across species, as well as the limitations on growth by other factors than temperature [5]. The effects of warming on ecosystem primary production are also diverse. Experimental warming increased NPP by up to 25% in a tallgrass prairie [5]. Soil warming increased the yields of crops by 19–50% and vegetables by 19–100% [75], and increased the stem-wood growth of trees in heated plots by 50% relative to controls after 5 years [76]. Total aboveground biomass was largely unresponsive to temperature manipulation in tundra [77]. Along a gradient of increasing infrared heating, shrub production increased, whereas graminoid production decreased in a bog. In a fen, graminoids were most productive at high infrared heating and forbs were most productive at medium infrared heating. The net ecosystem production and long-term carbon storage in ecosystems may be influenced by different warming methods. Buried heating cables only warm soil and have generally caused net carbon loss, such as in experiments at the arctic tundra [78] and Harvard Forest [25]. Ineson et al. [79] also showed a net carbon reduction of approximately 10% after 3 years of heating an upland grassland ecosystem at Great Dun Fell in the United Kingdom. The responses to whole-ecosystem warming using infrared heaters or greenhouse chambers show different responses, including decrease and increase, or cause no changes in net ecosystem exchange [5]. Using infrared heating, Marchand et al. [80] found a 24% increase in canopy carbon uptake and a nearly 50% increase in net carbon sink under warming in comparison with that under control in high-arctic tundra. Johnson et al. [81] reported that warming did not cause much change in canopy photosynthesis, ecosystem respiration, and net ecosystem carbon exchange in arctic tundra. The warming experiment at the southern Great Plains did not cause significant changes in net ecosystem production and soil carbon stocks [5]. But Saleska et al. [82] observed a decrease of soil organic carbon by 200 g C m 2 in warmed plots relative to control plots in a Rocky Mountain meadow.

Modeling Studies Modeling studies generally have predicted a positive feedback between carbon cycling and global warming [5, 54]. Using a global biogeochemical model, Cox et al. [83] projected that while terrestrial ecosystems will sequester 400  1015 g C due to CO2 fertilization in the twenty-first century, warming stimulates carbon loss, and results in a net source of 60  1015 g C from terrestrial ecosystems to the atmosphere. As a result, temperature will increase by 8 C, that is, 2.5 C greater than the climate-model simulation alone. Friendlingstein et al. [53] compared 11 coupled climate-carbon models and found that carbon cycle-climate feedbacks increase atmospheric CO2 at the end of the twenty-first

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century by 4–44% (multi-model mean, 18%), equivalent to an additional 20–224 ppm (multi-model mean, 87 ppm) [1, 53]. With temperature increase, almost all models predict carbon losses from terrestrial ecosystems (20–177  1015 g C  C 1). Other ecosystem models also projected a loss of carbon from terrestrial ecosystems in response to global warming [5, 10]. Global NEP responds positively to changes in CO2 concentration and precipitation, but negatively to changes in temperature [11]. Huntingford et al. [83] simulated ecosystem responses to global change using a simple terrestrial ecosystem model. They reported that soil respiration increases more rapidly with warming than net primary production, causing a gradual switch from a weak positive NEP initially to a weakly negative NEP. Die-back can occur at high temperatures and cause a large pulse of negative NEP. Using TECO, Zhou et al. [84] simulated NPP, heterotrophic respiration Rh, and NEP and all simulations show parabolic-curve responses to temperature anomalies from 2 C to +10 C compared to current condition. NPP and Rh increased with temperature, reached a peak at +8 C (NPP) or +6 C (Rh), and then declined, while NEP had an adverse trend with a lowest value at +7 C. Tian et al. [85] quantified ecosystem NPP and water use efficiency (WUE) in the Southern US by employing the integrated process–based ecosystem model (Dynamic Land Ecosystem Model, DLEM). They found that the mean regional total NPP was 1.18  1015 g C year 1 (525.2 g C m 2 year 1) during 1895–2007. NPP increased consistently from 1895 to 2007 with a rate of 2.5  1012 g C year 1 or 1.10 g C m 2 year 1. The average WUE was about 0.71 g C kg 1 H2O and increased about 25% from 1895 to 2007. They also found that NPP and WUE showed substantial inter-annual and spatial variability, which was induced by the nonuniform distribution patterns and change rates of climate factors across the Southern US (> Fig. 13.8). Using a process-based terrestrial biosphere model (ORCHIDEE) and satellite vegetation greenness index observations, Piao et al. [86] find that both photosynthesis and respiration increase during autumn warming, but the increase in respiration is greater. In spring, however, warming increases photosynthesis more than respiration. As a result, northern terrestrial ecosystems may currently lose carbon dioxide in response to autumn warming, with a sensitivity of about 0.2  1015 g C  C 1, offsetting 90% of the increased carbon dioxide uptake during spring. If future autumn warming occurs at a faster rate than in spring, the ability of northern ecosystems to sequester carbon may be diminished earlier than previously suggested.

Meta-analysis Studies There are a few meta-analysis studies conducted on the effects of global warming on terrestrial ecosystems [87]. A meta-analysis of 13 tundra experiments shows that the vegetative growth of herbaceous species was more responsive to warming than woody species [88]. They found that the primary forces driving the response of ecosystems to soil warming do vary across climatic zones, functional groups, and through time. Herbaceous

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Table 13.1, [2]). The studies of O3 and UV have been conducted mostly in cropland ecosystems. A few studies also consider multiple climatic factors, such as warming, precipitation, O3, nitrogen, and elevated CO2.

Experimental Studies Plant Photosynthesis, Respiration, and Soil Respiration Of the existing experiments with precipitation, the Konza Praire irrigation study in Kansas, USA is one of the longest, continuously running precipitation manipulation

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experiments [2]. Initiated in 1991, the treatment involves the addition of supplemental water to meet plant–water demand in a tallgrass prairie ecosystem. Results from the first 8 years of the study (1991–1998) showed that (1) water availability limited aboveground NPP (ANPP) 6 of the 8 years, (2) supplemental water increased ANPP by 25% in the irrigated plots compared to the controls, and (3) the response was due to physiological changes in the dominant plant species [90]. Results for the next 5 years (1999–2003), however, showed that (1) supplemental water increased ANPP by 70% compared to the control and (2) the response was due to an increased cover of Panicum virgatum, and thus a shift in community composition [90]. These results once again highlight the importance of decadal-scale responses in ecosystem manipulation experiments [2, 10]. There are many experimental studies on O3 effects in terrestrial ecosystems, but mostly in managed croplands such as soybean, rice, and wheat. Changes in stratospheric O3 and hence in solar UV-B (280–315 nm) radiation have many different effects on global carbon cycling. Longer wavelength UV-A radiation (315–400 nm) is little affected by O3 depletion, but can be affected by global climate change [91]. UV (280–400 nm) radiation modifies carbon cycling through changes in photosynthesis and respiration. Certain plant species and communities are vulnerable to increased UV-B radiation. UV-B was also found to affect soil microbial community structure and the chemistry of leaf litter. More and more experiments now consider more than one climatic factor of elevated CO2, temperature, precipitation, O3, and nitrogen. For example, Zhou et al. [92] reported the effects of warming and precipitation on soil respiration in a grassland ecosystem. Warming increased soil respiration by 22.9% with a 4.4 C increase. Double precipitation resulted in an increase of 9.0%. Warming decreased soil temperature sensitivity, while the precipitation slightly increased soil temperature sensitivity in warmed plots. Wan et al. [93] studied the effect of elevated atmospheric CO2 concentration, air warming, and changing precipitation in an old-field grassland in eastern Tennessee, USA. They found that higher CO2 concentration and soil water availability significantly increased mean soil respiration by 35.8% and 15.7%, respectively. There were no interactive effects on soil respiration among any two or three treatment factors irrespective of time period. Treatment-induced changes in soil temperature and moisture together explained 49%, 44%, and 56% of the seasonal variations of soil respiration responses to elevated CO2, air warming, and changing precipitation, respectively. Additional indirect effects of seasonal dynamics and responses of plant growth on C substrate supply were indicated. Given the importance of indirect effects of the forcing factors and plant community dynamics on soil temperature, moisture, and C substrate, soil respiration response to climatic warming should not be represented in models as a simple temperature response function, and a more mechanistic representation including vegetation dynamics and substrate supply are needed. While the importance of multiple factors has been well recognized, there are still not many studies that have been conducted, due to many reasons such as experimental costs of facility construction and maintenance, difficulty in experimental design implementation, requirement of large homogeneous lands, and time and efforts for measurements. One of the longest, continuously running and most complex multi-factor experiment is the

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Jasper Ridge Global Change Experiment in the Santa Cruz Mountains of California, USA [2]. Initiated in 1998, the experiment includes a full factorial combination of warming, nitrogen deposition, elevated carbon dioxide, and increased precipitation, with eight replicates of each experimental unit. Important results from this experiment include the existence of nutrient constraints on NPP responses to global changes, shifts in plant and microbial species composition, and associated changes in productivity [94], changes in phenology, and a surprising CO2- and warming-induced increase in growing season soil moisture. Perhaps the most important contributions of this long-term, multi-factor experiment are, however, to highlight the inherent complexity of natural ecosystems (even one as ‘‘simple’’ as an annual grassland in California, USA), the plethora of additive and non-additive responses to various global change factors, and the importance of interannual variations in climate drivers in determining overall ecosystem responses [2].

Modeling Studies Precipitation and soil moisture have been recognized as important factors regulating photosynthesis, respiration, and ecosystem carbon sequestration. Most of the ecosystem biogeochemical models consider precipitation/soil moisture impacts on ecosystem carbon processes, through the limitation on leaf photosynthesis, soil respiration, and water/ nutrient uptakes. Impacts of precipitation are also considered together with other climatic factors. Recently, Shen et al. [34] evaluated precipitation impacts on soil respiration and soil carbon pool size change in dryland ecosystems. The effects of O3 on ecosystem productivity and carbon sequestration have also been investigated [37]. Below are a few recent modeling studies considering precipitation, O3, or their interactions with other climatic factors. Gerten et al. [95] studied effects of precipitation on ecosystem carbon dynamics using four process-based ecosystem models (TECO, LPJ, ORCHIDEE, and DayCent) and found that NPP response to precipitation changes differed not only among different sites, but also within a year at given sites. Humid sites and/or periods were least responsive to any change in precipitation as compared with moderately humid or dry sites/periods. Using the same four models, Luo et al. [32] showed that two-way interactive effects on NPP, Rh, and NEP were generally positive (i.e., amplification of one factor’s effect by the other factor) between temperature and elevated CO2 or between temperature and double precipitation (> Fig. 13.7). Zhou et al. [54] simulate responses of NPP, Rh, and NEP to precipitation changes from 40% to +100% compared to current condition and reported that the responses increased with precipitation at the beginning and then reached a plateau. If ‘‘threshold’’ is defined as a point at which there is an abrupt change in response to external stimuli, the modeling results indicate that precipitation threshold values were about +30% for NPP and NEP and near current condition for Rh. Shen et al. [34] used a process-based ecosystem model (PALS) to simulate how dryland soil respiration (Rs) and soil C pool size responded to precipitation changes at multiple

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temporal scales. They found that increases in precipitation amount stimulated Rs and increased the contribution of Ra to Rs, whereas reductions in summer rainfall and strong increases in rainfall event size reduced total Rs and decreased the contribution of Ra to Rs. Increases in annual rainfall and decreases in summer rainfall benefited dryland soil C sequestration, whereas strong increases in rainfall event size resulted in a loss of soil C, with labile soil C pools being more responsive to precipitation regime changes than recalcitrant C pools at a decadal scale. These simulation results implied that dryland soils may act as C sinks with increased precipitation amount or C sources with decreased precipitation amount, but the strength of the sink/source may be mediated by accompanying shifts in rainfall seasonality and event size distribution. Several studies considered the effects of O3 on terrestrial ecosystems. For example, using the DLEM, Ren et al. [37] investigated the effects of O3 along with climate change, increasing CO2, and land use change on NPP and carbon storage in terrestrial ecosystems in China during 1961 and 2000. They found that elevated O3 results in a mean of 4.5% reduction in NPP and 0.9% reduction in total carbon storage. Under the influence of O3 and CO2, the simulation results illustrate that mean annual NPP in the 1990s increased by 140.6  1012 g C compared to the 1960s; the total carbon storage increased by 46.3  1012 g C. The increased carbon storage may be attributed to the direct effects of increasing atmospheric CO2 [96]; however, O3 can partially compensate for the positive effects of CO2 fertilization [37].

Meta-analysis Studies Meta-analysis has not extensively applied on other climatic factors. So far, there is no meta-analysis of precipitation effects on terrestrial ecosystems [2]. But quite some studies have been conducted on the effects of O3 on terrestrial ecosystems, particularly croplands. In general, elevated O3 significantly decreased photosynthesis rates, decreased wheat grain yield and aboveground biomass. But the magnitudes of changes vary with different cropland ecosystems. Ainsworth [97] synthesized the research on rice responses to two elements of global change, rising atmospheric carbon dioxide concentration and rising tropospheric O3 concentration. On an average, elevated CO2 concentration (627 ppm) increased rice yields by 23%, but 62 ppb O3 showed a 14% decrease in yield. Many determinants of yield, including photosynthesis, biomass, leaf area index, grain number and grain mass, were reduced by elevated [O3]. Feng et al. [98] quantitatively evaluated the effects of elevated concentration of O3 (31–59 ppb) on growth, gas exchange, and grain yield using a database of 53 peer-reviewed studies published between 1980 and 2007. They found that elevated O3 decreased wheat grain yield by 29% and aboveground biomass by 18%. Grain yield decreased by 18% and biomass decreased by 16% relative to the control. Using another data set of 39 effective references, Feng et al. reported that the elevated O3 decreased grain yield and grain weight by 26% and 18%, respectively. Light-saturated photosynthetic rate, stomatal conductance decreased by 40% and 31%, respectively. Feng et al. [99] also assessed the effects of rising O3 concentrations on yield and yield

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components of major food crops: potato, barley, wheat, rice, bean, and soybean in 406 experimental observations. They reported that with potato, current O3 concentration (31–50 ppb) reduced the yield by 5.3%, and it reduced the yield of barley, wheat, and rice by 8.9%, 9.7%, and 17.5%, respectively. In bean and soybean, the yield losses were 19.0% and 7.7%, respectively. They also found that compared with yield loss at current O3, future O3 (51–75 ppb) drove a further 10% loss in yield of soybean, wheat, and rice, and 20% loss in bean. These findings confirm the rising O3 as a threat to food security for the growing global population in this century [98, 99].

Future Directions: New Experiments, New Models, and New Approaches Responses of terrestrial ecosystems to climate change play an important role in regulating future climate change. Biogeochemical cycling, specifically carbon cycling in terrestrial ecosystems, may have significant influences on future atmospheric CO2 concentrations and global warming. Lack of knowledge about feedback from the biosphere is a major limiting factor to our forecast of future climate change. Due to the complexity of biogeochemical processes and components and each of these research approaches has some shortcoming, different approaches are needed and could be integrated together to minimize their weaknesses. Results from observations, experiments, modeling, and metaanalyses reveal one common: ecosystem responses to global change are complex, varying across different plants, functional types, ecosystems, and interact with many other environmental factors. More studies need to be conducted to fully understand climate impacts on terrestrial ecosystems. For experimental study, field and controlled experiments will continue to be an important approach, particularly, the long-term and multi-factor experiments are urgently needed. As both experimental and modeling results indicated, the magnitude and even direction of response may change over time. It is imperative to provide longterm support for long-term global change experiments [6]. Terrestrial ecosystem responses to multiple, interacting factors of global change can be nonlinear and nonadditive [34]. It is imperative to continue to initiate and support multi-factor experiments to explore these interactions at different ecosystems and different locations [2]. The gradual change of climatic factors in nature versus step-increase in experiments for some climatic factors and changes in the timing and intensity of other climatic factors should also be considered. For ecosystem biogeochemical modeling study, data-model need to be better integrated. Inverse modeling techniques need to be applied to better parameterize the model. Uncertainty analysis in terms of measurement error, model structures, model parameters and parameter combinations need to be conducted to improve confidence of model estimation and prediction. Applications of inverse analysis to Duke Forest FACE experimental data demonstrated that uncertainty in both parameter estimations and carbon sequestration in forest ecosystems can be quantified to improve our understanding of

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ecosystem carbon responses to climate change. As more data are accumulating in long-term manipulative experiments, inverse modeling and data assimilation will play a more important role in global change ecology. Besides climate variability, climate disturbances such as drought, cold-spell, heat-wave, fire, and biological disturbances such as disease, insect outbreak need to be built into biogeochemical models. Recently, Medvigy et al. [100] assess the significance of high-frequency variability of climatic factors (temperature, precipitation, and solar radiation) for terrestrial ecosystems under current and future climate, and report that the terrestrial ecosystems will be affected by changes in variability almost as much as by changes in mean climate. At large scale and for long-term prediction, dynamic changes of vegetation need to be considered in the models. For meta-analysis study, the applications need to go beyond CO2. As more experimental data and modeling results accumulate, meta-analysis needs to be performed on other climatic factors, such as precipitation. New analytic methods need to be developed to be able to deal with multiple treatment levels and multi-factors. At present, many global change meta-analyses consist of sets of contrasts, functionally equivalent to performing multiple sets of single classification analysis of variance (ANOVA) or Student’s t-test [41]. More advanced statistical approaches (e.g., two-way ANOVA, analysis of covariance (ANCOVA), regression, and multivariate analysis) are rarely undertaken in ecological and global change meta-analyses [41], but need to be applied. The inconsistence among different meta-analyses highlights the need for careful selection of effective size metrics and weighting functions, and criteria for study selection and independence. Such decisions need to be justified carefully because they affect the basis for inference [43]. How to use meta-analysis to generate true and meaningful insights beyond only providing a general picture also needs to be considered when conducting meta-analysis.

Closing Remarks Considerable progress has been made during the past several decades to better understand ecosystem responses to global change. In order to advance the field of research, it is necessary to better integrate observational, experimental, ecosystem modeling, and metaanalysis techniques into a multidisciplinary approach [2, 5, 24, 31]. Adequately conducted meta-analyses will summarize individual experimental results and provide general conclusions that are helpful for public and policy makers, but mechanisms of diverse response across different ecosystems and at different locations need to be understood using experiments and built into ecosystem models. Better communication between experimentalists and modelers would improve data-model integration by not only improving the model simulations, but also generating testable hypotheses [2, 5]. Uncertainty in ecosystem modeling can be reduced by improved experimental data and better understanding of biogeochemical processes. New experimental studies designed with multifactor, multi-level of climatic factors and conducted over long-term are still needed to understand the complex impacts of climate change in terrestrial ecosystems. New metaanalysis methods are also to be developed to handle multi-factor and multi-level of

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treatment factors. The mechanisms of climate change, climate interannual variability, and climate disturbances should be built into biogeochemical models to improve our understanding of climate impacts on terrestrial ecosystems. For long-term prediction, ecosystem biogeochemical models also need to consider indirect effects of climate change such as phenology and vegetation dynamics and the impacts of human activities such as land use change and urbanization. With the improved understanding of carbon cycling in terrestrial ecosystems and its feedback to global climate built into the earth system models, we will have a better and more accurate understanding of our future climate change.

Acknowledgments We thank Dr. Toshio Suzuki for his constructive comments and suggestions that improved the presentation of this chapter. Our work has been supported by grants from the Office of Science (BER), U.S. Department of Energy, grant DE-FG03-99ER62800, and National Science Foundation (DBI0923371 and DBI0933958).

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14 Sea-Level Rise and Hazardous Storms: Impacts on Coasts and Estuaries Yan Ding National Center for Computational Hydroscience and Engineering, The University of Mississippi, University, MS, USA Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472 Future Global Main Sea-Level Projection/Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474 Local/Regional Sea-Level Rise Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475 Global Warming, Sea-Level Rise, Hurricanes, and Storms . . . . . . . . . . . . . . . . . . . . . . . . . . 476 Geophysical and Socioeconomic Impacts of Sea-Level Rise on Coast and Estuary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478 Assessment of Impact of Local Sea-Level Rise for Coastal Zone Management . . . . . . 480 Numerical Modeling for Assessing Dynamic Impacts of Local Sea-Level Rise and Hazardous Storms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482 Projection Approach and Numerical Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482 Downscaling Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483 Challenges to Planning and Management of Coastal Zone Under Conditions of Sea-Level Rise and Hazardous Storms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484 Brief Review on Coastal and Estuarine Process Modeling . . . . . . . . . . . . . . . . . . . . . . . . . 484 A Case Study: Assessment of Impacts of Sea-Level Rise and Hazardous Storm in an Estuary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487 Information of the Study Estuary and Model Validations . . . . . . . . . . . . . . . . . . . . . . . . . 488 Hydrodynamic and Morphodynamic Responses to Sea-Level Rise and Storm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489 Discussions on the Impacts of Sea-Level Rise in Touchien Estuary . . . . . . . . . . . . . . . 496 Concluding Remarks and Future Research Topics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_14, # Springer Science+Business Media, LLC 2012

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Abstract: Because unsteady and multiscale hydrodynamic and morphodynamic processes are dominant in coastal/estuarine zones, numerical simulation of dynamic responses to sea-level rise and storms becomes the most effective approach to systematically assess the impacts of hazardous storms under the future sea-level rise. Thus, this chapter focuses on the following three objectives: (1) investigation of the impacts of hazardous storms and sea-level rise on coasts and estuaries due to climate change, (2) reviews of impact assessment approaches by using numerical simulation models, and (3) demonstrations of impact assessment of coastal floods and erosions under the combined conditions of hazardous storms (extreme events) and the future sea-level rise scenarios. It emphasizes a system approach for the impact assessment of sea-level rise by using integrated coastal process models, which are widely used to simulate coastal/estuarine hydrodynamic and morphodynamic processes to predict flooding/inundation and coastline erosion/deposition under complex hydrological, morphological, oceanographic, and meteorological conditions. It also demonstrates an application of an integrated coastal model, CCHE2D-Coast, to simulate waves, tides, sediment transport, and morphological changes in an estuary and to predict the hydrodynamic and morphodynamic impacts of hazardous storms and five hypothetical sea-level rise scenarios. It shows that the integrated physical-process modeling technique is the only effective method to accurately predict the impact of sea-level rise under natural dynamic conditions of sea and coast and to facilitate coastal flood management, erosion protection, and infrastructure designing/planning against extreme hydrological conditions and climate changes.

Introduction The increasing trend of atmospheric concentrations of carbon dioxide and other gases in the past decades, especially due to anthropogenic greenhouse gas emissions, leads to increase in the earth’s temperature, thermal expansion of the upper ocean, and the melting of small ice caps [1]. Consequentially, a primary effect of global warming is an increase in the global volume of the ocean and accelerated global mean sea-level rise, which will speed up the permanent inundation and land loss of low-lying coastal/estuarine areas. Historically, global mean sea level has risen over 120 m at some locations from the low stand of the last glacial maximum 20,000 years ago when temperatures were between 5
C and 10
C cooler than today [1, 2]. Geologic evidence suggests a global mean sea-level rise rate of 0.1–0.2 mm/year over last 3,000 years with a significant acceleration that may have occurred around the mid-nineteenth century [1]. Based on global tide-gauge data, global mean sea levels are estimated to have risen 10–20 cm during the twentieth century (or 1.0–2.0 mm/year) [1, 3, 4]. It has since been argued that an estimated average of a 20-cm rise during the past century is most consistent with the available data [5]. Thus, a significant sea-level rise during the twentieth century occurred, which has been arguably one stress factor contributing to many of the existing coastal problems. Predictions from the Fourth Assessment Report by Intergovernmental Panel on Climate Change (IPCC)

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suggest that sea level may rise by as much as 60 cm by 2100 [6]. Uncertainty, however, remains about how projected melting of the Greenland and Antarctic ice sheets will contribute to sea-level rise. Based on the selected long-term tide gauges on the East Coast of the United States, it has been found that along the Atlantic coast of the United States, over the last century, relative sea-level rise rates have ranged between 1.8 mm/year to as much as 4.4 mm/year [7]. The lowest rates (1.75–2.00 mm/year) are close to the present global rate of 2.0 mm/year and occur along coastal New England and from Georgia to northern Florida. The highest rates (4.42  0.16 mm/year) have been observed in the mid-Atlantic region between northern New Jersey and southern Virginia. It is also found that subsidence of the land surface due to a range of factors contributes to the high rates of relative sea-level rise observed in this region. Global mean sea-level rise does not translate into a uniform rise in sea level around the world. Considerable variation often exists between global and local changes over a range of time/spatial scales. For example, based on available tide-gauge data collected by the National Oceanic and Atmospheric Administration (NOAA) on the mid-Atlantic coast [8], Cooper et al. [9] obtained an approximate relative sea-level rise trend of 3.53 mm/year during the twentieth century, which is almost double the global mean value of sea-level rise. In general, the local sea-level change at any coast location can be determined by the sum of global mean sea-level rise, regional sea-level change due to meteo-oceanographic factors (i.e., atmospheric pressure, storm surge, wave set-up, and ocean circulations), and vertical land movement (i.e., subsidence and/or uplift) due to various geological processes such as tectonics, glacial-isostatic adjustment, sediment consolidation, groundwater withdrawal, etc. [10]. The development of a coastal zone management plan considering a local/relative sealevel rise and its impact area is of utmost importance. Due to existing multiscale and unsteady physical processes driven by waves, tides, storm surge, sediment transport (erosion and deposition), and tectonic movement (subsidence and rise), a local sealevel rise is not equal to the estimate by the IPCC and generally varying with time and locations (i.e., coasts and estuaries). For coastal hazard management and coastal defense planning in a specific coastal/estuarine zone, it is essential to predict the dynamic impacts of the local/relative sea level under local hydrological conditions such as waves, storms, and morphology, especially generated by hazardous weather. Because unsteady and multiscale hydrodynamic and morphodynamic processes are dominant in coastal/estuarine zones, numerical simulation of dynamic responses to sealevel rise and storms, in fact, becomes the only effective approach to systematically assess the impacts of storms under the future sea-level rise scenarios conditions. (Hydrodynamic processes in a coast or an estuary are the surface water motions driven by astronomical tides, waves, river flows, wind-induced currents, turbulence, etc. Morphodynamic processes include the evolutions of landscapes and seascapes in response to the erosion and deposition of sediment.) Thus, the objectives of this chapter are (1) to study the impacts of sea-level rise due to climate change on coasts and estuaries, (2) to review impact assessment approaches for flood water management, coastal erosion protection, and

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infrastructure designing/planning against extreme hydrological conditions, and (3) to demonstrate impact assessment of coastal floods and erosions under the combined conditions of hazardous storms and the future sea-level rise scenarios. It focuses on the regional-scale assessment of the dynamic impacts of hazardous storms (i.e., extreme events in ocean) including hurricanes and typhoons under the conditions of sea-level changes, using numerical simulation modeling techniques, which are applicable to directly predict flooding/inundation and morphological changes in coastal zones and estuarine regions. By employing an integrated coastal process modeling system, CCHE2D-Coast, simulations of waves, tides, sediment transport, and morphological changes in an estuary are demonstrated under these natural physical conditions and sea-level rise scenarios. Assessment of impacts of a hazardous storm combined with sealevel rise scenarios in the estuary is discussed accordingly. This chapter in the following context is organized as follows: At first, the global mean sea-level scenarios, as well as some regional relative sea-level rise projections in the United States, are briefly reviewed and discussed. Second, the relationship between regional/local sea-level rise and hydrological, meteorological, and oceanographic conditions are discussed; accordingly, geophysical and socioeconomic impacts of local sea-level rise on coasts and estuaries are summarized. For coastal zone management, general impact assessment approaches under sea-level rise scenarios are discussed. Then, a detailed review on numerical modeling, using Global Circulation Models (GCM), coastal process models (or inundation models), and downscaling techniques, for predicting coastal hazards under sea-level rise conditions in the future is given. By applying an integrated coastal process simulation model, a case study on the assessment of sea-level rise impacts in an estuary located at the west coast of Taiwan is demonstrated. Finally, concluding remarks and discussions on the future research directions are presented.

Future Global Main Sea-Level Projection/Scenarios In the Third Assessment Report (TAR) by Intergovernmental Panel on Climate Change (IPCC), the projected sea-level rise from 1990 to 2100 was between 9 and 88 cm with a mid estimate of 48 cm [1], which however does not include the contribution from Antarctica. Based on the emission scenarios in the twenty-first century, the latest IPCC Special Report on Emission Scenarios (SRES) has projected the six SRES marker scenarios [6], i.e., the SRES B1, A1T, B2, A1B, A2, and A1FI as shown in > Table 14.1. The SRES scenarios represent mutually consistent characterizations of how the world might evolve during the twenty-first century. Each scenario is a short narrative of a possible pathway of future development from the current world. They explore what might happen if political, economic, technical, and social developments took specific alterative directions at the global level, including consideration of potential differences and interactions. Approximate CO2-equivalent concentrations corresponding to the computed radiative forcing due to anthropogenic greenhouse gases (GHGs) and aerosols in 2100 for the six SRES scenarios are about 600, 700, 800, 850, 1,250, and 1,550 ppm, respectively.

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. Table 14.1 Projected global surface warming and sea-level rise at the end of the twenty-first century [6] Likely range of temperature Approximate carbon dioxide (CO2)- equivalent change (
C at 2090–2099 relative to 1980–1999) Scenario concentration (ppm)

Sea-level rise (m at 2090–2099 relative to 1980–1999)

B1 A1T B2

600 700 800

1.1–2.9 1.4–3.8 1.4–3.8

0.18–0.38 0.20–0.45 0.20–0.43

A1B A2 A1FI

850 1,250 1,550

1.7–4.4 2.0–5.4 2.4–6.4

0.21–0.48 0.23–0.51 0.26–0.59

(Radiative forcing is a measure of the influence a factor has in altering the balance of incoming and outgoing energy in the Earth-atmosphere system and is an index of the importance of the factor as a potential climate change mechanism [p 36] [6]. In the IPCC report, radiative forcing values are for changes relative to preindustrial conditions defined at 1,750 and are expressed in watts per square meter [W/m2].) Based on these GHG emission scenarios, estimates about temperature change and sea-level rise are assessed from a hierarchy of models that encompass a simple climate model, several Earth Models of Intermediate Complexity, and a large number of Atmosphere-Ocean General Circulation Models (AOGCMs) as well as observation constraints [6]. The model-based results of sea-level rise, excluding future rapid dynamic changes in ice flow, show that the bottom line of GHG emission (i.e., 600 ppm) will cause a global mean sea-level rise at 2090–2099 within a range from 18 to 38 cm. The top line (1,550 ppm), however, will give the sea-level rise about 26–59 cm, relative to 1980–1999. Following the SRES scenarios, Nicholls [11] has investigated coastal flooding and wetland loss in the twenty-first century corresponding to only four SRES scenarios (i.e., A1FI, A2, B1, and B2) with a global mean sea-level rise range from 22 to 34 cm by the 2080s, relative to 1990. The conclusion is that sea-level rise increases the flood impacts in all cases, and coastal wetland will be lost due to sea-level rise in all scenarios with 5–20% losses by the 2080s in the A1FI scenario.

Local/Regional Sea-Level Rise Scenarios For the purpose of local/regional impact assessment, local sea-level change can be estimated from tide-gauge data measured at tide gauge stations over a century. Tide gauges, usually placed on piers, measure the mean sea-level change relative to a nearby geodetic benchmark. Therefore, the local sea-level rise trends usually do not follow the above-mentioned IPCC SRES storylines owing to local vertical movement. Due to tectonic uplift or subsidence, tide gauges may also move vertically with the region. These vertical crustal movements greatly complicate the problems of determining local/ regional sea-level change from tide gauge data.

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For instance, by using available tide-gauge data in the New Jersey coast [8], Cooper et al. [9] estimated that the New Jersey coast may have a local component of sea-level rise of 2 mm/year attributed to land subsidence and sediment compaction. Based on the range of global mean sea-level rise from 0.09 to 0.88 m between 1990 and 2100 [1], adding the local estimation of subsidence and consolidation (2 mm/year), they suggested a local/ relative sea-level rise for the New Jersey coast will be between 0.31 and 1.10 m, giving a central value of approximately 0.71 m. Furthermore, in the study of the sea-level rise and land use using 7.5 min digital elevation models (DEMs) with 10 m horizontal resolution, they provided the assessment results on two specific (median-projected) sea levels, 0.61 m (2 ft) and 1.22 m (4 ft), for 2050 and 2100, respectively, by means of the so-called contourline projection approach. On the other hand, some studies of sea-level rise only evaluated the impact of hypothetical sea-level rise. For example, US-CCSP [7] used three assumed sea-level rise scenarios (0.3, 0.5, and 1.0 m of sea-level rise by 2100) to evaluate several aspects of their impacts for the Mid-Atlantic US coast using a range of elevation data sets, which have large variations in vertical resolution and horizontal accuracy. In the New Orleans region, land-surface altitude data collected in the leveed areas of the New Orleans metropolitan region during five survey epochs between 1951 and 1995 indicated mean annual subsidence of 5 mm/year [12]. By considering this rate of land subsidence and the IPCC mid-range estimate of sea-level rise (0.480 m), Burkett et al. [12] suggested a net 1.0-m decline in elevation during the next 100 years relative to present mean sea level in the New Orleans region. They estimated accordingly that the areas of New Orleans and vicinity, which are presently 1.5–3.0 m below mean sea level, will likely be 2.5–4.0 m or more below mean sea level by 2100.

Global Warming, Sea-Level Rise, Hurricanes, and Storms Climate variability and any resulting change in the characteristics of tropical cyclones (tropical storms, subtropical storms, and hurricanes) have become topics of great interest and research within the past years. An emerging focus is how the frequency of tropical cyclones has changed over time and whether any changes could be linked to anthropogenic global warming. A special attention to Atlantic hurricane activity and its relation with tropical Atlantic warmth has been paid, because the Atlantic is the one tropical cyclone basin that has quantitative records back to the mid-nineteenth century for the whole basin (i.e., North Atlantic Ocean, Caribbean Sea, and Gulf of Mexico) [13]. Mann and Emanuel [14] analyzed those data to conclude that there is a strong historical relationship between tropical Atlantic sea surface temperature (SST) and tropical cyclone frequency for the period of 1871–2005. Similarly, Holland and Webster [15] investigated Atlantic tropical cyclone frequency and found a doubling of the number of tropical cyclones over the past 100 years. With no conclusions about the existence of the Atlantic Multi-decadal Oscillation (AMO) which is a natural climate cycle, both papers linked these changes of Atlantic tropical cyclone frequency to anthropogenic greenhouse warming. However, Landsea [13] pointed out that both analyses, with no indication of

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uncertainty or error bars, presumed that tropical cyclone counts are complete or nearly complete for the entire basin going back in time for at least a century. And this presumption is not reasonable and that improved monitoring in recent years is responsible for most, if not all, of the observed trend in increasing frequency of tropical cyclones. Through reanalyzing the historical data of Atlantic basin storms, Landsea [13] indicated that large, long-term ‘‘trends’’ in tropical cyclone frequency are primarily manifestations of increased monitoring capabilities and likely not related to any real change in the climate in which they develop. From the point of view of coastal hazard (flooding and erosion) management, increasing tropical storm and hurricane activity may cause more frequent flooding and inundation in the current coastal floodplains. Even if it is assumed that strength of storms shows no change in the future, under the future conditions of sea-level rise, current flood levels and inundation areas will be exceeded and low-lying lands will still be permanently inundated. For example, Cooper et al. [9] studied the future sea-level rise in the New Jersey coast by introducing only two sea-level rise scenarios, i.e., 0.61 m (1 ft) and 1.22 m (2 ft). By comparing with the US Federal Emergency Management Agency (FEMA) tidal surge frequency for 5, 10, 20, 30, 50, 100-year flood water levels for Atlantic City, New Jersey, they found that sea-level rise will allow current flood levels to be exceeded and lowlying lands to be flooded with increase frequency. In the case of 0.61 m rise in sea level, the current 30-year storm will produce a flood water elevation of 2.96 m, which exceeds the current 100-year FEMA flood level (2.90 m at Atlantic City). After a 1.22 m rise in sea level, the current 5-year storm will cause water levels above the current 100-year flood level. In other words, provided that other factors being equal, New Jersey’s current 100-year flood levels could become the 30-year flood level after a 0.61 m sea-level rise and the 5-year flood level after a 1.22 m rise. Cooper et al. [9] further estimated that 6.5% of the state’s total land area will be inundated in the case of the current FEMA 100-year flood level due to storm; the inundation area due to the same storm after 0.61 m rise in sea level will increase up to 9% of the state’s total land area. In low-lying areas, subsidence and uplift play an important role in flood management. As mentioned above, an average 5-mm per year land subsidence in the New Orleans region and IPCC mid-range estimate of sea-level rise (480 mm) suggests a net 1.0-m decline in elevation during the next 100 years relative to present mean sea level [12]. A storm surge from a Category 3 hurricane (estimated at 3–4 m without waves) at the end of this century, combined with global mean sea-level rise and land subsidence, would place storm surge at 4–5 m above the city’s present altitude. The effect of such a storm on flooding in the New Orleans Metropolitan Statistical Area (MSA) will depend upon the height and integrity of the regional levees and other flood-protection projects at that time [12]. US-CCSP [7] examined the effects of sea-level rise on coastal floodplains and on coastal flooding management issues confronting the US FEMA, the floodplain management community, the coastal zone management community, and the public, including private industry. From the analysis of historical tide station records for the highest storm tides in the Mid-Atlantic Coast, this report shows that storms today with slightly lesser storm surge than historical storms have had slightly higher storm tide elevations relative

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to the land due to sea-level rise. This suggests that any given storm could have higher flooding potential in the future due to higher sea levels than it would if it occurred today. During storm events, local water elevations at coastal zones will significantly increase due to nonlinear physical processes such as storm surges, high tides, wave setup, and their combinations. These combinations largely determine temporally/spatially varying flooding/inundation, coastal erosion, and overwash in barrier islands in coastal regions. Additionally, sea-level rise will lift up flood levels by providing a higher base for a storm surge to build upon. Even if the frequency and strength of storms will keep no change in the future, sea-level rise undoubtedly will cause flooding/inundation over a wider coastal area due to shoreline retreat, higher wave setup, and storm surges. Because of the nonlinear and unsteady behavior of storms, the linear contour-line project approach can lead to poor depiction of reality of sea-level rise impacts. It is, therefore, essential to assess the dynamic, interactive, and nonlinear impacts of hazardous storms under conditions of sea-level rise for the purpose of better coastal protection management in a local or regional area.

Geophysical and Socioeconomic Impacts of Sea-Level Rise on Coast and Estuary Human populations have a tremendous impact on the quality of coastal and estuarine environments. The ultimate goal of assessment of sea-level rise and climate change is to quantify these impacts on coastal communities as human society. In 2001 just over half the world’s population, around 3.2 billion people lived within 200 km of a coastline [16]. The rate of population growth in coastal areas is accelerating and increasing tourism adds to the pressure on the environment. In the United States, around 37% of the total US population lives in the 364 ‘‘coastal counties,’’ including the Great Lakes, which contains V zones (a coastal hazard zone defined by FEMA [17]) [18]. In their recent publication [19], it is shown that about 8.2% of the coastal population (86,541,000 people) live in 1% annual chance (or 100-year) coastal flood hazard areas as defined by FEMA. Therefore, the impacts of sea-level rise on coastal and estuarine area are, in principle, closely related to its geophysical and socio-economic effects to the natural habitat of human being in the areas. In General, there are four primary geophysical impacts of sea-level rise, i.e., ● Permanent Inundation and displacement of coastal lowlands, including loss of wetland ● Increased flood and storm damage ● Increased erosion ● Salinization of surface and increased waters In > Table 14.2, the geophysical impacts of sea-level rise and relevant interacting factors are summarized. This table indicates that the relevant interacting factors of the impacts of sea-level rise are related to multiscale physical processes including meteorology, oceanography, hydrology, and geomorphology. Assessment of the impacts of sea-level

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. Table 14.2 The physical impacts of sea-level rise and other relevant factors Impact of sea-level rise

Other relevant interacting factors

Permanent inundation and displacement of coastal lowlands

Wind, temperature, storm, hurricane, rainfall Wind setup, rainfall

Increased flood and storm damage Increased erosion

Salinization of surface and increased waters

Meteorology Oceanography Hydrology

Geomorphology

Wave, storm surge, tide, ocean current

Run-off, river flood, backwater effect

Sediment supply, morphological changes, land claim, subsidence

Wave setup, storm surge, strong surge tide current Rainfall Wave, storm surge, tide, current temperature, Tide, surge, ocean current storm, hurricane, rainfall

Run-off, river flood, backwater effect

Morphological changes

River flood

Sediment supply, subsidence, land claim Morphological change, subsidence

Run-off, groundwater table change, catchment management

rise strongly depends on understanding of nonlinear behavior of the integrated coastal system driven by these multiscale physical processes. Considering specific coastal regions, more detailed categories on the geophysical impacts of sea-level rise can be identified as follows: ● ● ● ● ● ●

Increased wave energy in the nearshore area (shoreline erosion and land erosion) Upward and land-ward migration of beaches (shoreline retreats) Accelerated coastal retreat and erosion Saltwater intrusion into coastal freshwater aquifers and rivers upstream Damage to coastal infrastructure due to increased wave energy, and Broad impact on coastal economy of coastal communities (coastal resilience)

Assessment of socioeconomic impacts of sea-level rise is an ultimate goal for building resilient coastal communities to alleviate coastal hazards generated from severe storms together with sea-level rise. Readers may find a large number of publications such as government reports and academic papers on the assessment of socio-economic impacts, management policies on this issue, e.g., IPCC report [6], US-Climate Change report [7], Nicholls et al. [20]. Although discussions of the socioeconomic impacts are out of this chapter’s range, potential socioeconomic impacts of sea-level rise summarized by Nicholls [10] are listed as follows: ● Increased loss of property and coastal habitats ● Increased flood risk and potential loss of life

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Sea-Level Rise and Hazardous Storms: Impacts on Coasts and Estuaries

Damage to coastal protection works and other infrastructure Loss of renewable and subsistence resources Loss of tourism, recreation, and transportation functions Loss of nonmonetary cultural resources and values Impacts on agriculture and aquaculture through decline in soil and water quality

In the following contents, the impact of sea-level rise means its geophysical impact if there is no special explanation.

Assessment of Impact of Local Sea-Level Rise for Coastal Zone Management The impacts of sea-level rise can be assessed in different ranges of spatial scales, i.e., global, regional, and local scales, in which some case studies are driven by policy making (e.g., [11, 21, 22]), and some are more science-orientated to examine the methodologies that can transfer scientific knowledge into decision-making tools (e.g., [9, 23]). Sea-level rise may significantly change the areas of coastal hazard maps in a specific coast. Therefore, coastal hazard management in coastal zones requires local assessment of impacts of sealevel rise. > Figure 14.1 presents a general procedure for assessment of impacts of sea-level rise from global scale to local scale. As for the sea-level rise assessment methodologies, since the contour-line projection approaches to assess sea-level rise only can give an average estimation (most likely underestimation) of the impacts, further accurate numerical simulations are needed to include the nonlinear variations of other physical factors such as storm surge, wave, tide, etc., along with sea-level rise. In fact, direct numerical modeling plays an important role on predicting multiscale physical processes including storm track, weather change, ocean volume increase, surge, tide, wave, and inland flood in atmosphere, ocean, and coast, as well as quantitative evaluation of sea-level rise impacts in time and space. It also has to point out that the reliability of the sea-level rise assessment results strongly depend on the accuracy of the coupled physical models. In order to assess the impacts of sea-level rise in a specific coast, coastal zone management is usually practiced through defining coastal flood plain and coastal flood hazard zones based on coastal processes. In general terms, a floodplain is any normally dry land surrounding a natural water body that holds the overflow of water during a flood. The US federal regulations governing FEMA [17] define floodplains as ‘‘any land area susceptible to being inundated by flood waters from any source.’’ The National Oceanic and Atmospheric Administration (NOAA) National Weather Service (NWS) defines a floodplain more specifically as the portion of a river valley that has been inundated by the river during historic floods. None of the formal definitions of floodplains include the word ‘‘coastal.’’ However, as river systems approach coastal regions, river base levels approach sea level, and the rivers become influenced not only by stream flow, but also by coastal processes such as tides, waves, and storm surges [24]. Coastal areas are periodically inundated by tides, waves, and surges. The slope and width of the coastal

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Climate change

Global scale Regional/local scale

Global mean sea level change

• Coupled ocean-atmosphere model • Tide gauge data projection

SLR scenarios

Socio-economic scenarios (population, economy, adaptation)

National/regional/ local SLR scenarios

• Coupled ocean-atmosphere model • Downscaling model • Tide gauge data projection

Storm/hurricane/ Typhoon scenarios

• Coupled ocean-atmosphere model • Historical storm data analysis

Flood levels / inundation area

Coastal-oceanic process model (surge, wave setup, subsidence, etc)

Morphological Changes (erosion/deposition)

Morphodynamic model (geomorphic data, sediment properties, structure data)

Management

Coastal hazard evaluation

Coastal protection Planning and management

. Fig. 14.1 Assessment of sea-level rise in global/regional/local scale

plain determine the size and inland extent of coastal influences on river systems. US-CCSP [7] has given a good working definition of a coastal floodplain, borrowing from the river floodplain definition, which is any normally dry land area in coastal areas that is susceptible to being inundated by water from any natural source, including oceans (e.g., tsunami run-up, coastal storm surge, relative sea-level rise) in addition to rivers, streams, and lakes. (Tsunami run-up occurs when a peak in the tsunami wave travels from the nearshore region onto shore. Run-up is a measurement of the height of the water onshore observed above a reference sea level. For more information, one may refer to USGS [25].) FEMA [17] has defined four coastal zones in cross shore for management of coastal flood hazards: Offshore Zone is the area, usually in the deep water, influenced by waves and water levels that are not substantially influenced by bathymetry (i.e., the water depth relative to sea level) or topography (i.e., the elevations above sea level). Dominant processes in this zone include swell, seas, astronomical tides, storm surge, and largescale climate perturbations such as El Nin˜o. Shoaling Zone is the area outside the surf zone where offshore conditions (mainly waves) are transformed by interaction with

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bathymetry or topography. This transformation of wave in the shoaling zone includes refraction, diffraction, dissipation, and generation of waves by wind. Surf Zone is defined as the area where waves break as they interact with the bottom. Dominant processes in the surf zone include wave setup, run-up, overtopping, erosion/deposition, and interaction with structures. Backshore Zone represents the area that is outside the normal surf zone but may be subject to inundation during coastal flooding events. This area is subject to development and is the critical area for determination of flood hazards. As for coastal hazard management, on the other hand, FEMA generally divided coastal flood hazard zones into three categories: (1) VE zone: the coastal high hazard area where wave action and/or high-velocity water can cause structural damage during the 1% annual chance flood including wave run-up zone, wave overtopping splash zone, high-velocity flow zone, breaking wave zone, and primary frontal dune zone, (2) AE zone: where flood hazards are not as severe as in VE zones, and (3) X zone: which is only subject to flooding by flood more severe than the 1% annual chance flood.

Numerical Modeling for Assessing Dynamic Impacts of Local Sea-Level Rise and Hazardous Storms Numerical modeling plays a decisive role in assessing various impacts of sea-level rise in different spatial scales. Since climate change is a global-scale phenomenon, a Global Circulation Model (GCM) is a first choice to predict the thermodynamic motion of atmosphere layers due to greenhouse gas emission. By coupling with ocean models which represent oceanographic processes, a coupled ocean-atmosphere model (OAM) is able to predict the variation of ocean water volume in response to the changes of atmospheric temperature. Usually, GCMs and OAMs can predict global-scale tempospatial variations of various physical variables such as air temperature, precipitation, concentration of greenhouse gases, sea-level change, etc. However, the spatial resolution of the numerical results is in general several hundred kilometers on the earth surface. So far, there is not a numerical model capable of directly simulating sea-level changes under local hydrological conditions with a local coastal scale (which can be several meters to several kilometers). As shown in > Fig. 14.1, a number of numerical models for different spatial scales are usually employed to obtain the sea-level rise scenarios in response to greenhouse gas concentrations on the global scale, to downscale the GCM model results to a local/regional scale, and then to use a coastal-ocean process model to predict the impacts of the sea-level rise scenarios together with a hazardous storm condition in a specific local coast/estuary.

Projection Approach and Numerical Simulation Other than numerical simulation modeling based on physical principles, projection approach (e.g., [9]) is a simple but quick way to delineate flood hazard areas due to mean sea-level scenarios by projecting the corresponding contour lines on terrain maps

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within GIS models. But its demerit is the underestimation of the impacts of sea-level rise such as area of inundation and erosion. The only way to predict the day-to-day weather and changes to the climate over longer timescales is to use numerical simulation models, such as a GCM or OAM. These models solve complex mathematical equations that are based on well-established physical laws that define the nonlinear and unsteady behavior of weather and climate. According to the 2001 IPCC Third Assessment Report, a total of seven GCMs were used for assessing the global climate change. In the 2007 IPCC Fourth Assessment Report, as many as 23 GCMs were adopted to predict the global climate change including sea-level variations in response to eight greenhouse gas emission scenarios (IPCC [26]). Owing to computer capacity limitations, it is highly impossible to represent all the detail in the real world in a computer model, so approximations have to be made. The models are tried and tested in a number of ways: (1) they are used to reproduce the climate of the recent past, both in terms of the average and variations in space and time [27]; (2) they are used to reproduce ancient climates what have been known (which are more limited) [28]. These climate models typically have three-dimensional representation of the ocean and sea ice, an interactive carbon cycle, interactive atmospheric chemistry models, and the coupled atmosphere–ocean–carbon-cycle–chemistry model [29, 30]. The global-scale climate simulations are extensive and usually carried out in highperformance parallel computers. In a regional/local scale, 2D or/and 3D coastal/estuarine models are used to simulate and to predict physical processes under a set of given conditions which typically represent storm/hurricane events and sea-level rise scenarios [31]. Coastal/estuarine models are to compute coastal and estuarine processes such as wave transformation, storm surge, tide, sediment movement, erosion/deposition, water quality, etc. so as to predict hydrological variables, e.g., water levels, velocities, bed changes, bio-mass properties, etc. Those process-based models can predict complex unsteady physical processes to provide a set of dynamic results (basic databases) for engineering assessment and coastal hazard mapping. They enable to handle various data inputs such as hydrological data (wave, wind, tide, runoff, river inflow, storm track, etc.), bathymetry/topography (e.g., DEM data from GIS application), boundary condition data, etc. So far, coastal/estuarine numerical modeling is the most accurate methodology to predict/plan coastal hazards and sea-level rise impacts on coasts and estuaries. They have been extensively adopted in coastal storm water management.

Downscaling Techniques GCMs are in general three-dimensional climate models which are based on physical principles and take into account as many physical variables as possible that could affect global climate. They are the only capable tools for predicting global-scale climate patterns in response to the increase of greenhouse gas emission. They are therefore widely applied to assess climate change impacts for various climate change scenarios. IPCC has provided

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all the output results generated by the selected IPCC GCMs in the online site of IPCC Data Distribution Centre at www.ipcc-data.org for public data download service. However, the horizontal resolution of the GCM model results is very coarse, up to several hundred kilometers in grid. For a regional assessment of climate change, a downscaling technique is needed to nest a higher resolution local/regional climate model within a coarse resolution GCM. Wilby et al. [32] categorized downscaling methodologies into four main types: (1) dynamic climate modeling, (2) synoptic weather typing, (3) stochastica weather generation, and (4) regression-based approaches. They give a detailed description and review on the downscaling techniques. Among them, dynamic downscaling together with a regional climate change model can resolve smaller-scale atmospheric features such as orographic precipitation (i.e., rain, snow, or other precipitation produced when moist air is lifted as it moves over a mountain range) or low-level jets better than the host GCM. Regression-based downscaling methods, which are relatively simpler, rely on empirical relationships between local-scale predictands and regional-scale predictors. Individual downscaling schemes differ according to the choice of mathematical transfer function, predictor variables, or statistical fitting procedure.

Challenges to Planning and Management of Coastal Zone Under Conditions of Sea-Level Rise and Hazardous Storms Planning and management of coastal zone are facing more new challenges due to sea-level rise and increasingly frequent storms and hurricanes in order to alleviate the damage of flooding, inundation, and erosion. Under the conditions of climate change and sea-level rise, these difficulties could happen to coastal zone management and planning to: ● Find new design criteria of coastal infrastructure, e.g., design parameters for storm, wave, surge, and tide ● Redefine extreme storm events, e.g., the 1% annual chance storm (i.e., 100-year storms due to global climate change) ● Update out-of-date flooding/inundation maps for most of coastal communities ● Redefine storm surge zones, evacuation route and evacuation zones, emergency shelter, etc. ● Re-evaluate coastal resiliency, hazard preparedness, coastal emergency management, first responding planning, coastal infrastructure planning, etc. ● Establish and maintain a premier data collection and delivery system such as a GISand Internet-based system

Brief Review on Coastal and Estuarine Process Modeling Understanding the nonlinear and unsteady features of coastal and estuarine processes driven by astronomical tides, storm surge, wind-generated waves, and river flows is

Sea-Level Rise and Hazardous Storms: Impacts on Coasts and Estuaries

14

essential to quantify the impacts of sea-level rise with hazardous storms for the purposes of coastal flood prevention, sediment management, shoreline erosion control, navigation channel maintenance, and designing coastal infrastructure. Sediment transport, consisting of longshore and cross-shore sediment movements and river sediment supply into coasts and estuaries, leads to complex morphological changes such as shoreline erosion/accretion, levee/barrier breaching, river bank erosion, variations of river mouth bar, navigation channel refilling, migration of offshore bar, etc. (A levee breach or levee failure is a situation where a levee fails and the water that was retained by that levee is allowed to flood the land behind the levee. A barrier breach happens in barrier islands in a coast when storm surges and/or high waves breached barrier.) Under increase of sea levels and shoreline retreat, some bathymetrical changes during storm and flood period may aggravate the problem of coastal flood and inundation. Numerical modeling is the only way to predict the temporal/spatial variations of sealevel rise impacts in a specific coast under naturally complex hydrological conditions. In the past decades, significant progress has been made in the studies of coastal and estuarine processes by means of physical experiments and computational simulations. Due to the complexities of physical processes, direct simulation of long-term (daily to yearly) hydrodynamic and morphodynamic responses to sea-level changes and storm events in a large-scale coast driven by astronomical tides, unsteady irregular waves, storm surges, wave-induced currents, and sediment transport has been a challenging goal. In recent years, with the process-based approach having been employed to the development of the coastal and estuarine process model, the long-term simulation of multiscale hydrodynamic and morphodynamic changes has become feasible (e.g., [33, 34]). In general, this multiscale simulation is accomplished by computing sequentially the wave field, the current field, and the seabed changes under the given boundary conditions and sea-level changes. Then a new bathymetry will be fed back to affect the computations of the wave and current fields in the next time step. By this iterative procedure going through the wave-current morphological models, it is possible to simulate the morphodynamic process by using an empirical sediment transport model for the time-scale morphological process (e.g., [35]). According to the existence of different spatial scales, the practical numerical model for simulating hydrodynamic and morphodynamic processes in coasts and estuaries has the following four types: (1) one-dimensional (1D) longshore coastline models, (2) twodimensional (2D) cross-shore coastal profile models, (3) 2D horizontal coastal/estuarine/ oceanic process models, (4) fully three-dimensional (3D) models. 1D coastline models can only describe behaviors of the longshore sediment transport and shoreline evolutions by using the sand budget approach; 2D cross-shore coastal profile models are able to predict the vertical variations of coastal profiles, but not the variations of the longshore sediment transport; 2D horizontal coast/estuary/ocean models can simulate hydrological and morphological variations over a coastal area with a rather wide range of spatial scales (e.g., 100 m2–100 km2) with the vertical variations of waves and currents ignored. Nevertheless, only fully 3D morphological models are expected to take into account both the vertical and horizontal variations of wave and current (e.g., [36, 37]). However, due to the time-consuming nature for practical problems, 3D models are restricted

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Sea-Level Rise and Hazardous Storms: Impacts on Coasts and Estuaries

generally to predict the temporal-spatial hydrological and morphological changes in a relatively small near-field and in a short duration. On the other hand, the horizontal 2D models have the potential to assess the impacts of storms and sea-level rise in local/ regional/global scales. Therefore, a quasi-3D model with the efficiency of the 2D depthaveraged model and better accuracy than 2D models would be a feasible tool for the longterm morphodynamic simulations in large-scale coastal engineering problems. Zyserman and Johnson [34] and Ding et al. [38] have presented, respectively, two quasi-3D coastal process models in which an empirical 3D shear stress distribution was used to take into account a quasi-3D effect of sediment transport. They concluded that quasi-3D coastal/ estuarine process models enable to compute accurately free-surface water motions, crossshore sediment transport, and morphological changes under natural hydrological conditions with high computing efficiency. Recently, semiempirical numerical approaches were presented by means of tideaveraging currents to assess long-term morphological changes on both the meso- and macroscale in coastal inlets and tidal lagoons in estuaries, e.g., Rapid Assessment of Morphology (RAM) by Roelvink [39]. But these tidal-phase-averaging approaches are not able to simulate nonlinear and highly unsteady hydrodynamic and morphodynamic processes during a short-term storm, as they cannot capture the peak surge and maximum flood inundation in storms/hurricanes. Nevertheless, due to the concern of computing time for assessing long-term impacts of sea-level rise over a few decades in the future, a similar approach based on tide-averaging hydrodynamic variables for rapid assessment of impacts of sea-level rise may be needed. As an example of quasi-3D coastal and estuarine process models, CCHE2D-Coast is capable of simulating tides, waves, currents, sediment transport, and morphological changes in various coasts and estuaries [35, 38]. It has been applied to assess the impacts of hazardous hydrological forcings including sea-level changes during storms and hurricanes (or typhoon) on coastal flood inundation, erosion and deposition, and navigation maintenance [24, 31, 40]. This model has systematically integrated three major submodels for simulating irregular wave deformations, astronomical tides, river inflows, waveinduced currents, sediment transport due to combined waves and currents, and morphological changes in coasts and estuaries. A validated algorithm in the CCHE2D [41] for the treatment of wetting/drying was directly used for predicting tidal flat variations and coastal inundations. This process-based model has been extensively validated by simulating waves, wave-induced currents, and morphological changes in coastal applications in various laboratory and field scales [35, 38, 42–44]. Some other commercial and in-house numerical models capable of modeling coastal and estuarine processes are briefly reviewed as follows: > Table 14.3 gives a short list of computer codes of phase-averaged irregular wave models, in which the wave transformation and deformation processes and mesh coordinates are evaluated. In > Table 14.4, some 2D hydrodynamic models have been compared with each other in respect to their numerical methods, grid systems, wetting/drying modeling capability, consideration of irregular waves, modeling capability for complex quasi-3D flow structures, and the effects of coastal structures. The different capabilities of the models available for modeling

Sea-Level Rise and Hazardous Storms: Impacts on Coasts and Estuaries

14

. Table 14.3 Summary of computer codes of phase-averaged wave models Models

Steady or unsteady

Mesh coordinates

Steady or quasisteady

Nonorthogonal Ding et al. [38]

Steady or optionally unsteady

Cartesian or spherical

SWAN [51]

Cartesian

WAMDI [52]

Steady

Cartesian

Steady

Cartesian

Holthuijsen et al. [53] Smith et al. [54]

Refraction, shoaling, breaking, steady diffraction, wave–current interaction, friction, wind-induced waves

Cartesian

Wave processes included

CCHE2D- Refraction, shoaling, breaking, Coast diffraction, wave-current interaction, friction, transmission through obstacles SWAN Refraction, shoaling, breaking, 40.41 whitecappinga, wave-wave interaction, reflection, diffraction WAM

Refraction, shoaling, breaking, Steady or whitecapping, wave-wave interaction optionally unsteady

MIKE21 Refraction, shoaling, breaking NSW STWAVE Refraction, shoaling, breaking, whitecapping CMSWAVE

References

Lin et al. [55]

a

Wave whitecapping is a situation that wave is blown by the wind so its crest is broken and appears white

sediment transport and morphological changes are shown in > Table 14.5. In addition, there are some other storm-surge models that can be used to predict storm surge and coastal inundation due to sea-level rise and storms, but incapable of simulating sediment transport and morphological change together with coastal hydrodynamic simulation, e.g., POM model [45], SLOSH model [46], and SHORECIRC model [47].

A Case Study: Assessment of Impacts of Sea-Level Rise and Hazardous Storm in an Estuary This case study is to demonstrate the assessment of impacts of sea-level rise and hazardous storms by simulating hydrodynamic variations and morphological changes in an estuary located in the west coast of Taiwan by using CCHE2D-Coast. This study did not estimate how much the sea-level rise will be; instead, it used several sea-level rise scenarios which are broadly based on recent sea-level rise forecasting studies and combined with historical storms as hydrological forcings. In this study, four scenarios, i.e., 0.5, 1.0, 1.5, and 2.0 m sea-level rise by 2100, were adopted to assess the impacts of sea-level rise in the estuary. CCHE2D-Coast was used to predict hydrodynamic processes (water elevations and velocities) and morphological changes under the conditions of the four scenarios and a storm flood event.

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Sea-Level Rise and Hazardous Storms: Impacts on Coasts and Estuaries

. Table 14.4 Some existing 2D coastal/estuarine hydrodynamic models Numerical method

Irregular waves

Undertow flow

Wetting and drying

FD

√

N/A

DELFT3D- FD FLOW

√

TELEMAC 2D

FE

CCHE2DCoast

Description of structures

Mesh system

References/ developers

Unstablea Not gooda

S.C.G.

MIKE 21 [56]//DHI

N/A

√

S.C.G.

Roelvink and Van Banning [57]//WL Delft Hydraulics

N/A

N/A

No √ validation

Unstructured TELEMAC-2D [58]/EDFDER, France

EE

√

√

√

N.O.G.

Ding et al. [38]/NCCHE

TRIM 2D

FD

N/A

N/A

No Unclear validation

R.G.

Casulli and Cheng [59]/ USGS, USA

ADCIRC2D

FE

√

N/A

√

Unstructured Westerink et al. [60]

Models MIKE2D HD

Unclear

√

√

FD finite difference, FE finite elemental, EE efficient element, FV finite volume, R.G. rectangular grid, S.C.G. staggered curvilinear grid, N.O.G. nonorthogonal grid, DHI Danish Hydraulics Institute, EDF-DER Laboratorie National de Hydraulique in France a Please refer to the report of CHL-ERDC by Scott [61]

Information of the Study Estuary and Model Validations The estuary of study site is located at the west coast of Taiwan called Touchien Estuary, facing to Taiwan Strait. As shown in > Fig. 14.2, this estuary has a 2.0-km wide river mouth, a rivermouth bar, two islands inside the bay, and two rivers (Touchien and Fengshan Rivers). A highly dense population lives in the coastal communities very close to the beaches. And the coastal zone is vulnerable facing storm (typhoon) attack and river floods and meanwhile is sensitive to sea-level rise. During storms or typhoons, this small estuary has equally important hydrodynamic and morphodynamic processes driven by tides, storm waves, surges, and river floods. The morphodynamic processes are therefore driven by multiscale physical forcing such as river flows, tidal currents, nearshore currents, and wave breaking across the surf zone. Morphological changes in the estuary are generally complex. To investigate floods and morphological changes in the estuary, a computational domain, as shown in > Fig. 14.2a, was used in the simulations. A nonorthogonal structural grid was generated by the CCHE2D mesh generator [48] to cover this entire estuarine and its adjacent coastal area. > Figure 14.2b shows a close-up view of the estuarine area in which several stations are marked for output of model results. Through simulating morphological changes during a 3-year period from 2004 to 2006 in which nine typhoon events (i.e., Mindulle, Aere, Haima, Haitang, Matsa, Talim, LongWang, Bilis, and Kaemi) were included, the CCHE2D coastal model has been

Sea-Level Rise and Hazardous Storms: Impacts on Coasts and Estuaries

14

. Table 14.5 Some models available for modeling morphological processes in coasts and estuaries Sediment transport modeling Spatial dimension

Flow

Stochastic Salinity process

Nonequilibrium

MIKE 21 CCHE2D CCHE2DCoast

2 2 2

SWE SWE SWE

√ N/A √

Uni. Non-uni. Uni

Equi. Non-Uni. Equi

CCHE3D MIKE 3 TELEMAC3D

3 3 3

RAE + HS N/A RAE √ RAE-HS √

Non-uni. Uni. Uni.

Non-Uni. Equi. Equi.

Model

SWE shallow water equations, RAE 3D Reynolds averaged equations, HS hydrostatic assumption, Uni. uniform sediment size, Non-Uni. nonuniform sediment sizes, Equi. equilibrium transport, Non-Equi. nonequilibrium transport

validated in this study area [49]. The boundary conditions of tidal elevations and wave properties at offshore in the 3-year simulation were prepared beforehand using a regional storm-surge model (a POM model) [45, 50] and the SWAN wave model. (The Princeton Ocean Model (POM) is an ocean model that is able to simulate hydrodynamic processes of free-surface flows such as circulation and mixing processes in rivers, estuaries, shelf and slope, lakes, seas, and ocean [45, 50]. SWAN is a wave model that computes random, short-crested wind-generated waves in coastal regions and inland waters. For more information, one may refer to SWAN [51].) The offshore incident wave properties, i.e., the significant wave heights, the periods, and the mean directions, were provided by field observations and the extracted results from the simulations by the SWAN model. The significant wave heights were usually lower than 2.0 m in most typhoons landed at the east coast and flood events in the coast. According to the grain size measurements, a uniform grain size, d50 = 0.2 mm, was used for representing the coastal sediments in the domain. A total load sediment transport formulation was used to calculate sediment fluxes and morphodynamic process from river to coast. Ding et al. [49] have shown that the computed morphological changes induced by all the storms during the 3-year validation period are in good agreement with the observations. As a result, CCHE2D-Coast was validated in the estuary using the field observation data. For the details on this site-specific model validation, one may refer to Ding et al. [49].

Hydrodynamic and Morphodynamic Responses to Sea-Level Rise and Storm As mentioned above, sea-level rise may cause disastrous flooding and inundation during storm periods in the low-lying areas of coasts and estuaries. In order to examine the impacts

489

14

Sea-Level Rise and Hazardous Storms: Impacts on Coasts and Estuaries

Ta

iw

an

Str

ait

N

F Ri eng ve sh r an

0

a

1km 2km

To Ri uch ve ie r n

Overview of the computational domain

St. 7 (Offshore)

0 -2

-30

N

-15 -10

-3

-2

-1

-5

St. 6 0 (Rivermouth)

1

0

0

1

S F t. 5 Ri eng ve sh r an

St. 1

3

St. 2

0

St. 4

2

-4

0

-2

4 3 2 1 0 −1 −2 −3 −4 −5 −10 −15 −20 −25 −30

-25

BED (m)

-10

490

0

b

1km

0

4

St. Tou 3 Riv chien er

Close-up view of the estuary

. Fig. 14.2 Grid and bathymetry in Touchien estuary: (a) overview of the computational domain, (b) close-up view of the estuary

of sea-level rise together with a storm event, a real storm (Typhoon Talim which occurred in August 2005), which attacked the Touchien estuary from 8/31/2005 to 9/2/2005, was used as the extreme event for this case study. As shown in > Fig. 14.3, two hydrographs, which represent respectively time series of flood flow discharges from the two rivers caused by

Sea-Level Rise and Hazardous Storms: Impacts on Coasts and Estuaries

14

Flood peak 2500 Touchien River Fengshan River

Discharge (m3/s)

2000

1500

1000

500

0

0

10

20

30 Hours

40

50

. Fig. 14.3 Hydrographs at two river upstream inlets during a storm flood event

rainfall of the typhoon, were applied to the two river inlets as the river inflow boundary conditions. These two hydrographs at the inlets of the two river upstreams were obtained beforehand by simulating, respectively, the storm flood flows in the two rivers from far upstream down to the estuary using a one-dimensional river flow model. The peak discharge was 2013.67 m3/s in the Touchien River and 992.66 m3/s in the Fengshan River, respectively. Then, the site-specifically validated CCHE2D-Coast was applied to simulate flood flows and sediment transport driven by this selected storm combined with the five sealevel rise scenarios (i.e., 0.5, 1.0, 1.5, 2.0 m sea-level rise, and a case without mean sea-level change). The mean sea-level changes were considered as the different scenarios of tidal elevations at the open sea. So the sea-level changes were added into the tidal elevations during the storm event to create new tidal elevation time series with the mean sea-level rise. > Figure 14.4 shows the five time series of tidal elevations at the offshore, which represent the tides under the conditions of the five sea-level rise scenarios. As the boundary conditions of a wave action model at offshore of the estuary, the wave properties (i.e., significant heights, averaged periods, and mean directions) at the offshore were specified on the offshore boundary for simulation of wave transformation from the offshore to the coast zone and the estuarine area. The offshore incident significant wave heights varied in the range from 0.5 to 1.6 m during the storm event [31]. In addition, the time series of prevailing wind speed and direction observed during the storm event were used in this study as the surface wind forcing over the estuary, in which the wind speed varies from 0.3 to 16.4 m/s.

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Sea-Level Rise and Hazardous Storms: Impacts on Coasts and Estuaries

Current SL SLR = 0.5 m SLR = 1.0 m SLR = 1.5 m SLR = 2.0 m

7.0 6.0 5.0 Tidal elevations (m)

492

4.0 3.0 2.0 1.0 0.0 −1.0 −2.0 −3.0

0

10

20

30 Hours

40

50

. Fig. 14.4 Tidal elevations boundary conditions at the offshore

Under these boundary conditions of tides and waves with the combined sea-level rise and storm, hydrodynamic and morphodynamic processes in the estuary were simulated using the site-specifically validated CCHE2D-Coast. The numerical simulations were performed by sequentially computing waves, currents, sediment fluxes, and morphological changes driven by the given hydrological conditions such as tides, waves, and river inflows at the five sea-level rise scenarios. To do so, the wave fields were updated every 1 h to reflect the changes of the offshore incident wave climate. And the sediment fluxes in the alluvial river reaches, the estuary, and the coastal area were calculated by an empirical sediment transport formulation, taking into account the variations of sediment transport due to waves and currents over the entire estuarine region from the river-flow-dominant upstream to the wave-dominant coast [35]. > Figure 14.5 shows the spatial distributions of computed significant wave heights and mean wave directions at the flood peak under the different conditions of sea-level rise. Along with the increase of the flooding area in the estuary from the current sea level (i.e., no sea-level rise) to 2-m rise, numerical results show that the offshore waves could invade the estuarine area from the river mouth toward the upstream river reaches. In comparison with the case for the current sea level (> Fig. 14.5a), sea-level rises from 0.5 to 2.0 m would promote the invasion of offshore waves inside the estuary and could further change the morphological features in the bay area. > Figure 14.6 shows the comparisons of the computed currents and water elevations at the flood peak in the five cases over a range from the current sea level to 2.0 m rise. The results indicate that significant increases in water elevations, offshore surge water invasion inside the estuary, and widening inundation areas occur when the sea-level rise is more than (and equal to) 1.0 m.

Sea-Level Rise and Hazardous Storms: Impacts on Coasts and Estuaries Computed wave heights and directions

14

Computed wave heights and directions N

Hs 1.5 1.4 1.3 1.2 1.1 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

N

Hs 1.5 1.4 1.3 1.2 1.1 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

Fe

Fe

ng

ng

sh

sh

an

0

1

2km

0

Tou

chie

Hs = 1.0m

a

an

b

Current sea level

2km

Tou

chie

Computed wave heights and directions N

N

Hs 1.5 1.4 1.3 1.2 1.1 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

Fe

Fe

ng

ng

sh

sh

an

0

1 Hs = 1.0m

c

1.0-m rise

2km

an

0

Tou

n

0.5-meter rise

Computed wave heights and directions Hs 1.5 1.4 1.3 1.2 1.1 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

1 Hs = 1.0m

n

chie

1 Hs = 1.0m

n

d

2km

Tou

chie

n

2.0-m rise

. Fig. 14.5 Comparison of computed wave height (unit: m) and directions at the flood peak for different sea-level rise scenarios. (a) Current sea level, (b) 0.5-m rise, (c) 1.0-m rise, (d) 2.0-m rise

In order to investigate the water elevation increases in the estuary which respond to the sea-level rise and the storm event, the time series of water elevations at seven selected monitoring stations are plotted in > Fig. 14.7. The locations of the stations are shown in > Fig. 14.2b, these stations represent respectively the offshore, river mouth, cross sections inside the estuary, and two rivers upstream. Intercomparisons of these water elevation changes clearly show that the tidal variations will affect the two river upstream if sea-level rises up to 1.0 m. With the sea-level rise up to 2.0 m, the entire river reaches will become tidal reaches and therefore possibly receive the saline water from ocean. Furthermore, the differences of water elevations at a same station generated by the five sea-level scenarios are shown in > Fig. 14.8. It also can be concluded that all the computational area could become tide-influenced estuary if there is 2.0-m sea-level rise, and most of the coastal community will be exposed to the attack of high tides, storm waves, and river floods. As it can be seen from > Fig. 14.8a, there is an increasing inundation area at the river mouth bar

493

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Sea-Level Rise and Hazardous Storms: Impacts on Coasts and Estuaries

Water elevations and currents

Water elevations and currents

WL 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 −0.5 −1

WL 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 −0.5 −1

N

N

Fe

Fe

ng

ng

sh

sh

an

0

1

2km

0 Tou

chie

Current = 1.0 m/s

a

an

1

2km

b

Current sea level

Tou

chie

Current = 1.0 m/s

n

n

0.5-meter rise

Water elevations and currents

Water elevations and currents

WL 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 −0.5 −1

WL 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 −0.5 −1

N

N

Fe

Fe

ng

ng

sh

sh

an

0

1 Current = 1.0 m/s

c

1.0-m rise

2km

an

0

Tou

chie

1 Current = 1.0 m/s

n

d

2km

Tou

chie

n

2.0-m rise

. Fig. 14.6 Comparison of computed water elevations and currents at the flood peak due to sea-level rise scenarios. (a) Current sea level, (b) 0.5-m rise, (c) 1.0-m rise, (d) 2.0-m rise

due to the sea-level rise; and the river mouth area behaves like the offshore after the rise is equal to and higher than 1.5 m. And the upstream river area is more susceptible to the tidal effect as it is shown in > Fig. 14.8d. The increase of sea level promotes the invasion of tidal waves inside the rivers, elevates the water levels in river reaches, and the tidal effect may even influence farther upstream. The morphodynamic processes are complicated in the estuary due to the highly irregular bathymetry and hydrological conditions. In particular, the existence of the two interior islands affects river courses and sediment transport. As depicted in > Fig. 14.9, the simulated morphological changes indicate erosion/deposition areas in the estuary, river mouth, and the adjacent coasts due to the storm and the sea-level changes. They show the gradually reducing areas of deposition in the offshore when sea-level rise increases from current sea level to 2.0 m mean sea level. This is because the increased water depth causes wave-breaking zone (or the surf zone) shifting to upstream (or landward), and the current

Sea-Level Rise and Hazardous Storms: Impacts on Coasts and Estuaries

15 St. 1 St. 2 St. 3 (Touchien River inlet) St. 4 St. 5 (Fengshan River inlet) St. 6 (Rivermouth) St. 7 (Offshore)

10

Water elevations (m)

Water elevations (m)

15

5

0

−5 0

12

a

24 36 Hours Current sea level

48

5

0

0

12

b

24 36 Hours 0.5-meter rise

48

60

15 St. 1 St. 2 St. 3 (Touchien River inlet) St. 4 St. 5 (Fengshan River inlet) St. 6 (Rivermouth) St. 7 (Offshore)

10

5

0

12

24 36 Hours 1.0-meter rise

48

Water elevations (m)

Water elevations (m)

c

St. 1 St. 2 St. 3 (Touchien River inlet) St. 4 St. 5 (Fengshan River inlet) St. 6 (Rivermouth) St. 7 (Offshore)

10

−5

60

15

−5 0

14

10

5

0

−5 0

60

d

St. 1 St. 2 St. 3 (Touchien River inlet) St. 4 St. 5 (Fengshan River inlet) St. 6 (Rivermouth) St. 7 (Offshore)

12

24

36 Hours

48

60

2.0-meter rise

. Fig. 14.7 Comparison of computed water elevation time series at seven stations under the same sealevel rise scenarios. (a) Current sea level, (b) 0.5-m rise, (c) 1.0-m rise, (d) 2.0-m rise

surf zones turn to be shoaling zones where wave breaking may no longer occur. Therefore, sediment transport at the offshore becomes less active. > Figure 14.9 also shows that with the increasing of sea levels, the river mouth bar is increasingly eroded, which consequently will cause a landward displacement of the shoreline. And the river mouth bar may migrate to the junction area of the two rivers in the estuary. > Figure 14.10 presents the profiles of computed bed elevations and bed changes at the river mouth along with the transect A–A0 , of which the location is shown in > Fig. 14.9d, after the storm flood with the conditions of the sea-level rise scenarios. The profiles clearly show that the erosion process in the river mouth is not linearly increasing, but typically nonlinearly varying with the sea-level changes; in fact, 1.0-m sea-level rise will cause a river mouth to be narrowed (turning to close), and the river mouth widening process could be accelerated only after the sea-level rises up to 2.0 m.

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Sea-Level Rise and Hazardous Storms: Impacts on Coasts and Estuaries

MSL 0.0 m MSL 0.5 MSL 1.0 MSL 1.5 MSL 2.0

Water elevations (m)

8 6 4 2 0

Water elevations (m)

6 MSL 0.0 m MSL 0.5 MSL 1.0 MSL 1.5 MSL 2.0

4

2

−2 −4 0

12

a

24

36 48 Hours Rivermouth (St. 6)

0

60

c

12

24

36 Hours Island (St. 1)

48

60

10

2

0

12

24 36 Hours South Bank (St. 2)

48

Water elevations (m)

MSL 0.0 m MSL 0.5 MSL 1.0 MSL 1.5 MSL 2.0

4

0

0

b

6

Water elevations (m)

496

8 6 4 2 0

60

d

MSL 0.0 m MSL 0.5 MSL 1.0 MSL 1.5 MSL 2.0

0

12

24 36 Hours

48

60

Touchien River inlet (St. 3)

. Fig. 14.8 Comparisons of computed water elevations at different stations according to different sea-level rise scenarios. (a) Rivermouth (St. 6), (b) Island (St. 1), (c) South Bank (St. 2), (d) Touchien River inlet (St. 3)

Discussions on the Impacts of Sea-Level Rise in Touchien Estuary In this case study, the site-specifically validated coastal process model, CCHE2D-Coast, was applied to compute hydrodynamic and morphodynamic responses to a set of hypothetical sea-level rise scenarios combining with a real storm event happened in Touchien Estuary located in the west coast of Taiwan. The hydrodynamic results show that there are obvious wet/dry cycle changes at all the upstream monitoring stations. And there is an increasing inundation effect at the river mouth bar in case of the mean sea level

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. Fig. 14.9 Comparisons of computed bed changes after the storm flood under the conditions of different sea-level rise scenarios (DZ is bed change. The contour lines are computed bed elevations). (a) Current sea level, (b) 0.5-m rise, (c) 1.0-m rise, (d) 2.0-m rise

higher than 1.5 m. The river area is more susceptible to the tidal effect at the 1.5-m mean sea-level rise. In addition, the morphodynamic results show that there is apparent change in erosion/deposition areas due to sea-level rise. Especially, the river mouth bar is more exposed to be eroded, which consequently could cause landward retreat of shoreline and displacement of rivermouth bar due to inundation and waves approaching inland. The preliminary test results in the case study demonstrate that the CCHE2D-Coast model is able to effectively simulate the nonlinear and unsteady hydrodynamic and morphodynamic processes in the coastal and estuarine area under different mean sealevel scenarios. Therefore, this model can be used for coastal/estuarine planning and management to assess the impacts of sea-level rise and storm events under naturally temporal/spatial varying hydrological conditions.

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5 4

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. Fig. 14.10 Comparisons of profiles of computed bed elevations and bed changes after the storm flood at the river mouth along with the transect A–A0 shown in > Fig. 14.9d. (a) Bed elevations, (b) bed elevation changes

Concluding Remarks and Future Research Topics This chapter investigates the dynamic impacts of sea-level rise by assessing hydrodynamic and morphodynamic responses to storms (hurricanes or typhoons) under natural physical conditions of coastal and estuarine processes, which are induced by astronomical tides, waves, storm surges, river inflows (floods), sediment transport, and morphological changes in coasts and estuaries. It also presents a review on the impact assessment

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approaches such as projection and numerical modeling to assess the impacts of sea-level rise in local/regional/global scales. A special attention in the chapter has been paid to emphasize the importance and applicability of numerical modeling to quantify the dynamic impacts of hazardous storms after sea-level rise occurs, since simulated results on flooding/inundation areas and erosion are the first-hand data base to engineers, managers, and decision makers to practice flood water management, shoreline erosion protection, and design/planning of coastal infrastructure against hazardous storms. It also gives a brief review on the existing coastal/estuarine process models which are applicable to simulate/predict hydrodynamic and morphodynamic responses to the complex hydrological conditions in coasts and estuaries. Finally, using an integrated coastal/estuarine process model called CCHE2D-Coast, the simulations of flows and morphological changes in an estuary located in the west coast of Taiwan under the conditions of several sea-level rise scenarios and a selected extreme storm are demonstrated. It shows that numerical modeling of coastal/estuarine processes can predict temporal/spatial variations of flows (water elevations and current velocities), sediment transport, and morphological changes due to the combined physical conditions from waves, tides, surges, and river floods. These numerical simulation results indicate that this integrated process model is capable of predicting the dynamic impacts of sea-level rise with storm events such as inundation of low-lying area, shoreline retreat, changes of coastal zones, tidal water intrusion, etc. These models enable to facilitate the assessment of dynamic impacts of sea-level rise and storms in different time and spatial scales (local/ regional scales) for various practical engineering application purposes such as flood management, coastal erosion protection, and coastal community development/planning. By integrating with other numerical models for prediction of water quality and ecological processes in the future, this kind of integrated physical process model will also be applied for assessment of the environmental impacts of sea-level rise such as saline water intrusion and pollutant transport in coasts and estuaries. As for the potential future research topics for better assessment of impacts of sea-level rise and hazardous storms (extreme events), basically, there are three aspects that need to be enhanced in the future: 1. Improve understanding of sea-level rise and coastal hazardous events or extreme events including other extreme events such as tsunami and large-scale oil spill. 2. Improve assessment tools by advancing all scale-level numerical modeling techniques with more accurate, efficient, and higher-resolution numerical simulations. 3. Develop mitigation and adaptation to sea-level rise and extreme storms with increasing storm strength and frequency. Nicholls et al. [20] pointed out that the level of knowledge and understanding on sealevel rise, storms/hurricanes, and their interactions is not consistent with the potential severity of the problem of climate change and coastal zones. Key uncertainties in the climate drivers and responses of coasts and oceans increase with the largest uncertainties concerning in their interactions. It is vital to establish better baselines of actual sea-level changes and

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coastal changes in morphology and ecology through observations and expanded monitoring. In addition to traditional tide gauge measurements, there is a need to collect more accurate data from altimetric satellites, such as TOPEX/Poseidon (launched in 1992 and still operating), which observe almost the entire planet and determine the absolute, not relative, sea level because they make measurements with respect to Earth’s center of mass (without uncertainty of subsidence existing in some tide-gauge data) [5]. For a better assessment of impact of sea-level rise and storms, it is also of vital importance to improve understanding of extreme tropical storms/hurricanes, particularly their strength and frequency increasing with global climate change. Better knowledge about occurrence of coastal extreme events will definitely facilitate a more accurate impact assessment and building a stronger coastal defense community. Assessment of human vulnerability in coastal and low-lying areas is an ultimate goal to build a sustainable coastal community, which though is out of the scope of this chapter; one may refer to Nicholls et al. [20] for detailed assessment of socio-economic impacts of sea-level rise due to climate changes. Numerical modeling is the only assessment tool to evaluate impact of sea-level rise with various spatial scales and to predict time-dependent variation patterns of physical variables including climate driving factors and coastal/oceanographic factors. It is essential to continue to develop numerical models with higher accuracy by including improved knowledge on climate changes and coastal/ocean processes so that uncertainties from natural processes can be reduced as much as possible. Detailed model validation/verification is always requested to control the quality of numerical simulations before a model can be applied to a real world problem. The models with different scales should be validated by the observation data sets obtained from relevant field measurements. To make the multiscale assessment more effective, multiscale modeling techniques have to be developed to meet the increasing demand for assessing local/regional impact of sea-level rise with the conditions of storms and hurricanes. Development of high-performance computing techniques is critical to improve the computing efficiency of climate models and local assessment models, especially due to multidimensional and unsteady physical problems in the interactions of climate changes and coastal/ocean processes. It is undoubted that an integrated modeling system with better accuracy and efficiency will be a unique powerhouse to help scientists, engineers, policy/decision makers to better assess coastal vulnerability and provide the costeffective plan for mitigation and adaptation against the impacts of sea-level rise and extreme coastal events, as well as their interactive impacts.

Acknowledgments This work was a product of the research partially sponsored by the National Center for Computational Hydroscience and Engineering in The University of Mississippi. The authors would like to thank Dr. Keh-Chia Yeh in National Chiao Tung University, Hsinchu, Taiwan for his help to provide the boundary conditions for the case study. Special thanks are given to Mr. Moustafa Elgohry for his research assistance.

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15 Impact of Climate Change on Biodiversity David H. Reed Department of Biology, University of Louisville, Louisville, KY, USA Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506 Importance of Biodiversity: Ecosystem Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507 Supporting Ecosystem Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508 Regulating Ecosystem Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511 Provisioning Ecosystem Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513 Cultural Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519 Impact of Global Climate Change on Biodiversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520 Current Rates and Causes of Extinction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520 Current and Future Rates of Global Climate Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521 Climate Change and Biodiversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_15, # Springer Science+Business Media, LLC 2012

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15

Impact of Climate Change on Biodiversity

Abstract: Biodiversity, the diversity of living things on Earth, is a critical measure of the Earth’s health. Biodiversity provides immense direct benefits to humans, with at least 40% of the world’s economy being derived from biological resources. Maintaining biodiversity provides greater food security, opportunities for economic development, and provides a foundation for new pharmaceuticals and other medical advances. Ironically, maintaining biodiversity levels and functioning ecosystems is critical to ameliorating climate change; yet, climate change is expected to cause serious disruptions to Earth’s ecological systems, resulting in an overall loss of biodiversity and a reduction in the goods and services provided to humans. Extinction rates in the future are very difficult to predict. However, with immediate and decisive action to mitigate climate change, losses of biodiversity can be minimized and humans can continue to reap many of the benefits nature provides; business as usual scenarios will likely lead to the loss of >50% of all plant and animal species on Earth and the collapse of many ecosystems worldwide. Such losses will drastically lower the quality of life for humans and will take millions of years to reverse.

Introduction Biodiversity refers to the sum variation of all living organisms (animal, plant, fungal, and microbial) on Earth, including their genetic diversity, species diversity, and the diversity in the ecosystems (e.g., rainforests, coral reefs, estuaries) they help build and regulate. There is a hierarchical structure to biodiversity. Genetic diversity is the most fundamental level of diversity and the one on which all other levels of biodiversity depend, and all levels of biodiversity contribute to the amount and diverse types of ecosystem services provided and the utilitarian and aesthetic value of biodiversity [1]. Biodiversity contributes to human welfare in innumerable ways. Examples of ecosystem services include the regulation of climate from a local to global level, purification of the fresh water supplies necessary for human survival, the storage and recycling of the nutrients on which all life depends, and the formation of soil necessary for agriculture. Biodiversity also provides resources such as foods, medicines, and wood products. At least 40% of the world’s economy, and 80% of the economy of less-industrialized nations, is derived directly from biological resources [2]. Biodiversity enriches the lives of humans in very tangible and utilitarian ways, but also provides us with emotional gratification and inspiration. Given the importance of biodiversity to human well-being and the irreversibility of its loss, the depletion of biodiversity is one of the most important environmental threats that humanity faces [3]. The golden toad (Bufo periglenes) is thought to be the first species to go extinct due primarily to global warming [4], and climate change has already been implicated in numerous population extinctions and at least one other species extinction [5]. However, this is just the tip of the iceberg. Examination of past extinction events and current warming predictions suggests that global climate change alone could drive more than half of the known species on Earth to extinction (> Fig. 15.1).

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. Fig. 15.1 The golden toad vanished from Costa Rica’s Pacific coastal-mountain cloud forest in the late 1980s. Several researchers have linked outbreaks of the chytrid fungus that drove the golden toad to extinction, and threatens dozens of other species of frogs and toads in the same region, to climate change [5]

This chapter will cover some of the many reasons why biodiversity is vital to human life and well-being, briefly describe global warming scenarios, present the results of data and models suggesting how many species are likely to go extinct in the near-future if steps are not taken to sharply decrease greenhouse gases, and conclude with suggestions for what needs to be done to ameliorate global climate change in a way that is compatible with minimizing biodiversity loss and maintaining the critical ecosystem functions that nature provides.

Importance of Biodiversity: Ecosystem Services Biodiversity and healthy ecosystems are vital to life and to human well-being. Biodiversity underlies everything from food production to medical advances. Humans, the world over, use at least 40,000 species of plants and animals on a daily basis [6]. Many people still depend on wild species for some or all of their food, shelter, and clothing. All of our domesticated plants and animals, including our closest companion the dog, came from wild-living ancestral species. Ecosystem services are the services provided for humans by natural ecosystems [7]. These ecosystem services can be divided into four major categories: supporting, regulating, provisioning, and cultural [3]. As an example, mature forests help regulate local and regional climates by contributing to rainfall and temperature in the areas they occupy. They do this in part by extracting carbon dioxide from the air and producing oxygen as a byproduct of photosynthesis. The health of ecosystems depends on having viable

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populations of the species that make up those ecosystems [8] and maintaining viable populations of plants and animals will require immediate and strong actions to limit global climate change and a commitment to biodiversity friendly land-use changes and conservation efforts.

Supporting Ecosystem Services These are the biogeochemical and biological processes underlying all other ecosystem processes, such as nutrient cycling, oxygen production, pollination, seed dispersal, primary productivity, and soil formation. Three of these are elaborated on in more detail below. Net primary productivity (NPP) is the amount of organic material generated through the process of photosynthesis. This underlies the capacity of all ecosystems to provide ecosystem services, as well as provisioning and regulating much of what humans use. Humans currently consume or forego about 35% of global terrestrial NPP (see > Fig. 15.2 for one example) [9–12]. Forego means that our altering of the natural environment

. Fig. 15.2 Maps of the human appropriation of net primary production (NPP), excluding humaninduced fires. (a) Land-use-induced reductions in NPP as a percentage of NPP0. (b) Total NPP as a percentage of NPP0. Blue (negative values) indicates increases of NPPact (a) or NPPt (b) over NPP0, green and yellow indicate low HANPP, and red to dark colors indicate medium to high HANPP. Reprinted from Fig. 1 of Ref. [12]

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diminishes the potential NPP of the planet, for example, by covering potentially productive land with asphalt and concrete, overgrazing and over-farming many formerly productive areas of the Earth’s surface until they become desert, and polluting many rivers and lakes. Thus, because we have already exceeded the carrying capacity of the planet the foundational productivity of the planet is slowly being eroded. Nitrogen is the single largest component of the Earth’s atmosphere. However, atmospheric nitrogen is unavailable for biological use, leading to a scarcity of usable nitrogen in many types of ecosystems. The nitrogen cycle is crucial for life on Earth and affects the rate of key ecosystem processes, including primary production and decomposition. Alteration of the nitrogen cycle by human activities is global and pervasive [13–16]. Human activities now convert more N2 from the atmosphere into reactive forms than all of the Earth’s terrestrial processes combined, mostly via the creation and use of fertilizers to enhance food production. Agricultural runoff and the burning of fossil fuels have boosted the supply of reactive nitrogen in the open oceans 50% above preindustrial levels. This excess nitrogen causes great harm to marine and freshwater ecosystems, contributes to global warming, and harms human health [13–16].

. Fig. 15.3 Iridescent green sweat bee (Agapostemon sp.) covered in pollen. Bees are the best known pollinators. Pollination by bees and other animals increases the quality and/or yield of harvests for 70% of leading global crops [113] (Photo courtesy of Jon Sullivan, pdphoto.org)

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. Fig. 15.4 Old-growth forests, such as the tropical rainforest around San Rafael Falls in Yasuni National Park (Ecuador) pictured below, provide a vast array of ecosystem services such as carbon storage and mitigation of climate change, micro- and macro-climate control, oxygen production, water purification, regeneration of nutrients, and maintenance of soils. They also provide food, fibers, timber, and other renewable resources for humans. Old-growth forests also contain a vast array of plants, animals, fungi species, along with their almost infinite variety of genes, which provide huge benefits to humans. The forests are also spectacularly beautiful

Pollination and seed dispersal of both domestic and wild plants is another essential ecosystem service provided free of charge by many diverse animal species. Approximately 80% of wild plants, and about 35% of the agricultural crop species that feed the world, require animal pollination for successful reproduction (> Fig. 15.3) [17, 114]. Similarly, without animal species acting as seed dispersers, many plants would fail to reproduce successfully. Animal seed dispersers, such as bears, birds, elephants, and monkeys play a central role in the structure and regeneration of forests [18–20]. Disruption of these complex services may leave large areas of forest devoid of seedlings and younger age classes of trees, and are thus unable to recover swiftly from human impacts such as land clearing. The great importance of forests will be expounded upon at several points in the chapter (> Fig. 15.4).

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In the United States alone, the agricultural value of wild pollinators is estimated in the billions of dollars per year. Meanwhile, the diversity of natural pollinators available to both wild and domesticated plants is diminishing and negative effects on plants clearly visible [21–23]. As an example of the value of pollinators, experiments preserving tropical forest fragments around coffee farms boosted crop yields roughly by 7%, as coffee plants near forested areas received twice as many visits from bees and produced 20% more coffee beans [24, 25].

Regulating Ecosystem Services Examples of regulating ecosystem services include climate regulation, flood regulation, nutrient retention, pest control, protection from soil erosion, and purification of both air and water. A few of these examples are elaborated on in greater detail below. Plants, trees in particular, have a major influence on local, regional, and even global climate. Approximately half of the annual rainfall in the Amazon basin is recycled by the forest itself. Extensive deforestation can dramatically reduce rainfall in a region, raise temperatures (via loss of shade and reduced evapotranspiration), increase fire frequency, and negatively affect agriculture and access to clean potable water [26–29]. According to the Intergovernmental Panel on Climate Change, and others, deforestation probably accounts for more than 20% of total anthropogenic carbon dioxide emissions [30]. Living trees extract carbon dioxide and other pollutants from the air, slowing the buildup of carbon dioxide in the atmosphere, while the burning of forests to clear land for agriculture releases large amounts of CO2 into the atmosphere, which contributes to global warming [31, 32]. The conversion of wetlands increases flooding rates, and deforestation of uplands and flood plains also increases the frequency and severity of flooding events, at least in some areas [33–36]. Wetlands store and slowly release surface water, rain, snowmelt, groundwater, and flood waters. Trees and other vegetation impede the movement of flood waters and distribute them more slowly over floodplains. This combined water storage and slowing action lowers flood heights and reduces soil erosion downstream and on adjacent lands. Preserving and restoring wetlands typically provides flood protection at a lower cost than dredging operations and levees and also serves as excellent wildlife habitat and carbon sinks. Flooding in Asia, Europe, and North America over the past several decades has claimed thousands of lives, destroyed hundreds of thousands of homes, and damaged more than 13 million hectares of farmland (> Fig. 15.5). Increased flooding rates along the Mississippi River are due to drainage of floodplain wetlands, the construction of levees, and the loss of beaver dams [32]. Though there are a number of factors impacting flooding severity and economic losses, it is worth noting that Missouri, Illinois, and Iowa suffered the most damage from the 1993 floods and all three have less than 15% of their original wetlands left [35]. Europe has seen a number of devastating floods over the past 15 years. For the River Meuse, an analysis suggests that landscape changes brought on by humans, especially deforestation and draining of wetlands are the primary causative agents for the

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. Fig. 15.5 Flooding in Thailand (2010) killed 232 people (top photo), flooding in Brazil (2011) killed 702 people (center photo), and flooding of the Mississippi River in the U.S. (2011) has killed at least 400 people (bottom photo is from Mississippi River flooding of 1993). Draining of wetlands, deforestation, and deleterious changes in rainfall patterns due to climate change will make floods like these more common in the future. (Center photo courtesy of Ageˆncia Brasil, permission does not imply that Ageˆncia Brasil endorses this use of their photo)

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increase in flooding, along with increased variability in rainfall [36]. Recent catastrophic flooding in Korea has been determined to be due to increased frequency of severe rainfall events with deforestation also contributing [37]. Note that the increases in severe rainfall events is a prediction of climate change models and their implication in recent flooding events is foreshadowing even more severe events in the future. In addition to inland flooding from rivers, coastal areas are also prone to flooding. Mangrove forests and coral reefs buffer the coast against ocean storm surges and prevent coastal erosion. The building of levees, along with the destruction of freshwater wetlands, contributed to the massive flooding of New Orleans following Hurricane Katrina [38]. Evidence suggests that mangrove forests are more effective than concrete sea walls in controlling floodwaters from tropical storms [39] and that areas with intact mangrove forests and/or coral reefs were less damaged during the Southeast Asian Tsunami of 2004 than areas without them [40–42]. However, both salt marshes and mangrove forests are rapidly being destroyed and coral reefs may be functionally extinct by 2050 due to climate change [43, 44]. Besides buffering from storms, coral reefs and mangrove forests harbor vast amounts of biodiversity and are among the most productive breeding grounds for commercially important fish. Studies have confirmed intense periods of soil erosion associated with the rise and subsequent decline of civilizations in the Middle East, Greece, Rome, Central and South America, as well as other regions around the world [45–49]. The high rates of soil erosion are due both to deforestation and agriculture [50–52]. When vegetation is removed, the rates of soil erosion increase rapidly. Clear cutting slopes lead to landslides that have killed tens of thousands of people across the world over the past few decades. Soil runoff into rivers and oceans kills freshwater and marine animals. Erosion and flooding can make the water supplies along rivers undrinkable. The UN Food and Agricultural Organization estimated that from 1990 to 1999, erosion damaged or destroyed more than 600,000 km [2] of the world’s cropland. In China, erosion has forced the abandonment of one third of all formerly arable land. China’s Loess Plateau was cleared of trees about 1,000 years ago, since then it has been eroding, causing 40% declines in agricultural output and flooding and landslides in the lower reaches of the river that killed thousands in 2010. Data from studies worldwide strongly suggest that erosion rates from conventionally plowed agricultural fields are 10–100 times greater than rates of soil production [52].

Provisioning Ecosystem Services Provisioning ecosystem services consist primarily of food, pharmaceuticals, and wood, but also include a number of other services such as use in biofuels, bioremediation of pollution, natural insecticides, and providing materials for building shelters and producing clothing. The focus of this section will be on food security and pharmaceuticals. It is obvious that humans rely on plants and other animals for food. For example, the world’s aquatic ecosystems are the leading source of animal protein for human

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consumption [53]. Three species of plant, wheat, corn, and rice provide about 60% of the calories humans consume. However, few realize the importance of biodiversity (both at the genetic and species level) for food security. The dangers of relying on genetically depauperate crops are illustrated by the Great Irish Potato Famine. Potatoes were introduced into Ireland from the New World and eventually most of the Irish people became dependent on this one crop. In 1845, the windborne Potato blight (Phytophthora infestans) spread throughout the country and caused almost complete failure of the potato crop over the next 3 years. It is estimated that at least one million people died of starvation and another million emigrated out of the country, reducing the population by 20–25%. The severity of the famine was greatly exacerbated by the lack of genetic variation in the potatoes, which made them particularly vulnerable to disease. More than a century later a wild relative of the potato would be discovered in Peru, that when hybridized with the standard crop plant, produces a variety of potato resistant to potato blight. Another wild potato species, Solanum fendleri, is used in breeding for resistance to a nematode species that attacks cultivated potatoes. A potato species from Mexico, Solanum bulbocastanum, has been used to genetically engineer the potato to resist new strains of the potato blight [54]. Despite evolutionary theory and history, much agriculture continues to depend on genetically uniform crops. For example, in most less-industrialized nations, more than half of the rice varieties come from a single mother plant. In the past century, about 75% of the genetic diversity of our most important domestic crops has been lost [55]. The widespread planting of a single corn variety contributed to the loss of over a billion dollars worth of corn in 1970, when the US crop was overwhelmed by a fungus (Bipolaris maydis). In 1991, the genetic similarity of Brazil’s orange trees made them easy targets for the worst outbreak of a citrus disease in the country’s history. And wild relatives of our domestic crops continue to come to the rescue of current food production. Agriculture and genetic resources are critically interdependent and agricultural production relies on continuing infusions of genetic resources from wild relatives for maintaining or increasing yield. A wild barley plant from Ethiopia (Hordeum bulbosum) provided a novel gene conferring complete resistance to the yellow dwarf virus that causes huge losses in barley, oats, wheat, maize, and rice worldwide. In the 1970s, an outbreak of grassy stunt virus decimated rice harvests across Asia. Scientists from the International Rice Research Institute screened 6,273 samples of rice plants looking for genetic resistance to the disease. They found it in a wild relative, Oryza nivara, which grows in India. The gene has been incorporated into most new rice varieties since the discovery. In fact, rice is protected from most major rice diseases and much more by genes brought in from at least a dozen wild species (> Table 15.1). The list of examples of wild species improving domesticated crops is very long, wild species genes contribute more than US$100 billion per year to profits from agriculture. Historically, agricultural varieties of cereals have had a life expectancy of only 5–10 years before diseases or insect pests evolve to take advantage of them and the crop must be replaced with a different genetic variety because the old one is no longer productive. With global climate change, increasing water shortages, increasing pollution,

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. Table 15.1 Introgression of genes from wild Oryza species into cultivated rice (Oryza sativa) Trait improved

Wild (donor) species

Grassy stunt resistance

O. nivara

Bacterial blight resistance

O. longistaminata O. officinalis O. minuta O. latifolia

Blast resistance Brown planthopper resistance

O. australiensis O. brachyantha O. minuta O. officinalis

Whitebacked planthopper resistance Cytoplasmic male sterility

O. minuta O. latifolia O. australiensis O. officinalis O. sativa f. spontanea

Tungro tolerance

O. perennis O. glumaepatula O. rufipogon O. rufipogon

Modified from Khush and Brar [56]

decreasing amounts of arable land, and increasing dispersal of insect pests and diseases, we need these wild species now more than ever. Unfortunately many of them have likely already gone extinct and thousands more face imminent extinction. In fact, not only have we tapped only a small amount of the genetic diversity within species already cultivated, we also only use a very small proportion of the edible species. About 30,000 species of plants are thought to be edible, but only about 150 are used as human food [57]. Of those species, only 15 species make up more than 90% of the food we eat. Genetic diversity is most important when environments are changing rapidly [58] and the environment may never have changed more rapidly during the history of life on Earth than it is changing right now. The pharmaceutical industry is very dependent on natural products (> Fig. 15.6). About a quarter of all prescription drugs in the USA (and up to 80% of pharmaceuticals in developing nations) are taken directly from plants and 73% of them are modeled on natural compounds [59–61]. These include artemisinin (antimalarial and a potential treatment for cancer), aspirin, atropine, codeine, cyclosporine (the immunosuppressive which transformed the field of human organ transplantation), digitalis, morphine, penicillin, pilocarpine (used to treat glaucoma), quinine (model for modern antimalarial

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. Fig. 15.6 Poison Dart Frogs, such as Dendrobates tinctorius and D. azureus shown above, may hold the key to improved pain-relief drugs and other medications. However, their habitat is rapidly disappearing

drugs), and warfarin. Most of these come from tropical forests, but less than 1% of rainforest plants have been tested for medicinal uses and at current rates of deforestation almost all rainforest will be gone within 40 years [62]. Several examples of potential cures, for diseases that kill hundreds of thousands of people, being lost or nearly lost due to the extinction of the plant or animal supplying it are available. In 1987, leaves were collected from Callophylum lanigerum in Malaysian Borneo. Years later, the National Cancer Institute determined that extract from the leaves completely stopped the replication of HIV-I [57]. A return trip was made to find the original tree, but the area had been clear cut and leaf samples from other C. lanigerum in the region failed to yield any of the original compound (calanolide). Luckily, a related species (C. teysmannii) also produced a slightly less potent anti-HIV drug called calanolide B. Calanolide B is currently in preclinical trials in the United States and seems to have low potential for cross-resistance with other therapies [63, 64].

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The gastric-brooding frogs consisted of only two species (Rheobatrachus vitellinus and R. silus), both native to Australia. The genus was unique because it contained the only known frog species that incubated tadpoles inside the stomach of the mother. Preliminary studies with gastric-brooding tadpoles demonstrated that the tadpoles secreted a substance, or substances, that both inhibits the secretion of stomach acids and prevents stomach emptying so that the tadpoles do not end up being digested by the mother. In the 1980s, both species became extinct, terminating studies which might have led to important new insights for treating human peptic ulcers [63]. The Pacific Yew tree (Taxus brevifolia) is a rare and slow-growing tree found only in old-growth forests of the Pacific Northwest, an area that is currently being logged under generous concessions to logging companies at US tax-payer’s expense. The tree also used to be the only source of a drug called paclitaxel, which appears to be very effective in treating ovarian cancer and has great promise for treating lung, prostrate, and breast cancer as well. Clinical trials were delayed for this drug as it takes six Pacific yew trees to extract enough paclitaxel to treat one patient and there were not that many trees. Fortunately, paclitaxel is now being produced by semi-synthetic conversion of precursor compounds found in a variety of yew trees [63]. Gastric-brooding frogs are not the only amphibians that produce(d) compounds of potential medical benefit to humans. The skin secretions of the phantasmal poison frog (Epipedobates tricolor), listed by the IUCN as endangered, yield a nonaddictive painkiller (epibatidine) that is 200 times stronger than opium and does not lead to tolerance [63]. Because of the very small difference between a therapeutic dose and a lethal dose, epibatidine has never been used in humans. However, research is under way to invent derivatives of epibatidine that are less toxic, but still have the desired qualities of being an extremely powerful and nonaddictive analgesic [65–67]. Epibatidine and other derivatives from the poisonous secretions of the frog are also being investigated for a number of other medical uses. In fact, 50 species within the family Dendrobatidae, many of which are critically endangered, have yielded 500 structurally complex compounds new to science and of medical interest [63, 68]. One drug investigated in clinical trials and a subject of much further research [68–73], tebanycline, was almost lost when one of the two sites of Ecuadorian forest from which the frog was originally collected were cleared for a banana plantation [74]. Amphibians as a whole are more endangered than any other group of vertebrates and more than 200 antimicrobial and antifungal compounds from the skin of frogs and toads have been discovered [62]. Given that the world now faces a severe problem due to the widespread resistance of pathogenic bacteria to multiple antibiotics, amphibian compounds can serve as powerful models for drug invention because they have novel forms of function. There has never been a comprehensive assessment of the risk of extinction for cone snail (Conus) species. However, 50% of the Earth’s coral reefs are close to collapse and at least 33% of mangrove habitat is already destroyed. These two habitats are the primary centers for cone snail diversity. Warming ocean temperatures, acidification of the ocean, coastal development, and direct exploitation of snails for their shells are all threats to this group. The species Conus magus produces a peptide that the commercial medication

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ziconotide is based on. It is about 1,000 times more powerful than morphine and relieves pain in 50% of advanced cancer and AIDS patients whose pain is unresponsive to opiates, and results in neither addiction nor tolerance [63]. At least seven other medicines derived from cone snail poisons are in clinical trials and others show promise for treatment of neurodegenerative diseases and epilepsy [63]. However, only about 100 of the estimated 70,000 cone snail toxins have been characterized [75]. Six species of bear are threatened with extinction, including a species I study, the Asian Black Bear (Ursus thibetanus) (> Fig. 15.7). The threats to bears are habitat destruction and fragmentation, direct harvesting, and global climate change. Several medical benefits have already arisen from the study of bears and others are being investigated [63]. For example, denning bears appear to produce a substance that inhibits cells that break down bone and promote substances that encourage bone and cartilage production; determining

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. Fig. 15.7 The Asiatic black bear (Ursus thibetanus) is one of six bear species threatened with extinction from sources as varied as habitat destruction, poaching, and climate change. Bears not only serve as important models for medical uses, but Asian black bears are important seed dispersers and polar bears (Ursus maritimus) are top carnivores helping to structure their ecosystems. The photo is of mother Asiatic black bear and her cub. The photograph was taken by remote camera in Khao Yai National Park, Thailand (Photo courtesy of Dusit Ngoprasert)

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the mode of action of these substances could lead to breakthroughs in treating osteoporosis and cartilage damage. Denning bears can survive for a period of 5 months or more without excreting their urinary wastes, whereas humans would die from the buildup of these toxic substances after only a few days. An estimated 1.5 million people worldwide are receiving treatment for end-stage renal disease, and the hope is that by studying bears, we may be able to learn how to treat them more effectively [75].

Cultural Services Biodiversity is worth conserving because it is beautiful, interesting, and provides inspiration to inventers, artists, and people all over the globe. Wild animals, plants, and natural areas contribute to our emotional and physical well-being [76]. Hundreds of millions of people visit natural areas or zoos each year and billions of dollars are spent on hunting, fishing, and nature tourism. Other living things have also contributed greatly to human progress by providing scientific and educational services that are usually overlooked. For example, most of what we know about genetic diseases in humans comes from studies on the fruit fly (Drosophila melanogaster) or the laboratory mouse/rat. Rats (Rattus norvegicus) have been used in many experimental studies, which have added to our understanding of disease processes, the effects of drugs, physiology, psychology, and genetics, and other topics in health and medicine.

Summary By this point you should be convinced that if all ecosystem services provided by Earth’s biodiversity were to stop, life on Earth would be impossible. Also, by this time it should be obvious that biodiversity makes a huge and undervalued contribution to the quality of life that humans enjoy. However, you might well say to yourself, We have already identified the organisms most valuable to humans and the species we rely on for food, and the ones that perform many of the more important ecosystem functions are in no danger of becoming extinct. This statement has some element of truth to it. However, it has two major weaknesses. First, we never know what species will turn out to be valuable in the future. Could you have predicted that discovery of a fluorescent protein from a bioluminescent species of jellyfish (Aequorea victoria) would be worthy of a 2008 Nobel Prize, a fungus (Amycolatopsis orientalis) found in soil samples from the rainforests of Borneo would yield the powerful antibiotic vancomycin, saliva from the canine hookworm (Ancylostoma caninum) would provide an anticoagulant (NAPc2) that has potential use in heart attack victims and the treatment of Ebola [63], ingredients from the venom of a pit viper Bothrops jaracara would yield a model for hypertension drugs, vincristine and vinblastine would be isolated from the rosy periwinkle plant (Catharanthus roseus) and increase the chances of remission to 99% in childhood leukemia and to 70% in Hodgkin’s disease,

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leech (Hirudo medicinalis) saliva would yield a powerful blood anticoagulant, the silk of a spider (Nephila clavipes) would prove useful in regenerating neurons [77], a bread mold (Penicillium notatum) would be the source of one of the most useful antibiotics and that other molds in the same genus would have statins isolated from them that may potentially reduce the risk of having a heart attack or stroke by 25% [62], the synthesis of the first effective antiretroviral drug AZT would be guided by compounds isolated from a sponge (Tethya crypta) [78], or that a revolution in the field of molecular biology would be achieved through isolation of a DNA polymerase from a bacterium (Thermus aquaticus) collected out of a Yellowstone hot spring? Thus, uncertainty surrounding the value of millions of yet undescribed species suggests that we should be cautious in our destruction of habitats and the short-sighted extirpation of species that have taken millions of years to evolve their specific characteristics. We also do not know how many species can be removed from an ecosystem before it collapses, though there is good evidence that such collapses will occur and the concomitant loss of ecosystem services [79, 80].

Impact of Global Climate Change on Biodiversity Current Rates and Causes of Extinction In the fossil record, an individual vertebrate (amphibian, bird, fish, mammal, or reptile) species lasts on average at least 1 million years before it becomes extinct. Thus, in an average year, no more than one out of one million species should go extinct. The current observed extinction rate since 1,600, for vertebrates, is 2.6 per 10,000 species per year. That is at least 260 times the background rate of extinction. At this rate, it would take less than 15,000 years to equal the extinction event that killed the dinosaurs over several million years. Further, because we know that the primary cause of modern extinctions is the loss, degradation, and fragmentation of habitat, and because we know the response to habitat loss is not linear, we expect that background rate to continue to increase and probably become an order of magnitude greater than it is currently [81, 82]. The reason for this increased and increasing rate of extinction is not difficult to fathom. Humans have been strongly implicated in global extinctions for tens of thousands of years [83, 84], but the current mass extinction is due to the fact that in the last 50 years we have used more of Earth’s resources than we have for the entire history of humanity before that point. We are losing topsoil at least ten times faster than it can be replaced [52], about 10% of the Earth’s agricultural land has become unfit for agriculture in the past 40 years while the population continues to expand, 80% of the world’s fish stocks for which assessment information is available are reported as fully exploited or overexploited, we are using more than 20% of the world’s renewable fresh water just for irrigation [85], and about 40% of the world’s rainforests have been lost in the past 50 years. The human population has increased from 3.0 to 6.9 billion during those same 50 years and we are expecting another two billion over the next 40 years.

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However, the current rate of extinction might pale compared to what anthropogenic climate change threatens [82, 83]. If we do not do something about climate change then all the money and the effort that has gone into saving species from extinction will likely be lost. This is particularly true because the current threat from habitat destruction and fragmentation interacts with climate change in a nonlinear way so that the negative impacts are greater than expected by looking at the threats independently.

Current and Future Rates of Global Climate Change Over the past century the Earth has warmed approximately 0.74 C, averaged over all land and ocean surfaces [30]. This warming of the Earth has clear effects on the species that live there. By the 1990s data started being published showing that 1,700 species had shifted their ranges an average of 6.1 km per decade toward the poles and that the timing of spring activities (e.g., breeding, migration, egg laying, flowering of plants) were occurring several days earlier each decade over the past 50 years. There is now a vast amount of data showing changes in the biology of plants and animals which are in accordance with expectations under a warming climate [85–91]. Predictions for the next century are for increases in average global temperature of anywhere from 1.1 C to 6.4 C [89], due mostly to unprecedented increases in the atmospheric concentrations of the three most important greenhouse gases, carbon dioxide, methane, and nitrous oxide. However, growth in emissions continues to far exceed expectations and it is possible that predicted increases in temperature are conservative. Further, temperatures are expected to increase for at least several centuries beyond this one, because of the half-life of CO2 in the atmosphere, loss of polar ice which reflects rather than absorbs the sun’s energy (Albedo effect), release of energy from the ocean into the atmosphere, and interactions between atmospheric warming and release of CO2 from sources such as melting permafrost. Another major impact of climate change includes effects on rainfall patterns and water storage. Rainfall is expected to become more variable with longer droughts and more flooding. Drought areas have more than doubled over the past 40 years [92]. In many parts of the world more precipitation will fall as rain instead of snow, snows at higher elevations will melt earlier, and this will cause deleterious changes in river flow. These changes are already causing a looming water crisis in the western USA [93]. Similarly, the Tibetan plateau and the Himalayas are sources for the five major rivers of Asia, all of which are vitally important to already threatened biodiversity and to 1.4 billion people. Changes in temperature and precipitation are expected to drastically alter snow melt patterns over the next 40 years, so that the Indus, Brahmaputra, and Mekong basins are likely to experience severe negative effects owing to the dependence on irrigated agriculture and meltwater in these areas [94, 95]. In terms of temperature, sea levels, and other climatic factors, we are headed towards conditions that have not existed for millions or probably tens of millions of years. Even the most rapid changes in the Earth’s climate that led to those conditions in the past took at least 100,000 years to occur, not a couple of centuries or less.

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Climate Change and Biodiversity There are three possible fates for populations and species making up the current biodiversity of Earth, in a rapidly changing environment: (1) Plants and animals can migrate in order to leave unfavorable environmental conditions in one area and take up residence in an area with environmental conditions that are more conducive to survival and reproduction. The evidence that plants and animals have migrated long distances during past warming and cooling periods over the past 250,000 years is irrefutable. We already see such movement in extant species and can expect to see much more in the future. (2) Adapt to changing conditions through selection on genetic diversity present or arising in the population during the period of climatic change. (3) Go extinct when some combination of the first two are not sufficient to keep the population or species extant. Over hundreds of millions of years, the Earth has experienced innumerable cooling and heating periods of different magnitudes and rates. Periods of rapid change are usually accompanied by increases in extinction rates. Projections of species extinction rates during the current period of global climate change are controversial because of uncertainty concerning how much the climate will change and how fast, because of methodological challenges especially concerning species ability to migrate through a human-dominated habitat matrix, and because of imperfect data from past extinctions. However, much is known and reasonable estimates can be made by looking at past extinctions under global climate change. An analysis of the fossil record over the past 520 million years provides a consistent relationship between global temperatures and biodiversity levels. During warm phases, extinction rates have been relatively high in both terrestrial and marine environments (> Fig. 15.8) [96]. Extinction rates may increase approximately 10% for every 1 C increase in temperature. The end-Permian event that caused the extinction of approximately 95% of all species on Earth was accompanied by a 6 C increase in global temperatures over a few million years [97, 112]. An increase in temperature of approximately 5 C over several million years caused a great loss of plant biodiversity in Greenland [96]. The biodiversity currently extant on Earth faces a much more difficult situation than does biodiversity during past periods of rapid climate change. There are two major reasons for this: (1) Species habitats are smaller than in the past. Smaller habitats support smaller populations which harbor less genetic diversity and have less evolutionary potential [58]. This evolutionary potential is critical for species’ ability to adapt to the changing environmental conditions. (2) Species habitats are more fragmented than in the past. The fragmentation prevents individuals from being able to shift their distribution in response to climate-related impacts as easily as in the past. Recall, these are the two fates available to species other than going extinct: adapt to climate change or migrate in response to climate change in order to track environmental conditions favorable to survival. The current rate of climate change is probably unprecedented and would present extreme challenges to the biota of the planet under normal circumstances [98]. However, the combination of the magnitude of change, the extreme fragmentation of habitats, and the fact that there are 6.9 billion people using a very large proportion of the Earth’s resources means that neither evolution nor migration will be sufficient to allow many species to cope with current rates of global climate change. They will go extinct and their value to humans and their beauty lost.

Impact of Climate Change on Biodiversity

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extinction rate

2

standardized residuals

4

1 0 −1 −2 −3 −2 −1 0 1 2 temperature

2

3

4

3

4

0

−2

a 3 2 1

standardized residuals

q

4

−1

2

−2 −3 −2 −1 0 1 2 temperature

0

−2 −500

b

0

−400

−300 −200 time (Myr)

−100

0

. Fig. 15.8 Increase in extinction rates, over the past 520 million years, with increases in temperature. (a) the per-taxon rate of extinction for families (Myr 1) using the maximum dating assumption and (b) the estimated per capita rate, q, of extinction (Myr 1) for marine animal genera. Rates and temperature were transformed, detrended and mean standardized. Closed circles and dashed lines represent temperature and open circles and continuous lines extinction rates. Large double open symbols represent periods of mass extinction, defined as the five largest positive extinction residuals (in order of decreasing age: end Ordovician; Late Devonian; end Permian; Early Triassic, end Cretaceous). Insets show the positive association between extinction rate and temperature residuals across the time series. (Reprinted with permission of the Proceedings of the Royal Society B. Fig. 3 from Ref. [97])

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Many of the extinction may not be due directly to global climate change alone. The interactions between climate change and other factors will likely be extremely important. Habitat destruction and conversion continues in Southeast Asia and the Amazon, both places where I have done research and both areas rich in biodiversity. The continued fragmentation and loss of these forested areas alone is cause for grave concern. However, when you factor in that destruction of forests in these areas further limits movement of species trying to track a changing environment and that this continues to fuel further climate change by dumping more CO2 into the atmosphere, it starts to appear catastrophic. Warmer temperatures will cause novel diseases to spread into naı¨ve populations and will act as a general stress causing species to be susceptible to diseases their immune systems once were able to fight. The interaction between global climate change and diseases is already manifest in the widespread extinction of amphibians [6]. Increases in the frequency of drought and the introduction of novel diseases form an almost perfect combination for driving populations extinct, as these are the two biggest causes for population collapse among vertebrates [99]. Temperature stress, and other forms of environmental stress incurred through climate change, will interact with declining population size and loss of genetic diversity in a way that makes populations more vulnerable than either factor independently [100–102]. Exactly how bad will it get? The prediction from a team of experts is that if temperatures increase by >3.5 C, 40–70% of plant and animal species will face extinction [103]. One prominent study suggests that about 25% of known plant and animal species will be committed to extinction by 2050 under current warming predictions (> Table 15.2) [104]. A recent study suggests that 20% of lizards may be extinct by 2080 as a direct result of increasing global temperatures [105]. Exact predictions are of course impossible, but the

. Table 15.2 Several million species of plant and animals face extinction due to global climate change, perhaps as early as 2050. Species most affected would be poor dispersers or those for which anthropogenic habitat fragmentation prevents dispersal and those with very narrow thermal tolerances and/or low genetic variation that prevent(s) evolution of new tolerances. The table below is based on the results of Thomas et al. 2007, who predicted extinction under different warming and movement scenarios. Migration rates are certainly somewhere between the extreme of no movement and the ability to track moving habitats perfectly, and current data suggests that warming trends will be close to the warmest predictions of Thomas et al. 2007. Consequently, 33% of known species may be doomed to extinction by 2050 Warming level

No movement

Perfect movement

Low Medium High

34% extinction 45% extinction 58% extinction

11% extinction 19% extinction 33% extinction

Impact of Climate Change on Biodiversity

15

combination of extremely rapid climate change, reduced population sizes, and fragmented habitats suggest that a very large proportion of Earth’s biodiversity (>50% of plants and animals) suffers a very high risk of extinction, particularly if definitive measures are not taken rapidly to ameliorate climate change. This level of species extinctions will be associated with an even larger percentage loss of populations and genetic diversity. This represents a very large proportion of the biodiversity and biological resources that humans need now more than ever.

Future Directions In order to stave off huge losses in biodiversity and to save vast amounts of human suffering, humans will have to change the way they live and use their boundless innovation to produce a high quality of life in a way that does not endanger the planet. The following are some urgent and important general suggestions for directions human societies need to head in to mitigate climate change: ● Limit land-use change and make intelligent choices in land-use changes that balance agriculture against biodiversity loss [106, 107]. This is especially urgent in tropical and subtropical regions, but also in boreal and temperate forests [108]. Zero-loss of oldgrowth forests must be the immediate goal and this be combined with reforestation. Manage forests more efficiently and create/enforce laws that protect forests from illegal logging and pillaging from corporations at the expense of the general populace. ● Aggressive climate change mitigation, including immediate implementation of existing cleaner energy technologies [109], increased research to develop cleaner energy sources, and immediate legislation to increase fuel efficiency for motor vehicles. ● Place a global cap on greenhouse gas emissions and sell permits up to that cap in a global auction. Use the profits to finance the other mitigation measures discussed. Include the economic price for land-use emissions [110]. Economic models must begin to include all costs associated with production of goods, governments must regulate rather than subsidize corporations and their impacts on the public, and people must hold their governments accountable for lack of enforcement or collusion with corporations. ● Stabilize and eventually reduce human population size through intense family planning, education, and a change in societal norms. ● Make human-dominated landscapes more hospitable to biodiversity. Reclamation of degraded lands and reintroduction of extirpated species. ● Education of people, especially in the rural tropics, concerning biodiversity and the value of nature. Shift in the education and reward systems of developed nations away from short-term profiteering and financial markets toward science, engineering, innovation, and longer-term good to society. ● Create space and opportunities for ecosystems to self-adapt and reorganize because novel climates without current analogs will appear [111].

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References 1. Reed DH (2010) Albatrosses, eagles, and newts, Oh My!: exceptions to the prevailing paradigm concerning genetic diversity and population viability? Anim Conserv 13:448–457 2. (1992) Convention on biological diversity. United Nations 3. Millennium Ecosystem Assessment (MEA) (2005) Ecosystems and human well-being: synthesis. Island Press, Washington, 155 pp 4. Pounds JA, Crump ML (1994) Amphibian declines and climate disturbance: the case of the golden toad and harlequin frog. Conserv Biol 8:72–85 5. Pounds JA, Bustamante MR, Coloma LA, Consuegra JA, Fogden MPL, Foster PN, La Marca E, Masters KL, Merino-Viteri A, Puschendorf R, Ron SR, Sa´nchez-Azofeifa GA, Still CJ, Young BE (2006) Widespread amphibian extinctions from epidemic disease driven by global warming. Nature 439:161–167 6. Primack RB (2002) Essentials of conservation biology, 3rd edn. Sinauer, Sunderland 7. Daily GC (1997) Nature’s Services: societal dependence on natural ecosystems. Island Press, Washington, DC 8. Reed DH, O’Grady JJ, Brook BW, Ballou JD, Frankham R (2003) Estimates of minimum viable population sizes for vertebrates and factors influencing those estimates. Biol Conserv 113:23–34 9. Vitousek PM, Ehrlich PR, Ehrlich AH, Matson PA (1986) Human appropriation of the products of photosynthesis. Bioscience 36:368–373 10. Rojstaczer S, Sterling SM, Moore NJ (2001) Human appropriation of photosynthesis products. Science 294:2549–2552 11. Imhoff ML, Bounoua L, Ricketts T, Loucks C, Harriss R, Lawrence WT (2004) Global patterns in human consumption of net primary production. Nature 429:870–873 12. Helmut H, Erb KH, Krausmann F, Gaube V, Bondeau A, Plutzar C, Gingrich S, Lucht W, Fischer-Kowalski M (2007) Quantifying and mapping the human appropriation of net primary production in earth’s terrestrial ecosystems. Proc Natl Acad Sci USA 104:12942–12947 13. Galloway JN, Cowling EB (2002) Reactive nitrogen and the world: two hundred years of change. Ambio 31:64–71

14. Gruber N, Galloway JN (2008) An earth system perspective of the global nitrogen cycle. Nature 451:293–296 15. Duce RA et al (2008) Impacts of atmospheric anthropogenic nitrogen on the open ocean. Science 320(5878):893–897 16. Galloway JN et al (2008) Transformation of the nitrogen cycle: recent trends, questions, and potential solutions. Science 320(5878):889–892 17. Klein AM, Vaissie´re B, Cane JH, SteffanDewenter I, Cunningham SA, Kremen C et al (2007) Importance of crop pollinators in changing landscapes for world crops. Proc R Soc Lond B Biol Sci 274:303–313 18. Lanner RM (1996) Made for each other: a symbiosis of birds and pines. Oxford University Press, New York 19. Nathan R, Muller-Landau HC (2000) Spatial patterns of seed dispersal, their determinants and consequences for recruitment. Trends Ecol Evol 15:278–285 20. Seidler TG, Plotkin JB (2007) Seed dispersal and spatial pattern in tropical trees. PLoS Biol 4(11): e344. doi:10.1371/journal.pbio.0040344 21. Buchmann SL, Nabhan GP (1996) The forgotten pollinators. Island Press, Washington, DC 22. Rodrı´guez-Cabal MA, Aizen MA, Novaro AJ (2007) Habitat fragmentation disrupts a plant-disperser mutualism in the temperate forest of South America. Biol Conserv 139:195–202 23. Anderson SH, Kelly D, Ladley JJ, Molloy S, Terry J (2011) Cascading effects of bird functional extinction reduce pollination and plant density. Science 331:1068–1071 24. Ricketts TH et al (2004) Economic value of tropical forest coffee production. Proc Natl Acad Sci USA 101:12579–12582 25. Ricketts TH et al (2004) Tropical forest fragments enhance pollinator activity in nearby coffee crops. Conserv Biol 18:1262–1271 26. Webb TJ et al (2005) Forest cover-rainfall relationships in a biodiversity hotspot: the Atlantic forest of Brazil. Ecol Appl 15:1968–1983 27. Werth D, Avissar R (2004) The regional evapotranspiration of the Amazon. J Hydrometeorol 5:100–109

Impact of Climate Change on Biodiversity 28. Lavelle P et al (2006) Nutrient cycling. In: Ecosystems and human well-being. Island Press, Washington, DC 29. Foley JA, Asner GP, Costa MH, Coe MT, DeFries R, Gibbs HK, Howard EA, Olson S, Patz J, Ramankutty N, Snyder P (2007) Amazonia revealed: forest degradation and loss of ecosystem goods and services in the Amazon Basin. Frontiers Ecol 5:25–32 30. IPCC (2007) Climate change 2007: the physical science basis. Contribution of working group I to the fourth assessment report of the intergovernmental panel on climate change. Cambridge University Press, Cambridge. http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter7.pdf 31. Korner C (2000) Biosphere responses to CO2 enrichment. Ecol Appl 10:1590–1619 32. Fearnside PM, Laurance WF (2004) Tropical deforestation and greenhouse-gas emissions. Ecol Appl 14:982–986 33. Hey DL, Philippi NS (1995) Flood reduction through wetland restoration – the upper Mississippi River basin as a case history. Restor Ecol 3:4–17 34. Bradshaw CJA, Sodi NS, Peh KSH, Brook BW (2007) Global evidence that deforestation amplifies flood risk and severity in the developing world. Glob Chang Biol 13:2379–2395 35. Ward PJ, Renssen H, Aerts JCJH, van Balen RT, Vandenberghe J (2008) Strong increases in flood frequency and discharge of the River Meuse over the late Holocene: impacts of long-term anthropogenic land use change and climate variability. Hydrol Earth Syst Sci 12(1):159–175 36. Chang H, Franczyk J, Kim C (2009) What is responsible for increasing flood risks? The case of Gangwon Province, Korea. Nat Hazard 48:339–354 37. U.S. Geological Survey (1999) National water summary on wetland resources. United States Geological Survey Water Supply Paper 2425. USGS, Reston 38. Stokstad E (2005) After Katrina: Louisiana’s wetlands struggle for survival. Science 310:1264–1266 39. Raven P, McNeely J (1998) Biological extinction: its scope and its meaning for us. In: Guruswamy L, McNeely J (eds) Protection of global biodiversity: converging strategies. Duke University Press, Durham

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40. Marris E (2005) Tsunami damage was enhanced by coral reef theft. Nature 436:1071 41. Kunkel CM, Hallberg RW, Oppenheimer M (2006) Coral reefs reduce tsunami impact in model simulations. Geophys Res Lett 33:23 42. Wells S, Kapos V (2006) Coral reefs and mangroves: implications from the tsunami one year on. Oryx 40:123–124 43. Carpenter KE et al (2008) One-third of reefbuilding corals face elevated extinction risk from climate change and local impacts. Science 321:560–563 44. Veron JEN, Hoegh-Guldberg O, Lenton TM, Lough JM, Obura DO, Pearce-Kelly P, Sheppard CRC, Spalding M, Stafford-Smith MG, Rogers AD (2009) The coral reef crisis: the critical importance of Figure 16.1 shows a schematic of a stratified lake including heat transfer components for the year-round water temperature model with typical temperature profiles in the summer open-water season and the winter ice cover period [23]. A lake is divided into a series of well-mixed horizontal water layers along its depth (> Fig. 16.1) because horizontal variations of water quality parameters are typically much smaller than in the vertical direction in a small stratified lake. The one-dimensional, dynamic heat transfer equation in a lake was solved for daily vertical water temperature profiles [24]:   @Tw 1 @ @Tw Hw Kz A ¼ ; þ A @z @t @z rCp

(16.1)

where Tw(z, t) ( C) is the water temperature in different horizontal layers, t (days) is the time, A (m2) is the horizontal area as a function of depth z (m), Kz (m2 day1) is the vertical turbulent heat diffusion coefficient, rcp (J m3  C1) represents heat capacity per unit volume and is the density of water (r) times heat capacity of water (cp), and Hw (J m3 day1) is the internal heat source strength per unit volume of water. Solar radiation absorption in the water column is the main contributor to the heat source term during the open-water season [18]. Heat exchange with the bottom sediment layer can be important in the shallow water layers [25]. Heat exchange between the lake and the atmosphere (climate conditions) is treated as a source/sink term (Hw = HSN + HA – HBR – HE – HC) for the topmost water layer of a lake during the open-water season. It includes incoming heat flux from net shortwave solar (HSN in > Fig. 16.1) and long-wave (HA) radiation and outgoing heat fluxes from back radiation (HBR), evaporation (HE), and convection (HC) related to wind speed (U). The heat budget components through the water surface are directly linked to climate parameters that are related to future climate changes. Heat fluxes received from shortwave solar radiation at the water surface and in the water column are computed as follows: HSN ¼ ð1  r ÞbHs

at

z ¼ 0 ðwater surfaceÞ

HSN ¼ ð1  r Þð1  bÞHs

at

z > 0;

(16.2) (16.3)

where Hs is the incoming shortwave solar radiation (kcal m2 day1), r is the reflection coefficient computed as a function of the angle of incidence and the concentration of suspended sediment in the surface layer [26], and b is the surface absorption factor set equal to 0.4. The attenuation of solar radiation with depth follows Beer’s law: HSN ðiÞ ¼ HSN ði  1Þ expðmDz Þ

(16.4)

Sediment

TA

U

HSED

HSN HA HBR HE

Open water season HC

Sediment

Water

Snow Ice

HSN HE

HC

Ice cover season

HSED

U

Temperature profile in winter

Sediment

TA T=0 °C

. Fig. 16.1 Schematic of a stratified lake showing heat transfer components for the year-round water temperature model including typical temperature profiles in summer and winter

Temperature profile in summer

T=0 °C

Meteorological forcing

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where HSN(i – 1) is the solar radiation at the top of a horizontal layer of water (kcal m2 day1), HSN(i) is the solar radiation at the bottom of the layer, Δz is the thickness of the layer (m), and m is the attenuation coefficient (m1) for solar radiation and light m ¼ mw þ mss SS þ mch Chla;

(16.5)

where mw is the attenuation coefficient of lake water (m1), mss is the specific attenuation coefficient due to suspended sediment [m1 (mg L1)1], SS is suspended inorganic sediment concentration (mg L1), mch is the attenuation coefficient due to phytoplankton expressed as chlorophyll-a (m1 (mg L1 Chla)1), and Chla is chlorophyll-a concentration (mg L1). Atmospheric long-wave radiation (HA) and back radiation from the water surface (HBR) are computed using the Stefan–Boltzmann law as functions of air temperature and surface water temperature, respectively. The emissivity of the atmosphere depends on cloud cover or sunshine percentage, but the emissivity of water is typically taken as a constant (0.97). Evaporative heat flux (HE) and convective heat flux (HC) across the water surface are calculated as follows: HE ¼ C1 f ðUw ÞðTws  Tair Þ

(16.6)

HC ¼ f ðUw Þðes  eair Þ;

(16.7)

where Tws and Tair are water surface temperature and air temperature, respectively; es and eair are saturation vapor pressures at the water surface and in the overlying air, respectively; f(Uw) is a wind function that defines the dependence of the heat transfer on wind velocity (Uw) over the water surface, and C1 is Bowen’s coefficient (0.47 mmHg C). During the ice cover period in cold regions, the model simulates thicknesses of snow and ice covers and sediment temperature profiles (heat conduction equation) first, then determines the heat source/sink terms, and finally solves the heat transfer > Eq. 16.1 to obtain water temperature profiles below the ice [23, 27, 28]. Lake water temperature characteristics are a function of lake geometry, trophic state, and climate conditions depending on latitude and elevation of a lake. Gorham and Boyce [29] examined the influence of lake surface area and depth on thermal stratification and the depth of the summer thermocline. Therefore, lakes are characterized by their size and depth (bathymetry) and by their productivity (trophic state) in the numerical lake simulation model, MINLAKE96. Lake surface area, maximum depth, horizontal area versus depth profiles, summer Secchi depth (SD), and summer chlorophyll concentrations are used as input to the MINLAKE96 lake model. Daily weather data is the basic but very important input for modeling of water quality dynamics in a lake using MINLAKE96. Daily meteorological data from the closest available weather station are typically used as atmospheric forcing boundary conditions for lake model simulations. Weather parameters used are daily air temperature, dew point temperature, solar radiation, wind speed, cloud cover or sunshine percentage, and precipitation (both rainfall and snowfall). Daily weather parameters are organized by weather station and year by year. Weather data from 209 weather stations in the contiguous USA were purchased from the

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Water temperature (°C) Water temperature (°C)

Solar and Meteorological Surface Observation Network (SAMSON) for the periods from 1961 to 1995. Weather data from 1995 to 2008 (more recent years) were downloaded from a web site of the National Climatic Data Center (NCDC) of the US Department of Commerce (ftp://ftp.ncdc.noaa.gov/pub/data/gsod/), at Asheville, North Carolina, and from the National Solar Radiation Data Base (NSRDB) (http://rredc.nrel.gov/solar/ old_data/nsrdb/1991-2005/). Solar radiation is only measured at a small number of weather stations in the contiguous USA, and most solar radiation data were modeled, for example, using SUNY model [30]. Only the SAMSON database provides sunshine percentage data; the NCDC web server does not. The sunshine percentages were estimated from solar radiation data for those stations and periods that had no sunshine percentage data using an algorithm developed for a reservoir water quality model [31]. The water temperature model was calibrated and validated against extensive daily Minnesota lake data (over 5,000 water temperature measurements for 48 ‘‘lake years’’) [2], and the average standard error between simulated and measured water temperatures year round was 1.4 C [32]. > Figure 16.2 shows time series of simulated and observed water temperatures at two depths (1.0 and 13.0 m below the surface) in Thrush Lake, Minnesota, from 1986 to 1991. Thrush Lake is a small and highly transparent lake, located about 20 km northwest of Grand Marais, Minnesota. The lake has a surface area of 66,200 m2 and a maximum depth of 14.6 m. > Figure 16.2 illustrates the seasonal change of water temperature near the surface (1.0 m) and near the lake bottom (13.0 m). Measured and simulated water temperatures near the lake surface respond to variations of weather with season every year; a strong thermal stratification develops in Thrush Lake every summer. Measured and simulated water temperatures near the lake bottom vary from 4 C in winter 30

At 1.0 meter depth

20 10 0 30 Measured 20

At 13.0 meter depth

Simulated

10 0 A J A O D F A J A O D F A J A O D F A J A O D F A J A O D F A J A O D 1986 1987 1988 1989 1990 1991

. Fig. 16.2 Time-series plots (1986–1991) of simulated and observed water temperatures at 1.0 and 13.0 m depths for Thrush Lake in Minnesota

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to about 7 C in summer; they have much smaller variations with season (> Fig. 16.2) than surface waters because of the attenuation of solar radiation with water depth and lack of vertical mixing. Potential effects of global climate change on four lakes in Wisconsin (Trout, Sparkling, and Crystal lakes, and Lake Mendota) were studied using another physics-based lake model, DYRESM, for 1
CO2 (past or present climate conditions) and 2
CO2 (doubling concentration of carbon dioxide – projected future condition) climate scenarios [6]. The average of the mean annual absolute error between simulated and measured water temperatures was 1.54 C for 12 base-year (1
CO2) simulations [6]. Mean water temperature was projected to be 1–7 C warmer, maximum surface water temperature increased by Fig. 16.3) in the contiguous USA. Longitude of the stations ranged from 68o010 W to 124o330 W and latitude from 25o480 N to 48o340 N. Elevations of weather stations above the mean sea level ranged from 2 m in coastal areas (Miami, FL) to 2,135 m in mountainous areas (Tucson, AZ). It was assumed that the lakes simulated had similar elevations as the weather stations used. To study the response of lakes to climate change on a continental scale, 27 types of lakes were chosen and investigated. Not all these lakes simulated actually exist at all 209 locations investigated. In many locations they are hypothetical lakes. However, this generic approach gives a good picture of how different lake types may behave in different parts of the country, especially under a 2
CO2 climate scenario for which there are no lake data. The study of ‘‘real’’ lakes found in different parts of the country under different climate conditions (based on elevation and geographic location) is certainly indispensable, but the records may be inconclusive to show how ‘‘real’’ lakes will respond to climate change. It may also be uncertain how the observed results can be transferred from one ‘‘real’’ lake to another. For these reasons the study of generic lake types is of value and an illustrative supplement to the study of individual real lakes. Lake surface areas AS chosen for the 27 lake types were 0.2, 1.7, and 10.0 km2 for small, medium, and large lakes, respectively. Lake maximum depths Hmax chosen were 4.0, 13.0,

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Projected increase of mean annual air temperature (°C)

5.5

6.5

6.

4 .0

4.5 0

5.0

6. 0

5.0

5.5 3. 5

5

4. Weather stations

3.0

2.5

4.0

CCC GCM grid center points

. Fig. 16.3 Locations of 209 weather stations (dots) and grid center points (crosses) of the 2
CO2 Canadian Climate Center General Circulation Model (CCC GCM 2.0) used in the simulations of 27 lake types in the contiguous USA. Increases of mean annual air temperatures projected by the CCC GCM 2.0 for a doubling of atmospheric carbon dioxide (2
CO2 climate scenario) are shown as isotherms

and 24.0 m for shallow, medium-depth, and deep lakes, respectively. With these numbers one obtains nine lake types ranging from relatively large and shallow lakes to relatively small and deep lakes. These numerical specifications are arbitrary but cover the range of lakes found in Minnesota [2] based on an in-depth data analysis of lake geometry characteristics of 3,002 lakes in Minnesota. More important than the geometric characteristics of individual lakes is the observation that the likelihood of a strong or weak stratification in a lake can be related to the lake geometry ratio: GR = AS0.25 Hmax1 [29]. The power factor 0.25 of surface area (AS) in the lake geometry ratio was developed by Gorham and Boyce [29] to estimate the depth of the thermocline of stratified lakes as a function of surface area, wind shear stress, and density difference. The above nine types of lakes defined cover geometry ratios from 0.9 to 14.1. According to Gorham and Boyce [29], polymictic behavior occurs at high numbers of the geometry ratio, while strongly stratified (dimictic) lakes have the lowest numbers. The transition occurs between 3 and 5. Hence, the full range of stratification behavior is included in the lake types selected for regional study [2]. Secchi depth was used to represent both the trophic state and the radiation attenuation of a lake. Secchi depths [37] of 1.2, 2.5, and 4.5 m for eutrophic, mesotrophic, and oligotrophic lakes were selected, respectively, based on analysis of lake survey data for 3,002 lakes in Minnesota. Therefore, the 27 ‘‘generic’’ lake types were characterized by combining three different lake surface areas, three lake maximum depths, and three Secchi depths (3
3
3).

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To project potential effects of climate change on lake water temperatures, projected changes in climate conditions were obtained from the output of the Canadian Climate Center Global Circulation Model (CCC GCM 2.0) [38] for a doubling of atmospheric CO2. The monthly increments or ratios of weather parameter values (between the 2
CO2 and the 1
CO2 climate scenarios) were applied to measured past climate conditions from 1961 to 1979 following a protocol proposed by the US Environmental Protection Agency [39]. Results of simulated water temperature characteristics of lakes in the contiguous USA were obtained for both the past 1
CO2 and the projected 2
CO2 climate scenarios [15]. Differences of water temperature characteristics between the projected and the past climate conditions were plotted on maps of the USA and other graphs. At the 209 locations (> Fig. 16.3) investigated in the contiguous USA, the annual maxima of daily surface water temperatures range from 19.6 C to 32.8 C

. Fig. 16.4 Past and projected changes (2
CO2 – PAST) of simulated maximum water temperatures near the surface of small lakes in the contiguous USA

Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

16

(> Fig. 16.4, top) and 22.9 C to 35.6 C under past (1962–1979) climate condition and a 2
CO2 GCM 2.0 climate scenario, respectively [15]. Geographic latitude has a strong influence on maximum surface water temperatures; the simulated difference from the northern to the southern border of the contiguous USA was 13 C. Climate change is projected to cause an increase on the order of 2–4 C in maximum surface water temperatures (> Fig. 16.4, bottom); the largest local change was by 5.2 C. Deep lakes (24 m) have slightly higher (2–3 C) minimum surface water temperatures than shallow lakes (4 m) under a 2
CO2 climate scenario. Up to 5.1 C increase in minimum surface or bottom water temperatures in southern latitude lakes is projected. Because the minimum surface and bottom water temperatures occur just before ice formation in northern lakes, they will be the same (between 0 C and 4 C dependent on the lake depth) after climate warming, but the time of occurrence for the minimum temperatures will be delayed [15]. The water temperature at the bottom of a lake, unlike surface water temperature, is not directly related to meteorological forcing, especially in deeper lakes. The simulated daily 1 maximum bottom temperatures increase strongly with the lake geometry ratio A0:25 Hmax S
0:25 1 or stratification strength. In a well-mixed lake AS Hmax > 8 maximum surface and bottom temperature are the same and strongly dependent on geographic location (> Fig. 16.4). In seasonally stratified lakes, maximum bottom temperatures range from about 6 C (e.g., in Duluth, MN; Boulder, CO; and Charleston, West VA) to 10 C (e.g., in Austin, TX) under past climate condition [15]. Climate change is projected to increase maximum bottom temperatures by a mean value of 2.6 C; a local maximum of 7 C occurs in deep stratified lakes near Glasgow, Montana. The maximum difference between surface and bottom water temperatures of a lake is an indicator of the strength of temperature and density stratification, for example, the strongest temperature stratification in lakes near Duluth (MN) and Austin (TX) is on the order of 19 C (see > Fig. 16.2 for Thrush Lake) and 22 C, respectively. In stratified lakes, this difference is projected to increase by 1–2 C with a local maximum of 3.2 C due to climate warming [40]. An open-water stratification ratio is defined as the total number of days when stratification stronger than 1 C exists, divided by 365 days. For very small and deep lakes in the southern USA, represented by lake geometry ratios less than 1.0, the open-water seasonal stratification ratio can be close to 1.0, which indicates that overturn and isothermal conditions last only a very short period of time. Increases of the seasonal stratification ratio with the projected 2
CO2 climate scenario range from 5% (18 days) to 15% (55 days) with a local maximum of 18% (66 days near Flagstaff, AZ). The changes are toward a longer stratification season under climate warming. This may cause serious ecological changes, for example, due to more frequent dissolved oxygen depletion in the lower hypolimnion, and consequences for fish survival.

Impacts on Ice Covers of Lakes Lake ice is not only a strong indicator of climate change but also very important to lake ecosystem in cold regions all over the world. Lake ice characteristics such as ice cover

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Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

duration, ice-on/ice-off dates, and ice thickness have a profound effect on lake ecology due to their influence on water temperature, water column stability, nutrient concentrations, gas exchange, and light availability. Ice thickness and structure are important factors explaining radiation distribution and availability through the ice cover season. Effects of ice cover duration are particularly pronounced at high latitudes where the ice-free period is relatively short. Under the ice cover the water column is typically (weakly) stratified, producing nutrient dynamics with strong vertical gradients with warmer, nutrient-rich water near the lake bottom. Any variation in the length of the ice cover duration will represent a change in nutrient availability: less time for anaerobic mineralization processes that may take place in winter would lead to a reduction in nutrients [41]. Pivovarov [42] and Ashton [43] reviewed the thermal regimes of lake ice. Prior to ice formation, there are three stages of cooling in a lake: (1) the lake becomes isothermal at about 4 C, (2) the surface water cools until it freezes as an inverse temperature stratification forms, and (3) latent heat is removed [27]. Ice will form first in calm areas, for example, on small lakes and sheltered bays. Daytime heating can break up an initial ice cover several times before it is established for the season [44]. In very windy conditions, the primary ice may be in the form of congealed floating slush. Snow may also create a surface slush layer if water temperatures are amenable [45]. Ice growth on the bottom of the initial ice cover occurs as a result of heat conducted from the relatively warm ice–water interface through the ice to the colder ice–air interface (see > Fig. 16.1 for ice cover season). Ice formed by this process is clear with columnar grains and is commonly referred to as ‘‘black’’ ice [45]. As a snowpack develops on the ice, its weight may sink the ice and move the free water level above the top of the ice surface. The lake water seeps up and saturates the snow, which freezes to create what is often referred to as ‘‘white’’ ice [45]. In spring, ice decays by melting and mechanical disintegration. Ice melting is largely caused by shortwave radiation penetration into the ice, long-wave radiation and turbulent heat fluxes from the atmosphere, and heat transfer from adjacent and lower water [46]. Projected climate change is expected to change aquatic/hydrologic systems strongly in cold regions. Assel and Robertson [47] demonstrated a strong correlation between change in winter air temperature and regional long-term (1851–1993) lake-ice records (freeze-up and breakup dates and duration of ice cover) from Lake Mendota in Wisconsin and Grand Traverse Bay of Lake Michigan. Ice breakup dates from 1968 to 1988 were examined for 20 Wisconsin lakes [48], and it was found that each ice record had a trend toward earlier breakup dates, indicating a recent warming trend. Long-term observations of ice covers in cold regions are still fairly sparse [49]. Therefore, model predictions of ice cover characteristics of lakes in the contiguous USA as a function of latitude, elevation, and climate conditions are valuable. Numerical models for simulating ice/snow cover were developed for Minnesota lakes [28], three Wisconsin lakes [50], an arctic lake [51], and for small north temperate lakes [23]. During the ice cover period, the MINLAKE96 model uses a stacked layer system that consists of lake sediments, water, ice cover, and snow cover (> Fig. 16.1). The snow cover forms on the ice surface of a lake and is typically thinner than direct accumulation of snowfall due to wind drift and compaction; a compacting factor (0.2– 0.4) is used before adding fresh snow to an existing snow pack [52]. The snow melting is

Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

16

calculated in response to internal solar radiation absorption (HSN in > Fig. 16.1), convective heat transfer (HC), evaporation (HE), and rainfall. The growth or decay of ice at the bottom of the ice cover is calculated using the heat conduction equation [28]:   ddi Tm  Tair @T ri li ¼ þ kw ; (16.8) @z z¼0 dt ðdi =ki Þ þ ðds =ks Þ þ ð1=hsa Þ where ri is density of ice, di is ice thickness, ds is snow thickness, li is latent heat of fusion of ice, ki and ks are thermal conductivity of ice and snow, Tm and Tair are temperatures at the ice–water interface (0 C) and of air, respectively, hsa is a bulk heat transfer coefficient at the snow–air interface and is a function of wind speed, kw is the turbulent conductive heat transfer coefficient of water under the ice layer, and ∂T/∂z is the water temperature gradient near the ice–water interface (z = 0). The ice decay rate at the top of the ice layer is calculated considering rainfall, surface heating, and internal absorption of solar radiation. Parameters and coefficient values used in the hydrothermal MINLAKE96 model are listed in . Table 16.1 Parameter and coefficient values used in the water temperature model (> Eq. 16.1) Coefficients and symbols

Units

Range and references

Open-water season – 0.4 [53] Radiation absorption for water bw Sediment specific heat Cpsed kcal kg1  C1 0.2–0.3 [54] Sediment thermal conductivity ksed kcal day1  C1 m1 8.64–51.8 [54]

Selected value 0.4 0.28 19.25

Radiation attenuation by Chla Radiation attenuation by water Sediment density Wind sheltering

mch mw rsed Wstr

m2 g1 Chla m1 kg m3 –

0.2–31.5 [55] 0.33–1.03 [56] 1,650–2,300 [54] 0.01–1.0 [57]

20.0 0.51 1,970 Varies

Winter ice cover season Surface reflectivity for ice Surface reflectivity for snow Radiation absorption for ice

ai asw bi

– – –

0.55 [58] 0.4–0.95 [59] 0.17–0.32 [60]

0.55 0.80 0.17

Radiation absorption for snow Snow compaction Ice thermal conductivity Snow thermal conductivity

bsw csw ki ksw

– – kcal day1  C1 m1 kcal day1  C1 m1

0.17–0.34 [61] 0.125–0.5 [59] 45.8 [54] 2.16 [54]

0.34 0.4 53.6 5.57

Ice density Snow density Radiation attenuation by ice Radiation attenuation by snow Ice latent heat of fusion

ri rsw mi msw li

kg m3 kg m3 m1 m1 kcal kg1

920 [54] 100–400 [59] 1.6–7.0 [42] 20–40 [62] 80 [43]

920.0 300.0 1.6 40.0 80.0

Snow latent heat of fusion

lsw

kcal kg1

80 [43]

80.0

543

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Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

Table 16.1 including ranges and references. Standard errors between simulated and measured values were 0.07 m for snow depths and 0.12 m for ice thicknesses for longterm simulations (128 ice/snow measurements over 8 years) [23]. Heat exchange between lake bottom sediments and overlaying water is very important in shallow lakes and in lakes with ice covers and has been included in each water layer in the MINLAKE96 model (HSED in > Fig. 16.1). To make projections of ice cover characteristics for lakes, a new, process-descriptive algorithm, which replaced previous empirical and lake size dependent criteria for the date of ice formation, was developed and incorporated in the model [27]. The new algorithm uses a full heat budget equation to estimate surface cooling, quantifies the effect of forced convective (wind) mixing and includes the latent heat removed by ice formation. The algorithm has a fine (0.02 m) spatial resolution near the water surface where temperature gradients before freeze-over are the greatest. Predicted freeze-over dates were compared with observations in nine Minnesota lakes for multiple (1–36) years [27]. The difference between the simulated and observed ice formation dates was less than 6 days for all lakes studied. Fang and Stefan [36] simulated potential climate warming effects on ice and snow covers on small lakes in the contiguous USA. The results indicate that there will be a substantial decrease in locations where ice cover is predicted to form on lakes every year. Under the 2
CO2 CCC GCM 2.0 climate scenario, lake ice covers are projected to form every year only in eastern Montana, North Dakota, Minnesota, Wisconsin, Vermont, New Hampshire, and Maine in the contiguous USA. Under past climate (1962–1979), the duration (cumulative days) of ice cover is up to 165 days near the northern border of the contiguous USA. Projected duration is reduced to less than 125 days under the 2
CO2 CCC GCM 2.0 climate scenario (> Fig. 16.5). The duration of ice cover is projected to shorten by up to 89 days; it will shorten by a mean value of 45 days due to climate warming. Climate change is projected to delay ice formation by up to 40 days. Climate >

. Fig. 16.5 Projected total number of days with lake ice cover in medium-depth lakes over the contiguous USA under a 2
CO2 future climate scenario (CCC GCM 2.0)

Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

16

warming also forces ice on a lake to melt earlier; differences between projected and past climate scenarios for the earliest ice-out date are up to 67 days; the mean value is 37 days for the country [36]. Under the 2
CO2 CCC GCM 2.0 climatic scenario, average maximum ice thicknesses are projected to be reduced by up to 0.44 m due to climate warming; the mean value is 0.21 m for the contiguous USA. These changes during the winter would eliminate fish winterkill in most shallow lakes [16], but may cause hazardous conditions for snowmobiles and fishermen because of reduced bearing capacity of lake ice. Hostetler and Giorgio [34] simulated ice and snow covers in Yellowstone Lake under past climate and 2
CO2 climate scenarios, and a reduction of the ice cover period by about 44 days was projected. Gao and Stefan [63] developed a series of regression equations for lake ice cover characteristics and climatic and lake geometry parameters. They showed that mean air temperature from October to December has a strong correlation with the latest ice-in date; mean air temperature from February to April has a good regression relation to earliest ice-out date, and maximum ice thickness shows a strong relationship to mean air temperature from October to March [63]. Gao and Stefan [64] studied potential climate change effects on ice-on and ice-off dates, ice cover duration, and ice thicknesses for four lakes in the USA and one lake in Canada using MINLAKE96 with minor modification of daily albedo for ice and snow cover. Projected ice cover durations are 25–33 days shorter and ice thicknesses are 0.18–0.3 m thinner under a 2
CO2 climate scenario. Dependence of lake ice cover characteristics (historical observations or records) on climatic, geographic, and bathymetric variables was studied for 143 North American freshwater lakes by Williams, Layman, and Stefan [65]. Their study concluded that a 1 C rise in average air temperature could result in a 5 days later ice-in date, 6 days earlier ice-out date, 11 days reduction on ice cover duration, and 7 cm reduction on the maximum ice thickness [65].

Impacts on Lake Dissolved Oxygen Dissolved oxygen (DO) concentration is viewed as perhaps one of the most important lake water quality parameters that indicate the overall ecological health of a water body. The DO concentration in different horizontal layers or at different depths of a lake (> Fig. 16.6) is the result of a mass balance between reaeration at the lake water surface and photosynthetic oxygen production (source), oxygen consumption by sedimentary oxygen demand (SOD), water column biochemical oxygen demand (BOD), and plant respiration, as well as mass transport mechanisms in a lake. The numerical simulation model (MINLAKE96) for daily DO profiles in a lake solves the one-dimensional, dynamic transport equation:   @C 1 @ @C Sb @A T 20 ¼ AKZ y þ PMAX yTp 20 Min½L Chla  @ t A @z @z A @z s (16.9) 1 T 20 T 20 kr y r Chla  kb yb BOD;  YCHO2

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Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

Meteorological forcing

Open water season DO = 0mg/l

O2

Ice cover season DO = 0mg/l

Fs

Ua

Phytoplankton P (Chl-a)

Snow Ice R BOD SOD

Water

Phytoplankton P (Chl-a) WODR

R=0

Sediment Sediment

DO profile in summer Oxygen source

Sediment

Oxygen sink

DO profile in winter

. Fig. 16.6 Schematic of a stratified lake showing oxygen sources/sinks for the year-round DO model including typical DO profiles in summer and winter

where C(z, t) is the DO concentration in mg L1 as a function of depth (z) and time (t), A(z) is the lake horizontal area in m2, Kz(z, t) is the DO vertical turbulent diffusion coefficient in m2 day1, Sb is the coefficient for sedimentary oxygen demand at 20 C in mg O2 m2 day1, PMAX is the maximum specific oxygen production rate (photosynthesis) by aquatic plants at 20 C under saturating light conditions in mg O2 (mg Chla)1 day1, Min[L] is the light limitation determined by Haldane kinetics [66], Chla is the chlorophyll-a concentration in mg L1 to represent biomass of aquatic plants, YCHO2 is the yield coefficient, i.e., the ratio of mg chlorophyll-a to mg oxygen, kb and kr are the firstorder decay rate coefficients for BOD and plant respiration (day1), respectively, ys, yp, yb and yr are the temperature adjustment coefficients for SOD, photosynthesis, BOD, and plant respiration, BOD is the biochemical oxygen demand concentration in mg L1, and T(z, t) is the water temperature in  C. Diffusive oxygen flux at the lake bottom is set equal to zero as a boundary condition. The rates of most reactions in natural waters increase with temperature [8]. A more rigorous quantification of the temperature dependence is provided by the Arrhenius equation [8]. In water quality modeling, many reaction constants (e.g., kb and kr) are reported at 20 C. Therefore, the reaction rate, k(T), at any temperature T, is usually expressed as kðT Þ ¼ k ð20ÞyT 20 ¼ k ð20Þe ðT20Þ=Tre [8], where T  20 ( K or  C) used above and in > Eq. 16.9 is the difference in temperature that is identical whether an absolute or a centigrade scale is used and Tre in  K is derived from the Arrhenius equation and related to activation energy, gas constant, and reference temperature. Oxygen production by photosynthesis is associated with the growth process of plants containing chlorophyll-a. It depends on three principal external conditions: (1) temperature, (2) solar radiation, and (3) available nutrients. In the lake model, photosynthesis is assumed to be a first-order kinetic process limited by light and biomass of aquatic plants (Chla). In the model, chlorophyll-a is specified by a mean annual value which depends on the specified trophic state of a lake and a function that calculates typical seasonal

Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

16

chlorophyll cycles [67] based on observational data from 56 lakes and reservoirs in Europe and North America [68]. Sedimentary oxygen demand (SOD) is treated as a sink term for each water layer, because each water layer is in contact with sediments. Biochemical oxygen demand occurs in the water column along all water depths, and plant respiration for all water layers is a function of chlorophyll-a concentration. Two-film theory and surface renewal models are widely used to describe gas transfer in natural waters [8], and various formulas have been developed to predict surface reaeration. In the MINLAKE96 model, the oxygen transfer rate through the lake water surface (Fs) is expressed as follows: Fs ¼

ke ðCs  CÞ ; D zs

(16.10)

where Cs, Dzs , and ke are the saturated DO concentration at the surface water temperature, thickness of the surface layer (m), and the surface oxygen transfer coefficient calculated as a function of wind speed [69], respectively. The oxygen transfer rate (Fs) is treated as an oxygen source or sink term in the topmost water layer of a lake. Secondary effects of atmospheric CO2 increases on photosynthesis, for example, through pH changes are not included in the model. > Equation 16.9 is solved numerically for time steps of 1 day and layer thicknesses from 0.02 m (near the ice–water interface) to 1.0 m (when z > 1.0 m) for small lakes using an implicit finite difference scheme and a Gaussian elimination method. The DO model coefficient and parameter values are summarized in > Table 16.2. For the simulation of DO in lakes of cold regions (> Fig. 16.1), modifications must be made in > Eq. 16.9 to account for an ice cover and low water temperatures. These modifications include: (a) reaeration is zero (ke in > Eq. 16.10 is set equal to zero) because the lake ice cover prevents any significant gas exchange between the atmosphere and the water body; (b) oxygen consumption by plant respiration is very small and is not presented as a separate sink term (kr in > Eq. 16.9 is set equal to zero) because, in winter, chlorophyll-a concentrations are fairly small [74] and low water temperatures keep plant respiration rates low; (c) BOD in > Eq. 16.9 is replaced with water column oxygen demand by detrital and other matter (WOD), and WOD is set constant at 0.01 g O2 m3 day1) regardless of trophic status of a lake [75]; and (d) sedimentary oxygen demand (Sb) is made dependent on trophic state and set equal to 0.226, 0.152, and 0.075 (g O2 m2 day1) for eutrophic, mesotrophic, and oligotrophic lakes, respectively, based on field studies summarized by Barica and Mathias [76] in ice-covered temperate zone lakes in Canada. During the winter months when irradiance is naturally low and light attenuation in snow and ice covers can be very strong, photosynthesis in ice- and snowcovered lakes is assumed to be predominantly light limited. DO concentrations were simulated after water temperature and snow/ice covers had been simulated. The year-round results of daily DO simulations obtained with the model were tested against extensive DO measurements in Minnesota lakes for a total of 48 ‘‘lake years’’ [77]. Average standard error between year-round simulations and measurements for 5,378 data pairs of dissolved oxygen concentrations was 1.94 mg L1. In a recent investigation of potential refuge lakes for cisco (a cold-water fish species), DO profiles in

547

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Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

. Table 16.2 Parameters and coefficient values in the dissolved oxygen model (> Eq. 16.9) [67] Coefficients and symbols

Units

Range and references

Selected value

Independent of trophic status BOD decay coefficient Respiration rate coefficient BOD temperature adjustment Photosynthesis temperature adjustment Respiration temperature adjustment Sediment temperature adjustment

kb kr

day1 day1

0.02–3.4 [70] 0.05–0.5 [70]

0.1 0.1

yb

–

1.047 [70]

1.047

yp

–

1.066 [21]

1.036

yr

–

1.045 [71], 1.047 [57]

1.047

1.034–1.13 [72]

1.065

Respiration ratio Water column oxygen demand during winter

0.0083 [73] YCHO2 – 3 1 WOD g m day 0.01

ys

0.0083 0.01

Coefficients and symbols

Units

Eutrophic

Mesotrophic

Dependent on trophic status Oxygen equivalent BOD

mg L1

1.0

0.5

Chlorophyll-a Sedimentary oxygen demand

15 6 mg m3 2 1 g m day 1.0 0.5 Hmax = 24 m Hmax = 24 m

2 0.2 Hmax = 24 m

0.75 Hmax = 13 m 1.0 Hmax = 4 m

0.4 Hmax = 13 m 0.5 Hmax = 4 m

0.152

0.075

Chla Sb20

1.5 Hmax = 13 m 2.0 Hmax = 4 m Sedimentary oxygen demand during winter

Sb

g m2 day1 0.226

Oligotrophic 0.2

Hmax = 4 m = shallow lake; Hmax = 13 m = medium depth; Hmax = 24 m = deep lake

28 additional lakes in Minnesota were simulated with an average standard error of 1.49 mg L1 for 7,581 data pairs over 487 days with measurements. During the winter ice cover period alone the average standard error between measured and simulated DO concentrations was 2.6 mg L1 [77]. Errors are due to under- or overestimated photosynthetic oxygen production during the ice cover period. This is related largely to the difficulty in predicting photosynthetically active radiation (PAR) available under the ice cover when a thin snow cover controls light penetration. > Figure 16.7 shows examples of measured and simulated profiles of water temperature and DO concentrations in Bear Head Lake in northern Minnesota. Stratification

Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

16

0 Bear Head Lake

2

June 07, 2008

Depth (m)

4

Aug 11, 2008

6 8 10 12 14

Simulated temperature Measured temperature

Simulated DO Measured DO

16 0

4

8

12

16

0

4

8

12

16

20

24

28

Water temperature (°C) and dissolved oxygen (mg/l)

. Fig. 16.7 Measured and simulated water temperature and DO profiles in Bear Head Lake in Minnesota

started to develop in June, and anoxic conditions appeared in the deep water layers in August. Bear Head Lake is 14.0 m (46 ft) deep and has a surface area of 674 acres. It is a mesotrophic lake having mean summer Secchi depth of 2.7 m (9 ft) and mean summer chlorophyll-a concentration of 6 mg L1. The impact of potential climate warming on DO concentrations in Lake Erie were studied by Blumberg and Di Toro [1]. They used an area-averaged hydrodynamic and eutrophication model and used three climatic change scenarios: GISS (Goddard Institute for Space Studies), GFDL, and OSU (Oregon State University). The projected maximum epilimnetic DO change is about 1.0 mg L1 during July in Lake Erie, and the projected hypolimnetic DO losses are typically 1–2 mg L1 [1]. These results are very similar to values obtained for large (10 km2) shallow (4 m deep) lakes in Minnesota [78]. This is not surprising since Lake Erie has a geometry ratio AS0.25 Hmax1 of 16.0 (surface area AS = 25,657 km2 and maximum depth Hmax = 25 m), almost the same as the geometry ratio of 14.0 for the large shallow lake class in Minnesota, and the lake geometry ratio controls lake stratification characteristics [29]. Stefan and Fang [78] simulated daily DO profiles in northern and southern Minnesota lakes during the open-water season (March to November) under the past (1955–1979) and the 2
CO2 GISS future climate scenario using the regional lake DO model [67]. Simulation of daily DO profiles from 1955 to 1979 were made for each of the 27 lake classes in Minnesota, and daily DO profiles were then averaged over 19 years. Model simulation results [78] indicate: (1) The daily mean epilimnetic DO concentrations are near saturation over the entire season and therefore decrease as the climate becomes warmer. The maximum decrease of epilimnetic DO is slightly less than 2 mg L1 due to climate warming. (2) The daily mean hypolimnetic DO concentrations show great variability throughout the open-water season and among lake classes. The largest hypolimnetic DO change in response to climate warming is on the order of 8 mg L1 and occurs in May or October in deep lakes. (3) Lake volume in which DO is below 0.1 mg L1

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Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

(near anoxia) is on the order of 17% and 12% of the total lake volume in small (0.2 km2), deep (24 m), eutrophic lakes under past (1955–1979) climate and projected 2
CO2 GISS climate scenarios, respectively. The period between the earliest and latest date when bottom DO is 0.1 mg L1 or less was projected to increase by as much as 80 days in southern Minnesota lakes and 60 days in northern Minnesota lakes due to climate warming [78]. Fang and Stefan [77] extended the regional DO model from the open-water season to a year-round model including winter DO model simulations during the ice cover period. They summarized climate change effects on DO characteristics in ice-covered lakes in Minnesota. Oxygen depletion in ice-covered lakes is strongly related to trophic state, for example, oligotrophic shallow lakes have no DO problems, whereas eutrophic shallow lakes suffer from DO depletion in winter under identical weather conditions [77]. The effect of trophic state on anoxia remains pronounced regardless of climate. Under past (1962–1979) climate conditions, lake anoxia reaching from the lake bottom to the ice– water interface can last from 7 to 43 days in northern, shallow, eutrophic lakes of the contiguous USA. An example is shown in > Fig. 16.8. These lakes are threatened by winterkill if artificial aeration is not implemented. Under the 2
CO2 climate scenario, winterkill resulting from winter anoxia was projected to disappear from all northern shallow lakes (> Fig. 16.8, and this will make artificial aeration unnecessary) due to a shorter ice cover period. The maximum percentage of lake volume with anoxic conditions is only up to 9%. Solid diamond symbols in > Fig. 16.8 identify the 27 lake types in a coordinate system of lake geometry ratio versus Secchi depth Z s; simulated values at those 27 locations were used to develop contour plots. Shallow oligotrophic lakes (due to low oxygen demand) and medium or deep lakes (due to large lake volume or oxygen

Past climate (1962–1979)

5 Secchi deepth ZS (m)

550

9.5 12.0

5.0

4 3

4.0 3.0

8.5 Ice cover period

7.5

2.0

11.0

6.5

1.0 10.0

2

Future climate scenario

12.5

5.5

0.0

4.5

9.0

3.5

8.0

2.5

7.0

1

11.5

6.0

10.5

0 0.8 1.0

2.0

4.0

6.0 8.010.0

As0.25/Hmax (m−0.5)

20.0 0.8 1.0

2.0

4.0

6.0 8.0 10.0

20.0

As0.25/Hmax (m−0.5)

. Fig. 16.8 Simulated minimum lake dissolved oxygen concentration 1.0 m below the lake surface during the ice cover period in Duluth, MN under past (1962–1979) climate conditions (left) and the CCC GCM 2.0 projected future climate scenario (right). Results are for small lakes of different bathymetry (expressed by lake geometry ratio on the horizontal axis) and different trophic state (expressed by the Secchi depth on the vertical axis) located near Duluth, MN

Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

16

content) in the northern temperate climate regions of the contiguous USA, for example, in Duluth, MN (> Fig. 16.8) and in other northern states [40, 77] do not appear to have problems of anoxic conditions (no fish winterkills). Several characteristic DO parameters, for example, minimum DO concentrations on the lake surface and lake bottom, the number of days with anoxic lake bottom conditions, the maximum percentages of anoxic lake volume in the open-water season and the ice cover period, were determined and examined to better understand the importance of geographic location and climate warming on DO conditions in small generic lakes all over the contiguous USA. In > Fig. 16.9, simulated annual minimum bottom (hypolimnetic) DO concentrations for 27 lake types are shown for geographic locations in Duluth, Minnesota, and Kansas City, Missouri, under a projected future climate scenario. All

Duluth, Minnesota

0

6.

4 0.0

3 4. 0 2.0 3.0 1. 0

2

0

5.

Secchi depth ZS (m)

5

1 0 Kansas City, Missouri 6.

0

4

5. 0

3 2

0 4.

0 2. 1.0 0.0

0

3.

Secchi depth ZS (m)

5

1 0 0.8 1.0

2.0

4.0

6.0 8.0 10.0

20.0

AS0.25/Hmax (m−0.5)

. Fig. 16.9 Simulated annual minimum lake bottom (1.0 m above the lake maximum depth) dissolved oxygen concentrations in small lakes of different bathymetry (expressed by lake geometry ratio on the horizontal axis) and different trophic state (expressed by the Secchi depth on the vertical axis) under the CCC GCM 2.0 projected future climate scenario for Duluth, MN (upper) and Kansas City, MS (lower)

551

16

Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

stratification lakes (when lake geometry is less than 3) have anoxic conditions in the lake bottom as shown in > Fig. 16.9. Shallow or polymictic lakes can maintain bottom DO greater than 3 mg L1 even under future climate scenario, but water temperature can be too warmer for certain fish species (It will be discussed in the next section).

Impacts of Climate Warming on Fish Habitat in Lakes Water temperature and DO concentrations are the two most important water quality parameters affecting survival and growth of adult fishes [3, 79, 80]. Isotherms and DO isopleths derived from water temperature and DO profiles measured in lakes throughout a season or a year and plotted on a coordinate system of time versus depth in the lake illustrate the water temperature and oxygen regime of a lake and can be found in every textbook of limnology. Each fish species has an upper lethal temperature (LT) limit and a minimum DO requirement. The LT isotherm and the limiting DO isopleth on the above described plot can be used to identify viable or good growth fish habitat for a given fish species in a lake. When the LT isotherm and the minimum DO isopleth for a fish species intersect and overlap on the above described plot for a certain length of time, as is schematically illustrated in > Fig. 16.10, a stratified lake becomes uninhabitable over its entire depth for that fish species. Summerkill of a fish species in a lake was assumed to occur if these conditions last more than 7 days. This criterion was used to study the impact of climate change on fish habitat in small lakes over the contiguous USA. GSL1

GSL2

GSB

NSB

Depth (m)

552

NSL

Area

GSE

NSE

Volume

T > LT

LT UG

GT

T

G

LG

DO < 3 mg/L

Jan

Feb

Mar

Apr

May

Uninhabitable

Jun

Jul

Aug

Good growth

Sep

Oct

Nov

Dec

Restricted growth

. Fig. 16.10 Schematic distribution over time and depth of the isotherms and DO isopleths that are relevant to the survival and growth of a fish species in a stratified lake. GSB good-growth season beginning date, GSE good-growth season ending date, GSL good-growth season length, LGGT lower good-growth temperature, LT lethal temperature, NSB non-survival beginning date, NSE non-survival ending date, NSL non-survival period length, T temperature, UGGT upper good-growth temperature

Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

16

Water temperature criteria for three fish guilds were assembled from laboratory and field studies as described by Eaton et al. [81] and Stefan et al. [82]. The guild designations suggested by Hokanson [83] were adopted for the fish habitat study: 8, 7, and 14 species of cold-water, cool-water, and warm-water fish guilds, respectively, were considered. > Table 16.3 summarizes three temperature levels for fish guilds: the lower good-growth temperature limit (LGGT), the upper good-growth temperature limit (UGGT), and the lethal temperature threshold (LT). Fish have good growth potential when water temperature falls between LGGT and UGGT. The LT is the upper water temperature to which fish cannot be acclimated without causing death. In essence, the LT was determined from field data that relate maximum annual water temperature to fish presence [81]. The optimum temperature (OT) in > Table 16.3 is a water temperature at which fish have maximum physiological ‘‘strength.’’ Guild values are the means of available LT, LGGT, UGGT, and OT values for species in each guild, and ranges of these parameters for species within a guild are also given in > Table 16.3. DO concentrations, besides water temperatures, control the presence or absence of a freshwater fish species in a lake [3, 84]. Fish guilds have DO concentration requirements (> Table 16.3), below which mortality is more likely to occur or growth is impaired [85]. The dissolved oxygen criteria for three fish guilds are summarized in > Table 16.3. The criteria were developed from an available US EPA database plus expert consultation [84]. . Table 16.3 Thermal and dissolved oxygen criteria for three fish guilds (guild means and ranges for species within a guild) [7, 81] Lower goodgrowth temperature Guild LGGT ( C) Cold-watera Mean 9.0 Range (6.4–11.8) Cool-waterb Mean 16.3 Range (13.2–18.2) Warm-waterc Mean 19.7 Range (17.7–22.5) a

Upper goodgrowth temperature UGGT ( C)

Upper lethal Optimum temperature temperature Dissolved oxygen LT ( C) OT ( C) DO (mg L1)

18.5

23.4

15.3

(15.5–21.2)

(22.1–26.6)

(11.5–18.7)

3.0

28.2 (27.7–28.8)

30.4 (28.0–32.3)

25.1 (24.0–25.7)

3.0

32.3 (31.3–34.7)

34.5 (32.3–36.0)

29.2 (27.0–32.0)

2.5

Cold-water fish species are brook trout, brown trout, chinook salmon, chum salmon, coho salmon, mountain whitefish, pink salmon, and rainbow trout. b Cool-water species are black crappie, northern pike, sauger, walleye, white crappie, white sucker, and yellow perch. c Warm-water fish species are bluegill, brown bullhead, carp, channel catfish, flathead catfish, freshwater drum, gizzard shad, golden shiner, green sunfish, largemouth bass, rock bass, smallmouth bass, smallmouth buffalo, and white bass.

553

554

16

Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

DO criteria summarized in > Table 16.3 were developed for the open-water season. In icecovered lakes, DO concentrations often diminish over time during the winter due to bottom (sediment) and water column oxygen demands. In shallow, eutrophic or mesotrophic lakes, DO concentrations can therefore drop below 2.0 mg L1 near the end of an extended ice cover period. The low DO concentration has a major influence on the survival of fish assemblages in ice-covered lakes in cold regions (e.g., Minnesota, Wisconsin, Michigan and Maine). For ice-covered lakes, DO criteria for fish survival could be set at lower values than given in > Table 16.3, but data from the available literature were still inadequate to establish specific tolerance limits of dissolved oxygen for fish winterkill [76, 86]. The same DO criteria were used for the open-water season and the ice cover period to study impacts of climate changes on fish habitats. A sensitivity analysis of simulated winterkill to different winter DO limits showed that a lower DO limit of 0.5 mg L1 gave better agreement between simulations and observations in Minnesota lakes [87]. The use of the open-water DO criteria may slightly overestimate the possibility of winterkill under past climate conditions, but it has no effects on projections of winterkill under a 2
CO2 climate scenario because no winterkill was projected despite using higher DO limits [16]. > Figure 16.10 shows schematic water temperature isotherms (LT, LGGT, UGGT) and DO isopleths that are used to determine various fish habitat parameters (e.g., NSL, GSB, GSL, etc. that are defined in the figure caption) for both the open-water season and the ice cover period. Between these isotherms/isopleths, three fish habitats are identified: 1. Uninhabitable space: if temperature is above or DO is below the survival limit 2. Good growth habitat: if temperature is between the upper and lower good-growth limits (i.e., LGGT < T < UGGT) and DO is above the survival limit 3. Restricted growth habitat: if temperature is above the upper good growth temperature but below the survival limit (i.e., UGGT < T Fig. 16.10). The DO survival limit (isopleth) can occur not only during the open-water season (summer) but also in the ice cover period (winter period) for northern lakes as shown in > Fig. 16.10. Fish habitat for three fish guilds was estimated from simulated average daily water temperature and dissolved oxygen profiles in lakes. A similar approach was used by Christie and Regier [79] in their study. Fish thermal and DO criteria for survival and good-growth (> Table 16.3) were applied to the simulated 18 year average year-round daily water temperature and DO profiles as shown in > Fig. 16.10. This schematic figure is for a lake where fish cannot be present during much of the open-water season because the LT isotherm and the limiting DO isopleth intersect. In general, low DO concentrations near the lake bottom in summer force fish upward, and warm water temperatures near the water surface force fish downward in search of conditions for survival. Graphical representations of the three habitat types in a shallow and a deep lake in Duluth, Minnesota, under both past (1962–1979) climate and a projected GCM 2.0

Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

16

climate scenario are shown in > Fig. 16.11 as examples. To quantify whether fish habitat can exist in a lake, three parameters (NSB, NSE, and NSL) illustrated in > Fig. 16.10 were extracted from the depth-time contours of fish habitat in > Fig. 16.11. NSB and NSE indicate the beginning and the end dates of non-survival at all depths in a lake, respectively. NSB and NSE can occur during the open-water season or during the ice cover season as shown, for example, for large shallow eutrophic lakes in > Figs. 16.8 and > 16.11). These NSB and NSE values bracket the fish ‘‘summerkill’’ or ‘‘winterkill’’ period of length NSL, the latter primarily due to low DO values. NSL is the total number of days when either temperature or dissolved oxygen does not meet the fish presence criteria at all depths of a lake. When NSL is greater than 7 days during the winter ice cover period, ‘‘winterkill’’ is assumed to occur. Suitable fish habitat conditions during the ice cover period and the summer openwater season were quantified for all 27 types of small lakes (surface area up to 10 km2) at 209 locations (> Fig. 16.3) over the contiguous USA. [88]. For Minnesota, simulated

0

Uninhabitable Past (1961–1979)

Good growth 0

Restricted growth Projected 2xCO2

Depth (m)

Shallow 1

1

2

2

3

3

4 0

4 0

Depth (m)

Deep 4

4

8

8

12

12

16

16

20

20 24

24 Feb 1 Apr 1 Jun 1 Aug 1 Oct 1 Dec 1

Feb 1 Apr 1 Jun 1 Aug 1 Oct 1 Dec 1

. Fig. 16.11 Depth-time contours of cold-water fish habitat in large (10 km2 surface area) shallow (4 m) and large deep (24 m) eutrophic lakes at Duluth, Minnesota, under past (1961–1979) climate conditions (left) and a projected 2
CO2 CCC GCM 2.0 climate scenario (right)

555

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16

Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

suitable fish habitat was compared with fish observations by the Minnesota Department of Natural Resources in 3,002 lakes. Model predictions of fish habitat agree with fish observations in all medium-depth and deep lakes for all three fish guilds [87]. Winterkill was predicted to occur in shallow, eutrophic and mesotrophic lakes under past climate conditions. The death of fish due to oxygen depletion under ice (winterkill) is a significant problem in shallow lakes, both in the north central USA and in Canada [89]. Hundreds of aeration permits are issued by the Minnesota Department of Natural Resources to protect lakes that are annually threatened by winterkill in Minnesota. Depth-time contours for simulated fish survival and good growth habitat were reported for all 3 fish guilds and 12 lake types near Duluth, MN, Kansas City, MS, and Austin, TX [88]; one example is given in > Fig. 16.11 for cold-water fish. > Figure 16.11 clearly shows that in a shallow eutrophic lake near Duluth, MN, winterkill of cold-water fish can occur under past climate conditions due to lack of oxygen under the ice cover. It is projected that winterkill will disappear under a projected future 2
CO2 climate scenario due to shortening of the ice cover period, but summerkill of cold-water fish due to elevated water temperatures will develop in the same shallow lakes. A deep lake (24 m maximum depth) shows suitable cold-water fish habitat under both past and projected future climate scenarios (> Fig. 16.11). Geographic distribution over the contiguous USA of lakes with suitable fish habitat, fish habitat changes in individual lakes, and fish habitat parameters (e.g., good-growth period, good-growth habitat area and volume) were developed for the three fish guilds and are discussed elsewhere [88, 90]. > Table 16.4 summarizes the number of locations (out of 209 investigated in the contiguous USA) with simulated winterkill, summerkill, or suitable habitat for cool-water fish under past climate and projected future climate scenarios. The key conclusions of the fish habitat study in small lakes over the contiguous USA are: 1. Climate warming is projected to eliminate fish winterkill (due to low DO) for all three fish guilds in shallow, eutrophic and mesotrophic lakes in the contiguous USA, and this is a positive impact of global climate warming on fish habitat for 30 locations in northern states over the contiguous USA. 2. Summerkill due to elevated water temperatures after climate warming is likely to eliminate suitable cold-water fish habitat in almost all shallow lakes (maximum depth of 4 m) of the contiguous USA. Fish summerkill will also have a large negative impact on cool-water fish in southern lakes of the contiguous USA, where suitable habitat exists under present conditions. The strongest negative impact is projected for coldwater fishes in lakes of medium-depth (maximum depth up to 13 m) and cool-water fishes in shallow lakes (maximum depth up to 4 m). 3. Climate warming is projected to reduce substantially the geographic area (number of locations), where lakes have suitable cold-water and cool-water fish habitat. Based on the 27 lake types investigated, the reductions are projected to be up to 45% and 30% (94 and 62 locations over the contiguous USA), respectively. Cold-water fish have the best chance of survival in deep, stratified lakes near the northern border of the contiguous USA.

Medium (1.7)

(13.0)

1.6

2.8

4.3

(0.2)

Medium (1.7)

Large (10)

Medium Small

14.1

9.0

(0.2)

(4.0)

Large (10)

5.3

Small

0 0 0 0 0

O E M O E

M 0 O 0

14 0 0 0

29 14 0 30

M O E M

E M O E

E 18 M 7 O 0

0 0

0 0 0 0 0

0 0 0 0

0 0 0 0

0 0 0

Winterkill (2
CO2)

Number of Locations for

Winterkill Geometry ratio ZS (Past)

Shallow

AS Hmax (m) (km2)

Lake characteristics

1 1

3 0 0 2 1

16 19 1 2

5 19 23 10

15 23 36

Summerkill (Past)

42 47

50 37 38 47 45

71 77 37 42

58 72 85 67

66 76 96

Summerkill (2
CO2)

208 208

206 209 209 206 208

179 190 208 207

175 176 186 169

176 179 173

Habitat (Past)

167 162

159 172 171 162 164

138 132 172 167

151 137 124 142

143 133 113

Habitat (2
CO2)

–41 –46

–47 –37 –38 –44 –44

–41 –58 –36 –40

–24 –39 –62 –27

–33 –46 –60

Habitat change (2
CO2-Past)

. Table 16.4 Number of locations (out of 209 investigated) with simulated winterkill, summerkill, or with suitable habitat for cool-water fish under past and projected 2
CO2 climate

Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

16 557

0.9

1.5

2.3

Small (0.2)

Medium (1.7)

Large (10)

0 0 0 0 0 0

O 0

0 0

Winterkill (2
CO2)

0 0 0 0 0

E M O E M

E 0 M 0 O 0

Winterkill Geometry ratio ZS (Past)

Number of Locations for

0

0 0 0 0 0

0 0 0

Summerkill (Past)

2

19 7 1 17 8

8 4 1

Summerkill (2
CO2)

AS0.25

209

209 209 209 209 209

209 209 209

Habitat (Past)

Note: Hmax and AS stand for maximum lake depth and lake surface area, respectively. Geometry ratio is defined as Hmax state: Zs = 1.2 m for eutrophic lakes (E), Zs = 2.5 m for mesotrophic lakes (M), and Zs = 4.5 m for oligotrophic lakes (O).

(24.0)

Deep

AS Hmax (m) (km2)

Lake characteristics

1

(m

0.5

207

190 202 208 192 201

201 205 208

–2

–19 –7 –1 –17 –8

–8 –4 –1

Habitat change (2
CO2-Past)

). Zs (Secchi depth) indicates trophic

Habitat (2
CO2)

16

. Table 16.4 (Continued)

558 Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

16

4. Cool-water fish can exist in many lakes of the contiguous USA excluding shallow, eutrophic lakes in the north central US states (due to winterkill) and in south central US states, for example, Louisiana, part of Texas, south Arkansas and Alabama, parts of Georgia and Florida (due to summerkill). Summerkill of cool-water fish in shallow lakes will expand significantly in south central and southeastern states under a 2
CO2 climate scenario. 5. No summerkill of warm-water fish, due to elevated temperature and/or dissolved oxygen deficiency, is projected to occur in any lake in any location of the contiguous USA investigated under both climate scenarios. Under the projected 2
CO2 climate scenario, the good-growth period for warm-water fishes extends from about 72 days at northern latitudes to an entire year (365 days) at southern latitudes, which are positive impacts of climate warming on warm-water fish.

Identification of Refuge Lakes for Cold-Water Fish After Climate Warming Climate warming has the potential to reduce cold-water fish habitat in the cold regions of the contiguous USA [88] significantly. The effect of climate warming on cisco (a coldwater fish species) habitat in Minnesota, especially to identify refuge lakes important for sustaining cisco habitat under climate warming scenarios, was investigated. It is expected that a refuge lake sustains cisco habitat under future climate warming scenarios. Cisco is a salmonid fish of the genus Coregonus and is also known as lake herring and inland tullibee. Ciscoes are common in Lake Superior, but they also live in many inland lakes in Minnesota. Minnesota Department of Natural Resources (MN DNR) netting assessments have sampled cisco from 646 lakes since 1946. These lakes are scattered throughout much of the central and northern portions of the state and are found especially in two ecoregions (boreal forest and hardwood forest). The distribution suggests that cisco are somewhat more eurythermal than other native, lentic cold-water stenotherms such as lake whitefish Coregonus clupeaformis (sampled in 155 Minnesota lakes), lake trout Salvelinus namaycush (124 Minnesota lakes), and burbot Lota lota (233 Minnesota lakes). The wide distribution and a requirement for cold, oxygenated water make cisco an excellent and sensitive indicator of climate change. The spawning season for cisco starts in late fall (usually late November) just as or a little before the ice forms on the water. The spawning sites are commonly in shallow water (1–5 m deep) over bottoms of clean rock, gravel, or sand. In the Great Lakes, spawning often occurs in much deeper water (3–15 m). Cisco used to be an important commercial fish in the Great Lakes. Their populations are now very low in all but Lake Superior. In some inland lakes in the fall, a limited amount of noncommercial gill netting is permitted for this species. There are also a few anglers who fish specifically for cisco in winter and in the early summer when ciscoes feed on emerging insects. Cisco is a cold-water fish that needs well-oxygenated water and stays deep in the lake during summer time. Ciscoes usually do best in deep, clear water lakes.

559

560

16

Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

The characterization of Minnesota’s cisco lakes was a necessary first step for identifying refuge lakes. Lake parameters of 620 cisco lakes in Minnesota were available in a MN DNR database. To facilitate the interpretation of the cisco lake data, cumulative frequency distributions were developed for six selected lake parameters. Three of the selected parameters are bathymetric parameters (surface area, maximum depth, and geometry ratio) and the other three are related to lake trophic status (Secchi depth, mean chlorophyll-a concentration, and total phosphorus concentration). The surface areas of the 620 cisco lakes ranged from 0.04 to 2847.0 km2, about 10% of them had surface area greater than 10.0 km2 and 60% of them had surface areas between 0.9 and 10.0 km2. The maximum depth of the 620 cisco lakes ranged from 3.0 to 64.9 m, about 10% of them had Hmax greater than 32.9 m and 60% of them had Hmax between 12.2 and 32.9 m. The Secchi depth of the 620 cisco lakes ranged from 0.7 to 9.5 m, about 10% of them had SD greater than 5.0 m (oligotrophic lakes) and 60% of them had SD between 2.8 and 5.0 m (mesotrophic or oligotrophic lakes). Stefan et al. [91] divided 3,002 Minnesota lakes into 27 regional lake classes and classified lakes having Secchi depth less than 1.8 m as eutrophic lakes; 94% of the cisco lakes are either mesotrophic or oligotrophic lakes, only 6% of the cisco lakes are eutrophic. About 46% of cisco lakes are deep lakes, and about 73% of the 620 cisco lakes are seasonally stratified lakes with lake geometry ratio less than 3.0. Cisco lakes in Minnesota are typically more transparent and less trophic than other lakes. The year-round water quality model, MINLAKE96, had to be modified and refined in order to simulate all cisco habitat lakes in Minnesota; the resulting model was called MINLAKE2010. The maximum number of horizontal layers in MINLAKE2010 was increased to 80, so that the model could handle deep lakes with a maximum depth up to 75 m, if the 1.0 m layer thickness is used; the first five layers near the water surface have thicknesses less than 1.0 m for winter ice cover simulation. The model was calibrated and validated against data from 28 selected study lakes in Minnesota using six calibration parameters. Seven of the 28 study lakes were non-cisco lakes and 21 were cisco lakes. Only three of the study lakes, South Twin Lake, White Iron Lake, and Elephant Lakes, were weakly stratified lakes with lake geometry ratio greater than 4.5; all other 25 lakes were strongly stratified lakes. The model performance after calibration of the 28 study lakes was satisfactory. The average standard error of estimate (SE) between simulation and measurements for all 28 study lakes was 1.47 C for water temperature (range from 0.8 C to 2.06 C) and 1.50 mg L1 for DO (range from 0.88 to 2.76 mg L1). The average regression coefficient (R2) (in hydrological modeling also called Nash–Sutcliffe coefficient or coefficient of determination or modeling efficiency) was 0.92 for water temperature (range from 0.84 to 0.97) and 0.75 for DO (range from 0.12 to 0.91). For reference, R2 = 1 is the best possible model performance. The average slope (S) for the model to field data regression was 1.00 for water temperature (range from 0.93 to 1.05) and 0.97 for DO (range from 0.85 to 1.07). For reference, if the model is overpredicting, the slope is less than 1.0; if the model is underpredicting, the slope is greater than 1.0. The average standard error of estimate for the 21 cisco lakes was 1.51 C for water temperature (range from 0.8 C to 2.06 C) and 1.39 mg L1 for DO (range from 0.88 to 2.38 mg L1). The average standard error of estimate for the seven non-cisco lakes was 1.34 C for

Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

16

water temperature (range from 0.97 C to 1.72 C) and 1.50 mg L1 for DO (range from 1.06 to 2.05 mg L1). The original MINLAKE96 model has been calibrated on nine Minnesota lakes and one oligotrophic lake, Thrush Lake; the average SE between simulations and measurements for 5,976 data pairs of dissolved oxygen was 1.94 mg L1 with a range from 1.61 to 2.59 mg L1 [77]. Available water temperature and DO profile data for the 21 cisco lakes, needed for model calibration, covered periods from 4 to 46 days and from 1 to 10 years. In total, 80 years or 331 days with measured profiles and 5,608 total pairs of temperature and DO profiles in the 21 cisco lakes were available for model calibration. For the seven non-cisco lakes, a total of 25 years or 156 days with measured profile data giving 1,973 total data pairs were available. The calibrated water quality model MINLAKE2010 was used to simulate daily water temperature and dissolved oxygen profiles in the 28 study lakes from 1961 to 2008 or 1991 to 2008 depending on weather stations used. Daily weather parameters as lake modeling input were organized by weather station and year by year. Weather stations selected for the study include six National Weather Service (NWS) Class I stations with data available from 1961 and three NWS Class II stations with the data available from 1991 only. Projected water temperature and dissolved oxygen concentrations were simulated under two, recently developed future climate scenarios: CCCma CGCM 3.1 and MIROC 3.2. CCCma CGCM 3.1 is the newest version of the Coupled Global Climate Model (CGCM) from the Canadian Centre for Climate Modeling and Analysis (CCCma) [92, 93]. This third generation model makes use of the substantially updated Atmospheric General Circulation Model (AGCM). MIROC 3.2 (Model for Interdisciplinary Research on Climate) [94] was developed by the Center for Climate System Research (CCSR), University of Tokyo, National Institute for Environmental Studies (NIES), Frontier Research Center for Global Chance (FRCGC), and the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). The high resolution version of MIROC 3.2 with a surface grid of 1.12 resolution for latitude and longitude was used. Two fish habitat models were applied. One was described in the previous section and used constant lethal temperature and DO survival limits (see > Table 16.3 for cold-water fish species). The other used variable temperature and DO survival limits. Both were used to simulate and project the number of fish kill days of adult cisco in the 28 study lakes under past and two future climate scenarios. For the second fish habitat model, Jacobson et al. [95] developed a fitted regression equation for the lethal niche boundary of adult cisco by remapping the oxygen concentrations and temperatures from the profiles measured in 16 Minnesota lakes that experienced cisco mortality in midsummer 2006. The regression equation (shifted exponential function) is: DOlethal ¼ 0:40 þ 0:000006 e 0:59Tlethal ;

(16.11)

where DOlethal and Tlethal are the dissolved oxygen concentrations (in mg L1) and the water temperature (in  C) values that define the lethal niche boundary [95]. For the regression > Eq. 16.11, coefficients 0.40 and 0.000006 are in mg L1 and coefficient 0.59 is in  C1 (or per  C). The computed DOlethal is the required minimum DO concentration

561

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Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

at a given temperature Tlethal for cisco to survive. > Equation 16.11 indicates that the DO survival limit for cisco is not constant (such as shown in > Table 16.3) but instead depends on water temperature. A notable difference between the two fish habitat models is that the fixed lethal temperature for cold-water species in general was 23.4 C [81], but the lethal temperature from > Eq. 16.11 with 3.0 mg L1 as DO survival limit, is only 22.0 C [95]. When the second fish habitat model was used, the required DO concentration, DOlethal, was computed from the simulated water temperature in each water layer of a lake for each simulated day using > Eq. 16.11; this DOlethal value was then compared with the simulated (actual) DO concentration in the same layer; fish kill was assumed to occur if the simulated (actual) DO was less than the DOlethal value in all water layers (from lake water surface to lake bottom) on that day. If simulated (actual) DO concentration was less than the DOlethal value in only some of the water layers, fish mortality was not assumed to occur on that day because cisco could swim to other water layers having suitable DO and temperature condition. Days with possible cisco kill were extracted year by year using simulated daily water temperature and DO profiles in this study. In previous regional fish habitat projections [96], water temperature and DO profiles were first averaged over the entire simulation period first before the fish habitat model was applied. Cisco habitat was simulated year by year beginning in 1962 or 1992, depending on available weather data, and going to 2008 using simulated daily temperature and DO profiles. Results for the first simulation year were not used in order to remove possible effect of initial conditions. Both fish habitat models (constant or variable survival limits) projected no cisco kills in any of the simulation years in 6 of 15 study lakes: Carols, Cedar, Elk, Kabekona, Ten Mile, and Trout. All six lakes are classified by the MN DNR as cisco habitat lakes. South Twin and White Iron are also classified as cisco habitat lakes, but simulations of both lakes with both fish habitat models produced some days with cisco kill. South Twin Lake and White Iron Lake are relative shallow lakes and have maximum depths of 8.8 and 14.0 m, respectively. For a simulation period of 17 years 10–12 days per year with fish kills were estimated on average for South Twin Lake and 5–10 days for White Iron Lake depending on the method used. Seven of the 15 study lakes have no known cisco populations and are listed as ‘‘noncisco lakes.’’ Both cisco habitat assessment methods were applied to these seven lakes, and cisco kill for six of the seven lakes was projected on a recurring basis; a viable cisco habitat was projected by the simulations for Bear Head, although no cisco has been recorded in the lake. A sensitivity analysis of the dependence of fish habitat projections on DO survival limits was conducted. The number of days with cisco kill was simulated with DO limits of 2.0 and 4.0 mg L1 for eight known cisco lakes and seven known non-cisco lakes. Projections for the first six cisco lakes indicated consistently no cisco kill, even when the higher DO limit of 4.0 mg L1 was used. A consistent projection was also developed for six of the seven non-cisco lakes. Cisco kills were projected in all of them. Hill Lake had no cisco kill when DO = 2 mg L1 was used. For lakes that were projected to have possible summer kill, use of the constant nonsurvival limits (LT = 23.4 C and DO = 3 mg L1) always gave fewer simulated years and

Impacts of Climatic Changes on Water Quality and Fish Habitat in Aquatic Systems

16

days with cisco kill than the use of > Eq. 16.11 did. For example, Elephant Lake was projected to have a total of 94 days in 12 years with summer kill (no winter kill) with the constant non-survival limit, but to have 263 days in 27 years with summer kill with > Eq. 16.11. This is because the constant value method would not project fish kill until the water temperature reaches 23.4 C at DO = 3 mg L1, while > Eq. 16.11 gives a lethalniche-boundary temperature equal to 22.0 C at DOlethal = 3.0 mg L1. For projecting winterkill, the situation is just opposite. > Equation 16.11 projected fewer days with winterkill than the constant value method did. > Equation 16.11 projected no winterkill until DO was less than 0.4 mg L1 during the ice cover period when water temperature was low (less than 4–5 C), while the constant value method used 3.0 mg L1 for winter or summer. For example, Carrie Lake was projected to have a total of 2,556 days of winterkill based on the constant value method and only 947 days of winterkill based on > Eq. 16.11. A previous sensitivity analysis of simulated winterkill to different winter DO limits showed that a lower DO limit of 0.5 mg L1 gave better agreement between simulations and observations of winterkill in Minnesota lakes [87]. Projection of winterkill using > Eq. 16.11 is therefore considered more accurate. It is still uncertain how many days with violation of non-survival or lethal-nicheboundary limits are necessary to have an actual fish kill. In previous regional fish habitat projections [2] when daily water temperature and DO concentration profiles were longterm (30-year) averages, fish kill was assumed to occur when the total number of nonsurvival days exceeded seven (either consecutive or discontinuous 7 days). In our more recent studies, daily profiles were not averaged to project potential fish kill. Therefore, additional information on fish kill days or years was extracted and reported. The information includes: (1) number of years with more than seven projected cisco kill days (consecutive or discontinuous days), (2) number of years having more than seven consecutive cisco kill days, and (3) the maximum number of consecutive days with fish kill conditions in a year and the year when it occurred. Under future climate scenarios, a considerable increase in the number of annual fish kill days in non-cisco lakes is projected, with either of the two fish habitat models. Projections of the increase in the number of annual kill days under three future climate scenarios (including previously used CCC GCM 2.0 model) are consistent. The CCC GCM 2.0 scenario projects relatively higher numbers of cisco kill days, because future CO2 emission are higher in this earlier future climate model. The other two future climate scenarios are based on output of the CCCma CGCM 3.1 and MIROC 3.2 models and project almost same numbers of cisco kill days. All three future climate scenarios project a reduction in cisco kill days in a shallow lake, Lake Carrie, where most of the kill occurs in winter (Simulated DO concentrations are lower than the DO survival limits from surface to bottom of the lake during winter). This is consistent with previous projections of winterkill in shallow lakes over the contiguous USA [16] because of the projected decrease in ice cover duration during winter [36]. Model simulations were performed for an additional 13 cisco lakes in a second stage of the study. The number of annual kill days in the 13 additional cisco lakes was projected under the CCCma CGCM 3.1 future climate scenario. For 12 of the 13 cisco lakes, no fish

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10.0 620 cisco lakes 19 cisco lakes without kill 2 cisco lakes with kill Geometry ratio < 3.0 m−0.5 Secchi depth > 2.5 m

9.0 8.0 7.0 Secchi depth (m)

564

6.0 5.0 4.0 3.0 2.0 1.0 0.0 0.4

0.6

1.0

2.0

4.0

6.0

Lake geometry ratio

(m−0.5)

10.0

20.0

. Fig. 16.12 Distribution of 21 cisco study lakes among 620 cisco lakes showing no cisco kill and 2 cisco study lakes that have potential cisco kill. Preliminary recommended limits of Secchi depth and lake geometry ratio for cisco refuge lakes are shown as dashed lines

kill was projected under the future climate scenario; only Blue Lake among the 13 additional lakes is projected to have a few days with potential kill of adult cisco. In conclusion, it was suggested that 19 of the 21 cisco lakes in the 28 study lakes can be considered as cisco refuge lakes, i.e., to support cisco habitat under future climate conditions. Only 2 cisco lakes in the 28 study lakes, White Iron Lake and South Twin Lake, had to be excluded as refuge lakes (> Fig. 16.12). Based on the bathymetric and trophic characteristics of 620 cisco lakes compared to the 21 selected study cisco lakes (> Fig. 16.12), it was determined, on a preliminary basis, that refuge lakes for sustaining cisco habitat in Minnesota after climate warming should have (1) Secchi depth greater than or equal to 2.5 m (mesotrophic or oligotrophic lakes) and (2) lake geometry ratios less than 3.0 m0.5 (typically seasonally stratified lakes). Further study is still necessary to narrow down the criteria to select specific refuge lakes and to rank the 19 cisco lakes. On a plot of Secchi depth versus lake geometry ratio, lakes that can support cisco habitat under future climate scenarios will fall into a particular region. Work is in progress to identify that region.

Future Directions Modeling of lake water quality in small lakes of the contiguous USA under past and projected future climate scenarios was described and applied. Lakes were treated as

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isolated water bodies, and the discussion focused on two water quality parameters, temperature and DO, because both control fish survival and growth. Research development in the next step needs to include hydrological and water quality simulations in upstream and surrounding watersheds of a lake. Nutrient inputs from watersheds can directly affect water quality dynamics in a lake. Best management practices can reduce nutrient inputs from watersheds to a lake and decelerate cultural eutrophication. Lake management and protection has to include watershed management and protection, as is well known. In southern USA, water quality modeling has to include man-made reservoirs and reservoir systems where inflows from upstream watersheds and controlled/uncontrolled outflows are important to water quality dynamics under projected future climate scenarios. Integrated watershed and lake or reservoir modeling is important to natural resources management in the future. In earlier studies, fish habitat projections were conducted for three fish guilds (cold-, cool-, and warm-water fish) using long-term (averaged), simulated water temperature and dissolved oxygen conditions. It will be necessary to investigate individual fish species under past (for model calibration) and several future climate scenarios to possibly quantify uncertainty of habitat projections. Currently a year-round water quality model and a refined fish habitat model based on field observations are being used to identify refuge lakes for cisco (Coregonus artedi, lake herring, tullibee) in the State of Minnesota. Cisco is a cold-water fish that is commercially harvested in Lake Superior and also is foraged upon by walleyed pike and northern pike in many inland lakes. Part of the study results are reported in the previous section, and further research to identify specific refuge lakes is continuing. To identify refuge lakes for cold-water fish, water quality indices can be useful, but have not been developed. For example, water temperature at the water depth where dissolved oxygen is 3 mg L1 was found to be a useful oxythermal habitat variable that is strongly correlated to cold-water fish presence (cisco, lake trout, lake whitefish, and burbot) in Minnesota lakes [97]. It should be obvious that more precise criteria on the duration of exposure to temperature and dissolved oxygen for different fish species and for adult and juvenile fish are needed to define ‘‘good-growth’’ and ‘‘survival.’’ Assumption that ‘‘summerkill’’ or ‘‘winterkill’’ will occur when non-survival conditions persist for more than 7 days represents a very crude and not well supported approach. More precise information on how stressors affect fish and a better understanding of fish kill is needed. Frey [98] postulated that young ciscoes are more tolerant of high temperatures and low oxygen concentration than are the larger and older individuals; they can survive through hot summers in a thin stratum above the thermocline. Therefore, summer mortality events generally affect only adult cisco. Cisco populations can persist in lakes with multiple years of mortality as long as some juveniles remain in the system. Recruitment of juvenile fish is therefore as important to a fish species’ survival as is the duration of exposure to lethal conditions, but recruitment is not included in current simulations and projections.

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Overall, the projection of fish kill and fish growth in lakes is still a challenging and growing research area, and needs further model validation with more field observations of fish species in different lakes.

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17 Climate Change Impacts, Vulnerability, and Adaptation in East Africa (EA) and South America (SA) Anne Nyatichi Omambia1 . Ceven Shemsanga2 . Ivonne Andrea Sanchez Hernandez3 1 National Environment Management Authority, Nairobi, Kenya 2 Department of Eco-tourism and Nature Conservation, Sebastian Kolowa University College, Tumaini University, Lushoto-Tanga, United Republic of Tanzania 3 Settlements Research Group, Santa Maria de la Loma Experiences Exchange Centre, Las Rosa de Cabal, Risaralda, Colombia Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573 The East African (EA) Picture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575 Brief Introduction of EA Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575 Brief Introduction of Climate Change in EA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577 Regional Climate Change Vulnerability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 578 Natural Disasters: Droughts, Flooding, and Wildfires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 579 Sea Level Rise and the Salt Water Intrusion into Fresh Water Sources . . . . . . . . . . . . 581 Impacts on Water Availability, Agriculture, and Food Security . . . . . . . . . . . . . . . . . . . . 581 Impacts on Human, Livestock, and Wildlife Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583 Malaria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583 Rift Valley Fever (RVF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584 Cholera . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584 Impacts on Environment: Deforestation, Fisheries, Biodiversity, Wildlife, Ecosystems, and Sea Water Intrusion into Fresh Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585 Climate Change and Energy Crisis in EA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 586 Livestock Sector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588 Other Sectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 589 Socioeconomic Implications of Climate Change on EA Mountains . . . . . . . . . . . . . . . 590 Coping with Extreme Climate Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592 Indigenous Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592 Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_17, # Springer Science+Business Media, LLC 2012

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Adapting Major Regional Sectors to Climate Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595 Livestock Sector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595 Health Sector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595 Agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596 Clean Energy and Energy Serving Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596 Fight Against Disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 598 Flooding Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 598 Water Harvesting, Irrigation Scheme Development, and Water Serving Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 599 Environmental Conservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 599 Challenges and Opportunities for Combating Climate Change in EA . . . . . . . . . . . . . . 600 The South American Picture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 600 A Brief of South America . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 600 Climate Change Evidence in South America . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 601 Climate Change Vulnerability in South America . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602 Ecosystems Vulnerability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602 Socioeconomic Vulnerability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604 Agricultural Vulnerability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 605 Impacts and Potential Risks Caused by Climate Change . . . . . . . . . . . . . . . . . . . . . . . . . . 605 Adopting Climate Change Adaptation and Mitigation Measures in South America . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 607 Adapting to Climate Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 607 The Regional Role in Global Climate Change Mitigation . . . . . . . . . . . . . . . . . . . . . 608 The Climate Change Challenge for South America . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 609 Future Direction to Combating Climate Change in SA and EA . . . . . . . . . . . . . . . . . . . . . 612 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 615

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Abstract: In recent decades, global climate change has continued to cause devastating impacts to various places on Earth. Geographic and socioeconomic characteristics in East Africa (EA) and South America (SA) make the regions among the most vulnerable to the current temperature variations attracting several studies with wider implications. Presently, in these two regions, remarkable evidence of climate change includes repeated droughts and increase in dry lands affecting water and food availability for humans, livestock, and wildlife (EA), intensification of climatesensitive diseases, sea level rise, fast retreat of glaciers on Mount Kilimanjaro in Tanzania, Mount Kenya in Kenya, and Andeans Mountains of South America, change in the rainfall patterns in the Amazon forests and in the whole of EA, and increasing of the frequency and intensity of the El Nin˜o and La Nin˜a phenomenon in the South Pacific that affect both EA and SA, among others. Although these two regions are not major contributors of greenhouse gases (GHGs), the poor conservation of strategic ecosystems through deforestation of the Amazon forests in SA and various forests in EA coupled with intensification of agriculture, land degradation, rapid rates of urbanization and industrialization all driven by rapid population increase are putting a strain on valuable natural resources whose conservation would be critical in mitigating climate change. Adaptation measures have been constrained by climate change impacts. In both regions, poverty is widespread and climate change impacts have jeopardized most poverty alleviation initiatives including realization of some of the Millennium Development Goals (MDGs). Moreover, both regions have a strong dependency on rain-fed agriculture for economic development with hydroelectricity and biomass as main sources of energy. Consequently, adaptation measures are required for all the sectors, but especially in agriculture, health, and energy where the loss of soil productivity, increasing spread of climate-sensitive diseases, reduction of water and energy source supply are already threatening the social and economic security of both regions. Both regions have a wealth of indigenous knowledge and coping mechanisms of various local communities that should be incorporated into conventional adaptation measures of climate change. This chapter describes the main climate change impacts in EA and SA, vulnerabilities thereon, and adaptation measures that offer an opportunity to the two regions to develop in a sustainable way.

Introduction Increasingly, many people across the world agree that climate change is the latest challenge facing humanity today and that nations must unite in addressing it. The reality of global climate change has been more evident in the recent past as significant scientific evidence clearly shows a warming trend in changing Earth climatic systems. Human development, especially industrialization, is largely blamed for significant release of greenhouse gases (GHGs) into the atmosphere in recent decades that have led to

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catastrophic changes in, sea level rise, increase in natural disasters, and an increase in global temperatures, among others. Climate statistics and models indicate that over the course of the past century, the global surface temperature has warmed by about 0.8
C, where 0.6
C is likely to be from the last 3 decades alone [1]. Traditionally, the bulk of the global GHGs contribution was credited to industrialized countries. Presently, major growing economies (Brazil, China, and India) and the transport and manufacturing sectors from other big cities in the developing world have observed a more significant contribution. For other developing countries including those in South America and the East African region, their contribution toward climate change is largely blamed on land use change, land degradation, deforestation and increased household energy needs, especially fuel wood consumption. Although a few conflicting stands still exist across the globe regarding climate change issues, the heated debates that were not uncommon in the past few years have become less important. Consequently, global efforts toward addressing climate change have thus been seen through the establishment of the United Nations Framework Convention on Climate Change (UNFCCC) which came into force on March 21, 1994 with an overall framework to address climate change through intergovernmental efforts. In addition, the Kyoto Protocol was established alongside the UNFCCC which commits Annex I countries to undertake measures aimed at stabilizing GHG concentration in the atmosphere. All countries of the East African Community (EAC) and South America have ratified both the UNFCCC and the Kyoto Protocol and have actively participated and put mechanisms in place to implement the various agreements accruing from the annual UNFCCC Conference of Parties serving as the meeting of Parties under the Kyoto Protocol (COPs/CMPs). This chapter has focused on two unrelated regions, EA and SA, that are very vulnerable to climate change impacts but at the same time offering interesting adaptation and mitigation mechanisms humanity can learn from. Major climate change impacts, vulnerability, and adaptation options have been discussed. Some climate change impacts still considered of potential effects elsewhere are already happening within these two regions and hence give a wake-up call to the rest of the world for immediate combating actions. For example, the presence of climate-sensitive equatorial glaciers in the region offers a good opportunity to follow climate change trends and vulnerability. Thus, because of the diverse regional environmental settings and socioeconomical characteristics, the regions offer the best opportunity to understand climate change details and how the developing countries live with climate change impacts, adaptation, and mitigation options thereby. For instance, it is now known that in EA, the ability to adapt to new conditions, exposure and sensitivity changes to climate are determinant factors to the extent to which individual places are vulnerable to climate change impacts [2]. In addition, the regions host some of the least developed countries and one of the emerging economies and thus a good platform for socioeconomical comparisons.

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The East African (EA) Picture Brief Introduction of EA Region In its widest sense, the EA region includes Kenya, Tanzania, Uganda, Burundi, Rwanda, Sudan, and Ethiopia. Traditionally, the region was known to include only the three countries, Kenya, Uganda, Tanzania while politically; the current East Africa Community (EAC) block hosts the first five countries. The latter block has a rapid growing population currently standing at about 120 million people most of who are directly or indirectly employed in the agricultural sector. The inhabitants of the region have more or less comparable lifestyles and some forms of cooperation, long existed even before and during colonialism. During colonialism for example, the former three countries had a welldeveloped cooperation in energy, monetary, transport, and communications sectors. To date, such important links continue to exist where they offer important contribution to regional economic growth and livelihood support during needy times like natural disasters which are not uncommon in the region [3]. Biologically, the diverse environmental setting of the region has resulted to a number of endemism and very rich biological diversities. A number of rare species of aquatic and terrestrial ecosystems flourish in the region, both of which have a very big contribution in the economic development of the region. Major wildlife ecosystems of which are internationally appreciated for their uniqueness, flourish in the region, including, among others the Masai Mara Game Reserve in Kenya; Ngorongoro, Kilimanjaro, and Serengeti Wildlife Parks in Tanzania. One of the five internationally recognized centers in terms of high species richness and endemism, otherwise known as biological hot spots are found in the Eastern Arc Mountain forests of EA [4]. The region also hosts a large portion of the Savannah, the richest known grassland in the world. The Eastern Arc Forests and other regional forests make an important contribution in the energy sector in the region in which up to 90% of the total energy usage is biomass dependent [3]. Moreover, the forests and the vast ocean area are very crucial in the control of carbon via the carbon cycle while the diverse water bodies like large rivers and lakes are crucial for the socioeconomical sustainability of the region. These water bodies offer important services like irrigation, hydropower, and domestic water to its fast growing population, especially because the region has frequently been affected by severe water shortages [5]. In addition, EA hosts Africa’s tallest mountains (Mt. Kenya and Kilimanjaro) that still harbor rare tropical glaciers. The mountains have attracted several climate change studies that have added regional and extra-regional understanding of climate change trends. Geologically, the region is marked by the presence of the Rift Valley, semiarid to arid regions, and some of the most spectacular waterfalls that have been harnessed for hydropower projects. Furthermore, the region is rich in natural gas, coal, and different precious minerals including diamond, gold, and tanzanite among others [3]. The neutral gas of coal is a notable contribution to the regional energy balance while Tanzanite is globally found in Tanzania only [4].

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Demographically, the region is home to thousands of pastoralists who remarkably herd their livestock mostly in the semiarid to arid areas of the region. The pastoralists provide a major portion of the livestock to the markets both within and beyond the region [7, 8] and as such are an important part to the regional gross domestic product (GDP) besides providing employment and important nutritional balance in the region. However, the livestock industry in the region is threatened by periodic droughts, the use of low breeds, and livestock diseases inter alia. On the other hand, agriculture is the most important sector in the region considering the number of people it directly employs and its contribution to GDP and foreign exchange. Unfortunately, agriculture is mostly rain-fed and severely impacted by uncertainty in rainfall patterns and intensity. Characteristically, agriculture in EA is largely subsistence, low input, and rain-fed with only isolated cases of large-scale agriculture. This in turn leaves the region vulnerable to repeated crop failures, food insecurity, and increases in food prices [5]. Irrespective of the presence of the most productive soils and numerous water bodies, sadly the region is among the places where malnutrition is very high and periodic food aid has had to be provided. The situation has been made worse by the present climate change where rainfall has continued to be unpredictable, increasingly unreliable, and insufficient. Meteorologically, EA is located in a complex climatic region in which the diverse topographical and hydrological interactions play an important role. The climate is mostly controlled by interactions between sea surface temperature (SST) forcing, large-scale atmospheric patterns, synoptic scale weather disturbances (namely, trade winds and monsoons), tropical cyclones, subtropical anticyclones, easterly/westerly wave perturbations, and extra tropical weather systems that are superimposed with regional factors like large lakes, topography, and maritime influence [9, 10]. The above complexity renders climatic patterns within the region to change rapidly within a short distance and time. Consequently, the diurnal temperature range varies between 10
C and 20
C while the annual temperature range is only 2
C. On the other hand, mean annual bright sunshine is between 9 h/day in highlands and low lands respectively while the regional mean annual net radiation varies between 450 and 550 cals/cm2/day. The most important regional wind and pressure patterns include the Congo air stream with westerly and southwesterly airflow, together with the northeast and southeast monsoons. Unlike the Asian southwestern monsoon, both East Africa monsoons are relatively dry while the Congo air stream is humid and associated with rainfall [9]. Generally, East African rainfall is bimodal that is characterized by uncertainty both spatially and temporally. Predominantly, the rainfall occurs during boreal spring and comprises of long rains (March–May) while short rains come in autumn (September/October–December) seasons. The two rain seasons occur when the Inter Tropical Convergence Zone (ITCZ) migrates from south to north through the equator. However, the above pattern varies significantly across the region the uncertainty of which increases toward the dryer zones. In other words, rainfall is more patchily scattered in arid than in mesic systems [10]. Within the region, the fluctuations in rainfall intensity are largely associated with East–West adjustments in the zonal Walker circulations that are linked to El Nin˜o-Southern Oscillation (ENSO). Studies have shown that humid areas in EA will become wetter while dry parts will turn

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out to be drier. The former will respectively increase runoff while the latter will significantly reduce it. In Tanzania for example, two river basins are already said to have their runoff reduced [9]. In this chapter, the discussions will be limited to the EA political block, the socioenvironmental settings of which are considered useful in understanding local, regional, and extra-regional vulnerability and adaptations to global climate change.

Brief Introduction of Climate Change in EA Although vulnerability to climate change impacts is increasingly becoming of ubiquitous nature, the best way of understanding climate change in EA is to ask ‘‘why is the region particularly vulnerable?’’ EA is vulnerable because of various reasons, namely, the over-dependency on natural resources; primary production; over-reliance on rain-fed agriculture for livelihood support; low level of development; inadequate institutional and economic capacities all of which leaves many persons vulnerable [5, 11]. Climate change effects like changes in precipitation patterns and rising global temperatures are clearly affecting the region where they already disrupt people’s livelihood, biodiversity, and ecosystems [12]. Recent studies have shown that the region’s economy largely depends on agriculture, livestock, tourism, wildlife, forestry, mining, industries, and marine and coastal resources all of which are climate dependent and directly affected by the ongoing climate variability. Any impact on agriculture, which is the dominant contributor in terms of employment opportunity, income generation, and support to the population, leaves many livelihoods disrupted. In addition to the overdependence on natural resources, the vulnerability also roots from low level of development and generally of per capita income. The majority of the population in the region lives below respective national poverty lines and most of them with less than a dollar per day, especially in rural areas. Furthermore, socioeconomic inequality within the population increases vulnerability and limit adaptation options to some individuals. The most obvious such inequality could be seen between the urban and rural population in which the latter suffers more from low development, low income, and poor access to public services compared to their urban counterparts [4]. In some places like Tanzania, vulnerability to climate change has even taken a gender dimension in which women are categorized more vulnerable on account of the deep-rooted socioeconomic barriers in the country. Working with regional climate change projections, the region is set to observe both decreases and increases in rainfall of between 5% and 10% (June–August) and 5–20% (December–February) respectively. Sadly, the projections show that the increase in rainfall may come as a few large storms in early traditional wet season and hence complicate water management, soil erosion, and health services. Several development activities/projects in the region are either directly or indirectly impacted by climate change. This occurs when the variability impairs climate-dependent projects such as forests management, infrastructural developments, and agriculture while indirect impacts happens when

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socioeconomic projects like health and education are impacted. Regrettably, for a good number of years, most governments in the region did not strategically link climate change and socio-development projects. Climate change factor was not clearly reflected in individual national development plans and policies. Only recently, and after significant climate change impacts, some governments in the region have practically linked the two. Arguably, the negative impacts of climate change in the region are also complicated by other factors such as rapid population growth, widespread poverty of the inhabitants, human and livestock diseases among others. Even worse, under the current population growth rate, some studies already estimate a doubling in demand for water, food, and rangeland within the 30 years [13]. Such statistics put EA in a very desperate situation and effective measures must be taken sooner rather than later to counter the effects of climate change in the region. EA already has some social stressors which make the region even more vulnerable to climate change and thus limit adaptation ability. Such stressors include the following: governance problems, high population growth, land scarcity in some places, conflicts, and diseases such as malaria and HIV/AIDS. Given socioeconomical and technological capacity of the region, dealing with climate change will continue to be problematic because of numerous reasons. Most official strategies to livelihoods impacted by climate change are expensive and technical which renders poor implementation. This is where indigenous coping options which are plenty in the region, as will be seen later, could be integrated into the national strategies.

Regional Climate Change Vulnerability The global climate change impacts like intensification of extreme weather events, sea level rise, alteration in temperatures, and distribution of precipitation are all evident in EA. Within the region however, distribution of the effects of climate change are known to be nonuniform and arguably more noticeable from variations in precipitation than temperature. For example, most studies indicate that the region will warm by between 2
C and 4
C by 2100 which is notably less compared to inner South Africa and Mediterranean northwest Africa. Further projections show that regional warming in the twentieth century has been of the order of about 0.05
C per decade. However, within the region itself, the projected warming is unlikely to be uniform where inner parts of the region are likely to warm more than coastal regions. On the other hand, a number of climate change– related droughts have been recorded in recent years with severe consequences to livelihood support systems and even deaths of both human and livestock [11, 12]. For example, studies have indicated that warm sea surface temperature may be to blame for the recent droughts between the 1980s and 2000s in equatorial and subtropical EA. Interestingly however, historical records in the region show that over the course of the last century there has been a net increase in the amount rainfall [5]. Further studies show that the increasing rainfall and decreasing temperature in presently humid areas may increase river flow by up to 10–20% for example in Uganda [5]. However, more recent studies suggest that whereas parts of equatorial EA are likely to have a 5–20% increase in rainfall from

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December to February the region will also observe a 5–10% decrease in rainfall from June to August by as early as 2050. Certain parts of the region are known to be more vulnerable than climate variation than others. For instance, both increase in regional temperature and decrease in rainfall would leave most parts of Northern Uganda and many places in Tanzania with serious water scarcity [13]. Generally, presently wet and dry places within the region will become wetter and drier respectively. In Tanzania for example, two rivers have their flow reduced directly because of the dwindling regional rainfall. Even more worrying, the observations show that the decrease in regional precipitation will most likely occur in the rational dry spell in the region and hence worsen frequency and severity of drought hence desertification. Such relatively drastic changes in precipitation already have many socioeconomical and ecological negative impacts among them reduced agricultural harvests, increased insects and fungal infestations, decreased biological diversity, complicating hydropower availability, inter alia [5]. Although climate change affects many biophysical and social aspects in the regions, the following categories considered major issues will be used as a guideline for the discussion under this chapter. Worth noting, some of these impacts have far-reaching influences and tend to trigger other vulnerability.

Natural Disasters: Droughts, Flooding, and Wildfires Probably the claim that climate change is projected to aggravate frequency and intensity of extreme weather events (El Nin˜o events, storms, droughts, and flooding) and wild fires can superlatively be understood from EA region. The increased frequency and severity of the named natural disasters have in recent years caused injuries, deaths, famine, diseases outbreaks, and even population displacement. For example, the region has in recent years observed severe floods both in urban and rural areas [15–17]. Although considered natural hazards, floods increasingly happen in cities where human activities are to be blamed. Urbanization for example has been observed to cover large areas in cities with roofs, roads, pavements and thus restrict natural flow of water and percolation. Moderate storms in typical East African cities thus end up collecting enough water to cause floods and thus their intensity has been growing as cities expand. Major towns including Nairobi, Kampala, and Dar es Salaam have witnessed periodic flooding which have repeatedly left widespread infrastructural and humanitarian costs [17]. Flooding has also impacted the agricultural sector in which crop fields were swept away, nutrients leached, and top soils eroded. Even more worrying, both frequency and intensity of floods are worsened by the warm ENSO events. For example, the El Nin˜o event in 1997 resulted to heavy rainfall and widespread flooding that was responsible for up to 1.7 m rise in the water level in Lake Victoria and severe damage to the agricultural sector (see > Box 17.1 below). The flooding left many famers and pastoralists stranded with massive losses. Arguably as a sign of worsening situation, regional statistics show that between 1992 and 2008 up to 3, 137, 675 USD worth of humanitarian aids were spent on flooding-related disasters. Apart from flooding, drought is another climate disaster that has been very common in the region and

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is documented to be in close agreement with the regional climate change statistics. Between 1992 and 2008, droughts have claimed about USD 28,383, 288 in humanitarian contributions to rescue lives within the region. Based on regional meteorological data however, drought events may decrease in a few places while at the same time increase in other areas with major potential agroecological implications. Some of the most common implications in the region include desertification and deforestation that have been recorded to increase in many places. Based on the above statistics, it is clear that droughts bring more hardships to the people and have wider economical implication in the region than flooding [17]. Box 17.1. Showing Effects of El Nin˜o in EA Much of EA observed severe droughts in 1997 that was followed by devastating El Nin˜o rains from October 1997 to March 1998 [18]. The El Nin˜o season was responsible for up to a fivefold increase in rainfall [5] with severe consequences in infrastructure, agriculture, and health problems to both livestock and humans. The available statistics shows that up to 4,000 people died of flooding and many more died due to increased cases of malaria and cholera in the region. In addition, thousands of livestock died as a result of the flooding. The El Nin˜o was economically costly as two major cash crops in many areas within the region; tea and coffee were severely reduced. In addition there were widespread rotting of cereals notably wheat and maize in the region and consequently increased prices of the cereals [9, 19]. Furthermore, the much dependent source of foreign income, from tourisms was as well hampered due to infrastructural problems. Furthermore, movements of farm inputs to farming areas, agricultural produces, and livestock to marketplaces were all impacted with significant increases in production costs.

Apart from that, other recent studies already show a clear linkage between climate change and incidents of wild fire within the region. Cases of bush fire due to periodic droughts and high temperatures are presently not uncommon within the region. One of such studies was done on Mt. Kilimanjaro where apart from the receding glaciers that everybody is worried about, there is a silent danger, periodic fires that are feared to have more ecological consequences than the diminishing glaciers. Because of the periodic fires on the mountain, it is argued that one third of the forest cover has already been lost within the past seven decades alone. The fires on the mountain have been very serious to the extent that it is feared the water sources in the fog interception zone will completely disappear within the next few years. It is thus argued that fires on the mountain may have far-reaching impacts on the eco-hydrological balance of the receding glaciers [20, 21]. Apart from Mount Kilimanjaro, fire events directly connected to climate change have also been observed on other forest resources including on one of the world’s biodiversity hot spots, namely, West Usambara and Uluguru Mountains [22]. Incidents of wild fires have also been reported in other regional ecosystems and projected to have more detrimental impacts in countries like Kenya where already a large parts of the country lie in the arid and semiarid areas [23].

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Sea Level Rise and the Salt Water Intrusion into Fresh Water Sources The EA region hosts a long strip of coastal area along the Indian Ocean that is shared by both Tanzania and Kenya. The ocean resource supports millions of livelihood and important cities for regional growth are found along the coast. Hitherto, studies from many parts of the world have shown only a small increase in sea levels and/or reports still treat it among potential effects of climate change. The sea level rise due to climate change can clearly be studied in EA where small islands such as Maziwe Island in Tanzania that was once attractive for tourists, fishermen, and researchers is now most of the time submerged and only habitable for a few hours during the day. Located about 15 nautical miles from a coastal town of Pangani in Tanzania, Maziwe Island is a clear wake-up call that the region is already suffering from sea level rise and demands further studies to establish consequential hydro-geological and ecological impacts. Note: Because of its importance and richness, the island was named among the national marine reserves in 1975 and is home to 35 species of corals, more than 200 species of fish and a wealthy of algae, sponges, and sea grasses [4]. Although Maziwe Island is the clearest threat of sea level rise in the region, many coastal towns and cities in Kenya and Tanzania remain at risk from the rising sea level [24]. As seen earlier, most of these coastal towns in the region are of historical importance and attract many tourists every year. Indeed the submerging of the island would have significant socioeconomical and ecological implications like disruption of livelihoods and most importantly the regional GDP. Even more worrying, the sea level rise is already threatening fresh water availability through seawater intrusion affecting millions of coastal inhabitants who mostly depend on ground water for domestic water supply. One such place where sea level rise is threatening such an important source of fresh water is Tanzania in which her aquifers and deltas are known to be at high risk. Other potential risks of sea level rise in the region include coastal erosion, losses of coral reef and mangroves in both Kenya and Tanzania [24].

Impacts on Water Availability, Agriculture, and Food Security As seen earlier, it is worth mentioning that, even without climate change, agriculture in the region has many serious challenges, among them the overdependence on rainfall and soil degradation. Climate change is of a special concern in the agricultural sector since increasing temperature, changes in precipitation patterns, flooding, and generally water scarcity have all been linked to recent food insecurity in the region. About 80% of EA livelihood depends on agriculture which regionally contributes around 40% of the GDP [25]. Agriculture in EA is highly vulnerable to climate vulnerability which often results to repeated crop failures, lower export earnings, and low domestic revenues inter alia. Most EA countries are among the world leaders in terms of food insecurity and climate variability will worsen diminishing harvests [26]. Presently, over 40% of mortality rates

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among Uganda’s children are due to chronic droughts in the country. Many more children across EA are either stunted or underweight because of climate change–related malnutrition [27]. Research has shown that the overdependence in rain-fed agriculture has been leaving many rural livelihoods vulnerable to food insecurity partly due to the recent shift in growing season within the region. Although climate variability has been blamed for the worsening food insecurity, the vulnerability in the agricultural sector is also complicated by heavy reliance on the subsistence farming by the majority of farmers [5]. Note: African agriculture is the slowest in terms of productivity increase. Thus, global warming will only add tension to the already overstretched region and hence likely to affect even a greater number of individuals. Box 17.2. Showing Potential Impacts of Climate Change on Agriculture Tanzania is likely to lose up to 10% of its grain harvest per year by 2080 [22], among them, corn, which is a staple food and traditionally the most important source of carbohydrate in Tanzania. Already farmers are witnessing a significant decline in corn harvests and have attempted to grow other crops in its place. Should [CO2] double and temperature increase by between 2
C and 4
C, an average of 33% of maize harvests is likely to be lost by as early as 2075 [4]. In some places in central Tanzania, up to 80% decreases in the maize harvest have been linked to climate change [4, 22]. In Tanzania, the flood and/or drought-related famines have increasingly been common since the mid-1990s.

The recorded slight increase in temperature and decrease in rainfall within the region have already claimed many victims in terms of food insecurity. For example, the recorded decrease in rainfall of between 50 and 150 mm between March and May from 1996 to 2003 was observed to have a corresponding decline in long-cycle crops in the region. As a result, many households abandoned maize (one of the long-cycle crop) the harvest of which directly depends on the availability of enough rainfall during the mentioned season above (see > Box 17.2 above). In recent years generally, drought has been observed to decrease water supplies with consequences in reduced crop productivity and the associated widespread famine in Northern Kenya and the Southern and central parts of Tanzania (see > section ‘‘Natural Disasters: Droughts, Flooding, and Wildfires’’). Another droughtrelated disaster could be traced in Rwanda where in 2005, the country observed massive crop failures in the Eastern province. In addition to the decrease in the amount of rainfall, agricultural systems in certain parts of EA have also been affected by too much rainfall. Equatorial EA have particularly been receiving increased amount of rainfall during El Nin˜o season which resulted to periodic flooding often associated with sweeping away of crops [5]. Climate change impacts on the agriculture sector will also have significant economic implications via interference with cash crops (> Box 17.3 below). In Kenya for example, agricultural losses from three cash crops in coastal areas, namely, coconuts, mangoes, and

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cashew nuts could amount to about USD 500 million under a 1 m increase in sea level. The three crops also make a significant livelihood to many coastal dwellers in Tanzania and are under more or less similar threats [28]. Box 17.3. Showing Potential Impacts of Climate Change on Cash Crops and the Associated Economic Implications in Kenya Apart from food crops, climate change is also projected to affect major cash crops in the region with wider socioeconomic implications. Studies have shown that should the temperatures increase by 1.2
C and if the changes in precipitation patterns continue large areas of the world’s second producer of tea (Kenya) will be made unfavorable for the crop. The latter would mean interference with over 25% of Kenya’s foreign exchange and up to 10% loss of employment opportunity [28].

Impacts on Human, Livestock, and Wildlife Health Climate variability is ubiquitously known to be central in the reproduction and geographical distribution of a number of disease vectors. For example, recent projections show that a global rise of between 13
C and 3
C would enable mosquitoes to expand their natural range while survival chances of other disease vectors are likely to be increased with increasing rainfall. Within the region, the unprecedented extreme weather events, namely, high temperatures and severe rainfall are blamed for the initiation of malaria epidemic in highland Rwanda, Uganda, Western Kenya, and Tanzania. It is well known that mosquito vectors thrive better under warmer temperatures hence global warming will most likely worsen cases of malaria. Within the region generally, intensity and severity of climatesensitive diseases, namely, Dengue Fever, Rift Valley Fever (RVF), typhoid, cholera, malaria, dysentery, and a number of respiratory diseases are all projected to worsen with ongoing climate alteration [27].

Malaria Worsening of malaria cases have been recorded in many places within EA and the epidemic is directly a result of changes in rainfall patterns, higher temperatures, deforestation, and generally environmental degradation [5, 15, 22, 44]. In close agreement to increasing numbers of malaria victims, regional studies already indicate an upward creeping of malaria cases directly because of recent modifications of vector habitats due to climate change [29]. For example, between 1960 and 1980 there were no recorded cases of highland malaria in highland EA the case of which is no longer true in many highland areas like Lushoto and Kilimanjaro in Tanzania. The creeping of malaria into the

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highlands of EA is of particular concern since the local inhabitants of such places do not have a well-developed immunity against the disease and thus have a relatively increased mortality rate [22, 29]. Worrying predictions exist that more highlanders are likely to be further affected if the current trends will continue. The above trend is already witnessed in many places within the region where on top of climate change which is known to modify vector/microbial adaptations, the situation is also aggravated by regional socioeconomic changes, worsening of food production, and crippling health-care systems inter alia [15, 16, 22, 30].

Rift Valley Fever (RVF) Hitherto, it is ubiquitously known that outbreaks of RVF are usually associated with heavy rainfall and warm temperatures. Within the last decade, several outbreaks of RVF in EA were directly attributed to worsening climate change impacts. Thus, the effects of climate change on human health within the region can further be appreciated by the close correlation between regional El Nin˜o events and Rift Valley Fever (RVF) epidemics in recent years. The observed regional trend has been that during warm ENSO events, the EA highland tends to receive unusual high rainfall which has a positive relationship with the number of recorded RVF outbreaks. Going deeper into historical records would reveal that about 75% of all recorded cases of RVF occurred during the warm ENSO events between 1950 and 1998 [31]. Such statistics give a worrying sign of what is likely to happen if full-scale impacts of projected negative effects of climate change on health sector would occur.

Cholera The relationship between regional climate change and health sector can further be understood from cholera epidemics. Studies have shown that prolonged droughts often associated with scarce water resources, poor sanitation, and changes in rainfall and temperatures are periodical reasons behind regular out breaks of cholera and other waterborne and diarrheal diseases in EA. Cholera cases are known to be worsened by wet seasons thus any increase in the amount of rainfall as already is the case in some parts of EA (> section ‘‘Natural Disasters: Droughts, Flooding, and Wildfires’’) would further elevated cases of cholera. As seen earlier, regional rainfall is projected to increase in coastal areas and Lake Victoria Basin, the named localities above have already witnessed a relative increase in cases of cholera outbreaks [22]. The acute intestinal infection diseases that is caused by Vibro cholera can often become fatal and is now declared endemic in Lake Victoria Basin, and has been of repeated occurrence in the region since 1978 [22, 30]. Available statistics show that the disease first caught the attention of EA coastal dwellers in 1836 where it left over 20,000 deaths in Zanzibar (Tanzania) alone and killed many more people in Kilwa (Tanzania), Malindi and Lamu (the latter two in Kenya). As a direct sign

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of the climate variability factors in cases of cholera outbreak in EA is seen from the fact that cumulatively, more cases of the disease have been recorded over the past 3 decades the same duration in which there has been worsening of climate change impacts. Recently, the outbreak of poorly known diseases such as Chikungunya fever have also been linked to climate change in EA. It is known that warm and dry climatic conditions precede a typical outbreak of the disease. Following the prolonged drought for many seasons in EA, about 500, 000 people mostly in the coastal areas were reported to be afflicted by the mosquito spread viral disease [32]. Apart from human health, livestock health has also been impacted by climate change in which there could be further infestation of tsetse flies, ticks, snails, and other disease vectors to previously safe zones. The former are already observed to spread to North East Tanzania with the potential of reducing safe grazing range in the areas [22]. Furthermore, the impacts of climate change on healthy systems in EA have even affected wildlife ecosystems. In 1989 for example, large numbers of wild animals died of rinderpest and were directly attributed to regional climate change impacts [22]. Such big losses of wildlife coupled with declining biodiversity due to repeated drought in the region are likely to cripple tourism sector, the major sources of foreign currency in the region.

Impacts on Environment: Deforestation, Fisheries, Biodiversity, Wildlife, Ecosystems, and Sea Water Intrusion into Fresh Water Although major impacts on biodiversity in the region is presently believed to come from humans via overexploitation of natural resources and land use change, recent climate change scenarios have equally been threatening the biodiversity. Already studies show that there are changes in the migratory roots of wild animals in several precious ecosystems of in EA. Even more worrying, studies have shown an upward shift in vegetation composition in major mountains in the region particularly on Mount Kilimanjaro. Generally, the climate variability already has its detrimental effects in dynamics of regional biomes and biodiversity integrity and richness. Although most of the tropical fishes have adapted to warm waters, most of them might not survive temperatures beyond their critical thermal maxima due to recent climate change trends. The population of important fish species (Tilapia mariae) that occur in EA and used as important source of protein are likely to be affected if their preferred temperature (between 25
C and 33
C) will be exceeded. This particular species of fish has a thermal maximum of 37
C beyond which they will not survive [33, 34]. Ecologically however, global warming might have even more effects as any such ecological imbalances will disturb the ecosystem and might result to losses of many more species. Other studies show that due to recent climate variability impacts in Lake Tanganyika there has been a 20% decrease in primary production estimated to correspond to about 30% of fish yields [33]. In addition, researchers are already worried of the effects of climate change on the hydro-geochemistry of water bodies in EA that have a potential of significantly decreasing

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fish populations. Regional studies show that any slight increase in temperature is likely to affect the amount of dissolved (O2) and the limnology of major lakes in the region [35]. Already worrying studies show significant effects might occur in Lake Tanganyika and Victoria. The latter lake has in the 1980s observed massive deaths of fisheries due to low levels of dissolved oxygen as a result of decreased turnover in the lake [4]. It is widely believed that the trend is likely to be the same in other lakes in the region and calls for ecological studies to be carried so as to establish the situation. Any escalation in the effects of climate change on great lakes fisheries will have major socioeconomic implications as the lakes offer an important source of employment, food to millions of people within the region, and even foreign exchange [4]. Even more worrying, among the negative impacts of climate change that are already witnessed in EA include the problem of species invasiveness. It is already known that invasive species have better adaptive ability to climate change which puts them in a better competitive situation compared to other species. The latter is very worrisome as EA region has already witnessed a number of exotic species becoming uncontainable with detrimental ecological implications. Very delicate forest ecosystems in the Eastern Arc Mountains, like the East Usambara forest reserves are already struggling with ecological impacts of several invasive species including Lantana camara and Maesopsis eminii. The problems of species invasion are not limited to terrestrial ecosystems; marine ecosystems have also witnessed a number of invasions including the water hyacinth and Nile perch in Lake Victoria. Studies show that the region may further be victimized by more colonization of invasive and other exotic specifies directly because of the ongoing global climate change [4]. Although climate change is not the only problem affecting regional ecosystems, combined with other factors like overexploitation of resources and particularly land use changes (destruction of habitats), may result to severe effects to regional biodiversity. The latter has directly affected forest resources and availability of important products like fuel wood has been significantly affected. In addition, regional desertification has also been observed to expand.

Climate Change and Energy Crisis in EA In order to be able to get a better picture of how the global climate change is complicating availability of energy in EA, the following basic is information is considered vital. EA is blessed with a rich mixture of energy varieties that can be generalized into natural gas and coal in Tanzania, geothermal energy in Kenya and Tanzania, numerous hydropower sources, significant biomass in nearly all member countries, and recent discovery of oil reserves in Uganda and potentially in other countries. There are also rich potential for wind energy, biogas, and solar power in many places within the region [3]. Within EA however, low level of regional development is clearly reflected in the energy characteristics and can statistically be studied from the percentage (%) energy consumption characteristics (> Table 17.1).

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. Table 17.1 Showing levels of energy consumption in East Africa (EA) Electricity (%) (major Country Petroleum (%) source of electricity) Kenya

21.0

Uganda

6.1

Tanzania

8.0

Others (Natural gas, solar power, wind Biomass (%) power, etc.) (%)

3.0 (Mainly from hydropower, petroleum, and geothermal energy) 1.1 (Mainly from hydropower and petroleum)

75.0

1

92.8

–

1.2 (Mainly from hydropower, natural gas, coal, and petroleum)

90.6

0.3

In EA, the effects of climate change on regional energy stability can be observed from diverse angles. These include reduced availability of biomass, diminishing/dwindling water flow for hydropower generation, and most importantly destruction of infrastructures (roads, railways, electric poles) needed to transport and distribute various forms of energy. From the table above, it is clear that the energy balance in all countries is largely dominated by biomass (mostly fuel wood, charcoal, and agricultural wastes). Since the effects of climate change include desertification this is where it possess its effects on the major source of energy. Wood is increasingly becoming rare in many places due to both human pressure and climate change (desertification), see > section ‘‘Impacts on Environment: Deforestation, Fisheries, Biodiversity, Wildlife, Ecosystems, and Sea Water Intrusion into Fresh Water’’ above. One potential mitigation option in the region’s energy supply would be to embark on renewable which are not limited. However, the inclusion of the renewable into the energy mix has not been of any significant contribution in comparison to the massive potentials available among other reasons due to high initial costs involved and poor availability of necessary technologies [3]. A few promising attempts however exist in Kenya and much less in other countries where more than 150,000 solar PV units are installed contributing to over 5 MW to the country’s power needs. Kenya is again leading in terms of wind energy harvesting where some 450 kW wind power system is already installed. Other countries including Tanzania have already identified several potential locations where wind is abundant round the year and some implementation attempts are ongoing [3]. On the other hand, biogas would be another potential source of energy in the region on account of presence of many livestock. However, biogas technology has been around in the region for over 20 years but its implementation has faced similar problems like solar energy. Isolated hope exists in Uganda and in other countries where a few plants have been

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installed and running. Interestingly, Uganda has also been a leading player in terms of power generation from industrial biomass residues. Promising units of power are currently being produced in three different sugar mills in the country. Kakira sugar works for example, is currently producing 2.5 MW and plans to produce 15 MW when the unit is fully running. Tanzania has comparable installations in Kilombero Sugar Company with a few other potentials in other sugar industries like Mtibwa [3]. Efforts can still be made by individual governments within the region to invest in renewable energy as the current installation is mostly from private sector. Strengthening of such renewable energy sources into regional energy balance would help in dealing with periodic shortage of power due to repeated droughts in hydropower basins within the region which have hampered many developments projects [3]. Although EA is desperate in meeting its energy demands, if not carefully planned some adaptation to climate change impacts on energy sector are likely to leave the region to follow the destructive way as currently the situation is in Asia, particularly China. The recent incorporation of coal energy as a source of energy in Tanzania is seen to be as one adaptation options. Poor technology of harnessing energy from coal may add regional contribution to GHGs. The country has about 1,200  106 metric ton of proved coal reserves which could meet most of the energy needs in country and potentially of the neighboring countries. Already the country is contributing about 6 MW to the national grid from coal and the plan is to increase production to about 600 MW as an adaptation to the drought-prone hydropower. Given the low level of technology in the country however, the capitalization of coal into the energy mixture is likely to contribute further to the problems of global climate change [3]. Concomitant with the effects of climate change on availability as seen on biomass, hydropower is also periodically affected by drought the frequency of which has been very high in the recent years. Like the rest of EA countries, Rwanda is also facing power shortage because of the impacts of climate change in its hydropower plants. For example in 2006, the country spent 65,000 USD per day to generate emergence electricity because the Rugezi wetland had its water reduced to very low levels. Although, the 1997 El Nin˜o triggered heavy rain and subsequent flooding in many places in EA it left certain parts of Kenya with severe drought that badly disrupted hydroelectricity power generation [34]. In nearly all countries in EA, hydropower generation has suffered from climate change–related problems, namely, low water levels and siltation [3]. Worth noting, the proportion of electrification in the region is very low among other reasons due to financial constraints to expand the network, high prices of electricity, and generally low level of development [3].

Livestock Sector EA region is home to thousands of pastoralists. Interestingly, most livestock are mainly found in drier part of the EA like arid to semiarid regions. Worth noting, the dry lands comprises of about two-thirds of Africa’s land in which about 50 million people depend

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on livestock and/or dry land agriculture. Although, climate variability is a common phenomenon of most dry lands, in Africa and particularly EA it has particularly influenced ecosystem structures and functions and consequently land use and lifestyles. It is worried that in, arid and semiarid regions, climate change may lead to loss of palatable forage to livestock and more drought-tolerant vegetations that are not suitable to livestock [23]. The major climate change vulnerability to livestock sector in the region comes via repeated droughts that leave the areas with severe shortage of pasture and water (> Box 17.4 below). As a result, there has been an increase in the number of conflicts between pastoralists, farmers, and wildlife. The recent droughts have been severe to the extent of triggering communal fighting and even threatened to inter war between neighboring countries. Other vulnerabilities to livestock sector include flooding. In recent years, flooding has been reported to sweep a large number of animals and made pastureland unavailable for livestock. In addition to drought and periodic flooding, livestock industry in EA is also affected by other factors like diseases epidemic, intertribal raiding, and declining pastureland due to rapidly increasing human populations among others.

Box 17.4. Showing Effects of Drought on Livestock Husbandry in EA In 1997 the whole of EA, observed one of the worst droughts which led to huge economic impacts to the pastoralists [36]. In Uganda, frequency of environmental insecurity, livestock rustling, and intertribal fighting have increased, largely blamed on increased frequency of droughts; thus, pastoralists are forced to move beyond their land areas [14, 36]. It is projected that as a direct consequence of climate change, Uganda may have a significant reduction in suitable areas for dairy farming and entire livelihood of the some pastoralists would be disrupted [14].

Other Sectors Tourism is a very important regional sector in terms of foreign exchange earnings. Surprisingly, for a very few regional literatures exist patterning impacts of climate change on tourism sector. The effects of climate change on regional tourism mainly come through demolition of infrastructures that support tourism or disrupting the natural beauty of the tourism attractions. Major tourism attraction in the region, namely, Mount Kilimanjaro and Kenya, spectacular ecosystems such as wildlife and natural forests are all threatened by climate change (see > section ‘‘Impacts on Environment: Deforestation, Fisheries, Biodiversity, Wildlife, Ecosystems, and Sea Water Intrusion into Fresh Water’’). Furthermore, major tourism cities like Malindi, Mombasa, Lamu (in Kenya) Zanzibar, Dar es Salaam, Bagamoyo, Mtwara, and Tanga (in Tanzania) all lie in the coastal where the projected sea level rise will have major socioeconomic implications [22]. The livelihood of many people in the coastal areas directly depends on the sector for living. Major infrastructures like hotels and other recreation structures are also threatened by the projected sea level rise [3, 22]. Like in other developmental activities, infrastructures such as roads and railways

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are very important for the sector but have periodically been swept away by flooding. The recent flooding in Tanzania which was associated with El Nin˜o event swept a large part of the railway and it is estimated that the country would require at least 6 months to fixing it.

Socioeconomic Implications of Climate Change on EA Mountains Diverse verticality of mountain ecosystem offers numerous microenvironments which in turn creates rich biodiversity. However, mountains are known to be very sensitive ecosystems that are often faced with conflicts between environmental conservation and human activities. Yet, scientific evidence show that most mountains are among vulnerable ecosystems to global warming. Rare mountain glaciers close to equator in a phenomenon that is only present in three regions on Earth: the Ecuadorian Andes, New Guinea, and EA. The latter hosts the two tallest mountains in Africa, Mt. Kilimanjaro (5,895 m) in Tanzania and Mt. Kenya (5, 199 m) in Kenya both of which are socio-ecologically very important to millions of people within the region. Many similarities exist regarding these tropical mountains, both of which are important tourism attractions, serve as important source of water, very rich in biodiversity and probably the most important for now, both are badly threatened by climate change and human pressure [32]. EA Mountain slopes are under constant pressure from both commercial and subsistence farming. The most important climate-related threats on regional mountains include the unprecedented glacier recessions and periodic fires. The disappearance of the glaciers is not limited to the two mountains named above, another mountain in the region, Mount Ruwenzori has observed more less the same trend [32]. Apart from interference with regional hydrological balance, the thinning of the glaciers has reduced the scenic values of the mountains with potential negative ramification to the tourism sector. Historical records show that these three mountains in EA began thinning in 1880 proportional to the drop of water levels in regional great lakes. In this chapter, the impacts of climate change on Mt. Kenya and Kilimanjaro are discussed in the > Box 17.5 below.

Box 17.5. Showing Retreat of Glaciers on Mount Kenya and Kilimanjaro and the Associated Socioeconomical Impacts to the Society Mount Kenya On account of its uniqueness, Mt. Kenya is included among the list of world heritage sites and nicknamed a water tower in a semiarid region. The mountain contains several remnants of glaciers all of which have been receding rapidly in the recent past (> Fig. 17.2). For example, the Gregory and Lewis glaciers have been showing unprecedented recession since late nineteenth century. In 1990, there were 18 glaciers compared to only seven left by 2007. Studies show that the deteriorating water resources in the mountain and generally all other resources is attributed first and foremost to socioeconomic changes on the mountain but

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increasingly significant on climate change consequences and seasonal aridity within the mountain’s microclimates. The fast thinning glaciers have badly affected water supply to the already water stresses areas of the region. In addition, nearly all the major rivers in the Kenya begin from mountain, with majority of the water coming from the middle and the summit of the mountain. The water levels in Tana and Athi Rivers among several rivers that originate from the mountain are currently among the worst affected. Tana and Athi Rivers flowing are the main sources of water for the Seven Folk Dams, Kenya’s key hydroelectric power generation plant. In addition to domestic use, the water is also used for agricultural activities that are important for the livelihood of the people. Hence, climate change consequences on the mountain could as well have its impacts on energy balance of the country. In addition, the mountain provides an important source of water to more than seven million people in the surrounding communities. Other studies in the region has indicated that reduction in water volume of these two rivers due to glacier disappearance on Mount Kenya, will threaten the lives of over half of the Kenyan population [23]. Mount Kilimanjaro: The Roof of Africa Like Mount Kenya, Mount Kilimanjaro which is found in Tanzania near the border with Kenya (3
040 S, 37
210 E) offers an excellent opportunity to study and understand regional climate change trends and vulnerability. Because of its importance, the mountain has received a worldwide attention that has attracted a series of studies most of which giving worrying conclusions about its sustainability as a result of both climate change and human pressure. Arguably, the best way of studying the climate change vulnerability on Mt. Kilimanjaro is offered by its fast thinning glaciers and its implications to the hydrology of the surrounding areas (> Fig. 17.2). While the historical records show that the glaciers have been retreating since 1850, the current thinning is arguably the most alarming and fastest. Whereas the early retreat was likely due to natural climatic shifts, both the ongoing global warming and human pressure are blamed for the worse retreat ever recorded. Statistics show that there was about 4.2 km2 of glaciers in 1976 compared to only 2.6 km2 in 2000. The most recent studies on the mountain suggest that there will be no glaciers left on the mountain as early as 2020. The disappearance of the glaciers on the roof of Africa will have many negative consequences. The water from Kilimanjaro is feeding the Pangani basin where about 3.7 million Tanzanians live and many socioeconomic activities are carried out. The waters from the mountain are used for domestic, agricultural, and even hydropower production on the Nyumba ya Mungu dam. In addition, there are already changes in population dynamics and migration behaviors of species in the fragile ecosystems. Any further deterioration in the ecosystem would mean significant consequences as the Kilimanjaro national park is the number one tourists’ attraction in the country. Unfortunately, because of climate variability and human pressure, there has been an increase in the number of fire events burning on the mountain that are likely to further degrade the eco-hydrological balance of the mountain [6]. Recent studies show that the fire is responsible for the ecological shift in species zones within the mountain [4, 21, 22, 32, 37]. Note: Because of its richness and shortage of land in Kilimanjaro region, Mt. Kilimanjaro area is among the most densely populated land in the country, the population of which is comparable to that of a typical city in Tanzania.

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. Fig. 17.1 Showing loss of Kilimanjaro glaciers and vegetation cover in a period of less than a decade [4]

100% 90% 80% 70% 60% 50%

Thermal

40%

Others

30%

Nuclear

20%

Hydro

10%

ue

la

e ez

am

Ve n

rin

Su

u

a

ua y gu ay U ru

Pa ra g

Pe r

r

uy an

G

do

a

ua

bi Ec

C ol om

ia Br az il C hi le

liv

nt ge

Bo

in

a

0%

Ar

592

. Fig. 17.2 Electricity production structure by country in 2008. Based on information from Latin American Energy Organization-OLADE 2009. Energy Statistics Report 2009. Base Year 2008

Coping with Extreme Climate Events Indigenous Mechanisms East Africans have a long history of living with consequences of extreme events like famine, drought, and invasion of locusts among others. Historical records in Burundi, for example, show that during famine, affected population was forced to relocate to less affected places.

Climate Change Impacts, Vulnerability, and Adaptation in East Africa and South America

17

In addition to relocation, at times of extreme events, Burundians are documented to have worked as casual laborers in exchange for food. EA region is rich in such strategies albeit most of them need extra-local level enforcement and might only help in a short term and/or for non-severe impacts [4, 5, 14, 22]. Although most of the local initiatives are unlikely to help people in the long term they however do provide important help during disasters. Generally, important lessons can be learnt from such initiatives may be included in regional efforts to combat climate change. An array of such coping mechanisms is analyzed and their strengths and weaknesses are discussed. The adaptive ability at the local level however differs from regions, households, and/or communities based on their respective environmental settings, socioeconomic backgrounds, and resources availability [5]. Generally, most traditions in EA had strict customs and norms that ensured sustainable utilization of their natural conservation. One of such interesting forest ecosystems management could be traced to Burundi where certain biodiversity elements (plants and animals) were protected under traditional and religious beliefs. Apart from forests resources, such traditional conservation methods were presented for different plant types that were believed to have sacred values. Locally, referred to as Intatemwa and Ikidasha and translating respectively to what should not be cut and burned, such ecosystems were strictly prohibited from cutting and burning on account of their spiritual benefits. In the same society, felling down of live trees in Kibira forest was also firmly prohibited. Kinira forest, located high altitude, was believed to be a conjunctiva between the Earth and the sky and people generally respected both its virtual and physical services. In addition, only a few people including the King and members of his kingdom were allowed to hunt in the forest. Generally, the combination of the traditional and religious beliefs above ensured sustainability of many of the sensitive ecosystems. Such initiatives include the shamba system in Kenya and the Ngitili of the Sukuma agropastoralists of Tanzania. The former system works by allowing surrounding communities in the protected government forests to grow short seasonal food crops in the forest patches in which they are also expected to plant and manage trees. Farmers are not expected to establish permanent residence within the patches and after a short time (3–5 years) they usually move and establish the same procedure to other forest patches. No payment is made to the farmers as both parties are beneficiaries in one way or another. The farmers are allowed to use the land the government assisted in reforestation. If this system is well managed and reinforced, it can save the two folds smoothly and help in improved livelihood of the people and the carbon capture and storage [23]. The latter system on the other hand is a common practice among the Sukuma agro-pastoralists of Shinyanga, Tanzania. It works by retaining areas of standing vegetation from the beginning to the end of the rainy period. Such areas, locally referred to as Ngitili, are usually closed to livestock grazing at the beginning of the rainy season and only made available to livestock during the dry period. The Ngitili thus serves to protect livestock from severe drought spells which are not uncommon in this region and at the same time serves to protect the ecology of the areas. Apart from the strategies above, other communities of the region have other means of making a living during climate-related disasters. Such local level coping mechanisms

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may include any of the following or their combination: switching to non-farming activities, collection of wild-fruits/vegetables/honey, remittances from migrants relatives and friends, and rarely selling one’s assets [15, 16]. Non-farming activities may include things like charcoal burning, handcrafting, casual laboring, and brick making. Although the contribution/income from such activities might be seen insignificant, it provides cushioning household to go through calamitous times like droughts and flooding. Regional lessons show that families that regularly receive remittances adapt better to climate change impacts than their counterparts who received nothing. Likewise the gathering of fruits, vegetables, and honey enable the household members to survive such times. In the light of repeated droughts and their local experience, some societies in the region have turned into the use of local seed varieties and seed selection as a direct response to drought. Studies have shown that some local grain varieties, for example, in Tanzania have better tolerance to drought than improved/high yield seed and consequently farmers in drought-prone areas periodically to grow local varieties. Such studies also indicate that the local varieties have longer shelf life than improved seeds. Apart from that, some famers have replaced common crops like maize and beans with millet, sorghum, and cassava which are known to have better tolerance to drought. In addition, farmers cope with drought by including some livestock in their livelihood and establish some economic ties with pastoralists and markets and practice other off-farm activities so as to diversify survival options [38]. Some farmers use their local skills and change planting seasons when drought is anticipated. When drought is expected farmers have often changed the combinations in their intercropping, to determine when to grow certain crops and switch between crops. Apart from the survival strategies employed by indigenous farmers, EA pastoralists have also developed several coping mechanisms dealing with periodic droughts (> Box 17.6 below). Such strategies include but not limited to economicdiversification, migration to areas with better pastures, having diverse species of livestock, and intentional subjecting of herds to nutritional/drought like stress so as to adapt them to stress period and hence increase their survival chance during disasters [38].

Box 17.6. Showing Impacts of Climate Change on Sociocultural Aspects of Pastoralist Society in Tanzania and Their Subsequent Adjustments Among the traditionally strict pastoralists society in Tanzania include the Maasai who are entirely dependent on blood, milk, and meat from their herds for nutrition. Interestingly, the Maasai have started to practice crop farming in their means of livelihood [42] and nonpastoral foods like tea, corn, and sugar are increasingly becoming common. One of the reasons why the Maasai alongside other pastoralists in Tanzania have shifted to crop farming is the fact that their means of coping with climate variability to their livestock have been constrained by the current climate change pressure [43].

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Adapting Major Regional Sectors to Climate Change Over the recent decades, the region has faced a number of climate-related calamities, namely, floods and droughts which have crippled livelihood support systems. These have necessitated an array of adaptation strategies at various kinds of sectors including governments, private sectors, and individuals. For a long time however, regional governments had failed to link climate change impacts on development projects. Major adaptation in this chapter will be discussed below guided by vulnerability categories discussed above. Other specific adaptation strategies are also addressed. In recent years also, there has been recognition of the climate change challenges in regional policy issues.

Livestock Sector Many methods have been suggested in dealing with climate change challenges on livestock sector. The most important adaptation method in practice includes reducing the number of livestock by keeping fewer healthier, more productive breeds. The latter has the potential of reducing pressure on pasture and water resources thus survive through calamitous periods like droughts [10]. Other widely used adaptation strategies include zero grazing and other improved methods of grazing that reduce environmental destruction [4]. The creation of livestock watering centers has a potential of reducing the number of livestock deaths due to shortage of water. The challenge with the latter option is on how to balance the water needs for the animals and avoid concentrating large numbers of livestock on the centers which might end up with further environmental degradation. Moreover, natural resource laws and policies especially on water and land need to be reviewed to allow pastoralists access the resources without triggering tensions with farmers [39]. It is under such circumstances where traditional land laws like the ones in Tanzania may be capitalized and integrated into regional strategies [4]. Finally, improvement of livestock extension services is vital where disaster preparedness information would easily and effectively be made to pastoralists before they occur [5].

Health Sector The most important means of adaptation in the health sector has been breaking breeding cycle of the disease vectors. The ongoing procedures for the control of malaria for example include improving drainage systems, removing stagnating water points, and bush clearance in residential areas, all of which aim at reducing mosquito multiplication [22]. On the other hand, proper development and implementation of the early warning system for climate-sensitive diseases is another strategy that works better in reducing/ controlling disease outbreaks. In addition, inclusion of the local skills on vulnerability, risks and local coping options that have been used by the respective society is very

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important. For example, some local people within the region have well-developed skills on how to deal with both livestock and human health challenges [41]. Careful integration of local skills into the wider health sector may serve many lives. Tanzania’s Government has recognized potentials of traditional medicine and have included it in her medical research. Currently, a relatively well-advanced traditional medical center is fully operational at the Muhimbili National Hospital [22].

Agriculture Adaptation in agricultural sector probably requires the most attention as inhabitants in the region are among the global leaders in terms of food insecurity. Even more important, climate change is already estimated to have resulted to tripling food crises per year from 1980 to 2000. Intensification of pests and diseases, changes in cropping timing and shift in agricultural zones are consequences of climate variability that requires immediate actions. Among the frequently suggested adaptation option within the region include, inter alia, the use of fast maturing and drought resistant crop varieties, inclusion of cover crops in the field, conservation tillage practices, and the use of green manure. However, the former strategy would require full involvement of the local people as certain farmers in the region objected certain varieties of drought resistant crops on grounds of their low markets and relatively high labor in their production [22, 40]. As climate-related failures in agriculture system intensified, agricultural sectors took the necessary steps like research in diseases and drought resistant crops, and early maturing crop varieties. Kenya and Tanzania are leading the efforts in such researches and already promising results have been noted. In the former country for example, 14 varieties of maize adapted to low available water are already in the field [23]. Similar efforts are ongoing to other crops, namely, millet, sorghum, beans, and peas. In addition, different regional food security initiatives like national food reserves were created in nearly all countries in EA to help the population during times of disasters. Arguably, as a result of worsening situation, both governments, nongovernmental organizations (NGOs), private sectors, and in some cases United Nations agencies are usually involved in such initiatives. Such initiatives often go down to district level so as to quickly deal with disasters when they occur. However, most of the initiatives have been hampered by lack of enough funding, high food prices, and mismanagement [22].

Clean Energy and Energy Serving Technology In EA region, most of the energy balance is met from biomass (> Table 17.1). Any activity that would reduce the current rate of fuel wood consumption would thus help reduce deforestation and hence sequester more carbon. The use of fuel wood–saving stoves (efficient cook stoves) is regionally adapted as a promising strategy in dealing with

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energy crises. The latter is very important since land degradation, deforestation, and increase in desertification especially in arid and semiarid areas within this region have made availability of charcoal and fire wood very difficult and expensive [23]. Interestingly, the declining biomass has necessitated regional studies on ways of consuming less biomass and higher efficiencies. Several types of fuel wood–saving stoves are in use and are proved to be very efficient. Most of these energy-saving stoves whose technology is simple and generally cheap use between 60% and 70% less fuel wood compared to traditional stoves [3, 4, 23]. The potential of the stoves as a workable solution to reduce regional deforestation has caught the attention of nearly all regional governments, NGOs, CBOs, and other stakeholders and has been introduced to many parts of the region. As a result, the fuel wood efficient stoves are now widely used in public institutions, hotel industry, and households. For example, a recent survey in Kenya has shown that there has been an increase in the number of households using the stoves from 4% to 15%. In Kenya alone, it is estimated that the increase in the use of the stoves would save about 7.7 million tons of fuel wood annually [23]. Other countries in the region are also investing in these stoves and promising outcomes are already reported. In Tanzania for example, efforts are being led by a nongovernmental organization called Tanzania Traditional Energy Development and Environmental Organization (TADEDO) where many stoves have been distributed countrywide [4]. Replication of similar efforts across the region would greatly contribute toward reduction in land degradation and deforestation since biomass contributes over 70% of domestic energy source in the East African region. Apart from fuel wood, other materials, namely, saw dusts, plant residuals, animal droppings, and some commercial wastes have also been used in some of these energy-saving stoves. In addition to the fuel wood efficiency that has a wide regional advocacy, efforts are also being made to reduce energy use and maximize efficiency in industries. Specific standards are currently operational in nearby countries regarding air quality control and generally environmental protection. Less fuel and high efficiency would all add to reduced GHGs emissions. In addition, there has been limitation in the importation of used vehicles and other machines beyond a certain age limit that have started to be implemented in most of the EA countries which in turn will contribute toward reduction in carbon emission [3]. Other, regional adaptation strategies in the energy sector include cogeneration and bioethanol production. The former mostly involves generation of electricity and heat from bagasse, a sugar cane waste product, by sugar industries. Kenya has currently one registered Clean Development Mechanism (CDM) project in this field, namely, the ‘‘35 MW Bagasse Based Cogeneration Project by Mumias Sugar Company Limited (MSCL).’’ On the other hand, ethyl-ethanol, a by-product of sugar processing that is relatively a clean form of energy that has multiple uses and is currently being explored by various sugar industries in Kenya. Regionally, such relatively clean energy projects are already running in Kenya and Tanzania with the potential of even further improvement to other parts [3]. With climate change, regional cooperation in the energy sector is very important so as to compensate for potential shortfall in energy supplies. There exists a legal cooperation in

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energy sector within the East African Community (EAC) member states stipulated under article 101 of the Treaty for the establishment of the EAC. The treaty stipulates most legal issues that would ensure a smooth sharing of energy resources where member states are already sharing their energy resources [3]. Generally, coping with climate change–related energy scarcity would require a combination of actions. The most reliable alternative to oil and biomass would be to strengthen the use of renewable energies like wind, geothermal, and solar energy. For example, geothermal energy generation in Kenya has proved to be a reliable and clean form of energy and has made a significant contribution to the national grid [3]. Further exploration of the geothermal energy into Tanzanian side would reduce the overdependence in natural forests and petroleum. Furthermore, investment into the relatively abundant supply of natural gas in Tanzania should be made central as natural gas has proved to be a relatively clean energy compared to oil and coal. Both of these attempts would additionally reduce the little regional contribution of CO2 emission [3].

Fight Against Disease Because climate change has been observed to accelerate distribution and intensification of several diseases in EA, several adaptation strategies have been proposed in fighting diseases. Most regional efforts have been concentrated on malaria, the number one global killer that has been responsible for over a million people annually. Because of the high motility rate it inflicts to people, several campaigns have been launched to eliminate the disease. Such regional campaigns range from the use of treated mosquito nets, rising awareness to the general public to the use of insecticides both indoors and in the environment. The latter strategy however needs to be taken with care so as to avoid potential environmental effects. Special attention has recently been addressed in highlands where the local inhabitants do not have the natural immunity against the disease and are thus vulnerable [22]. Other efforts are also addressed to other diseases such as cholera and typhoid fever. Vis-a`-vis the latter case, water regional sanitation programs are threatened especially during wet seasons [30]. Apart from human diseases, isolated efforts are also directed toward the control of animal diseases. The latter efforts include the control of disease vectors by the use of insecticides and provision of sound breeding and extension services (However, a few biological control agents of mosquitoes introduced in some areas, for example rice growing village of Mwea in Kenya, should be taken with care and closely monitored and controlled as cases of species invasion are not uncommon in EA [23] (see > section ‘‘Impacts on Environment: Deforestation, Fisheries, Biodiversity, Wildlife, Ecosystems, and Sea Water Intrusion into Fresh Water’’).

Flooding Control With climate change, flooding calamities have been of repeated occurrence, the latter has necessitated several adaptation strategies across the region. Among such measures include

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the construction of dams and dykes to prevent flooding. In Kenya for example, such dykes are constructed on river Nzoia and Nyando. So as to reduce vulnerability to people, other efforts include coastal areas conservation and conservation agriculture [17, 23].

Water Harvesting, Irrigation Scheme Development, and Water Serving Technology Although the region is known for periodic droughts, there are periods of the year where surface runoff and flooding are common and could potentially be trapped for usage during water scarcity. The water which is most of the times wasted can potentially be trapped and used for domestic and industrial usage during drought episodes. Already efforts are being carried within the region where small-to large-scale water harvesting schemes are being done. For example, because of the increasing water scarcity in arid and semiarid regions in Kenya, roof top rainwater collection, and construction of water pans and dams are being facilitated by both the government and private sector [23]. In addition, East Africans have adapted to frequent droughts via irrigation development. As in the case with water harvesting, irrigation projects are well established in Kenya where recently some pastoralist societies have embarked on irrigated agriculture. The Narosura irrigation scheme run by the Maasai from the Narok district stands out to be the best example where horticultural crops are being produced. Similar irrigation schemes are also run in Rwanda, Tanzania, and Burundi. Apart from the efforts above as climate change continued to cause water shortage in the region, water-serving technology has also became a mandatory in many of the agricultural and industrial sectors [23].

Environmental Conservation As already discussed above, climate change is one of the factors for the recent environmental degradation in EA. In dealing with impacts of climate change on the environment such as soil erosion and water stress from flooding and rising global temperatures respectively, regional governments, private sector, and other stakeholders have taken several environmental conservation steps and management of degraded ecosystems. In some parts of Kenya and Uganda, famers have adapted to farming methods that addresses both soil erosion and water loss. Increasingly, agroforestry, contour farming, and green manure are increasingly becoming common farming methods in many places in the region. On the other hand, special sectors/programs are put in place to address coastal resources in both Kenya and Tanzania [24]. These include the coastal development authority in Kenya and the integrated environmental program in Tanzania [40]. Issues of afforestation and reforestation have also been given significant emphasis in the region. For example, there is a region-wide tree planting campaign that has generally done very well. In Kenya, for example, the Green Belt Movement (GBM) led by the Nobel Prize Laureate, Professor Wangari Mathaai, has received worldwide recognition for planting

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over 2,000 ha of trees. In collaborating with women groups in other parts of EA, the movement has successfully restored trees in farmlands, community lands, and even on school lands. Such local initiatives need to be assisted so as to deal with the increasing problem of regional desertification. The movement is now in the process of registering some of its afforestation/reforestation initiatives as Clean Development Mechanism projects and is already receiving financial assistants from the World Bank among others [31].

Challenges and Opportunities for Combating Climate Change in EA Before concluding on this chapter, it would be worth to discuss something regarding regional challenges and opportunities in combating climate change. The many opportunities available include the potential to develop reliable renewable energies within the region. As mentioned earlier, solar radiation and wind energy are not of short supply round the year [25]. Potentials for geothermal energy are also very promising in Kenya and Tanzania. The former country is already producing a significant amount of electricity from geothermal energy and plans to increase its capacity even further. Albeit, the region has observed a series of droughts and desertification has been reported in a number of places, it has many forests that can serve as important sink of carbon if long-term strategies regarding their sustainability would be ensured. Because of the presence of large land cover in some countries like Tanzania, the potential of afforestation and reforestation exist with the added advantage of the geographical position which favors rapid growth of trees and hence sequester carbon from the atmosphere [27, 39]. Generally, the region has the potential of being among best beneficiaries of the UNFCCC’s Reduction of Emissions from Land Degradation and Deforestation (REDD) mechanism. On the other hand, apart from the challenges discussed so far, high above the list, poverty food insecurity and natural disasters, namely, droughts and floods remain to be exigent. Within the region, poverty is strongly connected with deforestation and generally degradation and could thus limit the successful implementation of mitigation programs such as REDD. The challenge thus is to have effective disaster preparedness, reduce the proportion of populace that depend on rain-fed often unreliable agricultures, have a working health-care system especially in rural areas and the provision of alternative livelihood support mechanisms [18, 31, 40].

The South American Picture A Brief of South America South America occupies the landmass of the American continent located in the southern hemisphere, composed of 12 countries and covering 17 million square kilometers. It is bounded by Panama to the north, the Pacific Ocean to the west, and the Atlantic Ocean to

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the east. This region presented a population of 383 million and a gross domestic product (GDP) of 2.3 billion US dollars by 2007. The total exportations represented US$453 billion while the importations represented U$337 billion. The countries with the highest GDP per capita are Chile, Venezuela, Brazil, and Argentina [45]. In this region 27,602,792 of inhabitants are indigenous (about 7.2% of the region’s population), with Peru showing the 46%, Bolivia 21%,and Ecuador 20%. Additionally, for these countries indigenous population represents the 47%, 71%, and 43% of the total respective national population [46]. South America accounts for 27% of fresh water of the world and 8 million square kilometers of forest. The region is the main global food producer and exporter and represents a hydrocarbon (oil and natural gas) offer estimated for 100 years [47]. The main representative organs in the political and economic agreements are the Union of Nations of South America (UNASUR) which consists of all the 12 countries of South America; the Community of the Andean Countries (CAN) with the participation of the main four countries with a territory in the Andean Mountains (Bolivia, Colombia, Ecuador, and Peru), and the Common Market of the South (MERCOSUR) consisted of Argentina, Uruguay, Paraguay, Brazil, and Venezuela. Also, in the region the Amazon Cooperation Treaty Organization was created by the countries with territory in the Amazon Forest (Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, Surinam, and Venezuela).

Climate Change Evidence in South America The climate variability reported in the region is mainly indicated by the precipitation change, which presents an increase in Southern Brazil, Paraguay, Uruguay, North East Argentina, North West Peru, and Ecuador, while some decline is reported for Southern Chile, South West Argentina, and Southern Peru. The percentage of the variation in the precipitation presented a range variation between 5 and +6 in Colombia from 1961 to 1990, while in Uruguay, this tendency showed a positive variation of +20 between 1961 and 2002, which is also completely opposite to the one registered in Chile of 50 for the last 50 years [48]. The temperature variability and its effects on climate events are not only different by region, but also vary according to the season. Bolivia has showed major temperature variations in the humid months, a relationship which is also presented with the precipitation [49]. In the Central Andean Region, the temperature variations registered between 1974 and 1998 are about 0.34
C, which is a 70% more than the global average [50], and maximum temperature variations (
C/10 years) of +0.2 and +0.2 are during the months of December, January, and February in Argentina-Patagonia for the last 50 years, with Argentina central presenting negative variations for the same periods are presented by (0.2 to 0.8) [51]. The main climate events that have been identified in different ecosystems are strongly related to the Austral Oscillation and El Nin˜o phenomena [52–54]. The interannual oscillation between cold and warm sea surface temperature is known as El Nin˜o and the Southern Oscillation phenomenon (ENSO). This phenomenon presented unusually strong warm events in 1982, 1983, 1997, and 1998, which is believed to have a relationship with global warming [55]. This relationship has also been covered by other studies [56] that

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studied data of atmospheric CO2 concentration and the ENSO cycle to analyze the coupled climate–carbon cycle concluding that the terrestrial biosphere and the ocean carbon cycle behave in opposite senses, in which the land acts as source while the sea acts as a net sink. This is opposite to the dynamic described during La Nin˜a, when sea performs as source and land as sink of carbon dioxide. Moreover, including decadal trends analysis, studies are showing that ENSO could be higher with warmer phases which are increasing with the global warming [55]. On the other hand, studies have suggested that El Nin˜o is activated to reverse positive global warming while La Nin˜a reverse negative trends, concluding as well that ENSO could be sensitive to variation of global temperature but not at the actual value of global warming [56]. The temperature of the surface in the Pacific is linked to the variability of the precipitations, which causes negative trends during warming events, especially in the wet seasons in the Andean region of the North of Bolivia and to the South of Peru, while in the north of the Andean a systematic reduction is recorded in the North-East of Ecuador and in Colombia [52]. Global warming can also cause a permanent El Nin˜o state with major impacts in the Amazonia [67]. Because of the relationship between global warming and ENSO, and the influence of these events with land-climate dynamics, it is important to understand how sea sink dynamics can interact with land sources and the carbon cycle for creating mechanisms due to the protection and regulation of these cycles.

Climate Change Vulnerability in South America The vulnerability of the region is not a linear process but a complex one related to feedbacks that increase the different risks and the vulnerability in both, the natural and the human systems. In this way, the vulnerable factors described can be direct or feedbacks reactions resulting of the dynamic in social, natural, and/or linked human–natural systems, in which all are, associated to the climate events. The main threats related to global warming are mainly associated with the climate variations of ENSO. This relationship causes/will cause stronger precipitation and droughts in the South American region affecting the natural hydrological cycles. The responses to the different events derived in South America are demonstrating a high vulnerability in the ecological and human systems. Because of the natural, social, cultural, political, and economical heterogeneity of the region, this vulnerability also varies through all the geography. As a result several risks are recognized for the water resources protection and supply, agriculture, health, energy security, and ecosystems protection especially on the Amazon Basin.

Ecosystems Vulnerability The coastal area in South America is strongly exposed because the sea elevation, records show ranges in variations over 1 mm per year for Colombia, Argentina, and

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Guyana and up to 4 mm/year for Brazil. In Argentina, the coastal area is already affected by the increased precipitations and landward winds [48]. Mangroves are already exposed, and risks associated with hurricanes and the sea level elevation have been recorded. Soil degradation is also worsened with climate change, estimating that more than the 20% of the national territory could be degraded by the year 2050 in some countries like Chile, Ecuador, Paraguay, and Peru [57]. On the other hand, some studies estimated that the resilience of the Amazon Basin climate variations is zero, which in turn means that the conversion of this biome to a drier state threatens the key functionality of this ecosystem (representing the production of the 20% of the global oxygen) [58]. Some researches recognized that climate events, such as hurricanes, can expose the soil to erosion increasing the loss of nutrients. Vulnerability of these ecosystems is related to the Pacific temperature changes, to global warming but also to local climate effects resulting from land clearing or land use change [58]. In Brazil, almost the 50% of the country’s rainforest may disappear by 2050 [59]. The effect of the long-term climatic variability has also been recognized in the northern part of the Amazonia where drier conditions have been noted since 1977 [56]. Moreover, the hydrological regime in the Amazon Basin presents more vigorous water cycles as a consequence of the increase in the evaporation and transpiration. These specific ecosystems sustain water regimes depending on the relationships established between the sunlight, soil moisture, humidity, and cloud formation. As temperatures rise, the mountain cloud forests (also known as nebelwald which are forests with persistent wind-driven cloud) can present warming, affecting the hydrological cycles and exposing the local species to water stresses. As a result of extended dry seasons and lower water supply, vegetation is more vulnerable to fires and droughts [60, 61]. With the 90% of the Andean glaciers located in areas with exposed droughts and the 10% in tropical humid areas; the retreating of glaciers can represent not only a loss of species but also impacts on the society and economy as energy, agriculture, and water supply, which are severally impacted for the present reduction in the ice covering [62]. Studies on glacier dynamics have included different variables to understand the impact of the climate variation and the retreat presented during the last decades. Cloud cover convection, precipitation, temperature, and humidity are related variables that have helped to monitor and estimate the past and future trends of glacier retreat. The temperature variation has increased by 0.11
C every 10 years from 1950 [8], presenting a warming on the Pacific side and moderate variations in the eastern slopes [15]. Furthermore, increasing in the cloud cover is recognized over the North parallel 10
S in wetter seasons (December to February) while to the south of this parallel the cover cloud presents decreasing [52]. The cloud cover and convection has showed a decreasing in the east of the Andes over the Amazons, while information analyzed for the humidity cannot be reconciled with this tendency [63]. The suppression of rainfall in the Amazons is additionally estimated as a result of changes in El Nin˜o and weak Atlantic anticyclone [61].

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Socioeconomic Vulnerability The relationships of the damage ratio with the GDP show that countries like Peru, Bolivia, Ecuador, and Colombia (10%) are more vulnerable than other countries demonstrating a direct link between GDP and vulnerability [49]. This social and agro-economic vulnerability is as well noted in Colombia, Ecuador, Peru, Brazil, and Bolivia by the World Bank [64]. In addition to limited access to insurance, disparities in human development and lack of climate-defense infrastructure, the poverty and low human development are components that increase human vulnerability and reduce the capacity of society to adapt or respond to the climate impacts [65]. Driven by poverty and lack of proper planning, more population is localized on vulnerable zones. In Bolivia, the population growth rate in 1992 was 2.44% increasing 3.47% in the valley region by the year 2000. In the plains, the rates are higher with a growing rate of 3.89% by 1992 and 3.26% by 2000, with the 70% located in the urban area [66]. Additionally, by 1991 the homes under poverty were 78% for the valleys and 70% for the plains [67]. This is a regional tendency where human settlements locate frequently on vulnerable areas, which added to extreme climate events is increasing the risk to natural threats. Moreover, the vulnerability grows for indigenous population in the region. The major dependency of indigenous and traditional communities is on the natural resources, and because these resources could be more difficult to access or are reduced as a consequence of climate variation, these communities are exposed to negative effects [68]. Also, the location and economical activities of these communities are strongly associated to the services provided by the more affected ecosystems. Not only mountain or dry regions are occupied by different indigenous communities, but also tropical forests and some protected areas are the main zones of indigenous settlements. It is estimated that large part of Latin Americans living in poverty are indigenous [69]. The traditional and cultural backgrounds of these communities bring them to depend specially on the natural resources, creating dynamics of conservation and local development that can be threatened by the current effects of climate change. Poverty is a common factor in indigenous communities, and because of the loss and degradation of ecosystem services, the access to health systems, education, or information is more difficult for these populations. The agricultural frontier is expanded as a result of the desertification of the ecosystems and the increasing of urban areas, causing the clearing of forests and the increase of the vulnerability by firing, soil erosion, and local climate variations as well. Despite fossil fuels have been recognized as the main source of CO2, the changes of the use of land and deforestation are the main causes of these emissions in Bolivia (83%), Ecuador (70%), and Peru (42%) [49]. This tendency is representing a social threat as much as 20% of Brazilian Amazonia’s population depends on the region’s natural resources and more than four millions of rural inhabitants depending economically on these resources [57]. Resulting from the glacier retreating and changes in hydrological cycles, the water resources are increasingly stressed exposing the population in South America to reduced

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availability of freshwater resources. Capital cities depend on high vulnerable ecosystems; 70% of the population in Bogota is supplied with water from the Chingaza Natural Park, consisted of cloud forests and paramos, while Quito and Lima depend on water sources from important glaziers as the Antisana and Cotopaxi in Ecuador and the Chacaltaya in Peru [50].

Agricultural Vulnerability Agriculture is as well one of the main impacted components in South America. This sector is one of the most important in the regional economic development, accounting for 8.6% of the gross domestic product (GDP) [70]. The most extensive droughts and reduction of precipitation in some areas reduce the productivity of crops. In Paraguay decrease in cotton, wheat (by 2030) and soy (by 2050) are expected with sugar cane, cassava, and corn presenting increase in crop yields as a result of the A2 climate scenario (climate scenarios were developed by the Emission Scenarios of the IPCC Special Report on Emission Scenarios, the A2 scenario includes a storyline and scenario family describes a very heterogeneous world). For subsistence farms in Ecuador 1oC of temperature rising can increase crop yields but with a retreating after temperatures reach 2oC, also banana, plantain, and cacao can be negatively affected with a just rise of 1oC for intermediate farms [57]. In this way, it is also projected that small farmers (farms less than 30 ha) will get positive impacts for those situated in cold areas, but those located in warmer regions (Venezuela, Colombia, and the North of SA) may suffer negative consequences [71]. Some projections estimated different scenarios of temperature and rainfall variations to 2100, the first included an increasing of 1.9oC in the temperature and a 10% of rainfall increasing, other two estimated temperatures raisings of 3.3oC and 5oC with rainfall dropping by a 5% and 10% respectively. Following these projections a loss of land value of about 20% (by the year 2060) and 53% (by the year 2100) was calculated in the worst warming scenario, and with smaller magnitudes in the other two. The study underlines the representativeness of the precipitation changes in the final values, with small household farms showing more vulnerability with higher temperature while large commercial farms responded negatively to increasing in the precipitation (as these kinds of farms owned commercial livestock what can be more affected by precipitation increase) [71].

Impacts and Potential Risks Caused by Climate Change ENSO has been related with malaria outbreaks in South America and childhood diarrheal disease in Peru [34]. The IPCC predicts that the dry seasons can promote malaria, especially in the coast areas of Colombia, Venezuela, and Guyana, while with floods these epidemics are recurrent in the north coast of Peru. Also, prolonged droughts in Argentina, Chile, Paraguay, and Brazil increase the outbreaks of pulmonary hantavirus,

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while leishmaniasis, leptospirosis, and hyperthermia are outbreaks associated with the climate phenomenon [48]. Power energy stations are presenting decreasing and suspension of the services because of the precipitation changes, increasing temperatures, and longer dry seasons corresponding to more frequent steady El Nin˜o phenomena (see > Box 17.7).

Box 17.7. News Summary February, 2010 Paraguay faces energy shutdowns everyday as result of the heat wave presented in February with high temperatures that also raise the energy consumption overcharging the capacity of the hydroelectrical system. (BBC Mundo, 2010) October 21, 2009 The drought caused by El Nin˜o has forced to the energy interruptions in Venezuela. The reduction in the main rivers levels that supply the hydropower of different damns demands frequent electricity cut offs in all the country. (IPS, Venezuela, 2009) November, 2009 Ecuador faces the worst drought in the last 40 years that has reduced the reservoirs of the hydropower centrals and requiring the emergency declaration by the national government in the electricity sector. This situation has also required the increasing in the energy imported from Peru and Colombia. The emergency was clear when the Paute Hydroelectrical Plant reduced the production to 35% of the total demand while the normal condition was of 60%. (La Hora, Ecuador, 2009) Source: Arce E (2010) Paraguay also has Energy Crisis (in Spanish). BBC Mundo. Available on: http://www.bbc.co.uk/mundo/america_latina/2010/02/100208_1318_paraguay_energia_gz. shtml; Marquez H. (2009) El Nin˜o takes the water, the electricity and the water (in Spanish). Ambiente Venezuela; La Hora (2009) El Nin˜o El Nin˜o is merciless with the countries of Latin America (in Spanish). Available on: http://www.lahora.com.gt/notas.php? key=58448&fch=2009-11-14

This tendency is representing a risk for the energy system in SA as electricity production is mainly based on hydroelectricity (see > Fig. 17.2). The present clearing rates and the agricultural frontier expansion are threatening the Amazon forest, a key global ecosystem. The increasing of evapotranspiration caused for higher temperatures will impact water cycles in the Amazon’s Basin. On the other hand, with the loss of vegetation and increased temperatures a combination of lower evapotranspiration and precipitation causes a drying effect. Loss of species and ecosystem types shifts are resulting from the global warming and increasing the vulnerability of human communities as well [56]. Furthermore, some features of the human communities settled in the Amazons region result in an increased risk for the conservation of this ecosystem and the sustainability of the human communities.

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The high dependence on manual labor of small farmers in the Amazons and the information incompatibility between global and local dynamics increase the difficulty of these actors to develop adaptation and conservation measures [72]. As this ecosystem is one of the main regulators of the carbon dioxide and local climate, and one of the main biodiversity regions in the planet, the current human and natural dynamics are generating a high risk in the loss of these functions, and increasing the effects of climate variation in the region.

Adopting Climate Change Adaptation and Mitigation Measures in South America The adaptation measures vary in different scales. In Peru, subregional strategies can be developed for the Clean Development Mechanism (CDM) or Adaptation under the National Strategy on Climate Change implemented since 2003. As a result, different actions on water management, food security, risk prevention, or hydroelectricity can be found [31]. Moreover, Colombia is implementing the Integrated National Adaptation Plan (INAP): High Mountain Ecosystems, Caribbean Islands and Human Health [73] supported by a bilateral cooperation between the Netherlands and Japan. Additionally, many studies are still focused on the development of diagnostics and in pilot phases, some transversal programs are found in Bolivia, where a national mechanism for climate change adaptation covering water resources, food security, health, human settlement and risk management, and ecosystems create transversal programs in scientific research, capacity building and education, and anthropologic aspects and traditional knowledge [74].

Adapting to Climate Change Information management is also part of the adaptation measures. More investments and technological development will take place as much as information is reliable and open markets as result of the people perception on the necessity to adaptation [74]. Counting on reliable precisely and continuous information allow the governments to establish corrective measures for the different sectors. Projects like the Community-Based Risk Screening Tool – Adaptation and Livelihoods CRiSTAL (to assess the systemic vulnerability) or Opportunities and Risks from Climate Change and Disasters-ORCHID (to manage the risk, integrate adaptation, and identify opportunities to reduce vulnerability) are important developments with international support [75]. Also, the Tropical Ocean Atmosphere Program provides observations of the upper tropical pacific from the middle 1990 allowing the implementation of adaptive measures in the agriculture planning, fire prevention, stream flow prediction for hydropower, and with new applications in the health system [48].

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The Regional Role in Global Climate Change Mitigation Mitigation actions in this region are mainly directed for the conservation and protection of forests as clue elements for sinking CO2. In Colombia the first pilot project on adaptation by the Global Environment Facility (GEF) is being carried out, while Peru, Bolivia, and Ecuador are developing the proposal for the Andean Regional Project for Adaptation aimed at supporting pilot projects on glaciers and watersheds. Additionally, Ecuador is implementing a project through the water governance to reduce the vulnerability on climate change by an effective management of the water sources and better access to information on climate [49]. On the other hand, some projects showed results on the ecosystem services demonstrating the complexity using these mechanisms. In Brazil, after 4 years under implementation of a project to pay for conservation services to small-scale farmers located in the Brazilian Amazons has presented combined results. This program developed by Proambiente has gathered about 4,200 participating families, from which the 42% have reached payments over the R $650 (US$325) per household [59]. Also, the Juma Reserve REDD project has been established to prevent deforestation by the valuation of the services provided for the forests located in the southeastern region of the Brazilian State of Amazonas [76]. The PES (Payment of Environmental Services) presents a varied implementation; countries like Colombia and Ecuador counts on important projects (e.g., the Face Reforestation Program for Ecuador-PROFAFOR (Spanish abbreviation) carbon sequestration program, and the Pimampiro municipal watershed scheme) demonstrating advanced applications, however Colombia presents some disadvantages in the payment to services providers, while countries like Bolivia and Venezuela show a higher skepticism and political barriers [77]. Otherwise, some challenges are recognized for the legal hurdles, this aspect is observed on the Brazilian legislation for the concept of environmental services and their economic value which can be related with the water-use charges that does not place economical value on the water-conservation role of landowners [59]. Also, the complexity on the information related to the scientist and economical integration can affect the real operability of adaptation and mitigation measures. For this case, some studies have estimated that emission from both deforestation and fossil fuel combustion represents the 12% which is 8% less than the one estimated by the Intergovernmental Panel on Climate Change (IPCC) [78]. > Table 17.2 shows the ecological footprint for some countries in South America included in the estimations made by the Global Footprint Network [79] demonstrating the large biocapacity contained in the region and represented by their forests. South America counts on several advantages to develop adaptation and mitigation measures. Peru holds more than 40 projects equivalent to the reduction of about five millions of CO2 tonnes [49]. The Andean region including Venezuela and Chile counts with 570 millions of hectares of bio-productive area from which 200 millions supply goods and services and absorb their own wastes, representing 370 millions of global hectares valuated in 115,000 million dollars [50].

Climate Change Impacts, Vulnerability, and Adaptation in East Africa and South America

17

. Table 17.2 Ecological footprint, ecological deficit, and main contributor of biocapacity, by country, 2006 (Elaborated based on information from Global Footprint Network. Footprint for Nations 2010 data tables http://www.footprintnetwork.org/en/index.php/GFN/page/ footprint_for_nations/. Accessed September 29, 2010)

Country name

Ecological footprint

Ecological (deficit) or reserve

Main type of biocapacity

2006

2006

2006

Argentina Bolivia

3.0 2.4

4.1 16.9

Cropland (33%) Forest (82%)

Chile Colombia Ecuador Paraguay

3.1 1.9 1.9 3.4

1.0 2.0 0.4 7.4

Forest (53%) Forest (57%) Forest (57%) Forest (62%)

Peru Venezuela (Bolivarian Republic of)

1.8 2.3

2.3 0.3

Forest (67%) Forest (72%)

The PES offers a great opportunity for countries to develop mitigation programs for the conservation of ecosystems and reforestation. For example, in Pimampiro, Ecuador, a farmer receives 12 $/ha/year for the conservation of primary forest, however, payments can vary for the same land use (a farmer in Heredia, Costa Rica receives 57 $/ha/year for the same land use), the implementation of PES has turned on an opportunity for farmers to develop conservation and productive activities [80].

The Climate Change Challenge for South America South America CO2 emissions are relatively low, however, Brazil predominates the emissions of the region while all the countries (excluding Paraguay) are presenting increasing in the emissions, with Bolivia and Ecuador showing an increase of 69% and 79% between 1999 and 2008 relatively (see > Fig. 17.3). About the 50% of the ktCO2 registered by 2012 belongs to energy associated projects (see > Fig. 17.4). This tendency is demonstrating the important participation in the Carbon Market reached by the implementation of energy projects. Some projects in South America are demonstrating the potential of the region for implementing alternative energy and reduce CO2 emissions (> Table 17.3). Despite the low participation of SA in the CDM, energy projects represent more than the 80% of the ktCO2e registered by 2012 in all countries in the region (excluding Paraguay and Uruguay) (see > Fig. 17.5). SA requires technological transfer to take advantage of the alternative energy potential but better policies should be applied by

609

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Climate Change Impacts, Vulnerability, and Adaptation in East Africa and South America

450000 400000 350000 300000 250000 200000 150000 100000 50000

2008

0 1999

610

Argentina Ecuador Suriname

Bolivia Guyana

Chile Brazil Peru Paraguay Venezuela

Colombia Uruguay

. Fig. 17.3 CO2 emissions (Gg) by country, 1999 and 2008. Elaborated based on data from Latin American Energy Organization-OLADE 2009. Energy Statistics Report 2009. Base Year 2008

participating in Global Carbon Market to achieve technology and resources transfer while protecting natural resources. A good example was given by Ecuador when decided to pledge in a pioneering agreement with the United Nations to refrain from oil drilling in a pristine Amazon preserve in return for some US$3.6 billion ($4.9 billion) in payments from rich nations [81]. Because the ecological sensibility, the sociocultural and economic context, South America is one of the main vulnerable regions in the planet facing climate change. This situation requires more accelerated and practical adaptation programs in the real scenario. Because the main natural and social characteristics bring different levels of risk, also the application of these programs should vary and be approached to different scales. The main challenge for this region is to understand how global, regional, and local dynamics can impact the different local scenarios. At present, the main aim for combating climate change is to design more effective mitigation and adaptation measures for the specific and unique conditions, not only for the different countries, but also for the different communities and ecosystems contained within them. Policy integration of the countries to transform the natural resources and energy potential into operative projects is required. Regional scales, beyond national boundaries, should be integrated for designing regional actions toward the technological transfer for alternative energy development and conservation programs for vulnerable ecosystems like the Amazons, Glaziers, and forest cloud mountains.

Climate Change Impacts, Vulnerability, and Adaptation in East Africa and South America

17

0.50%

0.12%

5.91% 5.43% 0.59%

0.04% 6.11%

14.01%

49.41%

8.14% 9.74%

Biomass energy EE Own generation Fossil fuel switch

EE Household EE Supply side Hydro

EE Industry Energy distribution

Landfill gas

Wind

Other

. Fig. 17.4 Global sharing of ktCO2 registered by project type by 2012. Elaborated based on information from data available at Carbon Market Data World ETS Database http://www. carbonmarketdata.com/. Accessed February 17, 2011

. Table 17.3 CO2 reduction potential by energy projects in South America (Elaborated based on information from * General Secretariat of the Andean Community, the United Nations Environmental Programme (Regional Office for Latin America and the Caribbean), and the Spanish International Cooperation Agency (2007) and ** Gerardo Siva Dias PR, Ribeiro WC, Sant Anna Neto JL, Zullo Jr. J (2009)) Country

CO2 reduction potential (Tones equivalent)

Ecuador* Bolivia* Colombia* Brazil**

307,000 17.7 Millions 800,000 84,165

Kind of project Not specified Not specified Jepirachi eolic project Alta Mogiana Bagasse for electricity produced from fossil fuel energy stations by energy produced from sugarcane bagasse

611

612

17

Climate Change Impacts, Vulnerability, and Adaptation in East Africa and South America

100%

Other

90% Wind 80% Landfill Gas 70%

Hydro

60%

Fossil Fuel Switch

50%

Energy Distribution

40%

EE Supply Side

30%

EE Own generation

20%

EE Industry

10%

EE Household

0%

IL

A

N

TI

EN

G

AR

AZ

BR

E

R

A

BI

IL

H

LO

O

C

Y UA

O

D UA

M

C

EC

G

RU

U

A

VI

BO

LI

RU

PE

Y UA

Biomass Energy

AG

R PA

. Fig. 17.5 National Sharings of ktCO2e Registered by Project Type by 2012 (Elaborated based on information from data available at Carbon Market Data World ETS Database http://www. carbonmarketdata.com/. Accessed February 17, 2011)

Future Direction to Combating Climate Change in SA and EA Vis-a`-vis the present climate change impacts, it is very unlikely that the negative effects on the environment and people’s livelihood will improve any time soon. The latter necessitates helping vulnerable individuals/groups cope with the adverse effects and reestablish their means of livelihood after climate disasters. Worth noting, combating climate change in the regions would require both local and extra-local efforts in a number of ways. For instance, future adaptations and mitigations to climate change vulnerability will have to be reflected in all regional polices [23]. Coping with climate change challenges will have to go hand in hand with major adjustments in various policies and legislations. For instance, the potential for utilization of renewable energies, namely, biomass, solar power, geothermal, wind energy, biogas, and natural gas would require significant regional governments’ commitments in terms of policy adjustments and economic sacrifices. Successful harnessing of geothermal energy in Kenya, natural gas in Tanzania, and most of the renewable in Brazil could imply that proper policy adjustments could reduce power shortages in the regions. In recent years however, significant efforts in structuring climate change policies have been taken by nearly all regional governments. Although the efforts may be considered insufficient compared to the impacts, they do provide a fundamental framework to dealing with regional climate change challenges. These include the establishment of national bodies

Climate Change Impacts, Vulnerability, and Adaptation in East Africa and South America

17

with full mandates on climate change issues and environment management at large and creation of several laws and legislations on environmental issues [27, 40]. Arguably, as a sign of worsening situation, most recent government policy documents in the regions do recognize climate change as an important impediment to their sustainable development. For instance, most climate change issues are notably defined in the regional National Adaptation Program of Action (NAPA) reports [40]. In summary, the regional bodies dealing with climate change requires an inclusion of how such projects and/or policies with potential negative impacts to the environment will be addressed before being accepted for implementation. The latter makes it mandatory for extensive Environmental Impact Assessment (EIA) to be carried out to such projects before they would be approved for implementation [27, 40]. However, care must be taken as some of the suggestions in the NAPA reports provide suggestion that might not work in the region. For example, some suggestions in the reports are considered too expensive in the region and require unavailable technology. Failures to fully involve local people have had bad experience in the region (particularly in Tanzania) where local people in the region objected some drought resistant crops on ground that they were tasteless and lacked market value [29]. The latter have resulted to poor adaptation to climate change impacts and left on agriculture a significant number of the individuals vulnerable. While some of the suggestion might work in the long run, real solutions to the challenges of climate change vulnerability would come from an inclusion of a wealth of local skills dealing with climate change and disaster management at large. In appreciating the importance of forests in carbon sinking, forests have regionally been advocated as one of the most important gears to combat climate change. In accordance with the global move, regional efforts put a lot of emphasis on both reforestation and afforestation programs [23]. However, renewed efforts on forest management are needed as desertification has been increasing. In addition, special consideration needs to be taken on energy sector since a significant portion of regional energy balance is met from biomass energy [25]. Capitalization on the abundant potentials of renewable energy would reduce pressure on the natural forests and the amount of carbon emitted. Alongside the suggestions above, it is worth noting that the regions lack necessary expertise and economic ability to deal with climate change and associated issues. Emphasis must thus be concentrated on training local scientists, planners, and policy makers to prepare them to deal with the worsening situation in the regions. In addition, future direction of climate change in EA and SA will have to be concentrated on land use change since major regional contribution to the GHGs comes via land use change and deforestation. Furthermore, EA region has an abundant supply of carbon dioxide which requires purification only to be ready for industrial use. EA countries could capitalize on the natural supply of the gas and stop importation of the gas from other places. At present, most industries in Uganda, Tanzania, and Kenya still import carbon dioxide which is seen as a wasted regional opportunity both to control carbon and investment. As a potential investment, the Carbacid Company in Kenya has started mining the gas for commercial purposes. Thus, both regional and even neighboring countries could meet all their carbon

613

614

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Climate Change Impacts, Vulnerability, and Adaptation in East Africa and South America

needs from the region without requiring importation of the gas. Similar efforts need to be strengthened in other regional countries and potentially stop importation of the gas all together. Other areas where strengthening can be done to reduce vulnerability to climate change include accurate information gathering and dissemination. The latter is important since most times when climate disasters strike many people have been caught unaware/ unprepared and thus increased vulnerability. In addition to that, renewed emphasis on local capacity building and decision-making should be made central in helping vulnerable groups to adapt better to climate change impacts. Because of the poor resource base in the regions, it is very important for funds whether in the form of credit or otherwise to be available to vulnerable groups after climate change disasters. Such funds can help affected individuals or groups, to restock lost animals, buy farm inputs, and/or reestablish lost business or other means of livelihoods. The best way to ensure availability of funds to such groups/individual could be via rural credit mechanisms. Governments and other stakeholders should as well help rural credit mechanisms like pastoralists and/or cooperative unions get funds from financial institutions. This is important as regional studies have shown that individuals who have financial access like remittances from relatives generally recover faster and better from disasters. Another potential area for future strengthening includes effective early warning systems on climate change disasters and effective information gathering and dissemination. Recent regional experiences have shown that climate change vulnerability is often worsened by failures to forecast potential climate disasters and poor communication between responsible authorities and the general population [40]. In the future, it would be very helpful to have a mechanism that would ensure such information is well forecasted and the general population is well prepared for the potential effects. Vis-a-vis to the above, it will be very helpful for regional bodies like meteorological departments and disaster management units to be equipped with advanced early warning systems for potential climate disasters and effective mechanisms to spread the necessary information. Albeit governments in both regions have taken certain steps in improving their disaster management units, further effort is still needed to improve them further by purchasing more accurate meteorological equipments and proper training of staff. Finally, careful enforcement of environmental education in school curriculums may also prove to be a reliable means of reducing causes of climate change but most importantly help in regional adaptation and mitigation strategies. Because climate change and generally environmental degradation are presently appreciated to be developmental factors, it is crucial for regional education system to effectively prepare younger generations on environmental issues. Significant efforts have been made in recent years regarding inclusion of environmental aspects in school system and several environmental-related degree and nondegree programs are being offered in colleges [27]. Efforts can still be done to improve such curriculums to enable real solutions to local climate change–related challenges. Inclusions of environmental course in nonenvironmental programs in schools would as well help a larger part of the society become environmental sensitive.

Climate Change Impacts, Vulnerability, and Adaptation in East Africa and South America

17

Conclusion In SA and EA, the negative climate change impacts are no longer potential threats but rather ongoing problems that have long been underestimated. Climate variability is already affecting many development projects and even threatens to undo some of the achievements made, including to some of the Millennium Development Goals (MDGs). Generally, the regional climate change vulnerability requires immediate actions as several sensitive ecosystems like the coastal resources, Eastern Arc Mountain forests, the Amazon forests; Mount Kenya, Mount Kilimanjaro, and the Andean Mountains are already affected. The negative impacts on agricultural systems, water resources, biodiversity, energy availability, infrastructures, and health issues are unmistakably clear and worsened by the fast growing population, wide spread poverty, among others. Today, ordinary people in the villages know their ways of making a living are threatened and are left with no option but to return to their indigenous survival skills. The status quo leaves the regions with potentials of being significant contributors of GHGs in the next decades via land degradation and especially deforestation of its fast shrinking forest resources so as to meet basic needs such as fuel wood. The use of poor often polluting technologies in the struggle for economic development and the desires to meet the needs of the fast growing population will also add to GHGs contribution in the future. As these regions near their peaks in terms of economic and industrial development, would mean a more net contribution in GHGs is likely because the regions will be consuming more energy, a trend that is already evident. Most adaptations and mitigation options suggested by international bodies and which are largely reflected in the regional climate change strategies have local implementation difficulties. Since the economic base of the regions is among the world’s least, implementations of such technical, expensive, and often unavailable options might prove to be difficult and could leave many people vulnerable to climate change impacts. Fortunately, the regions have rich indigenous skills and adaptation measures that require strengthening and inclusion into the regional vision for combating and/or living with climate variability. Thus, meaningful relief from climate change vulnerability will have to include existing livelihood strategies and especially recognition of the traditional resource management including on land that are well developed in the regions. However, local survival skills to the harsh conditions like droughts have in recent years been overstretched and feared not to work in the long term. Unfortunately, governments and development planners within the regions were late to recognize that climate change was an issue of development and needed to be incorporated into all development projects. Climate change issues were for the long time not clearly reflected into the regional development plans and mistakenly treated as a separate entity resulting to bitter lessons. Because of the severity of the challenges of climate change to the delicate livelihood system in the regions, governments, private sector, and other stakeholders were forced to take decisive steps and recognize climate change to be an integral part of regional sustainable development. Since major contributions to climate change causes come via land use change and naturals resources exploitation, land and natural resources like forests need to be central in

615

616

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Climate Change Impacts, Vulnerability, and Adaptation in East Africa and South America

dealing with climate change in the regions. Land and forest policies necessitate reexamining and better enforcing so as to control/reduce desertification, a trend of which has in recent years been significant in the regions. Moreover, because both the courses and impacts recognize no regional boundaries, regions must move with the rest of the world in combating climate change. Regional governments, private sectors, individuals, and other stakeholders need to play their expected roles in both adaptation and mitigation measures to combat climate change. On the other hand, where as the international efforts do provide important generalizations regarding climate variability, they should try as much as possible to recognize special vulnerability in SA and EA where many of their frameworks dealing with the variability might not work as expected and should locally be assisted to deal with their problems in specific ways. While generalization simplifies things, specific issues in the regions, like over 70% of the population dependent on biomass on EA, need to be noted and treated in a special way.

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(Regional Office for Latin America and the Caribbean), and the Spanish International Cooperation Agency (2007) The end of snowy heights? Glaciers and climate change in the Andean Community. Secretary General Andean Community, Lima, Peru http://revistavirtual.redesma. org/vol5/pdf/publicaciones/cambio_climatico_fin_ cumbres_nevadas.pdf. Accessed Feb 2011 Wu Z, Schneider EK, Hu ZZ, Cao L (2001) The impact of global warming on ENSO variability in climate records. COLATechnical Report CTR 110 Jones C, Collins M, Cox P, Spall S (2001) The carbon cycle response to ENSO: a coupled climate–carbon cycle l study. J Clim 14:4113–4129 Tsonis AA, Hunt AG, Elsner JB (2003) On the relation between ENSO and global climate change. Meteor Atmos Phys 84:229–242 WWF (2006) Climate change impacts in the Amazon: review of scientific literature http:// assets.panda.org/downloads/amazon_cc_impacts_ lit_review_final.pdf. Accessed 9 Feb 2010 ECLAC (2009) Economics of climate change in Latin America and the Caribbean Summary 2009, United Nations Santiago, Chile http://www. eclac.org/publicaciones/xml/3/38133/2009-851Summary-Economics_climate_change-WEB.pdf. Accessed 23 Mar 2010 Thompson I, Mackey B, McNulty S, Mosseler A (2009) Forest resilience, biodiversity, and climate change. A synthesis of the biodiversity/resilience/stability relationship in forest ecosystems. Secre´tariat de la Convention sur la diversite´ biologique, Montre´al. Technical Series no. 43, 67 pp Hall A (2008) Better RED than dead: paying the people for environmental services in Amazonia. Phil Trans R Soc B 363:1925–1932 Foster P (2001) The potential impacts of global climate change on tropical montane cloud forests. Earth-Sci Rev 55:73–106 World Bank (2010) Climate change and clean energy initiative assessment of the risk of Amazon dieback main report http://www.bicusa.org/en/ Article.11756.aspx. Accessed 3 Mar 2010 InWent (2008) Climate change and retreat of glaciers in the Andean region: implications for water resources management. Revista virtual REDESMA 2(3):19–23 Vuille M, Bradley R, Werner M et al (2003) 20th century climate change in the tropical Andes:

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observations and model results. Clim Change 59:75–99 World Bank (2008) Social dimensions of climate change report 2008. The World Bank, Washington http://www.crid.or.cr/digitalizacion/pdf/eng/ doc17656/doc17656.htm. Accessed 28 Feb 2010 UNDP (2007) Human development report 2007/ 2008 fighting climate change: humanity solidarity in a divided world http://hdr.undp.org/en/media/ HDR_20072008_EN_Overview.pdf. Accessed 21 Mar 2010 Calvo AF (2000) Demographic situation analysis of the country (in Spanish). Serie Documentos Tecnicos OPS, 2 Garcia CL (1999) Urbanization, poverty and redistribution space of the Bolivian people (in Spanish). Revista electronic de Geografia y Ciencias Sociales 45 (32) UICN (2008) Indigenous and traditional peoples and climate change Summary (in Spanish) http://cmsdata.iucn.org/downloads/ uicn_pueblos_indigenas_y_cambio_climatico___ version_resumida. doc. Accessed 23 Mar 2010 Derruyttere A (1997) Indigenous and sustainable development: the role of the Interamerican development bank (in Spanish). Banco Interamericano de Desarrollo. Departamento de Desarrollo Sostenible. Unidad de Pueblos Indı´genas y Desarrollo Comunitario, Washington, DC Seo SN, Mendelsohn YR (2008) A Ricardian analysis of the impact of climate change on South American farms. Chilean J Agric Res 68(1):69–79 Rodrı´guez VA (2007) Climate change, water and agriculture (in Spanish). Direccio´n de Desarrollo Rural Sustentable IICA. Comunica,edicio´n Nº1,II Etapa Brondizio ES, Moran EF (2008) Human dimensions of climate change: the vulnerability of small farmers in the Amazon. Phil Trans R Soc B 363:1803–1809 World Bank (2006) Project document on a proposed grant from the global Environment facility trust fund in the amount of used 5.4 million for the benefit of the republic of Colombia through conservation international Colombia for the Colombia: integrated national adaptation program project, Bogota Commission on Climate Change and Development (2009) Closing the gaps, Sweden www. ccdcommission.org. Accessed Dec 2010

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75. Levine T, Encinas C (2008) Adaptation to the climate change: experiences in Latin America (in Spanish). Revista Virtual REDESMA 2(3):25–32 76. do Planeta B, Sustentavel FA, do Estado AG (2008) The Juma sustainable development reserve project: reducing greenhouse gas emissions from deforestation in the state of Amazonas, Brazil project design document (pdd) for validation at ‘‘climate, community & biodiversity alliance (CCBA)’’ version 5.0 http://www.fasamazonas.org/en/section/publications. Accessed Dec 2010 77. Wunder S (2007) Between purity and reality: taking stock of PES schemes in the Andes, Ecosystem Marketplace http://www.ecosystemmarketplace.com/pages/dynamic/article.page.php? page_id=4585§ion=home&eod=1. Accessed Dec 2010

78. Van der Werf GR, Morton DC, DeFries RS, Olivier JGJ, Kasibhatla PS et al (2009) CO2 emissions from forest loss. Nat Geosci 2:737–738 79. Footprint for Nations (2010) Data Tables http:// www.footprintnetwork.org/en/index.php/GFN/ page/footprint_for_nations/. Accessed 29 Sep 2010 80. Kiersch B, Hermans L, Van H (2005) Payment schemes for water-related environmental services: a financial mechanism for natural resources management experiences from Latin America and the Caribbean. Paper presented on Seminar on environmental services and financing for the protection and sustainable use of ecosystems Geneva, 10–11 Oct 2005 81. Yasuni-ITT (2010) To keep the oil reserves under earth (in Spanish) http://yasuni-itt.gob.ec/. Accessed Dec 2010

Section 3

Energy Conservation

18 Energy Efficient Design of Future Transportation Systems John Seiner1 . Maximilian Lackner2 . Wei-Yin Chen3 1 National Center for Physical Acoustics, University of Mississippi, Mississippi, USA 2 The Vienna University of Technology (TU Vienna), Wien, Austria 3 Department of Chemical Engineering, University of Mississippi, Mississippi, USA Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 624 The Issue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627 Carbon Emissions by Light-Duty Vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 630 Carbon Generated by Combustion with Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632 Alternative Fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 637 Alternative Power Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 640 Air Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641 Cargo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641 Means of Energy Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641 Comparison of Different Transportation Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_18, # Springer Science+Business Media, LLC 2012

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Abstract: Transportation of people and of goods plays an important role in modern life. It is a major source of anthropogenic CO2. This chapter, after introducing some fundamentals of natural climate fluctuations as caused by Milankovitch cycles, describes the causes and consequences of manmade climate change and the motivation for increased fuel efficiency in transportation systems. To this end, contemporary and future ground-based and air-based transportation technologies are discussed. It is shown that concepts that were already given up, such as turbine-driven cars, might be worthwhile for further studies. Alternative fuels such as hydrogen, ethanol and biofuels and alternative power sources, e.g., compressed air engines and fuel cells, are presented from various perspectives. The chapter also addresses the contribution of CO2 emissions of the supply chain and over the entire life cycle for different transportation technologies.

Introduction The purpose of this chapter is to introduce current concepts being examined to increase fuel efficiency in transportation systems in order to reduce their impact on unfavorable climate change. This is a daunting task that will take the cooperation and sacrifice of most of the entire human population to avoid a premature catastrophic event. Now other chapters of this book reveal the salient scientific reasons for climate change, and the reader is encouraged to consult these chapters. However, here it is only necessary to establish that global warming or cooling has continually occurred by natural causes since Earth’s formation. This can be deduced from examining the so-called Milankovitch cycles [1]. Transportation of people (passengers) and goods (freight, cargo) can be done on the land, the sea, and in the air. One can distinguish between individual transportation (cars, bikes) and mass transportation (trains, planes, buses). Land-based transportation is achieved on highways and on railroads. Goods can also be moved in pipelines. With the globalization of the economy and shifts in lifestyle habits, transportation has become more and more important over the last 100 years, both in the industrial and the developing world. > Figure 18.1 below, in an exemplary fashion, shows the increase in energy consumption for transportation in China. According to [2], highways have become the dominant mode of transportation in China. The energy consumption in this mode increased from 1980 to 2006 from 36.4% to 61.5%. Other economies have seen similar developments. As > Fig. 18.1 shows, other transportation systems have seen more and more usage as well. Transportation systems are mainly driven by fossil fuels, predominantly those made from crude oil. Energy efficiency of transportation systems can be defined as the amount of energy needed for a certain task, e.g., the transportation of one passenger or one unit of cargo over a certain distance. Transportation and energy is reviewed in [3]. Energy efficiency is the most economic way for climate change mitigation [4]. Therefore, efforts need to be taken to improve energy efficiency of transportation systems.

18

Energy Efficient Design of Future Transportation Systems

Railways

Highways

Waterways

Civil Aviation

Pipelines

3000 2500 2000 1500 1000

2006

2004

2002

2000

1998

1996

1994

1992

1990

1988

1986

1984

0

1982

500 1980

Energy consumption (PJ)

3500

. Fig. 18.1 Chinese transportation sectors and their energy consumption from 1980 to 2006 (Reproduced with permission from [2])

Since the year 2000, the world production of gasoline (petrol) has matched consumption of this product. This has led to sporadic shortfalls of gasoline at the pumps along with elevated costs. Whether one believes in climate change or not, it is fair to say that no one has come forth who predicts fuel in the future will take a smaller percentage of their incomes. Beyond the uncertainty of future fuel costs, the predictions for effects of global warming on the planet are very severe and it is important that mankind addresses the issue of how transportation systems contribute to this problem. Today there are over one billion vehicles in the world, and within 20 years, the number will double [5], largely a consequence of China’s and India’s explosive growth. > Figure 18.2 takes a look at the historic and the projected number of cars in China. An impressive increase is expected over the next years [6]. > Figures 18.1 and > 18.2 depict the situation in China, which was chosen as a showcase example here, as China is currently one of the world’s major emitters of anthropogenic CO2. At the present time, as shown in this chapter, there are only partial solutions to reduce the impact of transportation systems on Global Warming. Energy conservation by avoiding travel is one option. Technical improvements to transportation systems is another approach. Readers will note that the production of CO2, a by-product from the combustion of carbonaceous fuels such as gasoline with air, has been linked to a global increase in temperature. With an increase in the Earth’s temperature comes melting of the Ice Caps and a rise of the sea level on coastal cities. Of most concern is an accompanying change in composition of the Earth’s fragile atmosphere. Millions of years ago the Earth had a very different atmosphere than it does today, where both ice caps were melted and instead had lush forests. The percentage of O2 was over 30%, a level that would support large mammals, as it did, but not the present human population. Therefore it is imperative

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Energy Efficient Design of Future Transportation Systems

450 Dargay and Gately 1999 Walsh 2003 (High) Wei and Ba 2004 (High) Shen 2006 Huo et al. 2007 (High) Yan 2008 (Business as Usual) Dargay et al. 2007 Historical trend

400 Road vehicle population/Millions

626

350 300 250 200 150 100 50 0 1985

1990

1995

2000

2005

2010

2015

2020

2025

2030

2035

. Fig. 18.2 China’s road vehicle population (excluding motorcycles) as historical trend and prediction from several sources (Reproduced with permission from [6])

that economical methods be found to reduce the emission of CO2 if mankind is to have a sustainable future. Tim Flannery [7, 8] pointed out in his book that to stay below the threshold for melting of the ice sheets in Greenland and West Antarctica, it would be needed to reduce CO2 emissions by 80% from today’s levels. This corresponds to no more than 30 lb of CO2 per person per day. Further, Flannery predicts that if progress in reaching the above goal is not enough, only 20% of the present world population will reach the year 2050. Professor Tim Flannery is an Australian mammalogist, paleontologist, environmentalist, and global warming activist. In this chapter, the case for the reduction of CO2 emissions from transportation systems is made. Solutions to efficient reductions are an evolutionary process where incremental change may represent mankind’s only solution. With this viewpoint, prior automotive designs that were introduced years ago and that failed to gain acceptance but may deserve another evaluation will be discussed. Present-day automotive engines utilize fuel injection systems instead of carburetors and represent the main reason for increased fuel mileage. Consequently, this chapter will also examine various engine cycles. Other measures such as light-weight construction materials, car pooling, and traffic management can also reduce fuel consumption. There is also a need to consider alternate fuels not only for emissions but reduction of the dependence on oil. Thus the use of biofuels and hydrogen as substitutes for oil will be discussed. This is such a broad effort that this chapter will only be able to introduce a few concepts for automotive applications. Concepts for other land-borne, plus air- and seaborne, transportation will be touched

Energy Efficient Design of Future Transportation Systems

18

upon. The authors will also briefly discuss fuel cells, hybrid vehicles, and electric vehicles. Aircraft with respect to fuel efficiency will shortly be addressed. There is no question that aircraft play an important role in contemporary lifestyle, but they require significant energy to perform their mission. Thus it will be necessary to introduce radical designs that would substantially reduce the fuel burn rate. Adoption of these radical designs may not be an option but a necessity to mitigate climate change.

The Issue Since Earth’s formation, the atmosphere’s composition and temperature have changed dramatically due to the Earth’s cooling. However, there is another factor that affects the temperature of the atmosphere that is related to gravitational attraction between the planets and the sun. This gravitational attraction produces an eccentricity of the Earth’s orbit, obliquity of the Earth’s axis, and precession of the Earth’s axis of rotation. These effects have various periods as was first noted by Milankovitch who observed the following periods of the Earth’s axis: Wobble cycles of 19,000 and 23,000 years, Tilt cycle of 41,000 years, and cycles of 100,000 and 400,000 years to the Earth orbit around the Sun [1]. The Earth’s orbit transitions periodically between a circular and an elliptic orbit. When on an elliptical orbit, the Earth’s distance to the Sun has periods where it is the greatest, and the Earth’s atmosphere is cold (i.e., Ice Age). Currently the Earth is in a more circular orbit and its temperature is warmer. These Milankovitch cycles are of course natural events that mankind cannot interfere with. During previous periods, the Ice caps were melted and in the USA, alligators extended as far north as Denver. Data gathered from the Antarctic Ice Shelf allow researchers to infer the air temperature of the Earth at that location going back 400,000 years from analysis of cores drilled into the ice. Further analysis of these cores also permits one to estimate the percentage of CO2 in the atmosphere during this period of time. One can also deduce that during nearly circular orbits, the Earth’s temperature is the warmest and during elliptical orbits the coldest. For the warming periods that occurred beyond present day natural events controlled these warming periods. However during the present cycle, that includes the Industrial Revolution, there appears to be a large increase in the percentage of CO2 that is significantly higher than recorded for previous cycles: the CO2 concentration in the atmosphere is elevated by 100 ppm due to human action. During the warm periods where the Earth’s orbit is nearly circular, the peak concentration of CO2 has been in the order of 275 ppm CO2. Today (2011) it has spiked to approximately 391 ppm, and it is rising at a rate of approximately 2 ppm/year. This increase can be attributed to the presence of humans on Earth and their rapid consumption of energy, i.e., by the combustion of fossil fuels. A fair question to ask is which are the major contributors to CO2 production and how CO2 concentration is related to the Earth’s average temperature. From > Fig. 18.3 one can see that there are three main contributors to the production and emission of CO2 in the atmosphere from burning fossil fuels, and these are solid fuels such as coal, liquid fuels such as gasoline, and gaseous fuels such as natural gas. They account for 91% of the CO2

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Energy Efficient Design of Future Transportation Systems

40

5

Shipping & Air Transport

10

Cement Production

15

Gaseos Fuels

20

Liquid Fuels (e.g. gasoline)

25

Solid Fuels (e.g. Coal)

30

(e.g. natural gas)

35 % Contribution for 2000–2004

628

0

. Fig. 18.3 Leading contributors to production of CO2 (Reproduced from [9])

produced from the combustion of petrochemicals with air. These of course represent the areas where technology developments to reduce CO2 are needed. The question then is how this increase in concentration of CO2 modifies the average temperature of the planet. It is very surprising how small an increase in CO2 concentration contributes to the average temperature around the globe. Now the atmosphere has reached a level of said 391 ppm. This means that the world has seen a nearly 2
C increase in temperature over that of preindustrial times. Even with this small increase in average temperature many today can recall changes that have occurred and are noteworthy. In the early 1900s, people would drive their cars across Lake Ontario to Toronto/Canada on the frozen ice sheet. This lake has not frozen over for more than 50 years. In Southern Virginia, the James River used to freeze over as late as the 1950s, but no longer. Predictions by Flannery are that if an atmospheric CO2 concentration between 900 and 1,000 ppm is reached, in the future only one in five people would survive. Now aside from observations that have occurred with an increase in global temperature, one can observe that the ice sheets have already begun to melt. > Figure 18.4 shows the extent of the Arctic Sea Ice averaged over the period 1979–2007 for the months May to September. Following > Fig. 18.5, one can see that the ice shelf does not restore itself until September. In a typical year, the ice sheet would begin to grow again in August, but now in August it is still melting. With melted Ice Sheets, the Earth’s thermal energy balance is changed since more heat from the Sun is absorbed by the Earth rather than being reflected back into Space. Thus the cycle is intensified. > Figure 18.5 below shows the thickness of the ice sheet north of Greenland in the 1950s and the prediction by NOAA (National Oceanic and Atmospheric Administration) for the year 2050, which shows the ice sheet to have almost vanished.

18

14 12 National Snow and Ice Data Center, Boulder CO

Extent (millions of square kilometers)

Energy Efficient Design of Future Transportation Systems

10 8 6 4

2008 2007 1979–2000 Average

2 May

Jun

Jul

Aug

Sep

. Fig. 18.4 Arctic sea ice extent – Area with at Least 15% Sea Ice (Reprinted with permission from the National Snow & Ice Data Center [10])

Sea Ice Thickness (10-year average) 1950’s

2050’s

100% of 1955 volume (cm) 0

54% of 1955 volume

100 200 300 400 500

. Fig. 18.5 Melting of the Polar ice cap (Reprinted with permission from the National Snow & Ice Data Center [10])

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Therefore, there is a strong motivation to increase the fuel efficiency of transportation systems for people and freight to mitigate anthropogenic climate change. Several aspects will be discussed below.

Carbon Emissions by Light-Duty Vehicles It can be seen that since the beginning of the Industrial Revolution the planet’s atmosphere has increased in temperature by almost 2
C. Not a large increase, but big enough to start significant melting of the Ice Caps. One can see that the temperature increase can be linked to a large increase of CO2 in the atmosphere. Combustion of solid (coal), liquid (gasoline), or gaseous (natural gas) fuels is the major contributor to the production of anthropogenic CO2. Natural gas has a higher H/C ratio than diesel or gasoline. Therefore, it is more climatically benign when being burnt in engines (note that the greenhouse warming potential (GWP) of CH4 is 20 times that of CO2, so CH4 emissions are to be avoided). A natural question to ask at this point is what percentage of CO2 production is due to transportation and which countries are the major contributors. DeCicco et al. provide a graphic illustration of each sector’s contribution in > Fig. 18.6. The estimates shown in this Figure only include the use of fossil fuel. As can be seen, over 40% of the CO2 emissions are from the production of home electricity and heat. Light-duty vehicles only account for 10% of the production and almost half of that is produced in the USA with a significant nearly a quarter from Europe. One observes that only a little over 2% occurs in China and India. In the next 20 years, China and India are expected to grow and consume an amount equal to the USA (compare also > Figs. 18.1 and > 18.2).

Other sectors 9% Residential 8%

Electricity and heat production 41%

OECD Europe 21%

Industry 18%

Light duty vehicles 10%

Other transportation 14%

OECD Pacific 9%

Canada and Mexico 7%

United States 45%

Former Soviet Union and Eastern Europe 6% China 2% Other Asia 2% India 1% Middle East 1% Latin America 5% Africa 2%

. Fig. 18.6 Estimates for CO2 production by sector & light duty vehicles. Left: Global carbon emissions by sector (6,814  106 t). Right: Light duty vehicle carbon emissions by region (680  106 t) (Reprinted with permission from [11])

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Energy Efficient Design of Future Transportation Systems

A substantial growth in CO2 production by light-duty vehicles would require additional refineries throughout the world, or extreme shortages at the pump would occur. Energy conservation will play a more realistic role in the future to avoid the problem of fuel shortage, but this cannot be expected to take effect until existing vehicles are replaced with ones using new technology. DeCicco also addressed this issue, and in > Fig. 18.7a one can see that old SUVs dominate the carbon burden share and that both new and old midsize cars contribute equally. Carbon emissions by cars dominate those associated with

Small cars SUVs Pickups Midsize cars On-road stock New fleet

Vans Large cars 0%

10%

a

40%

99

General Motors Ford DaimlerChryster American Electric Power Southern Company Toyota Tennessee Valley Authority Honda Xcel Ameren Cinergy Dominion Edison International Progress Energy Nissan

80 51 41 37 27 26

Major automakers’ products

17 17 17 16 15 15 15 15 0

b

30%

20% Carbon burden share

20

Major electric producers

40

60

80

100

12

Carbon emissions (MMTc)

. Fig. 18.7 Carbon emissions by new versus old vehicles & electric producers. DeCicco et al. Global warming on the road [11]

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Energy Efficient Design of Future Transportation Systems

electric producers, see > Fig. 18.7b. These statistics indicate that there is a need to adopt a policy to retire existing vehicles as soon as possible and in particular SUVs. DeCicco et al. point out that there are three factors that govern the production of carbon dioxide per year. The first is related to travel demand, the second to automotive efficiency, and the third to carbon content per gallon of fuel. Aside from reducing the distance traveled per year by car or light-duty truck, it is of interest to know how alternate means for ground transportation compare to decide which mode to emphasize. > Table 18.1 shows a compilation of results by the US Department of Energy (DOE) for the efficiency of various transportation systems in terms of energy expended per passenger with an estimate of an equivalent number of liters per 100 km. The efficiency in > Table 18.1 is estimated in terms of BTU/mile and also in miles per gallon. > Table 18.1, from 2008, clearly indicates the value of carpooling with a van that would carry six passengers. On a per passenger basis, the vanpool achieves 87 MPGeUS, an efficiency that would be hard to match by an automobile with a single passenger. Only motorcycles nearly match the vanpool. Personnel trucks are listed as one of the most inefficient modes of transportation with cars only slightly better. Transit buses are the worst form primarily due to the constant stopping and starting needed to pick up and let off passengers.

Carbon Generated by Combustion with Air Each barrel contains 42 gal (159 l) of crude oil and consists of various petroleum products as shown in > Fig. 18.8. As one can observe, only about half a barrel of crude oil can be refined into gasoline. . Table 18.1 Efficiency of various transportation systems. 1 gal (~3.79 l) of gasoline contains approx. 114,000 BTU (120 MJ) of energy. MPGe = miles per gallon gasoline equivalent. This measure of the the average distance traveled per unit of energy consumed compares the energy consumption of alternative fuel vehicles. 1 MPGe  0.0182 km/kW·h  0.005 km/MJ Transport mode

Average passengers per vehicle Efficiency per passenger

Vanpool

6.1

1,322 BTU/mi

2.7 l/100 km (87 MPGe)

Motorcycles Rail (Amtrak) Rail (Transit light & heavy) Rail (Commuter)

1.2 20.5 22.5 31.3

1,855 BTU/mi 2,650 BTU/mi 2,784 BTU/mi 2,996 BTU/mi

3.8 l/100 km (62 MPGe) 5.4 l/100 km (43 MPGe) 5.7 l/100 km (41 MPGe) 6.1 l/100 km (38 MPGe)

Air Cars Personal trucks Buses (transit)

96.2 1.57 1.72 8.8

3,261 BTU/mi 3,512 BTU/mi 3,944 BTU/mi 4,235 BTU/mi

6.7 l/100 km (35 MPGe) 7.2 l/100 km (33 MPGe) 8.1 l/100 km (29 MPGe) 8.7 l/100 km (27 MPGe)

Energy Efficient Design of Future Transportation Systems

what’s in a barrel of oil

18

other 0.3 gal. kerosene 0.2 gal. lubricants 0.5 gal. feedstocks* 1.2 gal. asphalt/road oil 1.3 gal. petroleum coke 1.8 gal. still gas 1.9 gal. liquefied gases 1.9 gal. residual fuel oil 2.3 gal. jet fuel 4.1 gallons

distillate fuel oil 9.2 gallons

Source: API. Totals more than 44 gals. because of “processing gain”

gasoline 19.5 gallons

. Fig. 18.8 Products obtained from refining a crude barrel of oil (Reproduced with permission from Gibson Consulting [12] in [9])

The amount of CO2 emitted per gallon is governed by the code of Federal Regulations (40CFR600.113) [13]. The carbon content of gasoline per gallon is 2,421 g whereas the carbon content of diesel fuel per gallon is 2,778 g. Recall the words of Tim Flannery who said that to prevent the Ice Sheets from melting every human had to be on a diet of 30 lb or less of carbon a day. So each person could only use about a gallon and a half of gasoline each day. The ability to use only a gallon and a half each day strongly suggests an elusive goal. While one may not be able to meet this goal, earnest conservation steps can ease the way into the inevitable. One of the first conservation steps one can take is to consider engine thermodynamic cycles to see if there is any advantage. Toward this purpose, the bare essentials associated with the spark and compression ignition engines are discussed. The four-stroke engine cycle was first patented by Eugenio Barsanti and Felice Matteucci in 1854. An illustration of the four-stroke cycle, reproduced from Obert [14], is shown in > Fig. 18.9. Here, one sees the position of the cylinder head, intake valve, exhaust valve, and spark ignition for one entire cycle. > Figure 18.10a, b shows that the thermodynamic model for either SI (spark ignition) or CI (compression ignition) during intake and exhaust is considered to be an isentropic process (=constant entropy). During cycles of heat in or out, the thermodynamic model is far from isentropic. Note that for

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Energy Efficient Design of Future Transportation Systems

THE FOUR STROKE CYCLE

INTAKE

COMPRESSION

IGNITION

EXHAUST

. Fig. 18.9 Graphic illustration of four stroke compression ignition engine (Reproduced from [14] in [9])

P

3

P2

Wout

Qin is e

nt

P

2

ro p

ic

isen

Wout ise n

P4 P1

v

3

Qout 1

a

2

4

tropic

Win

P: pressure v: specific volume

Qin

b 0

Win

V2 V3

ise ntr opic

trop ic

4 Q out 1 V1 V

. Fig. 18.10 Idealized 4-stroke for SI and CI combustion models (Reproduced from [14] in [9]). P pressure, v volume, W work, Q heat, SI spark ignition, CI compression ignition

Energy Efficient Design of Future Transportation Systems

18

compression ignition engines, during combustion the process takes place at constant pressure. For the ideal combustion the efficiencies associated with the stoichiometric combustion of these fuels with air are illustrated in > Fig. 18.10. For gasoline this is given by: 1 C8 H18 þ 12 O2 þ 47N2 ! 8CO2 þ 9H2 O þ 47N2 2 where following > Fig. 18.10a one can note QArev ¼ cv ðT3  T2 Þ QRrev ¼ cv ðT1  T4 Þ


t ¼

QA þ QR T1 1 ¼ 1  ¼ 1  g1 QA T2 rv

where rv is the engine compression ratio. As an example consider the following: engine compression ratio rv = 8, ambient temperature Ta = 540
R (300 K), ambient pressure Pa = 14.7 psia (101.3 kPa = 1.014 bar). Then one has that
t ¼ 1 

1 rvg1

¼1

1 ¼ 0:565 ¼ 56:5% 80:4

Factoring in transmission and drive train, the overall gasoline-powered automobile efficiency is approximately 17% [14]. Quite remarkable, but 83% of available energy is wasted on the gas-powered internal combustion engine. Even the thermal efficiency of the four-stroke ideal diesel engine cycle appears more attractive. Consider the Pv diagram shown in > Fig. 18.10b, which shows air coming into the system at constant pressure and air being discharged from the system at constant pressure. Based on this cycle, one can QArev ¼ cv ðT3  T2 Þ derive that the reversible heat added and discharged is given by and QRrev ¼ cv ðT1  T4 Þ  g   since TT32 ¼ TT41 , the thermal efficiency is given by,
t ¼

   g   QA þ QR 1 T4  T1 1 r 1 ¼1 ¼ 1  g1 g T3  T2 gð r  1 Þ QA rv

Typical values for the diesel cycle are compression ratios near 25 to ensure autoignition. A diesel engine takes in just air, compresses it, and then injects fuel into the compressed air. The heat of the compressed air lights the fuel spontaneously. A typical thermal efficiency computed from the above equation using a compression ratio of 25 is a value
t ¼ 0:264. Note: Diesel engines are in general 30–35% more efficient than gasolinepowered vehicles; however, the efficiency strongly depends on the vehicle load. The energy efficiency of alternative powertrains in vehicles is discussed in [15]. Otto and Diesel engines are most commonly used in transportation. The Wankel engine is another concept with less proliferation. It operates without pistons. The Mazda RX-8 is one example of a car that deploys a Wankel engine. > Table 18.2 shows some aspects of Wankel engines.

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Experiments with turbine-powered cars were carried out in the US around 1960. Table 18.3 lists the pros and cons identified. Although the concept of turbine cars was abandoned soon after their appearance, they might still offer an interesting route to future efficient cars, so new research could be carried out in this area. Another technology is the ‘‘air fuelled engine.’’ It can be operated by compressed air [17] or by liquid air, yielding zero tailpipe emissions [18], compare > Fig. 18.11. Due to the high energy consumption of air liquefaction plants, the compressed air– powered engines have a better energy efficiency than the liquid air ones (28.3– 36.0% vs. 12.8–17.0% for the setups studied in [18]). A novel concept for engines is HCCI (homogeneous charge compression ignition) [19]. It is a kind of hybrid between a compression ignition and a spark ignition engine, in that a homogeneous fuel/air mixture is brought to autoignition. This combustion mode resembles the typical ‘‘knocking’’ in gasoline engines. It is fast and hard to control. However, HCCI offers the potential of low-pollution and high-efficiency automotive engines.

>

. Table 18.2 Assessment of the Wankel engine (Reproduced with permission from [16]) Pros

Cons

High power output/unit weight

Rotating seals reduce engine compression ratio

Good fuel/air mixing

Large fraction of unburned fuel lowers the efficiency Excessive noise due to rotating seals

Even combustion

. Table 18.3 Assessment of turbine-powered automobiles (Reproduced from [16]) Pros

Cons

Low maintenance

High fuel consumption at idle due to high rpm

Long engine life expectancy Reduction of number of parts by 80%

Throttle lag from idle as the engine spools up. High temperature of exhaust gases, low efficiency High noise emissions

No warm-up period, easy low-temperature start No stall at sudden overload Hot but clean exhaust gases Low oil consumption Operation on wide fuel variety

Expensive

Energy Efficient Design of Future Transportation Systems

18

Compressed Air Tank

Expander

a

Compressed air engine

Liquid Air Tank

Pump

Fan

Expander

b

Heat exchanger Liquid air engine

. Fig. 18.11 Air-fuelled engines (Reproduced with permission from [18])

Alternative Fuels With depleting fossil fuel resources, costs go up and supply shortages might occur, apart from the emission of CO2 into the atmosphere from the burning of these fuels. Alternative fuels are ‘‘renewable.’’ This means that they are produced directly or indirectly from sunlight, without the need to turn to fossil fuels. The following energy carriers have been envisaged as fuels (> Table 18.4). These fuels can be produced via various routes. Methane is also the main constituent of biogas. There are so-called flexible fuel (flex fuel) vehicles that can run on several fuels, e.g., ethanol. A blend of gasoline and up to 85% ethanol is called E85. Flex fuel vehicles (FFV) have been produced since the 1980s. Ethanol [21] and biodiesel [22] are two common ‘‘biofuels.’’ Fischer–Tropsch synthesis and biomass gasification are important processes to obtain fuels from biomass, apart from anaerobic digestion and fermentation. Fuels from waste are also considered biofuels. Oil crops yield fuels from extraction and pressing of suitable plants [23]. Also, aquatic biomass such as certain algae can be used, e.g., for biodiesel production.

637

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. Table 18.4 Potential fuels Energy source

Typical chemical energy density

Hydrogen

142.0 MJ/kg

Ethanol Ammonia [20] Methane Methanol

29.7 MJ/kg 17.0 MJ/kg 55.5 MJ/kg 22.7 MJ/kg

There is also some controversy around biofuels. Two issues associated with biofuels are: ● Potential competition over farmland with food crops ● Water consumption associated with their production (see concept of virtual water [24]) Here is an example of bioethanol: The energy demand has been rapidly increasing due to the increases in economic growth and population. At the same time, the concerns about global climate change and depletion of crude oil reserve have sparked an urgent need to develop an alternative, non-fossil-fuel-based energy infrastructure. The president of the USA has established a goal to supply 35 billion gallons per year of renewable and alternative fuels in the USA by 2017. Thermal energy produced from biomass is considered carbon-neutral because biomass is renewable through photosynthesis. Biochemical conversion of corn, sugar cane, and cellulosics to ethanol (bioethanol) has emerged as a technologically viable route for relieving the pressing energy demand. Cellulosics are abundant and widely available; they are in fact the most abundant natural organic material in the world. Controversies, however, have emerged about the various impacts of promoting the use of bioethanol. Major concerns about using bioethanol as fuel include the following: ● Corn is a food source, and corn ethanol production will reduce food availability. Developing countries that depend on the corn donation from the West have already experienced food shortages. ● Fertilizer is required in corn production; both cost and energy consumption are incurred during fertilizer production. Moreover, unprecedentedly large-scale use of fertilizer alters the natural nitrogen cycle and induces other ecological/environmental problems that have already been identified as threats. ● About 5 gal of water are needed in the production of each gallon of ethanol in a plant; this does not consider the amount of water it takes to grow the corn. So potable water shortages might result from excessive bioethanol production.

Energy Efficient Design of Future Transportation Systems

18

● Bioethanol production requires energy input. Ethanol purification by distillation is energy intensive and usually involves consumption of natural gas, which, in turn, produces CO2 from fossil fuel. As a result, while bioethanol utilization reduces fossil fuel dependence, it is not a completely carbon neutral process. Widespread adoption of bioethanol will cause redistribution of the world’s natural resources and wealth. The actual environmental and societal costs of bioethanol are likely to be much higher. A good starting point for a healthy debate on this issue can be found at [25]. The transportation of energy carriers also consumes, naturally, energy. In [26], the energy consumption of biofuel transportation from production site to point of use is discussed. The share of biofuels is expected to increase significantly over the next decade. An important aspect of alternative fuels, apart from their specific costs, is the energy density, see > Table 18.5. From > Table 18.5, one can see that compressed air has a low energy density both in terms of volume and weight. The energy density is important for the range of a vehicle. Gases can be stored in compressed form, as hydrides or as a liquid in cryogenic conditions. Liquefaction can consume a considerable amount of energy. For hydrogen, one can define the gravimetric storage density. It is the weight of hydrogen being stored divided by the weight of the storage and delivery system. Two to four percent is a typical value. Storage has to be achieved in a safe, cost-effective, and efficient way. Alanates are a promising material class for hydrogen storage [27]. Hydrides are compounds of chemically bond hydrogen in a solid material. This storage approach should

. Table 18.5 Energy density of various fuels Fuel

Volumetric

Gravimetric

Diesel Gasoline LPG (liquefied petroleum gas) Propane Ethanol

10,942 Wh/l 9,700 Wh/l 7,216 Wh/l 6,600 Wh/l 6,100 Wh/l

13,762 Wh/kg 12,200 Wh/kg 12,100 Wh/kg 13,900 Wh/kg 7,850 Wh/kg

Methanol Liquid hydrogen Hydrogen (150 bar) Nickel metal hydride

4,600 Wh/l 2,600 Wh/l 405 Wh/l 100 Wh/l

6,400 Wh/kg 39,000 Wh/kg 39,000 Wh/kg 60 Wh/kg

Lead acid battery Compressed air

40 Wh/l 17 Wh/l

25 Wh/kg 34 Wh/kg

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Energy Efficient Design of Future Transportation Systems

12000

60

10000

50

8000

40 30

6000

20

4000

10

2000 Carbon nanofibres

H3BH3 Thermal decomp

LIAIH4 + NH4Cl Thermal decomp.

Silanes

Primary hydrides hydrolysis

Liquid hydrogen

Secondary hydrides

Composite cylinder

0 Steel cylinder

0

Theoretical capacity (Wh/kg)

Excluding ancillaries Theoretical capacity (wt %)

640

. Fig. 18.12 Graphic illustration of hydrogen storage methods. Red color indicates that the technologies have not reached maturity yet (Reproduced from [14])

have the highest hydrogen packing density. However, storage media have to meet several requirements: ● ● ● ●

Reversible hydrogen uptake/release Lightweight with high capacity for hydrogen Rapid kinetic properties Equilibrium properties (p, T) consistent with near ambient conditions There are two solid-state approaches:

● Hydrogen absorption (bulk hydrogen) ● Hydrogen adsorption (surface hydrogen) For details on hydride storage, see [28]. Figure 18.12 compares several storage methods for hydrogen. For example, hydrogen can be produced by electrolysis (solar power) or gasification. Renewable energies for sustainable development are discussed in [29]. >

Alternative Power Sources Electric cars come as battery-powered and fuel-cell-powered models. For a comparison on ‘‘well-to-wheel’’ energy pathways, see, e.g., [30]. So-called hybrid vehicles use a combination of an internal combustion engine (ICE) plus an electric motor [31].

Energy Efficient Design of Future Transportation Systems

18

Air Transportation According to [32], world air traffic should increase by about 100% between 2008 and 2025. The world jet fuel demand is expected to increase by about 38% during the same period [32]. Aircraft manufacturers have reduced the specific fuel consumption of their equipment over the last decades, e.g., by using more efficient turbines, lightweight construction materials, and improved design. More radical concepts might help lower specific fuel consumptions further. Blended wing body (BWB) aircraft are promising constructions currently being studied. Their benefits are 10–15% less weight and 20–25% less fuel consumption. Challenges today are the integration of the propulsion system into the airframe, aerodynamics, and control. An important aspect for the fuel efficiency of aircraft is the so-called aerodynamic efficiency. It determines its range with all other parameters kept constant. For details, see [33]. CO2 emissions and energy efficiency of aircraft are treated in Refs. [34–37].

Cargo Freight transportation is a huge industry. Goods are moved by sea, air, and land, where seaborne transportation has the highest share with over 30,000 billion tonne-miles per year. Sea-transportation aboard large container ships has a particularly advantageous energy efficiency compared to other modes. Because of concerns for the air quality in harbors and port cities, the emissions from ships have recently received more attention. For details on CO2 emissions from shipping activities and their mitigation see [38–43].

Means of Energy Efficiency Energy efficiency improvements can be achieved in various ways. > Table 18.6 shows, in an exemplary fashion, that to increase energy efficiency not only technical improvements can be done. By training staff, an ‘‘energy saving mindset’’ can be created. It can yield fuel savings directly, without the need for significant investment costs. However, the impact will not be as long lasting as technical improvements. Building upon the above idea of different means to achieve energy efficiency gains, the following > Fig. 18.13 highlights four energy conservation strategies for road transportation and their monetary impact, reproduced with permission from [45].

Comparison of Different Transportation Technologies A key question related to energy efficiency in transportation is how various modes compare to each other. This is shown in an exemplary way for the greenhouse gas emissions (g CO2 equivalents) per PKT (PKT = passenger kilometer traveled). In that

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Energy Efficient Design of Future Transportation Systems

. Table 18.6 Efficiency measures carried out at 52 German road freight companies in 2003 (Reproduced with permission from [44]) Measure type

Percent of firms

Technical improvements Driver training Informal co-operation

53.8 51.9 40.4

Scheduling with IT On-board-systems Others Shift to rail/ship Scheduling with IT and telematics

23.1 17.3 15.4 15.4 9.6

Stacking area optimisation software Formal co-operation

5.8 3.8

$400 Change in Per Vehicle Annual Costs

642

$300 $200 $100

Noise Pollution Barrier Effect Traffic Services Roadway Costs Crash Externalities Local Air Pollution Traffic Congestion Parking Externalities Energy Conservation Consumer Surplus

$0 −$100 −$200

Fuel Efficiency Standards

Alternative Fuels

Fuel Taxes

Mobility Management

. Fig. 18.13 Cost impact of four different strategies for energy conservation. Above the 0-line, benefits are shown, and below costs. The barrier effect refers to delays that motorized traffic causes to other modes of transportation. In [45], it is valued at 0.7 Cent per vehicle-kilometer. For more details, the reader is referred to [45]

Energy Efficient Design of Future Transportation Systems 144

Conventional Gasoline Sedan

171

Conventional Gasoline SUV

263

Conventional Gasoline Pickup Urban Diesel Bus (Off Peak) Urban Diesel Bus (Peak) Commuter Rail (SFBA Caltrain) Light Rail (SF Munil) Light Rail (Boston Green Line)

18

295 37 39 25 46

Small Aircraft Midsize Aircraft Large Aircraft Vehicle Active Operation Vehicle Insurance Infrastructure Parking

121

Greenhouse Gas Emissions (g CO2e/PKT)

98 92 Vehicle Inactive Operation Infrastructure Construction Infrastructure Insurance

Vehicle Manufacturing Infrastructure Operation Fuel Production

Vehicle Maintenance Infrastructure Maintenance

. Fig. 18.14 Total GHG (greenhouse gas) emissions per PKT (passenger kilometer travelled). The components of vehicle operation are depicted in grey, while other vehicle components are shown in blue shades. Infrastructure components are shown in red and orange. Fuel production components carry green color. All components appear in the order of the legend (Reproduced with permission from [46])

paper [46], it is concluded that the total life-cycle energy inputs and greenhouse gas emissions for road, rail, and aircraft transportation on top of the tailpipe emissions are 63, 155, and 31%, respectively. This means that in the case of rail transportation, the major part of CO2 emissions does not occur during the use of the vessel for a journey, but rather in related areas such as infrastructure construction and infrastructure operation. The infrastructure for railways is more complex than that of large aircraft, for instance. As can be seen from > Fig. 18.14, it is important to consider infrastructure and supply chain aspects when comparing different transportation modes for their energy efficiency. The (assumed) passenger occupancy is one parameter that strongly affects the results of such studies. Energy efficiency of rail transportation is detailed in [47], of buses in [48], and of aircraft in [34–37].

Future Directions Over the last years, a ‘‘green’’ development has emerged, and sustainability has become a buzzword also among consumers and in the transportation industries [55]. In [49], the energy efficiencies of different sectors in several countries are compared (see > Fig. 18.15). One can spot that they range from 35 to 70%. There is a big potential for savings in all sectors, and it is the largest in the transportation area, followed by utilities, residential/ commercial, and industrial sectors. The efficiency of vehicles on US roads from 1923 to 2006 is discussed in [50]. In [51], Joseph Romm ponders on the car and fuel of the future, and in [52] global energy

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90 Energy efficiencies (%)

644

80 70 60 50 40 30 20 10 0

Countries Utility Transportation Power (End-use)

Industrial Agriculture

Residential End-use

. Fig. 18.15 Energy efficiencies of different countries by sector. In transportation, the potential for improvement seems biggest (Reproduced with permission from [49])

. Table 18.7 Potential to reduce the energy use per passenger-km in Sweden from 2000 to 2050. The occupancy and speed are kept constant (Reproduced with permission from [53] (see there for details))

Car, combustion mode, 1,2 pass/car ( Tables 18.7 and > 18.8, has attempted to quantify these potentials. For cargo transportation, airships might be an energy-efficient means of transportation in the future [54]. Future energy-efficient transportation systems can be developed based on new radical approaches such as blended wing body aircraft or by revisiting ‘‘old’’ ideas such as turbine cars. In this chapter, several aspects of energy and fuel efficiency on the transportation industries were touched upon. For further reading, see the cited references and also > Chap. 24, ‘‘Energy Efficiency’’ in this handbook. For an in-depth discussion of alternate fuels, see > Chaps. 26, ‘‘Biochemical Conversion of Biomass to Fuels,’’ > 29, ‘‘Hydrogen Production,’’ > 40, ‘‘Integrated Gasification Combined Cycle (IGCC),’’ > 41, ‘‘Conversion of Syngas to Fuels’’ in this handbook.

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9. Seiner JM, Fuel efficiency in transportation systems, Lecture Notes, National Center for Physical Acoustics, University of Mississippi, Mississippi, USA 10. National Snow & Ice Data Center (2011) http:// nsidc.org/ 11. DeCicco J, Fung F, An F (2011) Global warming on the road, environmental defense. http://www.edf. org/documents/5301_Globalwarmingontheroad. pdf 12. Gibson consulting (2011) http://www.gibson consulting.com/ 13. (2011) Title 40, Protection of Environment, Sec. 600.113-93, Fuel economy calculations, http:// edocket.access.gpo.gov/cfr_2010/julqtr/40cfr600. 113-93.htm 14. Obert EF (19973) Internal combustion engines and air pollution, 3 rd edn. Addison Wesley, ISBN 978-0700221837 (1973). 15. A˚hman M (2001) Primary energy efficiency of alternative powertrains in vehicles. Energy 26(11):973–989 16. Hege JB (2006) The Wankel rotary engine: a history. Mcfarland, Jefferson. ISBN 9780786429059 17. Miller FP, Vandome AF, McBrewster J (2010) Compressed-air energy storage: Compressed-air vehicle. Compressed-air engine, compressed air car, air compressor, load profile, compressed air, compressed natural gas, fireless locomotive, vehicle-to- grid. Alphascript 18. Chen H, Ding Y, Li Y, Zhang X, Tan C (2011) Air fuelled zero emission road transportation: a comparative study. Appl Energy 88(1):337–342 19. Zhao H (2007) HCCI and CAI engines for the automotive industry. Woodhead, Cambridge. ISBN 978-1845691288 20. Zamfirescu C, Dincer I (2009) Ammonia as a green fuel and hydrogen source for vehicular applications. Fuel Process Technol 90(5):729–737 21. von Blottnitz H, Ann Curran M (2007) A review of assessments conducted on bio-ethanol as a transportation fuel from a net energy, greenhouse gas, and environmental life cycle perspective. J Cleaner Prod 15(7):607–619 22. Ticker J (2003) From the fryer to the fuel tank, ISBN D-9707227-0 23. Tickell J (2000) From the fryer to the fuel tank: how to make cheap, clean fuel from free vegetable oil: the complete guide to using vegetable oil as an

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19 Thermal Insulation for Energy Conservation David W. Yarbrough R&D Services, Inc., Cookeville, TN, USA Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 650 Thermal Insulation Use in Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 651 Thermal Performance Evaluation of Building Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 653 Factors That Affect Thermal Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 655 Reflective Insulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 659 Envelope R-Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 660 Hybrid Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 666 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 666 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 667

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_19, # Springer Science+Business Media, LLC 2012

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Thermal Insulation for Energy Conservation

Abstract: The use of thermal insulations to reduce heat flow across the building envelope has been an accepted energy conservation strategy for many decades. Materials available for use as building insulation include naturally occurring fibers and particles, man-made fibers, reflective systems, cellular plastics, evacuated systems, aerogels, and hybrid insulations that combine two or more types of insulation. This chapter discusses the basic theory of insulation and the way they are evaluated. Performance limitations are identified and discussion of the performance of building elements that represent combinations of insulation and other building material are contained in this chapter. The importance of air infiltration and moisture control is discussed. The language associated with thermal insulation technology and key thermal properties have been included to help the reader use the vast literature associated with building thermal insulation.

Introduction The objectives of modern building design are to provide a comfortable living environment with minimum use of external energy for heating and cooling. In fact, the present target is the construction of ‘‘zero energy buildings’’ that provide conditioned living space, light, and utilities without net energy from exterior sources. This is accomplished by optimum use of wind energy, solar energy, and ground coupling combined with building envelope design that limits heat flow across walls, ceilings or roof cavities, and floors using thermal insulation, reduction of air infiltration, advanced window design, and reduction of thermal bridging. These objectives are major items of interest in the field of Building Science. This chapter will start with a discussion of thermal insulation: properties, evaluation, and use. This will be followed by observations related to thermal bridging, air infiltration, and new materials. This chapter discusses the reduction in heat flow by low thermal conductivity materials (insulations). The control of air movement and moisture transport across the building envelope (wall, ceiling, and floor) are additional factors to be considered. Fibrous or particulate insulations seldom provide significant resistance to air infiltration caused by wind-induced pressure differences between the inside and outside of the structure. When these materials are used additional steps such as caulking and sealing or housewraps are used to provide a barrier to air infiltration. Materials such as cellular plastic insulation (closed-cell) can provide a barrier to air flow when installed without cracks or defects. Thermal insulation also plays a role in controlling moisture transport and accumulation. Condensation within the building envelope occurs when the temperature at a location is equal or less than the ‘‘dew-point’’ temperature. The dew-point temperature depends on the actual air temperature (dry-bulb temperature) and the relative humidity. The temperatures within the building envelope depend on the interior temperature, the exterior temperature, and the materials including insulation that are present in the building envelope. Condensation and accumulation of water depends, as a result, on bulk movement of air through the building envelope, diffusion of water vapor through the construction materials, and the temperature profile in the building envelope.

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Thermal Insulation Use in Buildings Heat moves across the building envelope by three mechanisms: convection, conduction, and radiation. Thermal insulations are designed to reduce heat flow by radiation and convection without significantly increasing conduction. There are also insulations that reduce conductive heat transfer by altering the gas phase. The various types of insulation change each type of heat flow by different amounts. Heat transfer of convection can occur within porous materials if buoyant forces resulting from density differences overcome the friction between the moving gas (air, in most cases) and bounding surfaces, fibers, or particles. This ‘‘free’’ convection is eliminated in most cases by insulations such as fiberglass, rock wool, or cellulose. Air moving within a porous material or region will absorb energy from the warm side of a region and reject it to the cool side of the region. Air moving through a leaky-insulated region due to a pressure difference caused by wind or fans, forced convection, means that exterior air is being exchanged for interior air. Air flow into the building is matched by air moving out of the building. In addition, air moving through a porous or fibrous insulation changes the temperature profile within the insulation and the resulting heat flow by conduction and radiation is changed [1, 2]. Thermal insulations designed to reduce radiation by use of reflective (low thermal emittance) surfaces often have a significant amount of internal convection and as a result the performance of enclosed reflective air spaces depends on the direction of heat flow (down, up, or horizontal). The convective contribution to the overall heat flow is taken into account when reflective insulation is evaluated and labeled. A large number of building insulations rely of the low thermal conductivity of air for their performance. This type of insulation includes most of the fibrous materials like fiberglass, rock wool, cellulose, polyester, wool or cotton, and open-cell cellular plastic insulation. A second large class includes closed-cell cellular plastics that contain a gas with a thermal conductivity lower than air with correspondingly high thermal resistance values. The performance of closed-cell insulations requires that the low-conductivity gas remain in the cells unchanged. In general, these insulations are evaluated for average long-term thermal resistance since there are inevitable changes in the cell-gas composition due to air entering the cells or outward loss of the low thermal conductivity gas. There is also a type of insulation that contains fibers or cells that are so small that they interfere with the collisions between gas-phase molecules and consequently reduce the thermal conductivity below that of the gas under normal conditions. The thermal conductivity of a gas depends on both temperature and pressure and is the result of gas molecule collisions. If the gas-phase molecules do not collide then heat flow through the gaseous part of the insulation is reduced or eliminated. This occurs when the average distance between collisions is greater than the average dimensions of the space available. One type of super-insulation is based on the use of evacuated regions (elimination of the gas phase). All of these concepts are presently represented by commercial products. > Table 19.1 contains a listing of some insulations that are available for use in buildings. Insulation manufactured as batts are usually dimensioned to fit standard construction while loosefill insulation is pneumatically installed using especially designed equipment or poured in place. > Table 19.2 contains thermal resistance values for selected building materials and thermal insulations. These are example values not intended to represent any specific product.

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. Table 19.1 Building Insulations Insulating material

Type

Examples

Air

Fibrous

Fiberglass – batts and loose-fill Rock wool- batts and loose-fill Cellulose – batts and loose-fill Cotton – batts Polyester – batts

Cellular plastic

Particulate Reflective Gas other than

Cellular plastic

Wool – batts Spray-applied polyurethane (open cell) Expanded polystyrene (board or slab) Polyisocyanurate (board stock or slab) Perlite Vermiculite Reflective insulations Radiant barriers Spray-applied polyurethane (closed cell) Extruded polystyrene (board or slab) Polyisocyanurate (board or slab) Phenolic Gas-filled panels

Reduced pressure Nano-materials

Particulate

Evacuated panels containing silica Evacuated panels containing perlite Aerogels Nano-fibers

There are a wide variety of natural materials mostly fibrous or particulate that are used around the world as insulations. References such as the ASHRAE Handbook of Fundamentals [3], AIRAH [4] and Materials for Energy Conservation in Buildings [5] contain tables of physical properties for insulating materials and detailed discussions about use and evaluation. > Table 19.3 contains qualitative information about the relative performance for commonly encountered conditions for the insulations in > Table 19.1. Several entries in > Table 19.3 indicate an increase in conduction because solids such as glass, rock, paper, plastic, or wood have much greater thermal conductivity that air. If air is displaced by a solid particle or fiber, then the heat flow by conduction will increase. Fibrous materials such as fiberglass, rock wool, cellulose, or open-cell plastics present some resistance to air flow resulting from a pressure difference but do not perform as ‘‘air barriers.’’ Closed-cell plastic insulation can perform as an air barrier material in sufficiently thick and without cracks or holes due to shrinkage or weathering. Reflective insulations have an effect on

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. Table 19.2 Thermal resistivity values for selected building materials at 75
F (24
C) R for one inch of thickness (ft2·h·
F/Btu)

RSI for 25 mm of thickness (m2·K/W)

Wood Concrete High density Low density

0.8–1.4

0.14–0.25

0.1 0.5–1

0.018 0.09–0.18

Fiberglass batt Fiberglass-loose-fill Cellulose-loose-fill Cellular Plastic

3.1–4.2 2.0–2.4 3.5–3.7

0.55–0.74 0.35–0.42 0.62–0.65

3.0–3.5 5.0–6.5

0.53–0.62 0.88–1.15

Material

Open-cell Closed-cell

. Table 19.3 Relative performance of commonly used building insulations Type of insulation

Free convection

Conduction

Radiation

Fiberglass, rock wool, and cellulose Cellular plastics – air

Eliminates Eliminates

Increases Increases

Reduces Reduces

Cellular plastics – gas Reflectives

Eliminates Reduces

Decreases Increases

Reduces Greatly reduces

convection when they divide the space they occupy into discrete regions with reduced temperature differences and increased surface area to resist the movement of the enclosed air. Horizontally applied porous insulation can exhibit a loss in thermal resistance due to upward convection [6, 7]. This phenomena occurs in cold climates where there is a large temperature difference across the insulation that create significant air density differences in the air.

Thermal Performance Evaluation of Building Insulation The thermal performance of building insulation is commonly characterized by its thermal resistance designed by ‘‘R (ft2·h·
F/Btu)’’ or ‘‘RSI (m2·K/W)’’ depending on the system of units being used. The thermal resistance is defined by > Eq. 19.1 where the denominator is referred to as ‘‘apparent thermal conductivity.’’ This terminology is used since the equation used to describe heat flow by conduction (Fourier’s Law) is used to describe heat flow by all mechanisms.

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Thermal Insulation for Energy Conservation

R ¼ t=ka

(19.1)

[t] is thickness in inches [ka] is apparent thermal conductivity in Btu·in./ft2·h·
F [R] is thermal resistance in ft2·h·
F/Btu RSI ¼ t=l [t] is thickness in meters [l] is apparent thermal conductivity in W/m·K [RSI] is thermal resistance in m2·K/W Another property called thermal resistivity, R∗ or RSI∗, is related to thermal resistance as shown by > Eq. 19.2. > Equation 19.1 indicates that R or RSI scales linearly with thickness. This is valid as long as ka or l have been determined using test specimens thick enough to avoid surface effects (the thickness effect) [8]. R ¼ R=t or 1=ka

(19.2)

[R∗] has units ft2·h·
F/Btu·in. RSI ¼ RSI=t or 1=l [RSI∗] has units m·K/W Building codes and requirements are usually discussed in terms of R-values or RSI-values while manufacturers and marketers often quote resistivity values, R∗ or RSI∗. The total thermal resistance (RT or RSIT) of an assembly consisting of layers of materials perpendicular to the direction of heat flow are additive. RT ¼ R1 þ R2 þ R3 þ    :

(19.3)

A given section of a building envelope (a wall, for example) will likely consist of at least three materials: an inner sheathing, an insulation filled region, and an external sheathing or fac¸ade. The total thermal resistance from the interior surface to the exterior surface is the sum of the individual resistances. The design for energy conservation involves selection of materials with high thermal resistance in order to reduce heat flow across an area, A, as shown by > Eq. 19.4. The greater the RT or RSIT the smaller the heat flow. Q ¼ A  DT=RT [A] is area perpendicular to heat flow direction (ft2 or m2) [ΔT] is (Thot  Tcold) in
F or K [RT or RSIT] is total thermal resistance [Q] is heat flow in Btu/h or watts

(19.4)

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. Fig. 19.1 Photograph of two heat flow meters (open and closed). The brown test specimen is between two black isothermal plates. The front is closed during a test

Standardized test methods are used to determine the thermal resistance values for building materials for the purpose of labeling and design calculations. In the case of thermal insulation materials, the most commonly used apparatus is described in the test method ASTM C 518 [9]. > Figure 19.1 is a photograph of two heat flow meters. The apparatus is designed to provide values for three of the four quantities in > Eq. 19.4 (Q, A, and ΔT). A value for R can then be calculated. The apparent thermal conductivity, ka, can be calculated from the thickness of the test material using > Eq. 19.1. This test method provides steady-state physical property values for materials that have been conditioned to prevent water (moisture) movement in the test specimen during the test. Thermal testing of building elements is accomplished using a hot-box facility to be discussed later.

Factors That Affect Thermal Resistance The thermal resistance of practically all materials depends on the temperature of the material. The temperature is usually characterized as the average of the warm side temperature and the cool side temperature. Thermal resistance measurements are generally made with a relatively small temperature difference such as 50
F or 28
C and an

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average temperature specified by labeling conventions. The average temperature is 75
F (23.9
C) in some parts of the world and as low as 50
F (10
C) in some locations. The laboratory test methods are generally capable of measuring the thermal resistance over the temperature range anticipated for buildings. In most cases, the thermal resistance of building insulations decreases as the temperature increases (or increases as the temperature decreases) when other factors are held constant. This in easily understood for the insulations that are based on air. The thermal conductivity of air increases with temperature thus reducing the thermal resistance of the insulation in question. > Equations 19.5a and > 19.5b are relations between temperature and thermal conductivity of air for the limited temperature range likely to be encountered in buildings. Actual variation with temperature of the apparent thermal conductivity will differ from that of air because there are other heat-flow mechanisms. Variations of the thermal resistance of insulation materials with temperature have been measured and reported [10]. kair ¼ 0:18 þ 0:027 ðTð
FÞ  75Þ=100

(19.5a)




32 < T < 176 F ka with units Btu·in./ft2·h·
F lair ¼ 0:026 þ 0:0070 ðTð
CÞ  24Þ=100

(19.5b)

0 < T < 80
C la with units W/m·K An important observation about air-based insulations follows from approximate values given by > Eq. 19.5. The maximum possible R-value at a given temperature that can be achieved by an air-based thermal insulation can be calculated from the thermal conductivity of air. The maximum occurs when there is no convection present and all radiation has been eliminated. The heat transfer by conduction is all that is left. The solid components of the insulation will have thermal conductivities greater than air meaning that kair is a lower bound on ka. > Equation 19.1 gives Rmax = 5.56 for 1 in. thickness at 75
F and RSImax = 0.96 for 25 mm of thickness at 24
C. Practical air-based insulation invariable has R-values less than the maximum value because radiation is not completely blocked, and there is a conductive contribution from the solid material in the insulation. The thermal resistances of cellular plastic insulations containing a gas other than air or a gas mixture with thermal conductivity less than that of air also decrease with increase in temperature as long as the composition of the gas trapped in the cells does not change. In some cases, it is possible to have temperatures low enough to condense the low thermal conductivity gas components in a closed-cell foam thus changing the cell-gas composition. Generally, this means that the fraction of gas that is low thermal conductivity decreases and the overall thermal conductivity increases. If this phenomena occurs, then the thermal resistance decreases as the temperature decreases. As a result of the aging phenomena, the performance of closed-cell cellular plastic insulation is evaluated in terms of an average value over a long period of time such as 15 years. This is called the long-term thermal resistance (LTTR). There are consensus laboratory methods for determining LTTR [11].

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Thermal Insulation for Energy Conservation

Air movement through porous or fibrous insulations like fiberglass, rock wool, or cellulose changes the heat flow rates in or out of a building. The heat content of air depends on its temperature. Cold air entering a building must be heated to the interior set point temperature. Conversely, warm air entering the building is cooled to the interior set point temperature. In both cases, there is an expenditure of energy to maintain the temperature in the conditioned space. In addition, the movement of air through the insulation changes the temperature profile in the insulation which in term changes the rate of heat flow through the insulation. The movement of air through insulated regions can also carry water vapor into the building thus adding another item of cost, for example, removal of excess water by condensation and heating or cooling the water vapor transported by air. These factors provide motivation for construction that reduces air infiltration to as low a level as health considerations permit. The thermal resistance of compressible insulations like fiberglass, rock wool, polyester, or cellulose depends on the density (mass per unit volume) of the material as installed in the building envelope. Insulation manufacturers specify the thickness and density (or weight per unit area) of their product that is required to achieve a specific R or RSI. If the specified thickness and weight of material are not achieved, then the R or RSI will likely be

0.5 k

Apparent Thermal Conductivity

0.4

lambda x 5

0.3

0.2

0.1

0 0

1

2

3

4 Density

5

6

7

. Fig. 19.2 Apparent thermal conductivity as a function of density (lbm/ft3). The curve labeled k has units Btu·in/ft2·h·
F while the curve labeled lambda  5 has units W/m·K. Multiply the density in the figure by 16.02 to obtain density with units kg/m3

8

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Thermal Insulation for Energy Conservation

different from the target value. Each insulation type has a characteristic curve like that shown in > Fig. 19.2. The curve in > Fig. 19.2 shows data for an example material with constant composition and fiber diameter at a constant temperature [12]. As the density of the insulation changes, the three heat transfer contributions (conduction, convection, and radiation) change and the overall rate of heat transfer changes. When the density of the insulation is low, the curve indicates that the apparent thermal conductivity will decrease as density increases (thermal resistance will increase) while the high-density state shows increasing apparent thermal conductivity with increasing density (decreasing thermal resistance). Every thermal insulation product has its own characteristic curve. Thermal insulations are labeled and sold with a thickness at which the advertised R will be achieved. The thermal resistance will be different if compressed to thicknesses other than that on the label because as the thickness changes the density changes [13]. 5

R-value

4 3 2 1 0

0

1

2

3

4

5

6

7

8

Density

. Fig. 19.3 R-value for a one inch of insulation at the indicated density units: R-value (ft2·h·
F/Btu) Density (lbm/ft3) 0.8

0.6 RSI-value

658

0.4

0.2

0

0

20

40

60 Density

80

100

120

. Fig. 19.4 R-value for 25 mm of insulation at the indicated density units: RSI-value (m2·K/W) Density (kg/m3)

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> Figures 19.3 and > 19.4 show R-values for a one-inch thickness of insulation and RSI values for 25 mm thickness of insulation for the material illustrated in > Fig. 19.2. The important point here is the significant change in the insulation performance per unit thickness as the density (amount of material per unit volume) is changed.

Reflective Insulations Enclosed air spaces with low-emittance surfaces provide resistance to heat flow by reducing or nearly eliminating radiative transfer across the air space. This is readily shown by the following equation for the net radiation, Qrad, between large parallel planes with emittances e1 and e2 [12]. Qrad ¼ EfA  s  ðT4 hot  T4 cold Þg

(19.6)

Qrad is net radiation from the hot surface to the cold surface (Btu/h or watts) A is the area perpendicular to the heat flow (ft2 or m2) Thot and Tcold absolute temperatures (R or K) s is the Stefan-Boltzmann constant 0.1712  108 (Btu/h·ft2·
R4) or 5.669  108 (W/m2·K4) E ¼ ð1=e1 þ 1=e2  1Þ1

(19.7)

The heat transfer by radiation is directly proportional to the effective emittance (E), a quantity that varies from 0 (a perfect reflector) to 1 (a perfect absorber or block body). A large number of building materials (wood, masonry, and common non-metallic paints) have emittances near 0.9. A few emittance values (e) are listed in > Table 19.4 along with calculated values for E. The first column contains E with one surface having a low emittance wile the other surface is wood or a common building material. The second column contains E for low emittance surfaces on both sides of the reflective air space. The bracketed term in > Eq. 19.6 provides the maximum net radiation between the two surfaces for a given area and specific temperatures. > Table 19.5 contains a few examples of the radiation term between two wood or two masonry surfaces and the reduction that can be achieved by changing one surface to emittance 0.05.

. Table 19.4 Examples of effective emittance values Surface

e1

E with (e2 = 0.9)

E with (e2 = e1)

Aluminum foil Metallized film

0.03 0.05

0.030 0.050

0.015 0.026

Coating Wood

0.25 0.90

0.243 0.818

0.143 0.818

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. Table 19.5 Maximum radiation exchange and reductions Thot
F (
C)

Tcold
F (
C)

Q with E = 0.9 (kW)

Q with E = 0.05 (kW)

Reduction (kW)

70 (21.1)

65 (18.3)

1.54

0.09

1.45

100 (37.8) 100 (37.8)

90 (32.2) 85 (29.4)

3.59 5.31

0.20 0.30

3.39 5.01

. Table 19.6 Single reflective air space thermal resistance values at Tm = 77
F (25
C) Thermal resistance ft2·h·
F/Btu (m2·K/W)

Thickness in. (mm)

ΔT
F (
C)

0.47 (12)

18 (10)

2.38 (0.42)

2.33 (0.41)

1.87 (0.33)

0.94 (24) 1.50 (38) 0.47 (12)

18 (10) 18 (10) 27 (15)

4.43 (0.78) 5.85 (1.03) 2.38 (0.42)

3.41 (0.60) 3.24 (0.57) 2.38 (0.42)

2.04 (0.36) 2.16 (0.38) 1.70 (0.30)

Down

Horizontal

Up

The results in > Table 19.5 are for an area of 100 ft2 (9.3 m2) and the indicated temperatures. The total heat flow across a reflective air space can be approximated by > Eq. 19.8 where the term hc represents heat transport by convention and conduction [13]. The term hc is determined from an experimental measurement of total heat flow with a subsequent subtraction of the radiative term. The term hc can be determined from published equations and hot box data [13, 14]. Since hc includes convection, the values depend on the heat flow direction. The standard ISO 6946 also provides a method for determining hc [15]. Qtotal =A ¼ ðhrad þ hc Þ  DT

(19.8)

hrad ¼ 4  E  s  Tm 3 Tm ¼ ðThot þ Tcold Þ=2 DT ¼ ðThot  Tcold Þ > Table 19.6 contains some examples of enclosed reflective air space thermal resistances for a single enclosed air space with E = 0.03. The ASHRAE Handbook of Fundamentals contains reflective air space thermal resistances for various conditions [16].

Envelope R-Values Heat flow across a section of the building envelope depends on the temperatures of the regions on both sides on the element and the thermal resistances between the regions. The

Thermal Insulation for Energy Conservation

19

situation is best discussed for a wall section that does not include doors or windows. The resistance between the regions includes layers of different building materials and in many cases materials positioned in the direction of heat flow (thermal bridges). Heat flow calculations are commonly based on U-values (overall heat transfer coefficient) that take into account all of the materials between the bounding regions and surface film resistances. Q ¼ U  A  DT

(19.9)

U, Btu/ft2·h·
F or (W/m2·K) A, ft2 or (m2) ΔT,
F, or (K or
C) Q, Btu/h or (W) In order to avoid the complication of wind and the difference between the temperature of the outside air and the temperature of sunlit wall, the outside surface of the wall will be taken as region 1 and the inside air temperature will be taken as region 2. The U in this case will include an inside air film resistance (Rfilm), an interior sheathing material resistance (R1), the resistance of the wall structure (Rs), the exterior sheathing (R2), and final exterior wall material (R3). For this case U is given by > Eq. 19.10. U ¼ 1=ðRfilm þ R1 þ Rs þ R2 þ R3 Þ

(19.10)

RT ¼ 1=U

(19.11)

Rs is the complication in the equation for U since in many cases the region is not a homogeneous layer of material. If the wall is a layer of material like concrete, brick, or solid wood then the denominator in > Eq. 19.10 is a sum of resistances. If the wall is a wood frame or timber-wall type of structure then there are parallel paths (commonly two) for heat to move across this region. One path is through the insulated region while the second path is through the frame or timber region. > Equation 19.12 is often used to calculate a value for Rcav where fc is the fraction of the wall area that bounds cavity and fw is the fraction that bounds the wood framing (fc + fw = 1). The f values depend on the design of the framing. For example, nominal 2  4 in. wood framing placed 16 in. on center with double top plates and a single bottom plate has fw = 0.14 for a ceiling to floor distance of 8 ft. The corresponding value for fc is 0.87. This means that only 86% of the wall area is insulated by installing material in the cavity formed by wood framing members. f w ¼ ð14:5  91:5Þ=ð16:0  96Þ ¼ 0:86 If Rw 4.2 ft2·h·
F/Btu is taken as the resistance for the wood in the direction of heat flow and Rc 15 ft2·h·
F/Btu is taken for the resistance of the insulation, then the value for Rs from > Eq. 19.12 is 11.03. If Rc is 11, then Rs is 8.97. Rs ¼ 1=ðf w =Rw þ f c =Rc Þ

(19.12)

Specification of values such as Rfilm = 0.68, R1 = 0.5, R2 = 0.45, and R3 = 0.2 permits an evaluation of U for Rc 15. The RT describes the overall resistance of the structure between

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Thermal Insulation for Energy Conservation

the inside air and the exterior surface. If an exterior air film is included, then it can be added to the result for RT. U ¼ 1=ð0:68 þ 0:5 þ 11:24 þ 0:5 þ 0:45 þ 0:2Þ ¼ 0:0737 RT ¼ 13:57 This example is intended to show several factors to consider. The total thermal resistance of the wall is not equal to the thermal resistance of the cavity insulation even through it includes several additional resistance factors. The total resistance of the wall depends on the design (spacing, for example) of the structure and the materials used to build the structure. If metal is substituted for wood then the resistance Rw drops to near zero and thermal resistance in the path through the metal structure has to be added. A few examples of steel wall resistances taken from an American Iron and Steel Institute publication [16] are shown in > Table 19.7. The data for R 11, 13, and 15 cavity insulations are for 3.625 in. steel framing that is 24-in. on center, while R 19 is for 6.0 in. framing that is 24 in. on center. R sheathing refers to continuous insulation placed perpendicular to the direction of heat flow. This is R2 in > Eq. 19.10. The U-values for building assemblies can be measured using a hot box facility that can be used to test relatively large test specimens, 9 by 16 ft (2.7 by 4.88 m) for example. The total heat flow at steady state from a warm region to a cold region is determined from a measurement of heat input to maintain the temperature of the warm region [18]. A hot box measurement includes heat transfer by all mechanisms. > Figure 19.6 is a photograph of a rotatable hot box used for building assemblies. The outline of a test specimen can be seen between the two sections of the hot box. The two sections are closed to perform a test. Concrete masonry walls and concrete block walls represent a somewhat different type of situation in that the Rs is representing a layer of material. Solid concrete walls built using ‘‘standard’’ weight concrete (density of 100–125 lb/ft3) have thermal resistance values of approximately 0.1 ft2·h·
F/Btu per inch of thickness. An eight-inch thick wall

. Table 19.7 Rtot for steel stud walls R-cavity 2




R sheathing

Rtotal

2

ft ·h· F/Btu (m ·K/W) 11 (1.937) 13 (2.289)

1.0 (0.176) 1.0 (0.176)

7.0 (1.23) 7.3 (1.29)

15 (2.642) 19 (3.346) 11 (1.937) 13 (2.289)

1.0 (0.176) 1.0 (0.176) 5.0 (0.881) 5.0 (0.881)

7.6 (1.34) 8.0 (1.41) 13.0 (2.29) 13.6 (2.40)

15 (2.642) 19 (3.346)

5.0 (0.881) 5.0 (0.881)

14.3 (2.52) 15.0 (2.64)

Thermal Insulation for Energy Conservation

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Reduction in Load from Adding Insulation 100.0

% of Uninsulated Load

80.0

60.0

40.0

20.0

0.0 0

2

4

6

8

10

12

14

16

18

20

Added R Total Savings % saved at + R12

% saved at + R8 R 8 to R12

. Fig. 19.5 Example of diminishing return

using this material has a R of about 0.8 ft2·h·
F/Btu. Masonry blocks with interval cells (air filled) have slightly high R-values (range 1.5–2.0) that depend on the density of the concrete used to produce the blocks. Insulation can be added to cells to make modest increase in the resistance of the blocks. Application of the parallel path idea introduced above shows that a concrete block with insulation core region has a maximum R of about 3 ft2·h·
F/Btu that is achieved as the resistance of the core material becomes very large. This situation is remedied in part by adding layers of insulation usually on the interior side of the wall. When this is done, the concrete or block wall resistance becomes R2 in > Eq. 19.10 and the interior insulation system becomes Rs. In many cases, the performance of massive walls is improved by the dynamics of absorbing and discharging heat as the outside temperature changes. This is called ‘‘the mass effect.’’ The mass effect is sometimes described by a factor called the ‘‘Dynamic Benefit of Massive Walls (DBMS).’’ The DBMS is a multiplier that describes the thermal performance in terms of a ‘‘dynamic R’’ [18].

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Thermal Insulation for Energy Conservation

Dynamic R ¼ Conventional R  DBMS

(19.13)

DBMS values range from 1 to perhaps 4. The DBMS depends on the temperature variation in a given location and the mass, specific heat, density, and thermal conductivity of the construction material in question. The determination of a DBMS value generally requires computer simulations of the structure to determine the factor DBMS that will result in equal performances of the massive wall and a conventional wall with specified thermal resistance. For the present discussion, it is sufficient to note that massive walls can demonstrate thermal performance that is much better than anticipated from the relatively modest conventional R. Attic or roof cavity insulation receives a lot of attention since the roof surface can become very hot due to solar radiation and very cold due to radiation to the night sky. Attic spaces or roof cavities are often ventilated to remove moisture from the occupied part of the building and remove some heat. The attic spaces insulation is commonly located on the attic floor directly above the ceiling above conditioned space. In some applications, the insulation is placed directly below the roof deck. This latter application is sometimes combined with a non-ventilated attic strategy. Attic floor insulation is commonly viewed as a continuous layer of material of uniform thickness. A small correction can be applied to account for the presence of structural members buried in the insulation (ceiling joists) but this is a minor factor in modern times with insulation thicknesses that are much greater than the height of the ceiling joist. The depth of attic floor insulation is dictated in part by economic factors since there is often sufficient space for large thicknesses of insulation. This is in contrast with walls with fixed amount of space for insulation. Attic thermal resistance recommendations and requirements vary around the world with current recommendations as high as R 60 ft2·h·
F/Btu (RSI 10.6 m2·K/W) rated at 75
F or 24
C. A wide variety of insulations in the form of batts (or blankets) or loose-fill insulation that is pneumatically installed or poured is used. The important considerations in choosing attic insulation type and R-value include mechanical stability of the insulation, moisture absorption/desorption, and fire performance. Mechanical stability is important since the thermal resistance depends on thickness as shown by > Eq. 19.1. If the insulation loses thickness, then its thermal resistance will be reduced. In the case of loose-fill insulations, this phenomena is called ‘‘settling.’’ As an insulation settles its density increases and the apparent thermal conductivity changes. An analysis of data for most of the common types of insulation shows that settling or thickness reduction results in R-value reduction. Some insulation products, cellulose, for example, are labeled to account for settling after the material is installed. Some insulations contain binders pr adhesives to reduce settling after the insulation is installed. Stabilized cellulose is an example of this type of insulation [19]. A builder or designer should be aware of the settling phenomena and examine the care with which the insulation manufacturer deals with this issue. The resistance of attic insulation to ignition or spread of fire is important because the attic region operates at elevated temperatures in the summer, often contains electrical wiring, and sometimes contains hot surfaces such as lights, flues, or chimneys.

Thermal Insulation for Energy Conservation

19

Some types of insulation for example: cellulose, cellular plastic, plastic fiber, wool, and wood fiber: can be ignited and will burn. These insulations are often treated with fire retardant chemicals to reduce smoldering tendency and limit the spread of fire on the surface. Care must be taken to keep material that can ignite and burn away from potentially hot surfaces. The condition of electrical wiring can also be a safety issue especially if the wiring becomes buried in a material that will ignite and burn. An understanding of the fire retardant chemicals being used, their long-term stability, and the manufacturers testing and quality control is important and difficult. At a minimum, the user of the insulation should verify that the product undergoes regular verification of its fire resistance and that permanence of the fire retardant chemicals has been established. A combination of > Eqs. 19.6 and > 19.11 introduces an interesting and overlooked concept about insulation: a diminishing return. Consider, for example, the heat flux (Q/A) through a region when the temperature difference (ΔT) is specified. The heat flux is inversely proportional to R as shown in > Fig. 19.5. The diamonds in > Fig. 19.2 represent the percent of heat flux calculated for a ceiling with Added R value to an uninsulated Ceiling assigned the value R 2. Adding R 8 to the ceiling to provide a total R of 10 reduces the ceiling heat flux to 20% of the uninsulated value. Adding R 12 reduces the ceiling heat flux to 15% of the uninsulated value.

. Fig. 19.6 An open hot box (Photo curtest of the BTRIC, Oak Ridge National Laboratory, USA)

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> Table 19.8 extends the added R value to R 60 showing the rapidly declining savings to be expected. The same type of calculation would apply to other parts of the building envelope. Below floor insulation is used when there is space below the floor or when the building is positioned on a slab. Slab insulation is often limited to the perimeter region with insulation installed either on the interior or exterior side of the foundation perpendicular to the heat flow direction. The amount of thermal resistance recommended for perimeter application sis generally in the range R 5 to R 10 (RSI 0.9–1.8). There are several strategies for insulating floors above the ground (with crawl space). One technique involves installing fiberglass batt insulation between the floor joists. A water vapor retarder is usually installed below the insulation to keep water vapor from condensing on the bottom of the flooring. Reflective insulations are also used in below-floor applications either as single sheet materials attached to the bottom edge of the floor joists or between floor joists. Multilayer reflective insulation has also been used in the application.

Hybrid Systems Different types of insulations are being combined to economically enhance overall performance. Combinations of spray polyurethane insulation and fiberglass or reflective insulation are examples of this type of system. When installed in a wall cavity, the spray foam can provide an air-tight seal and a level of thermal resistance that depends on the thickness of the foam. The wall cavity is then filled with a mass insulation such as fiberglass or provided with a reflective insulation. In either case, the thermal resistance of the cavity is the sum of the thermal resistance of the foam and the thermal resistance of the insulation used to fill the cavity. The benefits of such a system are enhanced thermal resistance and a barrier to air infiltration. > Figure 19.7 shows calculated values for a wall element containing a layer of spray polyurethane foam and a reflective insulation assembly with R = 6.87.8 (RSI = 1.21.4). The curves in > Fig. 19.7 are for foams with thermal resistivities, R∗, from 3.5 ft2·h·
F/Btu (open cell) to 6 ft2·h·
F/Btu (closed cell). The total space for the hybrid system is 5.5 in. (140 mm).

Summary This chapter has outlined some of the fundamental considerations related to building insulation. Important properties have been identified and factors that affect performance have been discussed. The selection of thermal protection for the building envelope must include consideration of moisture transport and a requirement that air infiltration be addressed. In many cases, this means that materials in addition to thermal insulation will be required. Air barrier materials and water vapor retarders are examples. In some cases, thermal insulation serves dual purposes such as being an air barrier and a thermal insulation.

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Thermal Insulation for Energy Conservation

R Total for Foam with a Reflective Insulation 20 18 R-Total

16 14 12 10 8 0.25

0.5

0.75

1

1.25

1.5

1.75

2

2.25

Foam Thickness R* 6

R* 5

R* 3.5

. Fig. 19.7 Total R for a hybrid insulation system combining cellular foam and a reflective insulation

. Table 19.8 Anticipated savings from increased attic insulation R total

R added

Heat flux reduction (%)

Base heat flux (%)

2

0

0.0

100.0

10 14 15 20

8 12 13 18

80.0 85.7 86.7 90.0

20.0 14.3 13.3 10.0

25 30 35 60

23 28 33 58

92.0 93.3 94.3 96.7

8.0 6.7 5.7 3.3

Future Directions Future developments in the area of building insulation will no doubt find increased use of super-insulations such as vacuum panels, aerogel insulation, and gas-filled panels. Conventional insulations will be improved by adding components to block radiation (opacifiers). Phase-change material will be added to conventional insulation to provide for improved dynamic performance. The rate of advance in these areas is tied to cost of the materials, cost of energy, and availability of energy.

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Advanced technologies that proved materials or systems that provide thermal resistance that changes with conditions will lead to new levels of energy conservation and contribute to construction of ‘‘zero energy buildings.’’ Variable resistance insulations can be used to take maximum use of incoming solar energy.

References 1. Anderlind G, Johansson B (1983) Dynamic insulation – a theoretical analysis of thermal insulation through which a gas or fluid flows. Swedish Council for Building Research, Document D8 2. Yarbrough DW, Graves RS (1997) The effect of air flow on measured heat transfer through wall cavity insulation. J ASTM Int 4(5):94–100 3. ASHRAE (2009) Heat, air, and moisture control in building assemblies – material properties. In: Handbook of fundamental. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta (Chap 26) 4. AIRAH (2007) Technical handbook, 4th edn. The Australian Institute of Refrigeration, Air Conditioning and Heating, Melbourne 5. Hall MR (ed) (2010) Materials for energy efficiency and thermal comfort in buildings. Woodhead, Oxford 6. Graves RS, Wilkes K, McElroy DL (1994) Thermal resistance of attic loose-fill insulations decrease under simulated winter conditions. Therm Conduct 22:215–226 7. ASTM C 1373 (2010) Standard practice for determination of thermal resistance of attic insulation under simulated winter conditions. In: 2010 Annual book of ASTM standards, vol 04.06, pp 793–810 8. Fine HA, Jury SH, Yarbrough DW, McElroy DL (1981) Heat transfer in building thermal insulation: the thickness effect. ASHRAE Trans 87(Pt 2) 9. ASTM C 518 (2010) Standard test method for steady-state thermal transmission properties by means of the heat flow meter apparatus. In: 2010 Annual book of ASTM standards, vol 04.06, pp 152–166

10. Abdou AA, Budaiui IM (2005) Comparison of thermal conductivity measurements of building insulation materials under various operating temperatures. J Build Phys 29(2):171–184 11. ASTM C 1303 (2010) Standard test method for predicting long-term thermal resistance of closed-cell foam insulation. In: 2010 Annual book of ASTM standards, vol 04.06, pp 680–706 12. Siegel R, Howell JR (1971) Thermal radiation heat transfer. McGraw-Hill, New York 13. Robinson HE, Powell FJ (1957) The thermal insulation value of airspaces, Housing Research Paper 23. U.S. Department of Commerce, National Bureau of Standards 14. Desjarlais AO, Yarbrough DW (1991) Prediction of the thermal performance of single and multiairspace reflective insulation materials. ASTM STP 1116:24–43 15. ISO 6946 (2005) Building components and building elements-thermal calculation method 16. American Iron and Steel Institute (1995) Thermal design and guide for exterior walls, RG-9405 17. ASTM C 1363 (2010) Standard test method for thermal performance of building materials and envelope assemblies by means of a hot box apparatus In: 2010 Annual book of ASTM standards, vol 04.06, pp 741–784 18. http://www.ornl.gov, Dynamic thermal performance and energy benefits of using massive walls in residential buildings 19. ASTM C 1497 (2010) Standard specification of cellulose fiber stabilized thermal insulation In: 2010 Annual book of ASTM standards, vol 04.06, pp 863–866

20 Thermal Energy Storage and Transport Satoshi Hirano Thermal and Fluids Systems Group, Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 670 Fundamentals of Thermal Energy Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671 Solar System and Thermal Energy Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671 Functions of Thermal Energy Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 673 Classification of Thermal Energy Storage Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 674 Thermal Energy Storage Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 675 Thermal Energy Storage Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 677 Characterization of Thermal Energy Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 679 Phase Change Thermal Energy Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 680 General Feature of Phase Change Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 680 Thermal Energy Storage Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 682 Supercooling and Segregation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 684 Research and Development Situation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 686 Phase Change Heat Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 689 Transport Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 689 Research and Development Situation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 690 Examples of Recent Technical Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 690 Thermal Energy Storage System for Hot Water Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . 690 Heat Storage System for Heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 693 Steam Accumulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 695 Pipeless Heat Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696 Microcapsule Slurry Heat Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 697 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 698

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_20, # Springer Science+Business Media, LLC 2012

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Abstract: The efficient use of energy is important to restrain the emission of greenhouse effect gases. Thermal energy storage and heat transport technology enable to utilize the renewable energy and the waste heat which are generally unstable, maldistributed, and thin. They also enable to operate energy devices at a high efficient condition. This chapter introduces some basic research and development activities of thermal energy storage and heat transport, especially latent heat utilization. First, the following fundamental knowledge of thermal energy storage is explained: (1) the functions of thermal energy storage, (2) the classification of storage methods, (3) the characteristics of thermal energy storage materials especially phase change materials (PCMs), and (4) the constitutions of thermal energy storage devices. Other characteristics and challenges of latent heat thermal energy storage (LHTES) which utilize supercooling phenomenon are also explained. Second, several examples of the practical use of LHTES including the utilization of snow and ice are discussed. In the same way, several characteristics and examples of the practical use of the heat transport using latent heat are also explained. Furthermore, recent developments on the following research subjects are introduced: (1) thermal energy storage for hot water supply using the supercooling phenomenon of sugar alcohol, (2) heat storage for space heating using the supercooling of hydrate, (3) the improvement of thermal characteristics of paraffin wax as a PCM, (4) a steam accumulator using sugar alcohol, (5) pipeless heat transport using sugar alcohol or hydrate, and (6) heat transport method using the microencapsulated PCM slurry.

Introduction Global warming and depletion of fossil fuels are two major problems that are caused by large-scale energy consumption. To resolve these problems, the current practice of focusing on inexpensive energy use should be reconsidered, and the focus should be shifted to efficient energy use that does not adversely affect the environment. From the heat usage point of view, there are many heat demands within a temperature range of 0–200
C. Although the heat demands can be basically provided by waste heat and renewable energy such as solar heat, most of them are directly provided by combustion of fossil fuels (> Fig. 20.1). Such waste heat and solar heat are usually unstable and dispersing thinly. By using thermal energy storage, such thin heat can be stored temporarily, so that the instability of heat supply can be smoothed. Thus thermal energy storage is the essential technology for utilizing such unstable or thin renewable heat. Thermal energy storage has another important feature which enables to generate and use energy efficiently because thermal energy storage can store energy during slack demand times (e.g., at night) and provide energy during high demand times (e.g., during the day). To meet a given peak demand, energy storage permits smaller power plants to be built, and it also permits them to be continually run at peak operating efficiency. By using heat transport, various heat sources can be connected and various heat demands which are located far from the heat sources can be fulfilled. The heat transport technology also enables to use a variety of heat sources such as a boiler, waste heat, and solar

Thermal Energy Storage and Transport

20

. Fig. 20.1 Heat demands and heat sources by renewable energy and waste-heat from 0
C to 200
C

heat. Therefore, heat transport is the key technology to realize the thermal network among heat sources and heat demands, which can minimize the capacity of each heat source. This chapter describes fundamental technology and the recent research trend of thermal energy storage, and its application to heat transport.

Fundamentals of Thermal Energy Storage Solar System and Thermal Energy Storage The quantity and quality of heat supply from natural energy generally change with time. It is only during the daytime that solar energy can be acquired. Particularly, direct solar radiation is provided only at the time of fine weather. Heat demand in the commercial sector and residential sector, on the other hand, is apt to concentrate in the morning and evening rather than in the daytime. Therefore, to improve the utility value of solar energy and magnify the application field of the energy, the technologies to collect and store solar heat in the daytime and to supply the stored heat during the high demand times become important.

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. Fig. 20.2 (a) Component of passive thermal energy storage device and (b) application to heating by wall heat storage

Figures 20.2 and > 20.3 show general components of solar systems with the thermal energy storage which can temporarily store the heat from solar collectors and can supply the stored heat on demand. Three thermal processes, (1) charging, (2) keeping, and (3) discharging, are necessary for thermal energy storage. The simplest constitution of a thermal energy storage method is that an object of heating is contacted to a thermal energy storage body or is included in the body as shown in > Fig. 20.2a. In > Fig. 20.2, all the above thermal processes (1)–(3) are done passively. For example, there are houses and buildings which adopt this thermal energy storage method to use solar heat. The system using this method is called a passive solar system. If the system is designed such that the solar heat goes to the structure of a building through a transparent thermal insulation as shown in > Fig. 20.2b and such that the time taken for thermal conduction from the structure to the indoor wall is about half a day, this storage method can automatically supply solar heat for space heating in the nighttime. Although the passive thermal energy storage is simple in constitution, it is difficult to control the above processes (1)–(3) depending on the condition. Therefore, the thermal optimization of the system is important in designing such passive systems. > Figure 20.3 shows the example of an active solar system which carries out the above three thermal processes actively. Each device shown in > Fig. 20.3 is appropriately selected depending on the objective of the system. For example, a solar domestic hot water system corresponds to the simplest composition of the system shown in > Fig. 20.3. The domestic hot water system consists of a solar collector and a water tank for thermal energy storage, both of which are installed on a roof. Cold water which flows into the collector is heated by solar heat in the daytime, which causes natural convection of the water and circulates the water between the collector and the tank. Thereby the water temperature in the tank gradually rises to a high temperature for hot water supply after sunset. Water is the most convenient medium to transport heat among the components shown in > Fig. 20.3. In the system which deals with the lower temperature than the freezing point of water, nonfreezing fluid is usually used as a heat transfer medium. On the other hand, in the system which deals with the higher temperature than a room temperature, an organic compound or chloride is often used for a heat transfer >

Thermal Energy Storage and Transport

20

. Fig. 20.3 Configuration of an active solar system

medium. In the system in which heat transfer medium is not water, a heat exchanger is often used in the storage device to heat the water. Air is sometimes used for the heat transfer medium in the solar collector because air can directly be used for space heating or for heating. The thermal energy storage device (1) in > Fig. 20.3 can regulate the fluctuation of heat supply. When the output from the thermal energy storage device (1) is short in temperature or quantity for heat demand, boilers, heat pumps, or absorption chillers are used as an auxiliary heat source. The thermal energy storage device (2) in > Fig. 20.3 can regulate the fluctuation of heat demand. If the quantities of heat supply and heat demand can be patternized, either thermal energy storage device (1) or (2) is omitted by designing the system matching the fluctuation of the quantities. Optimization of operating temperature and equipment capacity based on the thermal performance of each component is necessary for designing the system with thermal energy storage.

Functions of Thermal Energy Storage The effects of thermal energy storage are classified into three functions as shown in > Fig. 20.4, that is to say, phase regulation between heat supply and heat demand (> Fig. 20.4a), an amplification of heat supply (> Fig. 20.4b), and smoothing of heat supply (> Fig. 20.4c). For example, the function of phase regulation is utilized when solar heat gained in the daytime is used to supply hot water in the nighttime. The amplification function of heat supply is utilized when solar heat gradually gained through a year is used for heating in winter concentratedly. The smoothing function of heat supply is utilized when solar heat gained under an unstable weather condition is used for solar thermal power generation at constant output. In many practical uses, these three functions should be properly selected and combined to fit applications. For example, the passive thermal energy storage device in > Fig. 20.2 uses two functions: the phase regulation shown in > Fig. 20.4a and the

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. Fig. 20.4 Functions of thermal energy storage. (a) Phase regulation, (b) amplification, (c) smoothing

smoothing shown in > Fig. 20.4c. The active thermal energy storage system in > Fig. 20.3 uses all the three functions: the phase regulation, the amplification, and the smoothing shown in > Fig. 20.4.

Classification of Thermal Energy Storage Methods A material absorbs or discharges heat when the kinetic energy or the potential energy of the atoms or the molecules in the material changes by temperature change or phase transition. Besides, a material absorbs or discharges heat when the condition of the atomic bond or the molecular bond changes by chemical reaction. Thermal energy can be temporarily stored by using these phenomena as necessary. > Table 20.1 shows the example of thermal energy storage methods classified by physical and chemical phenomena which are used to store heat. Thermal energy storage methods using the physical change of a material are classified into the following three methods: (1) The thermal energy storage method which uses the absorption and discharge effects of heat caused by the temperature change of materials is called sensible heat thermal energy storage (SHTES). The SHTES is applied to hot-water bags or electric water heaters with water tanks. (2) The thermal energy storage method which uses the absorption and discharge effects of heat caused by the phase change of materials is called latent heat thermal energy storage (LHTES). The LHTES is applied to ice pillows or ice storage air conditioners. (3) The thermal energy storage method which uses the adsorption and desorption heats of material is called adsorption thermal energy storage. The adsorption storage is applied to air conditioners or chillers. The particular classification of SHTES and LHTES in > Table 20.1 is mentioned later. Thermal energy storage methods using the chemical change of a material are classified into the following three methods: (1) The thermal energy storage method which uses the endothermic and exothermic reactions of materials is called chemical thermal energy storage (CTES). Because repeatability becomes premise as for the functions of thermal

Thermal Energy Storage and Transport

20

. Table 20.1 Thermal energy storage methods Use of physical change of materials ● Sensible heat thermal energy –Conventional SHTES (e.g., hot water storage) storage (SHTES) –Soil thermal energy storage/Underground thermal energy storage –Aquifer thermal energy storage –Solar pond ● Latent heat thermal energy storage (LHTES)

–Conventional LHTES (e.g., ice storage) –Supercooled thermal energy storage

● Adsorption thermal energy storage Use of chemical change of materials ● Chemical thermal energy –Conventional CTES (e.g., reversible reaction between storage (CTES) calcium hydroxide and calcium oxide) –Metal hydride thermal energy storage –Concentration difference thermal energy storage

energy storage, it is necessary for the reaction of CTES to be reversible. As subspecies of the CTES, there are (2) metal hydride thermal energy storage and (3) concentration difference thermal energy storage using heat of dilution.

Thermal Energy Storage Materials Any substance can be used as thermal energy storage material in theory. The effectiveness as thermal energy storage materials depends on thermophysical properties like specific heat, transition point, and heat of transition. However, practicable materials are limited by chemical properties like deliquescency, efflorescent, corrosiveness, noxiousness, heat resistance, and economy. > Table 20.2 shows heat capacities per 1 L of several familiar materials used as heat storage materials [1]. In a room temperature, water is the best material for SHTES system in point of cost, safety, and thermal energy storage density. At a high temperature over several hundred degrees Celsius, rocks and bricks are effective as materials for SHTES system, too. > Table 20.3 shows melting points and heats of fusion per 1 L of several familiar materials [2]. Water is also the most suitable phase change material (PCM) for LHTES systems which is operated near 0
C. Ice storage systems are good examples of LHTES systems and are widely spread today. Paraffin is one of usable PCMs. The heat of fusion per unit volume of paraffin is small because both density and heat of fusion per unit mass are small. Besides, inflammability of low melting point paraffin is

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. Table 20.2 Heat capacities of ordinary materials per 1 L Material

Heat capacity (J/K)

Water

4,170a

Mild steel Loam (water content 37%) Basalt Sand and clay (water content 22%)

3,720b 3,440a 2,670c 2,350a

Limestone concrete Chamotte brick Asphalt Cedar (water content 48%)

2,160a 2,000a 1,950a 540b

At 20
C At 27
C c At 127
C a

b

. Table 20.3 Heat of fusion of ordinary materials per 1 L Material

Melting point (ºC)

Heat of fusion (kJ/L)

Water

0

306

Polyethylene glycol #400 Sodium sulfate decahydrate Disodium hydrogenphosphate dodecahydrate Sodium acetate trihydrate Paraffin wax

8 32 36 58 4270a

97 334 384 356 120190a

Polyethylene glycol # 6000 D-Threitol Erythritol Mannitol

57 87 118 167

201 328 416 422

Tin Aluminum

232 660

422 940

a

Depending on the number of carbon atoms in a molecule

high. However, paraffin has low noxiousness, and the influence of supercooling (mentioned later) before freezing is small. Therefore, paraffin is used as a comparatively cheap PCM. Hydrate is also one of the useful PCMs. Noxiousness of most hydrate is low. However, supercooling and segregation (mentioned later) become a problem when the hydrate is used as a PCM. Sugar alcohol is one of the safe and promising PCMs. However, the

Thermal Energy Storage and Transport

20

supercooling and cost of sugar alcohol may be problematic. Thus the further utilization of hydrate or sugar alcohol is expected in the future LHTES systems because the thermal energy storage densities of hydrate and sugar alcohol are larger than that of paraffin.

Thermal Energy Storage Devices In the thermal energy storage device shown in > Fig. 20.3, suitable mechanisms are necessary to control the three processes: (1) charging, (2) keeping, and (3) discharging. For the control of the processes, most thermal energy storage devices take either constitution shown in > Fig. 20.5. When the storage space for a heat transfer medium is installed in the middle of piping shown in > Fig. 20.5a, the above-mentioned thermal processes, (1)–(3), can be carried out simply by injecting and extracting the heat transfer medium if necessary. For example, water as a heat transfer medium also functions as a heat storage medium in a solar domestic hot water system. The thermal energy storage is given only by sensible heat when the phase of the heat transfer medium does not change within the temperature range of operation. On the other hand, when hydrates, inclusion compounds, or clathrate compounds of hydrocarbon or fluorocarbon, or fluids like the ice slurry are used as the heat transfer media, latent heat is also available to use along with sensible heat. In the thermal energy storage tank shown in > Fig. 20.5a, the heat transfer medium is easily mixed if the agitating behavior by the inflow motion of the heat transfer medium is strong. In this case, the storage tank is called a mixed tank. The mixed-type heat storage tank provides a high performance in the smoothing function of > Fig. 20.4c. However, the available energy easily decreases in the mixed tank because the temperature difference is easily lost by the agitating behavior. On the other hand, if the mixing behavior by the inflow motion of the heat transfer medium is small, the thermal stratification due to density variations is easily formed in the heat storage tank. In this case, the storage tank is called a stratified tank. The heat storage tank of thermally stratified-type can easily maintain available energy in the tank. To promote the formation of plug flow in the stratified tank, a diffuser or a manifold is often used. For example, the thermal energy storage device for a solar system is considered. The efficiency of a solar collector which is installed in the upstream side of the thermal energy storage device becomes higher as the temperature difference between the solar collector and the ambient air becomes smaller. The efficiency of the thermal appliances such as a heat pump installed in the downstream side of the thermal energy storage device becomes higher as the output temperature of the storage device becomes higher. Therefore, the thermal energy storage device of thermally stratified-type is more profitable in efficiency of the solar system than the mixed-type device [3]. One practicable idea for solar energy systems is the use of a pond as the thermal energy storage tank and a solar collector. The pond for this purpose is called a solar pond. The heat transfer medium flows into the solar pond and flows out from the pond with

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. Fig. 20.5 Typical configuration of thermal energy storage device. (a) Combined use of heat transfer medium and heat storage material, (b) separation by pipe, (c) separation by capsule

gained solar heat to supply heat. A wide pond is advantageous to collect solar heat. However, the gained solar heat is usually going to be dissipated and lost easily from the surface of the pond to the ambient air because of natural convection in the pond. On this account, an inverse thermal stratification is applied to reduce the heat dissipation. Sodium chloride, polymer compound, porous structure, or honeycomb structure is added to the pond to form the inverted temperature profile in the direction of depth such that the temperature in the lower layer is higher than that in the upper layer. Salt lakes are just available to use as the solar ponds. In cold districts, it is necessary for antifreezing fluids to be used as the heat transfer medium to prevent freezing. When the antifreezing fluid can be just used for not only the heat transfer medium but also the heat storage medium, thermal energy storage devices shown in > Fig. 20.5a can be applied. On the other hand, the thermal energy storage device shown in > Fig. 20.5b, c is used when the heat storage medium is different from the heat transfer medium. The materials listed in > Tables 20.2 and > 20.3 can be used as the heat storage materials for the system shown in > Fig. 20.5b, c. In the constitution shown in > Fig. 20.5b, c, the heat exchange rate between the heat transfer medium and the heat storage medium is one of the most significant factors to determine the thermal time constant of the device. It is effective to broaden the contact area between both media for improving the heat exchange rate. It is also convenient to handle the heat storage medium when the medium is divided into small pieces. Therefore, the heat storage media are usually filled into the plural small capsules shown in > Fig. 20.5c whose shape is spherical, cylindrical, or flat. There are several methods which use the underground soil and rocks as the heat storage medium. The method which is called soil thermal energy storage or underground thermal energy storage uses the antifreezing fluid and the soil as the heat transfer medium and the heat storage medium shown in > Fig. 20.5b respectively. The method which is called aquifer thermal energy storage uses the underground water for the heat transfer medium and uses underground rocks and sands for the heat storage medium as in

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20

Fig. 20.5c. Above both methods using the earth are effective for a large quantity and long-term thermal energy storage. When the storage period is longer than a season, the method is particularly called seasonal thermal energy storage. For example, the surplus solar heat gained in the summer can be effectively utilized in the winter by the seasonal thermal energy storage.

>

Characterization of Thermal Energy Storage In a thermal energy storage system, quantity of stored sensible heat, Qs (J), quantity of stored latent heat, Q l (J), and quantity of stored heat of reaction, Qr (J), are given by next equations respectively. Z Qs ¼ m cðT ÞdT (20.1) Qs  mcDT ¼ rVcDT

(20.2)

Ql ¼ mD f HMf

(20.3)

Qr ¼ nD r HRf

(20.4)

where c(T): Specific heat at temperature T (J/g/K), Mf: Melting fraction (defined by [melted mass]/[total mass]), m: Mass (g), n: Number of moles (mol), Rf: Reacting fraction (defined by [reacted mass]/[total mass]), T: Temperature (K), V: Volume (m3), DfH: Heat of fusion (J/g), DrH: Heat of reaction (J/mol), DT: Temperature change (K), r: Density (g/m3) If the temperature dependence of specific heat of the thermal energy storage material is small or if the temperature change of the material during the storage processes is small, > Eq. 20.1 can be approximated by > Eq. 20.2. The quantity of stored heat in the SHTES system is governed only by the > Eq. 20.1. Storage process with the LHTES system is usually accompanied by temperature change before and after the phase transition. Therefore, the quantity of stored heat in the LHTES system is usually governed by the > Eqs. 20.1 and > 20.3. Storage process with the CTES system is usually accompanied by temperature change or by temperature change and phase transition before and after the reaction. Therefore, the quantity of stored heat in the CTES system is usually governed by the > Eqs. 20.1 and > 20.4, or the > Eqs. 20.1, > 20.3, and > 20.4. The efficiency of thermal storage,
, and the efficiency of a heat storage tank,
t, defined by the following equations are used for typical indexes to characterize the performance of a thermal energy storage device.
¼ Qout =Qin

(20.5)


t ¼ Qout =Qth

(20.6)

where Qout: Output thermal energy (J), Qin:Input thermal energy (J), Qth:Theoretical storage capacity of thermal energy (J)

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. Table 20.4 General merits and demerits of three methods of thermal energy storage Rating item

SHTES

LHTES

CTES

Storage density

X

D

O

Stability of output temperature Repetition stability Responsibility Safety

X O O D

O D D D

O X D D

Initial cost

O

D

X

SHTES sensible heat thermal energy storage, LHTES latent heat thermal energy storage, CTES chemical thermal energy storage

The efficiency of available energy, exergy, based on the environmental temperature is also important to evaluate the performance of the storage devices with which the charging and the discharging processes occur in a specific small temperature range such as the LHTES system. Each thermal energy storage method is characterized in > Table 20.4. The thermal energy storage density is defined by the quantity of heat which can be stored in a unit mass or in a unit volume of the storage material. The SHTES has a lot of embodiments, and is technically mature. The LHTES has some technical issues in repeatability, stability, or profitability except an ice storage system, one of the LHTES systems. Thus, the technology of the LHTES is in the middle of development. Although the CTES has the highest functionality, there are many pending issues including the material compatibility. The thermal energy storage density of the LHTES device is larger than that of the SHTES device. Therefore, LHTES is more advantageous than SHTES for the applications where the size of heat storage systems must be minimized, for example, in urban areas. The temperature of the heat storage medium during the charging and discharging processes of sensible heat varies with time. On the other hand, the temperature of the heat storage medium during the charging and discharging processes of latent heat is maintained at the transition point. This is the reason that LHTES is more advantageous than SHTES in point of the storage efficiency of available energy. In addition, the repeatability of the storage processes of LHTES is comparatively stable. Thus, further application of LHTES is expected. From the following section, thermal energy storage and heat transport which use latent heat of PCMs will be explained in detail.

Phase Change Thermal Energy Storage General Feature of Phase Change Materials It is well experienced routinely that ice absorbs large heat of fusion and cools surrounding substances during melting process. In this case, water functions as a PCM. Many candidates

Thermal Energy Storage and Transport

20

of PCMs were listed up in various kinds of literature especially in 1970s when we experienced two oil crises. Among those candidates, however, many of them were substances with toxicity, noxiousness, corrosiveness, irritation, oxidizability, combustibility, or inflammability. Thus the number of available materials for PCMs has been decreasing as regulations for the use of chemical substances have been strengthened. As typical examples of PCMs, paraffin, hydrate, and sugar alcohol are recently attracting attention. Major physical properties of water [2], n-eicosane [4], disodium hydrogenphosphate dodecahydrate (DHD) [5], erythritol [6] are given in > Table 20.5. Compared with water in > Table 20.5, the following points are given as the characteristics of the three materials: paraffin, hydrate, and sugar alcohol. Hydrate and sugar alcohol are profitable to densification of thermal energy storage because densities are larger than that of water. On the other hand, paraffin is disadvantageous for densification of thermal energy storage because the density is small. It is effective to use not only latent heat but also sensible heat of hydrate for thermal energy storage because the specific heat of hydrate is as large as that of water. The utilization effect of sensible heat of paraffin and sugar alcohol is not large compared with water due to the same reason. Hydrate and sugar alcohol are disadvantageous in the heat exchange during the phase change process because thermal conductivities of them are about a half of that of water. Paraffin is more disadvantageous in the heat exchange during the phase change process because the thermal conductivity of paraffin is only about a quarter of that of water. The selection of the suitable material for PCMs depends on the place where the heat storage device is used as well. For a mobile heat storage system, not only the volume

. Table 20.5 Comparison of physical properties of water, n-eicosane, DHD, and erythritol Property

(Phase) 3

Density (kg/m ) Specific heat (kJ/kg∙K) Thermal conductivity (W/m∙K) Melting point (
C) Heat of fusion 0.0
C 2.2
C c 32
C d 36
C e 20
C f 140
C a

b

Water

(Solid)

917

a

(Liquid) (Solid) (Liquid) (Solid) (Liquid) (kJ/kg) (kJ/L(liquid))

n-eicosane

DHD

Erythritol

830

c

1520

1480e

999.84a 2.101b 4.2174a 2.09a

780 1.9 2.3 0.34

1447d 2.00c 3.45d 1.02c

1300f 1.38e 2.77f 0.73e

0.565a 0 333.6 333.5

0.15 36.4 247 193

0.61d 35.54 265.6 384.3

0.33f 119 330 429

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Thermal Energy Storage and Transport

500 Heat of fusion per volume (kJ/L(liquid))

682

Polyhydric alcohol Hydrate

400 Water 300 200 Organic compound 100 Paraffin 0

0

50

100 150 Melting point (°C)

200

. Fig. 20.6 Example of heats of fusion per unit volume of some promising PCMs in the liquid phase

of the heat storage medium but also the weight becomes an important factor. For a stationary heat storage system, on the other hand, the volume of the heat storage medium is overwhelmingly more important than the weight of the medium. > Figure 20.6 shows the relationships between the melting points and heats of fusion per unit volume for several candidates of PCMs whose melting points exist between 0
C and 200
C. The unit volume of each material except water is based on the volume in the liquid phase at around the melting point because the maximum quantity of the material filled in a capsule is limited by the volume in the liquid phase. The unit volume of water is based on the volume in the solid phase at around the melting point because the volume of water decreases after melting. In comparison with the heat of fusion of water which is used for an ice storage air-conditioning system, the heats of fusion of hydrate and sugar alcohol are large, and the heats of fusion of paraffin and other organic substances are small.

Thermal Energy Storage Density It is extremely rare for practical LHTES systems to use only latent heat. The LHTES systems usually use not only latent heat but also sensible heat in the proper operating temperature range including the transition point of the heat storage medium. > Figure 20.7 expresses the variations of the thermal energy which can be stored in each proper temperature range about n-eicosane, disodium hydrogenphosphate dodecahydrate (DHD), sodium acetate trihydrate (SAT), threitol, and erythritol as typical examples of paraffin, hydrate, and sugar alcohol. Hydrate can store large energy because both specific heat and heat of fusion are large, thus it is effective to use hydrate with a wide temperature range. On the other hand, both specific heat and heat of fusion of paraffin are small. Thus the superiority of LHTES with paraffin over the SHTES with water becomes lower as the operating temperature range of paraffin becomes wider.

Thermal Energy Storage and Transport

20

For example, > Fig. 20.8 gives the variations of the thermal energy which can be stored per unit volume of water, n-eicosane, and DHD when the materials are heated from 20
C to 50
C. The thermal energy which can be stored with n-eicosane by the temperature rise of 30
C is about twice as much as that with water. By the way, when the temperature rise from 35.9
C to 36.9
C is considered, the thermal energy which can be stored with water by this temperature rise is 4.2 kJ/L. On the other hand, the thermal energy which can be stored with n-eicosane by the same temperature rise, 1
C, as that of water is evaluated at 195 kJ/L including heat of fusion. In this temperature change, 1
C, the thermal energy

Stored energy (kJ/L(liquid))

(Alcohol)

(Hydrate)

600

DHD 500 400

Erythritol Threitol

SAT Water (Paraffin) Eicosane

300 200 100 0 −20

0

20

40

60

80

100

120

140

Temperature (°C)

. Fig. 20.7 Temperature dependence of the thermal energy which can be stored per unit volume

Stored energy (kJ/L(liquid))

600 DHD 400

Eicosane 200 Water

0 20

30

40

50

Temperature (°C)

. Fig. 20.8 Comparison of the thermal energy which can be stored per unit volume in the temperature range from 20
C to 50
C

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Thermal Energy Storage and Transport

150 Stored exergy (kJ/L(liquid))

684

(Alcohol) Erythritol

100 (Hydrate) (Paraffin) Eicosane

50 Water

0 −20

0

20

Threitol

SAT DHD

40 60 80 Temperature (°C)

100

120

140

. Fig. 20.9 Temperature dependence of the thermal energy which can be stored per unit volume

which can be stored with n-eicosane is 46 times larger than that with water. That is to say, the superiority of the thermal energy storage density of LHTES against SHTES deteriorates when the range of the operating temperature of LHTES system becomes wide. Variations of the thermal exergy (available energy) which can be stored per unit volume of the PCMs are shown in > Fig. 20.9 when 20
C is assumed to be the standard environmental temperature. Sugar alcohol can store larger exergy than hydrate and paraffin because the melting point is high. In other words, the quality of the thermal energy which can be stored with sugar alcohol is high. Thus, LHTES with sugar alcohol has high added value for space heating or hot water supply. To use PCMs shown in > Fig. 20.6 effectively, it is important to make better use of the merits of each PCM, and to make up for the demerits of it. Besides, the development of new materials located in the upper part of the graph in > Fig. 20.6 is eagerly awaited in future.

Supercooling and Segregation A material changes its phase from solid to liquid (fusion) or vice versa (solidification) ideally at the melting point. Practically, however, the temperature gap between fusion and solidification processes occurs. For example, > Fig. 20.10 shows the temperature variation of D-threitol during melting and solidification processes. In > Fig. 20.10, a heating operation increases the temperature of the threitol in the solid phase. The threitol starts to melt at the melting point, 87
C. After the threitol completely melted, the melt is cooled to the room temperature. By the cooling operation, the temperature of the threitol falls to the melting point. However, the solidification process does not start at the melting point. The melt is continuously cooled to the lower temperature than the melting point, in the liquid phase called a supercooled state.

Thermal Energy Storage and Transport

20

Supercooled S S → L

L

L → S

S

80

Degree of supercooling

Temperature (°C)

100

60

40

20

0

5

10

15

20

Time (hr)

. Fig. 20.10 Example of the temperature variation of D-Threitol during melting and solidification processes. The letter ‘‘S’’ and ‘‘L’’ mean solid phase and liquid phase respectively

Supercooling phenomenon is caused by not the delay of thermal conduction in the melt, but the difference in free energy between a liquid phase and a solid phase. To generate a crystal nucleus in the melt, it is necessary for the radius of the molecular cluster in the melt to exceed the critical size which is determined from the relationship between the volume-free energy and the surface-free energy. Therefore, the supercooled state is maintained in the metastable state unless the melt is cooled to the spontaneous nucleation temperature, about 41
C in > Fig. 20.10. The difference between the spontaneous nucleation temperature and the melting point is equivalent to the maximum degree of supercooling of the material. The maximum degree of supercooling depends not only on the intensive properties, such as the melting point, but also on extensive properties, such as the mass of the material filled into a container. Once the solidification starts by the generation of a crystal nucleus, the temperature of the threitol recovers to the melting point as is shown in > Fig. 20.10. After that, the threitol continues releasing heat of solidification till solidification is completed. The supercooling phenomenon is easily observed in hydrate and sugar alcohol. There are two aspects to the supercooling phenomenon that the supercooling of a PCM is favorable for LHTES or unfavorable for it. When the heat of solidification of a PCM is kept in the supercooled state at the lower temperature than the melting point, the heat loss from the PCM to the ambient air can be reduced. In this case, the supercooling becomes a favorable phenomenon for LHTES. On the other hand, even when the heat of solidification of a PCM is demanded, the latent heat is not obtained due to the supercooling unless the temperature of the PCM falls to the spontaneous nucleation temperature below the melting point. In this case, the supercooling becomes an unfavorable phenomenon for LHTES. Most research on LHTES has been conducted from

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Thermal Energy Storage and Transport

the latter viewpoint. Thus, great efforts of research and development of PCMs have been focused on the prevention technology against supercooling. The research on the prevention technology against supercooling became in earnest from the research by Telkes in 1940s. Telkes discovered that the sodium tetraborate decahydrate was effective as a nucleating agent for sodium sulfate decahydrate [7]. The nucleation cannot be promoted easily even if the additive for nucleation is kept in the solid phase. It is considered that the effect of the nucleating agent and the factor of the induction of nucleation are different among base materials, so that it is necessary to discover the agents by a trial-and-error method. Discovery of nucleating agent by Telkes attracted next research, and from 1950s to 1980s, several nucleating agents were discovered, and several physical nucleation methods were invented. However, there are many PCMs whose proper nucleating agents are not found yet. Segregation in hydrate is another challenging phenomenon as well as the supercooling. In the melt of the hydrate, the hydrate of the lower order which crystallized in advance by peritectic reaction is going to precipitate in the melt due to density variations. The hydration reaction of the higher order does not completely proceed if the hydrate of the lower order precipitates before it takes in more water molecules and becomes the original hydrate of the higher order. Segregation causes the substantial decrease in heat of fusion and the functional deterioration as a PCM. Therefore, proper inhibitors for segregation or stabilizers such as thickeners and polymers for liquid adsorption have been developed. However, the optimization of the proportion of the segregation inhibitors to a PCM is necessary because the inhibitors cause decrease in the storage density of thermal energy. The maximum degrees of supercooling of paraffin and some other organic substances are smaller than those of hydrate and sugar alcohol. Besides, the segregation does not occur in paraffin and any other organic substances. Those advantages are two of the reasons why paraffin and other organic substances are often used as PCM at around a room temperature.

Research and Development Situation Looking back upon the progress, the two oil crises in the 1970s accelerated research and development on thermal energy storage methods in the industrial world and the academic world. From the second half of the 1970s to the first half of the 1980s, various kinds of materials and their application methods were searched for throughout the world and put in order. Besides, most of theoretical or experimental analyses concerning melting or solidification processes of PCMs, or performances of the thermal energy storage with PCMs were conducted in this epoch. After that, the number of the research and development on thermal energy storage temporarily decreased. Recently, however, the number is a little increasing by a cognitive surge to the global warming issue represented by the Kyoto Protocol. Many of the articles related to phase change thermal energy storage were reported from 1980 to 1990, and many books and literature summarizing the reports were published after that.

Thermal Energy Storage and Transport

20

However, physical properties of PCMs including mixtures are not fully known even though the names of the materials are well known. Besides, it is not rare that physical properties of PCMs listed in handbooks and literature include gross errors, or the transmitted errors by using references which made mistakes of numerical mentions when the properties are quoted from original references [5]. The LHTES systems are generally used in the broad temperature range from the lower temperature than the melting point of a PCM to the upper temperature. Therefore, the temperature and pressure dependences of the physical properties of PCMs are important to the effectual design of the system. However, such detailed data are available only for several PCMs. The technology of LHTES at the lower temperature than the room temperature has advanced by the research for more than 10 years after the oil crises. For example, an ice storage air-conditioning system has been downsized, improved in efficiency, and widespread. The research on LHTES by natural snow and ice was advanced as snowutilization and snow-persistence technologies, and demonstration tests came into operation. Food storage and transport are suitable for use of snow and ice because the added values of the food storage and transport are higher than that of space cooling. The food transport at a low temperature with ice has been used conventionally as methods to retain the freshness. As food culture became rich, the uses of natural snow and ice came to attract attention not only for simple freshness retainment but also for increase and retainment in flavor. The lower the storage temperature of food is, the longer the preservation term is. However, the storage at the optimal temperature around the freezing point of water is good for the point of increase and retainment in flavor. The proper storage temperature, humidity, and period are actually different among food. For example, from the room temperature to the ice point, the flavor of rice becomes much superior as the storage temperature becomes lower. However, it is reported that the additional improvement of flavor of rice is small even if the storage temperature is kept at the lower temperature than the ice point [8]. The PCMs are often filled in containers of proper size such as in > Fig. 20.5c and the containers are tightly sealed. The subdivision of the PCMs to the containers accelerates the heat exchange rate between the PCMs and the heat transfer medium, and stabilizes the characteristic of phase change. In addition, the subdivision to the containers improves handling ability and prevents the PCMs from contamination. The manufacturing technology of encapsulated PCMs of which the containers are mainly made of polyolefin resin was developed in the 1980s. The heat-resistant temperature of polyolefin resin for the containers is about 70–100
C. As a result, the spread of ice storage systems and floor heating systems with LHTES advanced. Examples of the physical properties of the commercial encapsulated PCMs are listed in > Table 20.6 [9, 10]. In the heat storage systems which use heat transfer media, convective heat transfer is dominant over the heat exchange between the PCMs and the heat transfer media. Thus spherical or cylindrical containers are often used in encapsulating PCMs to increase the contact area between the PCMs and the media. For example, the shapes of most PCM capsules on the market for hot water supply systems and for space cooling and heating systems are spherical or cylindrical. The melting points of the PCMs in the

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Thermal Energy Storage and Transport

. Table 20.6 Features of commercial encapsulated PCMs Melting point (
C)

Heat of fusion (kJ/kg)

Principal component

58

226

Sodium acetate trihydrate

47 29 25 17

212 188 150 145

Sodium acetate compound Calcium chloride hexahydrate (The same as above) (The same as above)

14 0 3 4

145 333 308 286

(The same as above) Sodium carbonate aqueous solution Ammonium carbonate aqueous solution Potassium chloride aqueous solution

10 15 16 21

283 293 289 222

Ammonium chloride aqueous solution (The same as above) (The same as above) Sodium chloride aqueous solution

spherical or cylindrical capsules are set to various temperatures which are shown in > Table 20.6, in response to the purposes of uses. In the heat storage systems which do not use heat transfer media, thermal conduction is dominant over the heat exchange between the PCMs and the cooling or heating objects. Thus, tabular containers are often used in encapsulating PCMs to increase the contact area between the PCMs and the objects. For example, the shapes of most PCM capsules on the market for floor heating systems are tabular. The materials of the container are selected from a soft film or a hard resin depending on applications. Several types of encapsulated PCMs which use sodium sulfate decahydrate (melting point is 32
C) or sodium acetate trihydrate (adjusted melting point is 43
C) are put on the market for floor heating systems [11]. Besides on the market, there are tabular encapsulated PCMs which use sodium sulfate decahydrate (adjusted melting point is 23
C) for the heat capacity of passive solar systems. For equipment of the blackout indemnification of communication repeating facilities, tabular encapsulated PCMs of which the melting points are 36
C are put on the market. For leveling the temperature of battery, there are resin packaged PCMs of which the melting points are 29
C. As unique examples of the use of PCMs, there are warm keeping trays which use PCMs for maintaining the temperature of food. The melting points of the PCMs in the trays are set to various temperatures in response to the purposes. For maintaining the temperature of the hot water of baths, warm keeping packs are put on the market. These warm keeping packs are also usable as hot water bottles. Furthermore, there are flexible warm keeping mats for pets. Both warm keeping packs and mats use the organic compounds such as polyethylene glycol whose melting point is between 40
C and 60
C.

Thermal Energy Storage and Transport

20

Phase Change Heat Transport Transport Methods Steam discharges large heat of condensation when it changes to liquid water. Therefore, steam has been used for long as a heat transport medium using the phase change between gas and liquid. However, to use the phase change between gas and liquid at around the room temperature, the decompression of the heat transport system or the use of the medium with a low boiling point is necessary. Besides, in using the phase change between gas and liquid, there is a problem of the thermal energy transport density defined by the quantity of heat which can be transported in a unit mass or in a unit volume of the transport material. For instance, > Table 20.7 gives the physical properties of ice, liquid water, and steam, respectively [2, 12]. The transporting power for gas is smaller than that for liquid, and the heat of condensation per unit mass is larger than the heat of solidification. However, the heat of condensation per unit volume is smaller than the heat of solidification because the density in the gas phase is small. Thus heat transport using the phase change between solid and liquid has been researched and developed as a promising method at around the room temperature. The heat transport methods with fusion and solidification are as follows: (1) a method to freeze the heat transfer medium partially and flow the slurry in piping, (2) a method to suspend fine grains of PCMs in the heat transfer medium and flow the emulsion in piping, (3) a method to suspend encapsulated PCMs with micro-dimensions in the heat transfer medium and flow the suspension in piping, (4) a method to fill up storage tanks with PCMs and carry the tanks by freight trains, freighters, or automobiles between heat source equipment and heat demand equipment. As for the transport density of thermal energy, the same argument as LHTES basically stands up. That is to say, the transport density depends on the content of PCMs in the base fluids, heat of fusion of PCMs, and so on.

. Table 20.7 Comparison of physical properties of ice, liquid water, and steam Property

Ice

Liquid water

Density (kg/m3) Specific heat (kJ/kg∙K) Thermal conductivity (W/m∙K)

917a 2.101b 2.09a

999.84a 4.2174a 0.565a

958.4c 4.217c 0.679c

0.5981c 2.077c 0.0250c

Phase transition point (
C) Heat of phase transition (kJ/kg) Heat of phase transition (kJ/L(liquid))

0 333.6 333.5

– – –

– – –

100 2256 1.349

0.0
C 2.2
C c 100
C a

b

Steam

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Thermal Energy Storage and Transport

The spread of phase change heat transport has not been advanced because of the same economical efficiency as phase change thermal energy storage. The clogging in the piping by the solidification or the aggregation of the PCMs is one of the serious issues in phase change heat transport. Therefore, suitable mechanism for preventing the clogging is necessary. Besides, the durability of the micro-capsule shell generally deteriorates in a hot water, so that the improvement of heat resistance of the shell is required in the future.

Research and Development Situation Around the 1990s, research and development of heat transport technologies by a hydrate slurry and a microcapsule slurry were conducted as the applications of phase change thermal energy storage technology at a low temperature, and part of the technologies was put to practical use. For example, a transport technology of latent heat at a low temperature with a tetra-n-butylammonium bromide (TBAB) aqueous solution (heat of fusion is 193–206 kJ/kg) was put to practical use [13]. The crystal deposition temperature of a TBAB aqueous solution is adjustable in the range from 0
C to 12
C by the concentration of the aqueous solution. When the crystal deposition temperature of the hydrate slurry is higher than 0
C, the coefficient of performance of chillers for generating the hydrate slurry becomes larger than that for generating the ice slurry, which reduces the consumption of electric power for generating the hydrate slurry holding the same latent heat as the ice slurry. The viscosity of the hydrate slurry is larger than that of water. On the other hand, the thermal energy transport density of the hydrate slurry is larger than that of water, which can reduce the flow rate of the heat transport medium for air-conditioning. Since the reduction of the flow rate reduces the pressure drop in piping, the consumption of electric power for transporting the slurry is less than that for water. Therefore, the reduction of the transportation power of a heat transport medium and the improvement of the operation efficiency of a refrigerating machine are concurrently achieved if high-density heat transport is taken at 7
C where the efficiency of cooling operation of the air in rooms is high. The application of subsumption compounds except TBAB to the heat transport is also examined. Besides, the research of freezing control technology by synthetic polymers is conducted as research to improve the latent heat transport [14]. The substitution effect of natural anti-freezing protein (AFP) was found in cheap heavy chemicals like polyvinyl alcohol.

Examples of Recent Technical Development Thermal Energy Storage System for Hot Water Supply In the temperature range for a hot water supply, paraffin waxes, organic compounds, and sugar alcohol shown in > Fig. 20.6 are considered to be comparatively safe PCMs.

Thermal Energy Storage and Transport

20

In respects of the storage density of thermal energy and thermal conductivity, however, paraffin waxes and organic compounds are inferior as PCMs. Besides, there are no proper hydrates which are safe, have reproducibility in repetition of phase change, and have the melting point in the temperature range for a hot water supply. Therefore, sugar alcohol attracts much attention in the 2000s, and the proper methods for using the material have been studied [6]. The attractive points of sugar alcohol are its safeness used as medicines and food, and its proper melting point for hot water supply. On the other hand, it was difficult to use sugar alcohol effectively as a PCM because the maximum degree of supercooling of sugar alcohol is large. For example in > Fig. 20.10, the solidification of D-Threitol whose melting point is o 87 C cannot be triggered unless the threitol is once cooled to around 40
C because the spontaneous nucleation temperature is about 40
C. That is to say, the heat of solidification of the threitol cannot be immediately extracted at the melting point. If the heat for cooling the threitol to the spontaneous nucleation temperature cannot be used, about 40% of the heat stored in the threitol will be lost for the nucleation process. On the other hand, the heat of solidification can be saved in the supercooled state at a low temperature for a long term if the release time of the supercooled state is controlled actively. Besides, if the heat for cooling the threitol to the spontaneous nucleation temperature can be used effectively, the stored heat can be discharged twice in separate hours before and after the storage period in the supercooled state. As an example of the applications of the LHTES using supercooling, a cogeneration system with the LHTES of D-threitol is shown in > Fig. 20.11 [15, 16]. The system was installed in a building of the university located in Sapporo, Japan. The heat engine of the system is a micro gas turbine (MGT). The shaft power of the MGT drives a generator (27 kW). The exhaust gas of the MGT heats water for hot water supply with heat exchangers. Thus the cogeneration system can simultaneously supply both electricity

. Fig. 20.11 Cogeneration system with hot water supply and space heating by thermal energy storage

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Thermal Energy Storage and Transport

and heat to the building. In the daytime, the hot water is partially supplied to the LHTES unit to store the surplus heat from the MGT. During the nighttime when the MGT is not operated, the LHTES unit can supply hot water in response to the demand of space heating. In this system, the supercooled thermal energy storage unit with dual tanks illustrated in > Fig. 20.12 enables the use of the threitol for thermal energy storage. The threitol is filled into thin and long cylindrical copper capsules. The capacity of each capsule is 912 mL. The storage tank is 166 L in capacity and is filled up with 96 capsules. The heat of fusion of the encapsulated threitol is 28 MJ in total. The storage tank is partitioned into two sections by thermal insulation. The PCM capsules exist in both sides of the partition. The upper large section, 152 L in capacity, is used for thermal energy storage. The lower small section, 1.6 L, is used for initiating nucleation in the supercooled threitol. The trigger for nucleation is the circulating water in the piping of the system at the room temperature. Circulation of the water through the nucleation section for only 5 min cools the bottom of each PCM capsule, which initiates nucleation in the supercooled threitol. > Figure 20.13 shows the variations of the thermal output and the outlet temperature of the circulating water from the storage unit during a daily storage cycle. As the charging

. Fig. 20.12 Supercooled thermal energy storage unit

Thermal Energy Storage and Transport

S

S→ L

L→S

L

100

20 Temp.

80

10

60

5

40 Output

0

0

6

12 Time (hr)

18

Temperature (°C)

Thermal output (kW)

15

−5

20

20

0 24

. Fig. 20.13 Thermal output and the outlet temperature of the circulating water from the storage unit during a daily storage cycle

process, the threitol is heated for 12 h by the exhaust heat from the MGT. After the threitol completely melted, part of the sensible heat is discharged from the storage unit as the first thermal output, which makes the threitol supercooled. As the keeping process, the heat of solidification of the threitol is completely kept for about 8 h in the nighttime. After the supercooled storage, the threitol is intentionally nucleated to discharge the remained latent heat and sensible heat from the storage unit as the second thermal output. The two thermal outputs from the storage unit are used for space heating after and before the operation of the MGT. The heat for cooling the threitol in the nucleation section to the spontaneous nucleation temperature was equivalent to only the 1% of the heat which is retained with the storage unit just after the charging process. Furthermore, the cooling heat for the nucleation operation can be used to preheat the circulating water in the piping effectively. By these processes, the 91% of heat retained with the storage unit just after the charging process can be effectively used for space heating in the nighttime.

Heat Storage System for Heating There are floor heating systems using solar heat gained in the daytime of fine weather day. The gained solar heat is partially stored with a thermal energy storage device or underfloor slab. The stored solar heat is emitted indoors gradually, and floor heating continues from night to the early morning of the following day. However, the additional heat is sometimes necessary for heating in the next morning because of the shortage of the available stored heat by the conventional thermal energy storage device. The reason for the shortage is that the stored heat by the conventional LHTES or SHTES is always dissipated into the

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Thermal Energy Storage and Transport

ambient air regardless of a demand. The active use of the supercooling phenomenon in addition to the conventional systems enables the thermal energy storage device to store solar heat, midnight power, and so on effectively for half a day, or beyond cloudy days, a weekend, or a season. In the operating temperature range from 30
C to 60
C, the hydrate is superior as a PCM for space heating in point of the storage density of thermal energy as is shown in > Fig. 20.6. Thus the research on the floor heating system as illustrated in > Fig. 20.14 has been conducted [17]. The PCM is disodium hydrogenphosphate dodecahydrate (cf. > Table 20.5). The DHD is filled into thin and long cylindrical capsules made of polypropylene. The capacity of the capsule is 1,810 mL. Fifty-six capsules are horizontally embedded in the floor between sub-floor joints. The heat of fusion of the encapsulated DHD is 25 MJ in total. By the supercooled storage of the hydrate, the system can effectively radiate the stored heat twice. For example, part of the sensible heat of the DHD in the liquid phase can be discharged in the evening, which makes the DHD supercooled. After the supercooled storage in the nighttime, the DHD is intentionally nucleated on the following morning and can discharge the remained latent heat and sensible heat. One of the most interesting applications of this storage method is the system which can store solar heat for cloudy or rainy days. If the storage system in the floor is divided into several sets and each set can be operated individually on demand, the stored solar heat can be partially discharged depending on more heat demands than twice. For example, after the supercooled storage in the nighttime, only a half of the sets is intentionally nucleated on the following morning and discharges the half of the stored latent heat and remained sensible heat as the second thermal output if it is cloudy or rainy. Then the remained latent heat can be discharged from the remaining half of the sets as the third thermal output on the next morning of the cloudy or rainy day.

. Fig. 20.14 Floor heating system with supercooled thermal energy storage

Thermal Energy Storage and Transport

20

Furthermore, research on the seasonal LHTES using the supercooling phenomenon has been conducted. For example, the performance of a long-term LHTES unit using DHD as a PCM was experimentally investigated [18]. The storage tank used in the experiment is partitioned into two sections by thermal insulation as is already shown in > Fig. 20.12. The PCM capsules exist in both sides of the partition. The capacity of the storage tank is 53 L in total and the tank holds 31 capsules of DHD. The heat of fusion of the encapsulated DHD is 9.1 MJ in total. The result of the experiments shows that the storage unit can control the nucleation of the DHD after the supercooled storage for 203 days. From the result of the storage operation between 22
C and 66
C, the sensible heat of the unit was released to the room and lost. However, the latent heat is kept in the supercooled DHD, and the 49% of the initial stored heat could be discharged by the nucleation operation after half a year. Paraffin is chemically stable and is comparatively cheap. Therefore, the development of application of paraffin to PCMs at around room temperature is still continuing. The thermal conductivity of paraffin, especially in the solid phase, is small as shown in > Table 20.5, which deteriorates the heat exchange with the heat transfer medium. In addition, the separation of the solid phase of paraffin from the wall surface of the container easily occurs with thermal contraction during solidification. Therefore, the heat exchange of paraffin in the solid phase with the heat transfer medium often becomes rate-determining process of the storage device. On this account, research to promote heat transfer by mixing carbon fibers in paraffin or impregnating paraffin into a porous metal has been conducted. Besides, the application of paraffin to the warm keeping containers to transport corneas, joints, and skin for grafting has been studied as the application to high value-added objects [11].

Steam Accumulator Steam accumulators are often used in the facilities that the consumption of thermal energy is large and the consumption of steam varies with time intensely. The steam accumulator is the device which stores the steam generated by a boiler as pressurized water, and smooths the temporally variable steam supply to manufacturing processes. The heat dissipation from the conventional steam accumulator to the ambient air tends to be large because the surface area of the accumulator is large. Besides, depending on thermal load, a steep output variation is sometimes demanded to the steam accumulator every several minutes. The heat of solidification per unit volume is larger than the heat of condensation as is mentioned in > section ‘‘Transport Methods.’’ Therefore, the steam accumulator can be downsized if the phase change between solid and liquid is applied to. The downsizing by the solid–liquid phase change reduces the surface area of the accumulator, which reduces the heat dissipation from the accumulator to the ambient air by around 50% at the maximum. Thus, the steam accumulator which uses one type of sugar alcohol, mannitol (cf. > Table 20.3), as a PCM is proposed [19]. The mannitol is filled into long and thin

695

696

20

Thermal Energy Storage and Transport

capsules made of copper. The storage tank is 190 L in capacity and is filled up with 190 capsules. Heat of fusion of the encapsulated mannitol is 23 MJ in total. To use mannitol as a PCM, there occurs a problem regarding supercooling in the discharging process because the maximum degree of supercooling of the pure mannitol amounts to about 50
C. Therefore, the method to restrain the maximum degree of supercooling to about 15
C by adding calcium sulfate as a nucleating agent has been adopted. The steam accumulator generated 200–250 kg/m3 of steam at the flow rate of 30–40 kg/h. Besides, the combined system of the steam accumulator of mannitol with solar collectors and a disk turbine of the organic Rankine cycle is proposed [20].

Pipeless Heat Transport Many factories and incineration plants, which are potential heat sources, are usually located far from office areas and residential areas where the heat is consumed. It is important to transport heat efficiently for using the exhaust heat from the factories effectively. Thus the transport methods using PCMs from the heat supply site to the heat demand site by car, freight train, or ship as shown in > Fig. 20.15 have been investigated. For example, truck transportation systems using erythritol (cf. > Table 20.3) or sodium acetate trihydrate (cf. > Table 20.3) as PCMs were proposed and tested in several fields [21, 22]. In the field tests, the PCMs filled into stainless steel tanks are melted and solidified by the heat exchange of direct contact with heat transfer oil. The proper capacity of the storage tank for the truck transport depends on the road condition and the traffic regulation. For example, the proper capacity of the storage tank for transportation in Japan is estimated to be 5–20 m3.

. Fig. 20.15 Pipeless heat transport

Thermal Energy Storage and Transport

20

The results of the field tests show that the charging process of thermal energy to the storage tank was completed in a heat supply site in about 2 h. The discharging process was completed in a heat demand site in about 4 h. The distance of conveyance that truck transportation is advantageous on energy is evaluated to be less than about 20 km. The most serious assignment at present is how to improve the investment effect. The promotion of the heat exchange rate between the PCMs and the heat transfer medium can improve the capacity utilization and cost-effectiveness.

Microcapsule Slurry Heat Transport Building materials, fibers of clothes, and heat transfer media are just available for heat storage media for SHTES. However, the thermal energy storage densities of those materials are smaller than those of PCMs. Thus several methods to improve the thermal energy storage densities of those materials have been studied. One of the methods is mixing those base materials with the fine grains of PCMs which are insoluble to the base materials. Encapsulated paraffin or polyethylene glycol is often used as fine grains of PCMs. The diameters of the PCM capsules are usually on the order of micrometer. Gelatin, melamine resin, or urea resin is used for the shell of microcapsules. The PCMs can be mixed into various kinds of base materials by encapsulating the PCMs in a micro-size. Besides, the capsulation makes it easy to handle the PCMs, and widens the surface area for heat transfer. The microencapsulated PCMs are applied to high density heat transport by the slurry mixed with heat transfer media. Besides, the PCMs are applied to the passive thermal energy storage as thermal mass and to warm keeping sheets. In the 1990s, several researches of slurry heat transport for space cooling were conducted. > Figure 20.16 shows the microencapsulated PCMs that n-octadecane is

. Fig. 20.16 Microencapsulated PCM particles produced by coacervation method (gelatin wall) (Photography by Takeuchi H et al.)

697

20

Thermal Energy Storage and Transport

100 MCs breakage fraction (%)

698

80 60 1000--1500μm 75-- 300μm 20-- 100μm 5-- 10μm

40 20 0

0

2000

4000 6000 Pump circulation

8000

. Fig. 20.17 Breakage fraction of the microcapsules by thermal cycles

coated with gelatin [23]. The addition of the particle dispersion agent prevents the aggregation among the PCM capsules, which is important to maintain the performance of the PCM slurry. It is necessary to raise the concentration of the microcapsules for increasing the thermal energy storage density of the slurry. When the concentration of the microcapsules in the slurry increases, the flow velocity range for laminar flow expands because the apparent viscosity of the slurry increases. Then there is the optimal flow velocity of the PCM slurry that the pressure loss for circulating the slurry becomes smaller than that for the pure heat transfer medium. When the PCM slurry is circulated at such optimal flow rate, the consumption of electric power by pumps can be reduced. The results of the endurance test of the PCM capsules and the heat exchange test of the PCM slurry are shown in > Figs. 20.17 and > 20.18 respectively. If the capsule diameter is smaller than dozens of micrometers, the damage of the capsule by the transportation pumps is prevented (> Fig. 20.17). Besides, if the particle concentration in the slurry increases, the overall coefficient of heat transfer of the slurry decreases (> Fig. 20.18). Decrease in coefficient of heat transfer reduces the heat dissipation from piping to the ambient air. Therefore, the microencapsulated PCM slurry becomes effective for longdistance heat transport.

Future Directions Thermal energy storage and heat transport enable to promote the utilization of waste heat and renewable energy which are unstable, maldistributed, and thin in general. In addition, high densities of thermal energy storage and heat transport enable to reduce heat loss during heat storage and transportation. However, except water or rock, the introduction of high density thermal energy storage and heat transport is not advanced in point of cost-effectiveness. The issue of the material cost can be improved by modification of manufacturing methods and mass productions. For example, although threitol has been produced by

Heat transfer coefficient (kW/m2·K)

Thermal Energy Storage and Transport

Heat transfer coefficient (kW/m2·K)

b

a

20

4

2 MCPCMs 0 8 Tap water

6

4

MCPCMs

0

2

4

6

8

Distance from inlet of heating section (m)

. Fig. 20.18 Heat transfer coefficients of the microcapsule PCM slurry for the cases of (a) turbulent flow (Particle size: 5 mm, Particles concentration: 15 vol.%, Reynolds number = 12,000, Flow velocity = 1.33 m/s) and (b) laminar flow (Particle size: 5 mm, Particle concentration: 25 vol.%, Reynolds number = 1,900, Flow velocity = 1.22 m/s)

a synthetic process conventionally, a fermentation method to produce D body was recently discovered [24], which leads the manufacturing cost of D-threitol to the same level as erythritol. The issue of the overall cost of the system can be improved by using technology like the supercooled thermal energy storage which raises added value. The 1970s and 1980s, when characteristics of various kinds of materials and applications for thermal energy storage were investigated, can be considered as the first golden age of research and development of thermal energy storage and heat transport. In the near future, the creation and application of novel PCMs which is designed by computational chemistry and synthetic process will be required as well as the revolution of the manufacturing methods which use microorganisms, and developments of high valueadded utilization technology.

References 1. The Japan Society of Mechanical Engineers (JSME) (2009) V-3 Properties of solid, V-4∙1∙1 properties of ordinary water. In: The Japan Society of Mechanical Engineers (JSME) (ed) JSME data book: heat transfer, 5th edn. JSME, Tokyo 2. Hirano S (2002) Phase change thermal energy storage. J Japan Inst Ener 81–8:691–699

3. Duffie JA, Beckman WA (1991) 8 energy storage. In: Duffie JA, Beckman WA (eds) Solar engineering of thermal processes, 2nd edn. Wiley, New York 4. Kosaka M, Asahina T, Taoda H (1980) Recent research on thermal energy storage (7) About latent heat type thermal energy storage materials

699

700

20 5.

6.

7. 8.

9.

10.

11.

12.

13.

14.

15.

Thermal Energy Storage and Transport

for space heating/hot water supply. Reports of the Government Industrial Research Institute, Nagoya 29–2:53–62 Hirano S, Saitoh TS, Oya M, Yamazaki M (2001) Temperature dependence of thermophysical properties of disodium hydrogenphosphate dodecahydrate. J Thermophys Heat Trans 15–3: 340–346 Kakiuchi H (2008) Development trend of latent heat or chemical thermal energy storage material. In: NTS (ed) Energy storage and transport, Electricity/heat/chemistry. NTS, Tokyo Telkes M (1954) Composition of matter for the storage of heat, US Patent No. 2677664 Hirano S (2006) 4∙4 Technology for utilizing thermal energy at low temperature. In: Japan Solar Energy Society (ed) Solar energy utilization technology. Ohmsha, Tokyo Mitsubishi Chemical Engineering (1999) Main ingredients of thermal energy storage materials in STL thermal energy storage system. Mitsubishi Chemical Engineering, Tokyo Phase Change Products (2009) Product range of phase change materials. Phase Change Products, Western Australia Hirano S (2009) Research and development trends on latent heat thermal energy storage. J Japan Solar Ener Soc 35–4:11–17 International association for the properties of water and steam (IAPWS) (1998) Revised release on the IAPS formulation 1985 for the thermal conductivity of ordinary water substance. IAPWS, London New air conditioning system division (2009) Hydrate slurry thermal energy storage airconditioning system. JFE Engineering, Yokohama Inada T (2006) Growth control of ice crystals by poly (vinyl alcohol) and antifreeze protein in ice slurries. Chem Engin Sci 61–10:3149–3158 Hirano S (2009) Field test study of cogeneration using supercooled thermal energy storage. In: New energy technology for society, http://www. aist.go.jp/aist_e/research_results/publications/ pamphlet/today/new_energy_technology_for_ society.pdf 26 May 2011. National Institute of

16.

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18.

19.

20.

21.

22.

23.

24.

Advanced Industrial Science and Technology (AIST), Tokyo Hirano S, Takeuchi H (2009) Performance of thermal energy storage unit using supercooling of D-threitol. Papers & Programme of the 8th International conference on sustainable energy technologies, Aachen, Germany, Paper 214 Hirano S, Shibasaki N, Kudo T (2010) Characteristics of thermal storage and radiation in floor heating system using supercooled thermal energy storage. Proceedings of renewable energy 2010, Yokohama, Japan, Paper O-Th-3-2 Hirano S, Saitoh TS (2007) Long-term performance of latent heat thermal energy storage using supercooling. Proceedings of ISES solar world congress 2007 V, Beijing, China, pp 2741–2745 Hoshi A, Saitoh TS (2001) A study of solar steam accumulator with high temperature latent heat thermal energy storage (2nd report; fundamental characteristics of steam accumulator). J Japan Solar Ener Soc 27–5:41–48 Saitoh TS (2008) Final version of solar SHINLA turbine generation system. In: Proceedings of JSES/JWEA joint conference, Tottori, Japan, pp 381–382 Aoki I (2007) Thermal energy storage transport system by erythritol (Waste heat transport system by direct contact latent heat thermal energy storage technology). In: Development of thermal energy transport system. Japan Society of Refrigerating and Air Conditioning Engineers, Tokyo Kawai A, Kamano H, Okuyama S, Shikata I (2006) Experimental report (I) by latent heat storage transportation system ‘‘TransHeat Container.’’ Kurimoto technical report 54, pp 12–17 Takeuchi H, Pyatenko AT, Yamagishi Y, Sugeno T, Ishige T (1998) Characteristics of microencapsulated phase change material slurry as energy transportation refrigerant. Therm Sci Engin 6–1:162–167 Ueda M, Yasuda M (2004) Microbial production of rare sugars by biotransformation and fermentation: L-Ribose and D-Threitol. Monthly fine chem 33(9):52–60

21 Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques Kailiang Zheng 1 . Helen H. Lou1 . Yinlun Huang 2 Dan F. Smith Department of Chemical Engineering, Lamar University, Beaumont, TX, USA 2 Lab for Multiscale Complex Systems Science and Engineering, Department of Chemical Engineering and Materials Science, Wayne State University, Detroit, MI, USA

1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702 The Basics of Pinch Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703 Energy Targets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 704 Heat Exchanger Network Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 710 Appropriate Placement and Process Modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 713 Data Extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 719 Total Site Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 722 Mathematical Programming Approach for HEN Design . . . . . . . . . . . . . . . . . . . . . . . . . . 727 Disturbance Propagation and Control Modeling for the Design of Highly Controllable Heat-Integrated Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 728 Disturbance Propagation Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 728 Disturbance Propagation and Control (DP&C) Model Embedded Synthesis Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 736 Emissions Targeting and Planning: CO2 Emissions Pinch Analysis (CEPA) . . . . . . . . 740 Future Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 746 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 746

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_21, # Springer Science+Business Media, LLC 2012

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Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

Abstract: Consuming about 20% of total energy annually in the USA (according to DOE in 1994), the chemical industry is a major source of greenhouse gas (GHG) emissions. It has been widely recognized that a significant reduction of energy consumption and GHG emissions in chemical processes must implement advanced heat integration technologies in a holistic way. Heat integration is a family of technologies for improving energy efficiency. The technologies can be applied to the design of heat exchanger networks, heat-integrated reaction-separation systems, etc. Pinch analysis is the foundation of heat integration. In this chapter, the applicability of pinch technology in GHG emission reduction is reviewed first. Furthermore, the concept of ‘‘total site,’’ which is valuable for energy targeting and integration at regional level, is described. A ‘‘total site’’ includes not only traditional industrial processes, but also commercial and residential energy users into the scope. Then more advanced concepts in heat integration are introduced. The concepts are developed based on the observation of problems arising in heat integration applications – stability of heat-integrated systems in operation. The known modeling work addressing these issues will be reviewed thoroughly. The basic principles on how the disturbancepropagation-rejection models for these major chemical processing systems can be adopted in process synthesis and analysis stages will be discussed. The concept of ‘‘total site’’ has been further extended to greenhouse gas emission targeting and reduction. Carbon dioxide (CO2) emission focused pinch analysis methodology is reviewed, which is valuable for obtaining the optimal energy resource mix of fossil fuel and renewable energy for the regional or national energy sector.

Introduction The chemical industry is one of the largest energy-consuming sectors in the USA. According to the US DOE’s analysis, this industry consumes approximately 20% of total industrial energy consumption (1994), and contributes in a similar proportion to the nation’s greenhouse gas (GHG) emissions. There are great potentials to reduce the energy demand and GHG emissions in chemical process systems using advanced heat integration technologies. The basic heat integration methodology was developed in the past decades under the label ‘‘Pinch Analysis.’’ Some key points have been published at the end of 1970, but it was Linnhoff and his coworkers [1] who developed the basis of pinch technology, which is now considered as the foundation of heat integration. Pinch analysis was originally developed based on thermodynamic principles to identify the optimal energy recovery strategies between the matches of hot and cold streams. It provides tools that allow the users to investigate energy flows within a process and identify the most economical ways of maximizing heat recovery and of minimizing the demand for external utilities purchased elsewhere (e.g., steam and cooling water), thus contributing to GHG emission reduction. The core concept is to match the available internal heat sources (hot streams) with the appropriate heat sinks (cold streams) to maximize the energy recovery and minimize the cost of external heat sources. Some specialized software

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21

packages for implementing the pinch point analysis are available, such as Super Target™ (KBC Energy Services), Aspen Pinch™, Hextran™ (Simsci), and Honeywell Exchangernet™. Taking the Super Target™ suite, for example, it allows the user to carry out an in-depth pinch analysis for the heat integration within processes, columns, and a large site, respectively, using the PROCESS, COLUMN, and SITE modules. Over the past decades, pinch analysis has been successfully used to reduce energy consumption site-wide [2] and in individual processes. The applications of pinch analysis in industrial sectors such as oil refining, chemicals, pulp and paper, etc., can typically identify opportunities for 10–35% energy consumption savings [3]. Due to its powerful function, the application of pinch analysis is extended to many fields, such as wastewater treatment [4, 5], hydrogen integration [6, 7], emission targeting [8], and even financial management [9]. In this chapter, the fundamentals of pinch analysis are briefly introduced first. It will cover all of the following aspects: setting energy targets by the construction of composite curves, grid diagram for developing the heat exchanger network (HEN), plus/minus principles for process modifications, appropriate placement of units, principles of data extraction, mathematical programming approach, total site concept, etc. Then more advanced concepts about the controllability and operability issues of heat integration system are addressed. A disturbance propagation and control (DP&C) model is introduced to the HEN design approach to handle the disturbance issue. This will lead to the optimal design solution both in the criteria of economic cost and controllability. At last, a novel carbon emission pinch analysis (CEPA) methodology, which is developed from traditional pinch analysis, is introduced for emission reduction targeting and planning from industrial sites to regional or national energy sectors. It can identify the minimal usage of low-carbon emission yet high-cost energy resources, and obtain the optional energy resources allocation scheme.

The Basics of Pinch Analysis Pinch analysis is a rigorous, structured approach for identifying the bottlenecks in industrial process energy use. The minimum theoretical utility requirement in a process (target) can be calculated for overall energy use, as well as for specific utilities (LP, HP steam, cooling water, etc.) ahead of any detailed heat integration system design activities. Pinch technology can be used to extend the analysis to the site-wide integration of a number of processes by means of utility systems. When considering any pinch-type problem, the same principles apply: ● A process can be defined in terms of supplies and demands (or sources and sinks) of energy. ● The optimal solution can be achieved by appropriately matching sources and sinks by following thermodynamic laws. ● The defining parameter in determining the suitability of matches is the temperature of streams. ● Inefficient transfer of resource can block identification of an optimal solution.

703

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Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

Energy Targets Constructing the composite curves. The most fundamental concept in pinch analysis is the so-called composite curve. Composite curves are used to determine the minimum energy consumption target for a given process system. The curves are profiles of heat availability (demonstrated by the hot composite curve) and heat demands (shown by the cold composite curve). The degree to which the curves overlap is a measure of the potential for heat recovery, as illustrated in > Fig. 21.1. The gray zone in > Fig. 21.1, where two composite curves overlap (heat duty-wise), is the amount of heat that can be recovered through heat integration. To construct the curves, it requires only a complete and consistent energy balance of the process. The data are used to define the process streams in terms of their temperatures, mass flow rates, as well as heat capacities and heating or cooling requirements. These data can be obtained from one or all of the following ways: plant measurements, design data, and simulation. Once identified, these process streams are then divided into sources and sinks. A source is the stream that has a certain amount of heat to be removed, out of which a fraction or whole can be recovered. Such process streams are called hot streams. A sink corresponds to a stream that must be heated, which is called a cold stream. In pinch analysis, process streams should be identified and then divided into source and sink

PROCESS STREAM DATA

T

Heat sources

Heat sinks

T

Q

Q

Composite curves T Energy recuperation potential

Hot composite curve

Cold composite curve Pinch point

Q

. Fig. 21.1 The composite curves [3]

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21

. Table 21.1 Example data for building composite curves [3] Stream Stream type 1 2 3 4

Hot Hot Cold Cold

Supply temperature ( C)

Target temperature ( C)

200 150 80 50

100 60 120 220

Heat duty (kW) CP (kW/ C) 2,000 3,600 3,200 2,550

20 40 80 15

streams. This step is called data extraction, which is crucial for any pinch analysis. The following example explains how to do the data extraction. > Table 21.1 presents the stream data chosen to illustrate the construction of the composite curves. The following elements are necessary: ● Stream or segment temperatures: the supply temperature Ts and the target temperature Tt ● Heat capacity flow rate of each stream or segment, defined as CP ¼ DH DT where ΔH is the enthalpy variation over the temperature interval ΔT, and CP is defined as mass flow rate (kg/s)  heat capacity (KJ/( C·kg)) and has a unit of kW/ C. For example, stream 2 is cooled from 150 C to 60 C, releasing 3,600 kW of heat. Its CP value is 40 kW/ C. > Figure 21.2a shows the hot streams plotted individually on a temperature-duty (or temperature-enthalpy) diagram. The slope of composite curve is the inverse of the CP value. By adding the enthalpy changes of the individual streams within each temperature interval, the hot composite cure is constructed as shown in > Fig. 21.2b. Note that in > Fig. 21.2b, from 150 C to 100 C, the slope of the composite curve in this section is reduced. In a similar way, the cold composite curve can be constructed, as illustrated in > Fig. 21.2c and d. Determining the energy targets. An important part of pinch analysis is the Minimum Energy Requirement (MER) for a given process or plant. This information is used to identify the maximal potential for improvement before starting the detailed process design. To determine the minimum energy target of a process, the cold composite curve is moved left horizontally toward the hot composite curve, as shown in > Fig. 21.3a. Please note that the enthalpy axis measures relative quantities and it only represents the enthalpy change of process streams. Moving a composite curve horizontally does not, in any way, change the stream data. The relative position of the composite curves depends on the minimum allowable temperature difference, ΔTmin, which is the minimum temperature difference that is allowed in a heat exchanger (note that the value of ΔTmin is usually given before design based on engineering experience; optimal determination of its value is a complicated problem). This also determines the pinch position where the heat transfer between the hot and cold streams is the most constrained. A value of 10 C is used in this example.

705

21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

In > Fig. 21.3b, the overlap between the composite curves is the maximum heat recoverable between the hot and cold streams in the process; the remaining heating and cooling needs are the minimum hot utility requirement (QHmin) and the minimum cold utility requirement (QCmin) of the process, respectively, for the chosen ΔTmin. In this T(°C)

T(°C)

200

20

200

100 60

0

CP

2 CP

CP

20

150

=

150

=

1 only

=

1 =6

CP

1 and 2

100

40

2 only

CP = 40 60 Q (kw)

a

0

2,000

4,000

Q (kw)

b

6,000

0

T(°C)

2,000

4,000

6,000

T(°C) 220

120

3 CP

80

4 only

CP

=1

5

4

=1

5

220

CP

706

120 CP

0 =8

5

=9

4 and 3

80 CP = 15

50

50

4 only

Q (kw)

c

0

2,000

4,000

6,000

Q (kw)

d

0

2,000

4,000

6,000

. Fig. 21.2 Constructions of composite curves [3] T(°C)

T(°C)

Cold composite curve

Maximum heat recovery

Hot composite curve

200 150

QHmin = 900

200

Pinch

150

Pinch

100

100 ΔTmin = 10 °C

60

a

ΔTmin = 10 °C

60 0

2,000

4,000

6,000

Q (KW)

b

Qcmin = 750 0

2,000

. Fig. 21.3 Determine the energy targets by using the composite curves [3]

4,000

6,000

H (KW)

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21

example, the minimum hot utility requirement (QHmin) is 900 kW and the minimum cold utility requirement (QCmin) is 750 kW, respectively, as indicated in > Fig. 21.3b. As demonstrated in the above example, pinch analysis enables the setting of targets for minimum energy consumption prior to any detailed heat exchanger network (HEN) design and allows to quickly indentify the scope of energy savings at an early stage of synthesis. The point of the closest approach between the two composite curves, where ΔTmin is reached, is known as the pinch point. The pinch point is determined by the minimum temperature difference that will be accepted in any heat transfer unit. The pinch principle states that any design where heat is transferred across the pinch will require more energy than the minimum requirement. Consequently, the pinch point divides the problem into two independent subsystems, that is, the hot-end subsystem and the cold-end subsystem. In principle, the region above the pinch only requires hot utility, while the region below the pinch only requires cooling utility (see > Fig. 21.4). According to pinch design rules, no heat should be transferred from the hot-end subsystem to the cold-end subsystem. For example, if a amount of cross-pinch heat is transferred from the subsystem above the pinch to that below the pinch, then this cross-pinch heat needs to be supplied by an equivalent amount of hot utility above the pinch plus the same amount of cold utility below the pinch. Needless to say, this situation should be avoided in any case. Selection of ΔTmin. Generally, saving energy may increase the capital cost, and thus often there is a need of trade-off between capital and energy costs. This can be demonstrated by examining the composite curves. As the separation between hot and cold composite curves (ΔTmin) increases, the overlap between the hot and cold streams becomes reduced, thereby decreasing opportunities for heat recovery, and in turn increasing the utility cost (> Fig. 21.5). Meanwhile, if ΔTmin is increased, which means the permissible minimum

Qhmin + α T α

Pinch Qcmin + α Q

. Fig. 21.4 Heat transfer across the pinch point [3]

707

708

21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

QHmin @ 10 °C

T(°C)

QHmin @ 20 °C

200 Hot composite curve 150 Cold composite curve 100 ΔTmin = 10 °C

ΔTmin = 20 °C

60 Qcmin @ 20 °C 0

2,000

4,000

6,000

Q (KW)

. Fig. 21.5 Effect of ΔTmin [3]

temperature driving force between the hot and cold streams is increased, this will allow a greater temperature difference in any heat exchanger. Then, heat exchangers would be smaller in size, thereby making the capital cost for individual heat exchanger lower. Thus, the higher energy cost may be offset by the reduced capital cost of heat exchangers. > Figure 21.6 shows a generalized trend of energy cost and capital cost when ΔTmin changes. It is very obvious that for any given plant, there exists an optimum value of ΔTmin which can minimize the total cost of energy and capital. If the cost of energy and the cost of heat exchangers are known for a given plant, it is possible to predict the optimum value of ΔTmin ahead of detailed design. In practice, ΔTmin for a particular process is often selected by the two factors: the shape of composite curves and the engineer’s experience. For chemical processes, and where utilities are used for heat transfer, ΔTmin values are typically in the range of 10–20 C. For low temperature process using refrigeration, a lower ΔTmin value, for example, 3–5 C, could be used to minimize expensive power demands in a refrigeration system. Targeting for multiple utilities: the grand composite curve. Most processes are heated and cooled using several different utility levels (e.g., different steam pressure levels, furnace flue gas, cold water, refrigeration levels, etc.). It is desirable to increase the use of cheap utility levels and decrease the use of expensive utility levels. For example, using lowpressure (LP) steam instead of high-pressure (HP) steam, and cooling water instead of refrigeration can reduce the energy cost.

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21

Cost

l

a Tot

gy

er

En

Captia

l

ΔTmin

. Fig. 21.6 Energy/capital trade-off [3]

Composite curves can provide the overall energy targets. However, they do not clearly indicate the exact amount of energy needed to supply by various utility levels. The grand composite curve, which plots process energy deficit (above the pinch) and energy surplus (below the pinch) as a function of temperature, can handle this problem and determine the multiple utilities targets. To construct the grand composite curve, a small mathematical adjustment must be made to the composite curves. The hot composite curve is shifted down and the cold composite curve is shifted up separately by 1/2 ΔTmin each, until they touch at the pinch point. The resulting composite curves are referred as the shifted curves, and have no real physical meaning. They are merely a step in the construction procedure, which ensures that the resulting grand composite curve shows the required zero heat flow at the pinch point. The grand composite curve is generated by plotting the heat load difference between the hot and cold composite curves as a function of temperature (> Fig. 21.7). It provides a graphical representation of the heat flow through the process, from the hot utility to those parts of process above the pinch point, and from the process below the pinch point to the cold utility. The pinch point is where the curve intercepts the temperature axis (> Fig. 21.7). > Figure 21.8a shows a grand composite curve where high-pressure (HP) stream is used for heating, and refrigeration is used for the cooling process. In order to reduce the utility costs, some intermediate utilities, such as medium-pressure (MP) steam, lowpressure (LP) steam, and cooling water (CW), can be used as an alternative. > Figure 21.8b shows targets for these alternative utilities. The target for LP steam is determined by plotting a horizontal line at the LP steam temperature from the T-axis until it intercepts the grand composite curve. The MP steam

709

710

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Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

T(°C)

QHmin = 900

200

Tshilted(°C)

QHmin = 900

200

200 Hot composite curve

150

150

150

α

Cold composite curve

100

QHmin = 900 Tshilted

α 100

100 ΔTmin = 10 °C

60

60

60 QCmin = 750 0

QCmin = 750

2,000 4,000 6,000 Composite curves

Q (KW)

0

QCmin = 750

2,000 4,000 6,000 Shifted composite curve

Q (KW) 0 1,000 2,000 Q (KW) Grand composite curve

. Fig. 21.7 Construction of the grand composite curve [3] HP

HP T

T

MP

LP

CW

a

Refrigeration

Q

b

Refrigeration

Q

. Fig. 21.8 The grand composite curve for multiple utilities targeting: (a) before targeting; (b) after targeting [3]

target can be obtained in a similar way. The remaining heating duty is satisfied by HP steam. A similar procedure can be done below the pinch to determine the use of cooling water instead of refrigeration. In summary, the grand composite curve is one of the basic tools used in pinch analysis for the selection of appropriate utility levels and for targeting optimal heat loads of various utility levels to minimize the total utility cost.

Heat Exchanger Network Design The targeting step in a pinch analysis includes targeting for minimal energy usage, targeting for process modifications, targeting for multiple utilities, and appropriate placement of heat engines and heat pumps. The aim of targeting step is to explore various

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21

process improvement options, such as energy recovery, process modification, and utility system integration, quickly and easily without going into the detail of heat integration design. The key improvement options identified in the targeting stage need to be realized in the detailed design. The heat exchanger network (HEN) design procedure which is based on pinch principle can translate the idea of improvement option into specific detailed design. This design procedure uses the so-called grid diagram to represent the heat exchanger networks. This method will systematically lead the designer to good network design schemes that achieve the energy targets within practical limits. Grid Diagram. > Figure 21.9 illustrates a grid diagram, which is a working frame for synthesizing a heat exchanger network (HEN). The hot streams run from left to right at the top, while the cold streams run in the opposite direction at the bottom, as illustrated in > Fig. 21.9. The vertical line with two arrows connecting the hot stream with cold stream represents the heat exchanger between process streams. Heaters on cold steams and coolers on hot streams are shown with circles. The process pinch location is represented by a dashed line dividing the grid diagram into two parts. The pinch hot and cold temperatures obtained from composite curves by the determined ΔTmin are shown at the top and bottom of the dashed line. The process above the pinch (heat sink) is on the left side of the dashed pinch line and the process below the pinch (heat source) is on the right side. Overall, in the grid diagram, the temperatures of streams decrease from the left side (above the pinch) to the right side (below the pinch). According to the pinch principles discussed before, the process is divided into two independent subsystems at the pinch point and any heat transfer across the pinch will require more energy than the minimum requirement. Thus, the HEN design should be conducted in two steps, above the pinch and below the pinch, respectively. The design

Hot pinch point

Cooler Hot stream 1 Hot stream 2 Exchanger between processes Cold stream 1

Cold stream 2 Heater Cold pinch point

. Fig. 21.9 Grid diagram for developing the heat exchanger network

711

712

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Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

starts at the pinch, where the heat transfer is most constrained. To determine the match of steams sequentially, heuristic feasibility rules could be used. Note that stream matching can be also determined by rigorous mathematical programming methods [10–14]. For a pinch match above the pinch (at the left side), the following heuristic rule can be followed, that is, CPhot  CPcold. In this context, CP means mass flow rate  specific heat capacity. This rule can be easily understood by the fact that only hot utility is needed above the pinch, so the CP value of the cold streams must be greater than the CP value of the hot streams. Similarly, below the pinch (at the right side), for each pinch match, the following heuristic rule holds: CPhot  CPcold. The two rules above can be summarized as CPin  CPout. It means for a match at the pinch, the CP value of the stream going out of the pinch must be greater than the CP value of the stream coming into the pinch. For example, when consider the process above the pinch, the CP of hot stream, which is coming into the pinch, is smaller than the CP of cold stream, which is going out of the pinch. Number of matches, paths, and loops. Linnhoff and coworkers [1] pointed out that the minimum number of units (matches) NE needed to recover the energy between Ns process streams using Nu utilities can be expressed by the following equation, if the synthesis problem cannot be feasibly divided into two or more energy-independent problems: NE ¼ Ns þ Nu  1 If there are Nloop loops present in the network, this equation can be modified as: NE ¼ Ns þ Nu  1 þ Nloop The concept of path means a physical connection through streams and heat exchangers for the transfer of energy between utilities. A path allows the modification of the temperature difference between hot and cold streams. Loop is a closed trajectory connecting several heat exchangers. These two concepts are very useful in the optimization of heat exchanger network design. Reducing the HEN. The HEN design for minimum energy requirements based on the pinch principle ensures the maximal energy recovery, thus minimizing the energy cost. However, this design may increase the number of units needed, and thus demanding a high equipment cost. In this case, merging some units and reducing the number of equipments may contribute more significantly to the total cost saving through trade-off between the capital and operating costs. The final optimization of the design will depend on the cost of energy and equipment in the particular case analysis. As a rule of thumb, breaking the loop including the heat exchanger with the smallest load and removing this unit in a loop can greatly reduce the total cost of the design. The loss of energy recovery capacity due to the reduction of small units can be partly compensated by increasing the heat transfer area of large units. This can be explained by the fact that for small heat exchangers, the fixed capital cost of equipment, which includes installation, instrumentation, control, supervising, and maintenance costs, is usually larger than the cost of incremental heat transfer area.

21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

Appropriate Placement and Process Modifications Appropriate placement of units. The appropriate placement principle determines the optimal location of individual units against the pinch. It applies to heat engines, heat pumps, distillation columns, evaporators, furnaces, and any other operating units which can be represented in terms of heat sources and sinks. In the process industry, the use of combined heat and power systems has been increased significantly. In such cogeneration units, the heat rejected by a heat engine, such as steam turbine, gas turbine, or diesel engine, is used as hot utility and integrated into the process. If a heat engine is integrated across the pinch, as shown in > Fig. 21.10a, the process will still require the same amount of utilities (QHmin). When the heat engine is completely integrated above the pinch as shown in > Fig. 21.10b, the heat is rejected to the heat sink region of the process, thus exploiting temperature differences between the utility and process, and producing work at a very high efficiency. After integration, the import of W amount of extra energy from heat sources can produce W amount of shaftwork and the efficiency of heat to work conversion appears close to 100%. A similar situation will arise when heat engine is completely integrated below the pinch. Heat pumps, such as vapor compression and refrigeration, are systems that absorb heat at a low temperature in an evaporator, consume shaftwork to compress the working fluid, and reject heat at a higher temperature in a condenser. If the pump is located completely above the pinch, it simply transforms power into heat, which is not economical. If it is placed completely below the pinch, the situation is even worse because work is

QHmin + QHE T

T QHmin

QHE

Heat engine (HE)

QHmin + W QHmin – (QHE – W) Q HE Heat engine (HE) QHE - W

W

QHE - W

Qcmin + (QHE - W)

a

b

Qcmin

. Fig. 21.10 Integration of heat engine exhaust: (a) across the pinch; (b) above the pinch [3]

W

713

714

21 T

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

T

QHmin - W

T

QHmin

QHmin – QHP – W

QHP + W Heat pump

QHP + W

W

QHP Pinch

Pinch QHP + W Heat pump

QCmin

QCmin + W

QHP

Pinch

W

Heat pump

W

QHP QCmin – QHP

. Fig. 21.11 Integration of a heat pump above, below, and across the process pinch [3]

transformed into waste heat. The only appropriate way to place a heat pump is across the pinch, where heat is absorbed below the pinch and rejected above the pinch, as shown in > Fig. 21.11. In fact, the principles introduced above can be concluded as the Townsend and Linnhoff heuristics [15]: 1. When positioning heat engines to reduce the total utilities, place them entirely above or below the pinch. 2. When positioning heat pumps to reduce the total utilities, place them across the pinch. Plus/minus principle in process modifications. For a process, the heat and material balance determines the shape of the composite curves and then the minimum energy requirements set by the curves. By changing the heat and material balance, the composite curves would change accordingly. Thus, it is possible to further reduce the energy requirement of the process. There are several parameters that could be changed, such as distillation column operating pressures and reflux ratios, feed vaporization pressures, etc. There are so many choices that a guide is needed to confidently predict the parameters that could be changed to reduce the energy consumption. By applying the thermodynamic rules based on pinch analysis, which is called the ‘‘plus/minus principle,’’ it is possible to identify the appropriate process modifications that will improve the energy recovery significantly. In general, the hot utility can be reduced by (1) increasing hot stream (heat source) duty above the pinch and (2) decreasing cold stream (heat sink) duty above the pinch. Similarly, the cold utility target can be reduced by (1) decreasing hot stream duty below the pinch and (2) increasing cold stream duty below the pinch. This is termed as the plus/minus principle for process modifications. This simple principle provides a reference for any adjustment in process heat duties, such as vaporization of a recycle, etc., and indicates which modifications would be beneficial and which would be detrimental. Often, it is possible to change temperatures rather than heat duties. It is clear from the composite curves that temperature changes confined to one side of the pinch will not have any effect on the energy targets. However, temperature changes across the pinch can change the

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21

energy targets for the process. For example, reducing the feed vaporization pressure (cold stream) may move the feed vaporization duty from above the pinch (minus) to below the pinch (plus). Hence, a reduction of vaporization duty is achieved in both hot and cold utilities. This can be considered as an application of plus/minus principle twice. When a cold stream is removed from the region above the pinch and placed below the pinch, certainly, the shape of cold stream composite curve will change accordingly. The hot utility needed will diminish by the exact amount of cold utility moved. Similarly, moving a hot stream from the region below the pinch to above the pinch will reduce the hot utility consumption. In general, the above observations for beneficially shifting process temperatures can be summarized as follows: (1) shift hot streams from below the pinch to above, and (2) shift cold streams from above the pinch to below. Modifications of distillation column. Distillation column unit is the basic processing step in many chemical plants. Although distillation is highly energy-intensive, consuming energy in the magnitude of several MJ/s, it has a low thermodynamic efficiency (less than 10% for a difficult separation). Thus, it is one of the important areas for heat integration. During the retrofit or new column design, pinch analysis can be exploited to identify the targets for appropriate column modifications in order to reduce utilities cost and to improve energy efficiency. Some software packages, such as Super Target™ (KBC Energy Services), Aspen Pinch™, provide advanced software tools for the implementation of column targeting and modifications. > Figure 21.12 shows an example of the column grand composite curve (CGCC) [17], a tool that is used for column pinch analysis. CGCC is based on the concept of minimum thermodynamic condition for a distillation column, which pertains to thermodynamically reversible column operation. In this ideal condition, a distillation column would operate at minimum reflux, with an infinite number of stages, and with side reboilers and side condensers placed at each stage with appropriate heat loads for the operating and equilibrium

T Side reboiler

Side condenser

Reboiler

Condenser H

a Converged

b

Simulation

. Fig. 21.12 Column grand composite curve [16]

Column Grand Composite Curve

c

Ideal Column

715

716

21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

lines to coincide, as shown in > Fig. 21.12c. In other words, the reboiling and condensing loads are distributed over the whole column. The stage-enthalpy (Stage-H) or temperatureenthalpy (T-H) profiles for such an ideal column therefore can represent the theoretical minimum heating and cooling requirements of the column operation. These profiles are termed as the column grand composite curves (CGCC). Most industrial columns have certain inevitable losses or inefficiencies. In order to set realistic targets for the column modifications, these losses must be allowed. To handle this problem, Dhole and Linnhoff [17] developed a practical near-minimum thermodynamic condition (PNMTC) approach, which is adopted by many software. This approach takes into account the losses or inefficiencies introduced through practicalities of column design, such as pressure drop, multiple side products, side strippers, sharp separations, etc. The procedure for constructing the CGCC starts from a converged column simulation. From the simulation, the necessary column information is extracted on a stage-wise basis. Then the equations for equilibrium and operating lines are solved simultaneously at each stage for designated light-key and heavy-key components. The enthalpy deficits used in plotting the CGCC are calculated at each stage. At last, these enthalpy deficits are cascaded to construct the CGCC either in Stage-H or T-H dimensions. Like the grand composite curve for a process, the CGCC provides a thermal profile for the column and can be used for identifying the targets for potential column modifications, such as feed location, reflux ratio, feed conditioning (preheating or precooling), and side condensing or reboiling. Based on the inspection of the CGCCs, the following order of implementation of different column modifications is recommended as shown in > Fig. 21.13: feed location (appropriate placement), reflux ratio modification (reflux ratio vs. no. of stages), feed conditioning (preheating or precooling), and side condensing or boiling. Feed location need to be carried out first since it may strongly interact with other column modifications. The feed enthalpy strongly influences the shape of CGCC near the feed stage. And the CGCC usually shows a pinch point near the feed stage. Inspection of the CGCC can identify any distortions due to inappropriate feed location. Normally, this kind of distortions will be apparent since the stage-H CGCC will have significant projections at the feed location (pinch point). This is due to a need for extra local reflux to compensate for the inappropriate feed location. The optimal feed stage can be obtained by trying alternate feed locations and observing its influence on the reflux ratio. When the feed is introduced too high up in the column, there will be a sharp enthalpy change on the condenser side of the stage-H CGCC and the feed should be moved down. Similarly, when the feed is introduced too low, there will be a sharp change on the reboiler side of the stage-H and the feed should be moved up. The optimal feed location not only removes the distortion in the stage-H CGCC but also reduces the condenser and reboiler duties. Out of many other column modification options, the scope of reflux improvement must be considered first since it results in direct heat load savings at both reboiler and condenser. In > Fig. 21.13a, the horizontal gap between vertical axis and T-H CGCC pinch point indicates the scope for reduction in heat duties through reduction of reflux ratio.

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21

Feed stage optimization T

Reboiler

Reflux modification

Scope for reflux

Condenser

H

Temp

Reboiler

a Stage No.

Reboiler

Scope for feed preheat

Order of modifications

Feed preheat

Condenser

Feed conditioning

Condenser H

b Temp

Reboiler

H

Temp

Reboiler Side reboiler

Side condensing /reboiling

Side cond. Condensor

Condensor

H

c . Fig. 21.13 Using column grand composite curve to identify column modifications [16]

When the reflux ratio is reduced (while increasing the number of stages to maintain the separation), the gap will decrease and the CGCC will move closer to the vertical axis, thus reducing the condenser and reboiler duties. It must be noted that when the reflux ratio is reduced, the number of stages will increase to maintain the desired separation. Thus, to obtain an optimal reflux ratio, the increase in the capital cost due to the increase of stages should be traded off against the savings in the operating cost due to reduced condenser and reboiler loads. Inappropriate feed condition usually results a sharp enthalpy change in the CGCCs near the feed location and increases the heat load of condenser or reboiler. The scope of feed conditioning can be identified from the sharp enthalpy changes on the stage-H or T-H CGCCs. > Figure 21.13b shows an example that the feed need to be preheated. The extent of the sharp enthalpy change on the CGCCs determines the appropriate preheating duty needed. Feed preheating not only reduces the reboiler duty but also

717

718

21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

reduces the temperature levels at which the hot utility (for the reboiler and the feed preheater) needs to be supplied. For feed precooling, the situation is similar. Changes in the heat duty of feed preheaters or precoolers will lead to similar duty changes in the reboiler or condenser loads. After the modification of feed conditioning, side condensing/reboiling should be analyzed. An appropriate side reboiler, like the feed preheaters, not only reduces the heat loads of column reboiler but also reduces the temperature levels at which the hot utility (for the main reboiler and the side reboiler) needs to be supplied. In > Fig. 21.13c, the two CGCCs show the potential for side condensing and reboiling, respectively. In general, feed conditioning is preferred to side reboiling or side condensing as it offers a more moderate and convenient temperature level. Meanwhile, the feed conditioning is external to the column and therefore easier to be implemented than side condensing/reboiling. Till here, several ways of improving column thermal efficiency by stand-alone column modifications and their sequence are presented. In many cases, it is possible to further improve the overall energy efficiency of the process by appropriately integrating the column with the background process. > Figure 21.14 illustrates three examples of integrating the distillation column with the background process. The background process is represented by its grand composite curve. Tshifted

Side condenser

Tshifted

H

Reboiler

b Using column modification for integration Column

Condenser

Tshifted Background process

H

Column P+

a Inappropriate placement

c Appropriate placement . Fig. 21.14 Appropriate integration of a distillation column with the background process [16]

H

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21

Figure 21.14a shows an example of an inappropriately placed column with its temperature range across the pinch temperature of the background process and without any potential for integration with the background process. > Figure 21.14b illustrates a case that although the column temperature range still crosses the pinch temperature of the background process, a side condenser can be added to further improve the overall thermal efficiency as identified by the CGCC. > Figure 21.14c presents a different alternative integration scheme, which allows a complete integration between the column and the background process. In this scheme, the column pressure is increased to move the CGCC to one side of the process pinch point instead of crossing the pinch. Thus, the overall energy consumption of this scheme is just the energy consumption of the background process. Although appropriate column integration can provide significant energy benefits, these benefits must be considered together with the relevant issues, like the associated capital investment and difficulties in operation. >

Data Extraction Before the pinch analysis can be done, various process information is needed. Note that the amount of information available from plant measurement, data acquisition systems, and simulation models of a process can be very large, and most of the data may be of no relevance to the analysis. It is thus necessary to identify and extract only the information that truly captures the relevant sources and sinks, and their interactions with the overall process. The required data involves process stream heating and cooling information, utility stream information, cost information, and some background information regarding the processes. In summary, the following data need to be collected for each process stream: mass flow rate (kg/s), specific heat capacity (kJ/kg C), supply and target temperature ( C), and heat related to a phase change (kJ/kg). Additionally, for the utilities and the existing heat exchangers, the following information needs to be acquired: existing heat exchanger area (m2), heat transfer coefficient of heat exchangers ðkW=ðm2   CÞÞ, and utilities available in the process (water temperature, steam pressure levels, etc.). Data extraction could be time-consuming and must be performed carefully as the results of pinch analysis strongly depend on this step. Poor data extraction can easily lead to missed opportunities for the process improvement. In extreme cases, poor data extraction can falsely show that the existing process design is already the optimal one in energy efficiency. Data extraction needs to be conducted in an appropriate way, which only accepts the critical parts of the existing design that cannot be changed. A key objective of data extraction is to recognize the parts of process that can be further modified during the analysis (e.g., adding new heat exchangers, changing the process temperatures, etc.). If during the data extraction, all the features of existing design are considered as fixed, then there will clearly be no scope for improvement. If the extraction does not consider any features of the existing design, then the pinch analysis conducted later may overestimate the potential benefits.

719

21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

At the beginning of a data extraction, it is recommended that all process streams be included. The constraints, such as distance between processes, operability, and control and safety issues, can be considered later on. The experienced specialists may include some constraints at the beginning of data extraction. This can speed up the overall analysis; however, lots of experience is required to ensure that potential possible heat integration opportunities are not excluded by adding these constraints earlier. Hence, data extraction requires lots of experience and there are many sector specifics for data extraction. Not all of them can be covered here; however, some important heuristic rules have been developed as guidelines over the past years. Do not mix streams at different temperatures. In a process flow sheet, the streams at different temperatures cannot be directly mixed together, as such direct non-isothermal mixing acts as a direct contact heat exchanger. Such mixing may involve cross-pinch heat transfer, and therefore increase the overall external utility requirement. It should not become a fixed feature of the data extraction. For example, if the pinch is located at 70 C, then mixing a stream at 90 C with a stream at 50 C will create a cross-pinch heat transfer and increase the energy targets. To avoid this, if mixing must take place due to process reasons, then the isothermal mixing must be considered. The streams involved in mixing should be considered independently and extracted separately as being mixed at the same target temperature. Do not carry over features of the existing solution. This rule is illustrated with the example whose process flow sheet is shown in > Fig. 21.15. Based on the original data extraction generated from the process flow sheet in > Fig. 21.15, a HEN design is conducted using pinch analysis. The original data extraction and corresponding HEN design are illustrated in > Fig. 21.16. Because the HEN design from pinch analysis, consisting of one heater, one cooler, and two exchangers, is identical to the existing

50°

100°

Reactor 1

250°

200°

200°

1,000

50° Feed

50° 4,000

200°

Reactor 2 250°

6,000

Separator

720

1,000 100° 50°

. Fig. 21.15 Example process flow sheet for data extraction [16]

Product

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

1 2 3

4 5

a

1

2

3

4

5

6

b

6

250.

H: 1000.0

200.

250.

H: 1000.0

200.

200.

H: 6000.0

50.

100.

H: 1000.0

50.

100.

H: 1000.0

50.

200.

H: 4000.0

100.

Hot 1 Hot 2 Hot 3

Cold 4 Cold 5 Cold 6

250.

200.

250.

200.

200.

50. Q: 6000.

100.

50. Q: 1000.

100.

50. Q: 1000.

200.

100. Q: 4000.

21

Hot 1

Hot 2

Hot 3

Cold 4

Cold 5

Cold 6

. Fig. 21.16 Original data extraction and HEN design [16]

process flow sheet design in > Fig. 21.15, it seems that the existing flow sheet design is already optimized and there is no opportunity for further improvement. The pinch analysis results no benefit. However, the original flow sheet is not an optimal design and the original data extraction is not appropriate. > Figure 21.17 shows an appropriate method of data extraction from the existing process flow sheet and the corresponding HEN design. All the three cold streams previously extracted can be denoted as just one cold stream, and likewise only one hot stream needs to be extracted. The improved design is much simpler and easier to control. It shows significant additional potential for improved energy recovery, and reduces both the equipment cost and energy cost. The ‘‘appropriate’’ data extraction does not exclude any potential energy-saving opportunities. As this example illustrates, the practitioner should be careful in separating the relevant stream data from the original process flow sheet design and should not take over features from it.

721

722

21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

1

2

1

2

250.

H: 8000.0

50.

200.

H: 6000.0

50.

250.

50.

200.

50.

Hot 1

Cold 2

Hot 1

Cold 2

. Fig. 21.17 Improved data extraction and HEN design [16]

Do not consider true utility streams. A true utility stream is a utility stream (steam, flue gas, cooling water, refrigerant, cooling water, etc.) that can be replaced in principle by any other stream (process or utility) for heat recovery. One of the goals of using pinch analysis is to reduce the usage of utilities. Therefore, if utility streams are extracted in a similar way to process streams, they will be considered as fixed features and thus no opportunities of reduction in utility use will be identified. However, in some cases, it is not practical to replace the utility streams by any other form of heat recovery. The utility streams are not true utility streams and need to be extracted as process streams. This is often the case for steam dryers, ejectors, and turbine drives. For example, when steam is required in a shift reactor to enhance the shift process, the steam is not a true utility. The steam is not just used for heating but is necessary for the reaction and cannot be replaced. In this situation, the steam must be extracted as a cold stream, to be heated and vaporized from the original feed condition to the appropriate steam temperature and pressure for the reaction. Identify hard and soft constraints. A hard constraint would be a constraint that cannot be changed in any way, like the inlet temperature of a reactor, while a soft constraint is often open to change within certain range. An example of soft constraint is the discharged temperature of a product stream going to storage, which is often flexible within a range. It is sometimes possible to achieve more heat recovery by changing the soft constraints, such as temperature, pressure, and enthalpy conditions of streams, at the data extraction stage. So the soft constraints should be ideally extracted and the plus/minus principle for process modifications should be applied.

Total Site Concept In the previous part, heat and power integration for a single process has been studied. Typically, industrial processes, such as refinery and petrochemical processes, operate as parts of large sites or factories. A total site is originally defined as an industrial system

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21

consisting of several processes, whose material and energy needs are supplied by a central utility system. For example, in a large site where direct heat integration between processes (e.g., heat exchange between two streams from different processes) is difficult due to a long distance between them, indirect heat integration may be achieved through a utility system. By integrating a number of processes via the steam system, additional interprocess heat recovery can be achieved. > Figure 21.18 shows a schematic of a typical process industry site involving several processes A, B, and C. These individually operated processes, some with their own utilities are served by a central utility system. The utility system consumes fuel, generates power, and supplies the necessary steam through several steam mains. There are both consumption and recovery of process steam via the steam mains between the different processes. Usually the individual production processes and the central services are controlled by different departments and operated independently. The site infrastructure therefore usually suffers from an inadequate overview design and control. For example, in a site involving 50 production processes, the grand composite curve of each individual process will suggest different steam levels. To minimize the total energy and capital cost of the whole site, it requires an approach to consider the individual process issues along with the site-wide utility planning together to identify the correct compromise in steam levels and loads.

Fuel Air

Power

W

Fuel

COND HIGH press steam MED. press steam LOW press steam

Fuel

Fuel Process A Refrigeration

Process B

Process C Cooling water

. Fig. 21.18 Schematic of a site whose separately operated processes are linked indirectly through the utility system [3]

723

724

21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

A graphical method, the so-called total site profiles, was first introduced by Dhole and Linnhoff in 1993 [8]. Klemes et al. [18] then extended this methodology to site-wide applications. This method allows a target to be set for the total site heat recovery. Sitewide analysis usually starts with a kick-off meeting to determine the detail levels each process should be studied and the scope of total site data extraction. In general, not all processes need to be analyzed at the same level. For example, some units may lack enough data for the analysis, and some processes do not need a detailed study due to their small size or low complexity. Three models, black box, gray box, and white box, are used to represent the broad categories of detail level that may be applied to a process. Black-box processes are not to be studied in detail and only the overall utility consumption is considered. This may be because their energy consumption is very small, or heat recovery projects may be difficult to implement, or it is just not the right time for the company to invest in that area. So these processes are simply represented by their existing utility consumption profiles. Gray-box processes only consider heat transfer that involves utilities. These processes usually have small scope of process–process heat exchange, but have significant utility use. In these cases, the process streams that are heated or cooled by utility are considered; however, the process–process heat exchange matches are not considered. In this way, the process/utility interface can be optimized in a site-wide area instead of internal optimization within the process. Again, there is no need to conduct individual pinch analyses for the processes. White-box processes need to perform a detailed pinch analysis. These are usually complex processes with significant energy consumption. For these processes, grand composite curves are constructed. The source and sink profiles of these white-box processes, together with those of black-box processes and gray-box processes, are further modified to construct the site source sink profile (SSSP) which consists of a site heat source profile and a site sink profile. The construction procedure involves selecting parts of the grand composite curves that are satisfied by the central utility system and shifting the temperature. It is not the same as simply combining all the process stream data together into a single site data set, which would allow some far from realistic scenarios. Those scenarios do not consider the realistic constraints, such as distances, controllability, flexibility, etc., which will reduce the number of integration possibilities. For the detailed construction procedure, please see Ref. [16]. > Figure 21.19 illustrates the construction site source sink profiles for a site consisting of four white-box processes (A, B, C, and D), and several other gray-box and black-box processes. In the total site profiles diagram, the site heat sources are shown on the left side and the site heat sinks are shown on the right side. Total site analysis is used to determine the potential for maximizing indirect heat integration through central utilities. The analysis can identify the optimal balance of process steam generation via heat recovery and consumption, and also the optimum steam header pressures. After the site source profile and site heat sink profile are plotted, the composite curves of steam generation and consumption are also constructed. The heat should transfer from the heat source profile to the steam generation profile to generate steams. And also the heat from the steam usage profile should transfer to the

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21

Full detail processes A

B

C

D

plus Grey Boxes and Black Boxes

Source profile

Sink profile Q

. Fig. 21.19 Construction of the site-wide source sink profiles [3]

heat sink profile by the consumption of steam. By superimposing the current utility balance onto the site source and sink profiles, thermodynamic targets for heat and power cogeneration can be set graphically. > Figure 21.20 shows the site source sink profiles and utility profiles for a site-wide analysis. On the left side of > Fig. 21.20a, the gap between the process heat sources profile and the current steam generation profile shows that there is a potential to generate additional high-pressure steam through heat recovery from process heat sources. Similarly, on the right side of > Fig. 21.20a, the gap between the process heat sink curve and the current steam consumption curve shows that much of the medium-pressure steam usage can be substituted by low-pressure steam to reduce the steam energy consumption. > Figure 21.20b shows the target for optimal steam generation through heat recovery from process heat sources and the target for optimal steam consumption (heat load and pressure levels). On the left side of > Fig. 21.20b, the optimal additional high-pressure steam generation can be identified through shifting the existing steam generation profile toward process heat sources profile. This will effectively increase the heat integration between processes indirectly through the utility system, and reduce the need of external hot utility for steam generation. Similarly, on the right side of > Fig. 21.20b, the optimal heat load and pressure levels of steam consumption can be targeted by shifting the existing steam consumption profile toward process heat sinks profile. Typically, a site-wide pinch analysis can be carried out in two phases. The objective of first phase is to get a reliable target for overall, site-wide savings and to identify the potential area that is likely to yield greatest benefits during the following second phase. In this way, engineering hours are minimized both in phase 1, through the judicious selection of black- and gray-box processes, and in phase 2, by not having to study every data in detail. In phase 2, further project packages need to be developed, and the strategic total site road map can be constructed. After the work of phase 1, it is possible to establish the relationship between investment and benefit of all the projects in the site.

725

21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

800 700 Temperature (°C)

600

Process heat sources Furnace

500 400 300

Existing steam generation profile

HPS MPS

200

Existing steam consumption profile

0 −100 −1200

Process heat sinks

LPS

100

−900

−600

a

−300 0 Enthalpy (MW)

300

600

900

800 700 600 Temperature (°C)

726

Furnace

500 400 300 200

HPS

Pinched steam generation profile

MPS LPS

100

Pinched steam consumption profile

0

b

−100 −1200

−900

−600

−300

0

300

600

900

. Fig. 21.20 (a) The existing total site profiles before targeting (b) Total site profiles after targeting [3]

Such a representation is called the road map for the site development. The road map includes project details such as savings, investment, effect on emissions, and the compatibility of projects with each other. Each route in a road map consists of a series of mutually compatible projects. Each project package is explored for its technical and economic feasibility. The road map forms a rigorous basis for the designer or planner to plan a route or a strategy for long-term site development on all energy-related issues. As a summary, the key steps in total site pinch analysis can be listed as follows: 1. Individual process pinch analysis: Starting from heat and material balances of individual processes, pinch analysis establishes key options for process modifications, energy recovery (savings in noncentral utilities), and targets for multiple utilities. The grand composite curves are ready for use in total site analysis. 2. Total site pinch analysis: The site source sink profiles and the central utility generation and usage curves are constructed. They can help to set targets for the utility system

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21

improvements and process-wise improvements. The assumptions of steam system in step (1), such as the pressure of steam mains, need to be reset if they are changed in this step (2). 3. Identification of specific projects and construction of road map: The targets obtained through previous steps need to be further implemented in detail. Then the specific projects are put together in a coherent plan involving alternative routes of compatible projects. 4. Final selection of project alternatives from total site road map. The site-wide analysis technique can be a very powerful approach for oil refining, petrochemical, and iron and steel plants, as well as regional energy sectors. Some software applications based on this approach are currently available. The SuperTarget software package (KBC Energy Services, UK), allows engineers to undertake total site pinch analysis using its site module. Kazuo Matsuda et al. [2] applied the total site pinch analysis to one of the largest heavy chemical complexes in Japan which has 31 sites consisting of process industries including petrochemical, refinery, and power company. Their study demonstrates that despite the very high efficiency of the individual process plants in the complex, the area-wide pinch technology can identify a huge amount of energy-saving potential. In their study, a large amount of energy saving, 0.9  106 GJ/year, was achieved by the implement of area-wide integration projects. An important innovation about the total site concept has been presented by Perry et al. [19], who extended this concept. Traditionally, a total site includes only a set of industrial processes. Perry et al. made a further improvement by including commercial and residential energy users into the total site concept. The resultant process collections are termed as locally integrated energy sectors.

Mathematical Programming Approach for HEN Design Over the past decades, heat-integrated system and HEN design have been extensively studied. Most of the contributions to this research can be classified as either a sequential or a simultaneous synthesis method [20]. Generally speaking, mathematical programming represents a class of alternative techniques in spite of pinch analysis. Linear programming (LP) method and mixed integer linear programming (MILP) [10] are both sequential methods. The simultaneous synthesis methods are primarily mixed integer nonlinear programming (MINLP) [21] formulations of HEN problems. The approach is based on a stagewise superstructure representation that contains all possible network configurations and process stream matches. In each stage, potential heat exchange may take place between any pair of hot and cold streams. This MINLP model can simultaneously optimize and synthesize the capital and energy cost, and other structural features, as steam splitting and bypass design. While the MINLP can be formulated easily, unfortunately, it is frequently difficult to obtain converged solutions using the algorithms available today

727

728

21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

in systems like GAMS, especially when the number of streams are large and the models are complex. It is beyond the scope of this text to cover in detail the approaches to formulating and solving MINLPs. However, in the next section of this chapter, disturbance propagation and rejection (DPR) embedded MINLP model is introduced for HEN design.

Disturbance Propagation and Control Modeling for the Design of Highly Controllable Heat-Integrated Systems Traditionally, in most process synthesis activities, only the cost is considered when targeting the optimal solution. This practice can give rise to the designs at the minimum total annualized investment. Process operational issues, especially structural controllability, are usually not a concern in the design procedure, while only steady-state condition is considered. As a consequence, the operational controllability of the ‘‘optimal’’ design solution generated by the aforementioned traditional method may be questionable. In the worst case, an (economically) optimally designed process may not be operable, as shown in Yang et al. [22], where a real industrial example is described, where the originally designed HEN experiences various disturbances of temperatures and heat capacity flow rates in operation. Industrial practice has made it clear that process controllability should be part of the process synthesis work. This has led to the introduction of an active research area, called integration of process design and control (IPDC) [23–25]. The analysis of disturbance propagation (DP) and disturbance rejection (DR) is conducted extensively in flexibility and controllability analysis. Flexibility is a system’s capability of absorbing long-term variations appearing at the inlet of process [26, 27]. Controllability is referred to the system’s capability of withstanding short-term disturbances. Yang et al. [22, 28–30] introduced a simplified, first-principle-based modeling approach to evaluate DP in HENs, MENs, distillation networks, and heat-integrated reaction system design at the steady-state level. Integrating this quantitative analysis approach into traditional process synthesis can lead to the optimal design satisfying both economic and operational objectives.

Disturbance Propagation Modeling The DP modeling approach introduced below is general and it will be integrated into a superstructure-based MINLP (mixed integer nonlinear programming) model, through a case study, to generate a cost-effective and highly controllable network. In process synthesis stage, the precise information of process disturbance is usually unavailable. Meanwhile, a worst-case design is usually sufficient, though may not be optimal. Thus, the estimated maximum magnitude of each disturbance can be used instead. For a HEN operated at a given normal operating condition, the known types of

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21

disturbances can be expressed as the maximum fluctuation of stream source temperature (dT s) and that of heat capacity flow rate (dMcp). After propagating these disturbances of input source streams, the resulting DP model can predict the stability of the target temperature of each stream by the obtained dT t, which stands for the largest deviation from the normal operating target points. Yang et al. [22] developed a DP modeling methodology for a heat exchanger unit as well as a HEN that can contain any number of hot and cold streams. By neglecting the high-order differentiation terms and replacing the logarithmic mean temperature difference by an arithmetic mean term [31], the model can be simplified to a linear one and is summarized below. Unit-based DP model. A DP model for a single heat transfer unit (HTU) can be written as follows: dT t ¼ Dt dT s þ Dm dMcp

(21.1)

or dTht dTct

! ¼

1a

a

b

1b

!

dThs dTcs

! þ

ð2  aÞah

ac a

bah

ac ð2  bÞ

!

dMCph dMCpc

! (21.2)

where a¼

Ths  Tht Ths  Tcs

(21.3)

b¼

Tct  Tcs Ths  Tcs

(21.4)

ah ¼

Ths  Tht 2MCph

(21.5)

ac ¼

Tct  Tcs 2MCpc

(21.6)

where Dt and Dm are temperature and heat capacity flow rate related disturbance propagation matrix, respectively; T and dT are the stream temperature and temperature fluctuation, respectively; Mcp and dMcp are the heat capacity flow rate and its fluctuation, respectively; superscripts s and t refer to source and target, respectively; and h and c refer to hot and cold stream, respectively. The above model can be used to provide a quick and accurate quantification of DP through the propagation in a heat exchanger. System DP model. The unit-based DP model in > Eq. 21.1 can be applied to any heat transfer unit (HTU) in a HEN. Thus, the DP model for the i-th HTU, named Ei, in a HEN can be expressed as: dTEout ¼ DtEt dTEini þ DmEi dMcpEi i

(21.7)

729

730

21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

If a HEN contains Ne heat exchangers, a system DP model can be established directly by lumping all the single unit-based models in the sequence of exchanger numbers. This procedure yields the following equation:  dT out ¼ DtE dT in þ Dm dMcp E

(21.8)

where T  T  T T in in dTE2  dTENe ; dT ¼  T  T  T T out out dT out ¼ dTEout dT  dT ; E2 ENe 1  T  T  T T dMcp ¼ dMcPE1 dMcPE2  dMcPENe ;

(21.11)

n o DtE ¼ diag DtE1 ; DtE2 ;    ; DtENe ;

(21.12)

n o  ¼ diag D ; D ;    ; D ; Dm m m m E E E E 1 2 Ne

(21.13)

in



dTEin1

(21.9) (21.10)

The superscript T in equations designates the transpose operation of corresponding matrix, which interchanges the rows and columns of matrix. The ‘‘diag’’ in > Eqs. 21.12  and > 21.13 means the matrix DtE and Dm are diagonal matrix, which is a square matrix E whose elements outside the main diagonal are all zero. The dimensions of vectors dT in,  T out, and dMCp are all 2Ne  1, and the DtE and Dm are both 2Ne  2Ne matrices. It is E in out needed to point out that dT and dT contain a number of Nm intermediate temperatures. An intermediate temperature is the temperature of a stream between two adjacent heat transfer units (HTUs). Nm can be calculated by the following > Eq. 21.14 Nm ¼ 2Ne  Ns  Nsplit

(21.14)

where Ne is the number of HTUs; Ns is the total number of hot streams and cold streams; Nsplit is the total number of stream branches after splitting. After several steps of mathematical processing, a general system DP model can be derived as bellow: dT t ¼ Dt dT s þ Dm dMcp

(21.15)

Dt ¼ Dt11 þ Dt12 ðI  Dt22 Þ1 Dt21

(21.16)

Dm ¼ Dm1 þ Dt12 ðI  Dt22 Þ1 Dm2

(21.17)

where

Those underbars in the equations do not have any mathematical meaning and are just symbols to differentiate from other matrix variables. For the detailed deduction of this model, please refer to the work of Yang et al. [32].

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21

DP-based network structure representation. To derive those matrices in the DP model, a structural matrix S, whose dimension is (2Ne  Nsplit)  2Ne, should be constructed. Matrix S can be decomposed into two sub-matrices, S1(Ns  2Ne) and S2(Nm  2Ne), whose definitions are given below. In sub-matrix S1, each row is designed for a hot or cold stream, and the columns are divided into Ne pairs. Each pair is assigned for a specific heat transfer unit (HTU). In each pair, the left column corresponds to the hot stream going through the HTU, and the right column corresponds to the cold stream through the unit. A stream may be split into a number of branches, going through different HTUs and mixing together. In this case, the splitting ratios are reflected by the matrix elements corresponding to the streams. Each element has a value between 0 and 1, where 0 represents streams not going through the units; a fraction represents the splitting portion going through the unit; and 1 means the stream going through units without splitting. In sub-matrix S2, each row represents the intermediate streams between two adjacent HTUs. The definition of columns are the same as sub-matrix S1. Each element of matrix S2 represents the connection modes of the intermediate stream with an HTU. [1], [1], or 0 are assigned to the element to represent an intermediate stream entering, leaving or not going through a HTU, respectively. DP model embedded HEN synthesis approach. HEN synthesis can be fulfilled by mixed integer nonlinear programming (MINLP) method, following the procedures of network representation, mathematical optimization model formulation, and optimal solution identification. The DP model introduced above can be integrated in the optimization model to take account of controllability issues in HEN design. Problem statement. In a HEN synthesis problem, there are a set I of hot process streams, a set J of cold process streams, and a set K of superstructure stages. Each hot or cold process stream has a specified heat capacity flow rate, and their inlet and outlet temperatures are also specified exactly or given as inequalities. A set of hot and cold utilities, along with their temperatures are also known. Meanwhile, the predicted max–min source temperature disturbance and flow rate fluctuations are also given along with the permissible target temperature fluctuations. The objective of the synthesis is to determine a network structure with the minimum total annual cost (TAC) satisfying the permissible target temperature fluctuations requirement. Stream-based superstructure. The first step of the synthesis is constructing a streambased superstructure. A HEN superstructure can be developed by a graph-theoretical approach [12]. > Figure 21.21 shows a two-stage superstructure for a two hot–two cold stream synthesis problem, which will be studied in this case. All units and their inputs and outputs are represented as a set of nodes in the graph, where all possible connections are linked between pairs of units. The key elements of a superstructure are HTUs, mixers, and splitters. A HTU is denoted as a large circle, while a mixer or splitter is denoted as a small dot. Each HTU has a splitter at its inlet and a mixer at its outlet. Problem formulation. After the construction of HEN superstructure, the next step is to formulate the synthesis problem with mathematical equations.

731

732

21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

Stage k = 2

Stage k = 1 M1

H1 C1

S1 H1

M3

H1 C2

C1

H1 C1

W1

H1 C2

M2 H2 C1

S2

H2 C1

C2

M4 H2 C2

H2

H2 C2

Temperature Location 2

Temperature Location 1

W2

Temperature Location 3

. Fig. 21.21 Two-stage superstructure for two hot streams and two cold streams [32]

Objective function. The total annual cost (TAC) is the combination of the utilities cost and heat exchangers related cost, such as the cold utility cost, hot utility cost, fixed charges, and area cost for heat exchangers between streams. TAC should be minimized and can be formulated as [32]: X X XXX X X min CCU Qcu;i þ CHU Qhu;j þ CFi;j yi;j;k þ CFcu;i ycu;i þ CFhu;j yhu;j i2I

þ

XXX i2I

þ

j2J

X

j2J k2K

Ci;cu þ

Ci;j

i2I

j2J k2K

i2I

Qi;j;k

1=3 t s ÞðDT s Ucu;i ½DTcu;i ðTit  Tcu cu;i þ Ti  Tcu Þ=2

X

Qhu;j

Cj;cu þ

j2J

Ui;j ½DTi;j;k DTi;j;kþ1 ðDTi;j;k þ DTi;j;kþ1 Þ=2 1=3 !0:6 Qcu;i

i2I

j2J

!0:6

!0:6

1=3 s  T t ÞðDT s t Uhu;j ½DThu;j ðThu hu;j þ Thu  Tj Þ=2 j

(21.18) where CCU is the per unit cost of cold utility; Qcu, i stands for the heat exchanged between hot stream i and the cold utility; CHU is the per unit cost of hot utility; Qhu, j stands for the heat exchanged between cold stream j and the hot utility; CF is the fixed charge for heat exchangers; C is the area cost coefficient; the exponent 0.6 in this equation is a constant used by many researchers to analyze the area cost of heat exchangers; T s and T t are inlet

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21

and outlet temperatures, respectively; U is the heat transfer coefficient; Qi, j, k is the heat exchanged between hot process stream i and cold process stream j in stage k; ΔTi, j, k, is the temperature approach for the match of hot stream i and cold process stream j in stage k; ΔTcu, i is the temperature approach for the match of hot stream i and the cold utility; ΔThu, j is the temperature approach for the match of cold process stream j and hot utility; variable yi, j, k stands for the existence of a match between hot process stream i and cold process stream j in stage k; ycu, i stands for the existence of a match between hot stream process i and cold utility; and yhu, j stands for the existence of a match between cold stream process j and hot utility. The binary variables represent the existence of unit for a match and the values are either 1 or 0. yi;j;k ; ycu;i ; yhu;j 2 f0; 1g;

8i 2 I; 8j 2 J ; 8k 2 K

(21.19)

Constraints. This MINLP problem should be subject to the following constraints. Energy balance constraints. The overall energy balance for each process streams should be observed. For example, the amount of energy each hot (cold) process stream releases (obtains) by the difference of source and target stream temperature should be equal to the sum of heat transferred between process streams and heat transferred to (from) cold utilities (hot utilities). Also, the energy balance for each stream is each superstructure stage and energy balance for the utility streams should be respected. Temperature feasibility constraints. The temperature of each stream should decrease monotonically along with the temperature locations. Logical constraints. The temperature approach between the streams that exchanged heat should not exceed the maximum temperature difference. Meanwhile, the exchanged heat of process streams and utilities cannot exceed an upper limit. System controllability constraints. Besides the above constraints, the target temperature fluctuations of streams should be limited in permissible ranges, which are the controllability-related constraints. tðÞ tðþÞ dTmax  dT t  dTmax

(21.20)

tðþÞ where dT t is the vector for target temperature fluctuations, dT tðÞ max and dT max are vectors for the maximum negative and positive target temperature fluctuations, respectively. The DP-based network structure matrix S can be constructed according to the approach introduced in the previous section. Then based on this structure matrix S and the binary variables, a HEN system DP model can be constructed as introduced before. Through the system DP model, the target temperature fluctuations dT t can be obtained from the source temperature disturbances dT s and source heat capacity flow rate disturbances Mcp . Optimal solution identification. After the formulation of objective function and various constraints, the last step in this synthesis approach is the optimization of the model. This DPembedded MINLP model can be solved using the general algebraic modeling system (GAMS). Case application of DP-embedded HEN synthesis approach. Yan et al. [32] studied the case of Yee et al. ([21]) for the incorporation of DP into the HEN design procedure.

733

734

21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

. Table 21.2 Stream data for the synthesis problem [32] Stream Hot 1

T s ( C) 180

T t ( C) 75

Mcp (kW/ C) 30

dT s(+) ( C)

dT s() ( C)

5

Hot 2 240 60 40 0 Cold 1 40 230 35 0 Cold 2 120 300 20 0 2  The heat transfer coefficients: Ui,j =Ucu,i = 0.8 kW/(m  C); Uhu,j = 1.2 kW/(m2 C)

0 0 5 5

The per unit cost of utilities: CCU = 20 $/(kWyear); CHU = 80 $/(kWyear) The area cost coefficients: Ci,j = Ci,cu = 1,000; Chu,j = 1,200

This design problem has two hot streams and two cold streams. The design data including the disturbance information are listed in > Table 21.2. The stage-wise superstructure is already shown in > Fig. 21.21. There are 12 possible matches and therefore 12 binary variables. According to this superstructure, a structure matrix S is also generated and listed in > Table 21.3. The ‘‘M’’ labeled stream in > Table 21.3 stands for the intermediate stream between two adjacent heat transfer units. In this case, three scenarios are studied and each has a different control requirement. In each scenario, the control requirements, which are tðþÞ the maximum negative and positive target temperature fluctuations dT tðÞ max and dT max , act as one of the constraints. The optimal HEN of this scenario can be obtained by solving the DP-embedded MINLP problem using GAMS. For further detailed calculations, please refer to the work of Yan et al. and only the results are provided here. > Table 21.2 listed the control requirements, the actual temperature fluctuations, and the TAC of each scenario. > Figures 21.22–21.24 give the optimal HEN solution of each scenario under different control specifications. The symbol ‘‘E’’ in these figures represents the heat exchangers. Comparing the three optimal solutions, it is obvious that solution A in scenario Ι has the simplest HEN structure (> Fig. 21.22) and the minimum TAC ($ 450,072 in > Table 21.2). This is because in scenario Ι, there are no constraints imposed on the maximum negative tðþÞ and positive target temperature fluctuations dT tðÞ max and dT max and actually this is the traditional synthesis case where no control issues are considered. However, when the strict control requirements are specified, this optimal solution may not qualify. For example, in tðþ  Þ of cold stream 2 is within the range of 1 C, scenario Ш, the control requirement dT max which is far beyond the actual temperature fluctuations of ð3:3; 6:6Þ C in scenario Ι. This indicates solution A will not meet the control requirements of scenario Ш and this indicates that integrating DP model into the HEN design procedure can generate the optimal result which meets the control requirements. Plus, different control specifications can be imposed on the synthesis problem according to the real process. Comparing scenarios П and Ш, stricter control requirements are imposed on cold stream 2 and hot stream 1 and a higher TAC is needed in scenario Ш. The higher TAC is kind of the tradeoff for stricter control requirements (> Table 21.4).

[1]

0

0

{1}

0

0

0

C2

M1

M2

M3

M4

0

0

0

0

0

0

{1}

0

0

0

C1

Q1;1;1 Q1;1;1 þQ2;1;1

0

H2

Q1;2;1 Q1;1;1 þQ1;2;1

0

0

Q1;1;1 Q1;1;1 þQ1;2;1

H1

HTU2

H

0

C

HTU1

H

Stream

HTU3

[1]

0

0

0

0

0

{1}

0

0

Q1;2;1 Q1;2;1 þQ2;2;1

0

[1]

0

0

0

Q2;1;1 Q1;1;1 þQ2;1;1

0

Q2;1;1 Q2;1;1 þQ2;2;1

0

0

C

0

H

0

0

0

C

. Table 21.3 Structural matrix for the superstructure of case study [32] HTU4

0

0

{1}

0

0

0

Q2;2;1 Q2;1;1 þQ2;2;1

0

H

[1]

0

0

0

Q2;2;1 Q1;2;1 þQ2;2;1

0

0

0

C

HTU5

0

0

0

[1]

0

0

0

Q1;1;2 Q1;1;2 þQ1;2;2

H

0

{1}

0

0

0

Q1;1;2 Q1;1;2 þQ2;1;2

0

0

C

HTU6

0

0

0

[1]

0

0

0

Q1;2;2 Q1;1;2 þQ1;2;2

H

{1}

0

0

0

Q1;2;2 Q1;2;2 þQ2;2;2

0

0

0

C

HTU7

0

0

[1]

0

0

0

Q2;1;2 Q2;1;2 þQ2;2;2

0

H

0

{1}

0

0

0

Q2;1;2 Q1;1;2 þQ2;1;2

0

0

C

HTU8

0

0

[1]

0

0

0

Q2;2;2 Q2;1;2 þQ2;2;2

0

H

{1}

0

0

0

Q2;2;2 Q1;2;2 þQ2;2;2

0

0

0

C

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21 735

736

21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

(146.7) [30] (180.0)

H1

[40] (240.0)

H2

E1

C

(75.0)

C

(60.0)

(73.8) E2

[35] (230.0)

E2

C1

(40.0)

C2

(120.0)

(170.0) [20] (300.0)

H

E1

Legend ( ): Temperature (° C) [ ]: Heat capacity flow rate (kW / °C)

. Fig. 21.22 Solution A for the HEN synthesis problem in scenario I [32]

[30] (180.0)

H1

[40] (240.0)

H2

E1

(146.7)

E3

(75.0)

(127.5) (60.0)

(101.4)

[35] (230.0)

E2 (170.0)

[20] (300.0)

C

E2

H

E1

E3

C1

(40.0)

C2

(120.0)

Legend ( ): Temperature (°C) [ ]: Heat capacity flow rate (kW/°C)

. Fig. 21.23 Solution B for the HEN synthesis problem in scenario П [32]

Disturbance Propagation and Control (DP&C) Model Embedded Synthesis Approach The DP model introduced above can be used to quickly estimate the maximum deviation of system outputs under various types of disturbances. However, the DP models do not consider any control actions for disturbance rejection (DR). This can lead to

21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

(165.0) [30]

(180.0)

H1

[40]

(240.0)

H2

E1

(75.0)

{0.875}

(130.0) E3

{0.125}

E4

(60.0)

E2 (120.0) [35]

(230.0)

[20]

(300.0)

E3 (170.0)

E2

H

E4

{0.8953}

C1

(40.0)

C2

(120.0)

{0.1047}

E1 Legend ( ): Temperature (°C) [ ]: Heat capacity flow rate (kW/°C) { }: Splitting fraction

. Fig. 21.24 Solution C for the HEN synthesis problem in scenario Ш [32]

. Table 21.4 Comparison of the solutions under different control requirements [32] Case I (solution A)

Case II (solution B)

Case III (solution C)

Streams

t ð Þ dTmax 

( C)

dT ( C)

tð Þ dTmax 

( C)

dT ( C)

dTmax ( C)

dT t ( C)

Hot 1 Hot 2

– –

3.7/4.2 0.0/4.2

6

4

2.0/5.5 2.0/4.0

2

4

1.0/1.3 0.6/3.9

Cold 1 Cold 2 TAC ($/year)

– – 450,072

0.0/0.3 6.6/3.3

1

10 450,759

0.2/0.4 6.6/3.3

3

1 468,013

1.0/2.8 0.9/0.8

t

t

tð Þ

a conservative network design. In operation, a HEN is always controlled through regulating bypass flow rates associated with heat exchangers. Thus, Yan et al. [31] further extend Yang’s DP model to a disturbance propagation and control (DP&C) model where control actions are taken into account. This model can be embedded into a HEN design procedure to optimally select the locations and nominal fractions of bypasses with the minimum penalty on capital cost. The system DP&C model is expressed below. For the detailed derivations, please refer to the work of Yan et al. [31].

737

738

21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

dT t ¼ Bdf þ Dt dT s þ Dm dMcp

(21.21)

B ¼ B1 þ Dt12 ðI  Dt22 Þ1 B2  T  1 Dt ¼ Dt11 þ Dt12 I  Dt 22 Dt21 ¼ Dth T Dtc T  T Dm ¼ Dm1 þ Dt12 ðI  Dt22 Þ1 Dm2 ¼ Dmh T Dmc T

(21.22)

where

(21.23) (21.24)

dT t and dT s are vectors of maximum stream temperature deviation for the target and source temperature, respectively; B is the process-gain matrix; df is the vector of maximum fluctuations of bypass nominal fractions; Dt ; Dm ; B1 ; B2 etc. are relative matrices. Disturbance rejection with minimum economic penalty. While a bypass of a heat exchanger can help to reject disturbances, its installation must cause an increment of heat transfer area and the capital cost. A trade-off between the DR and cost must be made in the bypass selection. > Figure 21.25 illustrates how the stream target temperature fluctuation (dTt) and the increment heat transfer area (ΔAE/AE) are related to the nominal fraction of a bypass (fE). The nominal fraction of a bypass (fE), can be selected from 0 (no ðlimÞ bypass) to the upper limit fE . As shown in > Fig. 21.25, when fE increases, dT t will

ΔAE / AE

dT t

0

fEopt

fE(lim) fE

. Fig. 21.25 Relationship of target temperature, heat transfer area, and bypass fraction [31]

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21

decrease, while ΔAE/AE will increase. In this study, the optimal solution is defined as the one realizing complete disturbance rejection at the steady state, and with minimum increment of heat transfer areas. Any nominal fraction value below the optimal value opt opt fE will not realize complete DR. Meanwhile any value above fE will have more area increment with the same complete DR level, and this is certainly not desirable. Case study: design of bypasses and control loops for a four-stream HEN. Yan et al. [31] developed an iterative design procedure to determine the optimal locations and nominal fractions of bypasses in a HEN design and applied this method to a four-stream HEN design case previously studied by Yee and Grossmann [21]. For simplicity, only the problem statement and the solution are provided here to demonstrate the efficacy of this approach. > Table 21.5 and > Fig. 21.26 show the steady-state design data as well as source disturbance information and control requirements of the selected case.

. Table 21.5 Design data for the four-stream HEN synthesis problem [31] t ðþÞ

Stream no.

T s (K)

T t (K)

McP (kW/K)

dT s(+) (K)

dT s(-) (K)

dTmax (K)

tðÞ

dTmax (K)

H1

620.0

385.0

10.0

5

0

0

0

H2 C1 C2

720.0 300.0 280.0

400.0 560.0 340.0

15.0 20.0 30.0

0 0 0

0 5 5

5.5 0 4.0

5.5 0 4.0

(620.0) H 1

E1

E2

(560.0)

E2

[10]

(400.0)

[15]

C1

(300.0)

[20]

C2

(280.0)

[30]

t¢

Th

m

(720.0) H2

(385.0)

T1

E3

(530.0)

2

C (410.0)

m

T2

E1

(417.5)

(340.0)

Legend ( ): Temperature (°K) [ ]: Heat capacity flow rate (kW/°K)

. Fig. 21.26 Original four-stream HEN design [33]

E3

739

740

21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

{0.015} (620.0) H 1

E1 {0.053}

(720.0) H2

E2

(560.0)

E2

{0.082}

m

T1

E3

(530.0)

(385.0)

[10]

(400.0)

[15]

C1

(300.0)

[20]

C2

(280.0)

[30]

t¢

Th

2

C

(410.0)

m

T2

E1 (417.5)

(340.0)

E3

Legend ( ): Temperature (°K) [ ]: Heat capacity flow rate (kW/°K) { }: Bypass fraction ... : Control loop connection

. Fig. 21.27 Optimal bypass design for the HEN by the DP&C approach [31]

The resulting optimal bypass design with control loops by the DP&C approach is shown in > Fig. 21.27. Uztruk and Akman [33] also studied the same problem and their result is shown in > Fig. 21.28. > Table 21.6 compares the different design results in total costs. The design solution by DP&C model is 6% cheaper than that by Uzturk and Akman. In addition, the RGA (relative gain array) analysis reveals that the solution by DP&C method has no system interaction among loops at steady state. By contrast, the design in > Fig. 21.28 has considerable interactions among loops. To sum up, the disturbance propagation and control (DP&C) method can quantify the disturbance propagation and disturbance rejection by using bypasses in the HEN design process. It can help to design the fewest bypasses with their nominal fractions for complete disturbance rejection with minimum economic penalty. The application strongly demonstrates the robustness and efficacy of this DP&C-based HEN design approach.

Emissions Targeting and Planning: CO2 Emissions Pinch Analysis (CEPA) Emission targeting by pinch analysis has been reported by Linnhoff and Dhole [8] using the total site analysis concept. Total site in their work refers to industrial systems incorporating several processes, which are serviced by a central energy utility system. Although emission

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21

{0.0821} (620.0) H 1

E1 {0.0532}

(720.0) H2

E2

(560.0)

E2

(400.0)

[15]

C1

(300.0)

[20]

C2

(280.0)

[30]

2

E3

(530.0)

[10]

t¢

Th

m

T1

(385.0)

C (410.0)

m

T2

E1 (417.5)

{0.2222} (340.0)

E3 {0.35}

Legend ( ): Temperature (° K) [ ]: Heat capacity flow rate (kW / ° K) { }: Bypass fraction

. Fig. 21.28 Bypass design for the same HEN by Uzturk and Arkam [33]

. Table 21.6 Comparison of different design results [31] Heat Original design (no exchanger bypass), area (m2)

DP&C design (with bypass), area (m2)

Uzturk and Akman design (with bypass), area (m2)

E1 E2

34.7 42.3

35.4 44.3

39.1 49.2

E3 SEi Cost

22.8 99.8 $24,386

23.7 103.4 $24,905

25.8 114.1 $26,408

targeting by pinch analysis was introduced in those studies, the early applications were limited to within industrial facilities. Tan and Foo [34] reformulated the traditional ‘‘total site’’ concept [8, 18, 35] and presented a novel application of pinch analysis for the preliminary planning of a country’s energy sector. The carbon emissions pinch analysis (CEPA) was first developed by Tan & Foo and coworkers [34, 36, 37] for emissions targeting and reduction from industrial sites to macroscales (e.g., regional or national energy sectors). Crilly and Zhelev utilized the CEPA method to analyze the Irish electricity sector [38]. Detailed description of the procedure for implementing the CEPA methodology can be found in [38]. The following is a brief illustration of the novel method.

741

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21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

When planning energy sectors, it occurs very often that emission constraints will present. This is especially common in the industrialized countries such as Germany and Ireland where CO2 emissions limits are applied during the Kyoto/post-Kyoto setting. Thus, the problem arises when considering how to identify energy allocation schemes to meet the specified emission limits. If only environmental issues are considered, it is naturally desirable to maximize the use of low-carbon or zero-carbon energy sources, such as wind, hydroelectric, solar, biomass energy, etc. However, in real-world planning scenarios, economic issues need to be considered. Due to the high cost of renewable energy sources mentioned above, it is often desirable to determine the minimum amount of low-carbon or zero-carbon energy sources required to meet the national or regional emission limits and energy demand, which is known as the defined pinch point. The CEPA method can be used to determine the minimum quantity of low-carbon or zero-carbon energy sources needed and the energy allocation scheme among different energy resources in order to meet the specified emission limits and energy demand. Ireland’s electricity sector. In Ireland, GHG emissions come from various industrial sectors, including electricity generation, transportation, other manufacturing and service industries, as well as agricultural and waste-treatment sectors. The emissions in 2005 have an overall 25.48% increase as compared with the 1990 level. This amount is far above Ireland’s permissible 13% increase in overall GHG emissions under the European Union (EU)’s burden-sharing agreement on the Kyoto protocol. For Ireland’s electricity sector, it contributed a 23.33% share of Ireland’s overall GHG emissions in 2005 (21.40% in 1990) and took a substantial 32.66% of Ireland’s total primary energy requirement (TPER), according to the publications from the government. In 2005, the TPER can be classified using the following actual energy resource (AER) mix [38]: 1. Fossil fuel: natural gas (NG)  40.09%, coal (C)  27.77%, oil (O)  15.16%, peat (P)  10.02% 2. Electricity: Imported electricity (IE) from Scotland  3.45% 3. Renewable energy sources (RESs): landfill gas, biomass, and other biogas  0.57%, hydro  1.06%, wind  1.88% In the short-to-medium future of Ireland’s electricity sector, a well-designed optimal energy resource (OER) mix is required to satisfy both the energy needs and emissions limit. The renewable energy source-electricity (RES-E) has its disadvantages, such as high cost, limited public acceptability, inherent intermittency/variability, lack of predictability and poor reliability, etc. Thus, only the absolute minimum amount of RES-E should be employed in the optimal energy resource (OER) mix for the sector. Application of CEPA. The basis of the approach is the construction of the composite curves of both the demand and the supply. These composite curves are then manipulated and shifted depending on the desired objectives. Crilly and Zhelev applied the CEPA to the electricity sector based on the data sources from the Sustainable Energy Authority of Ireland (SEAI), which is set up by the Ireland government as its national energy authority. The data for the actual energy resource (AER) mix in 2005 is shown in > Table 21.7. The energy demand (consumption) and resource (supply) composite curves (CC) before shifting are

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21

. Table 21.7 The past and forecasted AER mixes and OER mixes for the sector in 2005 and 2010, respectively [38]   CO EF t TJ2ðeÞ

RESs

NG

Oil

Coal

Peat

IE

Total

0

56.8

75.6

94.6

116.7

120.0

_

Past AER mix2005 % of Total TJ/year TJ/year

3.51 7,494

40.09 85,578

15.16 32,364

27.77 59,285

10.02 21,395

3.45 7,369

100.00 213,485

4.86

2.45

5.61

2.50

0.88

16.30 > KL2005

40.09 85,578

15.16 32,364

27.77 59,285

7.15 15,264

0.00 0.00

100.00 213,485

4.86

2.45

5.61

1.78

0.00

14.70 = KL2005

56.52 137,997

0.14 335

30.74 75,069

2.38 5,820

3.02 7,369

100.00 244,175

0.00 7.84 Mt CO2(e)/year Projected OER mix2010 (by CEPA) % of Total TJ/year 8.02 56.52 TJ/year 19,585 137,997

0.03

7.10

0.68

0.88

16.53 > KL2010

0.14 335

30.74 75,069

2.38 5,820

2.20 5,369

100.00 244,175

Mt CO2(e)/year

0.03

7.10

0.68

0.64

16.29 = KL2010

0.00 Mt CO2(e)/year Past OER mix2005 (by CEPA) % of Total TJ/year 9.83 TJ/year 20,994 Mt CO2(e)/year 0.00 Projected AER mix2010 % of Total TJ/year 7.20 TJ/year 17,585

0.00

7.84

plotted in > Fig. 21.29. More specifically, the figure depicts a correlation between the amount of CO2 or CO2(equivalent) per unit time and the amount of energy per unit time. It shows a slope of the amount of CO2 per unit energy for any line segments, which is also the emission factor. The resource composite curve is constructed by plotting cumulatively the quantity of electricity generated for the several fuel resources against total emissions from those resources. The emission factor (EF) (i.e., the amount of emissions produced CO per unit of electricity, t TJ2ðeÞ ) for each energy resources is also provided in > Table 21.7. The fuel source with the lowest emission factor is plotted first, followed by the next lowest and so on. In this resource composite curve, the renewable energy source is plotted first, followed by natural gas, oil, coal, peat, and imported electricity. The slope of each line segment is equal to the emission factor of corresponding energy resource. All emissions factors are expressed as carbon equivalent and include all relevant greenhouse gases. Ireland permitted an increase of its overall GHG emissions by no more than 13% per year during 2008–2012, as compared to the baseline year of 1990, which is 55.75 Mt CO2(e). Thus, Ireland’s environmental protection agency determined a leveled-out Kyoto limit (KL) of 62.99 Mt CO2(e) for each year between 2008 and 2012. The Kyoto limit KL2005 for 2005 is 61.78 Mt CO2(e) by the principle of interpolation. Because the electricity sector had a 23.79% share of the actual overall GHG emissions of 69.63 Mt CO2(e) in 2005, this sector should be allocated the same percentage of the KL2005, which equated

743

21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

CEPA for ireland’s Electricity Sector Over 2005

18 CO2(e) Produced & Kyoto Limit (Mt CO2(e) / Year)

744

End of Energy Resource CC At (213, 485 TJ / year, 16.30 Mt CO2(e) Produced/year)

16 14

Imported electricity

End of Energy Demand CC At (213, 485 TJ / year, 14.70 Mt CO2(e) Kyoto Limit/year)

12

Peat

10 Coal

8

Energy Demand Curve

CO2(e)

6

Oil

4

Energy Resources curve

Renewable

2

Natural gas

0

0

50,000

100,000

150,000

200,000

250,000

Energy Resource & Energy Demand (TJ /Year) Energy Demand Curve

Energy Resources Curve

. Fig. 21.29 CEPA applied to Ireland’s electricity sector over 2005: before shifting of energy resource CC [38]

to 14.70 Mt CO2(e). This value is the vertical ordinate for the top end of the energy demand curve as shown in > Figs. 21.29 and > 21.30. The energy demand composite curve is also constructed using the same method as the energy resource composite curve. It is assumed that the emissions from various demand sectors is proportional to the electricity usage and therefore will produce a straight line from the origin to the end of the demand composite curve. The horizontal ordinate for the top end of both the energy demand curve and energy resource composite curve should share the same value because the demand (or consumption) should match the resource (or supply) in any given year. The slope of the demand line is known as the grid emissions factor (GEF), which is simply the average emission factor for the entire system. In this CO case, the EF for the energy demand curve is 69.0 t TJ2ðeÞ . In > Fig. 21.29, it is easy to find that the top end of resource curve is above the top end of energy demand curve, which shows the AER mix led to more emissions than the permitted KL of the electricity sector. Thus, the energy resource composite curve needs to be shifted horizontally to the right to get rid of the excess emissions. > Figure 21.30 shows a shifted energy resource composite curve that meets the Kyoto limit for the sector. The energy resource CC is shifted horizontally to the right until it intersects with the top end of energy demand CC and this is the CO2 emissions pinch point. At this pinch point, the energy resources not only provide a total amount of 213,485 TJ energy per year (meeting the annual energy demand), but also release 14.70 Mt CO2(e) emissions (meeting the Kyoto limit of emission). In this way, the amount that the resource CC has been shifted then becomes the minimal amount of renewable energy that needs to be added in order to meet the emission target. The overhang of the resource CC to the right of the pinch point represents the amount and type of energy resources that need to be substituted by renewable energy. In this case, the renewable energy portion of the energy resource

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21

CEPA for Ireland’s electricity sector over 2005

CO2(e) Produced & Kyoto Limit (Mt CO2(e) / Year)

18 Excess IE energy not required and emission avoided

16 CO emission pinch point at

2 14 (213, 485 TJ / year, 14.70 Mt CO2(e) Kyoto Limit / year)

12

Peat

10 Coal

8

Energy demand curve

6

Excess peat energy not required and emission avoided

Shifted energy resources curve Oil

4 Renewable

2

Natural gas

0

0

50,000

100,000

150,000

200,000

250,000

Energy Resource & Energy Demand (TJ / Y ear) Energy Demand Curve

Energy Resources Curve

. Fig. 21.30 CEPA applied to Ireland’s electricity sector over 2005: after shifting of energy resource CC [38]

CC increases, the portion of imported electricity is totally substituted, and the portion of electricity from peat generation decreases as illustrated in > Fig. 21.30. By increasing the energy resources with low emission factors and decreasing energy resources with high emission factors, the shifting procedure achieved the desired objective, that is, the emissions produced by the resources equal to the Kyoto Limit of the demand. Meanwhile, the other objective of using the minimum amount of renewable energies due to their disadvantages is also achieved by this horizontal shift procedure. Each of the line segments of the shifted energy resource CC is measured off in order to get the optimal energy resource (OER) mix in 2005, which is also the optimal energy resource allocation scheme of the sector. The corresponding emissions produced by each of these optimal amounts are also measured. All of the measured data are listed in > Table 21.7. Further adaptations to CEPA. Crilly and Zhelev made a forecasting adaptation to the CEPA methodology, which is briefly introduced here. If the optimal energy resources (OER) mix in the future can be predicted, then the sector’s policy makers can use this information to guide the future development plan of the sector. For example, in the near future, Ireland will close old and inefficient power plants, and create new power generation plants. The ahead-of-time knowledge of the future OER mix will be particularly useful for the policy makers to decide which form of power generation plant should be constructed. As long as the future actual energy resources (AER) mix is available, the future OER mix can be obtained using the same CEPA procedure described in the proceeding section. The future AER mix can be projected based on the energy model linked with macroeconomic model together with many key forecast parameters, such as GDP growth, population growth, fuel prices, etc. In 2006, Sustainable Energy Authority of Ireland (SEAI), Ireland’s national energy authority, published the projected AER mix for

745

746

21

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

the electricity sector in 2010, which is shown in > Table 21.7. Crilly and Zhelev used that information to forecast the OER mix that the energy sector in 2010 should have. Their forecast is also listed in > Table 21.7. Analyzing those data, the OER mix in 2010 will need to have the input of RESs rising from 7.2% of the AER mix to 8.2%. This important and invaluable information will give the relevant policy makers and stakeholders 3 years time in advance to make up for this forecasted shortfall of renewable energies in 2010 for the analysis made in 2007.

Future Trends Heat integration is one branch of process integration technologies. In the authors’ view, there are several directions that can be considered as potentially promising for the future of process integration. Process integration, especially the newer development, has not been used as widely as it could be. It is likely to see a wider range of application in process integration. Still, there is much work to be carried out in the research of integrating heat-integrated network with separation systems and reactor designs, and the consideration of operational issues as well. Heat integration is closely related to mass integration by nature. Although extension of pinch analysis to mass integration field, such as water pinch and hydrogen pinch, has already been applied to industries successfully, systematic methods in this area are still in development. Utilizing advanced optimization techniques to solve process integration problems are very promising. With the advancement of computer technology, a new generation of more powerful software tools for process integration may emerge. Comparing to the process simulation software, which is relatively mature, the process integration software is at its infancy. Process integration problems are generally complex tasks at considerable scales and involve comprehensive interactions. The development of powerful commercial software for process integration is instrumental for its wider application. Climate change has recently become a major focus of industry and government. Pinch analysis has been extended to solve emissions and energy footprint problems to meet the environmental goals with technical and economic constraints simultaneously. Several methodological (graphical and numerical) approaches have been developed to handle problems such as energy allocation, segregated targeting, and retrofit planning. Meanwhile, similar approaches for considering energy, land, and water footprint issues in energy and biofuel systems have been developed. Regarding the increasing concerns on climate change, more methodologies and applications are expected in this area.

Conclusion Heat integration is a family of methodologies that can be used to improve energy efficiency, reduce energy consumption, and minimize GHG emissions. Pinch analysis can be considered

Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

21

as the foundation of heat integration. It can identify the maximal heat recovery and minimal external utility needs for the system before any detailed design. As a powerful tool, pinch analysis extends its application to many other fields, such as waste reduction, wastewater treatment, refinery hydrogen management, emission targeting, etc. In spite of the total annualized cost, the HEN design must always consider the operability and controllability issues as well. During operations, various disturbances of temperatures and heat capacity flow rates always present. The disturbance propagation and control (DP&C) model embedded HEN design approach can estimate the disturbance propagation and reject the severe disturbances through bypass design. This method can generate an optimal design solution satisfying both the economic and control objectives, thereby ensuring the achievement of high energy efficiency and low emissions. The novel carbon emissions pinch analysis (CEPA) methodology, developed based on traditional pinch analysis, can identify the minimal quantity of low-carbon emission energy resources needed to meet both the emission limit and energy requirement, and the optimal energy allocation scheme, for a regional or national energy sector. It can provide invaluable information for the decision makers and stakeholders.

Acknowledgments This work is in part supported by the National Science Foundation under Grants No. 0737104, 0736739s, 0731066.

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24.

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Greenhouse Gas Emission Reduction Using Advanced Heat Integration Techniques

of multi-stream exchangers. Comput Chem Eng 14:1151–1164 Floudas CA (1995) Nonlinear and mixed-integer optimization. Oxford University Press, Oxford Floudas CA, Grossmann IE (1986) Synthesis of flexible heat exchanger networks for multiperiod operation. Comput Chem Eng 10(2):153–168 Ciric AR, Floudas CA (1990) A comprehensive optimization model of the heat exchanger network retrofit problem. Heat Recovery Syst CHP 10(4):407–422 Seider WD, Seader JD, Lewin DR (2003) Product and process design principles synthesis, analysis, and evaluation, 2nd edn. Wiley, New York Linnhoff March (1998) Introduction to pinch technology. Linnhoff March, Cheshire Dhole VR, Linnhoff B (1993) Distillation column targets. Comput Chem Eng 17(5–6):549–560 Klemes J et al (1997) Targeting and design methodology for reduction of fuel, power and CO2 on total sites. Appl Therm Eng 17(8–10):993–1003 Perry S, Klemesˇ J, Bulatov I (2008) Integrating waste and renewable energy to reduce the CFP of locally integrated energy sectors. Energy 33:1489–1497 Furman KC, Sahinidis NV (2002) A critical review and annotated bibliography for heat exchanger network synthesis in the 20th century. Ind Eng Chem Res 41:2335–2370 Yee TF, Grossmann IE (1990) Simultaneous optimization models for heat integration-II. Heat exchanger network synthesis. Comp Chem Eng 10:1165–1184 Yang YH, Gong JP, Huang YL (1996) A simplified system model for rapid evaluation of disturbance propagation through a heat exchanger network. Ind Eng Chem Res 35:4550–4558 McAvoy TJ (1987) Integration of process design and process control. In: McGee HA, Liu YA Jr, Epperly WR (eds) Recent development in chemical process and plant design. Wiley, New York, p 186 Huang YL, Fan LT (1992) Distributed strategy for integration of process design and control: a knowledge engineering approach to the incorporation of controllability into exchanger network synthesis. Int J Comput Chem Eng 16(5):496–522 Elliott TR, Luyben WL (1995) Capacity-based economic approach for the quantitative assessment of

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22 Advanced Real-Time Optimization of Power Plants for Energy Conservation and Efficiency Increase Pal Szentannai Department of Energy Engineering, Budapest University of Technology and Economics, Budapest, Hungary Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 750 Environmental Benefits Offered by Advanced Control Methods in Power Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 752 Introduction of the Advanced Control Methods of Highest Potentials in Power Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 754 Soft Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 755 Gain Schedule and Multimode Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 756 Loop Decoupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 757 Model Predictive Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 758 Dynamic Matrix Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 760 Fuzzy Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 760 Neural Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 762 Proposed Ways of the Introduction of Advanced Control into Power Plants . . . . . . . 763 Successful Applications of Advanced Control in Power Plants . . . . . . . . . . . . . . . . . . . . . . 765 Some Published Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 765 An Optimum Control Application Discussed in Detail . . . . . . . . . . . . . . . . . . . . . . . . . . . 767 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 771 Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 772

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_22, # Springer Science+Business Media, LLC 2012

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Abstract: Real-time optimization takes place practically in all power plants. The main task of all automatic controllers is to assure the optimal values of their controlled variables under all circumstances. The quality of operation of these controllers has evidently a crucial effect on the way of operation of the entire power plant. Whether a power plant – based on either renewable resources or fossil fuels – is operated in a highly effective way, or is a rather resource-consuming one, is evidently of very high importance regarding emissions and other ecological aspects. This fact is the reason for discussing in this chapter the possible ways for increasing the level of control quality in power plants. An overview will be given at the beginning about the ways and tools the advanced control methods offer – in case of their more intensive applications in power plants – for protecting the environment and for mitigating the climate change. It will be followed by a concise but goal-oriented introduction of the most relevant control methods together with their evaluations regarding the aspects of their applicabilities in power plants. Because the way toward obtaining the environmental benefits offered by the advanced control methods is not a trivial one, some considerations, aspects, and hints will be given on this issue in the next part. A few successful power plant applications will be introduced afterward, and the actual main development directions will be outlined at the very end of this chapter.

Introduction The practically exclusively used control method in power plants is currently the PID (Proportional-Integral-Derivative [1]) algorithm. The well-known, clear-sighted effects of its three parameters, the easy and uniform methods for setting them, and the multiply proofed, stable operation assure its widespread success in many industrial branches, including the energy industry [2–7]. Besides these clear advantages, the PID controller does have its limitations (which will be discussed later in this chapter), and parallel, modern control theory offers a wide range of advanced control methods. The basic ideas of the most important such methods will be briefly introduced in this chapter, together with the conclusions in the special aspect of their applicabilities in power plants. These introductions will be extended with practical hints regarding their realizations in new or existing power plants of any type, and some practical examples will be introduced too. The problem discussed in this chapter is a rather unusual one! No compromise must namely be made between economical and ecological interests, because the benefits of applying advanced control methods in power plants serve both in the same time. It is evident, namely, that increasing the efficiency or decreasing the resource-consuming manner of operation (referring to any sorts of fuel, water, air, or even valuable components under decreased thermal stress) serves both of those goals in parallel. In spite of the limited number of advanced control applications in power plants, the published results show clear, numerically expressible benefits, an overview of which will also be given in this chapter. The total number of industrial applications of advanced control techniques has increased rapidly worldwide, but the distribution of these applications among industry

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branches is considerably unequal. While chemical industry alone had more than 7,000 running applications of the most popular solution (Model Predictive Control, MPC) in 2005, the number of similar applications in power plants at that time was definitely below 100 [8]. Interesting is also the dynamic rate of increase of those applications in the chemical industry: Their number has been doubled practically every 5 years since 1995. The goal of this chapter is nothing else but to encourage operators and owners of power plants together with decision makers for applying advanced control methods also in power plants in order to contribute to both global climate change mitigation and local financial benefits. For building a basis, some elementary ideas and notational practice of the control theory will be outlined here for those readers who are unfamiliar with this area. The central element of a control system is always the process (or: plant, P) to be controlled as shown in > Fig. 22.1. The process can be affected by its input signal u (plant input, or: control signal), and its response is its output signal y (controlled variable). The process is often affected by disturbances (d) too, which may be either measurable or unmeasurable. In the classical control theory, all the above signals are considered as scalars, but throughout this chapter they will be handled as vector variables – without any extra markings like boldfaced or underlined letters. It means that the current discussions may also refer to systems having multiple input and multiple output signals. In most cases of the following discussion, several signals (several real measuring points) can be handled jointly as components of one variable, which will be handled as a multidimensional vector variable (like in the algebra). The process to be controlled is generally not an entire system (e.g., a whole power plant or a boiler), much rather only a subprocess of it. In some books, papers, and theoretical discussions, the borders and list of inputs and outputs of the process are considered as predefined characteristics of the system. A definitely differing approach will be followed throughout this chapter. The theoretical and practical considerations on defining the borders of the process P are namely a key toward successful control, and a high level of knowledge of both power engineering and control sciences is required in this essential step. Another important element of a control system is the controller (C) itself. In the classical approach its input is the control error (e), which is the deviation between d r

+ −

e

C

u

P

y

. Fig. 22.1 Basic elements of a closed loop control system – introduction of the notation used throughout the discussion of advanced control methods. Each variable may represent several physical variables joined as a multidimensional vector variable

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controlled variable (y) and reference signal (or: set point, r). In some advanced control methods both controlled variable and reference signal will be considered, not only their actual difference. In case of multi-output processes also the reference signals must be multidimensional vector variables, of course. The goal of controller design is to set the internal behavior of the controller C so that the process output y could keep or follow the value prescribed by the reference signal r. Throughout this design procedure, the instationary behavior of the process also must be considered. The goal of the science of control theory is to develop such design procedures for many different plant types. The modern control theory has reached a really high amount of very useful results throughout its theoretical work; however, these results are still rarely utilized in power plants. The possible utilizations of these results and their environmental (and also financial) benefits will be discussed throughout the rest of this chapter.

Environmental Benefits Offered by Advanced Control Methods in Power Plants Energy conservation and efficiency increase of power plants are important goals to be considered throughout their basic design efforts. But how can these goals be supported by the real-time controllers? The next figure shows just one example. According to this example, a better control may keep the superheated steam temperature of a thermal power plant within a narrower band (> Fig. 22.2). This decreased fluctuation in turn allows a higher set point of the same temperature, since the properties of the steel material used determine the maximum permissible steam temperature. And a higher average live steam temperature directly increases the efficiency of the plant, which means a direct decrease in fuel consumption. As a further consequence, the amount of emitted pollutants (including CO2) will be significantly decreased while producing the unchanged amount of

T prohibited area

conventional control

advanced control t

. Fig. 22.2 Environmental benefit from applying advanced control. Narrower band of fluctuation allows higher average live steam temperature, which directly results in higher plant efficiency

Advanced Real-Time Optimization of Power Plants

22

electricity and heat. It is important to mention here that this positive effect is valid not only for fossil-fueled power plants, but in an identical fashion also for biomass fueled or other ones. Similarly, an increased efficiency of wind mills, photovoltaic power plants, or hydroelectric power stations will reduce the energy demand to be produced from fossil resources. An obvious case of obtaining direct environmental benefit in the steady state operation was discussed in this simple example only. It is important to mention already here that modern control techniques offer a much wider range of areas where direct environmental and economic benefits can be expected. The most important such benefits can be listed as follows: ● Reaching higher efficiency in steady states (which directly results in lower fuel consumption and emission – as introduced in the example above) ● Making load changes smoother and less resource-consuming (by means of considering and limiting thermal stresses which in turn results in increased lifetimes) ● Making the start-up periods faster (which directly results in savings in fuel consumption) ● Increasing the level of supply by making the power plant a more flexible one in the energy market (which increases the potential of thermal power plants for compensating the uneven supply of wind farms) Besides the steam temperature control discussed in the above example, a number of further control tasks exist in power plants. An excellent overall summary of their specific goals and classical solutions can be found in [9] and [10]. The basic components of power plants are often extended nowadays with different subprocesses in order to fulfill some specific or newly set requirements. These subprocesses require in most cases some own control tasks like the minimization of the ammonia slip in the flue gas in DENOX facilities. It is important to emphasize that advanced control techniques discussed in this chapter can be applied for all above-mentioned groups of power plant control tasks, and in all cases similar direct economic and environmental benefits are expected due to their higher level of intelligence. What is the secret behind advanced control techniques that allows them to offer such benefits? Let us answer this question using the example of one of the most frequently used techniques, Model Predictive Control (MPC). Its most important properties are as follows: ● Its control actions are based on future values calculated by an integrated process model. ● It can inherently consider constraints regarding, e.g., allowed operating areas and actuator positions; speed limits. ● Multivariable control is naturally handled allowing an integrated compensation of cross effects. This chapter and its approach are definitely not against the traditional PID (Proportional-Integral-Derivative) controller! There are the definite reasons for the worldwide and branchwide success and high proliferation of the PID controller technique. It is also

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certain that the PID controller technique has had a nearly exclusive role in all branches of the industry from the nineteenth century onward, and it will keep its role in the future as well. However, it is also obvious that the PID control technique does have its limitations. The most important cases – together with just a few power plant examples – for which the efficient application of the PID control technique is strongly limited, can be given as follows: ● For MIMO (multi-input, multi-output) systems with significant couplings (e.g., heat and power controls of turbogenerator groups) ● For strongly nonlinear processes (e.g., engines and turbines) ● For time-variant processes (e.g., waste incinerators) ● For cases where better control performance is required The examples given in brackets behind the above bullets could be extended with a really high number of cases from the power generation industry. This makes it an evidence that power plants are typical applications where it is definitely advisable to apply advanced controllers.

Introduction of the Advanced Control Methods of Highest Potentials in Power Plants Which are the most important advanced control methods? What are their basic ideas? In which cases are they advantageous and where are their limits? These questions will be discussed in this section – but from the special aspect of their possible applications in power plants. > Figure 22.3 gives a schematic overview of those advanced control methods that seem to be of the highest potential regarding their applications in power plants or have proven already their successful applicabilities in the energy industry. This figure will be used as a road map throughout this section. It will be seen – after studying the basic ideas of the above methods – that most of them use process models for reaching a better control quality. A wide variety of model structures, depths, and approaches is available, and their presences seem to be general

♦ Soft Sensor ♦ Gain Schedule for nonlinear advanced extensions processes also to classical control ♦ Multi Mode ♦ Loop Decoupling ♦ MPC (Model Predictive Control) ← most often used ♦ DMC (Dynamic Matrix Control) ← subset of MPC ♦ Fuzzy “intelligent” methods ♦ Neural Network

. Fig. 22.3 The most important advanced control methods from the aspect of their applicabilities in power plants

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22

characteristics of the advanced control methods. The reason for it can be understood easily, and it can be summarized as follows: the better the process is known by its controller, the higher control quality can be expected. According to this, the efforts in process modeling and simulation are of the highest importance. And further on this statement seems to be true also for the person who intends to design the control system of an entire energy technology system like a power plant. According to this, a deep knowledge of the power plant, its subprocesses, thermal, chemical, and practical engineering aspects, operation environment, etc., must be well known for realizing a successful, high-quality (advanced) control system. A mathematical description of the selected process may not be enough, since just the procedure of drawing the borders of the subprocesses requires all the above theoretical and practical knowledge and experiences, and this beginning step is crucial regarding the later success. The basics of the most important advanced control methods will be discussed in the next subsections. However, their detailed theoretical analyses are no goals of the current chapter, since these aspects (e.g., stability issues) are discussed in detail for numerous particular cases in the original research articles and textbooks. In spite of this, a special care will be taken throughout the current discussions on the aspects of their possible roles, advantages, and limiting characteristics regarding their possible applications in power plants for reaching environmental benefits and financial results.

Soft Sensor In some cases, a significant difficulty in building effective control loops is the lack of a measured variable characterizing well the actual state of the process. A wide variety of theoretical and simple practical reasons may cause this situation like a significant time delay between the core process and its measurable output signal, a signal being very difficult or expensive to measure accurately, a signal burdened with significant noise or other inaccuracies, and so on. Soft sensor may be a good solution for these cases. Its basic idea (see > Fig. 22.4) is to measure other, easily accessible process variables being in strong relationship with the

r + −

e

C

u

P1

y1

y P2

P2,M

yM

. Fig. 22.4 Soft sensor is practically a model (P2,M) of a subprocess (P2). The calculated version (yM) of an unmeasurable process variable (y) can be used for control on the basis of the measurement of another ‘‘primary’’ variable (y1)

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required one, and the later one will be deduced from the measured one. For doing this deduction, a model will be used in all cases. Some special cases of the approach of soft sensor are known in the literature under their own names. Kalman Filter is a broad set of tools for the cases where the measured data contains significant noise and other inaccuracies, while the Smith predictor gives a very interesting theoretical solution for processes with pure time delays. A significant technical relevance has in this field the so-called State Optimal Control. This advanced technique was applied successfully in several power plants in classical control environments in the 1990s, and it was mostly used for controlling the superheated steam temperature. This process can be, namely, characterized by a significant time delay being dependent also upon the actual plant load; however, modeling this SISO (Single-Input, Single-Output) system is not too difficult. Determining the actual rate of combustion in a boiler can be mentioned as a further example, because an accurate measurement on the steam or hot water side indicates any changes significantly later than the primary processes originated them.

Gain Schedule and Multimode Control A practical extension of all linear controller design methods toward nonlinear processes are gain schedule and multimode control. The idea behind both of them is to choose always among a number of predefined control configurations depending upon the actual operating point. The first step in designing such a control system is to identify an appropriate variable to be used as scheduling variable, which may be the plant load signal in most power plant applications. Thereafter, a set of operating points will be chosen within the whole range of the scheduling variable, and any (advanced or classical) simple control design methods will be applied to each. During the online operation of the system, always one control configuration will be activated according to the actual value of the scheduling variable. The only difference between the two subjected methods is that while in case of gain scheduling only the parameter settings of an unchanged controller will be updated according to the actual values of the scheduling variable, in case of multimode control, the whole controller itself – as visible in > Fig. 22.5. As an evident advantage of these approaches, well-known linear control methods can be used also for nonlinear processes. However, only slight nonlinearities can be handled on this way, because otherwise the frequent switches between the actually used controllers or control parameters would result in unpredictable behaviors. This phenomenon indicates also a drawback of this method: The switches may result in unsmooth operation. Regarding the applicabilities of these two similar control methods in power plants, it can be stated that they can be effectively applied, because the main nonlinearities in these applications can be easily characterized by the plant load signal as the scheduling variable. The nonlinearities caused by the varying actual load is in most cases exactly in the range where an unchanged linear controller cannot be used effectively anymore, but these nonlinearities still allow the applications of these simple methods. An advantage of the

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first subjected method is its simplicity, while the later one allows its application also in such cases where the use of different control algorithms at different operating points is necessary.

Loop Decoupling In many practical cases, the control loops are not really independent from each other. This fact can easily be observed very often in power plants when a change in one control loop affects the other. The reason is, of course, that because of the presence of strong couplings (dashed lines in > Fig. 22.6) inside the entire process, it cannot be considered as a set of independent one-dimensional (SISO) subsystems. It is in reality a coupled multidimensional process, which should be handled by the methods

Scheduling variable

Scheduling variable

Selector

Selector

parameter set 1

C1

parameter set 2 parameter set n

r + e −

d r + e −

C

u

P

C2

d u

P

y

y Cn

. Fig. 22.5 Basic ideas of gain schedule (left) and multimode control (right)

Virtual process r1 +− e1

r2 + e 2 −

C1

C2

v1

v2

D

u1

u2

P

y1

y2

. Fig. 22.6 Inserting a well-designed decoupler (D) between controllers (C1, C2) and process (P) results in a virtual process having no internal cross couplings. This virtual process can be controlled by means of independent, one-dimensional controllers designed according to any (e.g., classical) control design methods

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developed for multidimensional control problems, since the methods and tools developed for one-dimensional cases (e.g., the PID controller) cannot satisfactory solve the multidimensional problems. Control engineers often try to smooth out the most disturbing cross effects by means of several empirical tools. However, a relatively simple overall theoretical solution exists for tracing back the multidimensional problem to a set of one-dimensional problems, and these one-dimensional control tasks can already be solved by means of common (advanced or classical) controller design methods. A so-called decoupler (D in > Fig. 22.6) will be designed and applied according to wellknown, relatively simple design procedures the details of which will not be discussed here. The goal of such a decoupler is to build a virtual process the inputs of which are the inputs of the decoupler and the outputs are the outputs of the real process. The control loops of this resultant virtual process are independent from each other already. Loop decoupling can easily be realized also in the existing control system of an existing power plant, since most DCS (digital control system) software allows the insertion of extra multiplier blocks the decoupler is built up from in most cases. Their actual values shall be determined off-line by well-known standard procedures, which require also a process model. The controllers C1 and C2 will be designed afterward, also off-line, by considering the dynamic characteristics of the resultant virtual process Decoupler + Process (the inputs of which are v1 and v2, the outputs: y1 and y2 in > Fig. 22.6).

Model Predictive Control The control method having the highest potential regarding industrial applications (including power plant applications as well) and also the highest number of successfully running industrial realizations is Model Predictive Control (MPC). This is already a complete control method, which cannot be considered as a simple extension to the classical ones. This is a model-based method, which entirely handles also multidimensional processes. A further practical advantage of MPC regarding its industrial realization is its entire capability for handling constraints like maximal and minimal possible flow rates, valve positions, and other technological prescriptions. Model Predictive Control has several variations and development directions; its common basic idea will be summarized below – with special respect to its power plant applications for energy conservation and efficiency increase. The initial requirements of this control method are a process model, a set of constraints, a cost function, and the future values of the reference signal up to a certain horizon as shown in > Fig. 22.7. A process model can be used theoretically in any programmed form. In practical applications, empirical models (black box models) are often used because they can be generated relatively easily by means of available identification procedures based on pure input, output measurements. Nevertheless, physical modeling (or at least using semiempirical models) is rather advisable, because a deep understanding of the controlled process (represented in such a model) gives definitely a great help in controlling it successfully.

Advanced Real-Time Optimization of Power Plants

♦ Process model ♦ Constraints ♦ Cost function ♦ Reference signal

u

y = f(u,x,...)

22

y

≤, ... Q . (r–y)2 + R . u 2 → min r (n . tn)

. Fig. 22.7 A priory requirements of the MPC method

Processes, where identification-based empirical models are practically unusable, are the ones characterized by long-term conservation behaviors. It is important to emphasize here, because this is a frequent case in power plant processes! The long-term fuel and bed material accumulation in fluidized bed combustors (FBC) is a typical case, but grate firing and some other power plant processes are of very similar characteristics. The mathematical procedure of MPC does inherently handle also constraints, which should be given as relational operators referred to any available variables of the model or the control structure. This characteristics of MPC makes it a very practice-oriented one in case of its application in power plants, as discussed above. An interesting utilization of this property of MPC is the inclusion of some technological constraints (e.g., thermal stresses) which cannot be considered directly in case of most other control methods. A very clear formulation of the goal of the control is the cost function (or: target function), which gives the weighting between two opposite interests. A very low control error can namely be achieved at the expense of a very intensive actuator operation and vice versa. In > Fig. 22.7, Q and R are the weightings, which are matrices in the general, multidimensional case. They represent the relative importances of these two aspects, where the matrix elements refer to the individual physical control errors (differences between set points and measured outputs) and actuator activities. The reference signal can be either a constant set point or a function of time. Because the basic version of MPC is a timely discrete one, the future values of the reference signal should be available in the time steps n·tn. The task the controller has to execute online at each time step is to solve the quadratic optimization problem with constraints. Because this problem is a well-known one for a longer while, numerous effective solver algorithms are available in the literature of mathematics. They will be adapted and used in the Model Predictive Controllers, the operational procedure of which is the following. In each time step, the optimization problem formulated above will be solved numerically, its result is the optimal future time series of the control signal u (> Fig. 22.8). Not the whole time series, but only its first element will be applied to the system, because in the next time step the same optimization procedure will deliver a newer, updated control signal. In this way, the actually applied control signal will consider also the latest measured process data, which behavior acts as an effective tool against model inaccuracies being present of necessity. As a summary to MPC, it can be stated that this advanced control method offers excellent properties that can be utilized well also in power plants. That is why an increasing

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yˆu predicted future values of the controlled variable y, provided the control signal u remains unchanged y historical data of the controlled variable

yˆ predicted optimal future values of the controlled variable y, provided the optimized control signal u will be applied r given future values of the reference signal

u historical data of the control signal

u future values of the control signal as a result of on-line numerical optimization. The first element will be applied to the process only. past

present

future

time

. Fig. 22.8 Way of operation of the Model Predictive Control. This method inherently handles also multidimensional processes and timely changing reference signals, however, for a better visibility, the much simpler single-input single-output case is indicated here. The inherent consideration of constraints is also not visible in this figure

number of its applications in any types of power plants would be definitely a very effective tool for energy conservation, efficiency increase, and emission reduction. However, for realizing such applications, expert knowledge is required covering both power engineering and advanced control engineering.

Dynamic Matrix Control A rather simple version of Model Predictive Control (MPC) is Dynamic Matrix Control (DMC). Simplicity means here a procedure of significantly less online computational demand, which is an advantage regarding its applications in power plants. This early version of MPC can use the process model in a predefined simple form only, which is the so-called Dynamic Matrix. A drawback of this simplicity is, of course, the higher inaccuracy of the model in most cases. As a further difference compared to the basic MPC approach, DMC does not handle constraints entirely, which fact may also be either an advantage or disadvantage depending upon the specific application.

Fuzzy Control Both fuzzy control and neural network control came from the direction of artificial intelligence research, and that is why they are often called intelligent control

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classical set: 2 ≤ x ≤ 5 membership function

membership function

fuzzy set: youth 1

0 15

25

age

1

0 2

5

x

. Fig. 22.9 A fuzzy membership function to the fuzzy set described by the human expression ‘‘youth’’ (left). Membership functions can be used also in the classical set theory, but their borders are ‘‘crisp’’ (right)

methods (although this naming does not mean any rank differences compared to other advanced techniques). Fuzzy logic is an alternative direction of the set theory. According to the approach of the classical set theory, a point may either belong to a set or definitely not. In the fuzzy set theory, a membership function will be used instead, which is ranged from 0 to 1. It is important to mention at this point that human thinking seems to be much closer to the later approach, since nobody could clearly define the borders of the set ‘‘youth.’’ The unsharp borders of this set are indicated in > Fig. 22.9, which shows them as an example on fuzzy membership functions. All measured data in fuzzy control will be classified into fuzzy sets, and this initial step of fuzzy control is called fuzzification. A given actual value of a measurement may belong to more sets in the same time. According to the basic idea of fuzzy logic introduced above, several sets will be defined by their membership functions like ‘‘very low,’’ ‘‘low,’’ ‘‘medium,’’ etc., and these membership functions are usually overlapped. The next step does no more deal with exact measured data; it uses the fuzzified states only (like ‘‘pressure is low’’). In this second step, decisions will be made according to some rules implemented during the design process of the fuzzy controller. These rules are rather simple ones like ‘‘IF pressure is low THEN set discharge valve position to somewhat open.’’ The final step in fuzzy control is called defuzzification. Output values will be formed here from the resulted decisions by means of output membership functions in such a way that the parallel decisions will be weighted by those membership values which resulted from them. The whole procedure is indicated in > Fig. 22.10 in a simplified manner. Regarding its usability in power plants, fuzzy control can be characterized by the next advantages (+) and disadvantages (
): + Easy realization of human/expert knowledge, because the way of representation of the operational requirements is very close to the human thinking. + Low cost realization is possible, because fuzzification and defuzzification may be realized by means of low-cost sensors and actuators, respectively, and decision making is a procedure requiring relatively low computational capacities.

761

y measured value (steam temp., e.g.)

FUZZIFICATION

Rule Base DECISION MAKING

en so m e m wh i dd at so le ope m n e clo wha tc se l os e

op

no

IF ... THEN... • • • IF temp is very low THEN valve set to open IF temp is low THEN valve set to somewhat open analog input • • value • IF ... THEN...

membership

rm hi g al h ve ry hi g h

Advanced Real-Time Optimization of Power Plants

ve ry l low ow

22 membership

762

analog output value u output value (valve position, e.g.)

DEFUZZIFICATION

. Fig. 22.10 Internal structure of the fuzzy controller. Extension toward multivariable and dynamic control is possible


Unsmooth output signals may be resulted by the discretized way of operation of the decision-making procedure.
The overall stability of the control system can rarely be guaranteed because of the heuristic setup of the controller.

Neural Network Neurons are the basic elements of the nervous system. Many of them work in parallel, and the interactions between them determine the way of operation of the entire system. The junctions where these interactions take place are called synapses, and the magnitude of transferring signals from one neuron to another one through a certain synapse can be changed throughout the normal biological learning process. One neuron may receive several input signals from others, but it generates only one output signal. The above (general and simplified) description is the basis of the artificial neural networks (NN), which can be used also as controllers (> Fig. 22.11). A very important characteristic of neural networks is their abilities for learning. It practically means certain procedures for finding the optimal set of the weighting factors wi and additive constants b so that in case of a set of inputs the network would result in its desired set of outputs. Several search procedures are known, which depend also upon the actual form of the neuron output function f. The application of this theoretical background for the purposes of controlling a process still has a number of different approaches. If, for example, the neural network learns the inverse behavior of the process, applying the desired process output on the neural network input, its output will result the process

Advanced Real-Time Optimization of Power Plants

input1 input2

inputn

w1 w2

22

b

Σ

output f

wn

. Fig. 22.11 One artificial neuron. In a layer of a neural network, several neurons act in parallel. In a neural network, some layers will be applied. wi represent the weighting factors and b is an additive the actual settings of which is the result of the learning process

input necessary for that desired process output. Beyond this theoretically simple application, many further successful ways of industrial applications are known. Also several combinations of fuzzy control and neural networks are applied, and both of these ‘‘intelligent’’ methods are often used as value-added extensions to other control solutions.

Proposed Ways of the Introduction of Advanced Control into Power Plants The introduction of advanced control methods offers a number of ecological and economical benefits as discussed above; however, the way of their implementation is not an evident one [11]. One must be aware of the special requirements of modern control techniques compared to those of the traditional, PID-based ones. As a general and strongly simplified observation, it can be stated that modern techniques are based on more detailed calculations. This is the reason for their requiring significantly higher computational capacities. Computers capable of such performance became commercially available low-cost standard ones in recent years, and many people use equipment of that capacity in everyday life. However, the reliability of these computers is definitely below the level expected in power plants. Moreover, most industrial control systems were designed for lower computational capacities only. A further problem can result from the fact that only a few digital control systems (DCSs) are equipped with standard software tools required to program an advanced control application. In this actual situation, one must distinguish between two different cases: application in a new power plant or application in an existing power plant equipped with traditional controllers. The first case seems to be easier, since the new control system of a new power plant can be designed according to the special needs of the selected advanced control method. This first means the appropriate selection of the hardware and software structure of the DCS to be applied: a system capable of these control methods should be installed. In spite of this theoretically simple and straightforward method, a more conservative approach will be proposed here to realizing the benefits of advanced control

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strategies in new power plants. During the construction of a new power plant, it may be more advantageous and secure to program and use traditional control loops in the commissioning period of the whole power plant technology, and to set up advanced controllers in a second phase only after reaching stable and secure operation. In most cases, commissioning in any case is followed by a longer period of fine-tuning the entire power generation technology, which should be used also for setting up, finetuning, and testing the final, modern control system as software changes in the unchanged DCS. This approach also allows a final comparison between traditional and advanced controls. In the second case, an existing power plant is running with its complete, proved, and stable traditional control system. In this case, the purpose of the introduction of an advanced control technique is to achieve and utilize its benefits outlined above. While doing this, one should not forget that the existing stable operation is of much higher actual importance than any advantages the new controller may offer. In other words, the benefits of the introduction of the advanced controller must be achieved in such a way that stability of the existing control system will by no means be lost. A good practice for this is to retain the existing control system as a supervisor above the new one. The supervisor should stay idle as long as the difference between the outputs of new and advanced controllers remains below a given threshold. This limit may be increased stepwise by the control engineer after appropriate periods of reliable operation of the new control technique, allowing more and more effective utilization of its benefits. Another question in this case is the choice of hardware on which to run the new control algorithm. Since the existing control system is generally not capable of doing this, an external platform is required. A rather general configuration is proposed in > Fig. 22.12, which indicates both hardware and software structure, together with the necessary communication pathway. This scheme should be considered as a typical arrangement only, and must be modified according to the actual environment in each particular case. Positioners are, e.g., in many cases realized outside the DCS (digital control system), sometimes as distributed local ones. Some device border lines must be actualized in this case, however, even in such a case no change is proposed to the general concept of keeping the positioners outside the advanced controller. As visible on the above figure, the high-level parts (the traditional, one-dimensional PID controllers) of the existing control loops will be replaced by the advanced controller, but the replaced elements will become effective again if and when the new control outputs show an unlikely degree of variance from those of the original control system. This proposed method of implementation assures a secure way to realizing the benefits of advanced control techniques. This scheme may also be applicable in the case of a new power plant, the only difference being that the communication channel between old and new hardware can be omitted since the capacity of the DCS can be chosen for satisfy the higher computation needs of an integrated implementation of the advanced algorithm also. This is possible nowadays without any remarkable surplus in the DCS price.

Advanced Real-Time Optimization of Power Plants

Existing DCS

s

22

existing controllers

s

new hardware for advanced control algorithm +

+

−

+

+

−

+

I/O channel

existing low level controllers (positioners, e.g.)

+

M

M

a few new measurements, if necessary

. Fig. 22.12 Proposed typical hardware and software configuration for applying advanced control in a power plant originally equipped with a traditional control system. Benefits of the modern control will be utilized while the proven and secure operation of the original control system will be retained. (Thick lines: existing system; thin lines: advanced control extension)

Successful Applications of Advanced Control in Power Plants Applying the latest results of the control theory also in power plants is not only a theoretical possibility! A number of applications are known from the literature; some of them will be introduced in this section. A general, interesting characteristics of these applications is that they serve the ecological goals not only through increasing the plant efficiency (which directly results in energy conservation and reduced total flue gas emission including CO2), but most of them also bring about further environmental benefits. After the literature overview, a case study will be given where not only the basic idea and the results will be shown, but also the complete solution in detail. For those who want to go deeper or want to have a broader overview of advanced control applications in different types of power plants, a recently published book can be proposed [11].

Some Published Applications Ruusunen [12] applied the soft sensor technique on two grate-fired combustors based on solid biomass (wood chips, wood pellets, and fuel peat) of 30 kW and 300 kW thermal capacities. His goal was to compensate the combustion power fluctuations being present

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Advanced Real-Time Optimization of Power Plants

in these small-scale biomass fired boilers due to inhomogeneous fuel quality and unequal feeding capacity. The stabilized and accurate combustion power is namely critical for maintaining low emissions and stable operating conditions. Based on the model-based approach, fuel power changes could be compensated by the controller before they affected the heat output of the boiler, enabling continuous and delay-free monitoring of disturbances. As inputs of the soft sensor, some temperature measurements were used, the locations of which were found to be critical. Operational experiences have shown that through the applied advanced control strategy the standard deviations of the heat output and CO reduced by 40%. Also 25% reduction of CO concentration was measured during the test period, and the fluctuation of the oxygen concentration was reduced by 45% in the same time. The increase in boiler efficiency is also very attractive: 1–2.4% points! Havlena and Pachner [13] reported a successful application of multivariable Model Predictive Control (MPC). Their goal was to improve stability key process variables, effectiveness of limestone use, and boiler combustion efficiency under emission limits. Two circulating fluidized bed (CFB) boilers were originally operated with standard PID control strategy. As the fluidized bed combustion process shows strong interactions between process variables, standard PID control did not fully meet the operational requirements. The boilers are fueled by a mixture of coal and coke, and the nominal steam production is 310 t/h each. A very simple, half-empirical (gray box) model was set up including also the long-term storage characteristics of this combustor type. The bed temperatures were originally manually kept between 860 C and 900 C by the operators. After the introduction of the model-based advanced control technique, these temperatures are automatically maintained with standard deviation below 1 C at a given reference value, which is optimal for in situ SO2 removal. The SO2 emissions, originally only monitored, are now controlled and held within a very narrow band ( Fig. 22.13) according to the principle of the Extremum Seeking Control philosophy [16, 17]. All process variables of the fluidized bed combustor involved in the cost function will be continuously measured, of course. Their actual values will be forwarded to the block that calculates the actual scalar value of the cost function, the minimum of which should be found and set by the remaining elements of the control structure. Its gradient should be estimated in the next block. The space of search is two-dimensional spanned by the manipulated variables V_ P and V_ S , but in practice it often seems to be better to handle to use another space defined by the coordinate transformation V_ A ¼ V_ P þ V_ S ; r ¼ V_ P =V_ A , where V_ A is total air and r is air distribution. In the gradient estimator, a known identification method will be used first. A twodimensional, discrete-time ARX model will be identified online, which standard method delivers the model in the following form: AðqÞ  DyðtÞ ¼ B1 ðqÞ  Du1 ðtÞ þ B2 ðqÞ  Du2 ðtÞ þ eðtÞ;

(22.2)

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Advanced Real-Time Optimization of Power Plants

where q is the time shift operator, y(t) is the process output (which is the K value in the actual case), and Du1 and Du2 are the process inputs (V_ P and V_ S in the actual case). This procedure needs to know also the perturbation signal, which will be defined and added to the inputs by the controller block. The results of the identification procedure are in this case the coefficients of the polynomials A(q), B1(q), and B2(q). The final output of this block (the gradient estimates) can be calculated according to @K B1 ðqÞ ¼ AðqÞ q¼1 @ V_ A

(22.3)

@K B2 ðqÞ ¼ : @r AðqÞ q¼1

(22.4)

The controller block in the proposed control structure (> Fig. 22.13) can be any traditional controller. The set point is zero, and the process variable to be controlled is the estimated gradient delivered by the block described above. In the actual, first implementation of the scheme, a rather simple, conservative control law was built in: the (twodimensional) controller step will be set always proportional to the negative gradient received. A flat sawtooth signal of very low amplitude compared to the effective outputs added to a random binary signal (of low amplitude as well) was chosen as perturbation signal needed for the ARX identification. It is generated within the control block, it is added to the calculated control output, and it is forwarded extra to the ARX identifier located in the gradient estimator block. The load signal of the block is introduced to the controller block for further developments only, as an additional information for learning the optimum values once found. The control strategy was realized in the simulation environment Matlab-Simulink©. The model described above was used throughout the simulation tests, and also for plotting the surface of the cost function over the V_ A
r space. (The surface of this function is not visible for the online controller, of course.) > Fig. 22.14 shows the paths of some simulated searches started from different initial guesses far from the optimum. The results are satisfactory, the controller succeeded in shifting the fluidized bed combustion system close to its optimum in all cases. Based on the current results, further tests of the new control strategy are planned after implementing it on an industrial-sized fluidized bed combustor. The modelbased control development allows also a number of further investigations. The optimal primary and secondary air flows as functions of the actual boiler load were calculated for example, and the resulted functions were rather similar to those found by others experimentally to be the best [18, 19]. Further research will focus on the application of the programmed mathematical model in other model-based control procedures offered by the advanced control theory according to the bulleted list at the beginning of this section.

Advanced Real-Time Optimization of Power Plants

22

94

total air flow, Nm3/s

92 90 88 86 84 82 0.3

0.35 0.4 0.45 0.5 0.55 ratio of primary air to total air flow

0.6

. Fig. 22.14 Trajectories of the extremum seeking control from different starting points

Future Directions Actual trends and successful examples of numerous applications of advanced control techniques in power plants indicate their significant benefits both ecologically and economically. This double positive effect predicts their dissemination in the upcoming years, in spite of their current time lag compared to similar applications in other industry branches. Besides the somewhat higher computational capacities required by these methods, the most significant bottleneck in their dissemination seems to be the lack of technicians familiar with both power engineering and modern control theory. This aspect should be considered in the education already, where besides the theoretical background also the application-oriented issues together with the available controller realizations and software packages should be introduced to the future engineers. All advanced control methods have really good outlooks for successful applications in power plants; however, the model-based ones seem to be more advantageous and prosperous in this area. The explanation is simple: if a controller has more information about the process (e.g., in form of a model), it has better chances for a successful control. This statement explains also the handicap of the traditional PID controller, its whole knowledge about the process is namely only three digits, its three parameters. Model Predictive Control (MPC) is that model-based control technique which has really good inherent properties for its power plant applications and which seems to be the mostly used one. Very good commercial packages are available for its linear version, and theoretical and practical extensions toward strongly nonlinear cases can also be built up. The realization of these methods requires nowadays generally a computational platform outside of the

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Advanced Real-Time Optimization of Power Plants

standard Digital Control System (DCS) of the plant, but in the near future the commercial DCSs will be hopefully equipped with all the hardware and software components required for their integrated realizations. Some steps toward this direction can be observed already at the most significant DCS suppliers worldwide, and this further development will be warmly welcome by those who are interested in the environmental and financial optimization of the energy industry. Regarding the model types to be built into the model-based controllers, gray box models and mathematical models seem to be more advantageous and successful contrary to black box models, because the later types generally do not consider long-term storage effects, which are typical in some combustion processes. But not only because of this significant advantage can be predicted a more intensive dissemination of gray box models and mathematical models in the near future. The needed amount of work of power engineers for setting up such models are namely not so high in the control enhancement project, and their presence is needed by all means because drawing the borders of the multivariable process is a key, and it cannot be done without their technological knowledges.

Nomenclature A(q)

Polynomial in the ARX model

a1. . .a5

Free parameters of the cost function

B1(q)

Polynomial in the two-input ARX model

B2(q)

Polynomial in the two-input ARX model

b1. . .b5

Free parameters of the cost function

cCO mol/m3

Molar concentration of CO in the flue gas

cNO mol/m3

Molar concentration of NO in the flue gas

e

Control error

e(t)

Equation error of the ARX model

K

Cost function

q

Time shift operator

r

Air distribution: ratio of primary air to total air

r

Reference signal (set point)

ts

Time

u V_ A m3/s V_ P m3/s

Total air flow

V_ S m3/s

Control signal (process input) Primary air flow Secondary air flow

y

Controlled variable

yM

Controlled variable modeled

W,T K

Bed temperature

Advanced Real-Time Optimization of Power Plants

22

Acknowledgments The author is grateful to ProcessEng Engineering GmbH, Vienna, Austria, and to Periodica Polytechnika Civil Engineering, Budapest, Hungary, for permitting to use some materials published by the author earlier in [11] and [20].

References 1. Evans W (1954) Control-system dynamics. McGraw-Hill, New York Electrical and electronic engineering series ASIN: B00005XDYG, p 282 2. A˚stro¨m KJ, Ha¨gglund T (1995) PID controllers: theory, design, and tuning. International Society for Measurement and Control, Research Triangle Park, p 343. ISBN 1556175167 3. Datta A, Ho M-T, Bhattacharyya SP (2000) Structure and synthesis of PID controllers. Springer, London, p 233. ISBN 1852336145 4. Visioli A (2006) Practical PID control. Springer, London, p 10. ISBN 1846285852 5. O’Dwyer A (2009) Handbook of PI and PID controller tuning rules. Imperial College Press, London, p 608. ISBN 1848162421 6. Smith CL (2009) Practical process control: tuning and troubleshooting. Wiley-Interscience, Hoboken, p 431. ISBN 0470381930 7. Yu C-C (2006) Autotuning of PID controllers. Springer, London, p 261. ISBN 978-1-84628-036-8 8. Dittmar R, Pfeiffer B-M (2006) Modellbasierte Pra¨diktive Regelung in der industriellen Praxis. Automatisierungstechnik 54(12):590–601 9. Klefenz G (1991) Die Regelung von Dampfkraftwerken. BI-Wiss.-Verl, Mannheim, p 240. ISBN 9783411152841 10. Klefenz G (1986) Automatic control of steam power plants. Bibliographisches Institut, Zu¨rich, p 248. ISBN 9783411016990 11. Szentannai P (ed) (2010) Power plant applications of advanced control techniques. ProcessEng, Vienna, p 500. ISBN 978-3-902655-11-0 12. Ruusunen M (2010) Advanced combustion power stabilization method for a grate-fired biomass boiler. In: Szentannai P (ed) Power plant applications of advanced control techniques. ProcessEng, Vienna, pp 113–134. ISBN 978-3-902655-11-0

13. Havlena V, Pachner D (2010) Model-based predictive control of a circulating fluidized bed combustor. In: Szentannai P (ed) Power plant applications of advanced control techniques. ProcessEng, Vienna, pp 43–67. ISBN 978-3902655-11-0 14. Franke R, Doppelhamer J (2006) Online application of Modelica models in the industrial IT extended automation system 800xA, Modelica 2006, 4–5 Sep 2006. The Modelica Association, pp 293–302 15. Szentannai P Energetics for the environment: modelling of fluidized bed combustion. In: Ge´pe´szet ‘98, proceedings of first conference on mechanical engineering, Technical University of Budapest, 28–29 May 1998. Springer, Hungarica, pp 750–754. ISBN: 963 699 078 6 16. Blackman PF (1962) Extremum-seeking regulators. In: Westcott JH (ed) An exposition of adaptive control. Pergamon, Oxford 17. Zhanga C, Ordo´n˜ez R (2009) Robust and adaptive design of numerical optimizationbased extremum seeking control. Automatica 45:634–646 18. Bunzemeier A (1992) Mathematisches Modell zur regeldynamischen Analyse eines Dampferzeugers mit zirkulierender Wirbelschichtfeuerung. Fortschritt-Bericht VDI, Reihe 6, Nr. 273 19. Edelmann H (1992) Modellierung der Dynamik und des Regelverhaltens fu¨r einen Dampferzeuger mit zirkulierender Wirbelschichtfeuerung. Dissertation Universita¨t GH Siegen. Fortschrittsbericht VDI, Reihe 6, Nr. 275. 20. Szentannai P (2011) Mathematical modeling and model-based optimum control of circulating fluidized bed combustors. Periodica PolytechnicaCivil Engineering, PP-20-1029

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23 Mobile and Area Sources of Greenhouse Gases and Abatement Strategies Waheed Uddin Department of Civil Engineering, University of Mississippi, University, MS, USA Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 778 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 778 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 781 Environmental Sustainability Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 782 Sustainability Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 782 Environment, Energy, and GHG Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 782 Urgent Need for Environmentally Sustainable Transportation Policies . . . . . . . 783 Related Research Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 784 Mobile Sources of GHG Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 784 Mobility Needs and Transportation-Related CO2 Emissions . . . . . . . . . . . . . . . . . . . . . . 784 Transportation and Economic Prosperity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 784 Mobile Sources of GHG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 786 Science Models of CO2 Emissions from Traffic Volume Demand . . . . . . . . . . . . . . . . . 788 Methodology for CO2 Emissions from Vehicle-Mile Traveled . . . . . . . . . . . . . . . . . 788 Energy- and Transportation-Related Global CO2 Emissions . . . . . . . . . . . . . . . . . . 789 Multimodal Transportation and Travel Demand Management . . . . . . . . . . . . . . . . . . . . 790 CO2 Footprint Indicators of Multimodal Travel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 790 Repercussions of Traffic Congestion on Air Pollution and Commuters’ Woes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793 Urban Growth and Travel Demand, and Congestion . . . . . . . . . . . . . . . . . . . . . . . . . . 793 Travel Time Delay Comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794 Health Risks Associated with Transport Patterns, Travel Behavior, and Built Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794 Commuters’ Woes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795 Area- and Built Environment–Related GHG Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 797 Open-Area Sources and Built Environment Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 797 GHG from Open Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 797 Heat-Island Effects in the Built Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 798 Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_23, # Springer Science+Business Media, LLC 2012

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Impacts of Urbanization and Megacities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 799 Historical Overview of Urbanization and Current Trends in Growth of Megacities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 799 Urban Population Density Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 801 Urbanization and Motorization Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 802 Urban Growth and Travel Demand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 802 Geospatial Analysis of Built Environment and Traffic Demand Impacts . . . . . . . . . . 806 GIS Maps of Urbanized Areas, Urban Growth, and Built-Up Areas in the United States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 806 Imagery-Based Geospatial Analysis for Karachi Metropolitan Road Network GIS and Traffic Demand Volume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 808 GHG Abatement Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 809 Sustainable Transport and Traffic Management Solutions . . . . . . . . . . . . . . . . . . . . . . . . . 809 Transport Demand Management and Sustainable Strategies to Reduce CO2 Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 809 Metropolitan Transportation Demand Management . . . . . . . . . . . . . . . . . . . . . . . . . . 810 Smart Growth, Space Planning, and Sustainable Infrastructure . . . . . . . . . . . . . . . . . . . 812 Mixed Land Use and Compact Development to Reduce Cars on Roads in Cities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 812 Multimodal Alternatives for Travel in Cities, Intercity Connectivity, and Regional Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 813 Consumption and Hidden Cost of Petroleum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 813 Alternative Energy and Fuel, Vehicle Innovations, and Nonmotorized Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 814 GIS-Based Decision Support System and Value Engineering . . . . . . . . . . . . . . . . . . . . . . 815 Geospatial Mapping and GIS Decision Support System Examples . . . . . . . . . . . . 815 Value Engineering and Life Cycle Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815 Life Cycle Analysis of Sustainable Transport Solutions and Value Engineering Case Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 817 Monitoring, Targets, and Applicable Laws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 818 Terrestrial Remote Sensing and Space-Based Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . 819 Remote Sensing Monitoring of CO2 and Other Air Pollutants . . . . . . . . . . . . . . . . 819 Spaceborne Remote Sensing for Pollution Monitoring . . . . . . . . . . . . . . . . . . . . . . . . 819 United States and European Initiatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 820 Sustainable Transport Policies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 820 Recent Transport- and GHG-Related Regulations, Policies, and Initiatives in the United States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 821 Global Accords and Developing World Efforts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822 International Climate Change Mitigation Accords . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822 Lack of Multimodal Transport Strategy Consideration by International Lending Institutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 824

Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

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Best Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 825 Unites States Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 825 London, UK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 827 Mexico City . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 828 Sa˜o Paulo, Brazil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 828 Bangkok, Thailand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 829 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 829 Livable Cities and Eco-friendly Lifestyles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 829 Sustainable Accessibility, Mobility, Commuting, and Economic Prosperity . . . . . . 830 Equity and Shared Responsibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831 Passenger and Freight Rail Modal Share . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831 Involving Stakeholders and Public for Sustainable Transport and Mitigation Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 833 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 834

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Abstract: This chapter discusses mobile and area sources of carbon dioxide (CO2) and other Greenhouse Gas (GHG) emissions. The CO2 emissions from mobile sources accounted globally for 23% of world energy-related GHG emissions in 2004. In the United States, the CO2 emissions in 2004 from mobile sources included 28% of all anthropogenic GHG emissions and the missions from mobile sources grew 29% between 1990 and 2004. The CO2 emissions for several megacities, the carbon footprint expressed in CO2, and the CO2 per capita used as a sustainability scale are also reviewed. Traffic congestion and gridlock in most urban areas and cities have grown substantially worse over the years, causing commuters to waste millions of hours in traffic jams. The resulting vehicle emissions have adverse impacts on the environment, both in air quality degradation and increases in GHG. Examples are presented on contributions of built environment and transportation-related air pollution and GHG emissions from mobile sources, cities, and other populated areas. The heat-island effect causes an increase in surface temperature and air temperature in the built-up areas of a city. Urban sprawl and associated transportation-related emissions also tend to increase area temperature. An increase in air temperature results in a higher rate of photochemical reactions that form ground-level ozone and smog during hot summer days. Additionally, it requires extra electricity to cool down buildings in summer days, resulting in increased energy demands, larger air-conditioning bills, and elevated emissions of GHG and ozone precursors. Sustainable multimodal transportation network and urban infrastructure facilities are warranted to support urban communities in view of the demand of energy, reduce public health hazards resulting from air pollution and urban smog, and mitigate adverse impacts of GHG emissions on the environment. Innovative geospatial applications of high-resolution satellite imageries are presented to estimate built-up area and traffic volume. Real-time intelligent transportation system technologies can also improve traffic flow, reduce congestion and air pollution, and decrease GHG emissions. Government agencies and cities worldwide can use CO2 emission per capita sustainability scale for evaluating effectiveness of sustainable transportation and development policies.

Introduction Overview A well-maintained network of transportation infrastructure and an adequate supply of energy are two indispensible pillars of any economy as they support the transport and mobility needs of the public, industries, agriculture and other businesses, and quality of life. The highway network of a country forms the backbone of its transportation infrastructure by providing connectivity needs that allow for the safe and efficient mobility of people and goods. It also represents investments of billions of dollars in every country. > Figure 23.1 illustrates world ranking in road length, and > Fig. 23.2 shows vehicle

Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

23

7 6,430,366 km

258,340 km

368,360 km

388,008 km

1

426,906 km

956,303 km

2

1,183,000 km

3

1,75,1868 km

4

1,870,661 km

3,383,344 km

5

2,394,641 km

Total road length, million km

6

810,641 km

41. Malaysia 98,721 km 73. Thailand 57,403 km 158. Brunei 3,650 km

ni 2 on C hi 3 na Br 4 az Ja il 5 p C an an 6 ad Fr a 7 an c R e8 Au uss st ia 9 ra lia Sp 10 ai n Ita 11 Tu ly 1 rk 2 Sw ey ed 13 U e ni te Po n 1 d la 4 Ki nd ng 1 In dom 5 do So n 16 ut esi h a Af 17 r i P ca Ba akis 18 ng tan la de 19 sh 20

a

U

an

d Eu

ro

pe

te ni U

di

In

St

at

es

1

0

Countries (ranked from high to low road network length)

. Fig. 23.1 World ranking in road length

Automobile registration for selected countries, 1990 & 2002 Automobile registrations (thousands)

140,000 1990 120,000

2002

Total = Total 222 million vehicles in 2002 Source: Oak Ridge National Laboratory

100,000 80,000 60,000 40,000 20,000 0

U.S.A.

Japan

Germany

. Fig. 23.2 Car ownership trends in selected countries

France

U.K.

Canada

India

China

779

780

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Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

stocks of selected countries [1]. The United States (US) leads the world in automobile ownership with approximately 137 million registered cars as of 2008 that is 0.74% up from 136 million cars in 2007 [2, 3]. The proportion of cars in the vehicle fleet is much higher in the United States compared to most industrialized and developing countries. Approximately 25% of all world petroleum produced, which is a primary source of carbon emissions, is consumed in the United States [4]. About 66.5% of this is used by the transportation sector in the United States to provide safe and efficient mobility. As of 2007, the transportation sector includes over 254 million road transport vehicles which comprise of 93.3% cars and other automobiles, 2.8% motorcycles, 0.3% buses, and 3.6% trucks [3]. However, trucks travel almost twice as much as cars per vehicle per year and consume 3.5 times more fuel than cars per vehicle. Travel demand has been increasing consistently in the United States since the construction of the Interstate highway system causing congestion, gridlock, air pollution, GHG emissions, and physical deterioration of pavements from the higher proportion of truck traffic on the national highway system [5–8]. Additionally, aircraft, trains, and ships provide vital links in the transportation infrastructure network of the United States. In 2009, 704 million passengers were enplaned on US airlines domestically and internationally, which is expected to reach one billion passengers a year by 2023 [9]. Worldwide, 2.4 billion passengers are expected to depart on scheduled airline flights in 2010, compared to 2.1 billion passengers reported in 2006 [10, 11]. Growth in urban areas and cities [12] contributes to area and mobile GHG emissions resulting from consumption by buildings, industries, and roads [7, 13]. According to the IPCC report, 33 billion tons of anthropogenic CO2 are emitted annually, 7.3 billion tons absorbed by the ocean, 7.3 billions of tons absorbed by the forests, and 18.3 billon tons accumulated in atmosphere [14]. The industrialized countries contain 20% of the population and produce 46% of the greenhouse gases. Anthropogenic carbon emissions from transportation and populated areas are estimated to be 77% globally [14], in addition to the industrial emission from coal- and fossil fuel– based power-generating plants and industries. The CO2 emissions from mobile transportation sources accounted globally for 23% of world energy-related GHG emissions in 2004 and 28% in the United States. Between 1990 and 2007, the US inventory of anthropogenic GHG emission includes electricity, transportation, industrial, agriculture, and residential and commercial sectors (> Fig. 23.3). The transportation sector accounts for 28% of all anthropogenic GHG emissions in the United States, trailing the electricity sector at 34% [7]. Over 600 coal fire–powered plants contribute to electricity generation and GHG emissions in the United States, and coal remains the source of 50–70% of electricity in UK, India, and China. Worldwide, the number of vehicles has grown tenfold since 1950, and the present number is estimated to be about 630 million vehicles. Worldwide, vehicle inventory will continue increasing sharply as the world population migrates to urban areas, energy demand grows, and air quality degrades in cities [15–20].

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Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

40 34

35

GHG emissions, %

30

28

25 20

20 15

11 10

7

5 0 Electricity

Transportation

Industrial

Agriculture

Residential & commercial

. Fig. 23.3 Inventory of U.S. greenhouse gas emissions

Travel demands over the past 2 decades already surpassed capacity limits of the road infrastructure, not only in the United States, but also in most urban areas worldwide. This growth in travel demand and congestion directly contributes to increases in air pollution and greenhouse gases, mobility costs, user operation costs, public health costs, and other societal costs. The resulting vehicle emissions and demand on energy (due to the increased built areas and population migration from rural areas) have had adverse impacts on the environment, both in air quality degradation and increases in GHG [19–33]. The GHG emissions are well known contributors to global warming, rising sea levels and temperatures, and climate change mechanisms. This chapter focuses on traditional uses of petroleum-based gasoline and diesel which fuel the transportation sectors.

Objectives The objectives are to: 1. Review the current and future trends of emission contributions from transportation and area sources, including built-up urbanized areas and their adverse impacts on global warming and climate change indicators, ground-level air quality, and public health. 2. Discuss abatement strategies for greenhouse gas emissions by implementing sustainable transport and traffic management, smart growth and mixed use urban planning, mass transit multimodal solutions, alternative fuel, and vehicle fuel efficiency technologies.

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Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

3. Present best practices and use of geospatial analysis, life cycle costs and benefits, and value engineering to evaluate effectiveness of abatement strategies for sustainable transportation infrastructure and urban growth to reduce their contributions of air pollution and greenhouse gases.

Environmental Sustainability Challenges Sustainability Definition Sustainability has been defined in different variations. The following definition is used in this chapter: ‘‘to meet the current needs without depleting natural resources and compromising the ability of future generations to meet their own needs for sustaining a comfortable quality of life.’’ A ‘‘sustainability scale’’ is defined as carbon footprint in terms of carbon dioxide per capita. Sustainable transportation and development policies strive to minimize adverse impacts on the environment while conserving natural resources.

Environment, Energy, and GHG Emissions Environment and energy are greatly impacted by transportation system planning and operation, urban growth and land-use practices, and travel modes available to and used by the population. After the Clean Air Act of 1970, the EPA’s federal environmental regulations and vehicle technology innovations (such as catalytic converter) in the United States have resulted in the removal of lead from the fuel and vehicle emissions [21]. Other vehicle emissions affect the ground-level air quality and greenhouse gases. This creates significant changes in the ecocycle involving water, oxygen, and carbon dioxide; all essential in sustaining human, animal, and plant life. The following six criteria pollutants have been recognized as the most damaging to the public health and the environment for which the US EPA established National Ambient Air Quality Standards (NAAQS) [21, 34]: ground-level Ozone (O3), Carbon Monoxide (CO), Oxides of Nitrogen (NOx), Sulfur Dioxide (SO2), Particulate Matter (PM10 and PM2.5), and Lead (Pb). The notation PM10 is used to describe particles of aerodynamic diameter 10 mm or less and PM2.5 represents particles of aerodynamic diameter 2.5 mm or less. Ground-level O3 is formed through photochemical reaction of Nitrogen Dioxide (NO2) and Volatile Organic Compounds (VOC) in the presence of sunlight, which are produced by petroleum-fueled vehicles. Methane (CH4) is a species among VOC. Carbon Dioxide (CO2) emissions are directly proportional to fuel consumption. Nitrous Oxide (N2O) and VOC emissions are affected by vehicle emission control technologies for motorized vehicles on roads. The three pollutants (CO2, CH4, N2O), not specifically regulated in the United States, are the principal ‘‘greenhouse gases’’ which,

Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

23

through increased concentrations in the atmosphere, can contribute to global warming and associated climate change on global and regional scales. NOx and CO (predominantly vehicle emissions) also contribute to greenhouse warming [34]. In principle, all molecules having two or more atoms can contribute to greenhouse warming due to their absorption of light in the infrared region. CO is a short-lived species in the atmosphere and therefore cannot contribute much. NOx role is not all bad. NO induces OH radical in the stratosphere, which, in turn, breaks down CH4 – a GHG with a stronger warming force. The overall uncertainty in CH4 and N2O emission estimates for the US inventory of mobile sources of GHG emissions is relatively minor due to the fact that these emissions are a small part of total highway vehicle GHG emissions. The significance of uncertainty in non-road vehicle modes (such as snow mobiles, off-road tractors and desert vehicles, lawn mowers, etc.) is low given the relatively small quantity of GHG released by these sources [34].

Urgent Need for Environmentally Sustainable Transportation Policies The travel demand on the road infrastructure network in the United States has increased more than its capacity. Consequently, emissions from mobile sources grew 29% between 1990 and 2004 [35]. Commuters waste millions of hours and gallons of fuel in traffic congestion. Each year, about 20 million barrels of diesel fuel are consumed by idling long haul trucks in the United States, which produce about 10 million tons of carbon emissions [36]. Additionally, residential emissions have increased 13% in the last 2 decades. Both ground transportation and aviation emissions are adversely affecting the global atmosphere more than coal burning plants. They will have greater impacts in coming years due to the expected exponential growth of vehicle and aviation transport worldwide, and especially in the emerging economies. The emerging economies of China, India, and Brazil are all following the path of the United States and other industrialized nations in developing transportation infrastructure assets, increasing their transportation fleet, and accelerating carbon emissions. As reviewed in later sections, the rapid urban growth in developing countries and increase in the number of cities with five million inhabitants or more is expected to grow from 40 in 2001 to 58 in 2015. This growth in transport vehicles and urbanized areas will result in a higher energy demand and greater GHG emissions. A 50% rise in energy use and carbon emissions is expected worldwide by the year 2030 [37]. Therefore, mobile sources of CO2 emissions will remain significant contributors to the release of greenhouse gases and its transport into the upper atmosphere. There is an urgent need to improve assessment of contributing factors and find practical and costeffective solutions. This will help to evaluate the benefits and economic costs of alternative abatement strategies before making major decisions on regional and global levels for an effective mitigation approach.

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Related Research Sources This chapter summarizes an up-to-date literature review of the Internet sources, published papers and reports, news articles, as well as research studies undertaken by the author. The resources referenced and used include: ● Federal agencies in the United States, European agencies, and other International organizations [1–20, 37], including: – US Department of Transportation (USDOT), Federal Highway Administration (FHWA), Federal Aviation Administration (FAA), Oak Ridge National Laboratory (ORNL), Environmental Protection Agency (EPA), U.S. Energy Information Administration (EIA) of Department of Energy (DOE), U.S. Geological Survey (USGS), General Accounting Office (GAO), and Transportation Research Board (TRB) reports of the National Academies. – International Airlines Transport Association (IATA), International Energy Agency (IEA), Intergovernmental Panel on Climate Change (IPCC), Organization of Economic Cooperation and Development (OECD), United Nations Environment Programme (UNEP), United Nations Population Fund (UNPF), World Business Council for Sustainable Development (WBCSD), and World Health Organization (WHO). ● Funded and graduate research studies conducted by the author at the Center for Advanced Infrastructure Technology (CAIT), University of Mississippi since 1999, for air quality modeling and GHG analysis, terrestrial and spaceborne remote sensing, geospatial analysis, and built-up area and traffic attribute extraction from imagery [20–33]. ● Published books, papers, reports, news stories, and web documents, as referenced in the following sections.

Mobile Sources of GHG Emissions Mobility Needs and Transportation-Related CO2 Emissions Transportation and Economic Prosperity Having ‘‘Efficient public mobility’’ and ‘‘safe and secure transportation infrastructure assets’’ are imperative for mobility needs, distribution of resources and goods through intermodal facilities, assistance to communities during disasters and emergencies, and other services to society. The economic prosperity of a country is strongly associated with the relative size and physical condition of its road network, which is the most important component of its transportation infrastructure according to a World Bank’s study [38]. The study reports that the road infrastructure asset inventory shows high positive correlation with the gross national product (GNP) per capita of a country. The GNP

23

Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

per capita reflects a country’s total market value of the goods and services produced annually divided by the population. High paved-road density values in km per million inhabitants [22, 39] are reported for industrialized countries (> Fig. 23.4). Comparatively, low values of this important economic development indicator are observed in developing countries. However, China’s expressways and highways will exceed most other developed countries within the next decade due to accelerated construction programs. India, Brazil, and several other countries are also expanding their road and highway networks to provide connectivity to a larger number of their populated areas and serve the mobility needs of the public, agriculture, and industries. The World Bank’s use of only paved-road density for correlation with economic prosperity indicator is misleading because it ignores other transport infrastructure assets of a country such as rail and water transport. Rail infrastructure represents a significant modal share in Europe and most developing countries for serving passenger and freight travel demands. Regardless of a region’s characteristics such as culture, income, or geography, people on average spend a significant amount of time traveling on the road and/or wasting fuel on congested roadways. People in less developed regions spend a great deal of their time traveling to and from destinations due to lack of transportation facilities and/or urbanization, while people in more developed countries such as Japan, Western Europe, and the United States spend half of their time in leisurely travel and the other half in route [40]. The US automobile ownership in terms of persons per motor vehicle is estimated at 1.27 persons per car considering 235.9 million registered automobiles in 2007 which include cars, vans, pickup truck, sports utility vehicle (SUV). Brazil has 48 million vehicles

18,000

Paved road density, km/million pop USA

16,000

Central & Eastern Europe

14,000 12,000

EU

10,000

Afghanistan

Japan

8,000 6,000

Pakistan

Tajikistan Turkey

4,000

India

2,000

Iran Brazil China

an

gh an

is t

hi

na

1.3 b 26.8 m

Af

C

Br az

il

66.1 m 175 m

Ira n

a In di

Tu rk ey Pa ki st an

ta n is

1b

C

&

Ta jik

ro pe Eu

EU

128 m 6.6 m 66.5 m 145 m

E

U

SA

0 Population 290 m

Ja pa n

Paved road density, km/million inhabitants

20,000

Countries

. Fig. 23.4 Comparison of paved road density of industrialized and developing countries, 2001

785

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Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

as of 2006 and a population of 175 million that translates to 3.6 persons per vehicle. The 2008 automobile ownership rate (total number of motor vehicles per 1,000 population) of 842 in the United States is higher compared to other countries, such as Brazil’s rate of 156 motor vehicles per 1,000 population as of 2009. Vehicle mix indicates the utilization of different modes on roads. Traffic demand can also largely impact air quality, public health, and public safety on society as well. Accurate and timely collections of traffic attributes are necessary for traffic management, performance evaluation of transportation systems, and measuring emission inventory.

Mobile Sources of GHG > Figure 23.5 shows the US Greenhouse gas emissions from all mobile sources, by travel mode and vehicle type between 1990 and 2004 [7]. > Figure 23.6 shows the US transportation emissions by transport mode. Aviation produced about 9% of transportation GHG emissions in 2003, the largest source of non-road transportation GHG emissions. In total, aircraft GHG emissions decreased about 3% from 1990 to 2003. Following a substantial decline in travel after the terrorist attacks of September 11, 2001, in the United States, passenger travel rose more rapidly than the GHG emissions due to higher number of seats occupied. Aircraft emissions have risen due to increased passenger travel and freight activities, but this has been offset by the improved fuel efficiency of aircraft and their operations. Between 1990 and 2003, passenger-miles traveled on domestic services increased by 48%, from 345.9 to 505.2 billion passenger miles. This is higher than 31% increase in light-duty vehicle passenger-miles over the same period [8]. The United States

800 Cars GHG emissions (Tg CO2 Eq.)

786

Light trucks

600

Other highway Aircraft 400 Marine Locomotives 200

Mobile air conditioners and refrigerated transportation Other

0 1990

1995

2000

2001

2002

2003

2004

Year

. Fig. 23.5 U.S. greenhouse gas emissions from all mobile sources, by travel mode and vehicle

Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

Locomotives 3%

Motorcycles, pipelines and lubricants 2%

23

Mobile AC and refrigerated transport 2%

Ships and boats 3% Aircraft 9%

Passenger cars 34%

Heavy-duty vehicles 19%

Light-duty trucks 28%

. Fig. 23.6 U.S. Transportation-related GHG emissions, 2004

accounts for approximately 40% of all commercial aviation and 50% of all general aviation activity in the world [41]. The US airlines carried 20.4% more passengers and cargo traffic in 2007 compared to that in 2000, but they used 3% less fuel in doing so. This resulted in a reduction of 5.1 million tons of CO2 emissions in 2007 compared to that in 2000, and the FAA’s satellite-based Next Generation Air Transportation System (NextGen) is expected to increase efficiency and further reduce the aviation GHG emission [42]. Therefore, the main concern of mobile GHG emission is from on-road vehicles which make up 81% of transportation-related emissions. In the last 3 decades, the total number of vehicle-miles driven rose to 2.9 trillion miles per year, four times faster than the rate of population growth of the United States. Per capita vehicle-miles traveled (VMT) in 2003 was 9,941. This indicates that vehicle fuel efficiency and improvements in emission control may be offset by increased VMT in the United States [42]. The VMT distribution by vehicle on roads is plotted in > Fig. 23.7 [4]. The vehicle-mile travel proportions of 58.1% by automobiles and 36.5% by trucks show a significant amount of freight by roads at 3.46 times less fuel efficiency. Older model vehicles and absence of effective vehicle emission regulations and testing will yield higher amounts of emissions. Not all states in the United States have emission testing programs (such as Mississippi), but the manufacturers strictly follow federal emission and fuel efficiency regulations in all states. In many countries where there are no stringent emission regulations and/or no effective enforcement control, older model and relatively aged vehicles are used to make more trips and pollute roads more with both GHG and other pollutants. This was the case in China where, in the 1990s, most automobiles, including cars and trucks, were still using 10–20 years old technologies and polluting urban areas with more than ten times emissions compared to the United States

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Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

Combination trucks, 4.9% Buses, 0.2% Other single-unit trucks, 2.7%

Single-unit 2axle 6-tire or more and combination trucks, 226,963, 8%

Motor cycles, 13,612, 0%

Buses, 6,976, 0%

Passenger cars and other 2axle 4-tire vehicles, 2,782,271, 92%

Two-axle, four-tire trucks, 33.8% Automobiles, 58.1%

All motor vehicles miles traveled : 3,029,822 million miles in 2007

Motorcycles, 0.3% Automobiles

Other single-unit trucks

Motorcycles

Combination trucks

Two-axle, four-tire trucks

Buses

. Fig. 23.7 Vehicle fleet mix distribution (left) and VMT distribution (right) in the United States

and Japan. In view of rapidly growing economy and vehicle fleet, China has already embarked upon a national program to implement lead-free fuel, fuel economy requirements, and emission standards to reduce vehicular emission. Old vehicle technology is still common in many other cities of developing countries. Reportedly, some 70% of 18 million people in Kolkata (formerly known as Calcutta) in India suffer from respiratory disorders caused by air pollution [43].

Science Models of CO2 Emissions from Traffic Volume Demand Methodology for CO2 Emissions from Vehicle-Mile Traveled The CO2 emission problem inherent to the mobile transportation originates from the burning of petroleum-derived fuel (gasoline and diesel) for power. The burning of petroleum and natural gas fuel primarily emits CO2 which represents 82% of total U.S. anthropogenic GHG emissions [37]. The GHG emission inventory data are reported in units of tons of carbon dioxide equivalent (CO2e), which allows emissions of greenhouse gases of different heat trapping potential to be combined for a direct comparison of different GHG emission inventory. In the United States, 28% of all GHG emissions are from transportation sector as shown in > Fig. 23.3 [7]. Other criteria emissions contribute greatly to pollute ground-level air and cause smog, ozone, cancer, lung disease, and respiratory disease. The following methodology is used by the US EPA to estimate CO2 emission from vehicles-miles traveled data [44]. Assumptions: ● CO2 emissions from a gallon of gasoline = 19.4 lbs (assuming 99% of carbon is eventually oxidized)

Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

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● CO2 emissions from a gallon of diesel fuel = 22.2 lbs (assuming 99% of carbon is eventually oxidized) ● Average fuel efficiency for gasoline passenger car = 20.3 miles per gallon (mpg) ● Average fuel efficiency for diesel truck = 5.9 mpg ● Typical vehicle travel (cars, vans, light trucks combined) = 12,000 miles per year CO2 Emissions: fðnumber of miles driven per yearÞ=average vehicle fuel efficiency g pounds of CO2 emitted per gallon

(23.1)

Example: CO2 Emissions for passenger vehicle ¼ f12;000=20:3g  19:4 ¼ 11; 468 lbs ¼ 5:7 tons per year per passenger vehicle CO2 Emissions for diesel truck ¼ f12;000=5:9g  22:2 ¼ 45; 153 lbs ¼ 22:6 tons per year per truck This example shows that due to very low fuel efficiency, diesel trucks produce four times more CO2 in comparison to typical cars. Natural gas accounted for 28.5% of fossil energy use in 2008 but only 21.4% of total energy-related CO2 emissions in the United States [45]. Carbon intensity of natural gas is 55% of the carbon intensity of coal and 75% of the carbon intensity for petroleum. Therefore, a hybrid vehicle operating on mostly compressed natural gas (CNG) and liquid natural gas (LNG) may be assumed to emit 75% of the CO2 emission calculated for petroleum fuel using > Eq. 23.1. These types of hybrid vehicles are common in several countries, including Brazil and Pakistan [29], but the CNG and LNG consumption accounted for only 6.9% transportation share of energy consumption in the United States in 2003 [4].

Energy- and Transportation-Related Global CO2 Emissions Recent Department of Energy (DOE) data of the 2008 US inventory of anthropogenic GHG emission shows seven billion metric tons CO2e. This includes 5,814 million metric tons energy related emissions of which 40.6% is for electric power generation, 33.1% transportation related emission, and 26.3% produced by residential buildings, commercial sources, and industries [45]. About 25% of all world petroleum produced was consumed in the United States. About 66.5% of this was used by the transportation sector in the United States, as shown in > Fig. 23.8 [46]. Consumption of fossil fuel produces CO2 that is distributed by source in the United States as: 42% from petroleum, 37% from coal, and 21% from natural gas. The 1990 data from OECD countries shows that highways account for 94% air pollution from all transportation modes. About 81% of GHG emission comes from on-road vehicles, as shown in > Fig. 23.6 for 2004 emission

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Year 2002 Electric utilities 2.2%

Industrial 25.1%

Transportation Residential

Commercial 1.9%

Transportation 66.5%

Residential 4.4%

Commercial Industrial Electric utilities

Total consumption of petroleum = 19.74 million barrels per day

. Fig. 23.8 Distribution of annual consumption of petroleum fuel by sectors

inventory in the United States [46]. The United States, in turn, was responsible for 20% of energy related CO2 emissions worldwide in 2006, though the country accounts for only 5% of the world’s population. In comparison, China’s share of global energy related CO2 emissions was 21%, which is projected to grow to 29% in 2030, and China accounts for 51% of the projected increase worldwide during this period, followed by India with 7% projected increase [45].

Multimodal Transportation and Travel Demand Management CO2 Footprint Indicators of Multimodal Travel It is useful to compare CO2 emissions for vehicle distance traveled per person and freight distance traveled per ton to assess their impacts on the sustainability scale. Transportation accounts for 23% of all global CO2 emissions and > Fig. 23.9 shows the CO2 footprint (grams per passenger per km) contributed by each travel mode for one person to travel 1 km [18, 47]. Clearly, aviation and passenger car travelers are the most polluting modes of transportation and rail/train is one of the lowest polluting at one-third CO2 footprint emission. This shows that public bus and other mass transit modes will reduce emissions significantly in urban areas and cities. In 2005, public transportation (transit buses, mass transit rail) reduced carbon emission by 6.9 million metric tons and avoided 400,000 t of other GHG emissions in the United States [35]. The CO2 footprint emission

Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

CO2, Grams per kilometer per passenger

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130.2 124.5

27% increase in CO2 from 1990–2004

120 100 83 80 66.8 60 45.6

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oa C

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e

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. Fig. 23.9 Production of CO2 emission by transport mode

of freight truck travel per ton-km will be several times larger than that by freight train considering that: ● A diesel truck’s fuel efficiency is poor at 9.4 km (5.9 miles) per gallon, and on the average a truck travels approximately 40,000 km (25,000 miles) annually, about twice that of an average car travel. ● Truck CO2 footprint emission is estimated at 25 g per ton-km of freight travel by road assuming an average 20 metric tons of freight per truck per km at above fuel efficiency. ● Rail CO2 footprint emission is estimated at 5–10 g per ton-km of freight travel by rail/ train. However, the actual emission by rail/train will be even less because trains are able to carry several times more freight than a truck and it would be more economical than a freight truck. Traffic gridlock and delays on roads and highways further deteriorate air quality by producing excess vehicle emissions. Additionally, road user time is wasted at slower speeds in congested hours of travel. Unlike road vehicles, a dual-track rail infrastructure keeps trains moving at designated speeds safely, efficiently, and free of ‘‘gridlock’’ eliminating unnecessary emissions. > Figure 23.10 shows the growth trends in passenger and freight travel demands during 1970–2000 in the United States. An indication of the deficit between travel demand and capacity is the congestion, which is measured in terms of traffic density or travel time. The GAO stated that the US interstate highways have become more congested than other similar roads [5] and that metropolitan areas are reportedly

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792 Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

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having problems with congestion and degraded air quality [6]. The overall density of traffic on Interstate highway system has increased 31.7% over the past decade. More recent US studies on changes in mobility patterns, driving in the built environment, federal guidelines, and states’ efforts [48–51] indicate that CO2 footprints and GHG emissions are being used as one of the key performance indicators of urban and regional traffic management and transportation infrastructure asset management.

Repercussions of Traffic Congestion on Air Pollution and Commuters’ Woes Urban Growth and Travel Demand, and Congestion As of 2008, for the first time in history, more than half of the world’s population lives in towns and cities, as reported by the United Nations [15]. Urbanization is very high in industrialized and developed countries, where as of 2000, 75% of the population lives in urban areas. The urban growth during the last 5 decades has increased travel demand more than the infrastructure supply, resulting in frequent traffic jams and long peak hours. As reported in TIMES, the term gridlock apparently originated in New York City during a transit workers’ strike in 1980, when a surge of commuter autos paralyzed Manhattan’s street grid [52]. American workers are frequently caught in traffic because commuting patterns have changed drastically in recent decades. > Figure 23.11 shows that road bottlenecks and traffic incidents contribute 65% to congestion [31]. It is estimated that commuters spend millions of hours annually stuck in traffic congestion, and waste billion gallons of gas. In 2003, the US commuters suffered 43.8 million total person-hours delay in urbanized areas at an average 25 h delay per person and resulting in 15 gal of fuel wasted per person [4, 31, 53]. This increment in congestion

Special events Poor signal timing 5% 5%

Bad weather

Work zones

15%

40%

10%

25% Traffic incidents

. Fig. 23.11 Causes of traffic congestion (from U.S. data)

Bottlenecks

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Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

directly affects the increase in air pollution and greenhouse gases, mobility costs, user operating costs, public health costs, discomfort and stress, and other societal costs.

Travel Time Delay Comparisons The Travel Time Index (TTI) is another indication of traffic congestion used in the United States to compare travel time delays in several urbanized areas [53]. It is the ratio of peak period travel time during congested condition to free flow travel time for a given road section. A TTI of 1.3, for example, indicates a 20-min free-flow trip will take 26 min during the peak travel time periods, a 6-min (30%) travel time penalty. > Figure 23.12 illustrates the trend of average TTI for urbanized areas in the United States for the time period 1995– 2004. While it depicts that the TTI is on a rise for the period of data shown it was below 1.40. The TTI has increased 12% in the last decade in urbanized areas in the United States. This number is higher approaching 2.0 or more, for some cities such as Los Angeles and New York. The TTI value estimated in 2007 for Karachi, Pakistan, was of the order of 3.5– 4.0 during several hours of peak travel. This high ratio indicated undesirable congestion and provided basis to study traffic congestion in Karachi. Strategies were recommended using geographical information system (GIS) and Intelligent Transportation System (ITS) technologies to enhance traffic management as discussed later in > section ‘‘Geospatial Analysis of Built Environment and Traffic Demand Impacts’’ [54].

Health Risks Associated with Transport Patterns, Travel Behavior, and Built Environment Besides other environmental hazards, built environment and transport-related emissions pose serious health risks to cities in developed countries and the majority of cities in developing countries. In the United States [49, 51, 55, 56] and Europe [57, 58], U.S. average travel time index for all urbanized areas, 1995–2004 1.40 Average travel time index

794

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1.35 1.3 1.30

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. Fig. 23.12 Increased congestion trend in urban areas of the United States, indicated by average TTI

Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

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transport-related health and environment risks have been a major focus of research and transport policy formulation. However, in many developing countries, transport-related health risks have not received attention and priority for investment and policy actions [4, 57]. Important health risks and public health hazards due to transport and travel patterns include the following [22, 24, 29, 31, 56–58]: ● Public Health Hazards from Urban Air Pollution: Increased exposure to air pollution is associated with higher rates of cardiovascular and respiratory diseases, asthma, and other diseases, which are estimated to kill nearly one million people each year worldwide. ● Traffic Fatalities and Injuries: Road transport is responsible for another estimated 1.2 million deaths and 50 million injuries; pedestrians and cyclists are among the groups most at risk. A significant proportion of injuries in developing countries is related to the lack of safe space for bike/motorcycle and nonmotorized transport. ● Health Risks Due to Physical Inactivity : Motorization and built environment are driving force in lifestyles which lack physical activity, especially in the United States and other car-culture countries where urban sprawl requires many more trips. Physical inactivity is a risk factor for cardiovascular diseases, cancers of the breast, colon and rectum, and diabetes mellitus. Globally, the lack of or insufficient routine physical activity is reported to cause an estimated 3.2 million deaths annually. Additionally, the urban sprawl type land use favors car owners and promotes poverty and social inequalities [22, 31]. Over the past 2 decades, even as many developed cities have been rediscovering the health and environmental benefits of walking and cycling, nonmotorized travel is in decline in many cities of developing countries [57].

Commuters’ Woes Commuters stuck in long traffic jams lose patience and drive under stress. The 2010 report on IBM Global Commuter Pain Study surveyed 8,192 motorists in 20 cities on six continents to better understand consumer thinking toward traffic congestion crisis and environmental concerns related to higher levels of auto emissions [59]. The study Index gauges physical, emotional, and economic toll that everyday traffic has on commuters based on the following ten issues: (1) commuting time, (2) time stuck in traffic, (3) price of gas already too high, (4) traffic gotten worse, (5) start–stop traffic problem, (6) driving causing stress, (7) driving causing anger, (8) traffic affecting work, (9) driving stopped due to bad traffic, and (10) decision not to make trip due to traffic. The study’s Pain Index ranks each city on a scale of 1–100, with 100 being the most onerous, as shown in > Fig. 23.13. The following highlights of the study provide useful insight into traveler’s perception and evaluation of the transport and traffic management in their respective cities: ● Overall traffic has gotten worse in the past 3 years according to the 67% majority. ● Eight cities scoring 50 or more ranked as having horrible (worse) traffic, with Beijing and Mexico City topping the list of worst traffic and only Milan from Europe included in the list.

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Results of IBM pain study 2010 120 100

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0 B M eij e i Jo xic ng ha o C nn ity es bu M rg os Ne co w w Sa Del o hi Pa ul o Bu en Mila os n Ai re M s ad r Lo id nd on Pa T ris Am oro nt s o Lo terd s am An ge le s Be r M lin on Ne trea l w Y Ho ork M usto el bo n St urn e oc kh ol m

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Surveyed cities

. Fig. 23.13 Result of Pain Index summarized from 2010 IBM global commuter pain study

● Twelve other cities with bearable (better) traffic are in North America, Europe, and Australia with scores of less than 50, and the best two cities being Melbourne and Stockholm. ● While over 90% of the respondents in New York and Los Angeles reported driving to work, only 32% reported so in Paris, 34% in Amsterdam and Buenos Aires, and 37% in Milan. ● After driving, the most popular form of transportation was bus – at 12%. The two cities with the most painful commutes, Beijing and Mexico City, have 44% and 32% commuters using bus, respectively. (Traffic in these cities would be more horrible if so many people did not travel by bus.) ● The perception of worsening traffic stemmed in large part from being stuck in traffic for significant lengths of time. This was indicated by 87% of the respondents who were stuck in roadway traffic during the last 3 years. ● The average delay due to traffic congestion was 1 h for the surveyed cities worldwide – very similar to the figure for the United States alone in the previous two Commuter Pain surveys conducted by IBM. (Note: This number is not directly comparable to the delay hours stated in > section ‘‘Repercussions of Traffic Congestion on Air Pollution and Commuters’ Woes’’ for U.S. urbanized areas.) ● Responding to the harmful effects of traffic on the health of commuters in any way, 57% said yes. Among those respondents, increased stress (30%) and anger (27%) were the primary manifestations. Increased stress was most prominent in Mexico City (56%), Sa˜o Paolo (55%), New Delhi (45%), Buenos Aires (44%), and Beijing (40%), while anger prevailed in Beijing (53%), Moscow (51%), New Delhi (48%), and Mexico City (43%). All of these cities were among those identified in the survey as having especially ‘‘painful’’ commutes.

Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

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The above insights from the commuter’s survey in large cities are useful considering that cities are driving engines of a country and predicted to grow further and contribute more GHG emissions [60], as noted below: ● Seventy-eight percent of all CO2 emissions originate in cities (including mobile sources and built up areas). ● Eighty percent of economic growth is predicted in cities in emerging industrialized and developing countries. ● Sixty-six percent of population will be in cities by 2030 with 350 million more urban dwellers in China and India.

Area- and Built Environment–Related GHG Sources Open-Area Sources and Built Environment Effects GHG from Open Areas Open-area sources of GHG emissions include (predominantly CO2 except where noted different): ● Petroleum fuel–related emissions during extraction, shipment, refining, storage, and distribution ● Industrial emissions (manufacturing, factories producing steel and other metals) ● Construction material production (cement, asphalt mix, plastics) ● Fires from industrial and commercial incidents (e.g., the oil well fire of 2010 in the Gulf of Mexico) ● Forest fires due to heat and dry spells which is increasingly caused by climatic changes but also blamed on clearing forest land for agriculture and development purposes ● Open burning of solid waste (commonly seen around most cities in developing countries whereas some industrialized countries use for energy production such as incinerators used in Denmark for heating homes in winter) ● Portable electric generators running on gasoline (again a common scene in many developing countries) ● Wastewater treatment areas and solid waste landfill (primarily emitting methane) ● Livestock (methane emissions) and manure management practices (methane and N2O emissions) ● Agriculture land sources (N2O emissions from agricultural soils and methane emissions from rice cultivation) ● Deforestation (carbon stock loss) and land-use management (soil carbon pool changes) The IPCC report [61] provides further information on GHG inventory associated with wastewater and solid waste, manure management, agriculture, forest

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(including deforestation), and land-use changes. No further discussion is undertaken on the contribution of these open sources since the focus here is on mobile and built area sources of GHG emissions.

Heat-Island Effects in the Built Environment For the first time in history, more than half of the world’s population lives in towns, cities, and megacities. Towns are generally located in rural areas and smaller than a city in population. Cities are human settlements with a typical population of as small as a few thousand to several million. On the other hand, a city is called a megacity if it is inhabited by ten million people or more. A major detrimental effect of urbanization is runoff from rapid urban growth and constructed impervious surfaces that continues to degrade coastal and inland waters. Buildings use 36% of total energy, consume 65% of electricity, and produce 30% of greenhouse gas emissions in the United States [13]. These concerns must be addressed in the design and management of urban growth and cities. In most rural environments, people live amidst moderately abundant vegetation, but in most urban environments, trees are removed and vegetation is relatively sparse. Vegetation cover has a profound influence on solar energy flux because vegetation absorbs radiation in the most energetic infrared part of the solar spectrum to use in photosynthesis [62]. The unused fraction of the incoming solar energy is either transpired with water or reflected at near-infrared wavelengths. Most materials used in the built-up areas absorb a significant fraction of this incoming solar energy and reradiate it as sensible heat [62, 63]. Man-made dark constructed surfaces, such as buildings, concrete, and asphalt, absorb more heat from sunlight in comparison to other natural surfaces (soils, grass, trees, and water bodies). This is due to the low solar reflectivity of dark surfaces or albedo (the ratio of the amount of light reflected from a material to the amount of light incident on the material). These low albedo surfaces can raise the local ambient air temperature in an area by as much as 8 F (4 C) over the surrounding areas [64, 65]. This phenomenon is known as the ‘‘heatisland’’ effect. A growing percentage of the population lives in urban areas where this heat-island effect is more pronounced and induces physical stress, loss of productivity, and even death during heat waves. The heat-island effect has been observed even in smaller towns and on hot summer days, the surface temperature of the constructed surfaces (asphalt, concrete, buildings) during the hottest hours can be significantly higher than the daily maximum air temperature depending on solar radiation, clouds, and wind speed. Using 1-m satellite imagery to classify surfaces and conducting thermal analysis [66], a surface temperature map of Oxford, Mississippi, in the United States was developed. > Figure 23.14 shows the surface temperature plotted for a strip along the east–west cross section of the city layout plan [23]. The surface temperature difference between the inner city and outskirts can be much higher for larger metropolitan urban areas. A similar analysis for Memphis, Tennessee, showed built-up area about 67.3% of the total area of 1,211 km2.

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Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

50

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. Fig. 23.14 Heat-island effect in Oxford, Mississippi, United States

Other non-built natural surfaces include 16.9% trees, 12.5% grass, 2.8% water, and 0.5% soil. The average surface temperature on the hottest hour of summer is 55.9 C, which is 21.1 C higher than the maximum air temperature of 34.8 C that day due to about three times more built-up surfaces in Memphis than in Oxford, Mississippi. The heat-island effect is compounded in most urbanized and populated areas by higher energy use in summer, vehicle traffic density, and emissions from congested conditions. In many areas of the United States, a warming of 2.2 C (4 F) could increase groundlevel O3 concentrations by about 5% [67]. Air quality is also degraded due to the increase in O3 and PM levels. Additionally, it requires extra electricity to cool down buildings in summer days, which results in increased energy demands, larger air-conditioning bills, and greater demand on power consumption. In the United States, about one-sixth of all electricity generated (about $40 billion per year) is used to air-condition buildings [65]. This in turn increases air pollution.

Impacts of Urbanization and Megacities Historical Overview of Urbanization and Current Trends in Growth of Megacities The following discussions about historical development of cities, urbanization, and growth of megacities in modern times are based upon historical facts and extensive

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published research reviewed for this chapter [68–74]. A chronological account of birth of cities to modern era’s megacities follows: ● Pre-Christian era before Roman Empire: Probably the birth of world’s first city took place on the plains of Mesopotamia near the banks of the Tigris and Euphrates Rivers in what is now Iraq in the Middle East. The development of the metropolis of Athens in ancient Greece was a milestone for all future mankind, where a disciplined civil society evolved with planned buildings, iconic architectural structures, institutions of learning, and sports stadium facilities. ● Rome: The first major populous city in the world became Rome when the Roman Empire spread to most parts of Europe and the Middle East. Rome was populated by more than one million people in 5 AD when the world’s population was only 170 million. Romans were the first civil engineers and urban planners building roads and bridges for transportation, aqueducts for water supply, massive temples and sports structures, urban housing, and suburbs. It was the largest, wealthiest, and most politically important city in Europe for over a thousand years. Its population declined to about 20,000 during the Early Middle Ages, and it became city of ruins. However, Roman roads and bridges served Europe until the times of Late Middle Ages and Industrial Revolution since the modern roads were not built until the 1800s. ● Constantinople and Chang’an: The city of Istanbul in modern day Turkey was the Eastern Roman Byzantine Empire’s seat and known as Constantinople. With its wellplanned city streets, port, and commerce infrastructure, it remained a large prosperous metropolitan city for hundreds of years as well as during the Ottoman’s Islamic Empire until late 1800s. Istanbul has grown rapidly in the twentieth century and with ten million population, it is now ranked 21 in the list of the top 25 megacities in year 2006. The Chinese Imperial capital city of Chang’an was located northwest of today’s Xi’an during the Han Dynasty. Around AD 750, Chang’an had an estimated one million people within city walls as recorded in Chinese history. ● Cities in the modern era of 1800 to mid-twentieth century: In 1800, Beijing and London were the only major cities with populations of over one million. During the 1800s, only 3% of the world’s population lived in cities, which rose to 47% by the end of the twentieth century. The invention of steam power and railways facilitated intercity traffic and commerce. But the discovery of petroleum and invention of the gasolinepowered car in the early 1900s revolutionized transportation, provided freedom of mobility, promoted manufacturing and businesses, and accelerated growth of cities and urban population through migration from countryside and abroad. In 1900, North America and Europe possessed nine out of the ten largest cities in the world. ● Post–World War II era and emergence of megacities: A city with a population of ten million or more has been generally described as a megacity. In 1950, New York, London, Tokyo, Paris, Chicago, and Moscow were inhabited by the world’s largest metropolitan populations. New York City was the only megacity urban area with a population of over ten million. Since then, many megacities have evolved, and the

Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

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majority of these are outside North America and Europe. This increase has happened as the rest of the world’s population moves toward the high urbanization levels of North America and Western Europe, 75–85%. The largest megacity in the twenty-first century is the Greater Tokyo Area. Figure 23.15 shows the top 20 megacities in the world as of 2006, where New York is ranked number 4 and Los Angeles at 12 [70, 74]. There is no other city from North America or Western Europe in the list. The increase in urban population is expected to be most dramatic in the developing countries of Asia and Africa. One study predicts that Asia alone will have at least ten megacities by 2025 [68]. Additionally, the number of cities with five million inhabitants or more is expected to increase worldwide from 40 (year 2001) to 58 (year 2015). >

Urban Population Density Impacts The ratio of central city to metro population in the US urbanized areas decreased 30% in 50 years from 0.57 in 1950 to 0.38 in 2000 [49]. Suburbs and outskirts of cities have

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typically low density, resulting in longer driving distances to work, more cars on roads, increased congestion, and higher GHG emissions. Dense population and demand on energy and mobility make the environment of a large city and urbanized area different from the environment of smaller towns in rural and other uninhabited areas. Cities and urban areas are now major contributors of GHG emission, air pollution, and associated health risks [15–20, 24, 31, 33, 71–73]. Cities are sources of most of the anthropogenic GHG, other air pollutants, and aerosols that are known to alter the state of the global atmosphere and climate. Megacities produce 12% of the anthropogenic CO2 emissions and lesser fractions of the methane and nitrous oxide emissions. Even emission levels are maintained at that of the year 2005, simulation results show that megacities will be responsible for a 225 mK warming over the next 100 years with just under 90% of this warming due to the CO2 [73]. Cities drive economic and societal development in all countries and offer better economic prosperity than rural areas, which is the primary cause of urban migration. At the same time, they are the largest consumers of natural resources and the biggest sources of pollution and greenhouse gas emissions. City inhabitants own more automobiles due to higher income levels and greater needs for mobility. This highlights the important role cities should play in mitigating climate change mechanisms.

Urbanization and Motorization Links Uddin et al. [22] discuss linkage between road transport and urbanization which affect physical inactivity, safety and traffic fatalities, air pollution and environmental degradation, public health, societal costs, quality of life, and social integration problems. Additionally, diminishing energy resources are equally important issues for environmentally sustainable transportation policy and decision making.

Urban Growth and Travel Demand Travel demand (number of vehicles and vehicle-km-traveled) is at its highest level both for automobile and truck traffic. Particularly, high traffic density and associated congestion is a constant reminder of the adverse impacts of urbanization as indicated by road users’ woes in large cities (> Fig. 23.13). As reported by City Mayors Organization [74] based on the key findings of a survey of 522 decision makers from 25 megacities, ‘‘solving transportation issues has the highest priority in the cities surveyed, and air pollution is seen as the main environmental issue.’’ The link between urbanization and motorization has been strong in the United States and other industrialized countries due to greater mobility needs [12, 31, 48, 52, 75]. This link is also displaying in emerging economies and developing countries. The change in travel pattern has significantly impacted travel demand on roads, which is typically indicated by Average Annual Daily Traffic (AADT) volume and vehicle-mile traveled.

Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

23

These statistics have steadily increased over the years in the United States [31, 48], as shown by changes during 1970–2000: 58% increase in vehicles registered, 148% increase in total vehicle-miles, and 161% increase in total freight ton-miles. Significant travel demand indicators (in 2007 except where noted otherwise) in the United States were [2, 3, 31]: ● Number of vehicles registered: 254.4 million; 93.3% (cars, 2-axle 4-tire vehicles) and 3.5% (2-axle 6-tire or more trucks, combination) ● Total vehicle-miles: 3.08 billion; 92% (cars, 2-axle 4-tire vehicles) and 8% trucks; less than 0.5% (bus and motorcycles) ● Total freight ton-miles: 1,293 billion (Year 2005) ● Average miles traveled per vehicle: 11,720 miles (cars); 25,141 miles (trucks) ● Fuel economy (average miles traveled per gallon of fuel): 20.4 miles (cars); 5.9 miles (trucks); 6.1 miles (buses); 56.2 miles per gallon (motorcycles) Figure 23.16 shows the 2008 vehicle-miles traveled and GHG emissions [2], which indicate that though all trucks combined accounted for only 7.6% VMT, they emitted 60% CO2 of all on-road vehicles. In comparison, cars contributed 54.3% VMT but only emitted 39% CO2, implying that mobile GHG emissions are undesirably high even outside cities where most trucks operate. The results of a comparative study of national transportation policies over the last 25 years in the United States and France by Gires [76] show that in the early 2000s: >

● The US consumption of fuel and emission levels have not changed much due to the increase in car ownership, more travel mileage, and larger market share of fuel gulping SUVs and pickup trucks that has risen to 50%. ● The average gasoline consumption has remarkably decreased by more than 20% in France, but diesel market share rose by 70%.

U.S. vehicle miles of travel by Vehicle type, 2008 (Billions of vehicle miles)

Buses & motorcycles, 22, 0.7%

Passenger cars, 1,616, 54.3%

U.S. highway transportation GHG emissions, 2008 (Tg CO2e) Buses & motorcycles, 14.3, 1%

Single-unit trucks, 83,951, 2.8% Tractor-trailer, 144, 4.8%

Passenger cars, 632.1, 39%

Med & hvyduty trucks, 401.2, 25%

Pickup/SUVs, 1,109, 37.3% Lt-duty trucks, 552.4, 35%

. Fig. 23.16 Vehicle-miles traveled and GHG emissions in the United States, 2008

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Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

700 606 600

518

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h Zu ric

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Car ownership per 1,000 population

804

Cities Developing countries

Industrialized countries

. Fig. 23.17 Comparison of car ownership per 1,000 people in selected cities, 1990s

> Figure 23.17 shows that car ownership per 1,000 population in large cities of industrialized countries was 2–30 times that of major cities of developing countries based on the data from the 1990s [77]. This implies that the cities in developed and industrialized countries will have significantly higher GHG emissions due to higher AADT, larger number of car trips, and low fuel economy of on-road vehicles. A reasonably quantifiable sustainability scale is CO2 emission per capita that can be used by government agencies and cities for evaluating performance of sustainable transportation policies. Using the 2007 daily vehicle demand volume [3, 30, 71, 72, 77], vehicle fleet composition, typical vehicle-miles driven per day, and CO2 calculations (> Eq. 23.1), transportation-related on-road vehicle emissions were estimated for many US cities including two megacities (New York and Los Angeles) and compared with three megacities in developing countries (Sa˜o Paulo-Brazil, Mexico City-Mexico, and KarachiPakistan) as a part of research by Headrick [28, 31]. The CO2 calculations assumed that bus and trucks are operated on diesel and cars and other passenger vehicles run on gasoline. The results of annual CO2 emission per capita sustainability index, plotted in > Fig. 23.18 [28, 31], and population data show that:

● In comparison to US cities, the CO2 per capita for the three megacities of the developing world is substantially less (1.4 for Sa˜o Paulo, 0.4 for Mexico City, and 0.4 for Karachi). ● The CO2 per capita is the highest for Montgomery, Alabama (8.9 t) which is one of the eight US cities at 5.6 t or higher CO2 per capita, followed by five more populous cities at 5.1–3.4 t (Los Angeles, Phoenix, Chicago, New York, and New Orleans).

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Annual per capita roadway CO2 emissions, 2007 (Tons of CO2) 10.0 9.0

8.9

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Mexico City, Mexico Karachi, Pakistan

Sao Paulo, Brazil

New Orleans

New York

Chicago

Phoenix

Los Angeles

Fayetteville

Memphis

Mobile

Baton Rouge

Atlanta

Nashville

Jackson

Montgomery

0.0

. Fig. 23.18 Comparison of selected U.S. cities and three megacities abroad on sustainability scale

● New York and Los Angeles top the list at 68.4 and 62.7 million tons CO2 emissions annually for the two highest CO2 emissions, followed by Chicago (38.7), Atlanta (28.3), Sa˜o Paulo (25.0), and Phoenix (17.6), Mexico City (7.6), Nashville (7.4), and lesser emissions for all other cities. ● Except for New York (18.2 million), Los Angeles (12.3 million), and Chicago (nine million), populations of other US cities range from 0.2 to 4.5 million in 2007. Populations of megacities abroad range high, from 17.7 million (Sa˜o Paulo), 17.4 (Mexico City), and 14.0 (Karachi). ● However, population density (1,000 persons per sq. mile) of the three megacities abroad is 3.5–5 times higher than Los Angeles, the highest population density city in the United States (6.3 for Los Angele and 4.1 for New York). The above CO2 per capita analysis assumes all vehicular traffic is operated by gasoline for cars and other automobiles and diesel for trucks. The CO2 per capita will be less for Sa˜o Paulo, where up to 25% of cars operate on ethanol and biofuel, and Karachi, where up to 70% of cars and an increasing number of auto-rickshaws operate as hybrid vehicles mainly on CNG. Furthermore, this analysis shows that the three megacities of developing countries have less car traffic volume on roads and more people traveling by mass transit and other modes of public transportation in comparison to most US cities. The impact of utilizing efficient multimodal mass transit systems on reducing CO2 emitted by on-road vehicles is evident in large cities and urbanized areas both in the United States (such as New York City) and developing countries (for example, Sa˜o Paulo

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and Singapore). New York City Mayor’s office of planning and sustainability compiled 2005 GHG emission inventory results considering all mobile, buildings, and other area sources [78]. The results showed that: (1) contributions of 20% were from on-road vehicles and 3% from transit and (2) on the sustainability scale New York City, at 7.1 metric tons CO2e emission per capita, ranked next higher to London, while the average US emission per capita was 3.5 times that of New York City (> Fig. 23.19). The above comparison of citywide GHG emission per capita and preceding analysis of on-road GHG emission per capita for several US cities and megacities in emerging economies and developing countries clearly demonstrate the strong link between urbanization and motorization in producing GHG emissions.

Geospatial Analysis of Built Environment and Traffic Demand Impacts Modern geospatial analysis and GIS software tools and availability of aerial and spaceborne remote sensing data provide new opportunities for mapping and spatial analysis of the built environment including land use, urban growth, transportation network, and traffic demand volume and temporal characteristics.

GIS Maps of Urbanized Areas, Urban Growth, and Built-Up Areas in the United States The USGS has used Landsat satellite imagery data for mapping of the continental United States into the National Land Cover Dataset (NLCD) of 1992. This dataset has been

Greenhouse gas emissions, metric tons CO2e per capita 24.5

25 20 15 11.1

9.6

10

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5.9 5

at te d

St

an c

ni U

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Fr

D n

es

co is

go ie

on to Sa

rk Yo ew N

To r

ity C

on

0 Lo nd

806

. Fig. 23.19 New York City on sustainability scale based on 2005 GHG emission inventory

Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

23

updated by the NLCD 2001 project which uses both Landsat5 and Landsat7 data from 1999 to 2003. The purpose of using both satellites was to prevent clouds from adversely affecting data availability. The spatial resolution of both NLCDs is 30 m. During the period from 1973 to 1992, the urban area of Las Vegas, Nevada, grew dramatically throughout the level basin [12]. Built-up areas from imagery and geospatial analysis of NLCD 2001 land cover class maps were estimated for the City of Memphis, Tennessee, and used to create a surface temperature map (> Fig. 23.20) for a hot summer day. The weighted surface temperature for the study area of Memphis in Tennessee was 55.9 C as discussed in detail by Uddin et al. [25]. This was 21.1 C higher than the maximum air temperature of 34.8 C that day. The availability of high-resolution commercial satellite imageries provides new opportunities to develop computationally efficient geospatial analysis tools for estimating built-up and natural surface areas. For example, the NLCD 2001 map of Oxford, Mississippi, overestimated the built-up area by 43% in comparison to geospatial analysis of 1-m multispectral satellite imagery.

0–20°C

Percentage area from NLCD2001

Predicted surface temperature, °C

1. Built-up area

67.4

61.1

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46.8

3. Tree

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40–50°C (Tree, Grass)

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5. Water

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34.4

CAIT surface classes

Weighted average surface temperature

55.9

20–30°C 30–40°C (Water)

60–70°C (Built-up area) Weighted average surface temperature = 55.9 °C

. Fig. 23.20 (Top left) Memphis boundary shown on NLCD map, (top right) Surface temperature map of Memphis, (bottom left) Summary of built and non-built areas for Memphis, (bottom right) Legend used for surface temperature scale

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Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

Imagery-Based Geospatial Analysis for Karachi Metropolitan Road Network GIS and Traffic Demand Volume A recent traffic management study for the megacity of Karachi, Pakistan, was sponsored by the United States Agency for International Development (USAID) under its ‘‘US-Pakistan Science and Technology Cooperative Program’’ and implemented by the National Academy of Sciences (NAS) during 2007–2010 [33]. The project is primarily focused on improving urban traffic-flow management and air quality using GIS and spaceborne remote sensing technologies. Karachi is inhabited by more than 14 million people in 2007, and its population is growing at an annual 5% due to migration from countryside. Karachi’s existing roadways are over-congested and inadequate considering its rapidly growing daily traffic volume demand. More than 40% road fatalities involve pedestrians. No improvement in public transport, transit fleet, and operation is evident by overcrowded transit buses and vans [54]. However, the City’s Command and Control Centre (CCC), essentially an ITS-based traffic video surveillance system implemented during 2008–2010, is a significant addition to its infrastructure for incident management and crime prevention. The ITS video surveillance system is further helping to reduce emergency response time and promote timely utilization of traffic police for traffic-flow management during peak hours and crash incidents. There is no comprehensive road network and land-use GIS, infrastructure database, and traffic volume demand data. The 0.6-m multispectral satellite imagery (Karachi-1) was used to extract vector maps of transportation network, buildings, and other land-use footprint planimetrics [26, 30]. An innovative geospatial methodology for extracting traffic count data from highresolution imagery was developed and validated using selected road sections of Gulfport and Oxford, Mississippi, USA [27, 30]. This methodology extracts traffic counts from the imagery to calculate average measured density per lane. Posted traffic speed, jamming density, and measured density and flow relationships are used to calculate expected speed. Speed multiplied by density gives volume per hour for the hour of the imagery. Furthermore, daily traffic volume can be estimated if the fraction of traffic volume in that hour based on hourly volume distribution for the entire day is known. The geospatial methodology for traffic data extraction was then implemented for the Karachi road network. The hourly volume factor was estimated from on-road video data analysis of an arterial in Karachi. Average daily traffic volumes were calculated for 40 road sample sections selected from a factorial design, and a traffic volume map was created using GeoMedia Pro and 0.6-m Karachi-1 imagery as well as Google Earth Imagery for areas outside Karachi-1 imagery scene. The results for all sampled road sections of Karachi yielded an average AADT of 49,564 vehicles per day [27]. Most major and multilane roads experienced high hourly traffic volume and poor level of service [28, 30]. The results indicated that the average daily traffic volume was affected significantly by road classification and area of the city (71% inner city versus 29% outskirts). These data were used to calculate CO2 emissions as discussed later.

Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

23

GHG Abatement Strategies The worldwide reduction of greenhouse gases and the efficient use of energy in urban, transportation, and industrial applications are important issues for all countries. Recognizing the continuing global increase in mobile travel, the application of traffic congestion reducing strategies must be implemented in order to meet the target GHG levels and infrastructure needs. In the United States, several traffic management strategies have been widely implemented in recent years in order to improve traffic flow and reduce traffic congestion. These strategies include: Travel/Transportation Demand Management (TDM) in urban areas, mass transit deployment, use of ITS technologies, and signal-free corridors and road junction design alternatives. In 2005, public mass transportation in the United States reduced carbon emission by 6.9 million metric tons and avoided 400,000 t of other GHG emissions [35]. Simulation studies have shown the promise of reduction in CO2 and improved air quality as a result of increased vegetation in urban areas.

Sustainable Transport and Traffic Management Solutions Transport Demand Management and Sustainable Strategies to Reduce CO2 Emissions The transportation sector’s CO2 emissions are a function of vehicle fuel efficiency, fuel carbon content, and VMT. Energy and climate policy initiatives at the federal and state levels have focused almost exclusively on technological advances in vehicles and fuels. The evolving gridlock problems and their societal and environmental impacts require innovative solutions to manage urban growth, VMT, and vehicle use. Therefore, any ‘‘solution’’ to the global warming and climate change crisis must involve slowing the growth of CO2 emissions from mobile sources in the United States. The same is applicable to all other industrialized and rapidly developing countries where car ownership and singleoccupancy vehicle (SOV) use is increasing at alarming rates, such as China, Brazil, and India. The worldwide per capita passenger-kilometer traveled per year is expected to increase 48% between 2000 and 2050 with the highest increase (279%) projected for China [17, 18]. An important factor in energy consumption increase is population and urban growth rate, which is high in almost all emerging cities in developing countries. It is imperative to consider the following abatement strategies to reduce mobile GHG sources [33, 71, 79]: ● Motorized travel demand reduction: Reduce the amount of passenger-kilometers traveled and freight ton-kilometers traveled, discourage SOV trips to ease congestion, and decrease motorcycle traffic to improve road user safety. ● Idling long-haul trucks on highway rest stops and truck parks: Eliminate the practice of idling long-haul trucks for long hours (a common scene on US highways). States should use highway patrol to enforce, encourage trucker employers to pay for

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Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

motel/hotel accommodation for the night, and consider penalty charges for ‘‘polluting’’ trucks who follow this practice. Sustainable multimodal transport implementation: Implement less polluting mass transit transport strategies for urban mobility with less or fewer emissions per km travel, increase freight modal share of efficient freight rail. Nonmotorized travel promotion: Make policy and facilities to promote nonmotorized trips in congested inner city areas. Vehicle inspection and emission testing program: Develop and enforce regulations for annual vehicle inspection and emission testing programs by developing testing and maintenance facilities and workforce. Transport technology improvements: Improve performance of transport mode engines and vehicles (lightweight vehicles, smart/intelligent cars) for more safe and efficient use of petroleum fuel and design hybrids to use alternative energy sources with reduced or zero carbon emissions. Regulatory Measures Based on Technology: Enforce regulations on fuel efficiency, emission levels, and market share of hybrid and battery-driven vehicles. Market-based economic instruments (congestion pricing and emission trading): Consider densely trafficked downtown areas, urban roads, and other surrounding corridors as good candidates for congestion pricing to reduce congestion and emissions. Emission trading has been most widely applied in the United States to reduce power plant emissions and is a candidate for global CO2 trading. Public awareness campaigns: Develop and conduct public education and awareness campaigns (to implement any of the above strategies successfully) in cooperation with civil society groups.

Technology improvement programs initiated in California have resulted in a slow but consistent reduction in air pollution over the last 4 decades [71]. This is a testimony of regulatory enforcements and public awareness considering there has been consistent urban growth and increase in vehicle kilometers traveled. Congestion pricing schemes need public awareness and support (as implemented successfully in London and Singapore).

Metropolitan Transportation Demand Management Examples of travel demand and transportation system management actions and TDM marketing to improve traffic operations in large cities and urban areas include [31, 50]: ● Improved traffic flow: Replacement of stop-controlled intersections by modern roundabout, reversible lanes, transit-stop relocation, removal of encroachments, and ITS traveler’s information and congestion warning system. ● Priority treatment of high occupancy vehicles: Dedicated High-Occupancy Vehicle (HOV) lanes, bus preemption of traffic signals, ITS surveillance and traveler’s information technologies, toll policies, and all electronic toll charge system.

Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

23

● High-occupancy automobile use: Car pooling, van pooling, ridesharing, and discouraging use of single-occupancy vehicles. ● Non-automobile, biking, or pedestrian trips: Nonmotorized travel modes and autorestricted zones. ● Reduced peak-period travel and delays: Flexible hours, congestion pricing, and peakperiod truck restrictions. These strategies are also applicable for nonrecurring events such as adverse weather conditions (hurricane, snow, ice, or rain), work zones, special events, and major incidents and emergencies. ● Parking management: Enforcement of parking regulations, video surveillance, parkand-ride-facilities, and parking disincentives (for example, very high parking fee and charges for parking tickets). ● Transit and paratransit service improvements: Transit incentives and marketing, transit shelters, terminals, transit-fare-collection techniques, connectivity with other transportation services, ITS technologies for improved deployment and scheduling. ● Transit management of efficiency measures: Routing and surveillance, on-time and reliable service, vehicle communications, maintenance policies to provide state of good repair. ● Large capacity change alternative on existing roadways: Travel time reduction for a large capacity alternative is 30% for one-way operation, 30% for reversible flow, and 50% for left-turn prohibition. Additionally, crashes and incidents tend to reduce while capacity is increased for a large capacity change alternative. ● Innovative shared transport infrastructure alternative: Transportation and urban planning approach should be changed toward the green and cool approach by reducing the number of autos on the road and increasing innovative shared transportation and transit alternatives. Clearly, there is a need to design innovative transport infrastructure to operate at low speeds for shared use of commuters for many congested cities with thriving downtowns and existing ground-level mass transit systems and underground subway/metro tracks. Mass transit systems include bus transit, bus rapid transit (BRT), light rail transit (LRT). Examples of such metropolitan cities are Chicago, New York, Los Angeles, and many European cities where simply there is no space to increase capacity by building more traditional transport facilities. Costs are also very high for adding more bus lanes to expand BRT operations. The answer to the urban commuter problem in such developed and congested cities are dedicated elevated transportation pathways maximizing the use of existing right-of-ways of public roads. The key to the success of this innovative approach is in selecting the ‘‘right’’ vehicle technology that can be lightweight and energy efficient. Powered by electricity or magnetic levitation (Maglev) technology and operated at city speed range, a personal rapid transit system is a sustainable pollution free solution for urban areas and cities [31]. This innovative ‘‘green’’ transport alternative can be economically justifiable based on life cycle costs and benefits.

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Smart Growth, Space Planning, and Sustainable Infrastructure Mixed Land Use and Compact Development to Reduce Cars on Roads in Cities Encouraging mixed land use and compact development will mitigate and avoid the many flaws of traditional urban development. Urban sprawl and suburban development is characterized by: low densities, automobile intensive strip development, poorly connected streets, automobile-oriented transportation planning and traffic management, and detached single family homes and similar land use. Dense or compact development typically involves: medium to high densities, more vibrant-centered development, interconnected streets, pedestrian-friendly and transit-friendly road design, and mixed uses of land and roads. Cities should increase the deployment and use of public transport and cool commuting alternatives. Urban growth is inevitable worldwide as metropolitan cities offer more job opportunities, excellent community facilities, and a better quality of life to people migrating from rural areas or smaller cities. Realizing that a single solution is not the answer, a combination of following abatement strategies should be evaluated to explore practical solutions for reducing transportation-related emissions. ● Promote smart growth: Examples include high urban density, less travel distance for commuting to work and shopping, green spaces, energy conservation. ● Implement space planning applications: Space planning approach will be helpful to achieve sustainable growth on ground, below ground, and elevated structures. ● Establish green and cool cityscapes and communities in and around cities: Some examples include light-colored, eco-friendly block pavements for sidewalks and parking lots. Residents and homeowners should be given tax-break incentives for the use of white- and light-colored roofs to reduce heat-island effects. Similarly, use of solar panel and green roof should be supported to promote energy conservation and renewable energy. ● Develop sustainable multimodal infrastructure: Sustainable multimodal transport facilities and operations are possible by providing less polluting mass transit, discouraging SOV use, and introducing safe pathways for walking trips and dedicated bike lanes for nonmotorized travelers. ● Reduce congestion in cities and metropolitan areas: Congestion can be reduced by deploying efficient public transportation, ITS technologies to improve operational efficiency, and reducing number of vehicles on roads to ease congestion. ● Use GIS- and ITS-based speed data to visualize congestion and air pollution trends: Introduction of geospatial analysis and on-line GIS visualization products to show public near real-time status of congestion reduction, improvement in air quality from reduced pollution, and reduction in GHG emissions. This education and media campaign will promote wider voluntary use of fuel-efficient cars, public transport, and energy conservation.

Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

23

● Consider Sustainability Related to Natural Resources and Energy Demand: Life cycle analysis of sustainable transport infrastructure assets and mitigation strategies should look into all opportunities related to conservation of materials and energy sources, space-use and land-use planning, and multimodal transportation policies [32]. Two major areas for sustainable road infrastructure assets are: (1) pavement construction and maintenance and (2) non-pavement assets (such as bridges, sidewalks, drainage).

Multimodal Alternatives for Travel in Cities, Intercity Connectivity, and Regional Transport A multimodal transport system makes efficient use of the space and existing transport infrastructure in cities and urban areas having limited funding resources. Historically, an underground mass transit rail subway system provided good use of the space, but its construction and expansion is very expensive. Such rail subway systems may not be the best cost-effective solution in megacities of emerging economies and developing countries. In comparison, the construction of a designated bus lane costs only a fraction of a comparable subway rail line. The bus transit and BRT systems can be implemented in any megacity, adapted quickly, and provide good connectivity to rail network. Regional and intercity rail network should play an important role in a multimodal approach to reduce GHG emissions. Rail engines are becoming less polluting in compliance with the EPA’s clean air non-road diesel rules of 2004 and 2008 [80] with reductions of 99% in sulfur, up to 90% in PM, and 80% in NOx emissions. Rail locomotives are four times more fuel efficient than trucking and a train can carry the freight of 280 or more trucks reducing highway congestion and significant reduction in GHG and other emissions [81, 82]. Electric-powered high-speed rail technology for efficient intercity and regional passenger transport can alleviate plaguing problems of urban and highway traffic congestion, wastage of gasoline fuel, vehicle emissions of criteria air pollutants, and GHG emissions. In recent years, the US government has committed billions of dollars to several states for constructing high-speed rail corridors [31].

Consumption and Hidden Cost of Petroleum The hunger for petroleum fuel by transportation is enormous in every country. Most countries and especially developing countries spend a sizable amount of their national budgets on crude oil. In 2002, about 11 million barrels of crude oil equivalent per day was burnt by highway vehicles in the United States [4]. The share of light automobiles was 8.5 million barrels and medium/heavy freight trucks consumed about 2.4 million barrels. In comparison, total rail traffic consumed only 260,000 barrels per day with a major portion (245,000 barrels) by freight train and only 15,200 barrels by passenger rail. The US share of petroleum consumption was 25.3% of total world consumption of 79.08 million barrels of petroleum per day in 2003 [4]. The accelerated industrialization and economic prosperity

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Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

of China has made it the second largest petroleum consumer after the United States. The known worldwide petroleum reserves are being diminished every year. The protection of this commodity and its supply has been a major reason of US military expenditures in the Middle East. One such estimate of 1996 is 20–40 billion dollars annual cost to defend all US interests in the Persian Gulf [83]. The 2000s Iraq war cost is even substantially higher. (The gasoline cost at fill station may exceed $7 per gallon if the ‘‘petroleum protection war cost’’ is accounted for.) This hidden cost of petroleum is generally ignored in economic evaluation.

Alternative Energy and Fuel, Vehicle Innovations, and Nonmotorized Transport Cities face challenges of inadequate parking space and polluting transport services. Recent transportation policies and strategies, such as congestion pricing and the use of BRT and LRT systems have shown some benefits by reducing the number of cars on roads. The key to success for achieving sustainability in the transportation system is to reduce the number of vehicles and number of trips on roads. Increased share of nonmotorized trips by mixed land use and pedestrian-friendly road design are complimentary strategies to reduce vehicle volume on roads. Sustainable solutions to mobility requires a combination of multimodal strategies with reduction of cars on congested roads, reduction in gasoline vehicles, increase share of biofuel vehicles, and zero carbon battery-powered vehicles. Sustainable mass transit strategies include vehicles running on natural gas (CNG and LNG), liquid petroleum gas (LPG), biodiesel, and hybrid and other energy efficient technologies. Vehicle efficiency policies and government regulations can be effective if supported by the public. For example, California required that 2% of vehicle sales had to be zeroemission vehicles by 1998, considering that battery-powered vehicles would meet this need. Initially this was not achieved, but research in hybrid gasoline-electric vehicles paid off by creating small batteries that could be continuously recharged by a small gasolinepowered generator [71]. These near zero–emission hybrid vehicles are now popular and fuel efficient by almost doubling the mileage of a traditional small car. Some countries with CNG vehicles in use as of 2007 [29] rank in the following order (total number of CNG vehicles in parenthesis): Argentina (1.454 million), Brazil (1.303 million), Pakistan (1.300 million), Italy (0.410 million), India (334,000), United States (142,000), and China (125,000). The number of CNG vehicles in the United States is approximately 10% of the three highest ranking users of CNG vehicles (Argentina, Brazil, and Pakistan). The US consumption of CNG was only 6.4% followed by 0.4% LNG consumption in 2004. The United States should consider taking advantage of its large domestic reserves of natural gas for consumption in hybrid cars and other light vehicles. Federal government can take the lead by converting all government owned cars to gasoline/natural gas hybrid vehicles. Federal and state government agencies can require car manufacturers to produce certain percentage of new cars each year with CNG/gasoline

Mobile and Area Sources of Greenhouse Gases and Abatement Strategies

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hybrid technology. It will not take a new infrastructure to supply gas because a comprehensive gas pipeline network already exists throughout the United States.

GIS-Based Decision Support System and Value Engineering Geospatial Mapping and GIS Decision Support System Examples Spaceborne and airborne remote sensing technologies, GIS and geospatial visualization tools, and air pollution models can be used to prevent and mitigate the adverse effects of transportation systems. GIS-based decision support systems should be developed for identifying problem areas, the vulnerability assessment of transportation infrastructure, and life cycle benefit-cost analysis. A geospatial analysis of CO2 inventory by states for 1990 and 2003 in the United States, reported by EPA [8], indicates: ● Carbon dioxide emissions in 2003 are 15% above 1990 levels. ● The five states that produce the least amount of transportation emissions are: Vermont, Rhode Island, Delaware, South Dakota, and the District of Columbia. These are smaller and less populated areas. ● California, Texas, Florida, New York, and Pennsylvania remain the five states with the highest emissions in 2003 as in 1990. ● This shows that these five states, containing large populated urban metropolitan cities, produce more emissions than other smaller and rural states. The GIS maps are not shown here for brevity but this analysis shows an example of GIS-based decision support system on regional and national level. These results can be used by federal and state agencies to make decision related to allocation of funds among states and cities for planning and implementing GHG abatement strategies. Another example of GIS-based decision support system is quantification of built and non-built surface areas in a city. An increase in the percentage area of these built-up surfaces will definitely increase the weighted average surface temperature (by surface area). The increased urban area temperature and increased traffic emission result in air quality degradation which adversely impacts lung disease sufferers. The associated public health cost is about 19% of the total societal costs, as shown in a previous study of Oxford, Mississippi [23].

Value Engineering and Life Cycle Analysis Value engineering (VE) enables to evaluate a cost-effective solution by selecting alternative technologies and methods to achieve reduction in overall life cycle costs without compromise to safety and efficiency. The traditional life cycle analysis (LCA) considers agency costs and user costs associated with pavement life cycle [22]. Agency costs for building and maintaining roads require lots of natural resources, such as asphalt, aggregate, cement, concrete, and steel. User costs include vehicle operating cost (voc). For example, the

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pavement roughness condition deteriorates with time and traffic repetitions that can influence fuel and oil consumption, tire deterioration, and vehicle maintenance. These voc components have been well established in the World Bank’s and the U.S. FHWA studies [22]. The present worth of life cycle vehicle operating cost is in the range of 18–29 cents per vehicle-mile for two-lane rural roads in good to poor condition. The PSI scale (0 for worst and 5 for best) is used to define surface condition of pavements. > Figure 23.21 shows the relative weights of these voc components and influence of Pavement Serviceability Index (PSI) on voc [22]. As pavement surface deteriorates, PSI reduces and voc increases. Reduction in voc due to improved pavement condition and travel time saved due to increased capacity and reduced congestion have been traditionally used to calculate life cycle benefits. However, vehicle emission–related and air pollution–related environmental and societal costs have been lacking from the traditional LCA practice of highway project evaluation. The effects of transportation-related emissions and air pollution on public health and associated medical costs are reviewed and summarized by Uddin [24]. These cost models, congestion pricing, and carbon emission taxes can be used for a comprehensive life cycle analysis to evaluate sustainable alternative transportation and development strategies as a part of value engineering analysis. The life cycle analysis strategies for sustainable transportation system and development should consider: ● Providing sufficient and safe mobility to commuters to be productive in the workplace. ● Supporting commercial businesses to flourish without losing potential customers. ● Improving mobility using multimodal approach as a part of space planning concept. ● Increasing mass transit mode share by increasing car parking prices and using transit modes operating on alternative less polluting energy. ● Improving traffic-flow management through video surveillance and other ITS technologies to reduce congestion and gridlocks, user delays, wastage of fuel in queues, and emissions. Tire 8.4%

PSI = present serviceability index

5 4

Vehicle repair & maintenance 30.5%

PSI

816

Gasoline 34.7%

3 2 1

Oil 1.6% 0 Depreciation 24.8%

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20 30 40 % Increase in voc voc = vehicle operating cost

. Fig. 23.21 Road vehicle operating cost components (left) and voc increase due to pavement deterioration indicated by lower present serviceability index of road pavements (right)

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● Evaluating and implementing less polluting and more efficient rail and pipeline solutions for freight transport in place of current dependence on highway trucks. The diesel gulping trucks are highly polluting and emit several times more GHG emissions than alternative freight rail mode. This strategy will also require the construction and management of intermodal facilities. ● Creating new financing opportunities by collecting transportation-related carbon emission tax from trip makers and give incentives of no such tax for commuters who predominantly use transit. ● Constructing more green spaces and promoting nonmotorized cycling and walking. ● Monitoring air quality and striving for less air pollution and clear skies. ● Reducing backlog of infrastructure and preserving state of good repair using increased revenues by collecting higher fuel taxes on gasoline and diesel. ● Serving more people and creating/preserving jobs.

Life Cycle Analysis of Sustainable Transport Solutions and Value Engineering Case Study Agency costs for building and maintaining roads require lots of natural resources, such as asphalt, aggregate, cement, concrete, and steel. The process of constructing, pavement material processing, and compacting operations consume significant amount of fuel and energy. The service life of a typical asphalt highway pavement is 10–15 years, whereas the life of a typical concrete highway pavement is 15–30 years. Functional life of road vehicles is also limited to 10–15 years. In comparison, alternative mass transit of a regional/ national high speed rail (HSR) network and personal rapid transit (PRT) in urbanized areas can last several times longer with less maintenance cost. These alternatives are also safer due to operation on dedicated pathways with no vehicle conflict or congestion. Life cycle analysis of costs and benefits should be evaluated for a longer analysis period of 60–70 years as a part of value engineering evaluation. Over this analysis period, the trackbased mass transport system lasts without major rehabilitation or reconstruction, operated typically on electricity. During this period, road infrastructure and vehicle fleets need to be replaced one to three times. Road vehicle operating cost (> Fig. 23.21) is a large component of road user cost [22], which is substantially reduced by the proportion of the road users who switch to the new transit technology. Other benefits include reduction in fuel and low pollution cost. The benefits from each alternative should include user benefits as well as societal benefits per passenger-km or freight ton-kilometer which include: savings from reduced fuel consumption, time saved due to less delay, public health benefits from reduced air pollution, fewer crash/accident related costs, and lesser societal costs due to reduction in CO2 emissions. In metropolitan cities and urban areas, dedicated elevated PRT pathways provide a sustainable solution to the urban commute and congestion by maximizing the use of existing right-of-ways of public roads. This will require the selection of the ‘‘right’’ PRT vehicle technology that can be lightweight and energy efficient. The PRT infrastructure

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requires the use of elevated structures and efficient cleaner energy sources of electricity and Maglev for PRT operations designed to reduce congestion and impacts on the environment. Examples are Swedish SkyCab (electricity driven) and Brazilian Cobra Maglev vehicle/track systems [31]. The approach to determine economic cost is derived from a study of the traffic volume data, where there are new lines built, users’ time savings, number of users willing to pay for such a transport, release of capacity in congested roads, and broader economic benefits including development of less developed regions and creation of jobs. The life cycle economic evaluation includes several financial considerations such as present worth analysis of benefits and costs over a reasonable analysis period considering an appropriate discount rate and calculating net present value (NPV) of minimum two alternatives. The base alternative is ‘‘do-nothing,’’ and the reduction in user delay hours and emissions are considered indirect benefits from the new alternative transit strategy. To illustrate life cycle benefit and cost analysis of a PRT system, it is assumed that the agency cost for building a 30–40 miles/h speed PRTsystem on elevated alignment may cost around 4 million US$ per km, much lower than a HSR system. The PRT’s annual operating cost will also be significantly lower than a HSR alternative due to energy efficient and lightweight vehicle technology. The PRT construction cost of 10-km stretch is about 40 million dollars with annual 0.5 million dollar operating cost. Assume that each person using the PRT system saves annually 25 h of delay at $16 per hour and avoids wastage of 15 gal of fuel and oil at $3 per gallon. Therefore, for 20,000 commuters (or 20% car owners in the daily traffic volume) using PRT instead of driving single-occupancy cars, the total user saving is about nine million dollars annually. This example implies that the PRT’s initial construction cost is covered within 5 years (at 0% discount rate) just by considering annual user saving. This analysis simply ignores passenger fare revenue that will be an agency benefit. Additionally, the societal benefit will be enormous in terms of reduction in CO2 at 2,765 t daily or about one million tons annually [31]. Other indirect benefits include less air pollution, reduction in associated public health cost, less risk of on-road crashes, and increased productivity. Showing this type of evidence to the traveling public and other stakeholders, they can be persuaded to approve the PRT system implementation. Building and operating these innovative energy efficient and cleaner mass transit solutions in metropolitan areas and other large cities can be successful if disincentives are in place to discourage commuters from driving their cars.

Monitoring, Targets, and Applicable Laws The US EPA uses standard models for measuring and preparing inventory of GHG from all possible sources [8]. It is also important to make real-time measurements to assess impacts of mobile and area sources of air pollution and greenhouse gases on air quality and global warming. The methods reviewed will benefit practitioners and decisionmakers involved in federal, statewide, tribal, metropolitan, or small community transportation planning agencies.

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Terrestrial Remote Sensing and Space-Based Monitoring The annual emission inventories from transportation and industrial sources need to be verified by measuring CO2 and other air pollutants. Monitoring of air quality involves analysis of air samples for criteria air pollutants (short lived, requiring frequent measurements) and CO2 (long lived) emissions [71]. Monitoring methods range from simple passive sampling and measuring techniques to continuous gas analyzers and remote sensors. The measurement quantifies the amount of CO2 higher than the background level in which traffic or other anthropogenic emissions are absent.

Remote Sensing Monitoring of CO2 and Other Air Pollutants Remote sensing LIght Detection and Ranging (LIDAR) active sensor in infrared band is used for CO2, measurements. Tunable differential absorption LIDAR was used for realtime in situ measurements of air pollutants in a previous study for air quality modeling [84]. The remote sensing instrument can be set up near any highway or industrial area and measure CO2 and other emissions in different spectral bands using a target 1-km away [85]. An eddy covariance (EC) flux remote sensing equipment has been used in several studies for measuring CO2 levels, usually mounted at the top of towers or masts at least twice the mean height of the surrounding buildings. The EC system consists of an ultrasonic anemometer to measure wind fluctuations coupled with an infrared gas analyzer to measure water vapor and CO2 measuring from 2 to 20 times per second. The results of CO2 measurements from several cities in United States, Europe, South America, and Asia showed that built-up areas provide a constant source of CO2 [85–87]. The level of emissions is higher for densely populated larger cities with high traffic volume such as that shown for Sa˜o Paulo-Brazil by measuring CO2 and other pollutants inside and outside road tunnels [86], Mexico City and Singapore [85], Paris-France, and PhoenixUnited States [87]. The Paris study results revealed that atmospheric CO2 concentrations near surface throughout the country outside Paris averaged 415 ppm, which was significantly lower than 950 ppm observed in the city. Furthermore, considering other air pollutants and aerosols in addition to GHG, cities are the source of most of the pollutants that are known to alter the state of the global atmosphere and the climate. Therefore, cities play an important role in mitigating the GHG emissions [85].

Spaceborne Remote Sensing for Pollution Monitoring Recent National Aeronautics and Space Administration (NASA) satellites and European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) use both active and passive remote sensing instruments to probe throughout the troposphere [88]. These instruments measure atmospheric aerosols, clouds and trace gases across the spectrum from the ultraviolet to the microwave bands. The Atmospheric InfraRed

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Sounder (AIRS) and Advanced Microwave Sounding Unit (AMSU) are deployed onboard the NASA’s Aqua satellite. These spaceborne sensors see 70% of the Earth both day and night and provide detailed vertical retrievals of temperature and water vapor and weighted free tropospheric concentrations of CO, CH4, CO2, and O3 [88]. In addition to spaceborne remote sensing measurements of emissions, geospatial analysis of spaceborne satellite imagery provides a remote sensing alternative to estimate built-up area estimates and traffic volume for any city or urban area in the world, as discussed previously for Karachi [27, 28, 30, 33]. This approach is especially useful where these citywide data are not measured on routine basis. Karachi port area extracted from 0.6-m satellite imagery showed 58.7% built-up area and 41.3% non-built area (ocean, river, soil, grass, trees). Accurate and timely collections of traffic attributes are necessary for traffic management and calculation of mobile GHG emissions for sustainability performance evaluation of transportation systems. Furthermore, the imagery-based traffic volume method can be used to fill up missing daily traffic volume and identify candidate locations for ITS traffic video surveillance installation. The 2007 estimated daily traffic volume for the entire mega city was 9.3 million vehicles. Daily traffic volume per sq km in the Inner City buffer is about ten times more than the traffic volume in the Outskirt area. This also implies that vehicle emission of air pollutants is also higher in the Inner City area, which is adversely affecting the public health of residents and commuters alike. The traffic congestion on most major roads and vehicle emissions are adversely affecting travel times productivity and air quality. Based on the US EPA procedures (> Eq. 23.1), citywide CO2 emission from the imagery-based road traffic volume is estimated 5.5 million tons as of 2007 for Karachi [28, 30].

United States and European Initiatives Sustainable Transport Policies Although CO2 emissions from road transport and road passenger kilometers continue to grow, fuel efficiency per passenger kilometer is improving. Road ton-kilometers are increasing but truck fuel efficiency is not. It is important to recognize that improvements in energy efficiency of vehicles, less polluting fuel like CNG, and non-fossil fuels are still not enough to counteract the growth in transport demand. Therefore, measures focused on reducing transport demand or shifting demand to more sustainable modes of transportation are extremely important to provide significant emissions reduction results. A sustainable solution requires a shift to multimodal transportation systems with emphasis on reducing travel time to commute and better facilities for bikes and nonmotorized modes. It has been argued that improvements in energy efficiency of vehicles and nonfossil fuels are not enough to counteract the increasing road travel demand and transportation-related GHG emission [42]. Therefore, measures focused on reducing transport demand or shifting demand to more sustainable modes of transportation are extremely important to provide significant emissions reductions. A sustainable transportation and

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development policy should encourage building parks, preserving wooded areas, and providing additional water bodies as an integral part of the built environment and residential neighborhood ‘‘green’’ communities. Reduction of energy consumption and emissions require ecological-friendly pavement materials and related technologies with minimum use of traditional hot mix asphalt [32].

Recent Transport- and GHG-Related Regulations, Policies, and Initiatives in the United States The EPA and USDOT federal agencies are drawing on current laws to mandate fuel efficiency standards and reduced GHG emissions per mile traveled by passenger vehicles. Several legislative and regulatory actions, being undertaken in the United States to reduce transportation-related GHG emissions as reviewed in [45] and based upon the recent news, include: ● The EPA as required by Public Law 110–161 (December 26, 2007) developed a mandatory reporting rule for GHG on September 22, 2009. The rule requires emitters of GHGs from 31 different source categories to report their emissions to the EPA. Approximately 80–85% of total U.S. GHG emissions from 10,000 facilities are expected to be covered by the rule. Reporters must begin to monitor their emissions on January 1, 2010; the first annual emissions reports will be due in 2011. ● On April 2, 2007, the U.S. Supreme Court authorized the EPA under Section 202(a)(1) of the Clean Air Act (CAA) to announce that the six key GHGs pose a threat to public health and welfare for current and future generations and that GHG emissions from new motor vehicles and motor vehicle engines contribute to climate change. ● The draft rule of EPA, published in the Federal Register on October 27, 2009, limits the applicability of CO2 emissions standards under the CAA to new and modified stationary sources that emit more than 25,000 million tons CO2e annually. The EPA expects that 14,000 large industrial sources, which are responsible for nearly 70% of US GHG emissions, will be required to obtain Title V operating permits. This threshold rule would cover power plants, refineries, and other large industrial operations but exempt small farms, restaurants, schools, and other small facilities. ● EPA recently released the RFS2 volumetric requirements for 2010, calling for approximately 8% of the total gasoline and diesel pool to consist of renewable content, mostly from corn-based ethanol. ● According to the EPA requirements, a larger percentage of renewable fuels will consist of these second- and third-generation biofuels, such as algal diesel and cellulosic ethanol. By 2022, advanced biofuels will comprise almost 60% of the renewable fuel mandate. In this way, the move to renewable fuels will contribute a greater share of the drop in transportation’s GHG emissions. ● The American Recovery and Reinvestment Act of 2009 (‘‘The Stimulus Bill’’) was signed into law by President Obama on February 17, 2009. Under the Act, the DOE received $36.7 billion to fund renewable energy, carbon capture and storage, energy

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efficiency, and smart grid projects, among others. The projects are expected to provide reductions in both energy use and GHG emissions. The Energy Independence and Security Act of 2007 (EISA) mandated national GHG emissions standards for mobile sources, authorized by the CAA; and updated Corporate Average Fuel Economy (CAFE) standards, required by EISA. On September 15, 2009, EPA and USDOT formalized an agreement announced in May 2009 between the Administration and automobile industry stakeholders to accelerate the existing CAFE mandate and impose nationwide the tailpipe GHG standards sought by California. On September 25, 2009, the State of California imposed a fee on carbon emissions, the second government body in the United States (after Boulder, Colorado). The fee will be used to fund implementation of the State’s GHG cap-and-trade program. The fee is expected to raise $63 million per year from approximately 350 large emitting entities in the State. The state law will go into effect in fiscal year 2010–2011 and will be apportioned among entities on the basis of their annual GHG emissions, at a cost of approximately 15.5 cents per million ton CO2e. In March 2010, EPA and DOT released emissions and CAFE standard that will go into effect by 2012 and increase the fuel economy of passenger vehicles by 2016. By model year 2016, the combined car and truck standard will be 250 g of CO2 emissions per mile. Additional GHG standards to improve air conditioning systems in vehicles will achieve the fuel economy equivalent of 35.5 miles per gallon. In May 2010, President Obama’s a memorandum directed EPA and US DOT to begin the rule-making process for further reductions for model year 2017 through 2025. The memorandum also directed both EPA and National Highway Traffic Safety Administration (NHTSA) to establish fuel efficiency and GHG standards for commercial medium and heavy-duty trucks, starting with model year 2014, in accordance with the CAA and EISA. On September 15, 2009, the United States, Canada, and Mexico expressed their support for a proposal to include chlorofluorocarbons (HFCs) under the Montreal Protocol. These gases are used primarily in refrigeration and air-conditioning applications. The proposal calls for reductions in the consumption and production of HFCs around the world, with developed nations taking the lead.

Global Accords and Developing World Efforts International Climate Change Mitigation Accords The United Nations Framework Convention on Climate Change (UNFCC) has been the primary organization for international accords (http://unfccc.int/essential_background/ items/2877.php). The Kyoto Protocol was initially adopted on December 11, 1997, in Kyoto, Japan. Under the Protocol, 37 countries committed themselves to a reduction of greenhouse gases, and all member countries gave general commitments. The benchmark

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1990 emission levels were accepted by the Conference of the Parties of the Convention, which were the values of ‘‘global warming potential’’ calculated for the IPCC Second Assessment Report. These figures are used for converting the various greenhouse gas emissions into comparable CO2e when computing overall sources and sinks. In December 2008, the Fourteenth Conference of the Parties to the United Nations Framework Convention on Climate Change and the Fourth Meeting of the Parties to the Kyoto Protocol were held in Poznan, Poland. Key areas of discussion included the following: ● Governments shifted into ‘‘full negotiating mode’’ in hopes of delivering a comprehensive new climate change agreement in December 2009 in Copenhagen, Denmark. ● The European Union called on developed countries as a group to reduce their emissions to 30% below 1990 levels by 2020 and on developing countries to reduce their emissions by 15–30% below business-as-usual levels. ● Ministers encouraged the Parties to view the global economic crisis as an opportunity to address climate change and, simultaneously, contribute to economic recovery, rather than as a hindrance to progress on climate change. On March 28, 2009, US President Obama launched the Major Economies Forum on Energy and Climate. The Forum facilitated dialog among the major economies, leading up to an agreement at the Fifteenth Conference of the Parties to the UNFCC in Copenhagen. Further, the Forum seeks to advance joint ventures to develop clean energy resources. Discussions have centered on adaptation, mitigation, measuring, reporting and verification, and technological cooperation. At least 29 countries indicated they will join the accord representing more than 70% of global greenhouse gas emissions. Major countries committed to cut emissions below 1990 levels by 2020: the United States by 17%, China by 40%, India at least 20%, Brazil at least 36%, South Africa by 34% in emissions from coal, and the European Union by at least 20% in its overall emissions. The United Nations Conference on Climate Change in Cancun, Mexico, concluded on December 10, 2010. Over 190 countries of the UNFCC agreed on a new international deal ‘‘The Cancun Agreement’’ to mitigate global warming impacts. This is the latest climate change agreement after the Kyoto Protocol. The Cancun Agreement postpones until next year’s conference in South Africa a decision on whether to extend the Kyoto Protocol for a year. But it adopts 33 pages of text outlining a framework for further progress negotiating emission reductions, monitoring and verifying emissions, funding adaptation and forest protection. The key points of the agreement include: ● Carbon dioxide capture and storage in geological formations will be included as an eligible project activity. ● The 37 countries are allowed to fulfill their greenhouse gas emission obligations by investing in projects that reduce emissions in developing countries. ● Action is included to protect the world’s forests because deforestation accounts for nearly one-fifth of all global carbon dioxide emissions.

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● Technology transfer will be facilitated to reduce GHG emissions through innovation in transport infrastructures. ● A Green Climate Fund of US$30 billion of new contributions for the period 2010– 2012 is established to help the most vulnerable developing countries adapt to the unavoidable impacts of climate change and reduce their carbon footprints. ● In the longer term, developed countries committed to a goal of mobilizing jointly US$100 billion per year by 2020 to address the needs of poorer countries. A ‘‘significant share’’ of new multilateral funding for adaptation should flow through the Green Climate Fund, which will be managed by the World Bank for the first 3 years, delegates agreed. The United Nations Collaborative Programme on Reducing Emissions from Deforestation and Forest Degradation in Developing Countries (REDD) has lead REDD efforts in some countries in 2010, such as Bolivia, Congo, Indonesia, Panama, Tanzania, Viet Nam, and Zambia. More info is available from http://www.un-redd.org. Inventory and monitoring of forest is an essential step for such efforts, including the use of airborne and spaceborne remote sensing technologies. After the Cancun agreement, many developing countries are initiating REDD plans to preserve national forests, such as announced by the Environment Minister of Pakistan during the international biodiversity conference on December 31, 2010 [89].

Lack of Multimodal Transport Strategy Consideration by International Lending Institutions As a part of the infrastructure loan evaluation, the World Bank and other international lending institutions historically did not encourage multimodal strategy evaluation for transportation infrastructure loan projects in urban areas or at regional levels, as evidenced by the following discussion. Since the World Bank’s first loans during the late 1940s to finance the reconstruction of the post-war economies of Western Europe, the World Bank has loaned more than $330 billion to developing countries [90]. The latest data shows that the World Bank’s worldwide lending accounts for 20% in transport sector [91]. Total loan amount of about $33 billion in the last decade was dispersed to transport infrastructure and services. Of that, a significant 73% was spent on roads, with the remaining only 27% on rail, ports, aviation, and transport services [92]. Highway project analysis traditionally lacked considerations for congestion, vehicle emissions, and public health impacts in comparison of life cycle costs and benefits of roads versus rails transportation strategies. Additionally, the World Bank financing of transport vehicle fleet has been decreasing, and effort has been made to transition from public to private enterprises, especially for freight haul trucks. This in turn became impetus for building more roads with higher emitting vehicular traffic and increasing the decay of (lower emission per passenger) rail infrastructure in many countries. The World Bank increased its efforts in recent years to provide developing countries greater access to finance and technology for climate change mitigation efforts. However, climate change mitigation was considered in less than 20% of the World Bank’s energy

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sector lending in 2005 [93]. Additional funding sources in recent years include: the Clean Technology Fund (CTF) in 2008 [94], Climate Investment Funds (CIF) fund, and Global Environment Facility (GEF) funds, established in 1991 [95]. However, some groups of civil society [92, 93, 95] are skeptical of the World Bank’s CTF and other environment related financing programs because of the evidence of unsustainable growth outcomes of loan projects, including more spending on oil, coal, and gas (94% in 2007–2008 alone); privatization and export driven production which do not emphasize on environmental sustainability; lack of gender justice by ignoring women from loan negotiations; and priority for highway funding, resulting in decay of rail infrastructure. These concerns and future use of Green Climate Fund created by the UNFCC’s 2010 Cancun Agreement warrant that the World Bank and other international lending institutions should change their outlook of transport and energy loan evaluation policies, considering the adverse impacts of GHG emission, air pollution, and social and economic deterioration of the poor and women.

Best Practices Annually 33 billion tons of anthropogenic CO2 emission is produced worldwide [86, 96]. A significant part of the anthropogenic CO2 emission is produced by on-road vehicles, especially in cities. These emissions can be reduced by implementing more efficient and low fuel mass transit systems and other sustainable multimodal transport strategies. A successful sustainable transportation policy requires all stakeholders (car manufacturers and dealers, general public, and government agencies) and policy makers to set goals to reduce emissions on national levels. Examples of the best practices of abatement strategies for transport alternative and their effectiveness evaluation methods are discussed in this section. These best practices will be viable options for adaptation and implementation by other urbanized areas and megacities in the rest of the world.

Unites States Examples Reductions in transport related emissions and subsequent improvements in air quality have been made through government enforcements of regulations and voluntary participation by the industry and the public in the United States. The current economic recession has shown an inherent vulnerability in the automotive industry due to the slump in demand of new cars. The ‘‘Cash For Clunkers’’ program, initiated by Obama Administration in the United States, was extremely successful to remove older fuel drinking cars from the roads. Additionally, according to the US Treasury [96], the $3 billion spent on the program produced 42,000 jobs, sold 700,000 cars, and created 0.3–4% worth of gross domestic product (GDP). Statewide Efforts (California and Maryland): With 36 million inhabitants, California is the most populace state. California Department of Transportation (Caltrans) operates

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and maintains 15,269 highway miles which is less than 9% of total 170,000 miles of public roads. California’s highway network supports the sixth largest economy in the world due to its rich agriculture and timber production, diverse industries, computer technology firms, and movie industry [50]. Caltrans evaluates transportation project delivery using several key indicators of performance measures/outcomes: travel time and delay (mobility), travel modal choice (accessibility), person- and vehicle-traveled distance (productivity), condition index (system preservation), crashes/fatalities (traveler safety and security), and indictors of air quality, noise, and energy consumption (environmental quality). California’s Climate Action Team expects ‘‘smart land use and intelligent transportation’’ to make the second-largest contribution toward meeting the state’s ambitious GHG reduction goals [45]. Maryland is relatively a small state, ranked 42nd in area, but it is the fifth densest state in the United States with an estimated population of 5.6 million. Per capita VMT is nearly the same as the US average, with nearly 75% VMT occurring in urbanized areas [51]. Maryland State Highway Administration (SHA) operates and maintains 5,263 highway/ road centerline miles, which represents less than 20% of the total 29,265 roadway centerline miles in the state. However, the highway network carries 70% of the total VMT in the state. Mass transit infrastructure consists of subway, light rail, and bus service. Currently, 82% of freight moves by roads with half of the freight simply passing through the state. Maryland publishes the annual attainment report on transportation system performance in five categories against target values [50]. These performance measures include: driver satisfaction, percent of highway network in preferred condition, acres of wetland or wildlife habitats restored, fuel usage of light vehicle fleet, user cost saving due to incident management, transport-related emission by region, transport-related GHG emissions, vehicle emission reduction, travel demand management performance, reduction in VMT through park-and-ride, bicycle and pedestrian fatalities and injuries, percentage of highway centerline miles with a bicycle level of comfort target and miles of highways with marked bicycle lanes, and percentage of SHA road centerline miles in urban areas with sidewalks and percentage of sidewalks compliant with Americans with Disabilities Act (ADA). A success story for a multimodal highway project was the Intercounty Connector (ICC) designed to relieve congestion between two major corridors (Interstate Highway I-270 and I-95) in Montgomery and Prince George’s counties [50]. Sustainable Energy and Transport Strategies in Major Cities (Atlanta-Georgia and Austin- Texas): Atlanta, Georgia, has been a nonattainment urban area for many years due to higher level of air pollution. One of the factors for its program success is TDM marketing by the Georgia Department of Transportation (GDOT) to reduce congestion and GHG emissions, using reliable performance metrics to pitch its messages to the public [51]. For example, the Clean Air Campaign (CAC), a not-for-profit corporation, was formed in 1996 by collaboration between government, business, and civic organizations [51]. Originally funded by the GDOT as a public awareness campaign for air quality degradation associated with vehicle emissions, the CAC began to conduct employer outreach in 2000. For the most part, this role focuses on changing travel behaviors through informed decision making and public education campaign. The most effective

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TDM marketing programs involve a variety of partners within a community, including public officials, community organizations, and individuals support transportation alternatives. These partner organizations include: Transportation Management Association (TMA), Employer Service Organizations (ESOs), Rideshare matching and guaranteed ride home (GRH) service, and Vanpool services. Through these TDM efforts commuting alternatives in Atlanta metro area boasts an annual reduction in pollution and the following benefits each year [51]: ● ● ● ●

Sixteen million car trips eliminated from metro Atlanta roadways More than 200,000 t of pollution not released into the air More than $156 million estimated in reduced commute costs Thirty million dollars estimated in health-related costs savings due to improved air quality

Austin, Texas: The City of Austin, Texas, initiated its energy conservation and GHG reduction program in 2007. By winning the 2010 national climate protection award on September 29, 2010, Austin has been recognized nationally for reaching the 5th milestone of monitoring and verifying results of Cities carbon reduction plans [97]. This was announced by the Local Governments for Sustainability, USA, which is associated with the International Council for Local Environmental Initiatives (ICLEI). The City of Austin has implemented an innovative Transportation User Fee (TUF) which averages $30–40 annually for a typical household in their utility bills. This charge is based on the average number of daily motor vehicle trips made per property, reflecting its size and use. This regulation rewards households that reduce their vehicle ownership. The city provides exemptions to residential properties with occupants that do not own or regularly use a private motor vehicle for transportation, or if they are 65 years of age or older. The Austin Climate Protection Plan, developed by the City to reduce GHG emissions, includes many elements [97] such as: ● Making all City facilities and operations carbon-neutral by 2020 ● Reducing Austin Energy’s carbon footprint and making any new electricity generation carbon-neutral ● Enhancing Austin Energy’s Green Building program for achieving energy efficiency in buildings ● Engaging businesses and citizens to reduce their carbon footprints

London, UK London implemented a congestion pricing program effective February 2003 that charges drivers £5 each time they enter the central city (22 km2 area, 1.2% of greater London), similar to the toll charged at major bridge crossings [71, 98]. This congestion-designated zone is surrounded by perimeter roads that serve as its boundaries. The charge is enforced by fixed and mobile surveillance cameras that are linked to automatic license plate number

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recognition technology. Heavy penalty of £80 is assessed against the vehicle owner if the charge is not paid by midnight. There is also a 90% discount for residents of the congestion zone. There is a concern about negative financial impact on the local retail sector and on wider economy [71]. The program showed the following benefits to Central London: a 30% reduction of car travel, average travel speed increased from 13 to 17 km/h, and congestion delay reduced by 30% [98]. The reduction in vehicular traffic volume also improved air quality. The levels of NOx, PM10, and CO2 concentrations in London decreased by 16–19% after the congestion pricing program was implemented [98].

Mexico City Metropolitan Mexico City ranks second in 2006 lists of megacities at 19.24 million population (> Fig. 23.15). The city expanded in the late 1930s when a combination of rapid economic growth, population growth, and a considerable rural migration filled the city with people. Mexico City houses 80% of all the firms in the country, and 2.6 million cars and buses bring people to work and shop in them. Street vendors make up an enormous part of Mexico’s job force [69]. The extensive industrial and commercial activities within the city are primarily responsible for its prosperity as well as many of the environmental problems. High levels of emissions are responsible for permanent respiratory problems suffered by more than one million people. Air quality degradation worsens by the fact that Mexico City is situated in a basin [69]. The geography prevents winds from blowing away the pollution, trapping it above the city. More than 30% of the city’s vehicles are more than 20 years old. The city has been striving to implement solutions which include [69, 70]: ● Bicycles and motorcycles are popular. Numbers of cars are reduced on roads by enforcing the law of banning cars on roads on certain weekdays. ● A thriving LRT system is in operation for years, with nine lines and 75 miles of tracks and more under construction. ● Metrobus public transport system has significantly contributed in improving both air quality and easing transport problems. Bus journey times have been halved and CO2 emissions have been reduced by 80,000 t a year.

Sa˜o Paulo, Brazil The megacity of Sa˜o Paulo has a population of 18.61 million and ranks 5th in the 2006 list of top megacities (> Fig. 23.15). Although it is home to only 15% of country’s inhabitants, this megacity consumes 60% of Brazil’s energy. The city emitted 83 million tons of CO2 in 2003. In metropolitan Sa˜o Paulo, there were 2,000 major industrial facilities and 7.2 million passenger and commercial vehicles as of 2006, which include 93.5% lightduty and 6.5% heavy-duty diesel vehicles [86]. Approximately 76.3% of the light-duty vehicles burn a mixture of 78–80% gasoline, 22% consume ethanol (referred to as

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gasohol), and 17.2% use hydrated ethanol (95% ethanol + 5% water). In comparison, up to 10% ethanol is used in gasoline in the United States for cars and light vehicles. On a daily basis, public transportation plays a key role in meeting transportation needs of people living in and commuting from 39 municipalities in Sa˜o Paulo. Sa˜o Paulo’s complex but successful public bus transit system operates over 26,000 buses on nearly 2,000 routes carrying up to 11 million people daily. The bus system uses especially constructed bus lanes, which enables bus commuters to avoid traffic jams on the streets and buses to travel faster than cars [71, 86]. There are also several rail transit systems and connecting train lines. A noncontact smartcard allows riders discounted prices for multiple rides and makes for easier transitions between bus, train, and subway transit systems.

Bangkok, Thailand Bangkok was long been considered a city plagued by congestion and poor air quality. The country and metropolitan city governments adapted several environmental strategies in the 1990s included the formation of environmental law enforcement bodies. The key steps for automobile emission reductions were: phasing out lead from fuel by the mid-1990s by making unleaded gas cheaper, introducing vehicle inspection and maintenance programs, and reducing the number of cars on roads by providing better public mass transport options. Bangkok Mass Transit Authority operates air-conditioned and ordinary buses. Articulated buses used in the BRT system are for 90 and other buses are for 40–50 passengers. However, the ordinary buses are being phased out [70, 73]. Most of the buses run on diesel, but they are being converted to cleaner and cheaper natural gas vehicle (NGV) engine. Recently, it operates new routes of NGV-powered air-conditioned vans, shuttling people between city center and suburban communities.

Future Directions There is a strong link between mobile sources of GHG, air quality, and the transportation sector. First, transportation emissions are the main cause of air quality problems in many megacities and large urban centers. This seems to be the trend in the megacities of the developing world, where these emissions will soon become the dominant source of air pollutants. Second, economic growth is closely linked to personal and freight transportation and efficient mobility, thus restrictions of transportation activities for improving air quality, could hinder economic growth. The challenge is thus to improve air quality and reduce GHG emissions while ensuring personal and freight mobility.

Livable Cities and Eco-friendly Lifestyles A 2004 report by the U.S. National Academies examined the influence of the built environment on physical inactivity in the United States and recommends that

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opportunities be provided to increase physical activity and study social marketing when changes are made to the built environment – whether retrofitting the existing facilities or constructing new developments and communities [56]. The lack of physical mobility and walking as a means of traveling about has attributed to obesity and related health problems in US cities. Similar concerns about transport equity are discussed in a 2009 WHO report [57]. Modern cities have typically been designed for cars and vehicular traffic. Unlike residents in urban areas, residents in rural places are less likely to walk to work or commercial establishments. This is the case in Mississippi, a rural state which has been ranked one of the top three states for obesity problems for the past several years. Transport infrastructure and traffic operation management also influence livability of a city and eco-friendliness of its people. Zurich, Switzerland, topped the 2007 list of the most livable cities in Western Europe. Zurich’ shares of commuter trips include 24% walking trips, 40% public transport, and 36% private automobiles [76]. The proportion of private automobiles is almost less than half the automodal share in other major cities of the western world and Australia. Additionally, bikeways, well-managed intercity rail services, and about 2,000 trains traveling daily to different destinations reflect the ecofriendly lifestyles of Zurich’s inhabitants. The long-term sustainability vision adopted by New York City also includes better transit mobility, less congestion, and nonmotorized transport facilities [78]. Many cities in Western countries have been recognizing the health and environmental benefits of walking and cycling and are trying to provide safe ecofriendly facilities for these activities. However, during the same period, nonmotorized trips in many cities of the developing world have been declining due to a focus on improving motorized vehicle flow on roads and ignoring the needs of pedestrians and other people who depend on mass transit vehicles to commute.

Sustainable Accessibility, Mobility, Commuting, and Economic Prosperity Mobility and access to affordable and clean transportation to all people in a city is the key to economic growth, social welfare, and quality of life. In emerging economies and developing countries, economic growth drives development and prosperity. Inadequate mobility places limitations on the poor and other disadvantaged groups to job access, educational institutions, medical care and hospitals, safe recreational facilities, as well as making them more susceptible to fire, rain, and other natural hazards. However, in many large cities of the developing world, adequate mass transit and public transportation modes are not sufficiently provided and managed. Millions of other inhabitants without cars waste long hours in congestion and unsafe travel. Traffic safety data from Karachi shows that in 2007 more than 40% road fatalities involved pedestrians [99]. People in many megacities suffer from stress, air pollution–related health problems, and deterioration of quality of life. Sustainable mobility is defined as the ability to meet people’s mobility needs without adversely impacting societal or ecological values for present and future generations.

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Due to the important role of nonmotorized modes of travel in promoting better livable cities, a more suitable term is sustainable accessibility. Transport strategies for sustainable accessibility and mobility should be environmentally sustainable, socially sustainable to ensure equity among all sectors of the society, and economically and financially sustainable [72]. Sustainable accessibility is imperative when planning and implementing nonmotorized and multimodal transportation strategies to support sustainable growth of cities while responding to mobility and accessibility needs of all sectors of the society.

Equity and Shared Responsibility Emissions from fuel combustion are growing faster for the transport sector than for other sectors; this growth is more pronounced in the developing world than in the industrialized and developed countries. Increases in CO2 emissions have been seen in all transport modes, but particularly in road transport.

Passenger and Freight Rail Modal Share Emissions from mobile sources in the United States grew 29% between 1990 and 2004 [35]. Residential emissions have increased 13% in the last 2 decades. Commuters waste millions of hours and gallons of fuel in traffic congestion in and around cities. Lots of emphasis for reducing congestion and GHG emissions has been on increasing the modal share of mass transit, increasing car fuel efficiency, and reducing volume of cars and other two-axle automobiles by travel demand management strategies (car pooling, HOV lanes, and increasing parking prices downtown). The executive branch of the US government and Congress has put forth little known effort to reduce truck travel and associated GHG emissions. Publicly, no pressure has been put on truck travel which produces three to four times more GHG emissions for every gallon of fuel in comparison to cars. Fuel efficiency drive has not been geared to trucks. Considering freight truck business employs millions of heavy truck drivers, both technologically and politically, there is little pressure on trucking industry to reduce GHG emissions. The EPA data [7] also shows that in United States: (a) medium and heavy trucks used for freight travel produced 410.8 million tons of CO2e emissions in 2007, amounting to 79.5% increase from 1990, and (b) truck share of total transportation-related GHG emission was 20.5% in 2007. But what is the real cost of trucks-related GHG emissions and physical damage to road and highways? Here are some underlying facts: ● Trucks occupy more lane space on publicly owned and financed urban roads, intercity roads, and all types of public highways. ● Trucks worsen congestion on urban and suburban highways and cause safety problems and crashes. ● Trucks pay a small share of their use of roads and highways and none for construction or maintenance costs.

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● Trucks cause most of the physical damage to pavement structures and bridges, which are structurally designed for truck weight and cumulative applications over the highway design life. Car traffic has virtually no deterioration effect on pavements. ● The road and highway infrastructure is totally built and maintained by tax payer’s money, and trucking companies do not have to factor these costs in their business decisions. ● In other words, freight trucks are being subsidized heavily by tax payer money for providing and maintaining the road and bridge infrastructure. A national transport policy decision is needed to apply additional charge or fee on trucks for: (1) road use charge on lump-sum annual basis or truck-travel distance basis, (2) pavement damage cost attributed by annual distance driven, and (3) carbon emission charges per ton-mile or ton-km because of their significant carbon footprint. The revenue should be used to improve road infrastructure condition, build more intermodal facilities at primary distribution centers throughout the United States, and encourage businesses to use rail mode more often and for longer regional destinations. For example, Norway and Germany have implemented road-use pricing and road tolls on freight trucks; however, several civil society groups argue that this toll revenue should not be simply used on road maintenance and reducing congestion on roads, but to invest in other alternatives, for example, fuel-efficient and mass transit transport. Compliance with EPA rules for emission reductions of locomotives [80] and more use of fuel-efficient rail transportation of freight throughout the United States and passenger travel on heavily trafficked road corridors will reduce the mobile GHG emissions significantly and improve air quality. Moreover, freight rail mode is privately owned in the United States and, unlike freight trucks, no tax-payer money is used to subsidize freight rail and bridge infrastructure costs. Here are some numbers reported by the US rail industry [81, 82]: ● Rail locomotives are four times more fuel efficient than trucking; therefore, moving freight by train instead of truck reduces GHG emissions by 75%. ● Replacing just 10% long haul freight trucks by rail can reduce GHG emissions annually by 12 million tons. This reduction is equivalent to taking off two million cars from roads or planting 280 million trees. ● A train can carry the freight of 280 or more trucks reducing highway congestion and creating space for 1,100 or more cars. ● Rail track costs about 2–4 million dollars per mile in relatively short time in comparison to about 10–15 million dollars per mile for highway construction and 5–10 years to build and higher life cycle costs due to pavement maintenance needs. Unlike road vehicles, a dual-track rail infrastructure keeps trains moving at designated speeds safely and efficiently with no ‘‘congestion’’ and no extra emission. The purpose of this discussion is that equal opportunity should be provided by the authorities to rail/train operators on selected long-distance corridors to compete with freight truck operators and expressways for regional commuters. This approach should be considered as a national

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policy and priority matter. The freight trucks in the United States are subsidized by operating on public highways, whereas the rail/train operators do not have similar assistance of public funds for constructing and maintaining rail infrastructure. Unfortunately, similar disparity is happening in most developing countries where rail generally is operated by public agencies like highways but rail gets little or no funding to modernize its train stocks and rail infrastructure. National transportation policies have been derived from lack of understanding of the mobile sources of GHG emissions and effects of other road transportation–related pollutants on public health and quality of life. This led to a gradual decline in rail service quality over the last 3 decades because passenger rail transport has been predominantly used by the poor people.

Involving Stakeholders and Public for Sustainable Transport and Mitigation Strategies Successful implementation of socially equitable and environmentally sustainable development requires area monitoring of air pollutants including CO2, life cycle cost analysis, marketing plans, involvement of all stakeholders (oil and motor vehicle industries, retail businesses, and transport services), and public awareness campaigns for shared responsibility within a region and globally. It is estimated that 30% fuel is wasted in congested cities in finding parking places. Many car manufacturers are working on future concept cars for megacity markets to serve the city center area without traditional carbon footprint [100]. These small lightweight lithium battery–powered green cars are designed for lower speeds and very small or zero CO2 emission per mile. By reducing vehicular emissions, air quality will be protected, greenhouse gases will be reduced, and the effect on global warming will diminish. In order to develop and implement green transport technologies to reduce GHG emissions, it is recommended for governments at national, state/provincial, and local levels to institute policies and provide initiatives for green technology growth. At the same time, a push for public support is crucial for the future success of green technology implementation so that it may be firmly established in the long term. Stakeholders’ cooperation and involvement are required for the following: (1) sustainable development of the built environment, (2) identification of less polluting transportation technologies, and (3) implementation of abatement strategies to mitigate congestion and its adverse impacts on traffic safety, global warming, and air quality. Stakeholders should be identified at community, regional, and national levels. An integrated approach involving all stakeholders can help manage and reverse many blighted parts of our cities, urban and suburban communities, and rural and industrial areas to livable conditions. Governments must take initiatives to increase public awareness of mobile GHG problems, mitigate adverse transportation impacts and sprawl, and improve air quality and quality of life of millions of people each year. The use of nongovernmental organizations (NGOs) [72, 79, 99] and public–private partnerships should be promoted to create environmentally and financially sustainable transport management strategies.

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Concluding Remarks The vehicle emission and demand on energy (due to the increased built areas and population migration from rural areas) have adverse impacts on the environment, both in air quality degradation and increases in greenhouse gas emission. Governments throughout the world must consider reduction in greenhouse gas emissions and other air pollution a national priority. Further, they should involve all stakeholders in finding multimodal solutions including nonmotorized trips for the mobility and accessibility in growing cities and long-haul transport needs to support development and economy. A reasonably quantifiable sustainability scale is CO2e emission per capita that can be used worldwide for evaluating performance of sustainable transportation and development policies by government agencies and cities. The worldwide reduction of greenhouse gases from transportation sources and the efficient use of energy in urban and industrial applications should be important for sustaining the quality of life of current and future generations. Although awareness has increased in the public related to the global damaging effect of greenhouse gas emission and public health hazards from other air pollution, when it is directly tied to economic prosperity, survival, and individual freedom to travel by car, vehicle emissions and air pollution becomes secondary. By providing knowledge to decision-making authorities in both industrialized and developing countries, it is expected that they will be able to adapt and implement many available high pay-off research products in response to sustainable national transportation planning priorities.

Acknowledgments The author’s research was primarily conducted at the Center for Advanced Infrastructure Technology (CAIT) of the University of Mississippi. Thanks are due to author’s former graduate students Katherine Osborne, Jessica Headrick, Bikila Wodajo, Carla Brown, and Kanok Boriboonsoms for their contributions. Thanks are also due to CAIT research assistants Eric Shackelford for CO2 calculations associated with road vehicle emissions in selected cities and Cherrelle Williams for editorial assistance.

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93. Sohn J, Nakhooda S, Baumert K (2005) Mainstreaming climate change at the multilateral development banks. World Resources Institute, Washington, DC 94. Weiss MA, Logan J (2008) The World Bank’s clean technology fund. RS 22989, Congress Research Service Report to U.S. Congress 95. Rooke A, Zuckerman E, Schalatek L (2009) Doubling the damage: World Bank climate investment funds undermine climate and gender justice. Gender Action, Washington, DC. www.genderaction.org 96. The Realignment (2009) Gas-free cars and high speed rail. http://realignmentproject. wordpress.com/2009/09/16/gas-free-cars-andhigh-speed-rail/. Accessed 15 Sept 2010 97. City of Austin (2010) City of Austin wins national climate protection award. http://www.ci.austin.tx. us/acpp/default.htm. Accessed 10 Oct 2010 98. Limanond T (2010) Travel demand management policies. Sustainable Urban Transport Project (SUTP). http://www.sutp.org/ index.php?option=com_content&task=view&id= 136&lang=uk. Accessed 15 Sept 2010 99. Jumma R (2008) Road traffic injury research and prevention centre (Presentation). Urban Resource Centre, Karachi, 8 Feb 2008. http:// www.urckarachi.org/Forums.HTM. Accessed 15 Sept 2010 100. Megacity Moves (2010) Motor Trend Magazine, July 2010, pp 20–22

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24 Energy Efficiency: Comparison of Different Systems and Technologies Maximilian Lackner The Vienna University of Technology (TU Vienna), Wien, Austria Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 844 What Is Energy Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 846 Significance of Energy Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 848 Benefits of Energy Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 850 Downside of Energy Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 850 Energy Efficiency versus Energy Demand: The Rebound Effect . . . . . . . . . . . . . . . . . . . . . 851 Energy Intensity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 851 Emission Intensity (Carbon Intensity) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 852 Historical Development of Energy Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 852 Assessing Energy Efficiency Improvements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854 Innovation and New Technologies for Energy Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . 856 Typical Energy Efficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 857 Benchmarking of Energy Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 858 Energy Efficiency World Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 859 Some Not-So-Energy-Efficient Inventions and Practices . . . . . . . . . . . . . . . . . . . . . . . . . . 859

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_24, # Springer Science+Business Media, LLC 2012

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Barriers to Energy Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 860 Levels of Energy Efficiency: From Process to Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861 Energy Efficiency Investments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 862 Introducing Energy Efficiency Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 863 Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 864 Power Plants and Electricity Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 865 Energy Transmission and Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 866 Energy Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 866 Life Cycle Assessment (LCA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 867 Total Cost of Ownership (TCO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 869 Energy Efficiency in Various Sectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 870 Agriculture and Food . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 870 Transportation and Logistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 871 Road Transporation and Internal Combustion Engines . . . . . . . . . . . . . . . . . . . . . . . 871 Passenger Cars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 872 Ships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 873 Rail Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 873 Air Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 874 Pipeline Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 874 Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 875 Crosscutting Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 875 Steam and Boilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 878 Energy-Intensive Industries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 878 Iron and Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 879 Aluminum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 880 Other Primary Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 880 Pulp and Paper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 881 Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 882 Glass Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 883 Petroleum Refining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 883 Petrochemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 883 Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 884 Chemical Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 885 Pharmaceutical Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 888

Energy Efficiency: Comparison of Different Systems and Technologies

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Public Sector and Community Infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 888 Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 889 Appliances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 890 Lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 891 Consumers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 892 Tips and Tricks for Consumers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 893 Initiatives for Energy Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 893 Other Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 894 Energy Conservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 894 Further Study and Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 895 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 896

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Abstract: The efficient use of energy, or energy efficiency, has been widely recognized as an ample and cost-efficient means to save energy and to reduce greenhouse gas emissions. Up to one third of the worldwide energy demand in 2050 can be saved by energy efficiency measures. In this chapter, several important aspects of energy efficiency are addressed. After an introduction and definition of energy efficiency, historic development, state-ofthe-art, and future trends of energy efficiency are presented in the light of life cycle assessment and total cost of ownership considerations. Energy efficiency in various sectors, viz. energy production, energy transmission and storage, transportation, industry, buildings, appliances, and others, is reviewed. Concurrent measures such as recycling or novel materials are also discussed and touched upon. Energy conservation is covered in the final section of this chapter. References for deeper study are provided with an emphasis on guidelines on how to improve energy efficiency. Given the breadth of the subject, only exemplary coverage can be aimed for. The purpose of this chapter is to highlight the significance of energy efficiency and to provide cross-learnings from achievements in different sectors so that energy efficiency in the readers’ own facilities and installations can be assessed and improved with cost-effective means as a contribution to climate change mitigation, cost savings, and improved economic competitiveness.

Introduction Energy stands for a range of commodities, for instance, thermal or electrical. It is a scalar physical quantity and can be defined by the amount of work that can be done by a force. Energy comes in different forms: Classical mechanics distinguishes between kinetic and potential energy. In the everyday world, one can see chemical, thermal, gravitational, light, and electrical energy, to name but a few. These forms of energy can be transformed into each other. The SI unit of energy is joule (J), with other common units being kilowatt hour (kWh), ton of oil equivalent (toe), and British thermal unit (Btu or BTU). 1 J = 1 kg/m2/s2 = 1Ws 1 kWh =3.6
106 J 1 toe = 41.868 GJ = 11,630 kWh 1 btu = 1.060 kJ; 1 Quad = 1015 (1 Quadrillion) btu = 1.06
1018 J The worldwide energy consumption is on the order of 500 exajoules (5
1020 J) per year, which corresponds to an average consumption rate of 15 terawatts (1.5
1013 W). Energy efficiency, i.e., the efficient use of energy, describes the use of less energy to achieve the same level of energy service. Energy efficiency is a universally applicable concept relevant for consumers and industry alike. It can be achieved by a more efficient technology, an improved process, or a change of individual behavior. Obstacles toward the introduction of energy efficiency are often not imposed by technical or economic reasons, but rather by the habits, norms, and mindset of our social institutions, often termed ‘‘market barriers.’’ Therefore, apart from increasing research and development (R&D) to create and improve energy-efficient technologies and appliances, one has to address the

Energy Efficiency: Comparison of Different Systems and Technologies

24

issue from other angles such as policy making [1], too. The proliferation of energyefficient technologies requires stimuli outside the scope of technical, and economic, logic arguments. Also, it has to be noted that the proliferation of technically and economically superior technology is a gradual one [2]. Subsidies can have an important effect on the penetration rate of new energy technologies [3], as can industry agreements [4]. In its most current World Energy Outlook [5], released in autumn 2009, the International Energy Association (IEA) has compared the ‘‘reference scenario,’’ a kind of baseline or BAU (business as usual) scenario, to its suggested course of action to control climate change, which is termed ‘‘450 scenario’’ (discussed below). In the reference scenario, worked out for the period of 2010–2030, the world is set for a rise in temperature of up to 6 C, leading to severe global challenges in terms of irreversible environmental damage and energy security. The notion that energy security can be an issue has existed since the OPEC oil embargo of 1973 (otherwise known as the oil crisis), followed by the second energy crisis 6 years later. It was recently revived in Central Europe in the winter of 2009 [6, 7]. Globally, crude oil prices, exceeding for the first time 100 USD per barrel in the same year, have also led to concerns about energy security in terms of affordability and sustainability. There is no straightforward definition for energy security. In [8], indicators based on availability, accessibility, affordability, and acceptability were created. With depleting fossil fuel sources and concentration of these in fewer regions, not all of which are considered politically stable, it can be anticipated that fossil fuel prices will go up and will fluctuate more strongly, partly driven by speculation. Today, the world relies to 80% on fossil fuels for primary energy production. Within the 20 years considered by the IEA, the worldwide energy demand is predicted to increase by 40% based on today’s level. The ‘‘450 scenario,’’ in which the concentration of greenhouse gases in the atmosphere has to be kept below 450 ppm CO2 equivalent, would only lead to a temperature increase of 2 C compared to preindustrial times (because other greenhouse gases such as CH4 and N2O have different greenhouse warming potentials [GWP], they are expressed in CO2 equivalents for easier comparison, see later). That IEA ‘‘450 scenario’’ demands for fossil-fuel consumption to peak by 2020 and for energy-related CO2 emissions to be cut from 28.8 Gt in 2007 to 26.4 Gt in 2030 [5]. In the reference scenario, the world’s primary energy demand grows by 1.5% per year from 2007 to 2030, compared to 0.8% per year in the ‘‘450 scenario.’’ The two scenarios are depicted in > Fig. 24.1, reprinted from [5]. As it can be seen from > Fig. 24.1, the largest contribution to CO2 abatement – more than half of total savings – can be made by energy efficiency measures of end-users. One half (2030) to two thirds (2020) [5] of the total required CO2 reduction can be achieved with energy efficiency. Another strong contribution comes from changes in the mix of power generation technologies. The reference scenario, by contrast, assumes 1,000 ppm of CO2 equivalent in the atmosphere. > Table 24.1, based on [5], shows the worldwide energy-related CO2 emissions. Similar results, focused on the USA, were found in [9]. As a conclusion, one can say that energy efficiency has a huge potential. In this chapter, several aspects of energy

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. Fig. 24.1 Global CO2 emissions in the ‘‘reference scenario’’ and in the ‘‘450 scenario’’ in the 2009 World Energy Outlook of the IEA. The table on the right provides the estimated figures for CO2 emission abatement and the required projected investments needed to achieve the ‘‘450 scenario.’’ While one fifth of the CO2 reduction in 2020 stems from renewables, two third can be attributed to energy efficiency measures (Reprinted from [5] with permission from OECD/IEA) . Table 24.1 Global CO2 emissions in the ‘‘reference scenario’’ and the ‘‘450 scenario’’ in the 2009 World Energy Outlook of the IEA, compare > Fig. 24.1 [5] CO2 emissions

1990

2007

2030, reference scenario

2030, 450 scenario

Total

20.9 Gt

28.8 Gt

40.2 Gt

26.4 Gt

Per capita Power generation Transport Industry

4.0 t 36% 22% 19%

4.4 t 41% 23% 17%

4.9 t 44% 23% 15%

3.2 t 32% 29% 17%

Buildings Others

14% 10%

10% 10%

8% 9%

10% 11%

efficiency for climate change mitigation are highlighted. Complete coverage of the topic cannot be provided within the scope of this chapter, so a selection has been made to present some of the most relevant areas related to energy efficiency.

What Is Energy Efficiency Energy efficiency is, as the term implies, the efficient use of energy, i.e., using a lower amount of energy to achieve the same level of energy service [10]. It can be achieved by improved behavior or by more efficient technology.

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Thermodynamics teach that energy can only be transformed. According to the First Law, energy can neither be created nor destroyed. A change in the internal energy of a system, U, can be achieved by adding heat Q or work W: dU ¼ dQ  dW

(24.1)

where dQ and dW are incremental changes in heat and work, respectively (the minus denotes that positive work is being done by the system). Equation > 24.1 can be rewritten as dU ¼ T dS  pdV

(24.2)

where the work done by the system while expanding is pdV. The amount of heat added to the system can be described by dQ = TdS with T being the temperature and S the entropy. In a heat engine, thermal energy is converted to mechanical energy by exploiting a temperature gradient between a hot and a cold reservoir for an energy transfer. The efficiency of such a heat engine is given by the ratio of useful power to heat energy input. It can be derived as follows: dW ¼ dQc  ðdQh Þ

(24.3)

dW = pdV, i.e., the work done by the engine Qh = ThdSh, i.e., the heat energy taken from the high-temperature reservoir Qc = TcdSc, i.e., the heat energy delivered to the cold temperature reservoir. In the reversible Carnot heat engine cycle (dSc = dSh, i.e., no net change in the entropy), the maximum efficiency is
max ¼ 1 

dQc ðTc dSh Þ Tc ¼1 : ¼1 ðTc dSh Þ dQh Th

(24.4)

The Carnot efficiency is a theoretical one because it considers an infinitesimally small temperature change. As for ‘‘real’’ heat engines, such as internal combustion engines or power plants, one is typically after a sizeable power output, which is an irreversible process. Therefore, the ideal, reversible Carnot process does not well describe the efficiency of a technical system. Taking the concept of endoreversible thermodynamics [11] into consideration, the efficiency of a heat engine operating in irreversible mode can be obtained as rffiffiffiffiffi Tc
¼1 (24.5) Th This expression is known as the endoreversible efficiency or Chambadal–Novikov efficiency [12, 13]. It allows a more realistic estimation of the efficiency of a heat engine, which can be termed semi-ideal. The endoreversible efficiency takes the destruction of exergy in an irreversible process into consideration. Exergy is the highest possible useful work during a process that brings the system into equilibrium with a heat reservoir [14–18]. It was introduced by Gibbs as a special form of the Gibbs available energy. Exergy is the work potential of a system; it can be potential (gravitational or magnetic force field), kinetic (velocity), physical (pressure, temperature), or chemical (composition) [15]. Exergy analysis can be used to determine inefficiencies.

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. Table 24.2 Efficiencies of power plants [19, 20] Power plant A B C

Technology Coal-fired Nuclear power Geothermal power

Tc ( C) Th ( C) 25 25 80

565 300 250

h (Carnot) h (Endoreversible) h (Observed) 0.64 0.48 0.33

0.40 0.28 0.178

0.36 0.30 0.16

> Table 24.2, compiled from [19, 20], compares the Carnot and Chambadal–Novikov efficiencies to the actual ones of three power plants. From the above table, it can be seen that the endoreversible efficiency predicts the observed one well. In [21], theoretical efficiency limits for energy conversion devices are reviewed. The combination of energy efficiency and renewable energy is often referred to as ‘‘sustainable energy.’’ Sustainability was defined in 1983 by the UN World Commission on Environment and Development as follows: ‘‘Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.’’ ‘‘Energy productivity,’’ similar to energy efficiency, has a narrower scope. Another aspect related to energy efficiency in the context of climate change mitigation is the concept of greenhouse gas emission factors. Apart from CO2, other greenhouse-active gases can be emitted, such as CH4, N2O, or halocarbons. Reference [22] provides an overview. There is a huge potential for energy efficiency improvements. Three recent studies on this topic are [23] and [9], making projections until 2020, and [5], which extends its forecasts to 2030. It needs to be stressed that such impressive potentials can only be turned into reality if significant initiatives are launched. Program costs have to be catered for, too. Different approaches to measure energy efficiency in industry are shown in [24]. Indicators of energy efficiency are discussed in [25] and [26]. Another important consideration in energy efficiency is the entire life cycle of a product. Life-cycle energy efficiency [27] not only considers actual use of a piece of equipment but also its production and disposal (see section on > ‘‘Life Cycle Assessment (LCA)’’ later). Energy efficiency trading can only be mentioned here. It is discussed in [28]. A detailed overview on energy efficiency is provided in [29].

Significance of Energy Efficiency There is – unfortunately – no such thing as a perpetuum mobile. As a consequence, energy can only be transformed from one form into another one, which happens under certain losses (see also above). Users of mobile phones, notebooks, and any other mobile device

Energy Efficiency: Comparison of Different Systems and Technologies

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will naturally and subconsciously appreciate energy efficiency – because energy is obviously a scarce resource in these applications. Service life and hence usefulness will depend on the efficiency and energy density of the gadget [30]. However, energy efficiency is a much broader topic. Energy is the leading source of anthropogenic greenhouse gas emissions, approximately 65% [5], and hence needs to be at the core of climate change mitigation actions. In the IEA’s reference scenario, the global energy demand is set to increase by 40% from 2007 to 2030, reaching 16.8 billion toe [5]. Ninety percent of this increase is predicted to happen in non-OECD countries, with India and China accounting for half [5]. Global electricity demand is projected to grow by even 76% from 2007 to 2030, requiring 4,800 GW of additional capacity. This is five times the existing US capacity [5]. In the proposed course of action, the ‘‘450 scenario,’’ more than 50% of all (necessary) energy savings are realized by energy efficiency measures. The target is an energy-efficient and low-carbon economy. By 2050, energy efficiency measures could cut the total worldwide energy consumption by as much as one third [5]. Energy efficiency has a large scale effect. Apart from addressing global warming, energy security and fossil fuel depletion are tackled alongside solid savings for individuals, enterprises, and nations at large. Air quality, particularly in urban areas and in developing countries, can also be improved by energy efficiency measures. There are other environmental co-benefits, too, from implementing energy efficiency measures. By focusing on energy efficiency rather than on increasing energy production, a costeffective, ‘‘soft’’ energy path is followed. The term ‘‘negawatt’’ was coined two decades ago to describe electricity that ‘‘was not created due to energy efficiency’’ [31]. Energy efficiency has been widely recognized as a vast, low-cost energy source [9]. The reason why this unused potential is so large stems from the multitude of barriers that impede energy efficiency today [2, 9, 32]. Unlike the production factors of labor and capital, which have seen impressive optimization since the industrial revolution, energy is far from being at the lowest possible level. Energy efficiency has become part of the political agenda in many countries [33]. Monitoring energy intensity is common practice since the 1973 oil crisis. How policies can increase energy efficiency is shown in [34] for the OECD countries (OECD = Organization for Economic Co-operation and Development; 34 member countries, which are considered highly developed) and in [35] for the state of California, a leading region for energy efficiency as will be referred to in this chapter of the handbook. For corporations, energy efficiency is an important pillar for the ‘‘triple bottom line,’’ i.e., their performance in economic, social, and environmental aspects. Businesses and consumers alike start taking energy considerations into account for decision making. It is estimated that energy is a strategic factor for 40% of all global revenue [36]. Unpredictable volatility in fuel prices, driven by depletion of crude oil and speculation, places a burden on companies and economies as a whole, which they feel needs to be controlled. Reference [37] provides an overview on the economic aspects of climate change. With energy efficiency being the easiest way to save energy, it is highly relevant to mitigate climate change effects and their detrimental consequences.

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Benefits of Energy Efficiency Energy efficiency offers several direct and indirect benefits, some of which are obvious. The reduction of pollution and greenhouse gas emissions aids the environment. For businesses, reduced energy bills will translate into competitive advantages. Also, energy efficiency measures can lead to higher worker productivity and reduced sick-leave rate [9] as concurrent benefits. Consumers can enjoy increased comfort levels [2], particularly those living in low-income households. Indirect benefits, as an example, are also related to health (less drafty and damp rooms after the implementation of energy efficiency measures in private homes such as insulation upgrading). As a nation, a key benefit is an improvement in energy security, another one the reduced exposure to volatility in energy prices. There has also been a wide discussion on job creation by the quest for energy efficiency. While it is true that energy-intensive production processes are shifted toward developing countries, leading to job losses in countries of the European Union and the USA, for instance, there should be a net positive effect from the job market stimuli provided by energy efficiency. For instance, the market for building insulation is estimated at $10–12 billion for the USA alone [9]. An overview on the market size for energy efficiency in the USA is provided by [38]. Some considerations on actual and potential job creation by energy efficiency improvement programs are provided by [9], where the potential for the USA is estimated to lie between 600,000 and 900,000 jobs over the next decade in direct, indirect, and induced jobs. A national commitment to green buildings has the potential to generate 2.5 million and to support 8 million American jobs [39], with similar prospects being offered in other countries. The job market potential of clean energy is reviewed in [40]. Energy efficiency will not be the sole solution. There will still be a need for new, additional power plants, partly to meet increased demand, partly to replace old ones. Also, there might be additional demand that is now unaccounted for, e.g., to power electric vehicles [9] that are likely to replace traditional cars to some extent.

Downside of Energy Efficiency While energy efficiency as such is indisputably a good thing, there are several aspects that have to be considered to avoid detrimental overdoing. First, the economics have to be considered. In a competitive landscape, corporations will only implement energy efficiency measures that ‘‘pay for themselves’’ (see also later). High upfront investments are one of the barriers toward better energy efficiency. Apart from costs, complexity is another aspect to consider. In order to improve the efficiency of a plant or an engine, advanced control systems are required, which need to be maintained. Capable technicians and additional resources have to be provided to that end. The most economic process might not be the most reliable one. As operability of technical equipment, particularly in the capital-intensive process industry is of utmost importance, some concessions to energy efficiency are sometimes well accepted from a process point of view. For many production

Energy Efficiency: Comparison of Different Systems and Technologies

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plants, 1 day of additional, unplanned shutdown per year will mean the difference between profit and loss. Also, plant personnel might focus on other aspects than energy efficiency when operating a unit or equipment [41] to safeguard ‘‘trouble-free’’ operation, or simply be too busy to concentrate on continuously optimizing energy usage. Another extreme, hypothetic example of an inefficient energy saving attempt would be a person having an accident at home because of not turning on the light when fetching something from the cellar or during night. For these reasons, it might happen and even be advisable not to squeeze out the last bit of energy efficiency from a given system, but rather to act with commonsense.

Energy Efficiency versus Energy Demand: The Rebound Effect The effect that energy efficiency improvements on the micro level (i.e., machines and individual plants in industry) do not fully translate into the expected energy savings on the aggregate level (such as the economy) is termed ‘‘rebound effect’’ or ‘‘Jevons’ paradox.’’ It is also called the Khazzoom–Brookes postulate. The rebound effect can be direct or indirect. If it is >100%, it is called ‘‘backfire’’ [42]. Simply put, energy efficiency makes energy services cheaper, so demand tends to increase. This concept is called ‘‘elasticity of demand.’’ A more economic car might tempt its owner to driver faster and further, thus partially offsetting potential energy savings. A car producer can decide to install more electronic devices for increased driver comfort in a car that has been made more fuel efficient thanks to the use of lightweight construction materials and a better engine. The extent of the rebound effect depends on the elasticity of demand, which tends to be stronger with consumers than with industrial plants [42]. William Stanley Jevons studied the rebound effect during the industrial revolution [42]. In his 1865 book ‘‘The Coal Question’’ [43], he was pondering over the question whether efficiency measures would really lower actual coal consumption, based on empirical evidence that after efficiency improvements with steam engines and in steel production, the actual energy consumption had soared. For more information, see [44, 45].

Energy Intensity Intensity is an ambiguous term. In physics, it is power per unit area (W/m2), a timeaveraged energy flux. In heat transfer, intensity commonly denotes the radiant heat flux per unit area per unit solid angle (W/m2/sr). Here, energy intensity is an economic concept as a measure of the energy efficiency of a nation’s economy. It is calculated as units of primary energy consumption per unit of GDP (gross domestic product) or value added, measured in (MJ/$) or (toe/$). The energy intensity of a country is influenced by many factors, for instance, the climate. Economic

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productivity and standards of living contribute as well as the energy efficiency of buildings and appliances, traffic patterns (public transportation vs. individual cars), and the way energy is being produced [46]. Energy intensity can hence be used as a surrogate for aggregate energy efficiency. Countries differ strongly by energy intensity, and within countries, there are marked differences amongst regions. In the USA, a state with superior energy efficiency performance is California, which has established leadership in, e.g., per capita energy consumption [47, 48]. The energy efficiency of different countries is assessed in [49]. The term ‘‘energy intensity’’ can also be applied to a production process as a synonymous expression for specific energy consumption, based on quantity (kg) or value added ($) or (€) (see also section on > ‘‘Energy-Intensive Industries’’).

Emission Intensity (Carbon Intensity) Another concept is the emission intensity. It is the average emission rate of a given pollutant from a given source related to the intensity of a specific activity, e.g., grams of CO2 per megajoule of energy produced (g/MJ). The term emission intensity is often used interchangeably with ‘‘carbon intensity’’ and ‘‘emission factor’’ in the climate change discussion. Other greenhouse gases and pollutants can be considered, too, by calculating CO2 equivalents. > Table 24.3 provides an overview on emissions intensities, compiled from [50]. The subscripts in > Table 24.3 stand for ‘‘thermal’’ and ‘‘electric.’’ In combined heat and power (CHP, cogeneration), both heat and power are produced from a combustion process, boosting overall efficiency (see later).

Historical Development of Energy Efficiency A proverb says ‘‘Things that cost nothing have little value.’’ In this sense, as long as easy access to energy is available, there are few incentives to use it wisely. History tells several lessons here. Visitors to Greek islands will witness testimony of one such unsustainable . Table 24.3 Emission intensities [50]. The ratio of H/C is 4 in natural gas, which is higher than in oil and especially coal, leading to lower CO2 emissions per kWh Fuel/resource

Thermal g(CO2-eq)/MJth

Electric g(CO2-eq)/kWhe

Coal

88–94

863–1,175

Oil Natural gas Nuclear power (U) Hydroelectricity

73 51–68

893 587–751 60–65 15

Photovoltaics Wind power

106 21

Energy Efficiency: Comparison of Different Systems and Technologies

24

practice exercised several thousand years ago, i.e., chopping down trees to build ships without reforestation. There are countless other examples of unsustainable acts related to resource and energy efficiency in the past, some of which have even led to the extinction of a local human population [51]. The global oil crises in the 1970s were a series of events that have triggered several measures for energy efficiency on a large scale, e.g., the creation of the DoE (Department of Energy) in the USA. In the following decade, when crude oil prices went down again, there was reduced motivation to focus attention on energy efficiency in many areas. The industrial sector has improved its energy efficiency continuously over the last 30 years, partly in order to reduce variable production costs and to improve competitive advantage (one also has to take into account that a significant part of energy-intensive production facilities was transferred to low-labor-cost countries in, e.g., Asia). Economic growth, a trend toward increased personal mobility and toward larger homes and the use of more and more appliances, amongst others, has led to a steady increase of absolute energy demand in most industrialized countries. As a result, the overall energy intensities in the USA have declined as follows between 1980 and 2005 [9]: Residential sector: 11% Commercial sector: 21% Industrial sector: 42% While the national per-capita energy consumption in the USA has grown by 1.3% per year from 1977 to 2007, which means a doubling, it remained almost constant in California. In the EU, the average efficiency of gas-fired power plants has increased from 34% in 1990 to 50% in 2005, and is expected to increase to 54% by 2015 [52]. For coal-fired power plants, the efficiency, also based on the lower heating value, went up from 34% in 1990 to 38% in 2005 and is expected to increase to 40% by 2015. These trends are visualized in > Fig. 24.2 below. As the developed world has built its industry, specific energy consumption was constantly improved. Yet the largest share of historic and current global emissions comes from developed countries. Many people now fear that while other countries race through their development, they might expel ‘‘their share,’’ i.e., high amounts of pollutants, into the atmosphere. China, for instance, has been able to maintain economic growth of greater than 9% from 1980 to 2000, while the energy demand only increased by 3.9% per year [53]. This shows that energy demand does not necessarily have to outpace economic growth during the early stages of industrialization and development [53]. A word of caution: Many scientific publications, as well as the public opinion, believe in decreasing energy intensity over time. This hypothesis is often only an assumption, which needs to be proven. In [54], the authors conclude that many energy efficiency trends on a national level follow a stochastic nature, see > Fig. 24.3 below. In [55], historic developments and future trends of energy efficiency are discussed. Megatrends [56] will also have an impact on energy efficiency. How they are perceived can differ strongly [57]. In general, there have been marked improvements in certain areas with respect to energy efficiency, some of which were countered, though, by rebound effects.

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. Fig. 24.2 Energy efficiency trends of fossil fuel combustion in the EU27 (Reprinted with permission from Elsevier from [52])

2

x10–6

4.5

1.4 1.2 1 0.8 0.6 0.4 0.2 1965 1970 1975 1980 1985 1990 1995 2000 2005

Oil consumption (bl.) / GDP

1.6

x10–8

4

1.8 Oil consumption (bl.) / GDP

854

3.5 3 2.5 2 1.5 1 0.5 0 1965 1970 1975 1980 1985 1990 1995 2000 2005

. Fig. 24.3 Stochastic movement of energy consumption. Left: Oil consumption per unit of GDP for OECD countries from 1965 to 2005. Right: Same data for non-OECD countries (Reprinted with permission from Elsevier from [54])

Assessing Energy Efficiency Improvements Energy efficiency improvements can be achieved by technological progress or by changes in behavior. They can be measured. However, for a correct assessment, the following factors have to be taken into account: ● Erosion of part of the improvements by the rebound effect (see above) ● Comparability of data (same year, same boundary conditions) ● Selection of a proper baseline

Energy Efficiency: Comparison of Different Systems and Technologies

24

Comet 4

100

90

% of Base (Comet 4)

80

70

B707-120

B707-320 DC8-30

SVC10 B707-120 B707-320 DC8-30 DC8-63 B707-120B DC8-61 B707-320B B747SP B747-100B

B747-100

B707-120B SVC10

B747-200

DC8-61 B707-320B

Engine fuel consumption

DC10-30

B747-200B

60

A330-300 B777-200

DC10-30

50 B747-100

B747-200

40

B747SP

Aircraft fuel burn per seat

B747-100B

B747-200B A300-600R B747-300 A340-300 A310-300 B747-400 A330-300

30

1960

B747-400

A300-600R A340-300

DC8-63

20 1950

B747-300 A310-300

1970

1980

1990

B777-200

2000

Year of model introduction

. Fig. 24.4 Fuel efficiency of commercial aircraft over the last 50 years. See text for details (Reprinted with permission from [58])

The baseline for measuring energy efficiency is of utmost importance to avoid wrong conclusions. This is elaborated with an example from the transportation industries below, viz. the fuel consumption of aircraft over time. > Figure 24.4 shows a data compilation of how fuel efficiency of commercial aircraft was improved over the last decades. Taking the Comet 4 as a baseline, fuel efficiency was reduced by 70% in modern aircraft. Approximately 40% of the improvements are attributed to engine efficiency improvements, and 30% to airframe efficiency improvements [58]. The de Havilland Comet was the world’s first commercial jet airliner [59]. > Figure 24.4 was taken from an IPPC report. The IPCC (Intergovernmental Panel on Climate Change) is a renowned, scientific intergovernmental body established to evaluate the risk of climate change caused by human activity [60]. It was awarded the 2007 Nobel Peace prize together with Al Gore. In [61], the authors argue that the pre-jet era was ignored in the above IPCC discussion, and that the Comet 4 is an unsuitable baseline. From the conclusions of that report [61]: "

The later piston-powered airliners were at least twice as fuel-efficient as the first jet-powered airliners; If, for example, the last piston-engine aircraft of the mid-fifties are compared with a typical turbojet aircraft of today, the conclusion is that the fuel efficiency per available seatkilometre has not improved. . ..The last piston-powered aircraft appear to have had the same energy efficiency per available seat-kilometre as average modern jet aircraft. The most modern jet aircraft (such as the B777-200 or B737-800) are slightly more efficient per available seat-kilometre.

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. Fig. 24.5 IPCC graph with additional data (Reprinted with permission from [61])

The findings from this study are depicted in > Fig. 24.5 below. As it can be seen from Fig. 24.5, slight changes in the assumptions will lead to strong deviations in the results. This has to be borne in mind when assessing and comparing energy efficiency studies presented by various interest groups.

>

Innovation and New Technologies for Energy Efficiency In order to increase energy efficiency, innovation [62] is needed. By innovation, either of the following energy efficiency improvements can be achieved: ● Carrying out the same task or process with less energy ● Utilizing the same amount of energy to produce more output or higher value ● Redefining the task or process so that the new way consumes less energy Innovation can take place in incremental steps, or in a disruptive way, when a new technology is developed, for instance. The electric light bulb, being condemned as energy inefficient today, was one such disruptive innovation, which has been around for more than a century. So in order to innovate, engineers and researchers might be tempted to search and build more knowledge in their own area of expertise, and to innovate as much as possible in their very own fields. This strategy has proven successful – take the famous Bell Labs [63] as an example. Fifty years ago, the Bell Labs were generating every new technology that the telephone business needed, and the telephone business, in turn, was using all of Bell Labs’ innovations. Bell Labs were virtually unbeatable. However, the rules

Energy Efficiency: Comparison of Different Systems and Technologies

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of innovation have changed somehow over time. The Bell Labs invented the transistor, which clearly is one of their greatest discoveries. However, Bell Labs did not recognize the value of the transistor, and they gave it away for little money. The transistor, hence after, was extremely successful, but with the main use not being in the telecommunications industry. On the other hand, the very innovation that revolutionized the telecommunications industry – the fiberglass cable – was developed outside that industry. This phenomenon has been observed in many industries over the last 50 years [64] – the major innovations with the biggest impact for an industry are not likely to come out of the industry itself, but will rather be ‘‘born’’ in a different area. The significance of this development for the realm of energy efficiency is as follows: Energy efficiency can be improved in many ways. In a passenger car, for instance, an improved engine, lightweight plastics components instead of steel, or tires causing less rolling friction will all serve the same final purpose of energy efficiency. Innovation takes time until its full potential is being realized, though. In [3], the market penetration rates of new energy technologies were studied. It is concluded there that the time for a takeover of market share from 1% to 50% varies from less than 10 years to 70 years, with takeover times below 25 years being associated with end-use technologies. Long investment cycles render the energy production industry inert to change.

Typical Energy Efficiencies The energy efficiency of photosynthesis is on the order of 1%, with a fraction of approximately 0.2% being stored as biomass. Sugarcane exhibits peak storage efficiencies of up to 8% [100]. The first steam engines, designed as external combustion engines, had efficiencies on the same order of magnitude. To visualize the energy balance, i.e., the energy efficiency, of a process or machine, a Sankey diagram can be used. For exergy, Grassmann diagrams [65] are deployed (though both terms are sometimes used interchangeably in the literature). An example for a Grassmann diagram for nitric acid production is shown below in > Fig. 24.6 [65]. The Grassmann diagram can be seen as an energy flow diagram, visually explaining which fraction of the total, initial energy ends up in the final product. In order to obtain typical energy efficiencies, or reference energy efficiencies, a benchmark is deployed. The benchmark in energy efficiency is given by the state-of-the-art and so-called BAT (best available technology) values. However, BAT values are often difficult to obtain as corporations tend to keep them secret and patents do not always provide full disclosure. The energy efficiency and carbon intensity of a given process depend on the system boundaries that are considered, and on the energy path. For instance, whether electricity for a hybrid car has been produced in a coal-fired power plant or by solar cells will heavily impact the overall efficiency (see also ‘‘Life Cycle Assessment’’ and well-to-wheel efficiency, later). Actual efficiencies will depend on a large number of factors such as the condition of a given system or appliance. Examples are the load of an engine, maintenance on motors,

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Power + air

Internal and external losses Internal and external losses

Power + air Natural gas

Ammonia Conversion process

Conversion process

Steam credit

Nitric acid

Steam credit

. Fig. 24.6 Simplified Grassmann diagram for the production of nitric acid [65]. Reproduced by permission of the Royal Chemical Society (RCS).

and usage patterns. This is obvious for every car owner who wants to reach the ‘‘official’’ fuel consumption of her car. When energy efficiency potentials are presented in the literature, one has to be careful not to overestimate or mix up the various potentials, which are: ● Technical potential ● Economic potential ● Maximum achievable potential (considering factors such as demographics, market conditions and regulatory factors) ● Realistic achievable potential (taking historic data into account) People adapt to change at different rates. Take popular technologies as an example. Even for microwave ovens and mobile phones, it took 10–15 years for market penetration. Therefore, the realistically achievable potential is never equal to the full technical potential. Also, the effort to obtain a large part of any potential saving will increase along the way. For energy efficiencies of various technologies, processes, and appliances, the reader is referred to the respective chapters of this handbook and to the specialized, referenced literature.

Benchmarking of Energy Efficiency There are no useful reference data for absolute energy efficiency from a thermodynamic or theoretical point of view. Rather, one can only compare a given process or technology route, device, or method to other solutions in the lab or in the field so that the best available technology (BAT) or state-of-the-art can be determined empirically. Such a benchmarking exercise focused on energy efficiency will yield interesting results.

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In [66], for instance, it was found that the energy efficiency of the steel-making plants in several countries was 25–70% above the best plant. In the cement industry, the average was 2–50% higher than the very best plant energy efficiency. Benchmarking can be used by operators of industrial plants to compare their energy efficiency, and ultimately their competitiveness, to that of their contenders. Consumers can use relative indications of energy efficiency, such as the Energy Star® label, to easily spot energy-efficient appliances as a guide for purchase decisions. It needs to be mentioned that comparing like with like is crucial. If, for instance, steel making plants in two countries are to be compared, sectoral differences must be taken into account [66] (if, for example, there is plenty of secondary steel available, energy efficiency will ‘‘automatically’’ be better). Also, regional differences in feedstock quality [67] or climatic conditions will affect the energy efficiency of a given plant. More information of reliable reference data for energy efficiency comparisons on a national level can be found in [68]. In mature industries, energy efficiency differences from plant to plant are not expected to be very large because improvements tend to be incremental. Generally, there is a lack of energy efficiency benchmark standards for industry at large and factories in various sectors [69], secrecy and antitrust legislation being important impeding factors. There exist corporate benchmarks in some companies that operate multiple plants or sites. Several consultants carry out benchmarking studies in various industries, e.g., Solomon Associates for steam crackers, Phillip Townsend Associates for polymerization plants, Plant Services International for ammonia and urea plants, and PDC (Process Design Center) for more than 50 petrochemical processing plants [70], to cite a few examples. These benchmarks present generalized and anonymized data with which the energy efficiency and the competitiveness of one’s own plant can be compared to the industry average.

Energy Efficiency World Records Here is a brain-teaser: A world record in energy efficiency of a car was set in 2005 as 5,134 km/l of gasoline equivalent, operating on a hydrogen-powered PEMFC (polymer electrolyte membrane fuel cell) [71] during the Shell Eco Marathon. On the website of this annual competition [72], additional records on energy efficiency are highlighted, e.g., an equivalent of 3,771 km with 1 l of fuel with a combustion-engine powered car in 2009 (5 years earlier, the record was 3,410 km). These figures, equally impressive and irrelevant for current practical road transportation, show that there is plenty of potential left to increase energy efficiency, even beyond current imagination.

Some Not-So-Energy-Efficient Inventions and Practices Here are some examples of low-energy-efficiency appliances and habits, most of which might soon astonish people that they even existed in our times: ● Incandescent light bulbs ● Huge private cars such as SUV with single occupancy

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● ● ● ● ●

Standby function on electrical appliances in households Patio heaters to warm open areas outside the house Melting snow in cities such as New York City to dispose of it Flaring of hydrocarbons of low value in petroleum refineries Room temperature regulation by opening and closing a window, while keeping the heater switched on ● Water ring pumps to produce an industrial vacuum In a typical household, appliances on standby use up 10% of the total amount of electricity consumed. This is equivalent to 400–500 kWh annually, virtually wasted with no energy service rendered.

Barriers to Energy Efficiency There is no doubt about the fact that energy efficiency offers cost-effective energy savings. However, the full potential has barely been tapped into. There are several barriers, associated with financial limitations, uncertainty, or others. They can also be classified as structural, behavioral and related to availability [9]. Though businesses and households are responsible for implementing most energy efficiency investments, it is their governments to provide the right bordering conditions to catalyze investments in energy efficiency by offering tax incentives, education, or other facilitation. One reason why the potential for energy efficiency has not yet been realized to its full extent is the fact that high upfront investments are often necessary, whereas the savings accrue incrementally over the subsequent years [9]. Also, the energy efficiency improvement potentials are highly fragmented [9]. Apart from low awareness, the difficulty to measure energy efficiency improvements in several areas contributes to slow progress. Barriers to energy efficiency are discussed in [9], alongside the following potential actions to break down these barriers: ● Information and education ● Incentives and financing ● Codes and standards Experience shows that consumers are particularly hostile toward funding of energy efficiency measures, compared to businesses, even if the economics are reasonable. They apply hyperbolic discounting, meaning that immediate value is regarded significantly higher than future one. Barriers toward energy efficiency improvements in industrial settings are reviewed in [32]. Another interesting question is the durability of energy efficiency measures, which was studied in [73], the results of which are given in > Table 24.4. The percentages in > Table 24.4 reflect the portion of the first year energy savings that remain throughout the full lifetime of the studied energy efficiency measures. A distinction was made between measures focused on saving electrical energy and measures to save fuel. It can be seen that already after a few years, considerable losses from the initial gains are encountered, which

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. Table 24.4 Estimated persistence of energy efficiency measures [73] Years following implementation (installation)

Remaining energy efficiency impact Electricity-related measures Fuel-related measures

1

99.69%

100%

2 3 4 5

95.97% 89.59% 85.14% 84.02%

99.46% 98.51% 97.84% 97.11%

6 7 8 9

78.32% 78.22% 78.22% 74.58%

89.75% 89.75% 89.75% 89.70%

10

66.73%

87.45%

can be explained by various factors depending on the efficiency measure. ‘‘Hard-wired’’ energy efficiency initiatives will generally be lasting longer than those based on behavioral changes (see also below). An example how energy efficiency can stagnate if the economic and organizational conditions are not in favor of it, such as prevailing low electricity prices, is shown for the Swedish building industry in [74] and [75]. Aspects of financing energy efficiency, another prominent barrier, are outlined in [76–79]. Barriers to energy efficiency in general are reviewed in [80].

Levels of Energy Efficiency: From Process to Behavior Energy efficiency can be achieved by various means. A product can be manufactured in a way that energy is used efficiently, either during its production or during its use. A process can be energy efficient by itself, or it can produce energy-efficient outcomes. The same applies for services. Here are some examples of more and less efficient products and processes: ● ● ● ●

Office lighting by compact fluorescent lights vs. traditional incandescent light bulbs Modern compact passenger car vs. older, midsized model Cement production by the dry process vs. the wet process Air separation by pressure swing adsorption vs. air separation by cryogenic air cooling and fractionated distillation ● Steel manufacture from scrap metal vs. ore It is desirable to have efficient equipment and processes in place. However, these can be operated in very inefficient ways. The magnitude of loss in energy efficiency by ‘‘bad’’

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operation can be as large as the difference between competing processes and equipment items [41]. Some examples of these ‘‘bad’’ operation aspects are ● ● ● ● ●

Excessive speeding with a car, which strongly increases fuel consumption/km Neglected maintenance on insulation of window frames in a private home Keeping office lights on overnight when they are not needed Operating plant utilities at full capacity during idle production times Not repairing leakages on compressed air pipelines

In contrast to the installation of new, more energy-efficient equipment, or the design of a more energy-efficient process, operation thereof requires constant attention (compare also the table above, showing the stunning erosion of energy efficiency gains over a few years’ time). By continuously working on a mindset toward energy efficiency, for instance, by having employees turn off idle equipment and by fostering continuous improvement, also small, individual savings can add up. In [41], some aspects of why operators in control rooms do not always give utmost importance to energy efficiency are listed: ● ● ● ● ● ● ● ●

Lack of urgency, little incentives to value long-term performance vs. the short term Preference of steady state operation vs. short-term optimization efforts Comfort, trading economy against less effort Individual work history and anecdotes making risk perception highly personal Different levels of skills and knowledge Instinct to preserve assets rather than maximize their utilization Little effect of administrative control measures alone Focus drift due to distraction

The most economic mode of operation of a plant in the process industries, for instance, is not always the most convenient one [41]. This will lead operators to at least partly refrain from energy efficiency optimization. Such ‘‘human factors’’ can be improved by considering the usability of processes and equipment. Whereas the usefulness of a man-made tool or installation is related to user satisfaction, the term us(e)ability denotes the ease with which it can be deployed. In general, usability can be defined as a measure of the ease with which a system can be learned or used, its safety, effectiveness and efficiency, and attitude of its users toward it [81]. In [82] and [83], two examples of the successful application of usability and usability engineering in process control systems and industrial plants are given.

Energy Efficiency Investments As energy-efficient technologies often have higher initial investment costs than older, lessadvanced ones, economic aspects will determine the extent to which energy efficiency is considered for new investments and for retrofits alike. The TCO (total cost of ownership) approach will clearly recommend energy efficient, but typically more expensive installations, in many cases. Investing in ‘‘the right technology,’’ if it is not supported by a sound

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business case of yearly energy-bill savings, will be easier during the construction of a new building or factory than when one wants to apply for funds, corporate and federal alike, later on. In industry, one can distinguish between ● Pure capacity investments ● Pure energy efficiency investments ● Hybrid capacity and energy efficiency investments Common appraisal methods for investment projects in industry are ● ● ● ●

Payback period Net present value (NPV) Internal rate of return (IRR): Discount rate where NPV = 0 Strategic fit

Approval can be based on an evaluation of several of these parameters, by a ranking or by fulfilling a certain cutoff criterion. To test the validity of the profitability calculation of such a project, a sensitivity analysis can be carried out by varying the most important parameters. Monte Carlo simulation enhances the quality of such simulations [84]. Real options [85] can also be used. While debottlenecking investments, which increase production capacities, usually have short payback periods and high IRRs, often exceeding 50%, energy efficiency investments sometimes cannot make it over the 10% hurdle. If the funds for investment projects are limited, which is said to happen more often than none, naturally those with higher IRR will be preferred. Energy efficiency investments can be carried out at a lower IRR than a corporation’s normal hurdle rate (IRR) because the associated risk is generally lower than for a capacity investment (energy savings can be predicted more reliably). Often, when ‘‘selling’’ an energy efficiency project in a corporation, one had better avoid the term ‘‘energy,’’ and describe potential projects as ‘‘efficiency’’ or ‘‘productivity’’ improvement projects when presenting them to decision makers. Energy has a different importance for various sectors. Those industries which are energy-intensive will suffer more from high and volatile energy prices than the ones incurring only a small percentage of their costs from energy bills. It is estimated that out of the total global economic activity (€91,000 billion in 2008), 40% comes from companies where energy plays a strategic role [36]. The sectors concerned are transportation, building and construction, energy-intensive industries, engineering, IT (information technology), and the energy industry. For companies in these sectors, energy can have a direct or indirect effect, i.e., on their own production costs or on the acceptance of their products. On the other side, there are industries such as education, retail, insurance, and health care, which do not depend as much on energy competitiveness.

Introducing Energy Efficiency Programs It is estimated that most organizations have a potential for 10–20% energy efficiency improvement, which will materialize in the bottom line. In order to improve energy

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efficiency in a company or another larger institution, an energy survey or an energy audit can be a first step to map out the savings potential. More information on such energy audits can be found in [86] and [87]. They consist of data collection (‘‘hard facts’’ such as electricity consumption and interviews on common practices) and internal and external benchmarking. There is currently a lack of qualified energy auditing staff [69]. Checklists can help to uncover inefficiencies in processes and equipment. Using off-peak hourelectricity is an option to shrink the electricity bill. How to manage energy efficiency in a corporation is described in [88]. To which extent agreements foster energy efficiency is analyzed in [89].

Combustion Combustion plays a critical role in energy efficiency considerations, as approximately 80% of global primary energy is produced by combustion processes. Combustion processes have the single largest human influence on climate with 80% of anthropogenic greenhouse gas emissions [90]. Fuels can be fossil or renewable (biomass). They are gaseous, liquid, and solid. Combustion is used in power plants for electricity and heat production, transportation, and other areas (see sections below for details). > Figure 24.7 shows the global trend in CO2 emissions over the last 140 years [90]. As it can be inferred from the above > Fig. 24.7, the increase in anthropogenic, combustion-derived CO2 emissions has almost been an exponential one. For the impact on climate change, not only the efficiency of a combustion process itself, but also emissions generated during fuel production and transportation have to be considered. For instance, for every kilogram of mined coal, 1.2–16.5 g of the greenhouse gas methane are emitted [22]. Combustion can be

. Fig. 24.7 Trend in CO2 emissions from fossil fuel combustion. Units: Gigatons of CO2 (Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, US Department of Energy, Oak Ridge, TN, USA. Reprinted with permission from Elsevier from [90])

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carried out in furnaces (see power plants below) and boilers, internal and external combustion engines, and in gas turbines [91–93]. Pyrolysis and gasification are special cases of combustion. These processes can be used to obtain gaseous or liquid fuels from biomass or coal in conjunction with a Fischer– Tropsch [18, 94] or other synthesis process. Due to the removal of moisture and ash, and the effect of deoxygenation, liquid hydrocarbons derived from biomass have a threefold energy density and are hence more advantageous for transportation and storage [16]. See also the chapter on gasification in this handbook. Heat recovery from flue gases is a particularly energy-efficient measure. For steam systems, for instance, 1% of fuel can be saved for every 25 C reduction in exhaust gas temperature [95]. In [90], recent trends on CO2 emissions from fuel combustion are reviewed. For combustion in general, see [96].

Power Plants and Electricity Production Twelve percent of man’s total energy is made up by electricity, a fraction that is expected to rise to 34% until 2025 [97]. Energy efficiency in electricity production can be defined as the energy content of the produced electricity divided by the primary energy input, with reference to the lower heating value [52]. The lower heating value (LHV, or net calorific value) assumes that the water formed in combustion remains as vapor. In cogeneration, the overall efficiency can be increased because the (by-product and formerly waste-) heat is used. Cogeneration is also dubbed CHP (combined heat and power). Power production is carried out by (large) public power and CHP plants and by socalled autoproducers. These are users such as chemical factories which produce their own power and heat. In the EU, autoproducers account for 8% of the total power generation [52]. Electricity production plants have an efficiency of around 30–40%, whereas combined heat and power (CHP, cogeneration) yields up to 90% [22]. For the installed base of CHP, see [98]. In the EU, the energy efficiencies for coal-fired power production range from 28% (Slovak Republic) to 43% (Denmark). On a global scale, the spread for oil-fired power plants is an efficiency of 23% for the Czech Republic and 46% for Japan [52]. The efficiency of a given power plant is dependent on its age. The younger a plant, the higher its energy efficiency was (intuitively) found to be [52]. These findings are in line with another study [65], which revealed that the least energy-efficient plants are not always located in developing countries. Apart from the age of a plant, its fuel mix, size, and load account for the big differences in efficiencies mentioned above (see also section below on > ‘‘Crosscutting Technologies’’). State-of-the-art power plants based on coal and gas have energy efficiencies of 46% and 60%, respectively [52]. It is estimated that the replacement of inefficient coal-fired power plants by more efficient coal- or gas-fired ones, particularly in China and in the USA, can reduce global CO2 emissions by 5% [5]. In Canada, in 1988, according to the Canadian Industry Program for Energy Conservation (CIPEC), the average CO2

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emissions in electricity production were 0.22 t/MWh, with a spread of 0.01 in Quebec to 0.91 in Alberta [22]. Demand side management (DMS) can help to level peak electricity demand [101]. Energy is increasingly being produced from waste. Methane can be extracted from landfills for power production in gas engines. Waste incineration uses the energy content of waste and converts it to a low-volume, inert residue. While previously, the focus of waste incineration plants was on low-emission combustion to get rid of the waste, today the energy efficiency of these plants has become important, too. In [99], an incineration plant for medical waste is presented. It is equipped with a heat recovery system and can extract 660–800 kW of usable energy from 100 kg/h of medical waste with an energy efficiency between 47% and 62%. New and innovative pyrolysis and gasification technologies for energy-efficient waste incineration are presented in [102]. In [103], waste incineration is compared to landfilling, and in [105], a life cycle assessment (LCA) [104] of waste management strategies is performed.

Energy Transmission and Distribution Today, electricity production is centralized, with large power plants being coupled to a complex distribution network. Energy transmission and distribution cannot be performed in a totally loss-free way (leaving apart superconductivity, where electrical resistance is exactly zero). In Europe, they typically amount to 4–10% and hence reduce the overall efficiency of power supply by several percent points [52]. Transporting the fuel to end users is more cost-effective, yet also consumes substantial amounts of energy (see sections on pipelines, land, and sea transportation below). Natural gas, for instance, is being pumped across long distances because placing a gas power station next to the gas field and transmitting the electricity and heat would result in a considerably lower overall efficiency than compressing and moving the gas through pipelines.

Energy Storage The need for more and cleaner energy leads to an increase in distributed generation (DG) and renewable energy sources (RES) [106]. Since such sources like wind power are not as reliable and as simple to adjust to demand fluctuations as conventional power plants, they could be coupled with energy storage systems. Power demand by (end)users fluctuates strongly. Typically, the lowest consumption during a 24 h-period is nearly half the peak demand, compare > Fig. 24.8. Today, with a mainly centralized electricity production scheme, there is only a small storage capacity available, amounting to approximately 90 GW or 2.6% of the total production of 3,400 GW [97]. With DG and RES on the increase, it is expected that energy storage, more specifically electrical energy storage, will gain significance on a local (small) and regional (large) level. Energy can be stored in various ways, for instance as

Reduced consumption

Energy Efficiency: Comparison of Different Systems and Technologies

24

1 0.8 0.6 Current consumption

0.4

Smoothed consumption

0.2 0 0

3

6

9

12

15

18

21

24

Hour of the day

. Fig. 24.8 Average daily power consumption in France, reprinted with permission from Elsevier from [97]. Peak demand happens in the morning and afternoon, with the lowest demand being met in the early morning hours

Potential energy: Pumped hydro storage (PHS, i.e., pumping water up into a reservoir so that it can later drive a turbine), or compressed air energy storage systems (CAES, i.e., compressing gas in a cylinder) Kinetic energy: Accelerating a flywheel Chemical energy: Batteries [107], fuel cells (H2) Thermal energy: Use of sensible or latent heat [97], e.g., of NaOH Lead batteries are well known for the storage of energy; however, they are heavy and inapt for high cycling rates. Reference [107] discusses the energy efficiency of batteries. In [97] and [106], an overview on current and future energy storage technologies is given. They differ in their maturity, target use (e.g., portable or fixed, long- or short-term storage), specific power (power density) (W/kg) and specific energy (energy density) (Wh/kg), the lifetime (number of cycles), the self-discharge rate, and the costs per installed kilowatt-hour. Hydrogen storage options are reviewed in [108]. In [97], the energy efficiencies of various energy storage technologies are compared.

Life Cycle Assessment (LCA) Life cycle assessment (LCA) [104], also called life cycle analysis, is a holistic view on a product or service. As the name implies, all steps from its raw material production, manufacturing, transportation, distribution, use, and disposal are considered to determine the overall effect that a given product has on the environment. LCA is rooted in the ISO14001 environmental management system standard, more specifically in ISO 14040, 14041, 14042, and 14043 [109]. Variants of life cycle analysis are ● Cradle-to-grave analysis (full life span) ● Cradle-to-cradle analysis (including recycling) ● Cradle-to-gate analysis (partial process)

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● Gate-to-gate analysis (one step) ● Well-to-wheel analysis (used in the automotive industry, see below) ● Wire-to-water efficiency (used for pumps, see later) Eco-balance is a synonymous expression for LCA. An illustrative example for the value of LCA is the use of plastics materials for insulation purposes. Within 4 months of use, the energy savings can equal the energy needed for production, with a service life of up to over 50 years [70]. In transportation, LCA is typically done as well-to-wheel (WtW) analysis, which is an overall fuel efficiency calculation (there are also the standard LCA studies for cars, ranging from production to use and disposal). WtW efficiency, detailed in [94, 110–112], is a similar concept as life cycle energy efficiency [27]. Both concepts can be understood as overall efficiencies of a process chain, calculated as the product of the individual efficiencies. WtW efficiencies allow meaningful comparisons between different technologies, for instance, internal combustion engines (ICEs) vs. fuel cell (FC) vehicle technologies. They provide for a fair comparison. > Figure 24.9, taken with permission from [113], shows the efficiency chain for different automotive propulsion systems under hot-start conditions. In > Fig. 24.9, the WtWefficiency is calculated as the product of conversion efficiency
c , distribution efficiency
t, and propulsion system efficiency
p as shown in > Eq. 24.6 below:
¼
c
t
p

(24.6)

The conversion efficiency
c for gasoline and diesel production in a refinery is quoted as 88% in [114] and as 63% for their production from methanol according to the Lurgi process (20 years ago), and the distribution efficiency
t as 97–98% in [70]. In > Fig. 24.9 above, it can be seen that the CNG-SOFC (compressed natural gas-solid oxide fuel cell) combination achieved the best overall efficiency of around 35%, with the best internal combustion engine performance being 29% for diesel from crude oil [70]. The eco-balance of biodiesel, for instance, has to consider the consumption of fossil fuels and materials for its production, e.g., the use of lubrication oil. Another important term is that of the ‘‘energy path.’’ The production process will strongly impact energy consumption. Methanol, for instance, can be produced via a path starting from sugar cane, or from natural gas, which will yield different eco-balances. An interesting website on LCA is run by the US Environmental Protection Agency EPA [115]. A related concept to LCA is the embodied energy [116]. It is often used for buildings (see later). Also in other industries, significant amounts of energy are ‘‘stored’’ in the final product. In the case of the petrochemical and chemical industries, which consume 30% of global industrial energy, more than half of the energy is locked up in the final products [70] and can be recaptured at the end of their lifetime. The total life cycle of a product can not only be assessed with regard to energy use and environmental aspects, but also from an economic point of view – in terms of costs. In this case, one speaks about life cycle costs (LCC) or total cost of ownership (TCO).

Energy Efficiency: Comparison of Different Systems and Technologies

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100% 90% 80% 70%

Petrol / diesel / ICE Petrol / gasoline / ICE

Efficiency

60%

NG / diesel / ICE NG / gasoline / ICE

50%

NG / CNG / ICE NG / NH3 / AFC

40%

NG / CNG / SOFC 30%

NG / CNG / PEMFC

20% 10% 0% Primary fuel

Conversion

Distribution

Propulsionsystem

. Fig. 24.9 Well-to-wheel efficiencies under hot-starting conditions. ICE internal combustion engine, NG natural gas, CNG compressed natural gas, AFC alkaline fuel cell, SOFC solid oxide fuel cell, PEMFC polymer electrolyte membrane fuel cell (Reprinted with permission from the Society of Automotive Engineers (SAE) from [113])

Recycling is an important aspect of life cycle assessment. The primary energy demand for ‘‘new’’ materials is often considerably higher than that needed to recycle them from waste. For instance, if aluminum cans are recycled, the energy consumption will only be 5% of the energy needed to make them from virgin bauxite ore. Scrap metal, glass, paper and plastics should be recycled to make best use of their ‘‘energy content’’ as primary production tends to consume more energy than secondary one. In the case of plastics, ‘‘thermal recycling’’ is an advantageous, final use if other uses are not feasible. The 3R (reduction, reuse, recycling) are approaches to limit the quantity of primary raw material demand, hence contributing to sustainability.

Total Cost of Ownership (TCO) The total cost of ownership (TCO) concept acknowledges the fact that the use of any equipment has two types of costs associated with it: ● Initial investment costs ● Running costs over the entire useful life time (energy, maintenance, disposal, etc.)

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For industrial pumps, for instance, which are typically in service for 15–20 years, the initial investment cost is often less than 5% of total incurred costs [117]. For a majority of industrial assets and facilities, the lifetime energy will dominate the life cycle costs, which is also the case for many equipment items in private homes. More information on TCO can be found in [118, 119], and [80], with the latter two providing ample coverage of economic evaluation of energy efficiency.

Energy Efficiency in Various Sectors In the following sections, energy efficiency in various areas is discussed. As it was shown in > Fig. 24.1 and > Table 24.1, major consumers of energy are end users, power plants, transportation, industry, buildings, and others, each of them showing potential for costeffective energy efficiency improvements.

Agriculture and Food Agricultural activities make a strong contribution to anthropogenic climate change. Greenhouse-gas emissions from this sector account for 22% of global total emissions, which is similar to the contribution level of industry and greater than that of transportation. Livestock production (including transport of livestock and its feeding) accounts for nearly 80% of the sector’s emissions [120]. The two strong greenhouse gases (GHG), methane and nitrous oxide (which are closely linked with livestock production), contribute much more to this sector’s warming effect than does carbon dioxide [120]. Emission factors of CO2 and CH4 for livestock are estimated at 36–3,960 and 0.01–120 kg per head and year, respectively [22]. Agricultural operations not only put strain on global climate by CH4 emissions from cattle, but also by energy consumption, which is concentrated in the areas of irrigation, process heat applications, and refrigeration. Irrigation pumps, refrigerated warehouses, greenhouses, and postharvest processing offer various potentials for energy efficiency improvements. A nice example is provided by some Dutch greenhouses, which are heated by gas engines, the CO2 from which is fed into the greenhouses to fertilize the plants and to boost their growth [121]. In [122], different heating methods for greenhouses are compared. In [123], the energy efficiency of the Dutch food industry is reviewed, and in [301], that of the European dairy industry. Additional case studies of recent improvements in energy efficiency in the agricultural industry are discussed in [124]. The energy use for the production of various agrichemicals, such as herbicides, growth regulators, and fungicides, ranges from 120 to 550 MJ/kg of active ingredient [125], taking production, packaging, and transportation into account [125]. The application rate of these chemicals further determines the total energy consumption per kg of agricultural product. Food miles are a very simplistic concept relating to the distance food travels as a measure of its impact on the environment [125]. While a lower number of ‘‘food

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24

miles’’ will generally render a product more energy efficient because transportation ways are shorter, a food commodity that is produced with high energy efficiency, e.g., by little use of fertilizers, and that has a long mileage to the consumer, can still have a lower environmental impact that foodstuff manufactured close to the end customer in an otherwise inefficient way. This simple example shows that energy efficiency aspects are closely interwoven and often difficult to compare, not only in the agricultural industry. Globalization affects the food industry as much as it does high-tech goods: The fraction of vegetable and fruit imports from New Zealand to the EU is 12% and 7%, respectively (figures of the year 2002) [125]. In [126], energy efficiency in the food industry is treated in detail.

Transportation and Logistics Our world has become global so that people and goods are being transported between countries and continents on a large scale. The IEA predicts significant improvements in energy efficiency in transportation; however, these will be more than offset by increased travel [5] and further globalization. Fuel efficiency in transportation ranges from a few megajoules per kilometer and passenger for a bicycle to several hundred megajoules for a helicopter. Approximately one third of the energy consumption in transportation is used for freight movement [127], which accounts for 8% of total anthropogenic CO2 emissions. Most of these emissions stem from trucks (heavy goods vehicles, HGV), which account for most freight activities in most countries, e.g., 68% of all ton kilometers in the UK [127]. Ample road networks make cargo distribution by HGV convenient and efficient in terms of time and costs.

Road Transporation and Internal Combustion Engines Although rail and ship transportation are more efficient and environmentally benign than road transportation, trucking is still heavily used for reasons of flexibility, costs, and timeliness, not only in weakly developed areas, to move goods and people. Most vehicles on the road today are powered by internal combustion engines (ICE). Engine and propulsion system selection for cars is based on various criteria such as driving performance, range, and safety. ICE burn gasoline and diesel, the latter being used for trucks and, in some countries, private cars, with natural gas-, ethanol- and hydrogenpropelled cars constituting a minor fraction next to those with alternative systems such as electrical batteries or air buffer tanks. Internal combustion engines have become more efficient over the last decades. The largest losses in gasoline engines are encountered by throttling the engine [113]. Reference [128] estimates that over the next decade, an efficiency improvement of another 6–15% is feasible. Various optimizations such as direct fuel injection, variable valve timing, supercharging, downsizing, exhaust gas recirculation, onboard fuel reforming, and power train improvements, e.g., on the gearbox, are being tested and

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implemented [113]. The reuse of losses also offers significant potentials, for instance, recuperative braking or the extraction of heat from exhaust gases. Stationary engines, such as large gas engines for power backup or landfill gas use, can be operated in steady mode at optimum efficiency. Combustion engines in mobile machines have to perform well over a wide range of load, which yields poorer overall efficiency. A novel, promising combustion technology for engines is HCCI (homogeneous charge compression ignition) [129]. HCCI is a hybrid between an auto-ignited Diesel engine and a spark-ignited Otto engine in that it deploys autoignition of a homogeneous fuel–air mixture. Alternative ignition systems [130] such as laser ignition are also expected to improve fuel economy. For a discussion on internal combustion engines for future cars, see [131].

Passenger Cars It is estimated that by 2030, 60% of all new cars sold will be hybrids, plug-in hybrids and electric vehicles, as opposed to 1% today [5]. Hybrid cars combine an electric engine and an internal combustion engine. Dual fuel concepts (natural gas and diesel, for instance), are also feasible. The CO2 intensity of the passenger car fleet in 2030 is estimated to be 90 g of CO2/km, compared to 205 g/km in 2007, as a worldwide average. In OECD countries, it should reach 80 g, in the EU 70 g, and in India and China 110 and 90 g, respectively, in 2030, the latter ones down from 225 and 235 g, respectively, in 2007 [5]. On the other hand, a large increase in the global number of cars is anticipated, particularly in developing nations such as China and India. Hybrids use regenerative breaking to recapture energy that would otherwise dissipate. The effect on fuel economy of such cars is particularly pronounced in stop-and-go city traffic. Fuel economy of private cars is governed by the following aspects: ● ● ● ●

Technology advances of the car, e.g., better engine Driving habits (use of air condition, cruising speed, payload in the car, etc.) Maintenance (no clogged air filters, correct tire pressure, etc.) Weight (lightweight construction materials can save fuel over the entire lifetime)

There is plenty of information available for consumers who want to pick an energyefficient car, e.g., one website run by the US EPA [132]. In California, partial-zero emission vehicles (PZEVs) were introduced to satisfy part of the state’s Zero Emission Vehicle (ZEV) Program [133]. In [134], options for carbon-neutral passenger transport are reviewed. Reference [135] compares fuel cell and battery electric vehicles. The primary energy efficiencies of alternative powertrains in vehicles are discussed in [136]. In [113], the energy efficiency of internal combustion engines and fuel cells for automotive use with different fuels is assessed. It is concluded there that fuel cells have an advantage during hot-start conditions but suffer from efficiency losses during cold starts [113]. Although the energy efficiency of a fuel cell-powered car is not the best, the environmental performance of a vehicle burning hydrogen from solar generation in a low-noise,

Energy Efficiency: Comparison of Different Systems and Technologies

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virtually emission-free fuel cell are outstanding. It is expected that the fraction of fuel cell cars will increase over the next decade, with an accompanying growth of the necessary infrastructure.

Ships Ninety percent of the world’s trade is carried by the international shipping industry, supported by 50,000 merchant ships [137]. Over the last four decades total seaborne trade is estimated to have quadrupled, from just over 8,000 billion ton-miles in 1968 to over 32,000 billion ton-miles in 2008 [137]. Seaborne shipping is one of the most energyefficient means of transportation, especially for large, bulky goods. Here is a comparison of energy efficiency of different transportation modes taken from a study by the Swedish network for Transport and the Environment (> Table 24.5) [137]. It has to be noted that this table is slightly biased in favor of sea transportation, as the aircraft mentioned is an outdated one used on a short-haul flight. Ships can be driven by different technologies [138] with diesel engines being most common. The resistance of the ship’s hull, the design, or the propeller and the tonnage are important factors for its energy efficiency as well. The impact of shipping on the atmosphere and on the climate is discussed in [139]. The auxiliary powering of ships by kite-like devices is discussed in [140] and [141]. Spinning vertical rotors installed on a ship to convert wind power into thrust based on the Magnus effect, so-called Flettner rotors, are another option to increase energy efficiency. Microbubbles as a means of reducing skin friction on ships are studied in [142]. Different propulsion systems for LNG carriers are discussed in [143]. LNG (liquefied natural gas) is expected to gain an increasing importance.

Rail Transportation Intuitively, rail transportation of people and cargo is amongst the most environmentally friendly modes of movement. Technological progress has increased energy efficiency in

. Table 24.5 Energy consumption in different transportation modes (dwt is the deadweight tonnage (also known as deadweight, DW or dwt), a measure of how much weight a ship can safely carry. It is the sum of the weights of cargo, fuel, ballast water, crew, etc.) [137] Mode

Air

Road

Sea

Sea

Comment

B727-200 (1,200 km flight)

Medium-sized Cargo ship, 2,000– truck 8,000 dwt

Cargo ship, >8,000 dwt

Energy consumption

4.07 kWh/t km

0.49 kWh/t km 0.08 kWh/t km

0.06 kWh/t km

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rail transportation, too. According to [144], aerodynamic drag per seat at 150 km/h was cut by half over 30 years. Train speed determines energy efficiency. The energy consumption for a high-speed train from London to Edinburgh increases from 30 to almost 60 kWh/seat as the speed goes up from 225 to 350 km/h [145]. The American railway corporation Amtrak reported an energy use of 2,935 BTU per passenger-mile (1.9 MJ/ passenger-km) in 2005 [146]. A critical factor in energy efficiency of trains is the occupancy. If a train is only 25% loaded, the fuel consumption per passenger and seat can be worse than with economic cars and modern aircraft as shown in [147].

Air Transportation Aviation has helped shape our current business dealings and lifestyles significantly. Virtually any point on the globe has got into easy reach within 24 h. Air transportation is used for cargo and people. It has contributed approximately 3.5% to global greenhouse gas emissions in 1990 with a projection of 15% or more in future [148]. The impact of aviation on climate change is not only driven by CO2 emissions, but also by H2O emissions at high altitude [149]. Due to the long residence time of water vapor at aircraft cruising altitude, it can disproportionally contribute to global warming by reflecting and retaining infrared radiation (compare the effect of natural clouds). Biofuels for aviation [150] were already tested in a proof-of-concept study [151], provoking mixed feelings amongst critics. Winglets [152] and lightweight materials [153] are two commonly known concepts to increase fuel efficiency of aircraft, hence increasing energy efficiency. See also > Figs. 24.4 and > 24.5 above.

Pipeline Transportation Pipelines [154], i.e., conduits of pipe, can be used to transport liquids, gases, and slurries. The Romans built aqueducts for water transportation some 2,000 years ago. An early industrial pipeline was installed in Austria in 1595 to transport brine from Hallstatt to Ebensee for salt production [155]. Today, pipelines are commonly used to transport petroleum, natural gas, and other commodities over large distances. A comparison of natural gas transportation by LNG tankers and pipelines is made in [156]. LNG compression and regasification consume 7–13% of the original amount of natural gas, as well as roughly 0.15% per day of marine transport, which adds about another 1% to overall energy losses. Pipeline transportation of natural gas results in energy losses of approximately 1% per 1,000 km. Therefore, an intercontinental 8,000 km pipeline would involve energy losses of roughly 10%, which is approximately half the amount of transportation by LNG tankers over the same distance [157]. The transportation of liquids in pipelines vs. onboard of trucks is compared in [157] and [158]. The conveying of coal as a slurry in pipelines is assessed in [159]. In industrial plants, pneumatic conveying (dense phase or dilute phase conveying of a solid in air) and hydraulic conveying (solids in liquid carrier

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media) are used to transport materials between various processing sections. Variable speed drives (VSD) for pneumatic conveying blowers are a means of enhancing energy efficiency vs. blowing off excess air at low conveying capacities for the transportation of solids in the gas phase. Reference [160] reviews the transportation of biomass in pipelines. It is concluded that long distances and high throughput rates make such systems economic, as is generally the case with pipeline transportation.

Industry Industry accounts for a high fraction of the global energy consumption, see > Table 24.1 above. The energy intensity varies strongly from 52.3 end-use BTUs per USD of value added in cement production to 0.4 end-use BTUs per USD in computer assembly [9]. Ten end-use BTUs per USD can be set as limit for energy-intensive industries as done in [9]. There is a huge potential for energy savings in industry, yet the biggest opportunities for optimization are not easily known to the people involved [69]. Approximately two third of the energy savings potential can be found in specific process steps of energyintensive industries, whereas one third resides in various areas of non-energy-intensive ones. Savings can be realized by more efficient processes or by more efficient equipment.

Crosscutting Technologies Equipment which is used in different sectors of industry, such as lighting, motors, boilers, and pumps, is subsumed as crosscutting technologies. For these, best practices (see, e.g., [161]) and general recommendations can be formulated that are valid for several branches and sectors of industry. Generally, there exist untapped-into savings potentials in ● ● ● ● ● ● ●

Waste heat recovery Steam systems Motor systems Pumps [117] Lighting Buildings Utilities

For quantifying energy efficiency potentials, there are various methods [24]. Here are some aspects of energy efficiency that are relevant for many industries: Process design: The largest contribution to energy efficiency is made during the design of a process. If a product, for instance, has to be heated up and cooled down several times, chances are high that the process is not energy efficient. Also, an implemented production process is difficult to change. Overcapacity: Design capacity should meet the needs for a process in terms of vessel size, engine power, etc. Overdesign always costs money – not only in the investment phase, but most likely also later on, when energy consumption is higher than necessary.

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Overcapacities of process equipment should normally not exceed 10% of the overall design capacity. Debottlenecking: If a plant can be deblottlenecked, i.e., the output can be increased by making some small modifications, one typically has a highly profitable project. Also from an energy efficiency perspective, debottleneckings frequently lower the specific energy consumption of a product, thus making it more energy efficient. Measuring, monitoring: In order to be able to track energy efficiency measures, it is necessary to measure accurately and regularly actual consumption values of electricity and other utilities such as compressed air or cooling water. Only by monitoring them actively will deviations be spotted. Automatic controls: Automatic process control is generally faster and more accurate than a manual one, and also less prone to errors. Therefore, a production process can be carried out in the most energy-efficient way if it is automatically controlled. Automation will be more economic for large processing plants where the investment costs can be diluted over the volume. Compressed air: Leaks of air from pipes can easily lead to 20–50% efficiency loss of a compressed air system. Preventive maintenance and the timely repair of leaks will help to minimize running costs. A pressure reduction of the entire system can often be considered, as instrument air (plant air) typically only needs to have 6 bar pressure, which is less than the design pressure of many compressor systems. If the operating pressure is reduced by just 1 bar, energy savings of over 5% can result. Maintenance: If industrial assets are not properly being taken care of, their energy consumption tends to increase. Advanced maintenance techniques such as risk-based maintenance, preventive maintenance, thermography, and others will help to keep energy efficiency up. Cutting costs on maintenance can bring short-term gains at the expense of increased risk and deferred costs. A typical yearly maintenance budget for industrial plants would be 2% of the investment value, depending of course on the process. Cogeneration: Production sites that produce their own electricity should seriously consider combined heat and power (CHP). If there is no need for heat in the installation itself, there might be an opportunity to sell the heat, e.g., for district heating purposes. Cogeneration will use the heat which would otherwise be wasted, thereby increasing the energy efficiency. Motors and drives: It is estimated that two third of all electricity consumption in industry is used to drive various motors [161], so there is a huge optimization potential. The ‘‘motor challenge’’ is a recent program to improve motor efficiency [162]. Typical energy efficiencies of motors are 80–90%, with advanced models reaching 97% [22]. Variable speed drives: An engine’s energy consumption can be matched to the load by using a variable speed drive (VSD). VSDs can be realized with a frequency converter coupled to an engine. Up to 50% of energy can be saved. Today, only an estimated 10% of all engines in industry are equipped with VSD. A large number of motors are still controlled by throttling valves in pump systems or vanes in fan applications. By throttling, a part of the produced output immediately goes to waste. Speed control with intermediate transmission such as belt drives, gearboxes, and hydraulic couplings adds to the

Energy Efficiency: Comparison of Different Systems and Technologies

24

inefficiency of the system, and requires the motor to run at full speed. Another drawback is that such systems typically require more maintenance. They can be noisy, too. Pumps: It is estimated that pumps consume 25% of the electricity in US manufacturing facilities [95]. Industrial pumps have a lifetime of 20 years and longer. Pump efficiency is defined as the pump’s fluid power divided by the input shaft power, and is influenced by hydraulic effects, mechanical losses, and internal leakages. Pump manufacturers have devised many ways to improve pump efficiencies. For example, the pump surface finish can be made smoother by polishing to reduce hydraulic losses. A ‘‘good’’ efficiency for a pump will vary depending on the type of the pump. A more useful efficiency term is the wire-to-water efficiency, which is the product of the pump and motor efficiency. An even better measure of efficiency for analysis purposes is the system efficiency, which is defined as the combined efficiency of the pump, motor, and distribution system. See also [117] and life cycle assessment (LCA) above. Fans: Fans move air as pumps move liquids. They can often be optimized for energy efficiency, e.g., by adding a VSD (see above). Energy management system: An energy management system (EMS) is the energy equivalent of an environmental management system. Generally, industrial sites or units that consume more than 1,000 toe/day should have a dedicated energy manager, who will ‘‘pay himself ’’ by economizing on energy bills. A guideline for energy management is provided by [22]. Several smaller units instead of one large one: Instead of one large pump which is controlled with a bypass, several smaller pumps might be more energy efficient, matching power consumption to the process needs. The same consideration might work for air compressors, etc. Energy audit and energy survey: These tools were mentioned already earlier in this chapter. They can be administered by internal or external staff. Generally speaking, it is vital for the success of an energy efficiency program in a corporation to have the support of a senior, recognized executive and to make the effort lasting by introducing energy performance indicators, which can be linked to employee’s targets and performance management. Improvement of power factor (cos f): Power companies will grant a discount on a corporation’s electricity bill if the power factor is OK. Load shifting (using off-peak electricity): If energy-intensive production processes can be concentrated in off-peak hours, the energy bill will be lower. This will also have positive effects on the environment, as peak electricity demand often needs to be produced in a not-so-efficient way. Load shedding: By reducing peak electricity consumption, energy costs can also be reduced. Insulation: Process insulation can be optimized for energy efficiency. A waterlogged insulation transfers heat 15–20 times faster than a dry one, and one filled with ice even 50 times faster [22]! Using waste heat: Heat losses are a major sink for energy. Process heat in general can be upgraded using absorption heat pumps (AHP). Heat losses in flue gases are a particularly large term: If flue gases exit the chimney too hot, significant amounts of heat are wasted

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Energy Efficiency: Comparison of Different Systems and Technologies

(up to 1% of fuel savings for 25 C colder flue gas temperature [95]), see also cogeneration. As for heat exchangers, cleaning and optimization can bring additional energy efficiency gains [163]. An overview on energy efficiency improvement potentials in industry is given in [164] and [165], the latter focusing on mechanical systems. Industrial energy efficiency in Asia, where a large part of global energy-intensive industry has settled, is treated in [166].

Steam and Boilers Steam engines are gone; however, still 37% of the fossil fuel burned in the US industry is used to produce steam [167]. Steam is the working fluid in steam turbines for electricity production. It is used in various industries to transfer and to store heat as it is a capacious reservoir for thermal energy because of the high heat of vaporization of water. The chemical industry uses significant amounts of steam as process heat, one reason being that steam is generated as a by-product in some processes in integrated chemical production sites. Steam in general can be produced efficiently in cogeneration plants. In contrast to district heating networks to heat private homes, cogeneration plants in industry can be operated at full capacity all year round. Steam is produced in boilers. Energy efficiency measures for boilers include ● ● ● ● ● ● ●

Improved process control Reduced excess air Improved insulation Maintenance Recovery of heat from flue gas Recovery of steam from blowdown Optimization of fuel mix For steam distribution systems, the following measures are effective:

● ● ● ● ●

Improved insulation Improved steam traps Steam trap monitoring Leak repairs Condensate return

In [167], information on steam systems in industry, their energy use and energy efficiency improvement potentials are outlined. Detailed information on boilers is given in [168].

Energy-Intensive Industries There are certain ‘‘heavy industries’’ that consume a large fraction of total energy output. In China, for instance, the top 1,000 energy-intensive enterprises consumed 30% of

Energy Efficiency: Comparison of Different Systems and Technologies

24

China’s total energy and 50% of the total industrial energy in 2007 [169]. Energy intensity is a specific quantity, expressed as kWh/kg of product or as kWh/monetary unit (value added, often in USD). Above an arbitrary threshold of ten end-use BTUs per USD, one can speak about energy-intensive industries [9]. This classification is valid for the production of ● ● ● ● ●

Cement (calcination process, clinker production) Steel (coke consumption) Aluminum (primary metal production by electrolysis) Ores (mining operations) Pulp and paper (mechanical pulping)

These industries have a strong effect on global energy consumption because they are not only energy-intensive as such, but because they produce high amounts of materials per year. The global steel production, for instance, is in excess of one billion tons [170]. The IEA predicts big improvements in energy efficiency in industry, which are expected to be more than offset by higher output of steel and cement [5], especially in the developing world, to which countries like Brazil, Russia, India, China (BRIC), Mexico, and South Korea belong. The following > Table 24.6 shows the changes in energy consumption in energy-intensive industries in China, reproduced from [171]. Energy production in China is largely based on coal combustion, with efficiencies being approximately 10% lower than in Europe or the USA [171]. The CO2 emissions from coal combustion are naturally higher than those from other fuels with a lower C/H ratio. Several technology options to reduce energy consumption and CO2 emissions in energy-intensive industries are reported in [172], see also below.

Iron and Steel In the iron and steel industry, as the name implies, iron production and steel production are the main processes [173]. Iron can be produced along different routes. The classic path is the production of pig iron from ore and coke in the blast furnace, which is then further processed into steel in the basic oxygen furnace (BOF) or the open-hearth furnace (OHF), the first one being more energy efficient. Smelt reduction and direct reduction (DR) are . Table 24.6 Energy efficiency in China for energy-intensive products [171] (Taken from the Annual Report on China’s Energy Development (2006) therein) Branch of energy-intensive industry in China Coal consumption in thermal power generation (gce/kWh) Comparable energy consumption per ton of steel (kgce/t) Overall energy consumption in cement production (kgce/t) Overall energy consumption in ethylene production (kgce/t) Gce gram of coal equivalent, kgce kilogram of coal equivalent

1990 427 997 201 1,580

2000 393 784 181 1,212

2004 379 705 157 1,004

879

880

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Energy Efficiency: Comparison of Different Systems and Technologies

. Table 24.7 Potential technologies to make energy-intensive production processes more efficient [172] (From IEA, DOE, AISI, Aluminum Association, Korean Energy Institute) Time frame

Technology option

Description

Pulverized coal and plastic waste injection

Pulverized coal is already used by more than 50% of ST-MT all US BOFs

New reactor designs Paired straight hearth furnace Molten oxide electrolysis

Uses coal and ore fines (COREX™, FINEX™) Substitutes coal for coke in blast furnaces, lower costs, uses two third energy Produces iron and oxygen, no CO2

Hydrogen flash melting Geological sequestration and steelmaking

Uses hydrogen in shaft furnaces, no CO2

MT MT-LT LT MT MT-LT

ST short term (2010–2015), MT medium term (2015–2030), LT long term (2030–2050)

two other, advanced routes to iron. The electric arc furnace (EAF) is used to produce secondary steel from scrap. In China, the energy consumption per ton of steel has declined from 1.43 to 0.52 toe between 1980 and 2005 [174]. Integrated steel plants have a specific primary energy consumption ranging from 19 to 40 GJ/t of steel [175], with minimills that use scrap steel being more efficient. Technology options for reducing energy use and CO2 emissions in the iron and steel industry are tabulated in > Table 24.7 below, reproduced from [172].

Aluminum Worldwide primary aluminum production is projected to increase from 23 to 38 million tons by 2020 [175]. The primary aluminum [176] production, starting from bauxite via electrolysis (Hall–He´roult process), is a very energy-intensive process, contributing 1% of total anthropogenic greenhouse gas emissions in 1995 with about 364 million tons per year CO2-equivalent [175]. Secondary aluminum production [177] consumes approximately 5% of the energy needed for primary production. Existing and potential future processes for bauxite processing are reviewed in [178]. Technology options for reducing energy use and CO2 emissions in primary aluminum are summarized in the following > Table 24.8, reproduced from [174].

Other Primary Metals Generally, one can distinguish between pyrometallurgical and hydrometallurgical processes. The ore content of a deposit influences energy efficiency as the chosen process does. The energy demand for comminution is described in [179]. Energy efficiency of a lead

Energy Efficiency: Comparison of Different Systems and Technologies

24

. Table 24.8 Potential technologies to make energy-intensive production processes more efficient [172] (From IEA, DOE, AISI, Aluminum Association, Korean Energy Institute) Technology option

Description

Time frame

Wetted, drained cathode technology MT-LT Alternative cell concepts Combines inert anode, drained cathodes LT Carbothermic and kaolinite reduction Alternatives to the Hall–He´rault process LT process on commercial scale MT medium term (2015–2030), LT long term (2030–2050)

smelter is discussed in [180], and energy efficiency of copper and magnesium production in [181] and [182], respectively. Processes for the production of steel, aluminum, copper, lead, and zinc are reviewed from an energy-perspective in [183]. Sintering processes and their energy efficiencies are discussed in [184] for one system, and scale-up in metallurgy in general in [170].

Pulp and Paper The pulp and paper (P&P) industry is a very energy-intensive one. Pulp is being produced from wood by the Kraft process, with electricity as additional input and output, plus steam as an output. An efficient Kraft pulp mill can be a net exporter of heat and electricity [185]. Industry practice shows that in the past, most energy-efficiency measures were limited to low-investment, high-return projects, with typically 5% energy savings with a 1-year payback time [186], with a lot of potential still untapped into. In current paper mills, steam savings of up to 30% are deemed feasible [187–191]. Energy efficiency savings can be obtained from the use of different fuels, which are typically wood, bunker oil, and black liquor [186], the latter being a by-product of the transformation of wood chips into pulp. Typical energy efficiencies in the industry for bark combustion are 67% (based on the higher heating value) and 80% for bunker oil combustion, respectively [186]. In [185], the utilization options for excess steam and heat at Kraft pulp mills are studied. Traditional ways are increased electricity production and district heating, whereas increased sales of biomass as bark and/or extracted lignin and carbon capture and storage (CCS) are new pathways. There is a trend toward additional products, complementing the traditional pulp and paper output, by biofuels, pellets, lignin, carbon fibers, and other specialty chemicals [185] from pulp and paper plants. In [186], the economics of trigeneration in a Kraft pulp mill are discussed. In trigeneration, pulp production, waste-heat upgrading, and power production are

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. Table 24.9 Potential technologies to make energy-intensive production processes more efficient [172] (From IEA, DOE, AISI, Aluminum Association, Korean Energy Institute) Time frame

Technology option

Description

Black liquor gasification

In demonstration, R&D; commercially available 2030; 15–23% gain

MT-LT

Efficient drying technology

R&D now; commercial demo: 2015–2030; commercial: 2030 onward

MT-LT

MT medium term (2015–2030), LT long term (2030–2050)

simultaneously carried out (compare polygeneration). Absorption heat pumps (AHP) can be used to cool waste-heat streams and to extract energy from them. Technology options for reducing energy use and CO2 emissions in the paper and paperboard industry, reprinted from [172], are summarized here in > Table 24.9. Recycling is another option to increase energy efficiency of paper products. For details on energy efficiency options in the pulp and paper industry, see [192].

Cement The cement industry, already 15 years ago, exceeded 1.5 billion tons of annual output, making it a huge consumer of energy. For cement production, first clinker has to be made, which is then blended with approximately 5–70% additives such as gypsum and fly ash to yield cement. This first step is the most energy-intensive one. Limestone (CaCO3) is burnt with silicon oxides, aluminum oxides and iron oxides. There is a wet process and a dry process, the latter one being more energy efficient. As cement plants [193] consume significant amounts of energy, approximately 4 GJ/t of cement produced [194], energy efficiency programs have been extensively applied to various plants [67, 195–198]. For each t of cement, approximately 0.5 t of CO2 are generated [22]. In [67], potentials for energy efficiency improvements in the US cement industry are discussed, and in [199], those for China. CO2 and energy intensity reductions in cement production can be achieved by ● ● ● ● ●

Modification of the product composition (less clinker) Use of alternative cements (e.g., mineral polymers) Improving the energy efficiency of the process and process equipment Introduction of a different process (e.g., change from wet to dry process) Replacement of high carbon fossil fuels by low-carbon fossil fuels

A trend in the cement industry is the use of waste fuels such as tires. Recommendations on energy efficiency and cost-saving opportunities for the cement industry can be found in [200].

Energy Efficiency: Comparison of Different Systems and Technologies

24

Glass Production Glass is a ubiquitous material that comes as sheet glass (produced in the float glass process), hollow glass (for glass containers), automotive glass, optical and other glasses such as glass fiber and glass wool. Its production is an energy-intensive process. According to [302], 74% of production costs are typically raw materials, fuels, and electricity. Recycling of glass offers a good way of increasing energy efficiency. One recycled bottle can save approximately 0.1 kWh [303]. In [304], best practices for energy efficiency improvements in the glass industry are provided. A detailed treatise of energy efficiency potentials in the American glass industry can be found in [305].

Petroleum Refining In a petroleum refinery (oil refinery) [201], crude oil is processed into various petroleum products such as naphtha, gasoline, diesel, and liquefied petroleum gas (LPG). Refineries are complex, chemical plants that are usually highly integrated. Crackers, for instance, can produce lightweight hydrocarbons as basic feedstock for the petrochemical industry (see also below). Energy efficiency in a petroleum refinery can be tackled from various angles. Like in industry in general, there is usually optimization potential in cogeneration, steam systems, heat transfer systems and motors (see also [202–208] for details reported in the literature). Reference [209] estimated the energy savings potential for refineries to be around 15%. The determination of the energy efficiency of a certain process is a somewhat tricky task as it depends on boundary limits to be drawn. Reference [210] attempts to allocate CO2 emissions in petroleum refineries to various petroleum products. One aspect of the petrochemical and chemical industry in general that has to be noted here with respect to energy efficiency is that the energy contained in the feedstock is partly converted to heat and power, but also remains in the final products to some extent, providing potentials for recycling at the end of the various materials’ lifetimes (feedstock recycling or thermal recycling). Recommendations on energy efficiency and cost-saving opportunities in refineries can be found in [211].

Petrochemicals Petrochemicals are products derived from petroleum [212] other than fuels for combustion. The petrochemical industry consumes approximately 8% of total oil production for the manufacture of various products [70], ranging from plastics, rubbers, and solvents to various fine chemicals. Two important upstream processes are cracking (fluid catalytic cracking, steam cracking) for the production of olefins such as ethylene and propylene, and reforming (catalytic reforming) for the production of aromatics. Worldwide, more than 107 t of propylene, 6.5
106 t of ethylene and 7
106 t of aromatics are produced per year. From these primary petrochemicals, to which also

883

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Energy Efficiency: Comparison of Different Systems and Technologies

. Table 24.10 Potential technologies to make energy-intensive production processes more efficient [172] (From IEA, DOE, AISI, Aluminum Association, Korean Energy Institute) Technology option

Description

High-temperature furnaces Gas-turbine integration Advanced distillation columns

Able to withstand more than 1,100 C MT-LT Higher-temperature CHP for cracking furnace MT-LT MT-LT

Combined refrigeration plants Biomass-based system options Feedstock substitution

Time frame

MT-LT LT

MT medium term (2015–2030), LT long term (2030–2050)

synthesis gas can be counted, a wide range of chemical products is made. Energy efficiencies of a steam cracker are reported in [213] and [214]. Naphtha crackers are estimated to consume 31.5 GJ/t of energy [215]. The gross energy requirement (GER) for major petrochemical products such as ethylene, propylene, butadiene, and benzene is reviewed in [209]. Technology options for reducing energy use and CO2 emissions for petrochemicals are shown here in > Table 24.10, from [174]. Below, details on some petrochemical products with respect to energy efficiency are reviewed.

Polymers The polymer industry has ramped up plastics production between 1950 and 2007 from 1.5 to 260 million tons [216] worldwide, which corresponds to an annual growth rate of more than 9%, making plastics ubiquitous and versatile construction materials. Polyolefins are the most common plastics, with polyethylene (PE) and polypropylene (PP) accounting for the largest fraction, followed by polyvinylchloride (PVC), polystyrene (PS) and expanded polystyrene (EPS), polyethyleneterephthalate (PET), polyurethane (PUR), and others, e.g., engineering plastics such as polycarbonate (PC). Polymers can be produced with different technologies, ranging from radical reactions (high-temperature and high-pressure processes such as for high density polyethylene [HDPE]) to catalytic processes (at more moderate conditions), which show varying energy efficiencies. The gross energy requirements for the production of low-density polyethylene (LDPE), PP, PS, and PVC are 69.8, 61.6, 81.5, and 55.7 GJ/t, respectively [209]. Plastic production uses 8% of the world’s oil production, 4% as feedstock and 4% during manufacture [217]. Cogeneration and heat recovery in polymerization processes are discussed in [218]. In Europe, the recycling rate of plastics has reached 51.3% (21.3% recycling and 30.0% energy recovery, i.e., combustion) [216]. Reference [209] investigated potential energy savings in the production of plastics. That study found that the technical potential for

Energy Efficiency: Comparison of Different Systems and Technologies

24

energy efficiency savings varies from 12% for PE to 25% for PVC. Further information on energy use in plastics production can be found in [219]. Alternative feedstocks, biopolymers, and feedstock recycling [220] are emerging trends in the industry with impact on energy efficiency.

Chemical Industry The chemical industry uses crude oil, natural gas, and coal, apart from electricity, both as raw materials and as fuels to produce more than 50,000 different products. More than half of the energy used by the chemical industry is processed as feedstock, which means that it is transformed into various products such as chemicals or polymers. Most energy is consumed by the production of a few small, intermediate compounds. In the chemical industry, energy costs account for 10–15% of total manufacturing costs [221]. For some processes such as electrolysis, energy costs can exceed 50% of production costs. The DOE estimates potential energy savings within the chemical industry to be approximately 20%. Strategies to improve energy efficiency in the chemical industry are process improvements, cogeneration, integration, and the introduction of energy management systems (EMS). Integration means that rather than producing a single chemical, a production location should strive to use its feedstock to make the desired final product, while utilizing by-products as well. If several production steps, such as crude oil distillation, cracking, and polymerization, can be done in one location, costly and wasteful transportation and storage steps can be avoided (compare the German concept of an integrated chemical complex, the ‘‘Verbund.’’ At the largest chemical Verbund site, BASF’s, Ludwigshafen, synergies amount to €500 million per year, €150 million out of which are attributed to energy savings [70]). Process design is also an important consideration for energy efficiency as different unit operations [222] have varying energy demands. In [215], energy use and energy intensity of the US chemical industry are analyzed. A general review on sustainability and energy efficiency in the chemical industry is provided by [223]. Below, some details on various products of the chemical and process industries with respect to energy efficiency are compiled. Actual energy consumption values for the production of chemicals are significantly higher than the theoretical demand stipulated by thermodynamics. A ‘‘clean-sheet redesign,’’ not considering cost-effectiveness, would offer a potential for energy savings in chemicals production of up to 95% [9, 65]. Catalysts, as they lower the activation energy, can generally increase energy efficiency, particularly enzymatic catalysts for several particular reactions. Process intensification and polygeneration are two emerging technologies that could reduce energy demand in the chemical industry. By process intensification [224], more compact and efficient plants can be designed. Polygeneration using natural resources is detailed in [225]. An overview on energy efficiency in the chemical industry is provided in [226–229]. Green chemistry is discussed in [230, 231].

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Energy Efficiency: Comparison of Different Systems and Technologies

Ammonia

Ammonia is one of the inorganic chemicals with the highest yearly production volume. Its global consumption is in excess of 107 t. NH3 is the precursor to most industrially produced nitrogen-containing compounds. More than 80% of ammonia is processed to fertilizers. Ammonia production consumes more than 1% of all man-made power [232]. CO2 emissions in ammonia production are estimated to be 1.58 t for each ton of product [22]. Energy consumption is quoted as 39.3 GJ/t for feedstock (natural gas) plus 140 kWh/t electricity, totaling to 40.9 GJ/t (based on higher heating value, corresponding to 37.1 GJ/t based on lower heating value) [215]. Without considering the natural gas, the primary energy consumption for ammonia production is 16.7 GJ/t [215]. For energy efficiency studies and improvement potentials in ammonia production, see [233] and [234]. The use of ammonia as a fuel is described in [235]. The specific energy consumption for the production of urea is estimated at 2.8 GJ/t (1994) [215]. Fertilizers

Nitrogen-bearing fertilizer production is a very energy-intensive industry. Ammonia is the most important intermediate chemical compound here (see also above). > Table 24.11 shows the energy use and emission intensity for the production of various fertilizer components, reprinted from [239]. An early review on energy efficiency in fertilizer production is provided by [237]. Energy efficiency in the fertilizer industry is reviewed in [237–241]. Methanol

Methanol can be produced by steam reforming from methane [242]. It can also be obtained from coal [243] and various biomass products [244] such as sugar cane. Methanol has seen increased interest for its use in ● Direct methanol fuel cells [245] ● Fuel for combustion engines [246] ● Feedstock for the chemical industry [247]

. Table 24.11 Energy requirements to manufacture fertilizer components plus associated CO2 emissions [236] Component N P K S Lime

Energy use [MJ/kg] 65 15 10 5 0.6

Emissions [kg CO2/MJ] 0.05 0.06 0.06 0.06 0.72

Energy Efficiency: Comparison of Different Systems and Technologies

24

In 1994, the specific energy consumption for the production of methanol was 38.4 GJ/t (based on higher heating value) [215]. Industrial Gases

A wide variety of gases is industrially produced and sold in compressed or liquid state. Apart from air, oxygen and nitrogen are amongst the most commonly used industrial gases [248], others being argon (welding), carbon dioxide, and methane. Oxygen and nitrogen have traditionally been produced through cryogenic air separation, where air is cooled and pressurized until it becomes a liquid with the various gases being extracted through fractionated distillation. The associated energy consumption is estimated to be 1.8–2.0 GJ/t of oxygen or nitrogen [215]. Other energy-efficient technologies such as pressure swing adsorption (PSA) [249] and membrane separation [250] are increasingly used. An article on energy efficiency gains in gas production (thermal gasification) is given by [251]. Chlorine

Chlorine is produced through electrolysis of a salt solution (brine), which is an energyintensive process requiring between 3,065 and 3,960 kWh/t [215]. The coproducts caustic soda (sodium hydroxide, NaOH) and hydrogen gas (H2) are obtained, with the major markets for chlorine being PVC (polyvinylchloride) manufacturing, inorganic chemicals, propylene oxide, water treatment, and organic chemicals. The chlorine industry is reviewed in [252]. Technology options for reducing energy use and CO2 emissions in chlor-alkali manufacturing are summarized from [172] in the > Table 24.12 below. Hydrogen

Hydrogen is regarded as an interesting option as transportation fuel and as storage medium for electricity, being produced from renewable resources. The ‘‘Hydrogen Economy’’ [253] is often seen as a straightforward solution to many issues around pollution and global warming. Despite all the potential that lies in the technical exploitation of hydrogen, it needs to be borne in mind that the hydrogen – as clean as it is as such – has to be produced. Hydrogen from nuclear power is treated in [254] and [255]. It is the overall

. Table 24.12 Potential technologies to make energy-intensive production processes more efficient [172] (From IEA, DOE, AISI, Aluminum Association, Korean Energy Institute) Time frame

Technology option

Description

Convert mercury-process and diaphragmprocess plants to membrane technology

Combined electrolytic cell with a fuel MT-LT cell, using hydrogen by-product

MT medium term (2015–2030), LT long term (2030–2050)

887

888

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Energy Efficiency: Comparison of Different Systems and Technologies

. Table 24.13 Pharmaceutical industry and energy use [95] Area

Distribution of energy use

R&D

30%

Offices Production of bulk pharmaceutical substances Formulation, packaging, and filling Warehouse

10% 35% 15% 5%

Miscellaneous Total

5% 100%

energy efficiency (system efficiency) that will determine whether hydrogen will be used on a large scale as energy carrier. For details, see [256].

Pharmaceutical Industry The US pharmaceutical industry has energy expenses of approximately $1 billion per year [95], which, being only a small fraction of total production costs, is still significant, given the fact that energy savings will translate into direct and predictable earnings. In the pharmaceutical industry, there are three overall stages: ● Research and development (R&D) ● Production of bulk pharmaceutical substances ● Formulation of the final products Table 24.13 shows the distribution of energy use [95] in this sector. Twenty-five percent of the total energy is used for plug loads and processes, 10% for lighting, and 65% for HVAC (heating, ventilation, and air conditioning). The biggest potential can hence be found in R&D and bulk manufacturing. >

Public Sector and Community Infrastructure The public sector is another area where energy efficiency potential exists. Awareness of energy efficiency and conservation is a major topic. In a typical office, nearly 40% of the electricity consumption occurs after closing hours [257]. Government institutions can apply energy-efficient procurement and create awareness for energy savings. Public buildings (see also next section) offer energy efficiency increase potential, as does for instance the lighting infrastructure of public roads. Desalination plants are important in several parts of the world. Their energy efficiencies for different technologies are assessed in [258–262].

Energy Efficiency: Comparison of Different Systems and Technologies

24

Buildings Buildings have a strong and long-lasting impact on global energy consumption because they are constructed for typically 50–100 years. In 2005, 39% of the total energy consumption in the USA stemmed from commercial and residential buildings [39]. They accounted for as much as 70% of total electricity consumption [39]. There is hence a huge potential for what is known as green buildings. The residential sector in the USA is expected to account for 29% of the US energy consumption in 2020 [9], driven by population growth, larger homes and more electric and electronic gadgets in private households. The specific energy use for heating of buildings, a major parameter for their energy efficiency, is given in kWh/(m2 year). Key determinants for energy efficiency of buildings are ● Location and surroundings ● Insulation ● Heating technology Sealing of ducts, basement insulation and improved heating equipment are seen as major efficiency opportunities in private homes in the USA [9]. Heat pumps are particularly energy efficient. There are three types of heat pumps: air-to-air, water source, and ground source. Ground source heat pumps typically use four times less electrical energy than direct electrical heaters. Deviations in energy efficiency from the design requirements to actual performance may come from ● ● ● ● ●

Errors in the design Errors in the construction Incorrect operation Lack of maintenance Changed use of the building

Various tools, such as an energy survey or an energy audit, can help uncover efficiency potentials. On average, heating and cooling account for almost half of a typical utility bill. Drafty rooms can be improved by checking windows and doors. The HVAC (heating, ventilation, air conditioning) system often offers potential for improvement, and so does the lighting. Compact fluorescent lights (CFL) are more efficient than electric bulbs. Passive buildings [265] and zero net energy (ZNE) buildings [263, 264] are more energy efficient than traditional ones. For ZNE buildings, embodied energy [116] can be considered. This is the quantity of energy required to manufacture and transport the materials utilized for their construction. According to [116], the total embodied energy of load bearing masonry buildings can be reduced by 50% when energy-efficient/alternative building materials are used. Landscaping around private homes can also bring measurable energy savings. Carefully positioned trees can save up to 25% of a household’s energy consumption for heating and cooling. They can, apart from giving a nice appearance, provide shade and shelter from wind. Payback times for such planting measures can be as low as several years [266].

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Energy Efficiency: Comparison of Different Systems and Technologies

0.12 2007 residential retail electricity price Cost of conserved energy (2007$/kWh)

890

0.10

1. Color television 2. Lighting 3. Other uses 4. Water heating 5. Clothes washer 6. Space heating 7. Furnace fan 8. Personal computer 9. Refrigeration 10. Space cooling 11. Dishwasher 12. Freezer

0.08

0.06

0.04

12

10 8 6 3

0.02

4

9

7

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. Fig. 24.10 Residential electricity savings potential in the year 2030 (Reprinted with permission from [268])

Micro-generation for individual houses is another interesting technology option for the energy-savy. A small combined heat and power (CHP) system to produce electricity and heat for a community or a single household is known as micro-generation [267]. The most promising technologies are Stirling engines and fuel cells in a size range of approximately 1–10 kWe. Total efficiencies can be typically 80–88% [267]. It is estimated that in US buildings, one third of the total energy consumption can be saved at a cost of 2.7 $c/kWh [268], see also for natural gas savings there. > Figure 24.10 below shows the electricity savings potential for the residential, and > Fig. 24.11 the same scenario for the commercial sector. It can be seen from > Fig. 24.10 that in the residential area, a huge potential exists for TV sets, lighting, and space cooling, with freezers already being rather optimized. > Figure 24.11 below takes a look at the commercial sector. In the commercial sector, space cooling and lighting offer large potential, with the most cost-effective opportunities residing in space heating and ventilation. Energy efficiency in the residential area is covered in [269]. A guide on energy efficiency for home owners can be found in [270].

Appliances Appliances are a collection of electrically powered devices, which can be found in nearly every household. They account for approximately 20% of a typical household’s energy

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Cost of conserved energy (2007$/kWh)

0.10 2007 commercial retail electricity price

0.09 1. Space heating 2. Ventilation 3. Water heating 4. Refrigeration 5. Other uses 6. Space cooling 7. Office Equip. – non-PC 8. Office Equip. – PC 9. Lighting 10. Cooking

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. Fig. 24.11 Commercial electricity savings potential in the year 2030 (Reprinted with permission from [268])

consumption, with refrigerators, washing machines, and dryers at the top of the consumption list. A ‘‘cheap’’ device can become very costly over its entire lifetime of up to 10 or 20 years (see TCO concept above). In 1978, California took a leading national role in the USA by establishing the first building and appliance standards in the country. Nearly 85% of all dishwashers in California are Energy Star® compliant (see later), and 50% of refrigerators and washing machines conform to these standards too. What is even more impressive, however, is that this increase in market share occurred within no more than 7 years, see > Fig. 24.12, reprinted with permission from [271]. Typical renewal cycles of appliances in industrialized countries, here the USA, are shown in > Fig. 24.13 below, reprinted from [272]. Modern appliances consume significantly less energy than older ones.

Lighting Lighting has played a large part in the public discussion on energy efficiency. As traditional incandescent bulbs, which have an efficiency on the order of 1% to produce light, are being phased out in many countries, mild panic-buying could be observed in 2009 [273]. Some consumers oppose the compact fluorescent lights (CFL), which typically cost four times as much as traditional bulbs. The fact that their energy consumption is one fifth and that payback times are typically short has not convinced all consumers (yet). There are

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. Fig. 24.12 Market share of Energy Star® appliances in California (Reprinted with permission from [271])

. Fig. 24.13 Appliance renewal cycles (Reprinted with permission from [272])

reservations against the hue of the CFL’s light. CFL that work in dimmers tend to cost more than standard CFL. In [274], a lifecycle analysis of CFL is made.

Consumers Up to two third of household energy use is for space heating, water heating, and refrigeration [9], with lighting playing a lesser role. Another significant share is held by the ‘‘plug load.’’ ‘‘Plug load’’ is a collective term for electrical devices and small appliances. These are virtually hundreds of small devices in private homes, consuming electricity. The biggest shares are held by TV sets (22%), DVD players (5%), PCs (5%), and microwave ovens (3%) [9]. Standby power consumption is a huge energy waster. In Japan, the annual per-household standby electricity consumption could be reduced from 437 to 308 kWh

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. Fig. 24.14 Annual average of expenditures of households on energy for heating and electricity (Reprinted with permission from Elsevier from [75])

from 2002 to 2005 [9]. > Figure 24.14 shows typical energy expenditures for Swedish households, reproduced from [75]. It is assumed that with a tripling of energy prices, energy use of private households would decrease by 30% [75]. Energy-consciousness of consumers has increased over the last years, partly induced by various initiatives such as Energy Star®, see also below.

Tips and Tricks for Consumers There are plenty of tips and tricks in various organizations’ and authorities’ brochures and internet pages for consumers on how to lower their utility bills. Most of them are commonsense, but it is worthwhile to take a look at them to capture some fast savings. Here are a few examples of often unused potential in private homes: ● ● ● ●

The temperature of the refrigerator is too low. The refrigerator is positioned in a confined space. The washing machine is operated half-empty with too warm water temperature. Open food is stored in refrigerators (liquids need to be covered, and food should be wrapped to avoid moisture release). ● Untight windows. ● Time is not considered (peak electricity is most costly).

Initiatives for Energy Efficiency Energy efficiency improvements do not come ‘‘naturally,’’ at least not at the desired speed. In order to overcome the known barriers toward energy efficiency, which were outlined

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above in this chapter, government action can help. Numerous programs and initiatives to educate people about and to promote energy efficiency have been started by governments, NGOs (nongovernmental organizations), NPOs (nonprofit organizations), for-profit entities and visionary individuals such as business owners and public celebrities. One such initiative is Energy Star®. Energy Star® label is used to identify energy-efficient appliances. It was initiated by the DOE (US Department of Energy) and the EPA (US Environmental Protection Agency). Products with the Energy Star® label usually exceed minimum efficiency standards by a substantial amount. More information on Energy Star® can be found at [275] and [276]. The impact of agreements on energy efficiency is reviewed in [4].

Other Aspects There are countless areas for hidden or for indirect energy efficiency improvements, some of which are being touched upon here. Advanced packaging, for instance, can save substantial amounts of materials to achieve the same level of goods protection. Lightweight packaging will make transportation over long distances more energy efficient. One example is the replacement of bulky glass bottles by composite containers of (recycled) cardboard and plastics. In information technology (IT), there is often an untapped potential for energy savings and efficiency improvements. Anyone who has witnessed the large air-conditioning systems for server rooms will immediately see the potential offered by what has become known as ‘‘green computing.’’ More details can be found in [277] and [278]. The service sector can also contribute to more energy efficiency. Electronic banking, video telephony and teleconferencing [279], telecommuting [280, 281], and fleet management [282] are just a few examples where energy for traveling can be economized. In general, shifting employment and economic activity from manufacturing to the services sector saves energy and cuts greenhouse gas emissions because the services sector is much lower in energy intensity. Energy efficiency potentials in hospitals are discussed in [283]. Energy efficiency under extreme conditions is reviewed in [284].

Energy Conservation Being a broader term than energy efficiency, energy conservation is about using less energy, with a lower energy service being delivered. Sometimes, it is used synonymously with energy efficiency. Energy saving is without doubt the quickest, most effective, and most cost-efficient way for reducing greenhouse gas emissions, as well as improving air quality, especially in developing countries and in densely populated areas. An example of energy conservation on a private level is, for instance, driving less with one’s car. An organization can study its office lighting setup to remove costly over-illumination, for example. For more information on energy conservation, see [53, 285–290].

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Further Study and Reading In this section, a few terms that are related to energy efficiency were compiled as a starting point for further exploration by the interested reader. Dematerialization: By this expression, one can understand the decline of weight and ‘‘embedded energy’’ (cf. embodied energy) of materials in industrial end products over time, or, more broadly speaking, the absolute or relative reduction in the quantity of materials required to serve economic functions [291, 292]. On the one hand, one can observe a decline in weight of certain goods such as PCs, and on the other hand, people tend to use more materials as their comfort level increases (e.g., larger homes, larger cars). Trends of dematerialization are reviewed in [291]. A similar term is ephemeralization, which was coined by R. Buckminster Fuller. It is the ability of technological advancement to do ‘‘more and more with less and less until eventually you can do everything with nothing’’ [293]. Industrial ecology: Being defined as a ‘‘systems-based, multidisciplinary discourse that seeks to understand emergent behavior of complex integrated human/natural systems’’ [294], industrial ecology strives at sustainability and eco-efficiency. More information on the topic can be found in [295]. Eco-efficiency: According to the World Business Council for Sustainable Development (WBCSD), it is expressed as ● ● ● ● ● ● ●

Reduction in the material intensity of goods or services Reduction in the energy intensity of goods or services Reduced dispersion of toxic materials Improved recyclability Maximum use of renewable resources Greater durability of products Increased service intensity of goods and services

More information can be found in [296]. Water efficiency: Water efficiency is closely linked to water conservation. It can be defined as the accomplishment of a function, task, process, or result with the minimal amount of water feasible. Effluent reuse is one important means of achieving water efficiency [297]. It is estimated that each m3 of water utilized in the industrial and service sectors generates at least 200 times more wealth than it does in the agricultural sector [298]. This suggests that water-intensive production will be shifted from arid regions to those with more water (compare the shift of CO2-intensive production to certain areas). Here, the concept of virtual water [299, 300] steps into place. Virtual water, also called embedded water, embodied water, or hidden water, refers to the water needed to manufacture a good or service. Yearly individual water consumption is on the order of 1 m3 for drinking, 100 m3 for domestic use, and 1,000 m3 embedded in food. This shows that the concept of virtual water is closely linked to water efficiency and ultimately to energy efficiency. Other burning topics related to energy are the affordability of energy and access to energy, which are both not secured for a high number of people.

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Conclusions This chapter has taken a look at energy efficiency in industry, transportation, the private sector, and other areas, exploring a topic of high relevance for climate change mitigation. Energy-use efficiency is the cheapest and easiest source of energy, with a huge unused potential. It is estimated that up to one third of the worldwide energy demand in 2050 can be saved by energy efficiency measures. In this chapter, aspects of energy efficiency from various sectors were presented, spanning historic data, current levels, and future trends. An emphasis is placed on providing brief information and references on how energy efficiency improvements can be realized.

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Section 4

Alternative Energies

25 Biomass as Feedstock Debalina Sengupta1 . Ralph Pike2 1 Chemical Engineering Department, Louisiana State University, Baton Rouge, LA, USA 2 Minerals Processing Research Institute, Louisiana State University, Baton Rouge, LA, USA Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 913 Biomass Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 916 The Calvin–Benson Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 919 The C4 Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 919 The CAM Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 920 Biomass Classification and Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 921 Saccharides and Polysaccharides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 922 Lignocellulosic Biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 922 Cellulose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 923 Hemicellulose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 925 Lignin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 925 Lipids, Fats, and Oils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 926 Proteins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 927 Biomass Conversion Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 927 Biomass Pretreatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 928 Fermentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 931 Anaerobic Digestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 932 Transesterification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 934 Gasification/Pyrolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 938 Biomass Feedstock Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 942 Forest Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 944 Forest Land Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 944 Types of Forest Resource . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 944 Limiting Factors for Forest Resource Utilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 946 Summary for Forest Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 947 Agricultural Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 948 Agricultural Land Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 948 Types of Agricultural Resource . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 948 Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_25, # Springer Science+Business Media, LLC 2012

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Limiting Factors for Agricultural Resource Utilization . . . . . . . . . . . . . . . . . . . . . . . . 951 Summary for Agricultural Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 953 Aquatic Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 953 Raceway Pond Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 955 Algenol Biofuels: Direct to EthanolTM Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 956 ExxonMobil Algae Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 957 Shell Algae Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 958 Green Fuels Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 958 Valcent Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 958 Algae Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 958 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 961 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 962

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25

Abstract: The world has a wide variety of biofeedstocks. Biomass is a term used to describe any material of recent biological origin, including plant materials such as trees, grasses, agricultural crops, or animal manure. In this chapter, the formation of biomass by photosynthesis and the different mechanisms of photosynthesis giving rise to biomass classification are discussed. Then, these classifications and composition of biomass are explained. The various methods used to make biomass amenable for energy, fuel, and chemical production are discussed next. These methods include pretreatment of biomass, biochemical routes of conversion like fermentation, anaerobic digestion, transesterification, and thermochemical routes like gasification and pyrolysis. An overview of current and future biomass feedstock materials, for example, algae, perennial grass, and other forms of genetically modified plants, is described including the current feedstock availability in United States.

Introduction The world is dependent heavily on coal, petroleum, and natural gas for energy, fuel, and as feedstock for chemicals. These sources are commonly termed as fossil or nonrenewable resources. Geological processes formed fossil resources over a period of millions of years by the loss of volatile constituents from plant or animal matter. The human civilization has seen a major change in obtaining its material needs through abiotic environment only recently. Plant-based resources were the predominant source of energy, organic chemicals, and fibers in the western world as recently as 200 years ago, and the biotic environment continues to play a role in many developing countries. The discovery of coal and its usage has been traced back to fourth century B.C. Comparatively, petroleum was a newer discovery in the nineteenth century, and its main use was to obtain kerosene for burning oil lamps. Natural gas, a mixture containing primarily methane, is found associated with the other fossil resources, for example, in coal beds. The historical, current, and projected use of fossil resources for energy consumption is given in > Fig. 25.1. Petroleum, coal, and natural gas constitute about 86% of resource consumption in the United States. The rest 8% comes from nuclear and 6% comes from renewable energy. Approximately 3% of total crude petroleum is currently used for the production of chemicals, the rest being used for energy and fuels. The fossil resources are extracted from the earth’s crust, processed, and burnt or converted to chemicals. The proven reserves, in North America, for coal were 276,285 million tons (equivalent to 5,382 EJ [exajoule = 1018 J]) in 1990, for oil were 81 billion barrels (equivalent to 476 EJ) in 1993, and for natural gas were 329
103 billon ft3 (equivalent to 347 EJ) in 1993 [1]. The United States has considerable reserves of crude oil, but the country is also dependent on oil imports from other countries for meeting the energy requirements. The crude oil price has fluctuated over the past 40 years, the most recent price increase over $130 per barrel being in 2008. The EIA published a projection of the price of crude oil over the next 25 years, where a high and a low projection were given in addition to the usual projection of crude oil price, as shown in > Fig. 25.2 [2].

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U.S. Energy Consumption by Fuel (1980-2035) (quadrillion Btu) 45

History

Projections

40

Liquids

35 30 Natural Gas 25 Coal 20 15 Nuclear

10

Non-Hydro Renewable

5 0 1980

Hydropower 1990

2000

2005

2010

2020

2030

2035

2030

2035

. Fig. 25.1 Energy consumption in the United States, 1980–2035 [2]

Oil Prices, Historical and Projected 250 Historical

Projected

200 2008 dollars per barrel

914

150

100

50

0 1980

1985

1990

1995 High

2000

2005 Low

2010

2015

2020

2025

AEO2010 Reference

. Fig. 25.2 Oil prices (in 2008 dollars per barrel), historical data and projected data (Adapted from [2])

Biomass as Feedstock

25

The projection shows a steady increase in price of crude to above $140 per barrel in 2035. With a high price trend, the crude can cost over $200 per barrel. The fossil resources are burnt or utilized for energy, fuels, and chemicals. The process for combustion of fossil resources involves the oxidation of carbon and hydrogen atoms to produce carbon dioxide and water vapor and releasing heat from the reactions. Impurities in the resource, such as sulfur, produce sulfur oxides, and incomplete combustion of the resource produces methane. The Intergovernmental Panel on Climate Change identified that changes in atmospheric concentration of greenhouse gases (GHG), aerosols, land cover, and solar radiation alter the energy balance of the climate system [3]. These changes are also termed as climate change. The green house gases include carbon dioxide, methane, nitrous oxide, and fluorinated gases. Atmospheric concentrations of carbon dioxide (379 ppm) and methane (1,774 ppb) in 2005 were the highest amounts recorded on the earth (historical values computed from ice cores spanning many thousands of years) till date. The IPCC report states that global increases in CO2 concentrations are attributed primarily to fossil resource use. In the United States, there was approximately 5,814 million metric tons of carbon dioxide released into the atmosphere in 2008 and this amount is projected to increase to 6,320 million metric tons in 2035 [2] as shown in > Fig. 25.3. The increasing trends in resource consumption, resource material cost, and consequent increase carbon dioxide emissions from anthropogenic sources indicate that a reduction of fossil feedstock usage is necessary to address climate change.

CO2 Emissions due to Fossil Feedstock Usage 2035

2008

Buildings and Industrial, 1,571 (25%)

Buildings and Industrial, 1,530 (26%) Electric Power, 2,359 (41%)

Total: 5,814 million metric tons

Transportation, 1,925 (33%)

Electric Power, 2,634 (42%)

Total: 6,320 million metric tons

Transportation, 2,115 (33%)

. Fig. 25.3 Carbon dioxide emissions in 2008 (current) and 2035 (projected) due to fossil feedstock usage (Adapted from [2])

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This has prompted world leaders, organizations, and companies to look for alternative ways to obtain energy, fuels, and chemicals. Thus, carbon fixed naturally in fossil and nonrenewable resources over millions of years is released to the atmosphere by anthropogenic sources. A relatively faster way to convert the atmospheric carbon dioxide into useful resources is by photosynthetic fixation into biomass. The life cycle of the fossil resources showed that the coal, petroleum, and natural gas all are derivatives of decomposed biomass on the earth’s surface trapped in geological formations. Thus, biomass, being a precursor to the conventional nonrenewable resources, can be used as fuel, generate energy, and produce chemicals with some modifications to existing processes. Biomass can be classified broadly as all the matter on earth’s surface of recent biological origin. Biomass includes plant materials such as trees, grasses, agricultural crops, and animal manure. Aquatic plants, such as algae, also undergo photosynthesis and provide good sources for carbohydrates and lipids. Just as petroleum and coal require processing before use as feedstock for the production of fuels, chemicals, and energy, biomass also requires processing such that the resource potential can be utilized fully. As explained earlier, biomass is a precursor to fossil feedstock and a comparison between the biomass energy content and fossil feedstock energy content is required. The heating value of fuel is the measure of heat released during the complete combustion of fuel at a given reference temperature and pressure. The higher or gross heating value is the amount of heat released per unit weight of fuel at the reference temperature and pressure, taking into account the latent heat of vaporization of water. The lower or net heating value is the heat released by fuel excluding the latent heat of vaporization of water. The higher heating values of some bioenergy feedstocks, liquid biofuels, and conventional fossil fuels are given in > Table 25.1. It can be seen from the table that the energy content of the raw biomass species is less than bioethanol, and biodiesel compares almost equally to the traditional fossil fuels. This chapter gives an outline for the use of biomass as feedstock. The following sections will discuss various methods for biomass formation, biomass composition, conversion technologies, and feedstock availability.

Biomass Formation Biomass is the photosynthetic sink by which atmospheric carbon dioxide and solar energy is fixed into plants [1]. These plants can be used to convert the stored energy in the form of fuels and chemicals. The primary equation of photosynthesis is given by > Eq. 25.1. 6CO2 þ 6H2 O þ Light ! C6 H12 O6 þ 6O2

(25.1)

The photosynthesis process utilizes inorganic material (carbon dioxide and water) to form organic compounds (hexose) and releases oxygen. The Gibbs free energy change for the process is +470 KJ per mole of CO2 assimilated, and the corresponding enthalpy change is +470 KJ. The positive sign on the energy denotes that energy is absorbed in

Biomass as Feedstock

25

. Table 25.1 Heating value of biomass components ([1, 40]) Component

Heating value (gross) (GJ/MT unless otherwise mentioned)

Bioenergy feedstocks Corn stover Sweet sorghum Sugarcane bagasse

17.6 15.4 18.1

Sugarcane leaves Hardwood SoftWood Hybrid poplar

17.4 20.5 19.6 19.0

Bamboo Switchgrass Miscanthus Arundo donax

18.5–19.4 18.3 17.1–19.4 17.1

Giant brown kelp Cattle feedlot manure Water hyacinth Pure cellulose

10.0 MJ/dry kg 13.4 MJ/dry kg 16.0 MJ/dry kg 17.5 MJ/dry kg

Primary biosolids Liquid biofuels Bioethanol Biodiesel Fossil fuels

19.9 MJ/dry kg 28 40

Coal (low rank; lignite/subbituminous) 15–19 Coal (high rank; bituminous/anthracite) 27–30 Oil (typical distillate) 42–45

the process. The initial product for biochemical reactions for photosynthetic assimilation is sugars. Secondary products are derived from key intermediates of the biochemical reactions and include polysaccharides, lipids, and proteins. A wide range of other organic compounds may also be produced in certain biomass species, such as simple low molecular weight organic chemicals (e.g., acids, alcohols, aldehydes and ethers), complex alkaloids, nucleic acids, pyrroles, steroids, terpenes, waxes, and high molecular weight polymers such as polyisoprenes. A detailed description of how these components are formed from the intermediates is beyond the scope of this chapter. The basic reactions for photosynthesis will be discussed in this section, and the key products will be explained. Photosynthesis is a two phase process comprising of the ‘‘light reactions’’ (in the presence of light) and ‘‘dark reactions’’ (in the absence of light). The light reactions capture light energy and convert it to chemical energy and reducing power. In the dark

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reactions, chemical energy and the reducing power from light reactions are used to fix atmospheric carbon dioxide. The light reaction in photosynthesis is explained using the ‘‘Z-scheme’’ diagram as shown in > Fig. 25.4 [4]. Solar energy in the wavelength range of 400–700 nm is captured by chlorophylls within the cells of plants and microorganisms like green algae or cyanobacteria. The flow of electrons is shown in > Fig. 25.4. Two photosystems, Photosystem I and Photosystem II, are used in the light reactions. All the terms in the > Fig. 25.4 are not explained in this text, but the most important intermediates are listed below the figure. In Photosystem II (PSII), light energy at 680 nm wavelength is used to split water molecules as shown in > Eq. 25.2. light energy

!

2H2 O

O2 þ 4Hþ þ 4e

(25.2)

The electrons are accepted by the chlorophyll in PSII and reduce it from a reduction potential of +1 V to approximately 0.8 V. The electrons are then transferred to Photosystem I (PSI) through a series of membrane bound electron carrier molecules. ATP (adenosine triphosphate) is produced as the electrons are transferred due to a proton-motive force that develops as protons are pumped across the thykaloid membrane. Acceptance of the electron reduces the potential of PSI to approximately 1.4 V. The reduction potential of PSI is then

−1.5

P700* FeS

−1.0

−0.5

NADP+

Ph

P680*

E(V)

918

NADPH

QA

ADP

QB

ATP ADP 0.0

Fd

ATP

Cyt bf PC

P700

Light quanta

Photosystem I +0.5

Light quanta

P680

+1.0 H2O

MSP

½O2 + 2H++2e−

Photosystem II

. Fig. 25.4 Z-scheme of biomass photosynthesis P680 and P700 are the chlorophylls of the photosystem II and I, respectively. (MSP manganese stabilizing protein, Ph pheophytin, Q quinone, Cyt cytochrome, PC plastocyanin, FeS nonheme iron-sulfur protein, Fd ferredoxin) (Adapted from [4])

Biomass as Feedstock

25

sufficient to reduce ferrodoxin, which in turn reduces NADP + to NADPH. This NADPH is used to reduce inorganic carbon for new cell synthesis. Thus, the light reactions are common to all plant types, where eight photons per molecule of carbon dioxide excite chlorophyll to generate ATP (adenosine triphosphate) and NADPH (reduced nicotinamide adenosine dinucleotide phosphate) along with oxygen [1]. The ‘‘Z-scheme’’ transfers electrons from a low chemical potential in water to a higher chemical potential in NADPH, which is necessary to reduce CO2. The ATP and NADPH produced in the light reactions react in the dark to reduce CO2 and form the organic components in biomass via the dark reactions and regenerate ADP (adenosine diphosphate) and NADP+ (nicotinamide adenosine dinucleotide phosphate) for the light reactions. The biochemical pathways and organic intermediates involved in the reduction of CO2 to sugars determine the molecular events of biomass growth and differentiate between various kinds of biomass. In photosynthesis, CO2 enters the leaves or stems of biomass through stoma, the small intercellular openings in the epidermis. These openings provide main route for photosynthetic gas exchange and water vapor loss in transpiration. The dark reactions can proceed in accordance with at least three different pathways, the Calvin–Benson Cycle, the C4 Cycle, and the CAM Cycle, as discussed in the following sections.

The Calvin–Benson Cycle The Calvin–Benson cycle is shown in > Fig. 25.5. The overall reaction for the Calvin cycle is given in > Eq. 25.3. Plant biomass species, which use the Calvin–Benson cycle to form products, are called the C3 plants [1]. 6CO2 þ 12NADPH þ 18ATP ! C6 H12 O6 þ 12NADPþ þ 18ADP

(25.3)

This cycle produces the 3-carbon intermediate 3-phosphoglyceric acid (3-phosphoglycerate) and is common to fruits, legumes, grains, and vegetables. C3 plants usually exhibit low rates of photosynthesis at light saturation, low light saturation points, sensitivity to oxygen concentration, rapid photorespiration, and high CO2 compensation points. The light saturation point is the light intensity beyond which it is not a limiting factor for photosynthesis. The CO2 compensation point is the CO2 concentration in the surrounding environment below which more CO2 is respired by the plant than is photosynthetically fixed. Typical C3 biomass species are alfalfa, barley, chlorella, cotton, Eucalyptus, Euphorbia lathyris, oats, peas, potato, rice, soybean, spinach, sugar beet, sunflower, tall fescue, tobacco, and wheat. These plants grow favorably in cooler climates.

The C4 Cycle The C4 cycle is shown in > Fig. 25.6. In this cycle, CO2 is initially converted to 4-carbon dicarboxylic acids (malic or aspartic acids) [1]. Phosphoenolpyruvic acid reacts with

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Biomass as Feedstock

3 CO2

3 ribulose-5-bisphosphate

6 3-phosphoglycerate

3 ADP

ATP

6 ATP

3 ATP

6 ADP 6 1,3-bisphosphoglycerate

3 ribulose-5-phosphate

NADPH

6 NADPH 2 Pi 6 NADP++ 6 Pi 5 glyceraldehyde-3-phosphate

6 glyceraldehyde-3-phosphate

1 glyceraldehyde-3-phosphate

Biosynthesis of sugars, fatty acids, amino acids

. Fig. 25.5 Calvin–Benson cycle for photosynthesis (Adapted from [4])

carbon dioxide to form oxaloacetic acid. Malic or aspartic acid is formed from the oxaloacetic acid. The C4 acid is transported to bundle sheath cells where decarboxylation occurs to regenerate pyruvic acid, which is returned to the mesophyll cells to initiate another cycle. The CO2 liberated in the bundle sheath cells enter the C3 cycle described above and it is in this C3 cycle where the CO2 fixation occurs. The subtle difference between the C3 and C4 cycles are believed to be responsible for the wide variations in biomass properties. Compared to C3 biomass, C4 biomass is produced in higher yields with higher rates of photosynthesis, high light saturation points, and low levels of respiration, low carbon dioxide compensation points, and greater efficiency of water usage. Typical C4 biomass includes crops such as sugarcane, corn, and sorghum and tropical grasses like bermuda grass.

The CAM Cycle The CAM cycle is the Crassulacean Acid Metabolism cycle, which refers to the capacity of chloroplast containing biomass tissues to fix CO2 in dark reactions leading to synthesis of free malic acid [1]. The mechanism involves b-carboxylation of phosphoenolpyruvic acid by phosphoenolpyruvate carboxylase enzyme and the subsequent reduction of oxaloacetic

Biomass as Feedstock

25

CO2

Pi

Phosphoenolpyruvic acid

Oxaloacetic acid

NADPH

ADP

NADP+

ATP

Pyruvic acid

Malic or aspartic acid

CO2 (to C3 cycle)

NADPH

NADP+

. Fig. 25.6 Biochemical pathway from carbon dioxide to glucose for C4 biomass (Adapted from [1])

acid by maleate dehydrogenase. Biomass species in the CAM category are typically adapted to arid environments, have low photosynthesis rates, and higher water usage efficiencies. Plants in this category include cactus and succulents like pineapple. The CAM has evolved so that the initial CO2 fixation can take place in the dark with much less water loss than C3 or C4 pathways. CAM biomass also conserves carbon by recycling endogenously formed CO2. CAM biomass species have not been exploited commercially for use as biomass feedstock. Thus, different photosynthetic pathways produce different intermediates leading to different kinds of biomass. The following section discusses the different components in biomass.

Biomass Classification and Composition The previous section gave the mechanisms for the formation of biomass by photosynthesis. The classification and composition of biomass will be discussed in this section. Biomass can be classified into two major subdivisions, crop biomass and wood (forest) biomass. There are other sources of biomass, like waste from municipal areas and animal wastes, but these can be traced back to the two major sources. Crop biomass primarily includes corn, sugarcane, sorghum, soybeans, wheat, barley, rice, etc. These contain carbohydrates, glucose, starch, or oils as its primary constituents. Wood biomass is composed of cellulose,

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hemicellulose, and lignin. Examples of woody biomass include grasses, stalks, stover, etc. Starch and cellulose are both polymeric forms of glucose, a 6-carbon sugar. Hemicellulose is a polymer of xylose. Lignin is composed of phenolic polymers. Oils are composed of triglycerides. Other biomass components, which are generally present in minor amounts, include proteins, sterols, alkaloids, resins, terpenes, terpenoids, and waxes. Apart from crop and woody biomass, a class of microorganisms exist which are capable of producing biomass. These are single-celled organisms like algae or cyanobacteria, and have the capability of photosynthesis to produce oils, carbohydrates, proteins, etc. These are discussed in details in a later section. The components of biomass are discussed in details below.

Saccharides and Polysaccharides Saccharides and polysaccharides are hydrocarbons with the basic chemical structure of CH2O. The hydrocarbons occur in nature as 5-carbon or 6-carbon ring structure. The ring structures may contain only one or two connected rings, which are known as monosaccharides, disaccharides, or simply as sugars, or they may be very long polymer chains of the sugar building blocks. The simplest six-sided saccharide (hexose) is glucose. Long chained polymers of glucose or other hexoses are categorized either as starch or cellulose. The characterization is discussed in the following sections. The simplest five-sided sugar (pentose) is xylose. Pentoses form long chain polymers categorized as hemicellulose. Some of the common 6-carbon and 5-carbon monosaccharides are listed in > Table 25.2. Starch is a polymer of glucose as the monomeric unit [5]. It is a mixture of a- amylose and amylopectin as shown in > Fig. 25.7. a-amylose is a straight chain of glucose molecules joined by a-1,4-glucosidic linkages as shown in > Fig. 25.7a. Amylopectin and amylase are similar except that short chains of glucose molecules branch off from the main chain (backbone) as shown in > Fig. 25.7b. Starches found in nature contain 10–30% a-amylose and 70–90% amylopectin. The a- 1,4-glycosidic linkages are bent and prevent the formation of sheets and subsequent layering of polymer chains. As a result, starch is soluble in water and relatively easy to break down into utilizable sugar units.

Lignocellulosic Biomass The non-grain portion of biomass (e.g., cobs, stalks), often referred to as agricultural stover or residues, and energy crops such as switchgrass are known as lignocellulosic biomass resources (also called cellulosic). These are comprised of cellulose, hemicellulose, and lignin [5]. Generally, lignocellulosic material contains 30–50% cellulose, 20–30% hemicellulose, and 20–30% lignin. > Figure 25.8a illustrates how cellulose, hemicellulose, and lignin are physically mixed in lignocellulosic biomass. > Figure 25.8b illustrates how pretreatment is necessary to break the polymeric chains before cellulose and hemicellulose

25

Biomass as Feedstock

. Table 25.2 Common 6-carbon and 5-carbon monosaccharides 6-Carbon sugars

Structure

5-Carbon sugars

D-Fructose

Structure

D-Xylose

O

O

O

O O

O

O O

O D-Glucose

O

O O

D-Ribulose

O

O O

O O O D-Gulose

O

O

O

O D-Ribose

O

O

O

O

O

O

O

O O D-Mannose

O

O O

D-Arabinose

O

O

O O

O

O O

D-Galactose

O O

O

O

O O

O O

O

can be used for chemical conversions. Some exceptions to this are cotton (98% cellulose) and flax (80% cellulose). Lignocellulosic biomass is considered to be an abundant resource for the future bio-industry. Recovering the components in a cost-effective way requires pretreatment processes discussed in a later section.

Cellulose Cellulosic biomass comprises 35–50% of most plant material. Cellulose is a polymer of glucose with degree of polymerization of 1,000–10,000 [5]. Cellulose is a linear unbranched polymer of glucose joined together by b  1,4-glycosidic linkages as shown

923

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Biomass as Feedstock

a

CH2OH

CH2OH

CH2OH

O

O OH

O

OH

OH

O

OH

O

OH

OH

b

OH 300−600

OH

OH O

O HO OH O

O

HO

OH

HO HO

O

O

OH

HO HO

O

O HO

HO

O

. Fig. 25.7 Structure of Starch (a) a-Amylose (b) Amylopectin

a

b Lignin Cellulose Hemicellulose

. Fig. 25.8 (a) Physical arrangement of lignocellulosic biomass (b) lignocellulosic biomass after pretreatment

in > Fig. 25.9. Cellulose can either be crystalline or amorphous. Hydrogen bonding between chains leads to chemical stability and insolubility and serves as a structural component in plant walls. The high degree of crystallinity of cellulose makes lignocellulosic materials much more resistant than starch to acid and enzymatic hydrolysis. As the core structural component of biomass, cellulose is also protected from environmental exposure by a sheath of lignin and hemicellulose. Extracting the sugars of lignocellulosics therefore involves a pretreatment stage to reduce the recalcitrance (resistance) of the biomass to cellulose hydrolysis.

Biomass as Feedstock

25

OH OH O

HO

O

O

HO

O

OH OH

n

. Fig. 25.9 Structure of cellulose O

HO HO

OH

OH

. Fig. 25.10 Structure of xylose, building block of hemicellulose

Hemicellulose Hemicellulose is a polymer containing primarily 5-carbon sugars such as xylose and arabinose with some glucose and mannose dispersed throughout [5]. The structure of xylose is shown in > Fig. 25.10. It forms a short chain polymer that interacts with cellulose and lignin to form a matrix in the plant wall, thereby strengthening it. Hemicellulose is more easily hydrolyzed than cellulose. Much of the hemicellulose in lignocellulosic materials is solubilized and hydrolyzed to pentose and hexose sugars during the pretreatment stage. Some of the hemicellulose is too intertwined with the lignin to be recoverable.

Lignin Lignin helps to bind the cellulose/hemicelluloses matrix while adding flexibility to the mixture. The molecular structure of lignin polymers is very random and disorganized and consists primarily of carbon ring structures (benzene rings with methoxyl, hydroxyl, and propyl groups) interconnected by polysaccharides (sugar polymers) as shown in > Fig. 25.11. The ring structures of lignin have great potential as valuable chemical intermediates, mainly aromatic compounds. However, separation and recovery of the lignin is difficult. It is possible to break the lignin-cellulose-hemicellulose matrix and recover the lignin through treatment of the lignocellulosic material with strong sulfuric acid. Lignin is insoluble in sulfuric acid, while cellulose and hemicellulose are solubilized and hydrolyzed by the acid. However, the high acid concentration promotes the formation of degradation products that hinder the downstream utilization of the sugars. Pyrolysis can be used to convert the lignin polymers to valuable products, but separation techniques to recover the individual chemicals are lacking. Instead, the pyrolyzed lignin is

925

926

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Biomass as Feedstock H2COH H2COH

CH2

CH2

CH2

OH

CH2

OCH3

CH3

CH

CH2OH

HC

HC

OH

O

H2COH

OCH3

O

HC

O

OCH3 HC

HC

O

OH H2C

HOCH2

HC O O CH3O

CH HOCH2

CH

CH

CH

O

CH

CH3O

HC

HOCH2

CHO CH CH

H2COH

HOCH O CH3O

CH

HC

HOCH2

HC

OCH3 O

CO

HC

CH

HC

CH2

O

OCH3

O

CH3O

H2COH

O

O

OH

CH

CH3O HO

HC CH H2COH

HCOH HCOH

H2COH

CH3O

CH2OH HC

O

HCOH

CHO

OCH3

O

HC

H2COH

CH3O

O

CO

OCH3 O

CH

O

H2COH O

HOC

HC

OH

HOCH

CH

H2COH

OCH3 CH3O

H2COH

CH

CH3O

H2C

(Carbohydrate)

OCH3

HOCH

HCO

CH3O

C2H CH

CH

HO

CH

O

HC

CH3O O

HC

CH3O

H2COH

O CH3O

CH

CH

CH3O

HCOH HOC

H2COH H2COH

O

CH2 HC

OCH3 O

HCOH

CH3O

H2CO

O

OCH3 OH

. Fig. 25.11 Structure of lignin [36]

fractionated into a bio-oil for fuels and high phenolic content oil which is used as a partial replacement for phenol in phenol-formaldehyde resins.

Lipids, Fats, and Oils Oils can be obtained from oilseeds like soybean, canola, etc. Vegetable oils are composed primarily of triglycerides, also referred to as triacylglycerols. Triglycerides contain a glycerol molecule as the backbone with three fatty acids attached to glycerol’s hydroxyl groups. The structure of a triglyceride is shown in > Fig. 25.12 with linoleic acid as the fatty acid chain. In this example, the three fatty acids are all linoleic acid, but triglycerides could be a mixture of two or more fatty acids. Fatty acids differ in chain length and degree of condensation. The fatty acid profile and the double bonds present determine the property

Biomass as Feedstock

25

O O

O O

Glycerol backbone O O

Trilinolein

Linoleic Acid Chains

. Fig. 25.12 Formation of triglycerides (linoleic acid as representative fatty acid chain)

of the oil. These can be manipulated to obtain certain performance characteristics. In general, the greater the number of double bonds, the lower the melting point of the oil.

Proteins Proteins are polymers composed of natural amino acids, bonded together through peptide linkages [1]. They are formed via condensation of the acids through the amino and carboxyl groups by removal of water to form polyamides. Proteins are present in various kinds of biomass as well as animals. The concentration of proteins may approach zero in different biomass systems but the importance of proteins arises while considering enzyme catalysis that promotes the various biochemical reactions. The apparent precursors of the proteins are amino acids in which an amino group, or imino group in a few cases, is bonded to the carbon atom adjacent to the carboxyl group. Many amino acids have been isolated from natural sources, but only about 20 of them are used for protein biosynthesis. These amino acids are divided into five families: glutamate, aspartate, aromatic, serine, and pyruvate. The various amino acids under these groups are shown in > Table 25.3. > Table 25.4 gives the composition of some biomass species based on the above components. The biomass types are marine, fresh water, herbaceous, woody, and waste biomass, and a representative composition is given in the table. Other components not included in the composition are ash and crude protein.

Biomass Conversion Technologies The conversion of biomass involves the treatment of biomass so that the solar energy stored in the form of chemical energy in the biomass molecules can be utilized. Common biomass conversion routes begin with pretreatment in case of cellulosic and grain biomass and extraction of oil in case of oilseeds. Then the cellulosic or starch containing biomass undergoes fermentation (anaerobic or aerobic), gasification, or pyrolysis. The oil in oilseeds is transesterified to get desired product. There are other process technologies

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Biomass as Feedstock

. Table 25.3 Amino acid groups present in proteins Family

Amino acids

Glutamate

Glutamine, arginine, proline

Aspartate Aromatic Serine Pyruvate

Asparagine, methionine, threonine, isoleucine, lysine Tryptophan, phenylalanine, tyrosine Glycine, cysteine Alanine, valine, leucine

. Table 25.4 Component composition of biomass feedstocks ([1], McGowan 2009) Name

Celluloses (dry wt.%)

Hemicelluloses (dry wt.%)

Lignins (dry wt.%)

Corn stover Sweet sorghum

35 27

28 25

16–21 11

Sugarcane bagasse Hardwood SoftWood Hybrid poplar

32–48 45 42 42–56

19–24 30 21 18–25

23–32 20 26 21–23

Bamboo Switchgrass Miscanthus Arundo donax

41–49 44–51 44 31

24–28 42–50 24 30

24–26 13–20 17 21

RDF (refuse derived fuel) Water hyacinth Bermuda grass Pine

65.6 16.2 31.7 40.4

11.2 55.5 40.2 24.9

3.1 6.1 25.6 34.5

including hydroformylation, metathesis, and epoxidation, related with direct conversion of oils to fuels and chemicals, the details of which are not included in this chapter.

Biomass Pretreatment Biomass is composed of components such as starch, sugars, cellulose, hemicellulose, lignin, fats, oils, etc., as described in the previous section. Often two or more of these components are physically mixed with each other, and a pretreatment is necessary before the chemical energy in biomass molecules can be utilized in a useful way. For example,

Biomass as Feedstock

25

lignocellolosic biomass is composed of cellulose, hemicelluloses, and lignin. The cellulose and hemicelluloses are polysaccharides of hexose and pentose. Any process that uses biomass needs to be pretreated so that the cellulose and hemicellulose in the biomass are broken down to their monomeric form. Pretreatment processes produce a solid pretreated biomass residue that is more amenable to enzymatic hydrolysis by cellulases and related enzymes than native biomass. Biocatalysts like yeasts and bacteria can act only on the monomers and ferment them to alcohols, lactic acid, etc. The pretreatment process also removes the lignin in biomass which is not acted upon by enzymes or fermented further. Pretreatment usually begins with a physical reduction in the size of plant material by milling, crushing, and chopping [6]. Some of the equipment used in the industry for size reduction include rotary breaker, roll crusher, hammer mill, impactor, tumbling mill, and roller mill. The size of biomass particles need to be reduced to nominal size of 1–6 mm [7]. For example, in the processing of sugarcane, the cane is first cut into segments and then fed into consecutive rollers to extract cane juice rich in sucrose and physically crush the cane, producing a fibrous bagasse having the consistency of sawdust. In the case of corn stover processing, the stover is chopped with knives or ball milled to increase the exposed surface area and improve wettability. Corn is hammer milled to flour before it is transferred to cook tanks. The physical reduction in size enables a wider surface area to come in contact for further chemical conversions. However, physical size reduction is an energy intensive process and an optimum size reduction is required to balance energy consumption and conversion efficiency. For example, recent research in corn fermentation using finer ground corn enables the liquefaction to be conducted at lower temperatures, and this process is known as cold starch hydrolysis. After the physical disruption process, the biomass may be chemically treated to remove lignin. This is shown in > Fig. 25.8b. Lignin forms a coating on the cellulose microfibrils in untreated biomass, thus making the cellulose unavailable for enzyme or acid hydrolysis. Lignin also absorbs some of the expensive cellulose-active enzymes. The following chemical pretreatment processes are employed for biomass conversion. Hot wash pretreatment: This pretreatment concept was developed at the National Renewable Energy Laboratory, and uses hot water or hot dilute acids at temperatures above 135 C to wash out the solubilized lignin and hemicellulosic sugars [8]. The hot wash pretreatment process involves the passage of hot water through heated stationary biomass and is responsible for solubilization of the hemicellulose fraction [6]. The hemicellulose is converted to pentose oligomers by this process which needs to be further converted to respective monosaccharides before fermentation. The performance of this pretreatment process depends on temperature and flow rate, requiring about 8–16 min. About 46% of lignin is removed at high rates and temperatures. The hydrothermal process does not require acid resistant material for the reactors, but water use and recovery costs are disadvantages to the process. Acid hydrolysis: Hydrolysis is a chemical reaction or process where a chemical compound reacts with water. The process is used to break complex polymer structures into its

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Biomass as Feedstock

component monomers. The process can be used for the hydrolysis of polysaccharides like cellulose and hemicelluloses [9]. When hydrolysis is catalyzed by the presence of acids like sulfuric, hydrochloric, nitric, or hydrofluoric acids, the process is called acid hydrolysis. The reactions for hydrolysis can be expressed as in reaction given by > Eqs. 25.4 and > 25.5. Cellulose ðGlucanÞ ! Glucose ! 5  Hydroxymethylfurfural ! Tars Hemicellulose ðXylanÞ ! Xylose ! Furfural ! Tars

(25.4) (25.5)

The desired products of hydrolysis are the glucose and xylose. Under severe conditions of high temperature and acid concentrations, the product tends to form hydroxymethylfurfural, furfural, and the tars. Dilute sulfuric acid is inexpensive in comparison to the other acids. It has also been studied and the chemistry well known for acid conversion processes [9]. Biomass is mixed with a dilute sulfuric acid solution and treated with steam at temperatures ranging from 140 C to 260 C. Xylan is rapidly hydrolyzed in the process to xylose at low temperatures of 140–180 C. At higher temperatures, cellulose is depolymerized to glucose but the xylan is converted to furfural and tars. The pretreatment conditions used in lignocellulosic biomass (corn stover) feedstock based ethanol process by [10] were acid concentration of 1.1%, residence time of 2 min, temperature maintained at 190 C, and a pressure of 12.1 atm. Concentrated acids at low temperatures (100–120 C) are used to hydrolyze cellulose and hemicelluloses to sugars [9]. Higher yields of sugars are obtained in this case with lower conversion to tars. The viability of this process depends on low cost recovery of expensive acid catalysts. Enzymatic hydrolysis: Acid hydrolysis explained in the previous section has a major disadvantage where the sugars are converted to degradation products like tars. This degradation can be prevented by using enzymes favoring 100% selective conversion of cellulose to glucose. When hydrolysis is catalyzed by such enzymes, the process is known as enzymatic hydrolysis [9]. The temperature and pressure for enzymatic hydrolysis depends on the particular enzyme and its tolerance to a particular temperature. A detailed discussion of the particular temperatures for enzymes is beyond the scope of this chapter. Enzymatic hydrolysis is carried out by microorganisms like bacteria, fungi, protozoa, insects, etc. [6]. Advancement of gene sequencing in microorganisms has made it possible to identify the enzymes present in them which are responsible for the biomass degradation. Bacteria like Clostridium thermocellum, Cytophaga hutchinsonii, Rubrobacter xylanophilus, etc., and fungi like Trichoderma reesei and Phanerochaete chrysosporium have revealed enzymes responsible for carbohydrate degradation. Based on their target material, enzymes are grouped into the following classifications [6]. Glucanases or cellulases are the enzymes that participate in the hydrolysis of cellulose to glucose. Hemicellulases are responsible for the degradation of hemicelluloses. Some cellulases have significant xylanase or xyloglucanase side activity which makes it possible for use in degrading both cellulose and hemicelluloses.

Biomass as Feedstock

25

Ammonia fiber explosion: This process uses ammonia mixed with biomass in a 1:1 ratio under high pressure (21 atm) at temperatures of 60–110 C for 5–15 min, and then there is explosive pressure release. This process, also referred to as the AFEX process, improves saccharification rates of various herbaceous crops and grasses. The pretreatment does not significantly solubilize hemicellulose compared to acid pretreatment. The conversions achieved depend on the composition of feedstock, e.g., over 90% hydrolysis of cellulose and hemicellulose was obtained after AFEX pretreatment of bermuda grass [11]. The volatility of ammonia makes it easy to recycle the gas [6].

Fermentation The pretreatment of biomass is followed by the fermentation process where pretreated biomass containing 5-carbon and 6-carbon sugars is catalyzed with biocatalysts to produce desired products. Fermentation refers to enzyme catalyzed, energy yielding chemical reactions that occur during the breakdown of complex organic substrates in presence of microorganisms [1]. The microorganisms used for fermentation can be yeast or bacteria. The microorganisms feed on the sucrose or glucose released after pretreatment and converts them to alcohol and carbon dioxide. The simplest reaction for the conversion of glucose by fermentation is given in > Eq. 25.6. C6 H12 O6 ! 2C2 H5 OH þ 2CO2

(25.6)

An enzyme catalyst is highly specific, catalyzes only one or a small number of reactions, and a small amount of enzyme is required. Enzymes are usually proteins of high molecular weight (15,000 < MW < several million Daltons) produced by living cells. The catalytic ability is due to the particular protein structure, and a specific chemical reaction is catalyzed at a small portion of the surface of an enzyme, called an active site [1]. Enzymes have been used since early human history without knowing how they worked. Enzymes have been used commercially since the 1890s when fungal cell extracts were used to convert starch to sugar in brewing vats. Microbial enzymes include cellulase, hemicellulase, catalase, streptokinase, amylase, protease, clipase, pectinase, glucose isomerase, lactase, etc. The type of enzyme selection determines the end product of fermentation. The growth of the microbes requires a carbon source (glucose, xylose, glycerol, starch, lactose, hydrocarbons, etc.) and a nitrogen source (protein, ammonia, corn steep liquor, diammonium phosphate, etc.). Many organic chemicals like ethanol, succinic acid, itaconic acid, lactic acid, etc., can be manufactured using live organisms which have the required enzymes for converting the biomass. Ethanol is produced by the bacteria Zymomonous mobilis or yeast Saccaromyces cervisiae. Succinic acid is produced in high concentrations by Actinobacillus succinogens obtained from rumen ecosystem [12]. Other microorganisms capable of producing succinic acid include propionate producing bacteria of the Propionbacterium genus, gastrointestinal bacteria such as Escherichia coli, and rumen bacteria such as Ruminococus flavefaciens. Lactic acid is produced by a class of

931

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Biomass as Feedstock

bacteria known as lactic acid bacteria (LAB) including the genera Lactobacillus, Lactococcus, Leuconostoc, Enterococcus, etc. [13]. Commercial processes for corn wet milling and dry milling operations and the fermentation process for lignocellulosic biomass through acid hydrolysis and enzymatic hydrolysis are discussed in details in > Chap. 28, ‘‘Chemicals from Biomass.’’

Anaerobic Digestion Anaerobic digestion of biomass is the treatment of biomass with a mixed culture of bacteria to produce methane (biogas) as a primary product. The four stages of anaerobic digestion are hydrolysis, acidogenesis, acetogenesis, and methanogenesis as shown in > Fig. 25.13. In the first stage, hydrolysis, complex organic molecules are broken down into simple sugars, amino acids, and fatty acids with the addition of hydroxyl groups. In the second stage, acidogenesis, volatile fatty acids (e.g., acetic, propionic, butyric, valeric) are formed along with ammonia, carbon dioxide, and hydrogen sulfide. In the third stage, acetogenesis, simple molecules from acidogenesis are further digested to produce carbon dioxide, hydrogen, and organic acids, mainly acetic acid. Then in the fourth stage, methanogenesis, the organic acids are converted to methane, carbon dioxide, and water. Anaerobic digestion can be conducted either wet or dry where dry digestion has a solids content of 30% or greater and wet digestion has a solids content of 15% or less. Either batch or continuous digester operations can be used. In continuous operations, there is a constant production of biogas; while batch operations can be considered simpler, the production of biogas varies. The standard process for anaerobic digestion of cellulose waste to biogas (65% methane-35% carbon dioxide) uses a mixed culture of mesophilic or thermophilic bacteria (Kebanli 1981). Mixed cultures of mesophilic bacteria function best at 37–41 C and thermophilic cultures function best at 50–52 C for the production of biogas. Biogas

Biomass Mixed Culture

Cellulose, Starch Proteins, Fats

Carboxylic Acids = Volatile Fatty Acids (VFAs) (like acetic, propionic, butyric.... heptanoic) (C2 to C7)

of Micro-organisms

Hydrolysis Free Sugars, Amino Acids, Fatty Acids

Acidogenesis Carboxylic Acids, NH3, CO2, H2S

. Fig. 25.13 Anaerobic digestion process

Acetogenesis

Methanogenesis

Acetic Acid, CO2, H2

CH4, CO2

Biomass as Feedstock

25

also contains small amount hydrogen and a trace of hydrogen sulfide, and it is usually used to produce electricity. There are two by-products of anaerobic digestion: acidogenic digestate and methanogenic digestate. Acidogenic digestate is a stable organic material comprised largely of lignin and chitin resembling domestic compost, and it can be used as compost or to make low grade building products such as fiberboard. Methanogenic digestate is a nutrient-rich liquid, and it can be used as a fertilizer but may include low levels of toxic heavy metals or synthetic organic materials such as pesticides or PCBs depending on the source of the biofeedstock undergoing anaerobic digestion. Kebanli et al. [14] gives a detailed process design along with pilot unit data for converting animal waste to fuel gas which is used for power generation. A first order rate constant, 0.011  0.003 per day, was measured for the conversion of volatile solids to biogas from dairy farm waste. In a biofeedstock, the total solids are the sum of the suspended and dissolved solids, and the total solids are composed of volatile and fixed solids. In general, the residence time for an anaerobic digester varies with the amount of feed material, type of material, and the temperature. Resident time of 15–30 days is typical for mesophilic digestion, and residence time for thermophilic digestion is about one-half of that for mesophilic digestion. The digestion of the organic material involves mixed culture of naturally occurring bacteria, each performs a different function. Maintaining anaerobic conditions and a constant temperature are essential for the viability of the bacterial culture. Holtzapple et al. [15] describes a modification of the anaerobic digestion process, the MixAlco process, where a wide array of biodegradable material is converted to mixed alcohols. Thanakoses et al. [16] describes the process of converting corn stover and pig manure to the third stage of carboxylic acid formation. In the MixAlco process, the fourth stage in anaerobic digestion of the conversion of the organic acids to methane, carbon dioxide, and water is inhibited using iodoform (CHI3) and bromoform (CHBr3). Biofeedstocks to this process can include urban wastes, such as municipal solid waste and sewage sludge, and agricultural residues, such as corn stover and bagasse. Products include carboxylic acids (e.g., acetic, propionic, butyric acid), ketones (e.g., acetone, methyl ethyl ketone, diethyl ketone), and biofuels (e.g., ethanol, propanol, butanol). The process uses a mixed culture of naturally occurring microorganisms found in natural habitats such as the rumen of cattle to anaerobically digest biomass into a mixture of carboxylic acids produced during the acidogenic and acetogenic stages of anaerobic digestion. The fermentation conditions of the MixAlco Process make it a viable process, since the fermentation involves mixed culture of bacteria obtained from animal rumen, which is available at lower cost compared to genetically modified organisms and sterile conditions required by other fermentation processes. The Mixalco process is outlined in > Fig. 25.14 where biomass is pretreated with lime to remove lignin. Calcium carbonate is also added to the pretreatment process. The resultant mixture containing hemicellulose and cellulose is fermented using a mixed culture of bacteria obtained from cattle rumen. This process produces a mixture of carboxylate salts which is then fermented. Carboxylic acids are naturally formed in the following places: animal rumen, anaerobic sewage digestors, swamps, termite guts,

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Biomass as Feedstock

Mixed Alcohols

Carboxylate Salts Biomass

Pretreat

Ferment

Dewater

Thermal Conversion

Mixed Ketones

Hydrogenate

Hydrogen Lime Lime Kiln

Calcium Carbonate

. Fig. 25.14 Flow diagram for the MixAlco process using anaerobic digestion [39] . Table 25.5 Carboxylic acid products at different culture temperatures [39] Acid

40 C

55 C

C2 – Acetic

41 wt.%

80 wt.%

C3 – Propionic C4 – Butyric C5 – Valeric C6 – Caproic

15 wt.% 21 wt.% 8 wt.% 12 wt.%

4 wt.% 15 wt.% Table 25.7 along with their advantages and disadvantages [17–19]. The mechanism of alkali-catalyzed transesterification is described in > Fig. 25.16. The first step involves the attack of the alkoxide ion to the carbonyl carbon of the triglyceride molecule, which results in the formation of a tetrahedral intermediate. The reaction of this intermediate with an alcohol produces the alkoxide ion in the second step. In the last step the rearrangement of the tetrahedral intermediate gives rise to an ester and a diglyceride. >

935

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Biomass as Feedstock

. Table 25.7 Commonly used catalysts in transesterification and their advantages and disadvantages [17–19] Type

Commonly used compounds/enzymes

Advantages

Disadvantages

1. Ineffective for high free fatty acid content and for high water content (problems of saponification) 2. Energy intensive 3. Recovery of glycerol difficult 4. Alkaline wastewater requires treatment Acid catalysts HCl, H2SO4, H3PO4, 1. Slow process 1. Good for processes Sulfonic acid with high water content compared to alkali (alkoxides) and free fatty acids 2. Require after treatment of triglycerides with alkoxides formed for purification purposes 1. Some initial activity Enzyme/lipase/ M. miehi, C. antarctica, 1. Possibility of regeneration and reuse can be lost due to heterogeneous P. cepacia, C. rugosa, volume of the oil of the immobilized P. fluorescens catalysts molecules residue 2. Free Fatty Acids can 2. Number of support enzyme is not uniform be completely converted to alkyl esters 3. Biocatalyst is more expensive that the 3. Higher thermal stability of the enzyme natural enzyme due to the native state 4. Immobilization of lipase allows dispersed catalyst, reducing catalyst agglomeration 5. Separation of product and glycerol is easier using this catalyst Alkali catalysts

NaOH, KOH, NaOCH3, 1. Faster than acid KOCH3 (other alkoxides catalyzed transesterification are also used)

The mechanism of acid-catalyzed transesterification of vegetable oil (for a monoglyceride) is shown in > Fig. 25.17. It can be extended to di- and triglycerides. The protonation of carbonyl group of the ester leads to the carbo-cation, which after a nucleophilic attack of the alcohol produces a tetrahedral intermediate. This intermediate eliminates glycerol to form a new ester and to regenerate the catalyst.

Biomass as Feedstock

− OH

Pre-step or

− RO

+ ROH

NaOR

Na+

O−

Step. 1. O +

C

R

RO−

R

C

OR

R

+ ROH

C

OR +

RO−

ROH+

OR Step. 3.

OR

O−

O− R

C OR

OR Step. 2.

H2O

+

RO− +

25

O− R

C

RCOOR

OR

ROH

+

ROH

+

Where R

= CH2 CH

OCOR

CH2

OCOR

R = Carbon chain of fatty acid R

= Alkyl group of alcohol

. Fig. 25.16 Mechanism of alkali-catalyzed transesterification (Adapted from [17])

Both the triglycerides in vegetable oil and methyl esters from the transesterification of vegetable oils can be used as monomers to form resins, foams, thermoplastics, and oleic methyl ester [20]. A thermosetting polymer is formed by the polymerization of triglycerides with styrene using a free radical initiator and curing for 4 h at 100 C that has very good tensile strength, rigidity, and toughness properties. Lignin can enhance toughness, and it can be molded to a material with an excellent ballistic impact resistance. Triglycerides can be functionalized to acrylated, epoxidized soybean oil that can be used for structural foam that has biocompatibility properties. Methyl esters can be functionalized to epoxidized oleic methyl ester and acrylated oleic methyl ester which can be polymerized with comonomers methyl methacrylate and butyl acrylate to form oleic methyl ester. A monolithic hurricane-resistant roof has been designed using these materials. The methyl esters formed from transesterification from vegetable oil can be used as diesel in diesel engines, and this is referred to as biodiesel. Haas et al. [21] describes an industrial scale transesterification process for the production of biodiesel from the

937

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25

Biomass as Feedstock − H+ + SO4

H2SO4

H+

O R

OR

R

OH R

+

O+H

OH

OH

R OR

O

+

R H

R

R

OR

OR−

OH

H

+

OR

−H+/ROH

O + R

O R

OR

: glyceride

OH R = carbon chain of fatty acid R = alkyl group of alcohol

. Fig. 25.17 Mechanism of acid-catalyzed transesterification (Adapted from [17])

transesterification of soybean oil. > Figure 25.18 gives a schematic overview of the process model. A two-reactor model was designed with crude degummed soybean oil as feedstock with phospholipid content of less than 50 ppm and negligible fatty acids, sodium methoxide catalyst, and methanol as the alcohol. The design contained three sections, a transesterification section, a purification section, and a glycerol recovery section. The transesterification section consisted of two sequential reactors. The purification section had a centrifugation column which separated esters from the aqueous phase. The glycerol recovery and purification section also consisted of a centrifugal reactor and subsequent distillation and evaporation columns for 80% (w/w) glycerol as a by-product. The cost analysis of the overall process was done with a depreciable life of 10 years and an escalation rate of 1%. Annual production capacity for the methyl ester plant was set at 10
106 gal. With a feedstock cost of $0.236/lb of soybean oil, a production cost of $2.00/gal of methyl ester was achieved.

Gasification/Pyrolysis Thermal conversion processes such as gasification can be used to convert biomass to synthesis gas, a mixture of carbon monoxide and hydrogen. The products and yields depend on feed composition, dimension of feed particles, heating rate, temperature, and reaction time [1]. A detailed discussion for gasification is included in a later chapter.

STR - 25

Centrifuge - 1

STR - 04

Ester - 1

STR - 06

STR - 06

Tank - 3

STR - 29

STR - 41

STR - 14

Centrifuge - 4

STR - 33

STR - 10

STR - 11

STR - 12

STR - 22

PH Tank

Tank - 4

STR - 14

Free Fatty Acid Waste

STR - 20

STR - 20

STR - 21

NaOH

HX - 10

STR - 16

Mixer 2

Washer 1

STR - 42

STR - 42

HCI

HCI

Centrifuge - 2

Ester - 2

H2O

STR - 10

STR - 06

GLYMH2O

STR - 10

STR - 03

HX - 01

Mixer 1

STR - 01

Tank - 2

Tank - 1

STR - 17

HX - 09

STR - 34

STR - 40

STR - 18

Distill - 1

STR - 35

HX -02

Centrifuge - 3

HX -04

STR - 27

. Fig. 25.18 A process model for the production of biodiesel and glycerol (Adapted from [21])

HX - 07

STR - 25

Oil

NaOCH3

MeOH

STR - 35

STR - 33

STR - 37

STR - 36

HX -03

STR - 43

Evaporator - 1

Reboiler 1

STR - 21

Dryer - 1

Condenser 1

STR - 19

STR - 20

STR - 46

STR - 47

STR - 42

Reboiler 2

Condenser 2 STR - 45

STR - 44

STR - 45

FAME

HX -06

HX -05

Glycerin

STR - 48

HX -06

STR - 25

STR - 22

STR - 24

Biomass as Feedstock

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Biomass as Feedstock

In biomass gasification, steam and oxygen are used to produce synthesis gas where the amount of steam and oxygen are controlled to produce carbon monoxide and hydrogen with a minimum amount of carbon dioxide and other products. Synthesis gas is a 1:1 mixture of carbon monoxide and hydrogen. In the 1800s coal gasification was used to provide syngas used for lighting and heating. At the beginning of the twentieth century, syngas was used to produce fuels and chemicals. Many of the syngas conversion processes were developed in Germany during the first and second world wars at a time when natural resources were becoming scarce for the country and alternative routes for hydrogen production, ammonia synthesis, and transportation fuels were a necessity. With the development of the petroleum industry in the 1940s and beyond, the economics of many of these syngas routes became unfavorable and was replaced by petroleum-based processes. The Fischer–Tropsch synthesis reactions for the catalytic conversion of a mixture of carbon monoxide and hydrogen into liquid alcohol fuels was one such process developed in Germany. The United States has the highest proven reserves of coal amongst all its natural resources. Coal co-fired with biomass and complete biomass gasification processes are alternatives that are being considered for the production of syngas for fuels and chemicals. The US DOE multiyear program plan for 2010 outlines the fuels, energy, and chemicals that can be produced from the thermochemical routes for biomass processing [22, 38]. Biomass gasification technologies are similar to coal gasification and both produce similar product gases. However, biomass contains more volatile matter, gasification occurs at lower temperatures and pressures than coal, and pyrolytic chars are more reactive than coal products. The increase in pressure lowers equilibrium concentrations for hydrogen and carbon monoxide and increases the carbon dioxide and methane concentrations. Biomass contains oxygen in cellulose and hemicellulose which makes them more reactive than oxygen deficient coal. Volatile matter in biomass is about 70–90% in wood as compared to 30–45% in coal. There are three types of biomass gasification processes – pyrolysis, partial oxidation, and reforming. Pyrolysis, as explained before, is the combustion of biomass in absence of oxygen. Partial oxidation is the process where less than stoichiometric quantity required for complete combustion is used, and partially oxidized products are formed. Steam reforming process involves the reaction of biomass with steam. The energy content of product gases from biomass gasification can be varied. Low energy content gases (100–300 BTU/scf) are formed when there is direct contact of biomass feedstock with air [1]. Dilution of product gases with nitrogen occurs during the gasification process. Medium energy gases (300–700 BTU/scf) is obtained from directly heated biomass gasifiers when oxygen is used and from indirectly heated biomass gasifiers when air is used and heat transfer occurs via inert solid medium. High energy product gases (700–1,000 BTU/scf) are obtained when gasification conditions promote the formation of methane and other light hydrocarbons. Commercial biomass gasification facilities started worldwide in the 1970s and 1980s. Typically, gasification reactors comprise of a vertical reactor that has drying, pyrolysis, and combustion zones. Synthesis gas leaves the top of the reactor and molten slag leaves the bottom of the reactor. The reactions that take place in the reactor are given in > Eqs. 25.7, > 25.8, and > 25.9 using cellulose as representative of biomass [1].

Biomass as Feedstock

25

Pyrolysis: C6 H10 O5 ! 5CO þ 5H2 þC

(25.7)

C6 H10 O5 þ O2 ! 5CO þ 5H2 þCO2

(25.8)

C6 H10 O5 þ H2 O ! 6CO þ 6H2

(25.9)

Partial oxidation:

Steam reforming:

Synthesis gas is used in the chemical production complex of the lower Mississippi river corridor to produce ammonia and methanol. Currently, ammonia and methanol are produced using synthesis gas from natural gas, naphtha, or refinery light gas. Nearly 12.2 billion pounds of methanol are produced annually in the USA and most of the methanol is converted to higher-value chemicals such as formaldehyde (37%), methyl tertiary butyl ether (28%), and acetic acid (8%) [5]. Ethanol can be produced from the synthesis gas, and Fischer–Tropsch chemistry is another approach to convert synthesis gas to chemicals and fuels. The chemicals that can be produced include paraffins, monoolefins, aromatics, aldehydes, ketones, and fatty acids. Pyrolysis is the direct thermal decomposition of the organic components in biomass in the absence of oxygen to yield an array of useful products like liquid and solid derivatives and fuel gases [1]. Conventional pyrolysis is the slow, irreversible, thermal degradation of the organic components in biomass in absence of oxygen and includes processes like carbonization, destructive distillation, dry distillation, and retorting. The products of pyrolysis under high pressure and temperature include mainly liquids with some gases and solids (water, carbon oxides, hydrogen, charcoal, organic compounds, tars, and polymers). The pyroligneous oil is the liquid product formed and mainly composed of water, settled tar, soluble tar, volatile acids, alcohols, aldehydes, esters, and ketones. The solid derivative from pyrolysis is referred to as biochar. Biochar can be used as a soil amendment and as a carbon sequestration medium. Depending on pyrolysis conditions and feedstock, the liquid product contains valuable chemicals and intermediates. The separation of these intermediates in a cost-effective manner is required. Pyrolysis can be slow, or fast, depending on the residence time and temperature. Slow pyrolysis occurs between 500 C and 900 C and produces low energy gas, pyrolytic oil, and charcoal. Fast pyrolysis is operated in the range of 400650 C and residence times of a few seconds to a fraction of a second. ConocoPhilips has funded a $22.5 million and 8-year research program at Iowa State University to develop new technologies for processing lignocellulosic biomass to biofuels [23]. The company wants to investigate routes using fast pyrolysis to decompose biomass to liquid fuels. Faustina Hydrogen Products LLC announced a $1.6 billion gasification plant in Donaldsonville, Louisiana. The plant will use petroleum coke and high sulfur coal as feedstocks instead of natural gas to produce anhydrous ammonia for agriculture, methanol, sulfur, and industrial grade carbon dioxide. The hydrogen is produced for ammonia production from the water gas shift reaction of synthesis gas. Synthesis gas will be produced from gasification of coal and petroleum coke instead of natural gas. Capacities of the plant

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include 4,000 t per day of ammonia, 1,600 t per day of methanol, 450 t per day sulfur, and 16,000 t per day of carbon dioxide. Mosaic Fertilizer and Agrium Inc. have agreements to purchase the anhydrous ammonia from the plant. The carbon dioxide will be sold to Denbury Resources Inc. for use in enhanced oil recovery of oil left after conventional rig drilling processes in old oil fields in Southern Louisiana and the Gulf Coast. The rest of the carbon dioxide would be sequestered and sold as an industrial feedstock. The facility claims to have the technology to capture all the carbon dioxide during manufacturing process. Eastman Chemical Company, a Fortune 500 company, will provide the Faustina gasification plant with necessary maintenance and services and plans to have a 25% equity position along with a purchase contract to buy the methanol produced in the plant. Eastman Chemicals will use methanol to make raw materials like propylene and ethylene oxide. Faustina is also backed by D. E. Shaw Group and Goldman Sachs. Eastman Chemicals also plans to have 50% stake in a $1.6 billion plant to be built in Beaumont, Texas, in 2011 [24]. The plant will use gasification to produce syngas. Eastman will use the syngas to produce 225 million gallons of methanol and 225,000 metric tons of ammonia per year at Terra Industries in Beaumont. Air Products & Chemicals will supply 2.6 million metric tons per year of oxygen to the gasifiers and market the hydrogen produced in the complex.

Biomass Feedstock Availability The challenge with biomass feedstock usage is the availability of biomass on an uninterrupted basis. Biomass, as a feedstock, has a wide variation due to a number of causes. These include climate and environmental factors like insolation, precipitation, temperature, ambient carbon dioxide concentration, nutrients, etc. The availability of land and water areas for biomass production is important for the sustainable growth of biomass. The land capability in the United States is classified according to eight classes by the USDA and is given in > Table 25.8. There have been numerous studies on the availability of biomass as feedstock in the United States, the most recent survey and estimation being undertaken by Perlack et al. [25]. Their findings are summarized in this section for land biomass resources. The land base of the United States is approximately 2,263 million acres, including the 369 million acres of land in Alaska and Hawaii [25]. The land area is classified according to forest land, grassland pasture and range, cropland, special uses like public facilities, and other miscellaneous uses like urban areas, swamps, and deserts. The distribution of the total land areas according to these categories is given in > Fig. 25.19. About 60% of the total land base in the lower 48 states having some potential for growth of biomass. The two major categories of biomass resources availability are forest resources obtained from forest land and agricultural resources obtained from crop land (or agricultural land). The detailed classification of the biomass resources are given in > Fig. 25.20. The primary resources are often referred to as virgin biomass and the

Biomass as Feedstock

25

. Table 25.8 Land capability classification (Source: USDA) Class

Description

Class I

Contains soils having few limitations for cultivation

Class II Class III Class IV Class V

Contains soils having some limitations for cultivation Contains soils having severe limitations for cultivation Contains soils having very severe limitations for cultivation Contains soils unsuited to cultivation, although pastures can be improved and benefits from proper management can be expected Class VI Contains soils unsuited to cultivation, although some may be used provided unusually intensive management is applied Class VII Contains soils unsuited to cultivation and having one or more limitations which cannot be corrected Class VIII Contains soils and landforms restricted to use as recreation, wildlife, water supply or aesthetic purposes

Land Base Resource Misc. Area, Urban Areas, 13%

Special Uses, Public Facility, 8%

Forest Land, 33%

Cropland, 20%

Grassland Pasture and Range, 26%

. Fig. 25.19 United States land base resource [25]

secondary and tertiary are referred to as waste biomass. Currently, slightly more than 75% of biomass consumption in the United States (about 142 million dry tons) comes from forestlands. The remainder (about 48 million dry tons), which includes biobased products, biofuels, and some residue biomass, comes from cropland.

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Biomass

Forest Resources

Primary – Logging residues from conventional harvest operations and residues from forest management and land clearing operations – Removal of excess biomass (fuel treatments) from timberlands and other Forestlands – Fuelwood extracted from forestlands

Secondary – Primary wood processing mill residue – Secondary wood processing mill residue – Pulping liquors (black liquor)

Tertiary – Urban wood residues ––– construction and demolition debris, tree trimmings, packaging wastes and consumer durables

Agricultural Resources

Primary – Crop residues from major crops ––– corn stover, small grain straw, and others – Grains (corn and soybeans) used for ethanol, biodiesel, and bioproducts – Perennial grasses – Perennial woody crops

Secondary – Animal manures – Food/feed processing residues

Tertiary – MSW and post-consumer residues and landfill gases

. Fig. 25.20 Biomass resource base (primary, secondary, and tertiary biomass) (Adapted from [25])

Forest Resources Forest Land Base The total forest land resource base in the United States is approximately 749 million acres (one-third of the total land resource). The forest land is grouped into unreserved ‘‘timberland,’’ ‘‘reserved land,’’ and ‘‘others.’’ The 749 million acres is divided into 504 million acres of timberland capable of growing 20 ft3 per acre of wood annually, 166 million acres of forestland classified as ‘‘other’’ (incapable of growing 20 ft3 per acre of wood annually and hence used for of livestock grazing and extraction of some nonindustrial wood products) and 78 million acres of reserved forestland used for parks and wilderness. ‘‘Timberland’’ and the ‘‘other’’ land are considered as the resource base that can be utilized for forest biomass resources.

Types of Forest Resource The primary forest resources include logging residues and excess biomass (not harvested for fuel treatments and fuelwood) from timberlands. Logging residues are the unused portions of growing-stock and non-growing-stock trees cut or killed by logging and left in

Biomass as Feedstock

25

the woods. Fuelwood is the wood used for conversion to some form of energy, primarily for residential use. The processing of sawlogs and pulpwood harvested for forest products generates significant amounts of mill residues and pulping liquors. These are secondary forest resources and constitute the majority of biomass in use today. The secondary residues are used by the forest products industry to manage residue streams, produce energy and recover chemicals. About 50% of current biomass energy consumption comes from the secondary residues. The various categories in which primary and secondary forest resources can be grouped are given below (> Fig. 25.21): – Logging residue: The recovered residues generated by traditional logging activities and residues generated from forest cultural operations or clearing of timberlands. These constitute about 67 million dry tons of residues, of which 41 million is currently available for bioenergy and biobased products. – Fuel treatments (forest land): The recovered residues generated from fuel treatment operations on timberland and other forestland. Fuel treatments are the procedures by which forests are treated so as to reduce the fuel value in the wood. The amount of biomass potentially available as feedstock for bioenergy and biobased products is 60 million dry tons per year. – Fuelwood: The direct conversion of roundwood to energy (fuelwood) in the residential, commercial, and electric utility sectors currently includes 35 million dry tons per year and used for space and process heating applications. – Forest products industry residues and urban wood residues: These include the utilization of unused residues generated by the forest products industry, urban residues including those discarded from construction and demolition operations, and residues from tree Sustainably Recoverable Forest Biomass Forest growth

89

Urban wood residues

37

Forest products industry wastes

106

Fuelwood

35

Fuel treatments (forestlands)

60

Logging and other residue

41 0

20

40

60

80

million dry tons per year

. Fig. 25.21 Estimate of sustainably recoverable forest biomass (Adapted from [25])

100

120

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trimmings, packaging residues, and wood-based consumer durables giving a total of 143 million dry tons per year. – Forest growth: Forest growth and increase in the demand for forest products will increase the contribution of forest biomass by an additional 89 million dry tons annually. The estimate of currently recoverable forest biomass is given in > Fig. 25.21. The approximate total quantity is 368 million dry tons annually. This includes about 142 million dry tons of biomass currently being used primarily by the forest products industry and an estimated 89 million dry tons that could come from a continuation of demand and supply trends in the forest products industry.

Limiting Factors for Forest Resource Utilization The 368 million tons of potential forest biomass feedstock base is constrained by some restrictions for exploitation. For forest resources inventory, development in forest utilization relationships and land ownership is expected to play a major role in utilizing the resource. There are three major limiting factors for forest residues from fuel treatment thinning resource, namely, accessibility (having roads to transport the material and operate logging/collection systems, avoiding adverse impacts on soil and water), economic feasibility (value of the biomass compared against the cost of removing the material), and recoverability (function of tree form, technology, and timing of the removal of the biomass from the forests). Forest products industry processing residues include primary wood processing mills, secondary wood processing mills, and pulp and paper mills. Residues from these sources include bark, sawmill slabs and edgings, sawdust, and peeler log cores, residues from facilities which use primary products and black liquor. A significant portion of this residue is burnt or combusted to produce energy for the respective industries. Excess amount of residue remain unutilized after the burning and combustion and can be used in biomass processes. Urban wood residues include municipal solid wastes, and construction and demolition debris. A part of it is recovered and a significant part is unexploited. Finally, future forest growth and increased demands in forest products are likely to affect the availability of forest resources for biomass feedstock base. In summary, all of these forest resources are sustainably available on an annual basis, but not currently used to its full potential due to the above constraints. For estimating the residue tonnage from logging and site clearing operations and fuel treatment thinning, a number of assumptions were made by Perlack et al. [25]: All forestland areas not currently accessible by roads were excluded. All environmentally sensitive areas were excluded. Equipment recovery limitations were considered. Recoverable biomass was allocated into two utilization groups – conventional forest products and biomass for bioenergy and biobased products.

25

Biomass as Feedstock

Summary for Forest Resources Thus, biomass derived from forestlands currently contributes about 142 million dry tons to the total annual consumption in the United Sates of 190 million dry tons. With increased use of potential and currently unexploited biomass, this amount of forestland-derived biomass can increase to approximately 368 million dry tons annually. The distribution of the forest resource potential is summarized in > Fig. 25.22. This estimate includes the current annual consumption of 35 million dry tons of fuelwood extracted from forestland for residential, commercial, and electric utility purposes; 96 million dry tons of residues generated and used by the forest products industry; and 11 million dry tons of urban wood residues. There are relatively large amounts of forest residue produced by logging and land clearing operations that are currently not collected (41 million dry tons per year) and significant quantities of forest residues that can be collected from fuel treatments to reduce fire hazards (60 million dry tons per year). Additionally, there are unutilized residues from wood processing mills and unutilized urban wood. These sources total about 36 million dry tons annually. About 48% of these resources are derived directly from forestlands (primary resources). About 39% are secondary sources of biomass from

Summary of Potentially Available Forest Biomass Resources 80 Growth 60

Unexploited Existing Use

16

50 40

22

8 16

15

11

30 49

20

11

Urban Wood Residue

Pulping Liquors (Forest Products)

8 Wood Residues (Forest Products)

Fuel Treatments (Timberland)

Logging Residue

28

8 9

0

52

35

Fuelwood

10

46

Fuel Treatments (Other Forestland)

32

Other Removal Residue

Million dry tons per year

70

. Fig. 25.22 Summary of potentially available forest biomass resources (Adapted from [25])

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the forest products industry. The remaining amount of forest biomass would come from tertiary or collectively from a variety of urban sources.

Agricultural Resources Agricultural Land Base The agricultural land resource base for the United States is approximately 455 million acres, approximately 20% of the total land base in the country. Out of this, 349 million acres is actively used for crop growth, 39 million acres constitutes idle cropland, and 67 million acres is used for pasture. Cropland utilization is affected by soil and weather conditions, expected crop prices, and government incentives. Crop land is also lost due to conversion of the land for other uses like urban development, etc. The major food crops planted acreage constitutes wheat, soybeans, and rice. The feed crops include corn, sorghum, and hay. The fallow and failed land is a part of cropland. Apart from cropland, there is idle land which includes acreage diverted from crops under the Acreage Reduction Program (ARP), the Conservation Reserve Program (CRP), and other federal acreage reduction programs. The cropland used only for pasture is also separately accounted for. The distribution of agricultural land base and planted crop acreages in the United States are shown in > Fig. 25.23.

Types of Agricultural Resource The agricultural resource base is primarily comprised of grains and oilseeds in the United States. Currently, grains are primarily used for cattle feed. Grains, primarily corn, can be used for producing ethanol and oilseeds, primarily soybeans, can be used to produce biodiesel. Approximately 93% of the total US ethanol is produced from corn. Apart from these, agricultural residues, like corn stover, can also be used for producing ethanol. In the United States, approximately 428 million dry tons of annual crop residues, 377 million dry tons of perennial crops, 87 million dry tons of grains, and 106 million dry tons of animal manures, process residues, and other miscellaneous feedstocks can be produced on a sustainable basis [25]. This resource potential was evaluated based on changes in the yields of crops grown on active cropland, crop residue-to-grain or -seed ratios, annual crop residue collection technology and equipment, crop tillage practices, land use change to accommodate perennial crops (i.e., grasses and woody crops), biofuels (i.e., ethanol and biodiesel), and secondary processing and other residues. Three scenarios were evaluated for availability of crop biomass, and they are given below. Current Availability of Biomass Feedstocks from Agricultural Land

The current availability scenario studies biomass resources current crop yields, tillage practices (20–40% no-till for major crops), residue collection technology (40% recovery

25

Biomass as Feedstock

Summary of cropland uses, idle cropland, and cropland pasture in United States 90 76.8

80 72.2 70

64.5

62

Million Acres

60 50

45.8 40

40 33 30 20 12.6 7.7

7.2

10 3.2

1.4

8.4

6.2

1

pl

ed ou

nt

tu cc na

C

ro

U

d an

d an d le Fa i

re

le Id

Pa s

n to ot

Fa l

d er th

lo w ed

ps C

ro

H

hu

Fe e

C

ay

m

n or

rg

C

ps ro C d

So O

O

th

er

Fo o

ga Su

rb

rc

ee

an

e

ts

e ic R

ga Su

ns ea

W

So yb

he

at

0

. Fig. 25.23 Summary of agricultural land usage by major crops in United States (Adapted from [25])

potential), grain to ethanol and vegetable oil for biodiesel production, and use of secondary and tertiary residues on a sustainable basis. The amount of biomass currently available for bioenergy and bioproducts is about 194 million dry tons annually as shown in > Fig. 25.24. The largest source of this current potential is 75 million dry tons of corn residues or corn stover, followed by 35 million dry tons of animal manure and other residues. Biomass Availability Through Technology Changes in Conventional Crops with No Land Use Change

This scenario analyzed the biomass availability of conventional crops achieved through technology changes. The land utilization for conventional crops projected for 2014 was used for this analysis. Technology changes to increase crop yields and improve collection equipment, and sustainable agricultural practices were considered in this scenario. The corn yields were assumed to increase by 25–50% from 2001 values while yields of wheat and other small grains, sorghum, soybeans, rice, and cotton are assumed to increase at rates lower than for corn. The increased production of corn contributed to increase in corn stover as residue. Soybeans contributed no crop residue under a moderate yield increase of about 13% but made a small contribution with a high yield increase of about 23%. The collection of these residues from crops was increased through better collection equipment capable of recovering as much as 60% of residue under the moderate yield

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Biomass as Feedstock

Biomass from agricultural lands, current availability 31

Other Residues

Manures

35

Grains to Biofuels

15

21

Other Crop Residues

6

Small Grains Residues

11

Wheat Straw

Corn Stover

75 0

10

20

30 40 50 Million dry tons per year

60

70

80

. Fig. 25.24 Current availability of biomass from agricultural lands [25]

increases and 75% under the high yield increases, but the actual removal amounts depend on the sustainability requirements. No-till cultivation method was assumed to be practiced on approximately 200 million acres under moderate yield increases and all of active cropland under high yields. The amount of corn and soybeans available for ethanol, biodiesel production, or other bioproducts was calculated by subtracting amounts needed to meet food requirements plus feed and export requirements from total quantities. All remaining grain was assumed to be available for bioproducts. Further, about 75 million dry tons of manure and other secondary and tertiary residues and wastes, and 50% of the biomass produced on CRP lands (17–28 million dry tons) were assumed to be available for bioenergy production. Thus, this scenario for use of crop residue results in the annual production of 423 million dry tons per year under moderate yields and 597 million dry tons under high yields. In this scenario, about two-thirds to three-fourths of total biomass are from crop residues, as can be seen in > Fig. 25.25. Biomass Availability Through Technology Changes in Conventional Crops and New Perennial Crops with Significant Land Use Change

This scenario assumes the addition of perennial crops, land use changes, and changes in soybean varieties, as well as the technology changes assumed under the previous scenario. Technology changes are likely to increase the average residue-to-grain ratio of soybean varieties from 1.5 to a ratio of 2.0. The land use changes considered in this scenario

Biomass as Feedstock

25

Biomass from agricultural lands, with increased crop yields and technology changes Other Residues

40 44

Manures

44 44 56

Grains to Biofuels

97 Moderate Yield Increase

28 28

CRP Biomass Other Crop Residues

High Yield Increase 37 48

Soybean Residues 0 0 15

Small Grains Residues

25 35

Wheat Straw

57 170

Corn Stover 0

50

100

150

256 200

250

300

Million dry tons per year

. Fig. 25.25 Availability of biomass for increased crop yields and technology changes [25]

included the conversion of land for growth of perennial crop on 40 million acres for moderate yield increase or 60 million acres for high yield increase. Woody crops produced for fiber were expanded from 0.1 million acres to 5 million acres, where they can produce an average annual yield of 8 dry tons per acre. Twenty-five percent of the wood fiber crops are assumed to be used for bioenergy and the remainder for other, higher-value conventional forest products. Perennial crops (trees or grasses) grown primarily for bioenergy expand to either 35 million acres at 5 dry tons per acre per year or to 55 million acres with average yields of 8 dry tons per acre per year. Ninety-three percent of the perennial crops are assumed available for bioenergy and the remainder for other products. A small fraction of the available biomass (10%) was assumed as lost during the harvesting operations. This scenario resulted in the production of 581 (moderate yield) to 998 million (high yield) dry tons as shown in > Fig. 25.26. The crop residues increased even though conventional cropland was less because of the addition of more soybean residue together with increased yields. The single largest source of biomass is the crop residue, accounting for nearly 50% of the total produced. Perennial crops account for about 30–40% depending on the extent of crop yield increase (i.e., moderate or high).

Limiting Factors for Agricultural Resource Utilization The annual crop residues, perennial crops, and processing residues can produce 998 million tons of potential agricultural biomass feedstock. The limiting factors for the

951

952

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Biomass as Feedstock

Biomass from agricultural lands, with increased crop yields, technology change and land use change for perennial crops Other Residues

40 44

Manures

44 44 56

Grains to Biofuels

87

18 18

CRP Biomass

Moderate Yield Increase High Yield Increase

36 47

Other Crop Residues 13

Soybean Residues

48 15 25

Small Grains Residues

35

Wheat Straw

52 170

Corn Stover

256 156

Perennial Crops 0

50

100

150 200 250 Million dry tons per year

377 300

350

400

. Fig. 25.26 Availability of biomass for increased crop yields and technology changes, and inclusion of perennial crops [25]

utilization of crop residues and growth of perennial crops for the purpose of feedstock generation will require significant changes in current crop yields, tillage practices, harvesting and collection technologies, and transportation. Agricultural residues serve as a land cover and prevent soil erosion after harvesting of crops. The removal of large quantities of the residue can affect the soil quality by removal of soil carbon, nutrients, and may need to be replenished with fertilizers. The fertilizers, in turn, require energy for production, and hence the optimum removal of the residues needs to be evaluated. Perennial crops require less nutrient supplements and are better choices for preventing soil erosion compared to annual crops, and they are considered for planting. Important assumptions made for this evaluation of agricultural biomass availability by Perlack et al. [25] included the following: Yields of corn, wheat, and other small grains were increased by 50%. The residue-to-grain ratio for soybeans was increased to 2:1. Harvest technology was capable of recovering 75% of annual crop residues (when removal is sustainable). All cropland was managed with no-till methods. 55 million acres of cropland, idle cropland, and cropland pasture were dedicated to the production of perennial bioenergy crops.

25

Biomass as Feedstock

All manure in excess of that which can applied on-farm for soil improvement under anticipated EPA restrictions was used for biofuel. All other available residues were utilized.

Summary for Agricultural Resources Thus, biomass derived from agricultural lands currently available for removal on a sustainable basis is about 194 million dry tons. This amount can be increased to nearly one billion tons annual production through a combination of technology changes, adoption of no-till cultivation, and land use change to grow perennial crops. The amount of biomass available without the addition of perennial crops but high crop yield increase would be 600 million dry tons. Approximately the same amount of biomass would be produced on agricultural lands with moderate crop yield increase and addition of perennial crops. The distribution of the agricultural resource potential is summarized in > Fig. 25.27.

Aquatic Resources The previous sections discussed conventional biomass feedstock options grown on land. Apart from the crop and forest biomass resources, other organisms that undergo

Summary of potentially available agricultural biomass resources 1200

Crop Residues Grains to Biofuels Process Residues Perennial Crops

Million dry tons per year

1000

377

800

600

87

87 156 97 400

84

84

53

56 446

413

200

87

286

284 0 Moderate Yield Increase

High Crop Yield Increase

No perennial crops

Moderate Yield Increase

High Crop Yield Increase

Perennial crops with land use change

. Fig. 25.27 Summary of potentially available agricultural biomass resources [25]

953

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25 Carbon Dioxide Sunlight

Biomass as Feedstock

Oil Heater

Flocculent

Refinery Hydrotreater Algae Growth

Harvesting

Lipid Extraction

Three Phase Separation Biodiesel Process

Water Recycle

Nutrients

Spent Algae

Anaerobic Digestion

Biogas

Power

Makeup Water Animal Feed and Lignocellulosic Biomass Feed

. Fig. 25.28 Model algae lipid production system (Adapted from [31])

photosynthesis are cyanobacteria and algae. There are several ongoing attempts to find the ideal growth conditions for cultivating algae on a sustainable basis. Key areas of research interests in algae include high per-acre productivity compared to typical terrestrial oilseed crops, non-food based feedstock resources, use of otherwise nonproductive, non-arable land for algae cultivation, utilization of a wide variety of water sources (fresh, brackish, saline, and wastewater), and production of both biofuels and valuable coproducts. The Energy Efficiency and Renewable Energy Laboratory at the Department of Energy commissioned a working group assess the current state of algae technology and to determine the next steps toward commercialization [26]. The workshop addressed the following topics and technical barriers in algal biology, feedstock cultivation, harvest and dewatering, extraction and fractionation of microalgae, algal biofuel conversion technologies, coproducts production, distribution and utilization of algal-based fuels, resources and siting, corresponding standards, regulation and policy, systems and techno-economic analysis of algal biofuel deployment, and public–private partnerships. This section aims to capture some of those efforts. A model algal lipid production system with algae growth, harvesting, extraction, separation, and uses is shown in > Fig. 25.28. Methods to convert whole algae into biofuels exist through anaerobic digestion to biogas, supercritical fluid extraction and pyrolysis to liquid or vapor fuels, and gasification process for production of syngas-based fuels and chemicals. Algae oil can supplement refinery diesel in hydrotreating units, or be used as feedstock for the biodiesel process. The research on algae as a biomass feedstock is a very dynamic field currently, and the potential of algae seems promising as new results are presented continuously. Methods to cultivate algae have been developed over the years. Recent developments in algae growth technology include vertical reactors [27] and bag reactors [28] made of polythene mounted on metal frames, eliminating the need for land use for cultivation. The NREL Aquatic Species Program [29] mentions ‘‘raceway’’ ponds design for growth of algae. This method required shallow ponds built on land area and connected to a carbon dioxide source such as a power plant. Productivity in these pond designs were few grams/ m2/day. Other designs include tubular cultivation facilities and the semi- continuous batch cultures gave improved production rates of algae. For example, the 3D Matrix System of Green Fuel Technologies Corporation have an average areal productivity of

Biomass as Feedstock

25

. Table 25.9 Comparison of productivity between algae and soybean [31] Algae

Productivity

Soybeans

Low productivity (10 g/m2/day) 15% TAG

Gallons/acre Total acres Gallons/year

48 63.6 million 3 billion

633 63.6 million 40 billion

2,637 25 million 66 billion

10,549 6.26 million 66 billion

61

100

100

Petrodiesel (%) 4.5

Med. productivity (25 g/m2/day) 25% TAG

High productivity (50 g/m2/day) 50% TAG

98 g/m2/day (ash free, dry weight basis), with highs of over 170 g/m2/day achieved during a run time of 19 days [30]. Algae have the potential for being an important source of oil and carbohydrates for production of fuels, chemicals and energy. Carbon dioxide and sunlight can be used to cultivate algae and produce algae with 60% triglycerides and 40% carbohydrates and protein [31]. A comparison in productivity between algae and soybean is given in > Table 25.9. The table shows that even at low productivity of algae, yields are more than 10 times in gallons per acre when all the United States soybean acreage is utilized for algae. Higher yields are obtained at medium and high productivity levels of algae (higher triacylglycerols) with reduced acreage requirements. The algae oil resulting from low productivity can replace approximately 61% of the total United States diesel requirements, as compared to only 4.5% for soybean oil–based diesel. The other advantage, at these yields, algae can capture up to 2 billion tons of carbon dioxide while photosynthesis. However, the growth of algae on a large scale for production of oil and chemicals seems to be the most important barrier at this stage. The following technologies developed seem promising ways to cultivate algae, apart from traditional open pond systems. These are discussed on a per case basis, with the companies that have developed these technologies. Some of the current research trends in algae bioreactor systems are presented in the following sections.

Raceway Pond Systems ‘‘Raceway’’ Design for algae growth included shallow ponds in which the algae, water, and nutrients circulate around a ‘‘racetrack’’ as shown in > Fig. 25.29 (inset) [29]. Motorized paddles help to provide the flow and keep algae suspended in water and circulated back up to the surface on a regular frequency. The ponds are shallow to ensure maximum exposure of sunlight (sunlight cannot penetrate beyond certain depths). The ponds are operated as continuous reactors with water and nutrients fed to the pond and carbon dioxide bubbled

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Water, Nutrients

CO2 from Recovery System CO2 Recovery System

Algae

Motorized Paddle

Algae/Oil Recovery System

Fuel Production

. Fig. 25.29 Algae raceway design (inset) and algae farm system for algae growth (Adapted from [29])

through the system. The algae containing water is removed at the other end of the pond. The algae is then harvested and processed for oil extraction. The concept of the raceway design for algae growth can be extended to an algae farm as shown in > Fig. 25.29. This consists of numerous ponds similar to the raceway in which algae is grown and harvested. The size of these ponds is measured in terms of surface area (as opposed to volume) as the surface area is critical to capturing sunlight. The productivity is measured in terms of biomass produced per day per unit of available surface area. These designs required large acres of land and thus obtained the scale of farms. The open bioreactor system for a 50 square meters and width 1.2 m algae cultivation facility at the microalgal culture facility of UH Marine Center is shown in > Fig. 25.30.

Algenol Biofuels: Direct to EthanolTM Process Algenol biofuels have developed metabolically engineered algae species to produce ethanol in closed bioreactor systems. The proprietary Capture TechnologyTM bioreactors hold single-cell cyanobacteria in closed and sealed plastic bag units preventing contamination, maximize ethanol recovery, and allow fresh water recovery. The advantage of the process lies in the fact that it is a one step process where the cyanobacteria utilize the carbon dioxide to convert it to ethanol, and secrete the ethanol from the cell [32]. There is a requirement for strict maintenance of growth parameters such as CO2, nutrients, water, pH, temperature, salinity, and other environmental conditions for the engineered species of microorganism. The process to make ethanol from algae utilizes 1.5 million tons of carbon dioxide per 100 million gallons of ethanol produced. Algenol, The Dow Chemical Company, and the Department of Energy have teamed to produce ethanol using this technology at Dow’s

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. Fig. 25.30 Microalgal culture facility at the UH Marine Center (Photo: Dr. Edward Laws, LSU School of the Coast and Environment)

Freeport, Texas, site. Dow would contribute with 25 acres of their site, carbon dioxide source, and technical expertise for the $25 million project. Dow plans to utilize their expertise in film technology to device ideal bioreactor for the system with optimum sunlight penetration.

ExxonMobil Algae Research ExxonMobil is funding $600 million for algae research partnered with Synthetic Genomics, Inc. to identify and develop algae strains to produce bio-oils at low costs [33]. The research will also determine the best production systems for growing algal strains, for example, open ponds or closed photobioreactor systems. The company also plans for scale-up to large amounts of CO2 utilization and developing integrated commercial systems.

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Shell Algae Research Shell and HR Biopetroleum formed a joint venture company in 2007, called Cellana, to develop an algae project for a demonstration facility on the Kona coast of Hawaii Island. The site was leased from the Natural Energy Laboratory of Hawaii Authority (NELHA) and is near existing commercial algae enterprises, primarily serving the pharmaceutical and nutrition industries. The facility will grow only non-modified, marine microalgae species in open-air ponds using proprietary technology. Algae strains used for the process are indigenous to Hawaii or approved by the Hawaii Department of Agriculture.

Green Fuels Technology GreenFuel Technologies developed a process that grows algae in plastic bags using CO2 from smokestacks of power plants via naturally occurring species of algae. The CO2 source can also come from fermentation or geothermal gases. Algae can be converted to transportation fuels and feed ingredients or recycled back to a combustion source as biomass for power generation. Industrial facilities do not need any internal modifications to host a GreenFuel algae farm. In addition, the system does not require fertile land or potable water. Water used can be recycled and wastewater can be used as compared to oilseed crops’ high water demand. With high growth rates, algae can be harvested daily.

Valcent Products 32A vertical reactor system is being developed by Valcent Products, Inc of El Paso, Texas, using the 340 annual days of sunshine and carbon dioxide available from power plant exhaust. Enhanced Biofuel Technology, A2BE Carbon Capture, LLC, are some of the firms that use the concept of raceway pond design and algae farm for production of algae for biofuels. Research is underway to determine the species of algae for oil production and the best method of extracting the oil. Extraction methods being evaluated include expeller/press, hexane solvent extraction, and supercritical fluid extraction and are the more costly step in the process. Approximately 70–75% of algae oil can be extracted using expeller press while 95% oil can be extracted by hexane solvent oil extraction and 100% oil extracted using supercritical fluid extraction.

Algae Species Algae are plant-like microorganisms that preceded plants in developing photosynthesis, the ability to turn sunlight into energy. Algae range from small, single-celled organisms to

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multicellular organisms, some with fairly complex differentiated form. Algae are usually found in damp places or bodies of water and thus are common in terrestrial as well as aquatic environments. Like plants, algae require primarily three components to grow: sunlight, carbon dioxide, and water. Microalgae are the most efficient in photosynthesis, with 60–70% of each cell’s volume capable of photosynthesis [34]. The algae also do not have roots, stems, or leaves, which diverts resources to produce hydrocarbons. Algae cells contain light-absorbing chloroplasts and produce oxygen through photosynthesis. Biologists have categorized microalgae in a variety of classes, mainly distinguished by their pigmentation, life cycle, and basic cellular structure. The four most important (in terms of abundance) are [29]: – The diatoms (Bacillariophyceae): These algae dominate the phytoplankton of the oceans, but are also found in fresh and brackish water. Approximately 100,000 species are known to exist. Diatoms contain polymerized silica (Si) in their cell walls. All cells store carbon in a variety of forms. Diatoms store carbon in the form of natural oils or as a polymer of carbohydrates known as chyrsolaminarin. – The green algae (Chlorophyceae): These type of algae are abundant in freshwater, for example, in a swimming pool. They can occur as single cells or as colonies. Green algae are the evolutionary progenitors of modern plants. The main storage compound for green algae is starch, though oils can be produced under certain conditions. – The blue-green algae (Cyanophyceae): This type of algae is closer to bacteria in structure and organization. These algae play an important role in fixing nitrogen from the atmosphere. There are approximately 2,000 known species found in a variety of habitats. – The golden algae (Chrysophyceae): This group of algae is similar to the diatoms. They have more complex pigment systems, and can appear yellow, brown, or orange in color. Approximately 1,000 species are known to exist, primarily in freshwater systems. They are similar to diatoms in pigmentation and biochemical composition. The golden algae produce natural oils and carbohydrates as storage compounds. The program initially looked into over 3,000 strains of organisms, which was then narrowed down to about 300 species of microorganisms. The program concentrated not only on algae that produced a lot of oil, but also with algae that grow under severe conditions – extremes of temperature, pH, and salinity. Algal biomass contains three main components: carbohydrates, proteins, and natural oils. Algae contains 2–40% of lipids/oils by weight. The composition of various algal species is given in > Table 25.10. These components in algae can be used for fuel or chemicals production in three ways, mainly production of methane via biological or thermal gasification, ethanol via fermentation, or conversion to esters by transesterification [29]. Botryococcus braunii species of algae has been engineered to produce the terpenoid C30 botryococcene, a hydrocarbon similar to squalene in structure [34]. The species has been engineered to secrete the oil, and the algae can be reused in the bioreactor. A further modification to the algae is smaller light collecting antennae, allowing more

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. Table 25.10 Percentage composition of protein, carbohydrate, lipids, and nucleic acid composition of various strains of algae [29] Strain

Protein

Carbohydrates

Lipids

Nucleic acid

Scenedesmus obliquus Scenedesmus quadricauda Scenedesmus dimorphus

50–56 47 8–18

10–17 – 21–52

12–14 1.9 16–40

3–6 – –

Chlamydomonas rheinhardii Chlorella vulgaris Chlorella pyrenoidosa Spirogyra sp. Dunaliella bioculata

48 51–58 57 6–20 49

17 12–17 26 33–64 4

21 14–22 2 11–21 8

– 4–5 – – –

Dunaliella salina Euglena gracilis Prymnesium parvum Tetraselmis maculata

57 39–61 28–45 52

32 14–18 25–33 15

6 14–20 22–38 3

– – 1–2 –

Porphyridium cruentum Spirulina platensis Spirulina maxima Synechoccus sp.

28–39 46–63 60–71 63

40–57 8–14 13–16 15

9–14 4–9 6–7 11

– 2–5 3–4.5 5

Anabaena cylindrica

43–56

25–30

4–7

–

light to penetrate the algae in a polythene container reactor system. A gene, tla1, is responsible for the number of chlorophyll antennae, can be modified to reduce the chlorophyll molecules from 600 to 130. Botryococcene is a triterpene and, unlike triglycerides, cannot undergo transesterification. It can be used as feedstock for hydrocracking in an oil refinery to produce octane, kerosene, and diesel. Dry algae factor is the percentage of algae cells in relation with the media where is cultured, e.g., if the dry algae factor is 50%, one would need 2 kg of wet algae (algae in the media) to get 1 kg of algae cells. Lipid factor is the percentage of vegoil in relation with the algae cells needed to get it, i.e., if the algae lipid factor is 40%, one would need 2.5 kg of algae cells to get 1 kg of oil. Carbon dioxide sources for algae growth can be from pipelines for CO2, flue gases from power plants, or any other sources rich in carbon dioxide. The flue gases from power plants were previously not considered as suitable algae cultivation land was not found near power plants. However, with newer designs of algae reactors linked with powerplants, the flue gases can be suitable sources for algae cultivation. Water usage for algae growth is also a concern for design. In an open pond system, the loss of water is greater than in closed tubular cultivation or bag cultivation methods. The water can be local industrial water and recycled after harvesting algae.

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CO2

Reclaimed Water CO2 N Waste

Algae CO2

P

N

O2 Water

Biomass

P Organics

Bacteria

. Fig. 25.31 Schematic diagram for wastewater treatment with algae and production of biomass [35]

Algae can be used in wastewater treatment, as wastewater contains nutrients for algae growth. The advantages for wastewater treatment using algae include the production of oxygen with low energy input, removal of soluble nitrogen and phosphorus, fixation of atmospheric carbon dioxide, and the production of biomass [35]. The simple schematic in > Fig. 25.31 shows how algae and bacteria can be used to produce biomass.

Conclusion The chapter aimed to give an overview of the use of biomass as the next generation feedstock for energy, fuels, and chemicals. The formation of biomass gave the methods in which atmospheric carbon dioxide is fixed naturally to different types of biomass. The classification of biomass into starch, cellulose, hemicellulose, lignin, lipids and oils, and proteins helped to understand the chemical composition of biomass. Biomass species are available in nature as a combination of the components, and it is important to separate the components for use as energy, fuels, and chemicals. Various conversion technologies are employed for the separation of the components of biomass to make it more amenable, and these include pretreatment, fermentation, anaerobic digestion, transesterification, gasification, and pyrolysis. The availability of biomass on a sustainable basis is required for the uninterrupted production of energy, fuels, and chemicals. The current forest biomass feedstock used per year is 142 million metric tons. This can be potentially increased to 368 million metric tons which include currently unexploited and future growth of forest biomass. The agricultural biomass currently available per year on a sustainable basis is 194 million dry tons. This amount can be potentially increased to 423–527 million metric tons per

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year with technology changes in conventional crops and 581–998 million metric tons with technology and land use changes in conventional and perennial crops. Apart from crop and forest biomass, research in algae and cyanobacteria is ongoing for the production of carbohydrate-based and oil-based feedstock. These processes are currently constrained primarily by the successful scale-up to meet the biomass needs. However, recent advances in photo-bioreactors and algae ponds show considerable potential for large scale growth of algae as biomass feedstock.

Future Directions The biomass resource base is capable of producing feedstock for a sustainable supply of fuels, energy, and chemicals. However, technological challenges, market drivers, fossil feedstock cost fluctuations, and government policies and mandates play a significant role in utilizing the full potential of the biomass resources. Ideally, the biomass is regenerated over a short period of time when compared to fossil resources. This period can be few years for forest resources, seasonal for agricultural crops, and days for algae and cyanobacteria. Biomass is the source for natural atmospheric carbon dioxide fixation. Thus, with the use of biomass as feedstock for energy, fuels, and chemicals, the dependence on fossil resources can be reduced, and climate change issues related to resource utilization can be addressed.

References 1. Klass DL (1998) Biomass for renewable energy, fuels and chemicals. Academic, California. ISBN 0124109500 2. EIA (2010) Annual energy outlook 2010. Report No. DOE/EIA-0383(2010), Energy Information Administration, Washington, DC 3. IPCC (2007) Climate change 2007: synthesis report. http://www.ipcc.ch/pdf/assessment-report/ ar4/syr/ar4_syr.pdf. Accessed 8 May 2010 4. Drapcho CM, Nhuan NP, Walker TH (2008) Biofuels engineering process technology. McGrawHill, New York. ISBN 978–0071487498 5. Paster M, Pellegrino JL, Carole TM (2003) Industrial bioproducts: today and tomorrow. Department of Energy Report prepared by Energetics Inc. http://www.energetics.com/resourcecenter/ products/studies/Documents/bioproducts-pport unities.pdf. Accessed 8 May 2010 6. Teter SA, Xu F, Nedwin GE, Cherry JR (2006) Enzymes for biorefineries. In: Kamm B,

Gruber PR, Kamm M (eds) Biorefineries – industrial processes and products, vol 1. Wiley-VCH, Weinheim. ISBN 3-527-31027-4 7. Womac AR, Igathinathane C, Bitra P, Miu P, Yang T, Sokhansanj S, Narayan S (2007) Biomass pre-processing size reduction with instrumented mills. http://www.biomassprocessing.org/Publications/2-Papers_presented/ASAE%20Paper%20 No%20056047%20biomass_instrumentedmills_ Womac%20et%20al.pdf. Accessed 8 Feb 2011 8. Tucker MP, Nagle NJ, Jennings E, Lyons R, Elander R (2011) Hot-washing of pretreated corn stover using integrated sunds horizontal screw and jaygo pretreatment reactors with pneumapress automatic pressure filter. http:// www1.eere.energy.gov/biomass/pdfs/34331.pdf. Accessed 8 Feb 2011 9. Katzen R, Schell DJ (2006) Lignocellulosic feedstock biorefinery: history and plant development for biomass hydrolysis. In: Kamm B, Gruber PR,

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21. Haas MJ, McAloon AJ, Yee WC, Foglia TA (2006) A process model to estimate biodiesel production costs. Bioresour Technol 97(4):671–678 22. DOE (2010b) National algal biofuels technology roadmap. Energy efficieny and renewable energy (US DOE). Draft document: https:// e-center.doe.gov/iips/faopor.nsf/UNID/79E3AB CACC9AC14A852575CA00799D99/$file/AlgalB iofuels_Roadmap_7.pdf. Accessed 8 May 2010 23. C & E News (2007) ConocoPhilips funds biofuel research. Chem Eng News 85(18):24 24. Tullo AH (2007) Eastman pushes gasification. Chem Eng News 85(32):10 25. Perlack RD, Wright LL, Turhollow AF, Graham RL (2005) Biomass as feedstock for a bioenergy and bioproducts industry: the technical feasibility of a billion-ton annual supply. USDA document prepared by Oak Ridge National Laboratory, ORNL/ TM-2005/66, Oak Ridge 26. DOE (2010a) Biomass multi-year program plan March 2010. Energy efficiency and renewable energy (US DOE) http://www1.eere.energy.gov/ biomass/pdfs/mypp.pdf. Accessed 8 May 2010 27. Hitchings MA (2007) Algae: the next generation of biofuels, Fuel Fourth Quarter 2007. Hart Energy, Houston 28. Bourne Jr. JK (2007) Green dreams. National Geographic Magazine. http://ngm.nationalgeographic.com/print/2007/10/biofuels/biofuelstext. Accessed 8 May 2010 29. Sheehan J, Dunahay T, Benemann J, Roessler P (1998) A look back at the U. S. Department of Energy’s aquatic species program – biodiesel from algae. NREL/TP-580-24190, National Renewable Energy Laboratory, Golden 30. Pulz O (2007) Evaluation of GreenFuel’s 3D matrix algae growth engineering scale unit. http://moritz.botany.ut.ee/olli/b/Performance_ Summary_Report.pdf, APS Red Hawk Power Plant, AZ. Accessed 8 May 2010 31. Pienkos PT, Daezins A (2009) The promise and challenges of microalgal-derived biofuels. Biofuels Bioprod Biorefin 3(4):431–440 32. Voith M (2009) Dow plans algae biofuels pilot. Chem Eng News 87(27):10 33. Kho J (2009) Big oil bets on biofuels. Renewable Energy World. http://www.renewableenergy world.com/rea/news/article/2009/07/bio-oil-betson-biofuels. Accessed 8 May 2010

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34. Arnaud C (2008) Algae pump out hydrocarbon biofuels. Chem Eng News 86(35):45–48 35. Lundquist TJ (2011) Production of algae in conjunction with wastewater treatment. http://www. nrel.gov/biomass/pdfs/lundquist.pdf. Accessed 8 March 2011 36. Glazer AW, Nikaido H (1995) Microbial biotechnology: fundamentals of applied microbiology. W.H. Freeman, San Francisco. ISBN 0-71672608-4 37. Zamora A (2005) Fats, oils, fatty acids, triglycerides. http://www.scientificpsychic.com/fitness/ fattyacids1.html. Accessed 8 May 2010 38. Spath PL, Dayton DC (2003) Preliminary screening – technical and economic feasibility of synthesis gas to fuels and chemicals with the

emphasis on the potential for biomass-derived syngas. National Renewable Energy Laboratory, NREL/TP-510-34929. http://www.nrel. gov/docs/fy04osti/34929.pdf Golden. Accessed 8 May 2010 39. Granda C (2007) The MixAlco process: Mixed alcohols and other chemicals from biomass in: seizing opportunity in an expanding energy marketplace, alternative energy conference. LSU Center for Energy Studies. http://www.enrg.lsu. edu/Conferences/altenergy2007/granda.pdf 40. McGowan TF (2009) Biomass and alternate fuel systems, American Institute of Chemical Engineers, John Wiley and Sons Inc., Hoboken, NJ. ISBN 978-0-470-41028-8

26 Biochemical Conversion of Biomass to Fuels Swetha Mahalaxmi . Clint Williford Department of Chemical Engineering, University of Mississippi, Oxford, MS, USA Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 966 Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 968 Process Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 969 Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 970 Pretreatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 970 Main Classes of Pretreatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 971 Hydrolysis and Fermentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 972 Biofuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 973 Hydrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 973 Methane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 977 Ethanol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 978 Pretreatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 980 Hydrolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 982 Fermentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 983 Butanol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 987 Biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 989 Genetic Engineering Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 992 Advanced Fuels from Biochemical Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 994 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 994

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Abstract: Biomass can provide both hydrocarbon fuels and chemical compounds such as alcohols, gums, sugars, lipid-based products, etc. Biomass-derived fuels have acquired a lot of attention during recent years because of the abundance of supply of resources and lower green house gas emissions. Grasses, agricultural residues, animal residues and waste, used oils, etc., can be used as starting materials in the production of biofuels. Ethanol and biodiesel have found greatest application and contribute significantly to fuels. However there is growing interest in other alternatives: hydrogen, methane, butanol, renewable diesel, and petroleum compatible fuels from advanced catalytic biotech processes. Characteristics of various feedstocks and fuels, processes for conversion of biomass to biofuels, the physical, chemical factors and limitations effecting the conversion of biomass to fuels are discussed in this chapter. Process parameters include pH, temperature, and residence time. Additionally, chemical parameters include carbon source, nutrients, acid and alkaline hydrolysis agents, and phenolic inhibitors and sugars generated within the process. Several limitations to bioconversion of biomass are described such as size reduction, crystallinity, by-product inhibition to fermentation, deactivation of cellulases, ethanol tolerance by yeast, and co-fermentation of various sugars. Recent innovations and future developments in recombinant DNA technology and protein engineering are aimed at overcoming limitations to bioconversion. Understanding the limitations and applying suitable biotechnological applications will support future developments for producing biofuels.

Introduction With increasing demands for transportation fuel, renewable sources of energy content, have gained importance in the recent years. Important fuel parameters are energy content, combustion quality such as octane or cetane number, volatility, freezing point, toxicity, and its adaptability to current combustion engines [1]. Biofuels such as hydrogen, methane, ethanol, butanol, and biodiesel are of current interest in replacing (in partial or complete) gasoline to mitigate greenhouse gas emissions. > Table 26.1 presents comparative data for various fuels against gasoline and can be produced from biochemical conversion of biomass. Current working status of these fuels is also mentioned in the > Table 26.1. Among the fuels mentioned in the table, butanol and biodiesel (biodiesel from pure vegetable oils) can be used in existing gasoline and diesel engines respectively with little modification. For others, engine modification is required. For ethanol, lower blends in gasoline do not require engine modification. Use in higher blends requires engine modification. Engine modification is required for some non-gasoline fuels due to difference in their air–fuel ratio, latent heat of evaporation, and corrosiveness. Air–fuel ratio of gasoline is 14.6 kg air for 1 kg of fuel. However, 10% v/v ethanol blend of gasoline has 3.5% w/w oxygen in the fuel which influences the air–fuel ratio at which the engine performs. Engine management systems in modern vehicles adjust the air–fuel ratio to maintain the stoichiometric oxygen in the fuel. Absence of

Biochemical Conversion of Biomass to Fuels

26

. Table 26.1 Properties of various biofuels (Adapted from sources [1] and http://en.wikipedia.org/wiki/ Energy_density) Hydrogen Methane Ethanol

Butanol

Biodiesel

Gasoline

Heat of vaporization (KJ/Kg)

451.9

760

920

430

2,639.9

360

Energy density (MJ/L) Research octane number Air to fuel ratio Freezing point (
F)

10.1 (liq)

0.0378

19.6

29.2

37.3

32.0

>130

135

129

96

>25

97–98

34 435

17.2 296.5

9.0 173.2

11.2 128.7

13.5 26–66

14.6 40

423 Flash point, closed cup (
F) Solubility in – water, volume%

306.4

55

84

212–338

45

–

100

9

Negligible Negligible

Technology

Microbial

Microbial Microbial

Status

Laboratory Industrial Industrial

Engine application Current engine modification

Blend Pure Required

Blend Blend Pure Pure Required Required for higher blends

Microbial Chemical Chemical Chemical Enzymatic Physical Laboratory Industrial Industrial Laboratory Blend Pure Not required

Blend Pure Not requireda

N/A N/A

a

not required for lower blending

engine management system or use of higher blend gasolines/biodiesel alters the air–fuel ratio, therefore requiring engine modification. Ethanol and biodiesel have higher latent heat of evaporation compared to gasoline, which may present difficulties with starting in cold conditions. To avoid cold start difficulties, vehicles require a small tank fitted to accommodate gasoline to initiate combustion. Moreover, viscosity of biodiesel increases during cold conditions requiring alternative starting methods for vehicles using higher blends of biodiesel. Higher blends of ethanol are known to be corrosive on fuel lines and tanks; therefore, vehicles using 20% v/v ethanol blend gasoline require to have nickelplated steel fuel lines and tank. Various sources such as agricultural residues, municipal waste, animal waste, perennial grasses, etc., are used for conversion to biofuels. In this chapter, processes of production of biofuels, hydrogen, methane, ethanol, butanol, and biodiesel are described with recent progress. Applications of recombinant DNA technology and bioengineering to overcome production bottlenecks and enhance fuel production are discussed.

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Sources Biomass represents all materials derived from plant, animal, and microbial origins. Classification of biomass used in conversion to biofuels, may be based on the origin (plant/animal), carbon source (woody/herbaceous), and physical and chemical characteristics. However, biomass from plant origin is considered highly desirable for its abundance and potential to mitigate emission of greenhouse gases. Carbohydrate monomers in plants are formed through photosynthesis, in which the atmospheric carbon dioxide is converted by sunlight to chemical energy. Moreover, the same amount of carbon dioxide is released, when biomass-derived fuels for energy are used, as taken up during the plant growth using sustainable means, therefore, production of more biomass, consequently mitigates and not add up to the atmospheric carbon dioxide [2]. Biomass can be majorly divided into woody plants, herbaceous plants or grasses, aquatic plants, and manures. Among these, some herbaceous plants, aquatic plants, and manures contain high moisture content and are suitable for wet processing or biochemical processing. Aqueous processing or wet processing is generally initiated through enzyme action. This method is suitable for high moisture content biomass because of challenged efficiency of overall energy retrieval, compared to the energy required for drying involved in dry processing. Moisture content, carbon source, and cellulose to lignin ratio are the most important factors affecting the wet process. Biomass with low moisture content is subjected to dry process or thermal treatment such as gasification, pyrolysis, and combustion. Factors that influence the dry processes are ash content, alkali, and trace components as they adversely affect the thermal conversion processes [2]. The products of wet processes are ethanol, butanol, and biogas. Ethanol and butanol products majorly depend on the plant composition – cellulose, hemicellulose, and lignin. Cellulose, hemicellulose, and lignin are the three main components of any plant material. Cellulose is a polymer of glucose with linear chains of (1,4)-D-glucopyranose units in b-configuration with an average molecular weight of around 100,000. Another polymer of glucose with linear chains of (1,4)-D-glucopyranose units in a-configuration, called amylose constitute about 20% of starch. Starch also includes amylopectin, a branched polymer chain of D-glucose molecules called a-1,6 glycosidic linkage [3]. Starch can be more easily digested to sugars compared to cellulose due to the beta configuration and high crystallinity offered by cellulose linear structure. Starch can be obtained from any of the food storage units of plants, while cellulose constitutes all the other parts of the plant. Hemicellulose is a heterogeneous polymer of pentoses (xylose and arabinose) primarily xylose, hexoses (mannose, glucose, and galactose), and sugar acids. Although it is not covalently bonded, it is tightly bonded to the surface of each cellulose microfibril. Cellulose digestibility to sugars partially depends on the hemicellulose content. After cellulose and hemicellulose, lignin is the third most abundant biopolymer, consisting primarily of phenylpropane units most commonly linked by ether bonds. It provides structural support and, through its hydrophobic nature impermeability and resistance to microbial and oxidative attack [4, 5]. Additionally, woody plants have

Biochemical Conversion of Biomass to Fuels

26

higher lignin than herbaceous plants, thus imparting lesser strength in the latter due to loosely bound fibers [6]. Lignin also inhibits the conversion of carbohydrates to ethanol making it imperative to maximize the elimination of lignin in biomass. However, woody plants having higher lignin proportions resist moderately severe treatments, unlike herbaceous biomass. Some herbaceous plants like switch grass and miscanthus (Miscanthus) require less severe treatments for lignin removal. Since lignin alone causes inhibition to conversion of sugars and to ethanol, cellulose to lignin ratio is an important factor effecting conversion. Removed lignin can be used for combustion in boilers for energy generation. For dedicated energy crops, cultivation of herbaceous plants is greatly encouraged for biochemical conversion to fuels compared to the woody biomass for several reasons such as, lesser harvest time, ease of harvesting, usage of surplus land, less intensive agricultural practices, less lignin content, and less severe treatment for conversion. Selection of plants for energy production depends on the climatic conditions, geographical location, availability and type of treatment employed (either thermal or biochemical). In the UK, a perennial crop, miscanthus, has attained a lot of attention for energy production through biochemical conversion due to the ease in growing, harvesting, and good annual yield. This thin-stemmed crop has been considered a good energy crop due to its annual harvest and low mineral content, and is grown in ten countries in Europe. In the USA, another thin-stemmed crop, switch grass, is a model crop for the Oak Ridge National Laboratory, as it yields high ethanol from fermentation with the existing technologies. Its low ash and alkali content allow it to be used for combustion. Brazil, one of the pioneers for the production of ethanol for fuel uses sugarcane as the source [2]. Sources of biomass other than herbaceous plants include agricultural residues such as wheat straw, rice straw, corn fiber, corn stover, baggase, etc. Animal residues such as pig slurry [7], cattle dung, horse dung [8], etc., are used for biogas production, which upon upgrading to >97% methane, can be used as transport fuel. Marine algae have gained importance as potential sources for biofuel production, both as substrates for fermentation to hydrogen, ethanol, and butanol, and as oil-rich sources for biodiesel production. Due to their less energy and water requirement, higher carbon dioxide capture and negligible lignin, they are considered as superior to terrestrial biomass [9, 10]. However, several factors including availability, moisture content, and cellulose/lignin ratio impact the biochemical production of biofuels.

Process Overview Major processes involved in the biochemical production of biofuels are biomass handling, biomass pretreatment, hydrolysis, and fermentation. However, depending on the source of biomass, the route of conversion to biofuel and the type of biofuel, the series of processes can alter. > Figure 26.1 shows a schematic representation of some common unit operations and processes for the biofuels mentioned in > section ‘‘Biofuels.’’

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Biochemical Conversion of Biomass to Fuels

Biomass Handling

Size Reduction

Biofuel Recovery

Pretreatment

Hydrolysis

Fermentation

. Fig. 26.1 Schematic representation of processes in biochemical conversion of biomass to fuels

Handling Biomass, either grown or obtained from various sources, needs to be transported to the production sites for biochemical conversion to fuels. Postharvest it is prepared as bales, pellets, and briquettes for which, the biomass has to be size reduced. Size reduction is an important mechanical preprocessing step to increase the bulk density and flowability of particles for transportation. Biomass is generally ground to 3–8 mm particles to compact it into pellets or briquettes of higher density. Important parameters in evaluating the efficiency of size reduction are particle size, particle size distribution, shape, surface area, density, and energy efficiency of mill used [11]. Due to the unavailability of a continuous supply of biomass feedstocks, storage of biomass becomes important to ensure uninterrupted supply for continuous production of biofuels. Although outdoor storing of wood chunks is a commonly practiced method, studies show that terpenes are emitted from wood due to exposure of direct heat from sunlight [12]. Large silos and specially constructed facilities are used for biomass storage to protect feedstock from the effects of weather, rodents, and microbial growth. Microbial growth during storage causes loss of substrate and also has the potential to result in self-ignition due to exothermic reactions. Therefore, it is required to maintain dry conditions to allow little microbial activity in the biomass during storage. Field drying postharvest is a common method for drying in sunny regions. However, thermal or mechanical drying techniques using drum driers are available for drying biomass after harvest and before storage in colder regions [13].

Pretreatment Pretreatment plays an important role in the biochemical conversion yields of biofuels. Complex structures in biomass are broken down into oligomeric subunits through pretreatment. These oligomers are further broken down into monomeric units during hydrolysis and fermentation. Pretreatment enhances the product yields by disrupting and solubilizing the hemicelluloses and lignin structures in biomass. Key properties affecting

Biochemical Conversion of Biomass to Fuels

26

the conversion of lignocellulose are the crystallinity of cellulose, degree of polymerization, moisture content, available surface area, and lignin content [5]. The aim of pretreatment is to disrupt the lignocellulosic structure by: (1) removing hemicellulose, increasing mean pore size, and facilitating the entrance of enzymes and hydrolysis; (2) removing or redistributing lignin to reduce its ‘‘shielding’’ effect [14]. Pretreatment processes will ideally achieve the following [15]: ● ● ● ● ● ● ● ● ● ● ●

High yields for multiple crops, sites ages, harvesting times. Highly digestible pretreated solid. Minimum amount of toxic compounds. Biomass size reduction not required. Operation in reasonable size and moderate cost reactors. Non-production of solid-waste residues. Effective at low moisture content. Obtains high sugar concentration (from hydrolysis). Fermentation compatibility (minimal production of inhibitors). Lignin recovery. Minimum heat and power requirements.

Main Classes of Pretreatment The main classes of pretreatment covered in this chapter are: mechanical, chemical, physiochemical, and biological. Mechanical pretreatment is discussed at this point as it applies to most process trains for biomass conversion. Chemical, physiochemical, and biological pretreatments are described in > section ‘‘Pretreatment,’’ as they pertain most closely to bioethanol production. At that point, characteristics making acid and alkali pretreatments suitable for methane production are also discussed. Mechanical

Milling uses grinding to reduce particle size and crystallinity. Specific surface area is increased and degree of polymerization gets decreased. Numerous milling systems can be employed: ball, hammer, roller, colloid, and vibro energy milling [14, 16]. Coupled with other pretreatment, milling can increase hydrolysis yield for lignocellulose by 5–25% and reduces digestion time by 23–59% [17, 18]. There are limits to effectiveness. Size reduction below #40 mesh does not improve hydrolysis yield or rate [5]. Power requirements are large, which will limit economic feasibility [19]. Chemical (> section ‘‘Pretreatment’’). Acid pretreatment – concentrated and dilute. Alkali pretreatment – NaOH, Ca(OH)2, or ammonia. Physiochemical (> section ‘‘Pretreatment’’). Thermal processes include liquid hot water (LHW) and steam pretreatment.

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Steam explosion. Ammonia explosion (and CO2 explosion). Other physiochemical methods include organosolv and wet oxidation. Biological pretreatment – brown and white soft-rot fungi (> section ‘‘Pretreatment’’). Alvira et al. conclude that chemical and thermochemical methods are the most effective and promising technologies for industrial applications [14]. They suggest combination of different pretreatments should be considered for optimal fractionation of components and high yields. They also stress the need for additional fundamental research plant cells to better understand the reactions induced by pretreatment. Taherzadeh and Karimi [16] concluded that concentrated acids, wet oxidation, solvents, and metal complexes are effective, but too expensive [20, 21]. They concluded that steam pretreatment, lime pretreatment, LHW systems and ammonia-based pretreatments have a high potential. Eggeman and Elander [22] presented an economic evaluation showing only small differences in cost for five different pretreatment technologies (dilute acid, hot water, ammonia fiber explosion (AFEX), ammonia recycle percolation (ARP), and lime). This analysis appears in the special issue ‘‘Coordinated development of leading biomass pretreatment technologies’’ [23]. Optimizing enzyme blends and hydrolysate conditioning may better differentiate process economics.

Hydrolysis and Fermentation During hydrolysis, breaking down of polymeric and oligomeric cellulosic structure, to simpler molecules such as glucose, cellobiose, xylose, galactose, arabinose, and mannose, takes place. It is done by the action of either chemical or enzymatic agents. Enzymatic hydrolysis is a complex process that takes place at the solid/liquid interphase. Several processes such as, chemical and physical changes in the solid biomass, primary hydrolysis of soluble intermediates from the surface, and secondary hydrolysis to ultimately simpler molecules such as glucose, take place simultaneously [24]. More discussion about enzymes used in hydrolysis is provided in > section ‘‘Hydrolysis.’’ Conversion of simpler carbohydrates to alcohol through action of microbes is called as fermentation. Fermentation is both substrate and microbe specific, more details about fermentation are mentioned in > section ‘‘Biofuels’’ for each biofuel, hydrogen, methane, ethanol, butanol, and biodiesel. A combination of hydrolysis and fermentation is another process where simultaneous breaking down of complex carbohydrates to simpler ones and converting to alcohol takes place. This process is commonly called as simultaneous saccharification and fermentation (SSF). Product yields from SSF are higher than separate hydrolysis and fermentation (SHF), as the end product inhibition during hydrolysis of higher carbohydrates to glucose and cellobiose, is relieved by simultaneous fermentation of glucose to ethanol [24]. Hydrolysis and fermentation are carried out in both batch and continuous modes. Batch reactors require higher reactor volume compared to the continuous reactors to

Biochemical Conversion of Biomass to Fuels

26

achieve similar product yields. Two basic types of continuous reactors used in biochemical reactions are continuously stirred tank reactor (CSTR) and plug flow reactor (PFR). Most commonly, CSTR is used for hydrolysis and fermentation during the biochemical production of biofuels. Studies show usage of a packed bed reactor (PBR) in comparison with upflow anaerobic sludge bed (UASB) for the production of hydrogen from organic fraction of municipal solid waste, where the PBR was packed with municipal solid waste. The retention times of 50 and 24 h gave maximum hydrogen yields of 23% v/v and 30% v/v (based on volume of waste) for PBR and UASB respectively [25]. Another study investigated combined or sequential two-stage processes involving coproduction of hydrogen and methane since hydrogen is an intermediate by-product of methane production [26–28]. Dissolved oxygen and heat transfer are known to be limited by reactor volume. Fermentation for hydrogen, methane, ethanol, and butanol production is anaerobic, and the reactor volume is not limited by the dissolved oxygen and heat transfer when run in continuous mode. Therefore, CSTR fermentation systems with recycling of cell mass are sufficient to overcome solvent toxicity and limited cell growth [29].

Biofuels Hydrogen Biohydrogen is considered as a potential biofuel for the future, it is produced from biomass through different routes and their combinations. Gasification of biomass is one of the routes; refer to the chapters on thermal conversion of biomass, integrated gasification for combined cycle (IGCC), and conversion of syngas to fuels in this handbook for more details about the gasification process. Hydrogen is a natural by-product of many microbial processes under anaerobic conditions. Certain microbes release hydrogen from water in the presence of sunlight and/or carbon dioxide. Microbes that derive carbon from carbohydrates and need sunlight as a source of energy to release hydrogen are called phototrophic or photosynthetic organism (e.g., Rhodobacter) and those that derive their carbon from carbon dioxide and energy from sunlight are called photoautotrophic organisms (e.g., green microalgae and cyanobacteria) [30]. Different fermentative processes, based on different sources of energy and their combinations, are anaerobic fermentation, dark fermentation, photo fermentation, direct photolysis, indirect biophotolysis, and fermentative water-gas shift reaction. The majority of these processes combine microbiological routes led by several microbes. Anaerobic fermentation is a four-stage process carried out by a consortium of microbes. In the first stage, the complex organic components are converted to simpler components (e.g., sugars) by hydrolysis. In the second stage, the products of hydrolysis are further broken down to short-chain fatty acids by acidogenic bacteria. During the third stage, acidogenesis, the products of second stage are converted to acetic acid, hydrogen, and carbon dioxide. In the final stage, methanogenesis, the products from the third stage are used by the methanogenic bacteria to produce methane. Thus, hydrogen in this

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Biochemical Conversion of Biomass to Fuels CH4

Acetate Methanogenesis H2

Syntrophic oxydation

CO2 Acetate

Fermentation productions

CO2

Anaerobic digestion

H2

H2 ADP

Acetate NADH

NADH Ethanol

ATP ADP

Butanol Butyrate etc.

Ethanol

ATP ADP

EchH2ase

Acetyl-CoA

H2

CO2

H2

FdH2ase

H2

NADHH2ase

Fd

Reverse e− transport

Organic acids

ATP

Photofermentation

CO2

ATP

ATP

ADP

ADP

NADH

H2

Power supply

e−

e−

Sugars Enterobacteracae

Dark fermentation 1st stage

Energy Crops

Cathode

Carbohydrate rich substrates

H+

Anode

Agro/food Forestry Wastes

e−

H+

Substrate

Clostridia

N2ase

Formate Pyruvate

NADH

e−

Bacteria

MEC 2nd stage TRENDS in Biotechnology

. Fig. 26.2 Different two-stage routes for conversion to hydrogen and methane [31]

process is an intermediate product, and its production can be increased by increasing the substrate content in the raw material used. > Figure 26.2 represents three different two-stage routes that are under active investigation. In the first stage, optimized technologies of above mentioned conventional methods are used to convert biomass to organic acids and hydrogen. In the second stage, additional energy such as light, electricity, and methane and hydrogen from the first stage are used for achieving stoichiometric conversions. Although this combination

Biochemical Conversion of Biomass to Fuels

26

of two stages produces a mixture of methane and hydrogen, the process can be developed to achieve hydrogen stream. Dark fermentation is carried out by the anaerobes that convert biomass substrate to hydrogen under the absence of light and is shown in > Fig. 26.2. This process is similar to the first three stages of anaerobic fermentation where the initial raw substrate is simpler carbohydrate. For a complex substrate, hydrolysis such as a chemical/physical pretreatment of biomass is required to break down the complex polymeric biomass substrate to simpler monomeric and oligomeric carbohydrates, which can be later converted to organic acid, carbon dioxide, and hydrogen by anaerobes during dark fermentation. Reaction (> 26.1) represents a general formula for hydrogen metabolism from glucose. It is evident that in the presence of hydrogenase enzyme, 4 moles of hydrogen are released for every 1 mole of glucose. Thermophilic bacteria, that grow at high temperatures (above 60
C) ferment biomass, produce hydrogen at higher rates than the mesophilic bacteria that grow at moderate temperatures (below 50
C), due to aseptic conditions maintained at high temperatures. Additionally, hydrogen production depends on the other by-product organic acids present in the effluent. Acetic acid and other organic acids have an inhibitory effect on the growth of microbes, consequently influencing hydrogen yield. Besides its inhibitory effect, acetic acid influences the pH of the system, thus affecting the activity of hydrogenase enzyme responsible for the production of hydrogen. C6 H12 O6 þ2H2 O ! 2CH3 COOH þ 2CO2 þ4H2

(26.1)

Photo fermentation involves series of biochemical reactions such as anaerobic digestion. However, unlike dark fermentation, it requires light for energy during the process of hydrogen production. Simple, short-chain fatty acids are converted to carbon dioxide and hydrogen catalyzed by nitrogenase enzyme in the absence of nitrogen by purple nonsulfur bacteria or green micro algae. Reaction (> 26.2) describes the conversion process. Theoretically, 4 moles of hydrogen are produced for every mole of acetic acid but, in practice, part of the acetic acid is used for the production of cells. Moreover, large surface area is required to capture the necessary light energy, making it practically challenging in terms of bioreactor design. Transparent tubular reactors and flat panel reactors consisting of transparent rectangular boxes are under investigation [30]. CH3 COOH þ 2H2 O þ light energy ! 4H2 þ 2CO2

(26.2)

Combination of the above mentioned fermentations enhances the yield of hydrogen production. One such combination is dark fermentation and anaerobic digestion in which the monomeric components of the polymeric biomass are converted to biohydrogen. Dark fermentation and photo fermentation is another combination process that theoretically yields 12 moles of hydrogen for every mole of hexose sugar. This approach, called ‘‘Hyvolution,’’ would allow complete digestion of biomass, enhancing small-scale, costeffective production of hydrogen, which otherwise is limited by thermodynamic considerations [30]. Another approach mentioned in the second stage (lower right of > Fig. 26.2) employs microbial electrohydrogenesis cells (MECs). In this method, electricity is applied to

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a microbial fuel cell that provides the necessary energy to convert the by-products (typically organic acids) of the first stage into hydrogen [31]. Several raw materials such as kitchen waste, animal waste, agricultural residues, etc., are used as substrates for biohydrogen production. Fermentation of kitchen waste devoid of plastic and bones was used to produce hydrogen with a maximum efficiency of 4.77 LH2/(L reactor day) in a continuous stirred tank reactor [32]. Use of second-generation feedstocks that are of cellulose origin such as corn stalks, wheat straw, switch grass, and miscanthus further enhance economical production of hydrogen. Pretreated lipid extracted microalgal biomass residue (LMBR) showed threefold hydrogen yields compared to the untreated LMBR [33]. However, noncellulosic components such as xylose require conversion by a fermentative organism. High-thermophilic mixed culture was developed for xylose fermenting to biohydrogen at 1.36  0.03 mol H2/mol xylose consumed [34]. Organisms belonging to genus Clostridium such as Clostridium butyricum, C. acetobutylicum, C. saccharoperbutylacetonicum, and C. pasteurianum are often used in the anaerobic production of hydrogen. Anaerobic thermophilic bacterial fermentation to hydrogen is the most suitable option due to increasing chemical and enzymatic reaction rates at high temperatures. Additionally, thermophilic processes yield lesser undesirable products as compared to mesophilic processes [35]. An optimized fermentation of hydrolysate, obtained from treating sugarcane bagasse with 0.5% H2SO4 under 121
C and 1.5 kg/cm2 in autoclave for 60 min was obtained at initial pH 5.5 and initial total sugar concentration of 20 g/L at 37
C [36]. Thus, initial pH and total sugar concentration are important factors for an optimal hydrogen yield. However, an increase in hydrolysate (sugar) concentrations from 25% (v/v) to 30% (v/v) led to no hydrogen production. Further, an increase in lag time was observed from 11 to 38 h for an increase in hydrolysate concentrations from 20% (v/v) to 25% (v/v) for a mixed thermophilic dark fermentation process [37]. Supplemental glucose and xylose with a ratio of 2:3 along with suitable pH control and inoculum concentration are realized to be the key factors for enhanced hydrogen production [38]. Finally, biophotolysis is a low productivity method for hydrogen gas production. It involves dissociation of water by solar energy using green micro algae. The process takes place in two ways, direct biophotolysis and indirect biophotolysis. In direct biophotolysis, the microbes split the water into oxygen and hydrogen using sunlight by releasing two photons, which can either reduce carbon dioxide or form hydrogen in the presence of hydrogenase enzyme. However the released oxygen has an inhibitory effect on the hydrogenase enzyme which can be overcome by indirect biophotolysis. Indirect biophotolysis is carried out by cyanobacteria, in which water and carbon dioxide form carbohydrates and oxygen via photosynthesis. The second stage involves either dark fermentation or a combination of dark and photo fermentation to produce hydrogen. Fermentative water-gas shift reaction is another biological route in which carbon monoxide in the presence of water is converted to carbon dioxide and hydrogen [30].

Biochemical Conversion of Biomass to Fuels

26

Methane Methane is the main component of natural gas which is used as an energy carrier and raw material all over the world [39]. Biogas produced from anaerobic digestion of biomass contains methane which can be used for energy purposes. The biochemical conversion of manure and other biomass to methane involves three stages. In the first stage, hydrolysis, enzymes produced by strict anaerobes such as Clostridia, Bactericides, and Streptococci, break up the complex molecules such as lipids, polysaccharides, proteins, fats, nucleic acids, etc., to simpler molecules such as monosaccharides, amino acids, fatty acids, etc. In the second stage, acidogenesis, a group of bacteria ferment the by-products of hydrolysis to acetic acid, propionic acid, and butyric acid. In the third stage, methanogenesis, methanogens convert the acetic acid, hydrogen, and carbon dioxide into methane and carbon dioxide. > Figure 26.3 shows a block diagram of biogas production from manure. Biogas production is greatly affected by temperature. Anaerobic fermentation is effective mostly at mesophilic (15–40
C) and thermophilic (50–60
C) temperature ranges. Therefore, the reactors are coated with biomass residues such as charcoal and even constructed in a sunfacing direction to avoid cold winds and make maximum use of heat available from nature [40]. Reactors have been designed to have a polythene sheet covering the top of it to utilize the energy from sun to heat up the reactor contents even during winter [41]. As acetic acid and hydrogen produced during the process decrease the pH of the system, pH maintenance is another important parameter affecting the methane production, the desired pH being 6.8–7.2. Several techniques are involved in enhancing the production of biogas, such as, addition of organic and inorganic additives, microbial strains, recycling of digested slurry, and maintaining C:N ratio. Additives, such as powdered green leaves, allow adsorption of substrate to increase localized concentration and enhance microbial growth. Addition of Ca and Mg salts act as microbial energy

Gas handling

Manure source and collection

Manure handling

Digester

Gas utilization: Electricity generation and/or heat

Manure handling

Manure storage

Land application

. Fig. 26.3 Block diagram of biogas production from manure (Source: http://pubs.ext.vt.edu/442/ 442-881/442-881.html)

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supplements and avoid foaming. Recycling of slurry avoids loss of active culture which otherwise occurs through the effluent stream. As the microbes tend to utilize carbon 25–30 times faster than nitrogen for the production of methane, maintaining C:N ratio is another critical factor in efficient production of biogas [42]. Biomethane can be distributed into the natural gas grid. In the case of existing pipelines in UK, Italy, and Germany, this concept is called the ‘‘green gas concept’’ [43]. However, to employ biogas as a transportation fuel, concentration of biogas to 97  1% of methane by removing the carbon dioxide is required [44]. About 30–60% of the wet biomass can be converted to methane by anaerobic digestion, while the remaining residue can be used as biofertilizer [43]. Coproduction of methane and hydrogen using a twostage anaerobic digestion process is another way to optimize simultaneous production of methane and hydrogen [27]. An energy input approximating 22% of the fuel value is utilized in the production of biomethane, compared to approximately 57% in the production of bioethanol [44]. The majority of the difference arises from the thermal energy consumption involved in the distillation of ethanol and drying of the residue obtained from fermentation. Thus methane’s gaseous nature has an added advantage over liquid biofuels. However, biomethane losses during digestion and upgrading constitute about 7.41% of total biogas produced. Minimizing these losses and improving infrastructure efficiency for biomethane is needed to enhance the utility of methane relative to ethanol [44].

Ethanol Ethanol is the most extensively studied biofuel to date and has gained great attention as sustainable biofuel. Bioethanol production and utilization is estimated to reduce green house gas emissions, improve agricultural economy, enhance rural employment, and increase national security [45]. Bioethanol has higher octane number, broader flammability limits, higher flame speeds, and higher heats of vaporization than gasoline, which allow for higher compression ratio, shorter burn time, and leaner burn engine. A major problem with ethanol is its water solubility and azeotropic mixture formation with water, limiting separation during distillation, consequently intensifying the cost of the separation process. Other major disadvantages include, lower energy density than gasoline, low vapor pressure (making cold starts difficult), and toxicity to ecosystems [24]. However, ethanol is a 35% oxygenated fuel and reduces particulate and NOx emissions. It increases combustion efficiency as it provides a reasonable antiknocking value. It can be blended with gasoline in various amounts, ranging from 5% to 85–100%, for use in the existing internal combustion engines, where 85% (E85, meaning 85% ethanol in gasoline) blends are used in flexible fuel vehicles (FFVs). > Table 26.2 shows various blends of ethanol in gasoline used in different countries worldwide. In pure ethanol cars, sulfur emissions have totally disappeared, gasoline-driven cars with ethanol replacing lead have negligible carbon monoxide emissions [46].

Biochemical Conversion of Biomass to Fuels

26

. Table 26.2 Common gasoline ethanol blends available in various countries [24] Common vehicles

Flexible fuel vehicles (FFVs)

USA

E10

E85

Canada Sweden India Australia

E10 E5 E5 E10

E85 E85 – –

Thailand China Columbia Peru

E10 E10 E10 E10

– – – –

Paraguay Brazil

E7 E20, E25

– Any blend available

Substrates used for the production of bioethanol vary with the availability of feedstock and geographical location. The USA and Brazil are the two major bioethanol producers in the world. Sugarcane and cane molasses are the substrates for the ethanol production in Brazil as is cornstarch in the USA [47]. Other substrates used are cassava, sugar beet, wheat, etc. However, use of food products like corn and cassava for ethanol production has an inflating effect on the prices of these staple crops and an effect on their supply. Additionally, storage of high concentration sugar substrates is liable to microbial contamination and requires sophisticated storage methods, such as refrigeration, which in turn requires energy use over long periods [48]. Work by Dodic et al. suggests use of intermediate products such as thick juice in sugar beet production as substrates for ethanol production, in order to reduce storage volume and microbial contamination. Use of lignocellulosic materials such as switch grass, miscanthus, sorghum, and corn stover is highly encouraged due to high substrate availability, economic feasibility of production and storage, and due to other reasons mentioned in > section ‘‘Sources’’ of this chapter. Waste mushroom logs have been studied for their potential as substrates for ethanol production where 12 g/L ethanol concentration was obtained as against 8 g/L concentration for normal logs [49]. Mahua flowers were investigated for their potential as substrates for ethanol fermentation, with ethanol productivity of 3.13 g/kg flower/h at 77.1% efficiency [50]. Lignocellulosic biomass consists of majorly cellulose, hemicelluloses, and lignin of which cellulose is the most desired component for ethanol production. Ethanol is produced from the sugars that are present in the cellulose in polymeric form. Biomass is initially preprocessed, such as size reduced and washed for ease of handling and removal of soil. As shown in > Fig. 26.4, the first major stage requires release of sugars from the cellulose–hemicellulose–lignin matrix; the second major stage involves hydrolysis of higher sugars and fermentation of the monomeric sugars to ethanol; and the third stage involves separation of ethanol from the fermentation broth.

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Size Reduction

Pretreatment

Enzyme Production

Lignin to the burners

Enzymatic hydrolysis of cellulose

Residual solids processing

Fermentation Ethanol Recovery

. Fig. 26.4 Cellulosic ethanol ‘‘sugar platform’’

Pretreatment Pretreatments for bioethanol production may be performed using chemicals such as sulfuric acid, sodium hydroxide, ammonium hydroxide, supercritical ammonia, and supercritical carbon dioxide at both high and low temperature and pressure conditions to separate undesirable components such as lignin from biomass. Pretreatment disrupts the biomass structure and increases the surface area to enhance enzyme access during the hydrolysis stage. Several pretreatment methods such as hot water treatment, steam explosion, dilute sulfuric acid treatment, and ammonia fiber expansion can be employed to remove lignin and/or depolymerize lignocelluloses structure in biomass. Thermal processes include liquid hot water (LHW) and steam pretreatment. At temperatures above 150–180
C, hemicellulose and then lignin begin to dissolve [51, 52]. Hot water pretreatment primarily dissolves hemicellulose to increase access for enzyme hydrolysis and to limit formation of inhibitors [21]. Liquid hot water has removed up to 80% of the hemicellulose to improve enzymatic hydrolysis by increasing the accessible surface area of the cellulose [21, 53]. pH should be kept between 4 and 7 to maintain hemicellulosic sugars in oligomeric, reducing formation of degradation products and thus inhibitors [21]. Hemicellulose can be hydrolyzed to form acids which further hydrolyze the hemicelluloses [54]. The main advantages for LHW are recovery of pentoses, minimization of inhibitors, compared to steam explosions and minimal need for chemical and neutralization as compared to dilute acid pretreatment [16]. Hot water pretreatment of lignocellulosic biomass has three types of reactor configurations, cocurrent, counter current, and flow through. In co-current pretreatment, biomass and water are heated to a desired temperature and held in the reactor for a controlled residence time before cooling. In counter current flow system, biomass slurry and water are allowed to flow in opposite directions into the reactor. In flow through configuration, hot water is allowed to flow through a stationary bed of biomass [55]. Therefore, pretreatment

Biochemical Conversion of Biomass to Fuels

26

technologies have been developed to be carried out in both batch and continuous flow reactor configurations. Steam explosion has been widely tested in lab and pilot-scale systems. Biomass is pressurized with steam at 160–260
C for several seconds to minutes and pressure is rapidly released. Mechanical forces separate fibers and the high temperature promotes conversion of acetyl groups to acetic acid [14, 16]. The main action of the acetic acid is probably to catalyze the hydrolysis of soluble hemicellulose oligomers [56]. Lignin is redistributed and some removed [57]. Removing hemicellulose increases accessibility of enzymes to the cellulose [14]. The advantages of steam explosion include use of larger chip size, reduced need for acid catalyst, high sugar recovery, and feasibility for industrial-scale use [14]. The primary disadvantages include partial hemicellulose degradation and generation of inhibitory compounds [58]. Steam explosion can be combined with addition of sulfur dioxide and sulfuric acid to enhance recovery of cellulose and hemicellulose. It improves the solubilization of hemicelluloses, lowers optimal treatment temperatures, and partially hydrolyzes cellulose [59, 60]. Acid addition is particularly effective with softwoods, which have a low content of acetyl groups [61]. Acid pretreatment removes hemicellulose to make cellulose more accessible. It can also hydrolyze fermentable sugars. Acid pretreatment can be practiced using high concentrations of acid (generally sulfuric) at low temperatures or low concentrations at high temperatures [16]. Use of concentrated acid requires corrosion resistant process equipment. Recovery of the acid is energy intensive, and produces degradation products inhibitory to fermentation [14, 16, 62]. Use of dilute acid is more promising, for example at 0.1–1% sulfuric acid at 140–190
C. This achieves almost total hemicellulose removal and high cellulose conversion [16]. Production of inhibitory compounds is lessened [19]. Addition of nitric acid greatly improves solubilization of lignin in newspaper [63]. The use of acid pretreatment for methane production is more forgiving because methanogens can tolerate the inhibitory compounds [63, 64]. Alkali pretreatment uses NaOH, Ca(OH)2, or ammonia. Lime is very effective [19]. It removes acetyl groups, has lower cost and less safety concerns. Solvation and saponification reactions [19] lead to swelling. The swelling increases internal surface area of cellulose, decreases polymerization and crystallinity, and disrupts lignin structure and removes some lignin and hemicellulose [16], increasing accessibility to enzymes enhancing saccharification [65]. Processing can be done at low (ambient) temperature [66] for long time periods (24 h), or at elevated (120–130
C) levels for minutes to a hours [67]. Production of inhibitory compounds is significantly less [16]. But, solubilization and redistribution of lignin and modifications in crystalline state of lignin can counteract the benefits of the method [54]. Addition of hydrogen peroxide to alkaline pretreatment enhances lignin removal and improves enzymatic hydrolysis [68]. Alkaline pretreatment, as with acid, is more forgiving for production of methane versus ethanol [69]. Ammonia fiber explosion or ‘‘expansion’’ (AFEX) is analogous to the steam expansion method. Anhydrous ammonia is added to biomass at approximately 1 kg NH3: 1 kg dry, and held at temperatures of approximately 100–120
C for several minutes. Pressure is rapidly released, swelling and disrupting the lignocellulose structure [14, 16]. Only a solid

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Biochemical Conversion of Biomass to Fuels

residue is produced and little hemicellulose and lignin are removed [23]. Enzyme hydrolysis yields and ethanol production are increased [70]. AFEX does not produce inhibitors, although some lignin may remain on the biomass surface [14]. It is more effective on lower-lignin crop residues and herbaceous crops than woody material [23]. CO2 explosion uses CO2 at high pressure to penetrate the pores of lignocellulose. Explosive depressurization disrupts the cellulose and hemicellulose structure and improves enzymatic hydrolysis. Supercritical conditions at 35
C and 73 bar remove lignin and increase digestibility more effectively [14]. However, pretreatment with appropriate conditions is a highly desirable step for lignocellulosic biomass to improve its digestibility. Other physiochemical methods include organosolv and wet oxidation. Organosolv uses organic solvents to dissolve lignin. Solvent recovery is essential, and inexpensive, low molecular weight alcohols are favored. The recovery of low molecular weight lignin as a coproduct is potentially a significant advantage [57]. Wet oxidation uses water and oxygen under elevated pressure and temperature [16]. Hydrogen peroxide can be used at ambient temperature can also be used to enhance enzymatic hydrolysis [71]. Batch treatment of corn stover using FeCl3 in tubular reactors resulted in the hydrolysis yield of 98% compared to 22.8% yield for the untreated corn stover [72]. Biological pretreatment primarily uses brown and white soft-rot fungi that degrade lignin and hemicelluloses [16]. White rot fungi in particular have been evaluated and several shown to have high delignification efficiency [73]. Increase in total sugar yields during hydrolysis has been reported for switch grass preprocessed with Phanerochaete chrysosporium for 7 days [74]. Advantages include low energy and chemical requirements and ambient conditions. However, hydrolysis rates after biological pretreatment are low, and more research is needed [14].

Hydrolysis Hydrolysis of the pretreated biomass can be performed both chemically and biochemically. Chemical hydrolysis uses a continuous two-step dilute sulfuric acid process. The first step involves low temperature treatment and the second step, a high temperature treatment, as hemicellulose depolymerizes at lower temperature than the cellulose polymer. In the first step, the hemicellulosic fraction is removed, followed by the second step in which hexose release occurs. A batch process, using concentrated sulfuric acid, is also used for biomass hydrolysis; however, use of concentrated acid requires high capital investment due to the requirement of corrosive resistant process equipment. Additionally, it requires acid recycling and recovery for economic viability of the process [24]. Biochemical hydrolysis is the most sought out process in recent years and is commonly called as saccharification. It is initiated by enzymes that cleave the cellulose–lignin matrix into various monomeric, dimeric, and oligomeric sugars. Most common enzymes that act synergistically for cellulose hydrolysis, called cellulases, are endoglucanases or endo-1,4-bglucanases (EG), exoglucanases or cellobiohydrolases (CBH), and b-glucosidases (BGL). While endoglucanases cleave the intramolecular bonds of the cellulose polymer, CBH and

Biochemical Conversion of Biomass to Fuels

26

BGL catalyze the release of cellobiose and glucose from oligomeric ends, and glucose from cellobiose respectively as shown in the > Fig. 26.5. A synergistic effect of an enzyme component system consisting of at least endo-b-glucanases, exo-b-glucanases, and b-glucosidases results in hydrolytic efficiency [61, 75]. Enzymes related to hemicellulose hydrolysis, hemicellulases, are majorly endo-1,4- bxylanase, b-xylosidase, a-glucuronidase, a-L-arabinofuranosidase, and acetylylan esterase as shown in > Fig. 26.6. Therefore, the hydrolysate contains both hexoses and pentoses and their oligomeric forms depending on the treatment [76]. Various bacteria such as Clostridium, Cellulomonas, Bacillus, Thermomonospora, Ruminococcus, Bacteriodes, Erwinia, Acetovibrio, Microbispora, and Streptomyces produce these enzymes to hydrolyze lignocelluloses. Fungi such as Trichoderma, Ceriporiopsis, Aspergillus, and Sporotrichum also possess the cellulolytic abilities to hydrolyze lignocellulosic biomass. Therefore, enzyme extracts from these cultures are used for hydrolyzing biomass and recent developments in enzyme technology have reduced their price of production significantly. The factors that influence the enzymatic hydrolysis are mainly temperature, pH, and substrate concentration. At low substrate concentration, increase in substrate concentration increases the yield and reaction rate of hydrolysis. However, at high substrate concentration, yield and reaction rate decrease due to substrate inhibition of enzymes [61, 62]. Temperature and pH for enzyme activity varies by the microbe source from which it is derived. However, most commonly used industrial cellulases are derived from wild and modified strains of Trichoderma reesei and have an optimum temperature between 45
C and 50
C. Hydrolysis yields are also increased by addition of surfactants such as Tween-20. It is reported that addition of Tween-20 resulted in 8% increase in ethanol and 50% reduction in cellulases dosage, increase in enzyme activity and the hydrolysis rate [77]. Consolidated microbial treatment of biomass is another method of saccharification of biomass. Loss of sugars during the process is inevitable, due to the consumption by microbes, which makes the use of enzyme extracts advantageous for hydrolysis. Enzyme hydrolysis is limited by-product inhibition, which requires continuous removal of hydrolysis products apart from use of BGL for subsequent conversion of the generated cellobiose to glucose. Therefore, simultaneous saccharification and fermentation (SSF) is a potential solution for product inhibition, where release of glucose using enzyme hydrolysis and its subsequent fermentation to ethanol by yeast take place in the same system [24].

Fermentation Fermentation of biomass to ethanol is commonly carried out using yeast such as Saccharomyces and Pichia, bacteria such as Zymomonas and Escherichia, and fungi such as Aspergillus. Products of hydrolysis and sugars are converted to ethanol producing carbon dioxide as by-product and energy for cell growth. The most commonly used microbe

983

OH

H

H

H

OH

H

O

H

O

H

O

H

H

OH

H H

OH

H

O

CH2OH

cellobiohydrolase

H

OH

CH2OH

H

OH

H O H O

H

H

OH

CH2OH

H

OH

H

O

H

H

OH

H H OH

H

O

CH2OH O H O

H

H

H

OH

CH2OH

H

OH

H

OH

H

O

H

H

OH

H

O

H

O

H

H

H

OH

CH2OH

H

OH

H

OH

H

CH2OH

H

OH

H

O

b-glucosidase

H H

H

OH

H

OH

H

O

CH2OH

O

H

O

CH2OH

. Fig. 26.5 Molecular structure of cellulose and site of action of endoglucanase, cellobiohydrolase, and b-glucosidase [76]

H

O

CH2OH

O

26

endo-b-glucanase

984 Biochemical Conversion of Biomass to Fuels

OH

H

H

H

OH

H

O

H

O

O

H

H

OH

H

H

H

H

OH

H

O

b-xylosidase

OH

H

H

O

H

H

H

H

OH

OH

H

H

O

H

O

H

H

OH

H

OH

H

H

H

OH

H

O O H H

H

OH

H

O

H

H

OH

HO H

O

OH

H

OH

H

H

OH

H

HO O

H

O

H OH

H

O O H H

H

OH

H

O

H

H

O

HOH2C

H

OH

a-glucuronidase

H O

H

H

O

H

O

H

O H

H

H

OH

H

O

H

H

OH

a-arabinofuranosidase

OH

H

OH

H

OH

H

H

. Fig. 26.6 Polymeric chemical structure of hemicellulose and targets of hydrolytic enzymes involved in hemicellulosic polymer degradation [76]

H

H

endo-b-xylanase

H

COOH

O

Biochemical Conversion of Biomass to Fuels

26 985

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26

Biochemical Conversion of Biomass to Fuels

H2O 2 x ADP 2 x ATP 2 x D-Glyceraldehyde 3-phosphate H2 2−O P OH 3 C H O PO43− O NAD+ NADH

Pyruvic Acid O

H3C

COOH

CO2 OH HO

OH

H3C

OH

HO

Enzyme (Pyruvate Decarboxylase)

H

O

HOCH2 Glucose

Ethanol H3C

NAD+ OH C H2

NADH H3C

O H

Acetaldehyde

. Fig. 26.7 Ethanol fermentation pathway of Saccharomyces

Saccharomyces cerevisiae ferments sugars to ethanol at almost anaerobic conditions, although it requires a certain amount of oxygen for essential poly-unsaturated fats and lipids. > Figure 26.7 depicts the ethanol fermentation pathway of Saccharomyces from glucose. It briefly describes the conversion of glucose to ethanol through intermediate biochemical reactions involving NAD+ and NADH (Nicotinamide adenine dinucleotide – oxidized and reduced forms respectively). Since, lignocellulosic biomass consists of several components such as pentoses, hexoses, acids (acetic acid), degradation products derived from the pretreatment stage could inhibit the fermentation process. Chemical, physical, and biological methods have been developed to overcome the inhibition effect of these compounds by detoxification. Trichoderma reesei has been reported to degrade the inhibitors present in willow hydrolysate after steam pretreatment. Overnight extraction of spruce hydrolysate with diethyl ether at pH 2 showed detoxification effects with ethanol yields comparable to the reference fermentation. Detoxification by alkali treatment at pH 9 using Ca(OH)2 and readjustment of pH to 5.5 allowed better fermentability due to precipitation of toxic compounds [78]. Usually, the temperature of operation is in the mesophilic range (15–40
C) for most of the species mentioned above. Increases in temperature beyond the optimum condition result in a decrease in ethanol yield and eventually in cell death. Another important factor

Biochemical Conversion of Biomass to Fuels

26

in maintaining good cell growth is pH, generally a pH range of 6.5–7.5 [79] is suitable for ethanol fermentation for most of the strains, although, yeast and fungal strains can tolerate up to 3.5–5.0. pH below 4.0 reduces the potential of bacterial contamination thus alleviating the requirement of severe aseptic techniques [24]. Fermentation of biomass is affected by several other factors such as ethanol tolerance, substrate concentration, and by-product inhibition. Ethanol tolerance is one of the factors which determine the maximum ethanol concentration that can be reached during fermentation, as most of the microbes responsible for fermentation cannot tolerate high concentrations of ethanol, eventually leading to cell death. Zymomonas has higher ethanol tolerance, and achieves 5% higher ethanol yields, as compared to the other yeast strains [80]. Increase in substrate concentration decreased the ethanol yield. However, batch-wise charging of substrate reduces this kind of inhibition. Therefore, fed-batch reactors are more suitable for industrial applications. By-product inhibition is overcome by chemical, mechanical, or biological detoxification as mentioned above [24].

Butanol Butanol is a colorless liquid which causes a narcotic effect at high concentrations. It is used as a solvent in biopharmaceutical, chemical, and cosmetic applications because of its high solubility in organic solvents and low water miscibility. Its physical properties very closely resemble those of gasoline, making it a potential additive in partial or complete to transportation fuel [1]. Butanol can also be used as a replacement fuel to gasolinedriven engines with minimum or no changes; it can also be blended with gasoline at much higher composition than ethanol as butanol has similar energy content as that of gasoline. It can be added to gasoline at the refinery and distributed through existing gasoline pipeline unlike ethanol, as butanol is less corrosive and does not absorb water [81]. Butanol, a four carbon primary alcohol, can be synthesized both chemically and biochemically, chemical synthesis of butanol is conducted majorly by three methods, namely, Oxo synthesis, Reppe synthesis, and crotonaldehyde hydrogenation. However, the discussion of this chapter is limited to biochemical conversion of biomass to butanol. In biochemical route, butanol is a fermentation product of anaerobic bacteria Clostridium acetobutyliticum, Clostridium butyricum, etc. Industrial production of butanol dates back to 1914 during World War Ι, as a by-product in the production of acetone (which was used in war ammunition) by fermentation using C. acetobutyliticum. Although there was no immediate application of butanol during that time, later in 1920s in the USA, it was used to replace amyl acetate, a product from amyl alcohol, a solvent for lacquers in the automobile industry. By the 1950s, 66% of the butanol used in the world was produced biochemically. However, due to increased biomass cost and low crude oil prices, crude oil replaced butanol as a transportation fuel [82]. Substrates used for butanol production can be of both starch and cellulose origin such as molasses, corn fiber, wheat straw, etc. However, the conflict of using food substrates for fuel production

987

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Biochemical Conversion of Biomass to Fuels

regulates the usage of starch-based substrates. > Figure 26.4, which depicts the flow of processes for ethanol, can also be applied for butanol. However, fermentation of biomass is carried out by butanol producing bacteria. The biochemical routes involved in butanol formation are given in > Fig. 26.8 [1]. Butanol formation takes place through the glucose–pyruvate–butyraldehyde route. Butanol fermentation is a biphasic transformation consisting of an acidogenic phase which occurs during exponential growth phase and solventogenic phase. During the acidogenic phase, acid-forming pathways are activated, and acetate, butyrate, hydrogen, and carbon dioxide are produced as major products. Acetone, butanol, and ethanol/propanol are the products of solventogenic phase which occurs after the exponential growth phase [1]. Both acidogenic and solventogenic phases can be seen in the > Fig. 26.8 based on the final products produced in the two phases. The solventogenic phase is a response to the increased acid production after acidogenic phase, which if not initiated, would lead to

Glucose ATP

NADH CO2

2[H]

Pyruvate 2-Acetolactate

Lactate

H2

CO2 2[H]

Acetoin CO2

Acetyl-CoA Acetylphosphate

Acetaldehyde Acetyl-CoA

Acetate

2[H] ATP

Ethanol

Acetoacetyl-CoA 2[H]

Acetoacetate Acetone CO2

3-Hydroxybutyryl-CoA H2O Crotonyl-CoA 2[H] Butyryl-CoA Butyraldehyde

Butyrylphosphate NADH

Butyrate ATP

Butanol NADH

. Fig. 26.8 Butanol fermentation pathway of Clostridium acetobutylicum [81]

Biochemical Conversion of Biomass to Fuels

26

a decrease in the extracellular pH, and finally to cell death due to increasing proton gradient between inner and outer cellular environments [81]. Therefore, pH control has a very crucial effect on butanol production, and it requires being in the acidic range for the solventogenic phase. Solvent toxicity is another major concern that causes cell death, due to cell wall weakening in the presence of acetone, ethanol, and butanol (the most toxic compound), leading to low product concentrations and productivity [1]. Solvent toxicity can be overcome by continuous removal of the solvents through various unit operations. Traditionally, butanol formed is separated by distillation which is a cost-intensive operation due to its high boiling point. Alternative methods for butanol separation are adsorption, gas stripping, liquid–liquid extraction, perstraption, pervaporation, and reverse osmosis [82]. Each of these processes has certain limitations, among which, gas stripping is simple and successful in spite of low selectivity, as it can be used in a continuous operation for removing butanol. Liquid–liquid extraction requires use of a solvent that is noninhibitory to the microbes. In pervaporation, butanol is selectively diffused through a membrane and evaporated without removing the medium components necessary for the microbial growth [83]. However, it is limited by fouling of membranes by the particles present in the fermentation broth.

Biodiesel Biodiesel is a biofuel derived from transesterification of fats and oils with properties similar to the petroleum diesel. It can be blended with diesel or used directly in the existing diesel engines without significant modifications. The main advantage of biodiesel is that, as a biomass-derived fuel, it produces 78% less (net) carbon dioxide emissions, compared with that for petroleum-derived diesel fuel. Because its structure is nonaromatic, it combusts more efficiently, producing 46.7% less carbon monoxide emissions, 66.7% less particulate emissions, and 45.2% less unburned hydrocarbons compared to conventional diesel. Therefore, it can be used in highly sensitive environments such as marine and mining environments [84]. Additionally, its high boiling point (about 150
C) and presence of fatty acids impart lesser volatility and higher lubricating effect respectively, on engines, eventually reducing wear and tear and enhancing longer service life [85]. Biodiesel is conventionally produced from transesterification of oil (triglycerides) with alcohol (methanol) in the presence of an acid, base, or enzyme catalyst with glycerin as byproduct as shown in > Fig. 26.9. The sources of oil include oil seed plants such as palm, rapeseed, soybean, castor, and jatropha, used oils, lard, animal fat residue, etc. Palm oil having the highest yield of around 4,000 kg of oil per hectare is considered to be the best source of oil for biodiesel production [85]. However, the majority of the cost involved in biodiesel production arises from the cost of the feedstock oil. Further, with the increasing edible oil consumption, it is more economical and environmentally sustainable to employ used oils and nonedible oils

989

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Biochemical Conversion of Biomass to Fuels

Ester group

R1

O

H

C

O C

O H

+

H

O

CH3

O R2

C

R1

H

+

H

O

CH3

R2

O R3

C

O CH3

H

O C

H

H

O C

H

H

O C

H

O

Catalyst Na+ O C

C

H

C

O CH3

+

O O C

H

+

H

O

CH3

R3

C

O CH3

H Triglyceride

H Methanol

Fatty Acid Methyl Ester

Glycerol

. Fig. 26.9 Formation of biodiesel (Fatty acid methyl ester)

for biodiesel production. The major differences between the fresh and used oils are the moisture and free fatty acid (FFA) content, with used oils having high moisture and FFA content, which affect the acid- and alkaline-catalyzed transesterification respectively. Alternatively, animal fats from waste residues are a useful source of oils. However, the heat at their high melting points denatures the enzymes used during enzyme-catalyzed transesterification. Other sources of oil are oleaginous yeasts and filamentous fungi which on their outer surface secrete oil [86]. As mentioned earlier, biodiesel production process can be alkali, acid, or enzyme catalyzed depending on the amount of FFAs and moisture present in the oil feedstock. The stoichiometry from > Fig. 26.9 suggests oil to methanol ratio to be 1:3. However, for equilibrium to proceed toward the formation of biodiesel, use of excess alcohol is suggested. During an alkali-catalyzed reaction, the oils in the presence of excess methanol are converted to fatty acid methyl esters and glycerin (> Fig. 26.10). Alternately, during an acid-catalyzed reaction the triglycerides are esterified followed by a transesterification process (> Fig. 26.11) [87]. Low FFA-containing feedstock is more suitable for alkalicatalyzed transesterification and high FFA-containing ones for acid-catalyzed reaction. FFAs present in oils during base-catalyzed reaction react with the oils to form soap and emulsions that hinder the purification processes of biodiesel apart from base consumption [88]. Alkaline methoxides are high biodiesel yielding base catalysts with short reaction times, even at very low (0.5 mol%) concentrations. However, they are more expensive than metal hydroxides (KOH and NaOH) [84]. On the other hand, acidcatalyzed reactions are 400 times slower than the alkali-catalyzed transesterification [85] and less sensitive to FFA content. The presence of water greatly inhibits the conversion due to catalyst deactivation.

26

Biochemical Conversion of Biomass to Fuels

MeOH

Catalyst preparation

Water washing or H3PO4

Transesterification at 60°C 1.4–4.0 bar

Catalyst neutralization

NaOH Refined vegetable oil

Phosphates

Separator

Glycerin/alcohol phase

Vacuum distillation 28°C, 0.2 bar

Filtration and

Methanol recycle

Vacuum distillation

Catalyst neutralization

H3PO4

Fatty phase

Separator

Phosphates

Aqueous phase

Oil waste

Vacuum distillation Aqueous phase

MeOH and water Glycerin (92%) Biodiesel (99.6%)

. Fig. 26.10 Block diagram for base-catalyzed production of biodiesel [84]

H2SO4

Oil

MeOH Biodiesel (99.6%)

H2SO4/MeOH Methanol and water

Yellow grease

Simultaneous esterification and transesterification reaction (main reactor)

Distillation

Vacuum distillation

Glycerin (92%) and water Vacuum distillation

Water washing

H2SO4+CaO→Ca SO4+H2O

Gravity separation

CaO

CaSO4

. Fig. 26.11 Block diagram for acid-catalyzed production of biodiesel [84]

991

992

26

Biochemical Conversion of Biomass to Fuels

The major reaction parameters affecting the biodiesel conversion are temperature, oil/ methanol ratio, FFA, and moisture contents. An increase in temperature will increase the conversion the most appropriate range being 60–70
C, the alcohol boiling range at atmospheric pressure. Enzyme-catalyzed transesterification is achieved using lipases obtained from organisms such as Candida rugosa, Pseudomonas fluorescens, Rhizopus oryzae, Burkholderia cepacia, Aspergillus niger, Thermomyces lanuginosa, and Rhizomucor miehei [85]. Enzymes are more compatible in terms of usage of a wide range of feedstocks, fewer processing steps, and fewer separation steps. Enzymes do not form soaps with the FFAs present in the feedstock, which allows the use of spent oils and animal fats for biodiesel production. They can convert both FFAs and triglycerides (TAG) simultaneously without another pretreatment step for converting FFAs to TAG [89]. An increase in temperature increases the enzymatic conversion of biodiesel due to increased rate constants and lesser mass transfer limitations [90]. Additionally, optimal water content increases the biodiesel conversion as lipase acts as an interface between the aqueous and organic phases which allow its activation by rendering suitable conformation for transesterification [91]. However, they are currently facing challenges related to lower reaction rate, high cost, and loss of activity. Methanol is the most widely used alcohol for biodiesel production due to its availability from syngas. However, it is required to use an alcohol produced from a renewable source, such as ethanol, to make biodiesel production a completely green process. Additionally, methanol is toxic and renders lipases inactive at high concentrations. Therefore, methyl acetate can be used as a methyl acceptor in place of methanol, as it still has no negative effects on Novozyme 435, the only commercial lipase known, used for biodiesel production from soybean oil [92]. Immobilization of lipases is considered an economical process to overcome the limitations of using a batch process and employing a continuous process to enable glycerol separation for higher conversion rates [93].

Genetic Engineering Approaches With the above background of conversion of biomass to fuels, it is evident that several factors such as biomass composition, pH, temperature, by-products, etc., have a potential impact on the biofuel production. Process factors such as pH and temperature can be maintained using appropriate reactor and process conditions. Intrinsic factors such as biomass composition, product tolerance such as ethanol and butanol tolerance, specific binding of enzymes and by-product inhibition will remain potential challenges without recombinant DNA technology. Recombinant DNA technology is comprised of five general procedures [94]: 1. A desired segment of the microbe DNA of interest is cut using sequence-specific endonucleases which are nucleotide cleaving enzymes, otherwise called restriction endonucleases. These endonucleases act as molecular scissors to obtain the required nucleotide sequence.

Biochemical Conversion of Biomass to Fuels

26

2. A small molecule of DNA capable of self-replication is selected. These molecules, called cloning vectors, are generally plasmids or viral DNA which can be coupled with the nucleotide sequence obtained from the previous step. 3. The two segments are incubated in the presence of DNA ligase to obtain a recombinant DNA. 4. Recombinant DNA is introduced into the host cell for replication. The most common host cell used is E. coli for its well-understood DNA metabolism and its wellcharacterized bacteriophages (viruses that live on bacteria) and plasmids. 5. After cell replication, the host cells with recombinant DNA are identified and used for expression. The most commonly used host cells for metabolic engineering are Escherichia coli, Zymomonas mobilis, and Saccharomyces cerevisiae as their genetic maps are the most well studied [95]. They are facultative anaerobes with fast growth rates and viability [96]. Incorporation and expression of pyruvate decarboxylase and alcohol dehydrogenase II genes from Z. mobilis into E. coli has resulted in high yields of ethanol from the utilization of both pentoses and hexoses, as against only hexoses [95]. Although the recombinant strains are helpful in exploring the solutions for pathway-related problems, their industrial sustenance is limited due to the lack of robustness. Recombinant E. coli can produce isopropanol, n-butanol, and fatty acid ethyl esters through various engineered pathways [97]. Modification of enzymes used in hydrolysis of biomass to produce sugars is generating immense interest. However, it is noticed that the enzymes belonging to the same class have different amino acid sequences conferring low level of homogeneity, for example CBH1 (T. reesei) has Table 27.1. The two most common types of boilers for biomass combustion are fixed-bed systems and fluidized bed combustors, both of which have good fuel flexibility and can be fueled

Thermal Conversion of Biomass

27

. Table 27.1 The corresponding capacity range of biomass combustion boilers Biomass combustion boilers

Capacity

Fixed bed

Stoves

2–12 KW

Boilers Pellets Understoker Moving grate

5–35 KW 5–100 KW 5 KW–2 MW 200 KW–50 MW

Bubbling fluid bed Circulating fluid bed Dust Co-firing with pulverized Coal

5–100 MW 5–100 MW 5–14 MW 10–250 MW

Fluid bed Dust

entirely by biomass or co-fired with coal. Suspension burners are often used to co-fire milled biomass pellets or raw biomass with pulverized coal or natural gas, in which the airdried biomass fuels (with relatively low moisture content, e.g., 50%) and low heating value, combustion problems (especially gas turbine) High cost of operation and air separation

Air CO, CO2, H2, gasification CH4, N2, tar

3–6 MJ/m [23, 24]

Oxygen CO, CO2, H2, gasification CH4, tar

10–12 MJ/m3

Steam CO, CO2, H2, gasification CH4, tar

10–15 MJ/m3 High H2 content (>50%), high [25, 26] heating value

An indirect or external heat supply, corrosion, and high tar content

Pyrolytic CO, CO2, H2, gasification CH4, tar

15–20 MJ/m3 Syngas with medium heating value

Low system efficiency

3

Due to its simple design, easy operation, and reliable performance, fixed bed gasifier is widely applied. However, compared with other types of reactors, low and non-uniform heat and mass transfer in the fixed bed reactors [28] lead to large quantities of tars and char in the syngas. That increases the system complexity and investment of subsequent processing. Therefore, small-scale gasifiers are more economical. Updraft gasifiers are mainly used for heating [29]. Its upper size is around 2.5 MWe. The most well-known manufactures of Updraft fixed bed gasifiers are Bioneer and PRM Energy. About 10 Bioneer gasifiers are operational for district heating in Finland and Sweden. PRM Energy has 18 units in operation producing heat for industrial drying application or low pressure steam [30]. Downdraft gasifiers are more attractive for smallscale application up to around 1.5 MWe. In principle, downdraft gasifier is suitable for electric power generation. But it has not achieved industrialization. Fluidized-bed Gasifier

Working characteristics: The pulverized raw material and inert sands are put into the reactor. The material particles, sands, and gasifying agents can be heated evenly by good contacting among each other under the blowing of gasifying agent. A certain state of ‘‘boiling’’ is presented in the reactor. Therefore, fluidized-beds have fast heat-up, high gasification rate, great production capacity, and high syngas yield. Tar content is low since its secondary cracking under the high temperature and uniform temperature field. But high dust content is in the gas phase. Due to the complicated structure and large equipment investment of fluidized bed reactor, large-scale gasification system is more economical. The types of fluidized bed gasifiers can be divided into single fluidized bed gasifier, double fluidized bed gasifier and circulating fluidized bed gasifier.

Thermal Conversion of Biomass

27

Atmospheric bubbling fluidized bed gasifiers at pilot scale and commercial application in small to medium scales (25 MWth) can be in reliable operation. Circulating fluidized bed gasifiers are more suitable for large scale (100 MWe) with attractive market. Examples include the TPS (Termiska Processer AB) atmospheric process [31], and the Varnamo pressurized system [32]. The world’s most mature biomass gasification technology is ‘‘fast internal circulating fluidized bed’’ (FICFB) technology. The most successful biomass gasifier for power generation is ‘‘Gussing’’ gasifier in Australia, which is based on the high temperature pyrolysis to produce syngas with medium heating value. It has been successfully run >15,000 h to generate electricity 2 MWe. According to the blowing pressure of gasification agent, gasifiers have atmospheric gasifiers (0.110.15 MPa) and pressurized gasifiers (1.82.25 MPa). The pressurized gasifier with high-temperature and high-pressure outgas is suitable for the large-scale system for power generation. Though a gas compression process in the downstream system for the gas turbine or liquefaction could be avoided in the pressurized gasification process, in the short term, either pressurized circulating fluidized bed, bubbling bed, or pressurized bubbling bed gasifiers are the lack of market appeal mainly due to the complex system and high construction cost of large pressure shell. And the pressurized gasification process often uses pure O2 as gasifying agent to improve the gas quality. Hence special security measures are required to guarantee safe operation. Entrained-flow Bed Gasifier

Work characteristics: fine biomass powder as raw material carried by the high-speed air flow is injected into the gasifier with gasifying agent. In the reactor, solid particles are dragged along with the gas stream. Their properties of dispersing and flowing in the airflow are similar to the flow of mass points of gas. This generally means short residence times (typically 1 s), and high temperatures (typically 1,3001,500 C). Hence entrainedflow gasification is of high reaction rate, large capacity, high carbon conversion, and improved syngas without tar and phenol and little environmental pollution. Now entrained flow gasification technology is mainly used in coal gasification industry. The most mature technology of entrained flow gasification is Koppers-Totzek (KT) technology, which is in the atmospheric pressure operation. And pressurized entrained flow gasification technology is successfully developed: Shell and Prenflo technology can feed dry coal powder, and Texaco and Destec technology can feed water-coal slurry or oil. Although there are many commercial coal-based entrained-flow gasifiers, the experience in the biomass-based gasifiers is still little. Experimental results show: biomass ash in the entrained-flow gasifiers is difficult to melt under the operating temperature (1,3001,500 C), due to ash containing high contents of CaO and alkali metal generally found in the gas phase, which can reduce the ash melting point. However, a slagging gasifier is preferred over a non-slagging gasifier: (1) little slagging can never be avoided; (2) a slagging gasifier is more fuel flexible, but it needs to add a fluxing material (silica or clay) to achieve melting properties at required temperature. Currently, the research on biomass entrained-flow gasification is at the stage of experimental study and numerical simulation. The CARBO-V system of Colin (CHOREN)

1013

1014

27

Thermal Conversion of Biomass

in the German city of Freiburg, Saxony, is the most advanced biomass gasification system for bio-oil production in the industrial level. Energy Research Centre of the Netherlands (ECN) studied the feasibility of biomass entrained flow gasification, ash melting properties, the feeding device, pressurization methods, and selection of gasification routes [33]. Biomass technology group of the Netherlands (BTG) investigated the bio-oil entrained flow gasification [34]. Zhejiang University of China designed reactor and investigated biomass gasification characteristics, residual carbon properties, the volatile issue of alkali metal, and pretreatment of raw materials, and established a dynamic model about the gasification process [35]. In recent years, countries in the world usually pressurized entrained-flow gasifiers for the research on the biomass gasification using powder materials. As a potential gasification technology, pressurized gasification has become a hot research spot. How to effectively realize the pressurized entrained-flow gasification of biomass is the focus of future research.

Syngas Quality Control and Cleaning Technology Any gasification process for synthesis gas will produce pollutants: particulate, condensable tars, alkali metal compounds, H2S, HCl, NH3, HCN and COS, etc. [36]. So deep purification is needed according to the requirements of the downstream gas appliances and the use restrictions of catalyst. In general, Fischer–Tropsch synthesis demands higher standards of gas cleaning than biomass integrated gasification combined cycle (BIGCC). At present, the common feedstock for Fischer–Tropsch synthesis is the relatively clean natural gas. Hence actual cleaning specifications for some specific biomass contaminants are not known. Some specifications for biomass gasification are estimated based on the practical experience. Ash Particles

Ash particles in the product gas can be mainly purified by mechanical clarification. The particle reduction of different methods can be seen in > Table 27.3. Most of them are operated at low temperatures. Some are at high temperatures, such as the operation . Table 27.3 The particle reduction of different methods Method

Particle reduction (%)

Particle size

Wash tower Jet scrubber Granular-bed filter

95–98% 95–99% 99%

>1 mm >1 mm

Bag filter Cyclone separator Inertial dust separator Wet electrostatic Precipitator

99% 90% 70% >99

>0.1 mm >10 mm 20–30 mm

Thermal Conversion of Biomass

27

temperature of ceramic filters is 600 C. Ceramic filter according to its structure types can be divided into bag type ceramic filters, webbing ceramic filters, tubular ceramic filters, cross flow ceramic filters, cellular-type ceramic filter, and so on. Low-temperature cleaning technology has been realized industrialization and more mature than hightemperature cleaning. But the pollution problems of low-temperature cleaning are more serious, such as secondary pollution caused by wastewater from washing and wet ESP. Compared with low-temperature cleaning, high-temperature cleaning can improve system energy efficiency, reduce the operating cost from the utilization of hightemperature syngas, and also can be combined with the high-temperature fuel cells for heat and power generation [37]. Tar

Biomass tar is a light hydrocarbon and phenolic mixture. ‘‘Naphthalene’’ is the most difficult compound to reform. Tar will cause many severe problems. It will condense into liquid below its dew point temperature to lead to clogged, blockage, or corrosion in the downstream pipeline, filters, or equipment. It is difficult to completely burn tar. Gas facilities such as internal combustion engines and gas turbines would be damaged. > Table 27.4 shows the tar yield of different gasification processes. Tar removal, conversion, or destruction has been one of the greatest technical challenges for the successful development of commercial gasification technologies [38]. For this reason, most applications require the product gas with a low tar content, of the order 0.05 g/m3 or less. The methods to remove tar are mechanical cleaning, low-temperature cleaning, hightemperature cleaning, thermal cracking, and catalytic cracking. The operation and economical analysis shows that mechanical cleaning and catalytic cracking are suitable for small-scale plants and large-scale plants, respectively. Mechanical Cleaning The common mechanical methods are considerably efficient in removing tar accompanied with effective particles capture [39]. > Table 27.5 shows the effect of different methods on removing tars. However, the cost of mechanical cleaning system is usually high. And it only removes the tar from the product gas, while the energy in the tar is lost. Now a new tar removal system called OLGA (OLGA is the Dutch acronym

. Table 27.4 The tar yield of different gasification processes Gasification method

Tar content in syngas (g/Nm3)

An air-blown circulating fluidized bed (CFB) Biomass gasifier 10 Updraft fixed beds gasifier 100 Downdraft fixed beds gasifier Other gasifier

1 0.5100

1015

1016

27

Thermal Conversion of Biomass

. Table 27.5 The effect of different methods on removing tars Method

Tar reduction (%)

Water scrubber

10–25

Venturi scrubber Fabric filter Rotating particle separator Wet electrostatic Precipitator

50–90 [41] 0–50 30–70 40–70 [42]

for oil-based gas washer) is developed. In this system, heavy tars, 99% phenol, and 97% of the heterocyclic tars can be removed [40]. The lab test results [41] show that active carbon has good removal efficiency for high boiling hydrocarbons and phenols. Meanwhile, the ‘‘tar’’ and the active carbon itself can be recycled as a feedstock. But the tars accumulation on the carbon is difficult to clean completely to cause the blockage of active carbon filters. In thermocracking method, the raw gas derived from gasification or pyrolysis is heated to high temperatures. The tar molecules can be cracked into lighter gases. Biomass-derived tar is very refractory and hard to crack by high temperature alone. Three ways are beneficial for tar’s splitting decomposition reaction. The first method is to increase the residence time such as the utilization of fluidized bed reactor. But the improving effect is not obvious. The second method is increasing the area of the heating surfaces, but it depends on the mixture grade of various compositions. The last method is adding oxygen or air to strengthen the partial oxidation of tar, which increases the CO content at the expense of conversion efficiency decrease and operation cost enhancement.

Thermocracking

Catalyst Cracking At present, the catalytic cracking is the most effective way to remove the tar. It is divided into low-temperature catalytic reforming (350600 C) and hightemperature catalytic reforming (500800 C). Catalysts are as follows: nickel-based catalyst, dolomite, alkali metals, and nano-catalyst. Nickel-based catalyst supported on SiO2 and Al2O3 can be used at low temperatures or at high temperatures for catalytic cracking. Although nickel-based catalyst has good effect on cracking tars, it is very expensive and easy to lose activation because of the carbon deposition, H2S poisoning, and catalyst attrition. Compared to nickel-based catalyst, the abundant naturally occurring catalysts such as dolomite CaMg(CO3)2 are cheaper. And it is the most common and effective catalyst for tar removal [25]. However, the conversion of tars over dolomite cannot reach 90–95% or more [43]. And it is difficult for dolomite to crack the heavy tar components [44]. In addition, due to its low melting point, dolomite is very easy to melt to cause deactivation. Adding inexpensive alkali metal catalyst to biomass raw material can significantly reduce tar content through dry mixing or wet impregnation. Many studies [45–47] suggest that potassium has a better catalytic effect on tar cracking compared to other

Thermal Conversion of Biomass

27

alkali metals (such as Na, Li, Ca, etc.). But the alkali metal in the furnace would lead to agglomeration, sintering, fluidization performance degradation, blockage in the pipes, and other metal catalyst deactivation. Currently, some novel metals have been widely used as catalysts for tar cracking. It is found that Rh/CeO2/SiO2 has the best catalytic performance: little carbon deposition at low temperatures, and high and stable activity even under the presence of high concentrations of H2S (280 ppm) [48]. In addition, nano-Ni catalyst (NiO/g-Al2O3) also can improve the quality of synthesis gas and reduce the tar in the gasification process [49]. Some studies demonstrated that corona discharge could also decompose the organic components, which can be used to reduce the tar content. Tests [50] were carried out on a wood gasifier, which was designed to produce a 100 kW electrical output. The dust removal efficiency was about 72–95%. Conversion efficiencies of heavy tar components and light tar componentswere 68% and 50%, respectively. In addition to capturing dust and tar, plasma technology can operate at high temperatures.

Plasma Methods

Alkali Metal

In the biomass gasification process, the problems associated with alkali metals are mainly caused by the main non-metallic components: Si and alkali metal potassium in the ash. Si reacts with K at temperature less than 900 C. For this reason, Si–O–Si bond is broken to form silicate or to react with sulfur to form sulfate. The melting points of Silicate and sulfate are lower than 700 C. So they are easy to deposit on the walls of reactors or pipes to cause sintering, corrosion, anti-fluidization, or blockage. These problems can be mitigated by leaching and fractionation as the two main pretreatment [51–53]. However, mechanical fractionation could reduce up to 50% of the ash content in the biomass. The remaining ash would still produce such problems [53]. Eighty percent of the alkali metals in the syngas can be separated together with the coke through the cyclone.

Syngas Utilization Gas Centralized Supply

In the developing countries, in addition to the heat and power supply, biomass gasification technology has been mainly applied for domestic cooking in the way of gas centralized supply. The process of biomass gasification system project for central gas supply: straw is put into the gasifier and converted into combustible gas through pyrolysis and gasification reactions. The dust and tars in the combustible gas are removed by the downstream cleaner. Then the clean gas stored in the air storage can be delivered to the every user of this system. The main types of gasifiers used in the biomass gasification system project for central gas supply are pyrolysis gasifiers, updraft fixed bed gasifiers, pressurized updraft fixed-bed gasifiers, downdraft fixed bed gasifiers, and fluidized bed gasifiers. Downdraft fixed bed gasifier is the most often used reactor in all of them.

1017

1018

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Thermal Conversion of Biomass

But the operation rate of village-level straw gasification system for centralized cooking gas supply is still very low. There are many reasons for this. Technically the syngas quality is low due to the low heating value and the high contents of CO and O2. Contents of tars and dust in the combustible gas are high. The whole centralized gas supply system is not fully used. The syngas should be utilized in many ways to improve the utilization rate of system such as power generation, preheating, and drying grain and other agricultural products. From a policy and economic point of view: limited by the capital cost, the system needs to be as simple as possible. Therefore, the system cannot be perfectly designed, leaving some operation difficulties and environmental problems [54]. Therefore, most of the domestic cooking fuel projects need government financial support now. Combined Heat and Power Generation

Due to its properties of energy saving and environmental conservation, combined heat and power generation (CHP) technology has been the focal point of worldwide attention as an alternate energy source for traditional source. The major conversion technologies of biomass-based CHP systems are combustion, gasification, pyrolysis, biochemical/biological processes, and chemical/mechanical processes. Combustion technology is widely used at large- and medium-scale systems. Although gasification technology is still developing, this technology has great potential for CHP. The main types of gasifiers for CHP systems are updraft/downdraft fixed bed gasifiers, fluidized bed gasifiers, circulating fluidized bed gasifiers, and entrained flow gasifiers. Internal combustion engines and turbine can use cleaned product gas to produce heat and power. Gasification-based CHP system potentially has higher electricity efficiency than a direct combustion-based CHP system. Moreover, syngas from biomass gasification can increase the bio-based fuel percentage used in the existing pulverized combustors without any concern about plugging of the coal-feeding system during co-firing of biomass coal. But gasification-based CHP systems have not been realized commercialization till now. The unstable gasification process leads to the great changed quality of the synthetic gas and higher content of tars, which seriously damage engines. And to reduce system cost, the gasification-based system is short of automatic measurement and control measures to result in the varied system performance. According to CHP capacity, it can be divided into large-scale, medium-sized, smallscale, and micro-scale CHP. Biomass is best suited for decentralized, small-scale and microscale CHP systems due to its intrinsic properties. On one hand, small-scale and micro-scale biomass CHP systems can reduce transportation cost of biomass and provide heat and power where they are needed. On the other hand, it is more difficult to find an end-user for the heat produced in larger CHP systems. Generally speaking, the concept ‘‘small-scale CHP’’ means combined heat and power generation systems with electrical power less than 100 kW. ‘‘Micro-scale CHP’’ is also often used to denote small-scale CHP systems with an electric capacity smaller than 15 kWe. Biomass-based CHP systems are generally smaller than coal-based systems. And the power efficiency of biomass-based CHP is also lower, only about 85–90%, as 30–34% and 22% of electricity will be used for biomass drying and solid-waste treatment, respectively. A typical CHP system at large scale is biomass integrated

Thermal Conversion of Biomass

27

gasification combined cycles (BIGCC). The overall efficiency of the BIGCC system is about 86% and the electrical efficiency is about 33% [55]. ‘‘VEGA’’ gasification system developed by Skydkraft AB Company of Sweden uses BIGCC technology for district heat and power supply. Buggenum IGCC system in the Netherlands uses the mixtures of biomass and coal to generate power (250 MW). Currently small- and medium-scale CHP systems have not been commercialized due to high investment, low return and some technical barriers.

Synthesis Techniques Syngas can be converted to a liquid fuel or chemicals through synthesis technology. The major synthesis technologies are methanol synthesis, Fischer–Tropsch synthesis, methane synthesis, hydroformylation of olefins synthesis, and hydrogen in organic synthesis. The features of different technologies are in > Table 27.6. Fischer–Tropsch synthesis is one of the biomass indirect liquefaction technologies. Under the appropriate condition (2040 bar, 180250 C), syngas as raw material is synthesized into the liquid fuels (hydrocarbons with different chain length). Fischer– Tropsch synthetic oil can be divided into three categories according to different raw materials (see > Table 27.7). The synthesis process includes gasification, gas purification, transformation and reforming, synthesis, and upgradation. The optimal molar ratio of H2 and CO for Fischer–Tropsch synthesis is 22.5, preferably 2.1. Currently the cheap Fe-based catalyst is commonly used for industrial Fischer-Tropsch synthesis. However, it will strengthen the water gas reaction to produce too much useless CO2 at the expense of large CO consumption. Moreover, when it is used in slurry bed reactors at low temperatures, the small particles of Fe-based catalyst are hardly separated from the product wax. The Co-based catalyst precisely overcomes these deficiencies. Hence the current developed catalysts are mostly cobalt-based catalysts with high activity, high factor of chain elongation, and long life. The main reactors are fixed bed and circulating fluidized bed. The F–T synthesis is used on a technical scale nowadays only at SASOL (coal-based) in South Africa and at Shell (natural gas–based) in Malaysia. However, biomass synthesis gas for the Fischer–Tropsch synthesis is still of less attention.

Obstacles to Commercialization The application obstacles are divided into technical and non-technical barriers to obstruct development of biomass gasification technology. Technical barriers are shown as follows: 1. Biomass resources: As a resource with the properties of low density and dispersion, there are substantial logistical problems in collection and transport as well as high costs. Moreover biomass has the characteristic of its seasonality. So it is difficult to achieve large-scale gasification plants for power generation.

1019

C

C

H

H R

+ CO + H2

Hygrogen in Chemicals A + nH2 ! BH2n organic synthesis

R

H

CH2 CH2 CHO + R

F–T synthesis F–T oil CO + 2H2 ! [–CH2–] + H2O  165 kJ/mol Methane Methane CO + 3H2 ! CH4 + H2O + 206.4 kJ/mol synthesis Hydroformylation Aldehyde

CO2 + 3H2 ! CH3OH + H2O + 49.6 kJ/mol

Methanol CO + 2H2 ! CH3OH + 90 kJ/mol

Methanol synthesis

Principle

Product

Synthesis

CHO

CH

CH3

Raney nickel, copper, molybdenum, especially inert metals (Pt, Pd)

High-pressure process: coppercontaining catalysts Low-pressure process: CuO/ZnO/M (M=Al, CrO, mixed oxide of zinc and aluminum) Cobalt or iron Mg-promoted Ni catalysts with diatomaceous earthenware as carrier Cobalt carbonyl hydride, cobaltor rhodium-phosphine complexes

Catalyst

No

Yes

Yes Yes

Yes

Industrialization

27

. Table 27.6 The features of different synthesis technologies [28, 56]

1020 Thermal Conversion of Biomass

Thermal Conversion of Biomass

27

. Table 27.7 The features of different Fischer–Tropsch synthetic oil Fisher– Tropsch synthesis fuels

Advantages

Disadvantages

Coal-based Oil quality is better than the High content of arene, a low cetane number for oil (Coal-to- products of direct diesel oil product, no liquefaction liquid) applications for CO2 zeroemission Natural gas–based oil (Gas-toliquid) Biomassbased oil (Biomassto-liquid)

Commercialization Sasol in Malaysia

A high cetane number, does No applications for CO2 not contain aromatic zero-emission compound and sulfur

Shell in South Africa

A neutral carbon fuel, does not contain the impurities that are always in mineral oil A high cetane number, can be used as additives or used as clean fuel for diesel engines

No

2. Feeding: In the feeding process, the problems with bridging, blockage, and instability are often caused due to low-dense materials and mixed residues with varying characteristics. 3. Gasification technology: There is a need to improve the equipment reliability. The immature technology makes it difficult to open market and commercialize. 4. Purification: The difficulties of purifying tail gas are how to solve the fouling and corrosion of the heat exchanger and pipes, tar removal/cracking, and continuous operation. 5. Prime mover: Experience about biomass syngas utilized in operation of prime mover is little, such as allowable contamination, allowable emissions, engine, fuel cell, Stirling, and turbine (specifications to product gas). Non-technical barriers are shown as follows: 1. Emission standard: The standards of allowable emissions differ from country to country. 2. Public perception: At present, due to large investment, small return and no significant effect of gasification technology on social benefits; so public are rather negative with no confidence. 3. Infrastructure: Many aspects affect economy of biomass gasification – investment channel, collection and transportation cost and so on. To take the power generation for an example, some countries do not have regulations regarding the incorporation of electricity derived from biomass into the existing grid network.

1021

1022

27

Thermal Conversion of Biomass

4. Capital cost: Investment cost of gasification projects are high, particularly the cost of collection and transportation of raw materials. Sometimes in order to reduce costs, the system has to be as simple as possible. Therefore, this results in some sectors such as tar treatment, and gas cleaning cannot be perfectly designed, leaving some operation difficulties and environmental problems. 5. Environmental protection: In recent years, countries in the world advocate environmental protection energetically, as well as energy saving and emission reduction. But the real fact is that not all the biomass gasification technology can meet environmental requirements. Although some techniques, such as centralized gas supply systems for domestic cooking in rural areas, can achieve obvious social benefits, but in practice gasification stations are difficult to really make a profit from it due to the high cost of antipollution measures.

Pyrolysis Pyrolysis is the initial chemical stage of combustion and has been used for charcoal production from wood since ancient Egyptian times. And biomass pyrolysis is a process in which biomass is heated in the absence of oxygen to decompose into char, gaseous products, and liquid product ‘‘bio-oil.’’ The significant development of biomass pyrolysis happens in the 1980s, when many researchers began to observe an increasing liquid product yield obtained from fast pyrolysis with a rapid heating rate and a short cooling time [57]. Crude bio-oils have a high water content of about 15–30%, a high acidity (PH value of 2.8–3.8), a high density of about 1,200 kg/m3, a low heating value of 14–18.5 MJ/kg, and a large range of viscosities depending on the feedstock and pyrolysis conditions [58]. And they are multi-component mixtures of different chemical families, such as acids, ketones, alcohols, aldehydes, esters, sugars, and phenols [59]. The deleterious properties of corrosiveness, high viscosity, and thermal instability limit the high-quality applications of bio-oils, but corresponding upgrading technologies are developed to explore promising ways for substituted transport fuel production [60, 61]. Moreover bio-oils from this conversion technology have a positive environmental effect compared to most coal- or petroleum-derived fuels due to the low levels of aromatics and sulfur.

Pyrolysis Process of Biomass The physical conditions of biomass pyrolysis, such as temperature, heating rate, and residence time have been identified to have a profound influence on the product yields and composition. As shown in > Table 27.8, pyrolysis is classified as slow, conventional, fast, and flash pyrolysis mainly depending on the temperature and heating rate. The terms of ‘‘slow pyrolysis’’ and ‘‘fast pyrolysis’’ are somewhat arbitrary and have no precise definition of the times or heating rates involved in each. Conventional pyrolysis may be in the range of slow pyrolysis, and flash pyrolysis is also termed as fast pyrolysis.

Thermal Conversion of Biomass

27

. Table 27.8 Classification of biomass pyrolysis technologies [64, 65] Pyrolysis type

Temperature (ºC) Heating rate Residence time Main products

Carbonization

400

Very low

Days

Charcoal

Slow pyrolysis Conventional pyrolysis Fast pyrolysis

400–600 600

Low Low

Hours 5–30 min

Charcoal, liquids, gases Charcoal, liquids, gases

400–650

High

0.1–2 s

Liquids

Flash pyrolysis

Table 27.10. Major compounds exist in the four kinds of bio-oils except for some differences in yields, which are caused by types of wood material, reactors, liquid collection methods, etc. In addition, properties and compositions of bio-oils from other feedstocks (like agriculture residues and forest residues) are also concluded by many researches [65, 68, 84–86]. Bio-oils are composed of molecules with different sizes derived from the depolymerization and fragmentation of cellulose, hemicelluloses and lignin. Moreover, the composition of bio-oils is influenced by various factors, such as reactor type, operating conditions, and feeding materials. For example, the results of conventional fast pyrolysis indicate that faster rates enhance the formation of levoglucosan and hydroxyacetaldehyde with a diminution of carboxylic acids [87]. Detailed classification systems use categories such as acids, aldehydes, phenols, furans, alkenes, aromatics, ketones, and saccharides [65], and representative compounds include acetic acid, formic acid, levoglucosan, hydroxypropanone, 2-furaldehyde, and hydroxyacetaldehyde [59]. The chemical composition of bio-oil can be manipulated by changing the thermal conditions of pyrolysis, but complex bio-oils are recalcitrant to complete chemical characterization, which is hindered by the limitations of modern analytical equipment.

Thermal Conversion of Biomass

27

. Table 27.10 Yields and boiling point temperature of bio-oil components [86] Compound

Tb (K)

Formaldehyde Acetaldehyde Glycolic acid Glyoxal

253.9 294 323 324

Methanol (5H)-furan-2-one Group I Water

337.8 360 300–360 373.2

Hydroxyacetaldehyde 5-Hydroxymethylfurfural Acetic acid Butanol

383 388 391.2 390.6

Group II Propionic acid Hydroxypropanone 2-Methyl-2-cyclopentenone

BTG (wt.%)

Dynamotive (wt.%)

Ensyn (wt.%)

Pyrovac (wt.%)

2.63 0.92 0.57 1.51

2.07 1.01 0.50 1.32

0.83 0.68 0.31 0.84

0.76 0.55 1.07 0.92

0.91 0.54 7.86 30.4

1.03 0.62 7.75 21.1

0.39 0.50 3.96 20.3

0.07 0.51 4.48 15.7

6.65 0.49 3.17 3.15

5.65 0.52 2.46 2.85

3.69 0.23 4.73 1.29

2.54 0.83 2.25 0.80

360–400 414.2 418.7 431.4

44.42 0.28 2.82 0.06

33.16 0.33 3.91 0.17

30.59 0.66 1.63 0.14

22.42 0.30 1.10 0.53

2-Furfural N-butyric acid Group III Phenol o-Cresol

434.7 436 400–450 455 464.3

0.35 1.08 6.51 0.08 0.02

0.53 0.98 8.37 0.10 0.04

0.53 0.93 5.39 0.23 0.08

0.30 1.43 5.39 0.32 0.13

Syringaldehyde p-Cresol Guaiacol 4-Methyl guaiacol

465.6 475 478.2 494.2

0.04 0.02 0.36 0.65

0 0.04 0.53 1.23

1.16 0.05 0.21 0.23

0.07 0.12 0.33 0.41

Group IV 1,2-Benzendiol Eugenol Syringol

450–500 518 526.4 536

1.57 0 0.42 0.16

2.86 0.13 0.71 0.14

2.54 0.10 1.80 0.61

2.57 0.91 0.24 0.21

Vanillin Isoeugenol (cis+trans) Group V Levoglucosan

538.7 540.5 500–550 659

0.82 1.41 3.08 2.96

0.29 2.80 4.66 4.48

0.08 0.49 3.49 3.71

0.25 1.18 3.25 3.72

Cellobiosan Group VI

– >550

1.80 4.93

2.30 7.22

0 4.04

0.70 4.89

1029

1030

27

Thermal Conversion of Biomass

Pyrolysis oils

Separate

Boiler

Heat

Engine

Electricity

Selective pyrolysis

Upgrading

Combust

Furnace

Chemicals

Fast pyrolysis

Esterification

Hydroupgrading

Transported fuels

Reforming

Hydrogen

Cracking

Syngas

Enriched chemicals

. Fig. 27.1 Applications of bio-oils from fast pyrolysis process

Applications of Bio-oils The most significant issues of bio-oils as fuels are poor volatility, high viscosity, coking, corrosiveness, and cold flow problems. Though these problems limit the utilization of bio-oils, they also have many applications, mainly including direct combustion in boilers or furnaces to supply heat or to generate electricity, and substitution for transported fuels after upgrading. > Figure 27.1 summarizes some existing concepts of bio-oil applications, which can be divided into two classes: primary and high-grade applications. Primary Applications of Bio-oils

Bio-oils are renewable liquid fuel, with a lower heating value of about 18 MJ/kg compared with 43 MJ/kg for diesels. They can be used as fuels in boilers, engines, or gas turbines for the production of heat, power, and combined heat and power (CHP). Compared to combustion and gasification of biomass, fast pyrolysis has the advantage that a liquid intermediate is produced, stored, and then transported to centralized locations economically. Thus bio-oil production and heat or power generation can be carried out independently at different locations and times, and at good efficient scales [88]. As discussed above, bio-oils have lower heating values compared with fossil fuels due to the high content of oxygenated compounds and water, but their combustion characteristics are similar to light fuel oils. So direct combustion of bio-oils can supply residential or industrial heating, which have been under operations in many regions. Currently, the consideration and improvement of this application are referred to three major issues. Bio-oils are too acidic to be used in the existing residential boilers, meaning that bio-oils should have to be processed or stainless steel used; the modification of nozzles or burners is also necessary to ensure efficient ignition or combustion. Researches on the removal of oxygenated compounds and part of water are essential to improve the combustion behaviors.

Heat generation

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One of the common applications for bio-oils is as a fuel for power generation. But attentions should be paid that boilers, especially engines and turbines are specially designed to use bio-oils, rather than the conventional commercial engines. Organizations testing bio-oil in engines include Wartsila Diesel in Finland, Onnrod Diesel in Great Britain, and Orenda in Canada. One of the alterations to the turbine includes changing the fuel system and nozzle to handle a higher flow rate. Because of the high viscosity of bio-oils, the efficiency of fuel atomization is also an issue that must be addressed to achieve complete combustion. All these changes in fuel pump, feed linings, and the injection system provide opportunities for applications for bio-oils to replace natural gas, diesel, and other fossil fuels in the industrial equipment. As bio-oils are insoluble with petro-derived fuels, it is not possible to mix the fuels before combustion without emulsification. Emulsions of bio-oil and standard diesel or other fossil fuels have been produced and tested in diesel engines. Some researches investigate the emulsification effect on thermal stability of the fuel blends and observe that the emulsions are more stable than the crude bio-oils; the higher the bio-oil content, the higher the viscosity of the emulsion; and the optimal range of emulsifier to provide acceptable viscosity is between 0.5% and 2% [89, 90]. Moreover, suitable emulsification can decrease the viscosity and corrosiveness of the fuel blends compared with original bio-oils [91]. Emulsification does not demand redundant chemical transformations, but the high cost and energy consumption input cannot be neglected. The accompanying corrosiveness to the engine and the subassemblies is inevitably serious. Power generation

More than 400 kinds of compounds have been identified in biooils. Some enriched compounds, such as acetic acid, hydroxyacetaldehyde, and phenols can be separated by adding solvents into bio-oils. Phenols, consisting of relatively small amounts of phenol, eugenol, and cresols and much larger quantities of alkylated phenols, which are also called lignin-derived fractions, are present in high concentrations. The lignin-derived fraction is comprised of a total phenolic content of about 30–80% and is considered more reactive in usage as an extender within resin formulations without requiring any further extraction or fractionation procedures. Many attractive results about pyrolyzed phenols substitution for resins have been reported [92, 93]. However, resin producers want to market the reproducible, precisely tailored resin compositions that the end users demand. So the variability of chemical compositions has gained resin producers attention in developing commercial resins from bio-oils.

Chemicals separation

Bio-oils Upgrading for High-grade Applications

Crude fossil fuel oils processing techniques typically focus on the removal of nitrogen and sulfur, as well as molecular weight reduction. In contrast, treatment of bio-oils will mainly be more focused on oxygen removal and molecular weight reduction. Hydrodeoxygenation of bio-oils involves treating bio-oils at moderate temperature of 250–400 C with high-pressure H2 (10–18 MPa), and continuous H2 feed rate (volume ratio of H2/bio-oil: 100–700) [94]. Processes refer to hydrotreating and hydrocracking, often in the presence of some catalysts. A number of different catalysts

Hydrodeoxygenation (Hydro-upgrading)

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. Table 27.11 Properties of bio-oils after hydrodeoxygenation [96] Properties

High-pressure liquefaction

Flash pyrolysis

Hydrodeoxygenation bio-oils

Elemental analysis C H O

72.6 8.0 16.3

43.5 7.3 49.2

85.3–89.2 10.5–14.1 0–0.7

S H/C ratio Density (g/mL) Moisture (wt.%)

Table 27.11, the energy content and the stability of bio-oils after upgrading are significantly increased. The high-pressure liquefaction is a method for bio-oil upgrading, which takes place in a water-rich phase, rather than an oil-rich phase, which eliminated the need for recycle but employed subsequent alkaline and acid treatments [97]. The disadvantages are that it consumes H2 and even requires high-pressure H2. Moreover, hydrodeoxygenation process needs complicated equipments, advanced techniques, and excess cost, and usually is forced to stop due to catalyst deactivation and reactor clogging. Future work in hydrodeoxygenation may be focused on developing decreased H2 combustion system modified through mass and energy balance calculation, and exploring and texting novel high efficiency catalysts. The strategy of catalytic steam reforming is based on producing hydrogen from bio-oils in conjunction with other products that have greater value and can reduce the cost of hydrogen, which firstly start to develop in the 1990s by NREL. The original concept is that bio-oils are fractionated into two fractions based on water solubility. The water-soluble fraction is to be used for hydrogen production, and the water insoluble fraction could be used in adhesive productions. Bio-oils are usually steam

Catalytic steam reforming

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reformed using a nickel-based catalyst at 750–850 C, followed by a shift reaction to convert CO to CO2. The reactions in catalytic steam reforming of bio-oils are described as followed. The yield of hydrogen is limited with a maximum of only 8.6 g H2/100 g bio-oil [98]. Control of coke formation is a key aspect of this process. Loss of activity of the nickel catalysts after a few hours forces periodic regeneration. It is well known that CO2 from a pressure swing absorption step can effectively remove the coke. There are currently no commercial deployment opportunities for hydrogen production, but this method remains viable. Several model compounds were successfully steam reformed, such as acetic acid, ethyl alcohol, acetone, phenol, cresol, and aqueous fraction of bio-oil. Biomass + Energy ! Bio-oil + Char + Gas impurities (pyrolysis) Bio-oil + Water ! CO + H2 (reforming) CO + Water !CO2 + H2 (shift reaction) CH1.9O0.7 +1.26 H2O ! CO2 + 2.21 H2 Steam reforming of bio-oils can also produce syngas, composed of CO and H2. Then syngas is converted into a range of fuels depending on the ratio of CO/H2. The fuels include hydrogen by the water gas shift reaction, methanol by methanol synthesis, alkanes by Fischer–Tropsch Synthesis, and ethanol by fermentation, etc. Catalytic cracking is one of the routes for obtaining gasoline and other lighter products from fast pyrolysis oils. The initial catalysts were clays and amorphous silica alumina and were evolved with time to zeolites, specially the use of Rare earth-Y (REY) and finally to the Ultrastable-Y (USY), REUSY and multi-zeolite catalysts used today [99]. Bio-oils can be upgraded using zeolite catalysts to reduce oxygen content and improve thermal stability. Zeolite upgrade is operated in the temperature range of 350–500 C, atmospheric pressure, and gas hourly space velocities of around 2. The products are consisted of hydrocarbons, water soluble organics, water, oil-soluble organics, gases, and coke. A number of chemical reactions occur including dehydration, cracking, polymerization, deoxygenation, and aromatization. By alternation cracking steps, bio-oils can be mainly decomposed into H2, CO or CO2, and coke. Then the coke is burnt by O2 addition in the regeneration step. Catalytic cracking provides an interesting means of controlling the coke formed during bio-oil cracking. Moreover, the process may run auto-thermally. Different chemical compounds in bio-oils have a significant difference in reactivity and coke formation rates. Therefore, separation prior to reaction is a positive prevention method for coke formation and catalyst attrition. It is necessary to incorporate the reactor and catalyst design as well as optimum process operation conditions in order to further improve the bio-gasoline production [100]. Catalytic cracking

In recent years, selective pyrolysis has aroused a great interest due to the advantages of operating at atmospheric pressure and in the absence of hydrogen. Selective pyrolysis is different from conventional fast pyrolysis, which is usually aimed at the maximum bio-oil yield, and is to drive the pyrolysis of biomass toward the products of interest [101]. The application of proper catalysts can effectively optimize the distribution of bio-oil composition and improve the quality of bio-oil, as well as produce

Selective pyrolysis of biomass

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value-addition chemicals. Many studies have been focused on the catalysts of acids and alkali metal salt. The application of sulfated metal oxides (SO42/TiO2, SO42/ZrO2, SO42/SnO2) significantly decreases or completely eliminates the formation of levoglucosan due to the enhancement of dehydration reactions [102], while suitable concentration of phosphoric acid can govern levoglucosan/levoglucosenone ratio produced from cellulose pyrolysis [103]. Alkali metal salts such as K2CO3, NaCl, KCl, MgCl2, and CaCl2 have an obvious influence on gaseous products resulting in an increase in gas yield and a decrease in tar yield [104, 105]. Currently catalytic upgrading of pyrolysis vapors using zeolites and noble metals is a potentially promising method for removing oxygen from organic compounds and converting them to hydrocarbons [106]. Zeolites (Y- and ZSM-type) exhibit a strong influence on pyrolysis behavior of cellulose, reducing the overall yields of anhydrosugars to convert into hydrocarbons [107]. Noble metals, for example, Pt and Ni are widely applied in bio-oil catalytic reforming to improve the yields of gaseous products especially hydrogen [108, 109].

Application of Biochar Biochar as the by-product of biomass pyrolysis is of increasing interest because of concerns about climate change caused by emissions of carbon dioxide (CO2) and other greenhouse gases (GHG). Biochar is a stable charcoal of rich carbon produced by biomass pyrolysis under fully or partially anoxic conditions and at relatively low temperature (below 700 C). The carbon content of biomass char varies as the pyrolysis temperature changes [110]. Biochar has a high surface area, high nutrient retention capacity, and high water retention capacity due to its porous structure [111]. Biochar as a Potent Soil Amendment

Biochar has a large surface area because of its pore structure just as charcoal. Therefore, biochar has a high water retention capacity. Application of biochar will increase the water holding capacity of agricultural soil. In addition, the application of biochar is related to soil moisture and soil texture [111]. But further studies are needed to clarify whether this may help balance fluctuations in water availability to plants [112]. There are several ways for biochar to improve soil fertility. In the first place, biochar in the soil has a high nutrient retention capacity because biochar can increase soil cation exchange capacity to enhance cation adsorption, and improve pH of the soil. For example, rice hull char can increase pH in both soils to some extent, mainly by decreasing the contents of exchangeable acid and exchangeable Al, and increase the content of exchangeable bases and the base saturation [113]. Furthermore, biochar addition benefits for the growth of fungus and nitrogen-fixing microbial groups, improving soil fertility and increasing crop yields [114, 115]. So, as a soil amendment, biochar makes soil more fertile, preserves cropland diversity, and reduces the need for some chemical and fertilizer inputs, which indirectly boosts food security and reduces water pollution.

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Application of biochar could not only improve the physical and chemical properties of soil, and increase soil fertility, but also adsorb heavy metals (such as cadmium, arsenic, etc.), prevent the plant from uptaking of pollutants, and improve the effect of environmental remediation to a certain extent. The effects on the mobility, bioavailability, and toxicity of specific elements vary with the applying amendments to multi-element contaminated soils [116, 117]. Biochar as a Powerful Tool to Combat Climate Change

The carbon in biochar resists degradation and can hold carbon in soils for hundreds to thousands of years. Biochar is produced through pyrolysis or gasification – processes that heat biomass in the absence (or under reduction) of oxygen. In addition to creating a soil enhancer, sustainable biochar practices can produce oil and gas byproducts that can be used as fuel, providing clean, renewable energy. When the biochar is buried in the ground as a soil enhancer, the system can become ‘‘carbon negative.’’ Biochar and bioenergy co-production can help combat global climate change by displacing fossil fuel use and by sequestering carbon in stable soil carbon pools. It may also reduce emissions of nitrous oxide.

Future Directions Combustion At present, large-scale biomass combustion power generation projects were mainly concentrated in Europe and the USA, and other developed countries. However, due to the variety of resources, most of the applied projects are using wood-based raw materials such as branches, wood chips, and waste wood as the main fuel, only a small part blending a small part of the crop stalks. In the area of crop stalk combustion power generation, Denmark has made outstanding achievement, represented by water-cooled vibrating grate technology of BWE. In 1988, the first crop stalk combustion power plant was constructed in Denmark. Since then, more than 100 plants have been established in the past years, and it makes biomass become the very important energy resource in Denmark. In order to overcome the biomass fuel supply fluctuations, large-scale power plants generally co-fire it with coal. Meanwhile, in order to improve the economics of biomass power plants and thermal efficiency, now the combined heat and power technology (CHP) is widely used. After many years’ development, there have been no major technical obstacles of biomass combustion power generation. However, lots of work still needs to be done. The biomass resources are of great varieties and scattered, which result in difficult collection and transportation. At present, the equipments and processing-flow for collection, transportation, and pre-treatment of biomass are not perfect, which is the key factor of scale-up biomass power generation.

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In the future, the utilization of high-alkali biomass will become more and more important. In order to improve the share of electricity generation from biomass combustion, co-firing represents a cost-effective, short-term option at large scale.

Gasification Among the different gasification technologies, the biomass gasification is the most promising biomass technology that has great potential to be further developed. Though there is a great achievement in the research and development of this technology, several developmental constraints exist including pollution issues, competitiveness with electricity generated by conventional fuel, and system scale. Environmental protection and energy conservation may be a driving force of further development of the biomass gasification technologies. 1.

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Scale: At present, due to financing problems, the development of small-scale gasification plants is restricted. But the development of large-scale plants is also restricted because of the problems with collection and transportation. To handle the relations of the two issues is the great impetus for gasification development. Feeding: Because of the seasonality of biomass, it is necessary to improve the feasibility of the gasification equipment for different raw materials either separately or in mixed form. Compared to the direct gasification of raw biomass materials, the overall efficiency of oil/gas gasification is low. But it is easier to realize continuous oil and system compression using oil as raw material, which can effectively reduce costs and achieve economy. Hence, it is necessary to research and develop the pyrolysis oil/gas gasification technology. Purification: Some specifications for biomass gasification are estimated based on the practical experience. So evaluation of different options is needed – both technical and economical. Combined heat and power (CHP) technology: Although large- and medium-scale CHP plants have been commercialized, small- and micro-scale plants used for heat supply for buildings are easier to find an end-user than larger CHP systems. So small- and micro-scale plants need more research. Contamination: Some specifications for biomass gasification are estimated based on the practical experience. So it is necessary to investigate the rules of pollutant emission in the biomass gasification process. Purification: A complete set of specific specification for pollutants in the product gas is needed. For example, the requirements for Fischer–Tropsch synthesis are very stringent. And the relatively clean natural gas is the common feedstock for Fischer– Tropsch synthesis. But the actual cleaning specifications are not known for some specific biomass contaminants. Policy: Since the industrialization process of biomass gasification would take a long period to reflect the importance of biomass gasification in an environmental

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protection field, the government should offer sustainable assistance for development, such as increasing support funds, setting up of special project assessment institute, and setting up of special funds with an aim to drive society investment and cultivate mature market.

Pyrolysis Bio-oils have the considerable advantages of being storable and transportable as well as the potential to supply the amount of valuable chemicals; there are many challenges facing fast pyrolysis that relate to technology, product characterization, and applications. The challenges are as follows: 1. Design a well-integral fast pyrolysis system, making the reactor in perfect cooperation with char separation, liquid quenching, liquid collection, and fuel applications. 2. Decrease the cost of bio-oil production and increase the energy efficiency. 3. Set up standards for testing the physicochemical properties of bio-oil. 4. Develop widely the applications of bio-oils before and after upgrading. 5. Bio-oil is incompatible with conventional fuels and its users are unfamiliar with this material. 6. Dedicated fuel handing systems are needed. 7. Develop environmental health and safety issues evaluation in handing, transport, and usage. 8. Encourage developers to implement bio-oil and by-product applications.

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Thermal Conversion of Biomass 90. Chiaramonti D, Bonini M, Fratini E et al (2003) Development of emulsions from biomass pyrolysis liquid and diesel and their use in engines– Part 2: tests in diesel engines. Biomass Bioenergy 25(1):101–111 91. Ikura M, Stanciulescu M, Hogan E (2003) Emulsification of pyrolysis derived bio-oil in diesel fuel. Biomass Bioenergy 24(3):221–232 92. Wang M, Leitch M, Xu C (2009) Synthesis of phenolic resol resins using cornstalk-derived bio-oil produced by direct liquefaction in hotcompressed phenol-water. J Ind Eng Chem 15(6):870–875 93. Wang M, Leitch M, Xu C (2009) Synthesis of phenol-formaldehyde resol resins using organosolv pine lignins. Eur Polym J 45(12): 3380–3388 94. Peterson A, Vogel F, Lachance R et al (2008) Thermochemical biofuel production in hydrothermal media: A review of sub- and supercritical water technologies. Energy Environ Sci 1:32–65 95. Furimsky E (2000) Catalytic hydrodeoxygenation. Appl Catal A 199(2):147–190 96. Elliott DC (2007) Historical developments in hydroprocessing bio-oils. Energy Fuels 21(3): 1792–1815 97. Davis H, Figueroa C, Schaleger L (1982) Hydrogen or carbon monoxide in the liquefaction of biomass. In: World Hydrogen Energy Conference IV, Pasadena 98. Milne T, Elam C, Evans R (2001) Hydrogen from biomass: State of the art and research challenges. NREL IEA/H2/TR-02/001 99. Tamunaidu P, Bhatia S (2007) Catalytic cracking of palm oil for the production of biofuels: Optimization studies. Bioresour Technol 98(18): 3593–3601 100. Ong Y, Bhatia S (2010) The current status and perspectives of biofuel production via catalytic cracking of edible and non-edible oils. Energy 35(1):111–119 101. Zhu XF, Lu Q (2010) In: Maggy Ndombo Benteke Momba (ed) Production of chemicals from selective fast pyrolysis of biomass, biomass. Sciyo, ISBN: 978-953-307-113-8 102. Lu Q, Xiong W, Li W et al (2009) Catalytic pyrolysis of cellulose with sulfated metal oxides: A promising method for obtaining high yield of light furan compounds. Bioresour Technol 100(20):4871–4876

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103. Dobele G, Rossinskaja G, Dizhbite T et al (2005) Application of catalysts for obtaining 1, 6-anhydrosaccharides from cellulose and wood by fast pyrolysis. J Anal Appl Pyrol 74(1–2): 401–405 104. Nishimura M, Iwasaki S, Horio M (2009) The role of potassium carbonate on cellulose pyrolysis. J Taiwan Inst Chem Eng 40(6): 630–637 105. Shimada N, Kawamoto H, Saka S (2008) Different action of alkali/alkaline earth metal chlorides on cellulose pyrolysis. J Anal Appl Pyrol 81(1):80–87 106. French R, Czernik S (2009) Catalytic pyrolysis of biomass for biofuels production. Fuel Process Technol 91(1):25–32 107. Fabbri D, Torri C, Baravelli V (2007) Effect of zeolites and nanopowder metal oxides on the distribution of chiral anhydrosugars evolved from pyrolysis of cellulose: An analytical study. J Anal Appl Pyrol 80(1):24–29 108. Zhao M, Florin N, Harris A (2009) The influence of supported Ni catalysts on the product gas distribution and H2 yield during cellulose pyrolysis. Appl Catal B 92:185–193 109. Iojoiu E, Domine M, Davidian T et al (2007) Hydrogen production by sequential cracking of biomass-derived pyrolysis oil over noble metal catalysts supported on ceria-zirconia. Appl Catal A 323:147–161 110. Bruun EW, Hauqqaard-Nielsen H, Ibrahim N et al (2010) Influence of fast pyrolysis temperature on biochar labile fraction and short-term carbon loss in a loamy soil. Biomass Bioenergy 35(3):1182–1189 111. Zhang WL, Li GH, Gao WD (2009) Effect of biomass charcoal on soil character and crop yield. Chin Agric Sci Bull 25(17):153–157 112. Karhu K et al (2011) Biochar addition to agricultural soil increased CH4 uptake and water holding capacity – Results from a short-term pilot field study. Agric Ecosyst, Environ 140:309–313 113. Yuan JH, Xu RK (2010) Effects of rice-hullbased biochar regulating acidity of red sail and yellow brown soil. J Ecol Rural Environ 26(5): 472–476 114. Song YJ, Gong J (2010) Effects of biochar application on soil ecosystem functions. Ludong Univ J Nat Sci Ed 26(4):361–365

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115. Diana N, Marco R, Kam-Rigne L et al (2010) Contrasted effect of biochar and earthworms on rice growth and resource allocation in different soils. Soil Biol Biochem 42:1017–1027 116. Luke B, Eduardo MJ, Jose LGE (2010) Effects of biochar and greenwaste compost amendments on

mobility, bioavailability and toxicity of inorganic and organic contaminants in a multi-element polluted soil. Environ Pollut 158:2282–2287 117. Luke B, Marta M (2011) The immobilisation and retention of soluble arsenic, cadmium and zinc by biochar. Environ Pollut 159:474–480

28 Chemicals from Biomass Debalina Sengupta1 . Ralph W. Pike2 1 Chemical Engineering Department, Louisiana State University, Baton Rouge, LA, USA 2 Minerals Processing Research Institute, Louisiana State University, Baton Rouge, LA, USA Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1045 Chemicals from Nonrenewable Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1047 Chemicals from Biomass as Feedstock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1049 Biomass Conversion Products (Chemicals) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1051 Single Carbon Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1051 Methane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1051 Methanol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1053 Two Carbon Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1053 Ethanol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1053 Acetic Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1065 Ethylene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1067 Three Carbon Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1069 Glycerol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1069 Lactic Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1071 Propylene Glycol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1071 1,3-Propanediol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1072 Acetone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1073 Four Carbon Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1073 Butanol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1073 Succinic Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1074 Aspartic Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1075 Five Carbon Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1076 Levulinic Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1076 Xylitol/Arabinitol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1078 Itaconic Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1078 Six Carbon Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1079 Sorbitol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1079 2,5-Furandicarboxylic Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1080

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_28, # Springer Science+Business Media, LLC 2012

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Biopolymers and Biomaterials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1081 Natural Oil–Based Polymers and Chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1082 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1086 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1087

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Abstract: The different biomass conversion routes to chemicals will be described in this chapter. > Chapter 25, ‘‘Biomass as Feedstock,’’ gives an overview of the methods used to obtain chemicals from biomass. These processes along with some other chemical conversions can be used for the manufacture of chemicals from biomass. A list of chemicals compiled based on the carbon number in the chemicals will be discussed in this chapter. Some of these chemicals are presently made from nonrenewable feedstock like natural gas and petroleum while others are new chemicals that have potential to replace nonrenewable feedstock-based chemicals. Transesterification process is used to produce propylene chain of chemicals from glycerin. Fermentation is used to produce ethanol which is converted to ethylene and can be used for ethylene chain of chemicals. The chemicals discussed in this chapter include recent advances in chemistry and processes discussed include new frontiers for research in biomass to chemical production.

Introduction Crude oil is the single largest source of energy for the USA, followed by natural gas and coal. Approximately 3% of the total crude oil is used as feedstock for the production of chemicals [1]. Natural gas is used for the production of fertilizers and supplies energy to the production processes. Petroleum refineries extract and upgrade valuable components of crude oil using various physical and chemical methods into a large array of useful petroleum products. While the USA is one of the world’s largest producers of crude oil, the country relies heavily on imports to meet the demand for petroleum products for consumers and industry. This reliance on international ties to petroleum trade has led to numerous upheavals in the industry over the last 4 decades, the most recent being when crude oil prices reached $134 per barrel in 2008 [2], as shown in > Fig. 28.1. Natural disasters such as hurricanes in the Gulf Coast region (Katrina and Rita in 2005 and Gustav in 2008) caused major damages to offshore oil drilling platforms and disruption of crude oil supply. The natural gas prices, shown in > Fig. 28.2, have also varied from $4 per cubic feet in 2001 to $13 per cubic feet in 2008 [3]. The consumption of energy resources in the world added 30.4 billion tons of carbon dioxide in 2008, an increase of approximately 12 billion tons higher than 1980 figures [4]. The rate of carbon dioxide emissions are expected to go higher, unless alternate methods for obtaining energy, fuels, and chemicals are developed. Renewable resources are considered for supplementing and eventually substituting the dependence on oil and natural gas. These resources include biomass, wind, hydroelectric, and solar energy. These resources convert an alternate form of energy (different from fossil resource) into power, fuels, or chemicals. Some of these resources (wind, solar, hydroelectric) do not emit large quantities of carbon dioxide during resource utilization and thus are cleaner choices compared to fossil resources. This also reduces the dependence on foreign oil imports. The processes for the production of chemicals involve the conversion of traditional or conventional forms of energy (petroleum and natural gas) to materials by rearranging

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-2 Ju 00 n- 1 N 200 ov 1 Ap 200 r-2 1 Se 00 p- 2 Fe 200 b- 2 2 Ju 00 l-2 3 D 00 ec 3 M 200 ay 3 O 200 ct 4 -2 M 00 ar 4 Au 200 g- 5 Ja 200 n- 5 2 Ju 00 n- 6 N 200 ov 6 Ap 200 r- 6 Se 200 p- 7 Fe 200 b- 7 2 Ju 00 l-2 8 D 00 ec 8 M 200 ay 8 O 200 ct 9 -2 00 9

Ja n

$/thousand cubic feet 78 19 79 19 80 19 81 19 82 19 83 19 84 19 85 19 86 19 87 19 88 19 89 19 90 19 91 19 92 19 93 19 94 19 95 19 96 19 97 19 98 19 99 20 00 20 01 20 02 20 03 20 04 20 05 20 06 20 07 20 08 20 09 20 10

19

2008 dollars per barrel

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28 Chemicals from Biomass

140 Historical Price of Crude Oil

120

100

80

60

40

20

0

. Fig. 28.1 Historical crude oil prices [2]

14 Natural Gas (Industrial Price Dollars per Thousand Cubic Feet)

12

10

8

6

4

2

0

. Fig. 28.2 Natural gas prices [3]

Chemicals from Biomass

28

the atoms from the components, mainly carbon, hydrogen, and oxygen. The shift to renewable resources for the production of chemicals offers biomass as the only choice of raw material because only biomass can provide the necessary carbon, hydrogen, and oxygen atoms. The rest of the renewable resources can be used as supplement for energy requirements for the conversion processes. Also, carbon dioxide utilized in photosynthetic processes to produce biomass is released when biomass is used. This allows the immediate use of atmospherically fixed carbon dioxide to be released to the environment, which in turn will be used for biomass formation. The transition from fossil feedstock to biomass feedstock requires extensive process technology changes, market penetration of new chemicals from biomass replacing existing chemicals and process energy requirements.

Chemicals from Nonrenewable Resources The chemical industry in the USA is an integral part of the country’s economy, producing more than 70,000 products each year. About 24% of the chemicals produced become raw materials for other products within the industry. For example, ethylene is the fourth largest produced chemical in the USA, with 24 million short tons produced in 1997 [5]. The Department of Energy gives an extensive list of chemicals and allied products manufactured in the USA, identified by SIC codes (Standard Industrial Classifications). The major US Chemical Industry SIC Codes and their corresponding products are given in > Table 28.1. Based on the classifications of industrial chemicals in > Table 28.1, they can be divided into five chains of chemicals. These include the ethylene chain, the propylene chain, the benzene-toluene-xylene (BTX) chain, the agricultural chemicals chain, and the chloralkali industry [5]. Among these, the production of ethylene, the building block for the ethylene chain of chemicals, depends on the availability of petroleum feedstock. Propylene, a building block for the propylene chain of chemicals, is almost entirely produced as a coproduct with ethylene in the steam cracking of hydrocarbons. The BTX chain of chemicals is coproduced by the catalytic reforming of naptha. The agricultural chemicals, like ammonia, urea, ammonium phosphate, etc., are primarily dependant on natural gas for the production of hydrogen. Thus, the present chemical industry is almost entirely dependent on fossil resources for the production of chemicals. A significant amount of carbon dioxide and other green house gases are also released during the production of these chemicals. Historically, there had been no governmental regulations on carbon dioxide emissions by chemical industries. However, the increased concerns due to global warming, climate change, and pollution reduction programs prompted the US Government House of Representatives to pass the American Clean Energy and Security Act of 2009 [6]. This bill, if passed, would introduce a cap and trade program aimed at reducing the greenhouse gases to address climate change. The Environmental Protection Agency issued the Mandatory Reporting of Greenhouse Gases Rule in December 2009 [7]. The rule requires

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. Table 28.1 Major US chemical industry SIC codes and their products (Adapted from [5]) SIC

Major products

281 Industrial inorganic chemicals 2812 Alkalies and chlorine 2813 Industrial gases

Caustic soda (sodium hydroxide), chlorine, soda ash, potassium, and sodium carbonates Inorganic and organic gases (acetylene, hydrogen, nitrogen, oxygen)

2819 Industrial inorganic chemicals, Compounds of aluminum, ammonium, chromium, (not otherwise classified) magnesium, potassium, sodium, sulfur, and numerous other minerals; inorganic acids 282 Plastics and rubbers 2821 Plastics materials and resins

2822 Synthetic rubber 286 Industrial organic chemicals 2865 Cyclic crudes and intermediates 2869 Industrial organic chemicals (not otherwise classified)

Synthetic resins, plastics, and elastomers (acrylic, polyamide, vinyl, polystyrene, polyester, nylon, polyethylene) Vulcanizable rubbers (acrylic, butadiene, neoprene, silicone) Distilling coal tars; cyclic intermediates, i.e., hydrocarbons, aromatics (benzene, aniline, toluene, xylenes); and organic dyes and pigments Aliphatic/acyclic organics (ethylene, butylene, organic acids); solvents (alcohols, ethers, acetone, chlorinated solvents); perfumes and flavorings; rubber processors and plasticizers

287 Agricultural chemicals 2873 Nitrogenous chemicals 2874 Phosphatic chemicals

Ammonia fertilizer compounds, anhydrous ammonia, nitric acid, urea, and natural organic fertilizers Phosphatic materials, phosphatic fertilizers

reporting of greenhouse gas (GHG) emissions from large sources and suppliers in the USA, and is intended to collect accurate and timely emissions data to inform future policy decisions. Under the rule, suppliers of fossil fuels or industrial greenhouse gases, manufacturers of vehicles and engines, and facilities that emit 25,000 t or more per year of GHG emissions are required to submit annual reports to EPA. With the government initiatives and increased global concerns for green house gas emissions, alternate pathways for production of chemicals from biomass are required. This chapter focuses on the use of biomass as feedstock for chemicals. This is an ongoing research area, and the chemicals discussed in this chapter are not an exhaustive list; however, an attempt is made to include the most promising chemicals from biomass that have the potential for commercialization and can replace the existing chain of chemicals from fossil resources.

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Chemicals from Biomass as Feedstock The world has a wide variety of bio feedstocks that can be used for the production of chemicals. Biomass includes plant materials such as trees, grasses, agricultural crops, and animal manure. The components of biomass are shown in > Fig. 28.3 and it can be seen that all the biomass components are molecules of carbon, hydrogen, and oxygen atoms. Biomass can be divided into five major categories as shown in the figure: starch, cellulose, hemicellulose, lignin, and oils. Cellulose, hemicellulose, and lignin are components of woody biomass, grasses, stalks, stover, etc. Starch and cellulose are both polymeric forms of hexose, a 6 carbon sugar. Hemicellulose is a polymer of pentose. Lignin is composed of phenolic polymers, and oils are triglycerides. Starch is primarily found in corn, sweet sorghum, and other crops. Sugarcane contains the sugar in monomeric form, but extraction of juice is required. Other biomass components, which are generally present in minor amounts, include sterols, alkaloids, resins, terpenes, terpenoids, and waxes. The feedstock availability in the USA currently includes 142 million dry tons per year of forest biomass with a possibility of increasing it to 368 million dry tons per year [8]. The agricultural biomass currently available is 194 million dry tons per year with a possible increase to 998 million dry tons per year. Forest biomass is the biomass obtained from forest land (land having at least 10% tree cover), and is naturally or artificially regenerated. Agricultural biomass is the biomass obtained from cropland designated for the harvested row crops and closely sown crops, hay and silage crops, tree fruits, small fruits, berries, tree

Biomass

Cellulose

Starch a

b

links

Lignin

Oils

links

O

H2C O O

HC * O O

C5 polysaccharides

H2C O

C6 polysaccharides

Hemicellulose

8

OH

OH

OH

12

OH

O

HO HO

9

HO HO

O

OH

15

Hexose

Pentose

. Fig. 28.3 Biomass classifications and components

Complex polymer containing phenolic compounds

ε

Triglycerides

1049

1050

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Chemicals from Biomass

nuts, vegetable and melons, and other minor crops. Apart from forest and agricultural biomass, algae can be produced from power plant exhaust carbon dioxide and used for chemicals synthesis. > Figure 28.4 shows the different routes for the production of chemicals from biomass. The feedstock base includes natural oils, sugars, and starches as carbohydrates, cellulose, and hemicellulose. The main conversion technologies used are transesterification, fermentation, anaerobic digestion, acid dehydration, gasification, and pyrolysis. The primary products given in the figure are not an exhaustive list, but some representative chemicals. There are primarily two different platforms of conversion technologies for converting biomass feedstock to chemicals, the biochemical platform and the thermo-chemical platform (DOE 2010a). The biochemical platform focuses on the conversion of

Feedstock

Conversion Technology

Primary Product

Derivatives

Glycerol Derivatives Glycerol

1,3-Propanediol

Propylene Glycol Natural Oils

Transesterification

Polyurethane Polyols

FAME or FAEE

Ethanol Methanol

Sugars

Ethanol Derivatives

Fermentation Ethanol

Ethylene

Ethylene Derivatives C6 Sugars

Starches

Cellulose And Hemicellulose

Enzyme Conversion

Succinic Acid

C5/C6 Sugars

Butanol

Succinic Acid Derivatives

Butanol Derivatives

Acid or Enzyme Hydrolysis Acid Dehydration

Levulinic Acid

Levulinic Acid Derivatives

Carbon Nanotubes

Single Walled CNT

Ammonia

Ammonia Derivatives

Methanol

Methanol Derivatives

Acetic Acid

Acetic Acid Derivatives

Syngas Gasification CH4 Anaerobic Biodigestion

. Fig. 28.4 Biomass feedstock conversion routes to chemicals

Chemicals from Biomass

28

carbohydrates (starch, cellulose, hemicellulose) to sugars using biocatalysts like enzymes and microorganisms and chemical catalysts. These sugars are then suitable for fermentation into a wide array of chemicals. Apart from this, chemical catalysis used in transesterification reaction can produce fatty acid methyl and ethyl esters (FAME and FAEE) and glycerol. The fermentation products such as ethanol and butanol can be starting material for numerous chemicals, for example, ethanol can be converted to ethylene and introduced to the propylene chain of chemicals. The glycerol produced as by-product in the transesterification process can be converted to produce the propylene chain of chemicals. The thermochemical platform uses technology to convert biomass to fuels, chemicals and power via thermal and chemical processes such as gasification and pyrolysis. Intermediate products in the thermochemical platform include clean synthesis gas or syngas (a mixture of primarily hydrogen and carbon monoxide) produced via gasification and bio-oil and bio-char produced via pyrolysis. Synthesis gas is conventionally manufactured from natural gas, so the gasification procedure to produce synthesis gas from biomass is a possible replacement for the fossil resource. The various chemicals that can be manufactured from biomass are compiled based on carbon numbers and given in the following section. Some of these chemicals are presently made from nonrenewable feedstock like natural gas and petroleum while others are new chemicals that have potential to replace nonrenewable feedstock-based chemicals. This description is not exhaustive but serves as a starting point for identifying the processes and feedstocks for conversion to chemicals.

Biomass Conversion Products (Chemicals) Biomass can be converted to chemicals using the routes described in the previous section. The Biomass Research and Development Act of 2000 had set up a Biomass R&D Technical Advisory Committee which has fixed a goal of supplying USA with 25% of its chemicals from biomass by the year 2030 [8]. Bulk chemicals can be defined as those costing $1.00–$4.00 per kg and produced worldwide in volumes of more than 1 million metric tons per year [9]. The production cost of these chemicals can be reduced by 30% when petrochemical processes are replaced by biobased processes. Some of these chemicals are discussed in the following sections.

Single Carbon Compounds Methane Methane from natural gas is an important industrial raw material for the production of acetylene, synthesis gas, methanol, carbon black, etc. [10]. Natural gas is a nonrenewable source, and ways to produce methane from biomass are needed.

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Methane can be produced from the anaerobic digestion of biomass, primarily waste biomass (e.g., corn stover, sewage sludge, municipal solid waste, etc.). Methanogenic bacteria are comprised of mesophilic and thermophilic species that convert biomass in the absence of oxygen. Anaerobic digestion of biomass is the treatment of biomass with a mixed culture of bacteria to produce methane (biogas) as a primary product. The four stages of anaerobic digestion are hydrolysis, acidogenesis, acetogenesis and methanogenesis. In the first stage, hydrolysis, complex organic molecules are broken down into simple sugars, amino acids, and fatty acids with the addition of hydroxyl groups. In the second stage, acidogenesis, volatile fatty acids (e.g., acetic, propionic, butyric, valeric) are formed along with ammonia, carbon dioxide, and hydrogen sulfide. In the third stage, acetogenesis, simple molecules from acidogenesis are further digested to produce carbon dioxide, hydrogen and organic acids, mainly acetic acid. Then in the fourth stage, methanogenesis, the organic acids are converted to methane, carbon dioxide and water. The last stage produces 65–70% methane and 35–30% carbon dioxide [11]. Anaerobic digestion can be conducted either wet or dry where dry digestion has a solids content of 30% or greater and wet digestion has a solids content of 15% or less. Either batch or continuous digester operations can be used. In continuous operations, there is a constant production of biogas while batch operations can be considered simpler the production of biogas varies. Advantages of anaerobic digestion for processing biomass include the ability to use non-sterile reaction vessels, automatic product separation by outgassing, and relatively simpler equipment and operations. The primary disadvantages for the process are slow reaction rates and low methane yields. The methanation chemistry from carbon monoxide and carbon dioxide is given by the reactions in > Eqs. 28.1 and > 28.2 [12]. Synthetically, the methanation process takes place over nickel catalyst fixed bed reactors, known as methanators. The reactions are highly exothermic and a catalyst system that can maintain its activity after prolonged exposure to high temperatures is required. Three types of methanation reactor configurations include equilibrium-limited fixed bed reactors in series, throughwall-cooled fixed bed reactor, and slurry bubble reactor [12]. CO þ 3H2 ! CH4 þ H2 O

(28.1)

CO2 þ 4H2 ! CH4 þ 2H2 O

(28.2)

An innovative process using pyrolytic gasification for methane production from biomass is given by Klass [13] and shown in > Fig. 28.5. Biomass is fed to the pyrolysis reactor operating at 800 C. The reactor temperature is maintained at this temperature by sand fed from the combustion reactor at 950 C. The biomass decomposes into pyrolysis gas (40% CO, 30% H2 and others) which exits from the top of the reactor. Char is deposited on the sand which is sent to the combustion reactor, and air is fed to this reactor to maintain the temperature at 950 C from combustion of the char. The pyrolysis gas can then be sent to a methanation reactor as shown in > Fig. 28.5.

Chemicals from Biomass

28

Char Combustion Products

Gas Char

Separation

Pyrolysis gas

CO Shift

40% CO 30% H2

Fluidized bed combustion 950 ⬚C

Air

Fluidized bed Pyrolysis Sand recycle

Scrubbing

CO2

Shredded Biomass feed

800 ⬚C

Methanation

CH4

Pyrolysis gas recycle

. Fig. 28.5 Pyrolytic gasification process using two fluidized bed reactors (Adapted from [13])

Methanol Methanol was historically produced by the destructive distillation of wood [14]. Currently, 97% of methanol production is based on natural gas, naptha or refinery light gas. Large-scale methanol manufacture processes based on hydrogen-carbon oxide (carbon mono and dioxides) mixtures were introduced in the 1920s. In the 1970s, low-pressure processes replaced high-pressure routes for the product formation. Currently, methanol is produced using adiabatic route of ICI and isothermal route of Lurgi. Capacities of methanol plants range from 60,000 to 2,250,000 t per year. Nearly 12.2 billion pounds of methanol are produced annually in the USA and around 85% of it is converted to higher value chemicals such as formaldehyde (37%), methyl tertiary butyl ether (28%), and acetic acid (8%) [15]. Synthesis gas, an intermediate in the conventional methanol process from natural gas, can be produced from gasification of biomass [16]. The details of gasification process have been discussed in an earlier chapter. The conventional process for methanol synthesis and the process modification for utilizing biomass as feedstock are given in > Fig. 28.6.

Two Carbon Compounds Ethanol Ethanol has been produced by fermentation of carbohydrates for many thousands of years [14]. Economic, industrial manufacture of ethanol began in the 1930s. Current processes to produce ethanol in the industry include direct and indirect hydration of ethylene and

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New Process Biomass

Separation and Handling Steam, O2 Existing Process

Natural Gas

Desulfurization

Steam Reforming

Syngas (CO/CO2/H2)

Compressor

Methane Converter

Cooling and Distillation

Methanol

Purge Gas

. Fig. 28.6 Conventional methanol process with modification for biomass derived syngas (Adapted from [16])

carbonylation of methyl alcohol and methyl acetate. Industrial uses of ethanol include use as solvents and in the synthesis of chemicals [14]. Forty-five percent of total industrial ethanol demand is for solvent applications. It is a chemical intermediate for the manufacture of esters, glycol ethers, acetic acid, acetaldehyde, and ethyl chloride and this demand as intermediate accounts for 35% of its production. Ethanol can also be converted to ethylene and that serves as a raw material for a wide range of chemicals that are presently produced from petroleum-based feedstock. Since ethylene is an important building block chemical and ethanol is its precursor, the processes for manufacture of ethanol are discussed in details in this section. There are four case studies presented for conversion of lignocellulosic biomass to ethanol. Increasing prices of crude petroleum has prompted the research for manufacture of ethanol from biomass sources. Ethanol can be produced by the fermentation of starch (corn), sugar (sugarcane), or waste lignocellulosic biomass like corn stover or switch grass. The processes for conversion depend on the feedstock used. The reaction for fermentation of glucose to ethanol is given by > Eq. 28.3. C6 H12 O6 ! 2C2 H5 OH þ 2CO2

(28.3)

Sugars can be directly converted to ethanol using Saccharomyces cerevisiae without any pretreatment [13]. For starch containing grain feedstock, the cell walls must be disrupted to expose the starch polymers so that they can be hydrolyzed to free, fermentable sugars as yeast does not ferment polymers. The sugar polymers in grain starches contain about 10–20% hot-water-soluble amylases and 80–90% water-insoluble amylopectins. Both substances yield glucose or maltose on hydrolysis. Cellulosic or lignocellulosic biomass

Chemicals from Biomass

28

is mainly composed of crystalline and amorphous cellulose, amorphous hemicelluloses, and lignin as binder. The main problems associated with using this feedstock lie in the difficulty of hydrolyzing cellulosics to maximize glucose yields and the inability of yeasts to ferment the pentose sugars which are the building blocks of the hemicelluloses. Capacities of biomass feedstock–based ethanol plants range from 1.5 to 420 million gallons per year in the USA [17]. Currently, 60% of the world’s biobased ethanol is obtained from sugarcane in Brazil. Sugar from sugarcane is used directly as a solution from the grinding of the cane and it is sent directly to fermentor rather than proceeding with clarification, evaporation, and crystallization to produce raw sugar that is sent to a sugar refinery. The corn dry grind process for production of ethanol is described by [13] and shown in > Fig. 28.7. The production of ethanol in the USA increased from nearly 2 billion gallons in 1999 to over 13 billion gallons in 2010 [18, 17] as shown in > Fig. 28.8. Cellulosic biomass refers to a wide variety of plentiful materials obtained from plants, including certain forest-related resources (mill residues, precommercial thinning, slash, and brush), many types of solid wood waste materials, and certain agricultural wastes (including corn stover, sugarcane bagasse), as well as plants that are specifically grown as fuel for generating electricity. These materials can be used to produce ethanol which is referred to as ‘‘cellulosic ethanol.’’ The cellulosic biomass contains cellulose, hemicellulose, and lignin. The cellulose and hemicellulose are converted to sugars using enzymes, which are then fermented to ethanol. > Figure 28.9 gives the BCI process for the conversion of cellulosic biomass (sugarcane bagasse) to ethanol. Six plants were selected by DOE to receive federal funding for cellulosic ethanol production [19]. These plants received a sum of $385 million for biorefinery projects for producing more than 130 million gallons of cellulosic ethanol per year. > Table 28.2 gives a list of these plants with their capacity of producing ethanol.

Water

Carbon Dioxide

Aldehydes Ethyl Alcohol (95%)

Precooker

Press

Continuous Cooker

Yeast

Vacuum Cooler Fermentor

Corn Oil Press Cake

Refining Column

Degerminator

Entrainment Separator

Malt

Beer Still

Steam

Scrubber

Grain Mill

Aldehyde Column

Water

Water

Corn

Converter and Cooler Stop Water

. Fig. 28.7 Corn dry grind operation to ethanol (Adapted from [13])

Fusel Oil

Water

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Ethanol Production Capacity 14000 12000 Million gallons per year

1056

10000 8000 6000 4000 2000 0 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2010

. Fig. 28.8 Production of ethanol in the USA from 1999 to 2010 [17, 18]

Ethanol

Sugarcane Bagasse

Xylose sugar and Water

Xylose Fermentation

Fermentation broth

(Xylose to Ethanol)

Hemicellulose Hydrolysis

Liquid/Solid separation

(for release of xylose from hemicellulose)

(to separate sugars from solids)

Solid cellulose/lignin cake

Distillation (to recover ethanol) Cellulose Hydrolysis (for release of Glucose from Cellulose) Glucose sugar and solid lignin

Glucose Fermentation

Lignin for boiler

(Glucose to Ethanol)

. Fig. 28.9 BCI process for converting sugarcane bagasse to ethanol (Adapted from [70])

Chemicals from Biomass

28

. Table 28.2 DOE-funded cellulosic ethanol plants [19] Plant name/ Location/ Start-up year

Feedstock

Feedstock capacity (t/day) Products

Notes

Abengoa Bioenergy Biomass of Kansas LLC Colwich, Kansas, 2011

Corn stover Wheat straw Sorghum Stubble Switchgrass

700

Ethanol: 11.4 million gal/year Syngas

Thermochemical and Biochemical processing

ALICO, Inc. LaBelle, Florida 2010

Yard Wood Vegetative wastes (citrus peel)

770

Gasification Fermentation of syngas to ethanol

BlueFire Ethanol, Inc. Southern California 2009 (plant in Fulton, MS) Broin Companies Emmetsburg, Palo Alto County, Iowa 2010 Iogen Biorefinery Partners, LLC Shelley, Idaho 2010

Sorted green waste 700 and wood waste from landfills

Ethanol: 7 million gal/year (first unit) 13.9 million gal/ year (second unit) Power: 6,255 KW Hydrogen Ammonia Ethanol: 19 million gal/year

Concentrated acid processing Fermentation

Corn fiber Corn stover

842

Ethanol: 125 million gal/year Chemicals Animal feed

Fermentation of starch and lignocellulosic biomass (25%)

Agricultural residues: wheat straw, barley straw, corn stover, switchgrass, and rice straw

700

Ethanol: 18 million gal/year (first plant) 250 million gal/ year (future plants) Ethanol: 10 million gal/year (first unit) 40 million gal/ year (commercial unit) Methanol: 9 million gal/year (Commercial unit)

Enzymatic process converting cellulose to ethanol

Range Fuels, Inc. Unmerchanteable Near Soperton, timber and forest Treutlen County, residues Georgia 2011

1,200

Thermochemical Catalytic syngas conversion

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Four case studies are given in this section where biomass is converted to ethanol. The first two cases are production of ethanol from cellulosic biomass, the third case is a fermentation process of glycerol to produce ethanol, and the fourth case discusses fermentation of syngas to ethanol. There are several other methods to produce ethanol from biomass including corn, sugarcane, sugarcane bagasse, etc. The fermentation of corn to ethanol is a well-established process [13] and detailed descriptions of corn wet milling and dry milling procedures have been given by Johnson [20]. Approximately 93% of the ethanol currently produced in the USA comes from corn and 3% comes from sorghum [18]. Other feedstocks include molasses, cassava, rice, beets, and potatoes. However, these are primarily food and feed crops and there is considerable debate on their usage, for example, the use of corn as feed versus feedstock. Cellulosic biomass to ethanol production is not yet fully developed for large-scale production, and some of these attempts are discussed in the following cases. The first two cases are discussed on the basis of selection on raw material and the optimum selection of plant size. These are the currently the major concerns for a cellulosic feedstock–based ethanol industry and research is ongoing to reduce the cost of ethanol for these factors. Case Study 1: Iogen Process for Ethanol Production from Wheat Straw and Corn Stover Tolan [21] discussed Iogen’s process for production of ethanol from cellulosic biomass. Iogen was one of the six companies identified by DOE to receive federal funding to produce ethanol from lignocellulosic feedstock. Iogen’s facility produces 2,000 gal/day of ethanol from wheat straw in a pilot plant, with proposal to scale up to 170,000 gal/day (60 million gal/year). The Iogen process uses steam explosion pretreatment for chopped, milled wheat straw mixed with corn stover. High-pressure steam and 0.5–2% sulfuric acid are added to the feedstock at a temperature of 180–260 C. The acid hydrolysis releases the hemicellulose and converts it to xylose. The residence time in the pretreatment reactor is 0.5–5 min. The pressure is released rapidly to enable the steam explosion process. Hemicellulose reacts first in the process according to the reaction given in > Eq. 28.4. The dilute sulfuric acid produces xylose monomer, which dehydrates to furfural according to the reaction given in > Eq. 28.5 under further pretreatment conditions. Similar reactions occur for arabinose. Small amounts of cellulose react to glucose according to the reaction given in > Eq. 28.6 and further degrade to hydroxymethylfurfural according to the reaction given in > Eq. 28.7. The lignin depolymerizes in this process but is insoluble in the acid or water. ðC5 H8 O4 Þn þH2 O ! ðC5 H8 O4 Þn1 þC5 H10 O5

(28.4)

C5 H10 O5 ! C5 H4 O2 þ 3H2 O

(28.5)

ðC6 H10 O5 Þn þH2 O ! ðC6 H10 O5 Þn1 þC6 H12 O6

(28.6)

C6 H12 O6 ! C6 H6 O3 þ 3H2 O

(28.7)

Chemicals from Biomass

28

The next step is the preparation of cellulase enzymes and cellulose hydrolysis. In the Iogen process, Trichoderma, a wood-rotting fungus is used to produce cellulase enzymes. The cellulases are prepared in submerged liquid cultures in fermentation vessels of 50,000 gal. The liquid broth contains carbon source, salts, complex nutrients like corn steep liquor and water. The carbon source is important and includes an inducing sugar (like cellobiose, lactose, sophorose, and other low molecular weight oligomers of glucose) promoting cellulase growth as opposed to glucose which promotes growth of the organism. The nutrient broth is sterilized by heating with steam. The fermenter is inoculated with the enzyme production strain once the liquid broth cools down. The operating conditions of the fermenter are 30 C at a pH 4–5. The temperature is maintained using cooling coils of water and pH is maintained using alkali. Constant stream of air or oxygen is passed to maintain aerobic conditions required for Trichoderma. The cellulase enzyme production process requires about one week and at the end of the run, is filtered across a cloth to remove cells. The spent cell mass is disposed in landfills. Cellulase enzymes can be directly used at Iogen’s ethanol manufacturing facility. The enzymes can also be stored provided that it is sterilized against microbial contamination by using sodium benzoate and protein denaturation by using glycerol. Iogen reduces the cost of their ethanol manufacture by having an on-site cellulase manufacture facility, reducing costs due to storage and transportation of enzymes. The cellulase enzymes are conveyed to hydrolysis tanks to convert cellulose to glucose. The slurry from pretreatment containing 5–15% total solids is fed into hydrolysis tanks having a volume of 200,000 gal. Crude cellulase enzymes broth is added in dosages of 100 l/t of cellulose. The contents are agitated to keep material dispersed in the tank. The hydrolysis proceeds for 5–7 days. The viscosity of the slurry decreases and lignin remains as insoluble particles. The cellulose hydrolysis process yields 90–98% conversion of cellulose to glucose. Enzymatic hydrolysis of cellulose occurs according to > Eqs. 28.8 and > 28.9. ðC6 H10 O5 Þn þ H2 O ! ðC6 H10 O5 Þn2 þ C12 H22 O11

(28.8)

C12 H22 O11 þ H2 O ! 2C6 H12 O6

(28.9)

The cellulose hydrolysis is followed by sugar separation and fermentation using recombinant yeast capable of fermenting both glucose and xylose. The hydrolysis slurry is separated from lignin and unreacted cellulose using a plate and frame filter. The filter plates are washed with water to ensure high sugar recovery. The sugar stream from pretreatment section is pumped into fermentation tanks. The lignin cakes can be used for power generation by combustion and excess electricity can be sold to neighboring plants. The sugar stream is fermented with genetically modified Saccharomyces yeast capable of fermenting both glucose and xylose. The yeast is well developed for plant operations with good ethanol tolerance. The rates and yields of xylose fermentation are not high in

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the current process leaving scope for further improvement. The fermentation broth obtained after fermentation is pumped into a distillation column. Ethanol is distilled out at the top and dehydrated. Yield of ethanol obtained in the process is 75 gal/t of wheat straw. The feedstock selection for the Iogen process depended on the following considerations: Low cost: Desired feedstock should be available and delivered to plant at low cost. Primary and secondary tree growth, sawdust, and waste paper have existing markets and were not considered for the process. Availability: Feedstock availability should be consistent and in the order of 800,000 t/year which is not generally available from sugarcane bagasse. Uniformity: Feedstock available should be consistent and hence municipal waste containing foreign matter was discarded. Cleanliness: High levels of silica can cause damage to equipment. Microbial contamination and toxic or inhibitory products should be prevented from the feedstock. High potential ethanol yield: Cellulose and hemicellulose should be present in high percentage in the feed to yield maximum ethanol by fermentation. Wood and forestry waste has high lignin content which inhibits fermentation. High efficiency of conversion: The efficiency of conversion in the Iogen process depended on arabinan and xylan content in feedstock. These are constituent hemicelluloses and low content of these required high quantities of enzyme for conversion to cellulose, thereby increasing the process cost. Case Study 2: NREL Process for Conversion of 2,000 t/day of Corn Stover Aden et al. [22] and Humbird and Aden [23] discuss the use of lignocellulosic biomass for the production of ethanol from corn stover. The plant size was such that 2,000 t/day of corn stover was processed in the facility. The overall plant diagram is given in > Fig. 28.10. The cost estimate is based on the assumption that the plant developed is an ‘‘nth’’ plant of several plants that are already built using the same technology and are operating. The target selling price of ethanol is $1.07 per gallon with a start-up date for plant in 2010. This cost was increased in an updated report [23] to $1.49 per gallon of ethanol. The conceptual design for this plant includes equipment design, corn stover handling, and purchase of enzymes from commercial facilities like Genencor International and Novozymes Biotech. The design did not take into account the sale of by-products which are important commodity and specialty chemicals, but the report mentions that reduction of price of ethanol is possible with the sale of these chemicals. The design of the facility is divided into eight sections: feedstock storage and handling; pretreatment and hydrolyzate conditioning; saccharification and co-fermentation; product, solids, and water recovery; wastewater treatment; product and feed chemical storage; combustor, boiler, and turbogenerator; and utilities. The process description for conversion of biomass is similar to the Iogen process for corn and wheat straw as raw material.

28

Chemicals from Biomass Lime

Enzyme

Steam Gypsum

Shredded Stover Recycle Water

Aerobic Vent

Recycle Water

PRETREATMENT AND CONDITIONING

Hydrolyzate

SACCHARIFICATION AND CO-FERMENTATION

Recycle Cond. Steam Waste Water

Nutrients

WASTEWATER TREATMENT

DISTILLATION DEHYDRATION SCRUBBER EVAPORATOR SOLIDS SEPARATION

Excess Condensate

Still Solids Evap. Syrup Boiler Blowdown Anaerobic CH4

BURNER/BOILER TURBOGENERATOR

Broth

FEED HANDLING

Vent

Feedstock

Nutrients

Vent

Recycle Cond.

EtOH Product

Acid

Steam STORAGE Electricity

. Fig. 28.10 Overall process diagram for corn stover conversion to ethanol [22]

The NREL report gave the following considerations for selection of plant size between 2,000 and 4,000 t/day. These are listed below: Economies of scale: The capital cost for equipment varies with equipment size according to the > Eq. 28.10. If exponential, ‘‘exp,’’ equals 1, linear scaling of plant size occurs. However, if the exponential value is less than 1, then the capital cost per unit size decreases as the equipment becomes larger. The NREL uses a cost scaling exponent of 0.7.   New size exp New Cost ¼ Original Cost (28.10) Old size Plant size and collection distance: The distance traveled to collect corn stover increases as the plant size increases because more stover is required for feed. This collection distance is estimated as the radius of a circle around the plant within which the stover is purchased. This area around the plant is calculated using the > Eq. 28.11. 

(28.11) Areacollection ¼ Dstrover Ystrover  Favailable acres  Fland in crops where Areacollection is the circle of collection around the plant Dstover is the annual demand for stover by an ethanol plant Ystover is metric tons stover collected per acre per year Favailable acres is the fraction of total farmland from which stover can be collected Fland in crops is the fraction of surrounding farmland containing crops

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The fraction of available acres takes into account the land use due to roads and buildings within the farm land. For example, if the farm area has 25% roads and other infrastructure, then the fraction of available land, Favailable acres, is 0.75. The Fland in crops is a variable parameter depending on the ability of farms around the ethanol plant to contribute to the corn stover demand. The parameter is used to vary the dependence of plant size on collection distance. The radius of collection is calculated from the Areacollection. The price of ethanol is also a function of plant size and percentage of available acres. Corn stover cost: The corn stover raw material cost depends on two direct costs: the cost of baling and staging stover at the edge of the field and the cost of transportation from the field to the plant gate. Apart from these, a farmer’s premium and cost for fertilizers also add up to the direct costs for corn stover as a raw material. A life cycle analysis of the corn stover represents that 47% of cost was in the staging and baling process, 23% was for transport of stover to plant, 11% was farmer premium for taking the risk of added work of collecting and selling the residue and the rest 12% for fertilizer supplement for the land. This method of analysis gave a value of $62 per dry metric ton of corn stover. The report suggests that this cost will be reduced considerably over time with new technology for collecting and transporting stover, and an assumption of $33 per dry metric ton of corn stover was taken for further analysis. However, the update to the report in 2009 suggested that the cost for feedstock increased to $69.60 per dry ton of corn stover in 2007, which can be reduced to reach $50.90 per dry ton in 2012 [23]. Corn stover hauling cost: The corn stover hauling cost (cost for farm to gate of plant) depended on distance from plant. The hauler cost is a function of radial distance from the plant. An increase in hauling cost shows the optimum plant size range to decrease. For 50% increase in hauling costs per ton – mile, plant size range decreases from 2,000 to 8,000 t/day to 2,000–5,000 t/day. For a 100% increase, the optimal plant size is at around 3,000 t/day and the price of ethanol increases drastically above or below this price. Total cost of ethanol as a function of plant size : The total cost of ethanol as a function of plant size was determined with the total feedstock and non-feedstock costs. The analysis was done with two plant sizes of 2,000 and 10,000 t/day of stover. A net savings occurred for plant sizes between 6,000 and 8,000 t/day of stover. Below 2,000 t/day, the selling price per gallon of ethanol increased rapidly. A minimum optimal plant size between 2,000 and 4,000 t/day of corn stover was obtained for collection from 10% corn acres around a conversion plant. Case 3: Ethanol from Fermentation of Glycerol Ito et al. [24] described a process where ethanol is produced from glycerol-containing waste discharged after transesterification process. Enterobacter aerogenes HU-101 microorganism is used to ferment the glycerol-rich waste and yields of 63 mmol/l/h of H2 and

Chemicals from Biomass

28

0.85 mol/mole glycerol of ethanol were reported using porous ceramics as support to fix cells in the reactor. There are no reports of scale-up of this process. Case 4: Ethanol from Synthesis Gas Fermentation Synthesis gas can be used as feed to a fermentor that uses anaerobic bacteria to produce ethanol. Although it uses some of the oldest biological mechanisms in existence, technical barriers to be overcome include organism development, gas–liquid mass transfer, and product yield [16, 25, 26]. Spath and Dayton [16] give a description of the process for conversion of synthesis gas to ethanol. The first step in the process is to convert biomass to synthesis gas and the syngas is then converted to ethanol using fermentation. The feedstock for this process was wood chips derived from forests. Wood chips are primarily composed of cellulose, hemicellulose, and lignin. However, this process can use any biobased feedstock as feed, which can be gasified to syngas. The overall schematic diagram is given in > Fig. 28.11. The feed is received and placed in temporary storage on-site. It is then sent to the gasifier where it is converted into a raw syngas mixture rich in carbon monoxide and hydrogen. The indirect BCL/FERCO process gasifier was used for the production of syngas from biomass [16]. The equipment include an indirectly heated gasifier with operating temperature at 700–850 C and pressures slightly greater than atmospheric. The biomass feed is dried and then fed to a fast-fluidized bed where it is converted into a raw syngas. The resulting syngas contains significant amounts of methane, ethylene and other light hydrocarbons, and tars which can be removed in the gasconditioning steps. The conditioned syngas is then fed to fermentation reactor where it is converted to ethanol using bacteria. The resulting fermentation broth is dilute, typically containing 2% or less of ethanol. The ethanol can be recovered from the broth using recovery schemes (distillation, molecular sieves) used in the existing corn ethanol industry. The cell mass produced can be recycled as a portion of the feed to the gasifier. One advantage of the syngas fermentation route is that the chemical energy stored in all parts of the biomass, Tail Gas

Biomass

Feedstock Handling

Syngas Generation, Conditioning, & Compression

Ash

Syngas Fermetation

Ethanol Recovery

Water Cell and Mass Nutrients

Water and Solubles

. Fig. 28.11 Synthesis gas to ethanol process (Adapted from Spath et al. 2003)

Ethanol

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Chemicals from Biomass

including the lignin fraction, contributes to the yield of ethanol. > Equation 28.12 gives the method to calculate the capacity of ethanol produced by this process. P¼

F  HHVF 
GasþCond  XCOþH2 =EtOH 1:5  105

(28.12)

where P, Production of ethanol, million gal/year F, Feed rate, tons/day (dry basis) HHVF, Higher heating value of the feed in Btu/lb (dry) ZGas+Cond Cold gas efficiency of gasifier + conditioning steps (a fraction less than 1) XCOþH2 =EtOH Average conversion of CO and H2 to ethanol, as a fraction of theoretical Spath and Dayton [16] give the overall reactions for the process as given in Eqs. 28.13–28.16. The microorganisms used for ethanol production from syngas mixtures are anaerobes that use a heterofermentative version of the acetyl-CoA pathway for acetogenesis. Acetyl-CoA is produced from CO or H2/CO2 mixtures in this pathway. The acetyl-CoA intermediate is then converted into either acetic acid or ethanol as a primary metabolic product. Carbon monoxide is a better substrate than carbon dioxide and hydrogen because the change in free energy is more favorable as shown in > Eqs. 28.13–28.16. >

6CO þ 3H2 O ! CH3 CH2 OH þ 4CO2

DG ¼ 48:7kcal=mol

(28.13)

2CO2 þ 6H2 ! CH3 CH2 OH þ 3H2 O

DG ¼ 28:7kcal=mol

(28.14)

4CO þ 2H2 O ! CH3 COOH þ 2CO2

DG ¼ 39:2kcal=mol

(28.15)

2CO2 þ 4H2 ! CH3 COOH þ 2H2 O

DG ¼ 25:8kcal=mol

(28.16)

The ratio of ethanol to acetate produced depends upon the strain and fermentation conditions. The organisms are inhibited by low pH and acetate ion concentration. Typically, the pH is kept at 4.5 for the production of ethanol [16]. The organisms used are mesophilic or thermophilic bacteria, with temperature optimums ranging from room temperature to 90 C. High operating temperatures, low carbohydrate levels, low pH, and high CO levels (inhibitory to methanogens) reduce the risk of contamination [16]. The fermentor can be a simple gas-sparged tank reactor, operating in batch or continuous mode. A two-stage fermentation system with cell recycle has been suggested as a better alternative. The syngas fermentation performance is not tied to a specific H2/CO mixture, but organisms prefer CO more than H2 [16]. Spath and Dayton [16] also report the cost analysis for the gasification process and fermentation. A facility for gasification processing 2,000 t (dry) per day of wood would produce 48.5 million gal/year of ethanol based on an ethanol yield of 71 gal per ton. Fixed capital was estimated at $153.6 million, or $3.17 per annual gallon of capacity. Cash costs were $0.697 per gallon with feedstock cost at $25 per ton. The price required for

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a zero net present value for the project with 100% financing and 10% real after-tax discounting, known as rational cost, was $1.33 per gallon. Phillips et al. [25] described the feasibility of a forest resource–based thermochemical pathway conversion to ethanol and mixed alcohols. Hybrid poplar was used as feed for the indirect gasification process. The detailed design included seven sections, namely, feed handling and drying, gasification, gas cleanup and conditioning, alcohol synthesis, alcohol separation, steam cycle, and cooling water. The syngas was heated to 300 C and 1,000 psi pressure and converted to the alcohol mixture across a fixed bed catalyst. The minimum cost of ethanol based on the operating cost was $1.01 per gallon. A similar study with syngas from high-pressure oxygen blown direct gasifiers gave a minimum cost of ethanol based on the operating cost as $1.95 per gallon [27].

Acetic Acid Acetic acid was first made by the fermentation of ethyl alcohol and a very dilute solution of it is used as vinegar [14]. Small quantities of acetic acid are recovered from pyroligneous acid liquor obtained from the destructive distillation of hard wood. The modern acetic acid industry began with the commercial availability of acetylene which was converted to acetaldehyde and then oxidized to acetic acid. The three commercial processes for the manufacture of acetic acid are oxidation of acetaldehyde, liquid phase oxidation of n-butane or naptha, and carbonylation of methyl alcohol. The carbonylation of methyl alcohol is the dominant technology because of low material and energy costs and the absence of significant byproducts. Capacities of acetic acid plants range from 30,000 to 840,000 t per year. Synthesis gas is the raw material for the carbonylation process at low temperature and pressure using a proprietary catalyst, rhodium iodide, developed by BASF and Monsanto. The synthesis gas can be produced alternately from biobased feedstock using gasification and pyrolysis as described in previous chapter. The fermentation of syngas can also be used to produce acetic acid, as shown in > Eqs. 28.15 and > 28.16. Acetic acid can be produced by the anaerobic digestion of biomass. The four stages of anaerobic fermentation are given in the section for methane. The fourth stage of methane formation can be inhibited by the use of iodoform or bromoform, thus producing carboxylic acids, hydrogen, and carbon dioxide. Biomass is converted to acetic acid (CH3COOH) under non-sterile anaerobic conditions according to > Eq. 28.17 [28]. Glucose (C6H12O6) is used for illustration for this reaction. C6 H12 O6 þ 2H2 O þ 4NADþ ! 2H3 CCOOH þ 2CO2 þ 4NADH þ 4Hþ

(28.17)

The reducing power of nicotinamide adenine dinucleotide (NADH) may be released as hydrogen using endogenous hydrogen dehydrogenase as shown by the reaction in > Eq. 28.18. NADH þ Hþ ! NADþ þ H2

(28.18)

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Methanogens are microorganisms that can produce methane by reacting carbon dioxide produced with hydrogen. The reaction is given in > Eq. 28.19. CO2 þ 4H2 ! CH4 þ 2H2 O

(28.19)

Acetic acid can also be converted to methane in the presence of methanogens. So, the potential to convert all biomass to methane exists. The production of methane according to > Eq. 28.19 can be inhibited by the addition of iodoform or bromoform. Thus, combining reactions in > Eqs. 28.17 and > 28.18, > Equation 28.20 is obtained where acetic acid is produced from glucose and the production of methane is inhibited. C6 H12 O6 þ 2H2 O ! 2H3 CCOOH þ 2CO2 þ 4H2

(28.20)

Conversion of biomass mixtures of sugarcane bagasse/chicken manure [29], municipal solid waste/sewage sludge [30], and corn stover/pig manure [31] to carboxylic acids has been reported. Forty-four percent of acetic acid is converted to vinyl acetate which is used to form polyvinyl acetate and polyvinyl alcohols used for paints, adhesives, and plastics. Twelve percent of acetic acid is converted to acetic anhydride which is used to manufacture cellulose acetate, paper-sizing agents, a bleach activator, and aspirin. Thirteen percent of acetic acid is used to produce acetates and esters used in solvents for coatings, inks, resins, gums, flavorings, and perfumes. Twelve percent of acetic acid is used in the production of terephthalic acid (TPA) used for polyethylene teraphthalate (PET) bottles and fibers. Cellulose acetate is a cellulose derivative prepared by acetylating cellulose with acetic anhydride [14]. Fully acetylated cellulose is partially hydrolyzed to give an acetone soluble product, which is usually between a di- and a tri-ester [10]. The esters are mixed with plasticizers, dyes, and pigments and processed in different ways depending on the form of plastic desired. The important properties of cellulose acetate include mechanical strength, impact resistance, transparency, colorability, fabricating versatility, moldability, and high dielectric strength [10]. Cellulose acetate is used to manufacture synthetic fibers like rayon, based on cotton or tree pulp cellulose. Research has been reported using waste cellulose from corn fiber, rice hulls, and wheat straw to produce cellulose acetate [32]. The raw materials are milled, slurried in dilute sulfuric acid, and pretreated in an autoclave at 121 C. This is followed by the acetylation to cellulose triacetate under ambient conditions at 80 C, using acetic acid, acetic anhydride, methylene chloride, and trace amounts of sulfuric acid. The cellulose acetate is soluble in methylene chloride and separated easily from the reaction medium. Conversions of cellulose to cellulose acetate have been 35–40% in a laboratory study. The incentive to pursue this line of work was the price of cellulose acetate, approximately $2.00 per pound, a more valuable product than ethanol.

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Ethylene Ethylene ranks fourth among chemicals produced in large volumes in the USA with about 48 billion pounds produced in 1997 [5]. It is a principal building block for the petrochemicals industry, with almost all of the ethylene produced being used as a feedstock in the manufacture of plastics and chemicals. Ethylene is used as a raw material in the production of a wide variety of chemicals and polymers as shown in > Fig. 28.12 [5]. Polyethylene (PE) is used in the manufacture of plastic films, packaging materials, moldings (e.g., toys, chairs, automotive parts, and beverage containers), wire and cable insulation, pipes, and coatings. Production of polyethylene in USA in 1997 was about 27 billion pounds [5], which increased to 60 billion pounds in 2008 [33]. Ethylene dichloride is used to manufacture polyvinyl chloride (PVC) which is used in drainage and sewer pipes, electrical conduits, industrial pipes, wire and cable coatings, wall panels, siding, doors, flooring, gutters, downspouts, and insulation. US chemicals production of ethylene dichloride was over 20 billion pounds in 1997. US production of PVC was about 14 billion pounds in 1997. Ethylene oxide is used for the production of ethylene glycol which is a commonly used antifreeze. Ethylene glycol also serves as a raw material in the production of polyester, used for manufacturing textiles. Ethylene oxide and ethylene glycol are both listed among the top 50 chemicals produced in the USA, with ethylene oxide ranking twenty-seventh (7.1 billion pounds in 1997) and ethylene glycol ranking twenty-ninth (5.6 billion pounds in 1997). World demand for ethylene was about 180 billion pounds in 1998, and was predicted to reach 250 billion pounds by 2005 [5]. The polyethylene industry was a 100 billion pound market with over 150 producers worldwide in 1998 [5]. The global market for polyvinyl chloride was estimated at about 7.5 billion pounds capacity.

Polyethylene

Ethanol

Ethylene

Ethylene Dichloride

Film coatings, bottles, containers, fibers

Poly Vinyl Chloride

Piping, vinyl siding hoses, latex paint, flooring

Ethanol-amines

Detergents, cosmetics, photo chemicals

Ethylene Oxide

Acetaldehyde

Vinyl Acetate and derivatives

. Fig. 28.12 Ethylene product chain (Adapted from [5])

Ethylene Glycol

Antifreeze, brake fluid, surfactants, inks

Acetic Acid and derivatives

Solvents for coatings, plastics pharmaceuticals, dyea, explosives, food products

Latex paint, safety glass, wood glue, emiulsifiers,leather

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The petroleum refining industry is the major supplier of raw materials for ethylene production, and a large percentage of ethylene capacity is located at petroleum refineries that are in close proximity to petrochemical plants [5]. Naptha and gas oil are the primary sources from which ethylene is obtained. In Western Europe and some Asian countries (South Korea, Taiwan, Japan), naptha and gas oil account for 80–100% of the feed to ethylene crackers. Overall, more than 50% of ethylene production capacity is currently located at refineries. However, the current resources of petroleum are being depleted for use as fuels and the rising price of petroleum feedstock opens up new areas for research for the production of ethylene. Ethanol can be used for the production of ethylene by dehydration. Ethanol, for the dehydration process to ethylene, can be produced from biomass feedstock as described in the earlier section. Ethanol is vaporized by preheating with high-pressure steam before passing over a fixed bed of activated alumina and phosphoric acid or alumina and zinc oxide contained in a reactor [14]. The reaction for dehydration of ethanol to ethylene is given in > Eq. 28.21. C2 H5 OH ! C2 H4 þ H2 O

(28.21)

The reactor can be isothermal or adiabatic, with temperature maintained at 296– 315 C. The reaction is endothermic and the heat is supplied by condensing vapor latent heat. The temperature control in the reactor is important to prevent the formation of acetaldehyde or ethers as by-products. The gas is purified, dried, and compressed using conventional steps. A fluidized bed modification of this process has been developed with efficient temperature controls and conversions up to 99%. Takahara et al. [34] has discussed the use of different catalysts for the dehydrogenation of ethanol into ethylene. The dehydration of ethanol into ethylene was investigated over various solid acid catalysts such as zeolites and silica–alumina at temperatures ranging from 453 to 573 K under atmospheric pressure. Ethylene was produced via diethyl ether during the dehydration process. H-mordenites were the most active for the dehydration. Philip and Datta [35] reported the production of ethyl tert-butyl ether (ETBE) from biomass-derived hydrous ethanol dehydration over H-ZSM-5 catalyst. Temperatures between 413 K and 493 K were studied for the process, at partial pressures of ethanol less than 0.7 atm and water feed molar ratio less than 0.25. Varisli et al. [36] reported the production of ethylene and diethyl ether by dehydration of ethanol over heteropolyacid catalysts. The temperature range studied for this process was 413–523 K with three heteropolyacids, tungstophosphoricacid (TPA), silicotungsticacid (STA), and molybdophosphoricacid (MPA). Very high ethylene yields over 0.75 were obtained at 523 K with TPA. Among the three HPA catalysts, the activity trend was obtained as STA > TPA > MPA. Tsao and Zasloff [37] describe a detailed patented process for a fluidized bed dehydration with over 99% yield of ethylene. Dow Chemical and Crystalsev, a Brazilian sugar and ethanol producer, announced the plans of 300,000 t/year ethylene plant in Brazil to manufacture 350,000 t/year of low-density polyethylene from sugarcane-derived ethanol.

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Braskem, a Brazilian petrochemical company announced their plans to produce 650,000 t of ethylene from sugarcane-based ethanol which will be converted to 200,000 t/year of high-density polyethylene [38].

Three Carbon Compounds Glycerol Glycerol, also known as glycerine or glycerin, is a triol occurring in natural fats and oils. About 90% of glycerol is produced from natural sources by the transesterification process. The rest 10% is commercially manufactured synthetically from propylene [14]. Glycerol is a major by-product in the transesterification process used to convert the vegetable oils and other natural oils to fatty acid methyl and ethyl esters. Approximately 10% by weight of glycerol is produced from the transesterification of soybean oil with an alcohol. Transesterification process is used to manufacture fatty acid methyl and ethyl esters which can be blended in refinery diesel. As the production of fatty acid methyl and ethyl esters increases, the quantity of glycerol manufactured as a by-product also increases the need to explore cost-effective routes to convert glycerin to value-added products. Glycerol currently has a global production of 500,000–750,000 t per year [39]. The USA is one of the world’s largest suppliers and consumers of refined glycerol. Referring to > Fig. 28.13, glycerin can potentially be used in a number of paths for chemicals that are currently produced from petroleum-based feedstock. The products from the glycerol are similar to the products currently obtained from the propylene chain. Uniqema, Procter & Gamble, and Stepan are some of the companies that currently produce derivatives of glycerol such as glycerol triacetate, glycerol stearate, and glycerol oleate. Glycerol prices are expected to drop if biodiesel production increases, enabling its availability as a cheap feedstock for conversion to chemicals. Small increases in fatty acid consumption for fuels and products can increase world glycerol production significantly. For example, if the USA displaced 2% of the on-road diesel with biodiesel by 2012, almost 800 million pounds of new glycerol supplies would be produced. Dasari et al. [40] reported a low pressure and temperature (200 psi and 200 C) catalytic process for the hydrogenolysis of glycerol to propylene glycol that is being commercialized and received the 2006 EPA Green Chemistry Award. Copper chromite catalyst was identified as the most effective catalyst for the hydrogenolysis of glycerol to propylene glycol among nickel, palladium, platinum, copper, and copper chromite catalysts. The low pressure and temperature are the advantages for the process when compared to traditional process using severe conditions of temperature and pressure. The mechanism proposed forms an acetol intermediate in the production of propylene glycol. In a two-step reaction process, the first step of forming acetol can be performed at atmospheric pressure while the second requires a hydrogen partial pressure. Propylene glycol yields >73% were achieved at moderate reaction conditions.

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PLA analogs Oxidation

Glyceric Acid

Vegetable oils

Propylene Glycol Bond Breaking

Transesterification

1,3-Propanediol

PLA and polyester fibers with better properties

Antifreeze, humectant, Sorona Fiber

Glycerol Direct Polymerization

Branched Polyesters and polyols

Possible conversions to propylene oxide and propylene; Acrylonitrile, acrylic acid and isopropyl alcohol

Unsaturated Polyurethane Resins for use in insulation

Auto parts, packaging, carpeting toys, textiles, plastics, computer disks, paints, coatings

Used in personal care products, food/beverages, drugs and pharmaceuticals

. Fig. 28.13 Production and derivatives of glycerol (Adapted from [5, 39])

Karinen and Krause [41] studied the etherification of glycerol with isobutene in liquid phase with acidic ion exchange resin catalyst. Five product ethers and a side reaction yielding C8–C16 hydrocarbons from isobutene were reported. The optimal selectivity toward the ethers was discovered near temperature of 80 C and isobutene/glycerol ratio of 3. The reactants for this process were isobutene (99% purity), glycerol (99% purity), and pressurized with nitrogen (99.5% purity). The five ether isomers formed in the reaction included two monosubstituted monoethers (3-tert-butoxy-1,2-propanediol and 2-tert-butoxy-1,3-propanediol), two disubstituted diethers (2,3-di-tert-butoxy-1propanol and 1,3-di-tert-butoxy-2-propanol), and one trisubstituted triether (1,2,3-tritert-butoxy propane). Tert-butyl alcohol was added in some of the reactions to prevent oligomerization of isobutene and improve selectivity toward ethers. Acrylic acid is a bulk chemical that can be produced from glycerol. Shima and Takahashi [42] reported the production of acrylic acid involving steps of glycerol dehydration, in gas phase, followed by the application of a gas-phase oxidation reaction to a gaseous reaction product formed by the dehydration reaction. Dehydration of glycerol could lead to commercially viable production of acrolein, an important intermediate for acrylic acid esters, superabsorber polymers, or detergents [43] Glycerol can also be converted to chlorinated compounds such as dichloropropanol and epichlorohydrin. Dow and Solvay are developing a process to convert glycerol to epoxy resin raw material epichlorohydrin [44].

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Several other methods for conversion of glycerol exist; however, commercial viability of these methods is still in the development stage. Some of these include catalytic conversion of glycerol to hydrogen and alkanes, microbial conversion of glycerol to succinic acid, polyhydroxyalkanoates, butanol, and propionic acid [43].

Lactic Acid Lactic acid is a commonly occurring organic acid, which is valuable due to its wide use in food and food-related industries and its potential for the production of biodegradable and biocompatible polylactate polymers. Lactic acid can be produced from biomass using various fungal species of the Rhizopus genus, which have advantages compared to the bacteria, including their amylolytic characteristics, low nutrient requirements, and valuable fermentation fungal biomass by-product [45]. Lactic acid can be produced using bacteria also. Lactic acid–producing bacteria (LAB) have high growth rate and product yield. However, LAB has complex nutrient requirements because of their limited ability to synthesize B-vitamins and amino acids. They need to be supplemented with sufficient nutrients such as yeast extracts to the media. This downstream process is expensive and increases the overall cost of production of lactic acid using bacteria. An important derivative of lactic acid is polylactic acid. BASF uses 45% corn-based polylactic acid for its product Ecovio®.

Propylene Glycol Propylene glycol is industrially produced from the reaction of propylene oxide and water [14]. Capacities of propylene glycol plants range from 15,000 to 250,000 t per year. It is mainly used (around 40%) for the manufacture of polyester resins which are used in surface coatings and glass-fiber-reinforced resins. A growing market for propylene glycol is in the manufacture of nonionic detergents (around 7%) used in petroleum, sugar and paper refining and also in the preparation of toiletries, antibiotics, etc. Five percent of propylene glycol manufactured is used in antifreeze. Propylene glycol can be produced from glycerol, a by-product of transesterification process, by a low pressure and temperature (200 psi and 200 C) catalytic process for the hydrogenolysis of glycerol to propylene glycol [40] that is being commercialized and received the 2006 EPA Green Chemistry Award. Ashland Inc. and Cargill have a joint venture underway to produce propylene glycol in a 65,000 t/year plant in Europe [46, 47]. Davy Process Technology Ltd. (DPT) has developed the glycerin to propylene glycol process for this plant. The plant is expected to start up in 2009. The process is outlined in > Fig. 28.14. This is a two-step process where glycerin in the gas phase is first dehydrated into water and acetol over a heterogeneous catalyst bed, and then, propylene glycol is formed in situ in the reactor by the hydrogenation of acetol. The per pass glycerin conversion is 99% and by-products include ethylene glycol, ethanol, and propanols.

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Hydrogen

Hydrogen recycle

Hydrogenolysis

Glycerol

Separation

Glycerol recycle

Propylene glycol

Product Refining

Byproducts

. Fig. 28.14 DPT process for manufacture of propylene glycol from glycerol by hydrogenolysis (Ondrey [47])

Huntsman Corporation plans to commercialize a process for propylene glycol from glycerin at their process development facility in Conroe, Texas [44]. Dow and Solvay are planning to manufacture epoxy resin raw material epichlorohydrin from a glycerin-based route to propylene glycol.

1,3-Propanediol 1,3-Propanediol is a derivative that can be used as a diol component in the plastic polytrimethyleneterephthalate (PTT), a new polymer comparable to nylon [48]. Two methods to produce 1,3-propanediol exist, one from glycerol by bacterial treatment and another from glucose by mixed culture of genetically engineered microorganisms. A detailed description of various pathways to microbial conversion of glycerol to 1,3propanediol is given by Liu et al. [49]. Mu et al. [50] gives a process for conversion of crude glycerol to propanediol. They conclude that a microbial production of 1,3propanediol by Klebsiella. pneumoniae was feasible by fermentation using crude glycerol as the sole carbon source. Crude glycerol from the transesterification process could be used directly in fed-batch cultures of K. pneumoniae with results similar to those obtained with pure glycerol. The final 1,3-propanediol concentration on glycerol from lipasecatalyzed methanolysis of soybean oil was comparable to that on glycerol from alkalicatalyzed process. The high 1,3-propanediol concentration and volumetric productivity from crude glycerol suggested a low fermentation cost, an important factor for the bioconversion of such industrial by-products into valuable compounds. A microbial conversion process for propanediol from glycerol using K. pneumoniae ATCC 25955 was given by Cameron and Koutsky [51]. A $0.20/lb of crude glycerol raw material, a product selling price of $1.10/lb of pure propanediol and with a capital investment of $15 MM, a return on investment of 29% was obtained. Production trends in biodiesel suggest that price of raw material (glycerol) is expected to go down considerably, and a higher return on investment can be expected for future propanediol manufacturing processes.

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DuPont Tate and Lyle bio Products, LLC, opened a $100 million facility in Loudon, Tennessee, to make 1,3-propanediol from corn [52]. The company uses a proprietary fermentation process to convert the corn to Bio-PDO, the commercial name of 1,3propanediol used by the company. This process uses 40% less energy and reduces greenhouse gas emissions by 20% compared with petroleum-based propanediol. Shell produces propanediol from ethylene oxide and Degussa produces it from acroleine. It is used by Shell under the name Corterra to make carpets and DuPont under the name Sorona to make special textile fibers.

Acetone Acetone is the simplest and most important ketone. It is colorless, flammable liquid miscible in water and a lot of other organic solvents such as ether, methanol, and ethanol. Acetone is a chemical intermediate for the manufacture of methacrylates, methyl isobutyl ketone, bisphenyl A, and methyl butynol, among others. It is also used as solvent for resins, paints, varnishes, lacquers, nitrocellulose, and cellulose acetate. Acetone can be produced from biomass by fermentation of starch or sugars via the acetone-butanolethanol fermentation process [53]. This is discussed in detail in the butanol section below.

Four Carbon Compounds Butanol Butanol or butyl alcohol can be produced by the fermentation of carbohydrates with bacteria yielding a mixture of acetone and butyl alcohol [14]. Synthetically, butyl alcohol can be produced by the hydroformylation of propylene, known as the oxo process, followed by the hydrogenation of the aldehydes formed yielding a mixture of n- and isobutyl alcohol. The use of rhodium catalysts maximizes the yield of n-butyl alcohol. The principal use of n-butyl alcohol is as solvent. Butyl alcohol/butyl acetate mixtures are good solvents for nitrocellulose lacquers and coatings. Butyl glycol ethers formed by the reaction of butyl alcohol and ethylene oxide is used in vinyl and acrylic paints and lacquers, and to solubilize organic surfactants in surface cleaners. Butyl acrylate and methacrylate are important commercial derivatives that can be used in emulsion polymers for latex paints, in textile manufacturing, and in impact modifiers for rigid polyvinyl chloride. Butyl esters of acids like phthalic, adipic, and stearic acid can be used as plasticizers and surface-coating additives. The process for the fermentation of butanol is also known as Weizmann process or acetone-butanol-ethanol fermentation (ABE fermentation). Butyric acid producing bacteria belong to the Clostridium genus. Two of the most common butyric acid producing bacteria are C. butylicum and C. acetobutylicum. C. butylicum can produce acetic acid, butyric acid, 1-butanol, 2-propanol, H2 and CO2 from glucose, and C. acetobutylicum can

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produce acetic acid, butyric acid, 1-butanol, acetone, H2, CO2, and small amounts of ethanol from glucose [13]. The acetone-butanol fermentation by C. acetobutylicum was the only commercial process of producing industrial chemicals by anaerobic bacteria that uses a monoculture. Acetone was produced from corn fermentation during World War I for the manufacture of cordite. This process for the fermentation of corn to butanol and acetone was discontinued in 1960s for unfavorable economics due to chemical synthesis of these products from petroleum feedstock. The fermentation process involves conversion of glucose to pyruvate via the EmbdenMeyerhof-Parnas (EMP) pathway; the pyruvate molecule is then broken to acetyl-CoA with the release of carbon dioxide and hydrogen [53]. Acetyl-CoA is a key intermediate in the process serving as a precursor to acetic acid, ethanol. The formation of butyric acid and neutral solvents (acetone and butanol) occurs in two steps. Initially, two acetyl CoA molecules combine to form acetoacetyl-CoA, thus initiating a cycle leading to the production of butyric acid. A reduction in the pH of the system occurs as a result of increased acidity. At this step in fermentation, a new enzyme system is activated, leading to the production of acetone and butanol. Acetoacetyl-CoA is diverted by a transferase system to the production of acetoacetate, which is then decarboxylated to acetone. Butanol is produced by reducing the butyric acid in three reactions. Detailed descriptions of batch fermentation, continuous fermentation, and extractive fermentation systems are given by Moreira [53]. DuPont and BP are working with British Sugar to produce 30,000 t/year or biobutanol using corn, sugarcane, or beet as feedstock [54]. UK biotechnology firm Green Biologics has demonstrated the conversion of cellulosic biomass to butanol, known as Butafuel. Butanol can also be used as a fuel additive instead of ethanol. Butanol is less volatile, not sensitive to water, less hazardous to handle, less flammable, has a higher octane number, and can be mixed with gasoline in any proportion when compared to ethanol. The production cost of butanol from biobased feedstock is reported to be $3.75/gal [54].

Succinic Acid Succinic acid was chosen by DOE as one of the top 30 chemicals which can be produced from biomass. It is an intermediate for the production of a wide variety of chemicals as shown in > Fig. 28.15. Succinic acid is produced biochemically from glucose using an engineered form of the organism Anaerobiospirillum succiniciproducens or an engineered Escherichia coli strain developed by DOE laboratories [39]. Zelder [55] discusses BASF’s efforts to develop bacteria which convert biomass to succinate and succinic acid. The bacteria convert the glucose and carbon dioxide with an almost 100% yield into the C4 compound succinate. BASF is also developing a chemistry that will convert the fermentation product into succinic acid derivatives, butanediol and tetrahydrofuran. Succinic acid can also be used as a monomeric component for polyesters. Snyder [26] reports the successful operation of a 150,000 l fermentation process that uses a licensed strain of E. coli at the Argonne National Laboratory. Opportunities for

Chemicals from Biomass

28

g- butyrolactone (GBL) Reduction

Biomass

Butanediol (BDO)

Solvents, fibers such as lycra

Glucose Tetrahydrofuran (THF) Fermentation

Succinic Acid

Reductive Amination

Pyrrolidione N-methylpyrrolidione (NMP)

Green solvents, water soluble polymers (water treatment)

Straight Chain Polymers Direct Polymerization

Fibers Branched Polymers

. Fig. 28.15 Succinic acid production and derivatives [39]

succinic acid derivatives include maleic anhydride, fumaric acid, dibase esters, and others in addition to the ones shown in > Fig. 28.15. The overall cost of fermentation is one of the major barriers to this process. Low-cost techniques are being developed to facilitate the economical production of succinic acid [39]. Bioamber, a joint venture of Diversified Natural Products (DNP) and Agro Industries Recherche et Development will construct a plant that will produce 5,000 t/year of succinic acid from biomass in Pomacle, France [56]. The plant is scheduled for start-up in mid2008. Succinic acid from BioAmber’s industrial demonstration plant is made from sucrose or glucose fermentation using patented technology from the US Department of Energy in collaboration with Michigan State University. BioAmber will use patented technology developed by [57], for the production of succinic acid using biomass and carbon dioxide.

Aspartic Acid Aspartic acid is a a-amino acid manufactured either chemically by the amination of fumaric acid with ammonia or the biotransformation of oxaloacetate in the Krebs cycle with fermentative or enzymatic conversion [39]. It is one of the chemicals identified in DOE top 12 value-added chemicals from biomass list. Aspartic acid can be used as sweeteners and salts for chelating agents. The derivatives of aspartic acid include amine butanediol, amine tetrahydrofuran, aspartic anhydride, and polyaspartic with new potential uses as biodegradable plastics.

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Five Carbon Compounds Levulinic Acid Levulinic acid was first synthesized from fructose with hydrochloric acid by the Dutch scientist G.J. Mulder in 1840 [58]. It is also known as 4-oxopentanoic acid or g-ketovaleric acid. In 1940, the first commercial scale production of levulinic acid in an autoclave was started in USA by A.E. Stanley, Decatur, Illinois. Levulinic acid has been used in food, fragrance, and specialty chemicals. The derivatives have a wide range of applications like polycarbonate resins, graft copolymers, and biodegradable herbicide. Levulinic acid (LA) is formed by treatment of 6 carbon sugar carbohydrates from starch or lignocellulosics with acid. Five carbon sugars derived from hemicelluloses like xylose and arabinose can also be converted to levulinic acid by addition of a reduction step subsequent to acid treatment. The following steps are used for the production of levulinic acid from hemicellulose [13]. Xylose from hemicelluloses is dehydrated by acid treatment to yield 64 wt.% of furan-substituted aldehyde (furfural). Furfural undergoes catalytic decarbonalytion to form furan. Furfuryl alcohol is formed by catalytic hydrogenation of the aldehyde group in furfural. Tetrahydrofurfuryl alcohol is formed after further catalytic hydrogenation of furfural. Levulinic acid is formed from tetrahydrofurfuryl alcohol on treatment with dilute acid. Werpy et al. [39] reports an overall yield of 70% for production of levulinic acid. A number of large-volume chemical markets can be addressed from the derivatives of levulinic acid [39]. > Figure 28.16 gives the production of levulinic acid from hemicellulose and the derivatives of levulinic acid. In addition to the chemicals in the figure, the following derivative chemicals of LA also have a considerable market. Methyltetrahydrofuran and various levulinate esters can be used as gasoline and biodiesel additives, respectively. d-aminolevulinic acid is a herbicide, and targets a market of 200–300 million pounds per year at a projected cost of $2.00–3.00 per pound. An intermediate in the production of d-aminolevulinic acid is b-acetylacrylic acid. This material could be used in the production of new acrylate polymers, addressing a market of 2.3 billion pounds per year with values of about $1.30 per pound. Diphenolic acid is of particular interest because it can serve as a replacement for bisphenol A in the production of polycarbonates. The polycarbonate resin market is almost 4 billion lb/year, with product values of about $2.40/lb. New technology also suggests that levulinic acid could be used for production of acrylic acid via oxidative processes. Levulinic acid is also a potential starting material for production of succinic acid. Production of levulinic acid derived lactones offers the opportunity to enter a large solvent market, as these materials could be converted into analogs of N-methylpyrrolidinone. Complete reduction of levulinic acid leads to 1,4pentanediol, which could be used for production of new polyesters. A levulinic acid production facility has been built in Caserta, Italy by Le Calorie, a subsidiary of Italian construction Immobilgi [59]. The plant is expected to produce 3,000 t per year of levulinic acid from local tobacco bagasse and paper mill sludge through a process developed by Biofine Renewables.

Chemicals from Biomass

28

g- butyrolactone (GBL) Hemicellulose

Reduction

Methyl tetrahydrofuran

Fuel oxygenates, solvents

Xylose 1,4-pentanediol

Acid catalyzed dehydration

Levulinic Acid

Acetyl acrylates Oxidation

Acetic-acrylic succinic acids

Condensation

Diphenolic acid

Copolymerization with other monomers for property enhancement

Replacement for bisphenol used in polycarbonate synthesis

. Fig. 28.16 Production and derivatives of levulinic acid (Adapted from [39])

Hayes et al. [60] gives the details of the Biofine process for the production of levulinic acid. This process received the Presidential Green Chemistry Award in 1999. The Biofine process involves a two-step reaction in a two-reactor design scheme. The feedstock comprises of 0.5–1.0 cm biomass particles comprised of cellulose and hemicellulose conveyed to a mixing tank by high-pressure air injection system. The feed is mixed with 2.5–3% recycled sulfuric acid in the mixing tank. The feed is then transferred to the reactors. The first reactor is a plug flow reactor, where first-order acid hydrolysis of the carbohydrate polysaccharides occurs to soluble intermediates like hydroxymethylfurfural (HMF). The residence time in the reactor is 12 s at a temperature of 210–220 C and pressure of 25 bar. The diameter of the reactor is small to enable the short residence time. The second reactor is a back mix reactor operated at 190–200 C and 14 bar and a residence time of 20 min. LA is formed in this reactor favored by the completely mixed conditions of the reactor. Furfural and other volatile products are removed and the tarry mixture containing LA is passed to a gravity separator. The insoluble mixture from this unit goes to a dehydration unit where the water and volatiles are boiled off. The crude LA obtained is 75% and can be purified to 98% purity. The residue formed is a bone dry powdery substance or char with calorific value comparable to bituminous coal and can be used in syngas production. Lignin is another by-product which can be converted to char and burned or gasified. The Biofine process uses polymerization inhibitors which convert around 50% of both 5 and 6 carbon sugars to levulinic acid.

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Xylitol/Arabinitol Xylitol and arabinitol are hydrogenation products from the corresponding sugars xylose and arabinose [39]. Currently, there is limited commercial production of xylitol and no commercial production of arabinitol. The technology required to convert the 5 carbon sugars, xylose and arabinose, to xylitol and arabinitol, can be modeled based on the conversion of glucose to sorbitol. The hydrogenation of the 5 carbon sugars to the sugar alcohols occurs with one of many active hydrogenation catalysts such as nickel, ruthenium, and rhodium. The production of xylitol for use as a building block for derivatives essentially requires no technical development. Derivatives of xylitol and arabinitol are described in > Fig. 28.17.

Itaconic Acid Itaconic acid is a C5 dicarboxylic acid, also known as methyl succinic acid and has the potential to be a key building block for deriving both commodity and specialty chemicals. The basic chemistry of itaconic acid is similar to that of the petrochemicals derived maleic acid/anhydride. The chemistry of itaconic acid to the derivatives is shown in > Fig. 28.18. Itaconic acid is currently produced via fungal fermentation and is used primarily as a specialty monomer. The major applications include the use as a copolymer with acrylic acid and in styrene–butadiene systems. The major technical hurdles for the development

Xylaric and xylonic acids Oxidation

New Uses Arabonic and arabinoic acids

Biomass Lignocellulose

Bond Cleavage

Polyols (propylene and ethylene glycols)

Antifreeze, UPRs

Lactic acid

Hydrogenation

Xylitol/Arabinitol

Xylitol, xylaric, xylonic polyesters and nylons Direct Polymerization

Arabinitol, arabonic, arabinoic polyesters and nylons

New Polymer opportunities

Non-nutritive sweeteners, anhydrosugars, unsaturated polyester resins

. Fig. 28.17 Production and derivatives of xylitol and arabinitol (Adapted from [39])

Chemicals from Biomass

Biomass

Sugars

Reduction

Methyl butanediol, butyrolactone, tetrahydrofuran family

28

New useful properties for BDO, GBL, THF family of polymers

Pyrrolidinones

Anaerobic Fungal Fermentation

Itaconic acid Direct Polymerization

Polyitaconic

New Polymer opportunities

Copolymer in styrene butadiene polymers (provides dye receptive for fibers); nitrile latex

. Fig. 28.18 Production and derivatives of itaconic acid (Adapted from [39])

of itaconic acid as a building block for commodity chemicals include the development of very low cost fermentation routes. The primary elements of improved fermentation include increasing the fermentation rate, improving the final titer and potentially increasing the yield from sugar. There could also be some cost advantages associated with an organism that could utilize both C5 and C6 sugars.

Six Carbon Compounds Sorbitol Sorbitol is produced by the hydrogenation of glucose [39]. The production of sorbitol is practiced commercially by several companies and has a current production volume on the order of 200 million pounds annually. The commercial processes for sorbitol production are based on batch technology and Raney nickel is used as the catalyst. The batch production ensures complete conversion of glucose. Technology development is possible for conversion of glucose to sorbitol in a continuous process instead of a batch process. Engelhard (now a BASF-owned concern) has demonstrated that the continuous production of sorbitol from glucose can be done continuously using a ruthenium on carbon catalyst [39]. The yields demonstrated were near 99% with very high weight hourly space velocity. Derivatives of sorbitol include isosorbide, propylene glycol, ethylene glycol, glycerol, lactic acid, anhydrosugars, and branched polysaccharides [39]. The derivatives and their uses are described in the > Fig. 28.19.

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Isosorbide Biomass

Dehydration

Anhydrosugars

Glucose

PET equivalent polymers such as poltethylene isosorbide terephthalates

Hydrogenation

Propylene glycol Sorbitol

Bond Cleavage

Antifreeze, PLA Lactic acid

Direct Polymerization

Branched polysaccarides

Water soluble polymers, new polymer applications

. Fig. 28.19 Production and derivatives of sorbitol (Adapted from [39])

Biomass Diols and Aminations C6 Sugars

Reduction

New useful properties for BDO, GBL, THF family of polymers

Levulinic and succinic acids

Oxidative Dehydration

2,5-Furan dicarboxylic acid

Polyethylene terephthalate analogs Direct Polymerization

Furanoic polyamines

Furanoic polyesters for bottles, containers, films; polyamices market for use in new nylons

PET analogs with potentially new properties (bottles, films, containers)

. Fig. 28.20 Production and derivatives of 2,5-FDCA [39]

2,5-Furandicarboxylic Acid FDCA is a member of the furan family, and is formed by an oxidative dehydration of glucose [39]. The production process uses oxygen, or electrochemistry. The conversion can also be carried out by oxidation of 5-hydroxymethylfurfural, which is an intermediate in the conversion of 6 carbon sugars into levulinic acid. > Figure 28.20 describes some of the potential uses of FDCA.

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28

FDCA resembles and can act as a replacement for terephthalic acid, a widely used component in various polyesters, such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) [39]. PET has a market size approaching 4 billion pounds per year, and PBT is almost a billion pounds per year. The market value of PET polymers varies depending on the application, but is in the range of $1.00–3.00/lb for uses as films and thermoplastic engineering polymers. PET and PBT are manufactured industrially from terephthalic acid, which, in turn, is manufactured from toluene [14]. Toluene is obtained industrially from the catalytic reforming of petroleum or from coal. Thus, FDCA derived from biomass can replace the present market for petroleum-based PET and PBT. FDCA derivatives can be used for the production of new polyester, and their combination with FDCA would lead to a new family of completely biomass-derived products. New nylons can be obtained from FDCA, either through reaction of FDCA with diamines, or through the conversion of FDCA to 2,5-bis(aminomethyl)-tetrahydrofuran. The nylons have a market of almost 9 billion pounds per year, with product values between $0.85 and $2.20 per pound, depending on the application.

Biopolymers and Biomaterials The previous section discussed the major industrial chemicals that can be produced from biomass. This section will be focused on various biomaterials that can be produced from biomass. Thirteen thousand million metric tons of polymers were made from biomass in 2007 as shown in > Fig. 28.21 out of which 68% is natural rubber. New polymers from biomass, which attributes to a total of 3% of the present market share of Other Polymers Nylon resins 12%

Polymers from Biomass

Urethanes 26%

Cellulosics 29% Glycerinbased materials 12% Natural Rubber 68%

Other Polymers 3%

PHA and others 12%

Polylactic acid 38%

. Fig. 28.21 Production of polymers from biomass in 2007 (13,000 million metric tons) and breakdown of ‘‘other polymers’’ [61]

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biobased polymers consists of urethanes, glycerin-based materials, nylon resins, polyhydroxyalkanoates (PHA), and polylactic acid (PLA) [61]. A new product from a new chemical plant is expected to have a slow penetration (less than 10%) of the existing market for the chemical that it replaces. However, once the benefits of a new product are established, for example, replacing glass in soda bottles with petrochemical-based polyethylene terephthalate, the growth is rapid over a short period of time. Most renewable processes for making polymers have an inflection point at $70 per barrel of oil, above which, the petroleum-based process costs more than the renewable process. For example, above $80 per barrel of oil, polylactic acid (PLA) is cheaper than polyethylene terephthalate (PET) [61]. > Table 28.3 gives a list of companies that have planned new chemical production based on biomass feedstock along with capacity and projected startup date. Government subsidies and incentives tend to be of limited time and short-term value. Projected bulk chemicals from biobased feedstocks are ethanol, butanol, and glycerin. Some of these biomaterials have been discussed in association with their precursor chemicals in the previous section. The important biomaterials that can be produced from biomass include wood and natural fibers, isolated and modified biopolymers, agromaterials, and biodegradable plastics [62]. These are outlined in > Fig. 28.22. The production process for poly(3-hydroxybutyrate) is given by Rossell et al. [63] and a detailed review for polyhydroxyalkanoates (PHA) as commercially viable replacement for petroleum-based plastics is given by Snell and Peoples [64]. Lignin has a complex chemical structure and various aromatic compounds can be produced from lignin. Current technology is underdeveloped for the industrial scale production of lignin-based chemicals, but there is considerable potential to supplement the benzene-toluene-xylene (BTX) chain of chemicals currently produced from fossilbased feedstock. Osipovs [65] discusses the extraction of aromatic compounds such as benzene from biomass tar.

Natural Oil–Based Polymers and Chemicals Natural oils are mainly processed for chemical production by hydrolysis and or transesterification. Oil hydrolysis is carried out in pressurized water at 220 C, by which fatty acids and glycerol is produced. The main products that can be obtained from natural oils are shown in > Fig. 28.23. Transesterification is the acid catalyzed reaction in presence of an alcohol to produce fatty acid alkyl esters and glycerol. Fatty acids can be used for the production of surfactants, resins, stabilizers, plasticizers, dicarboxylic acids, etc. Epoxidation, hydroformylation, and methesis are some of the other methods to convert oils to useful chemicals and materials. Sources of natural oil include soybean oil, lard, canola oil, algae oil, waste grease, etc. Soybean oil can be used to manufacture molecules with multiple hydroxyl groups, known as polyols [66]. Polyols can be reacted with isocyanates to make polyurethanes.

Chemicals from Biomass

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. Table 28.3 Companies producing biobased materials from biomass [61] Company name Location

Start-up date

Telles

Clinton, Iowa

Q2, 2009

Cereplast

Seymour, Indiana

Completed, Polylactic 2008 acid (PLA) based compound

25,000

PSM North America

China

In production

Plastarch Material (PSM)

100,000

Synbra

The 2009 Netherlands

Polylactic acid (PLA)

5,000

Green Tianjin, Bioscience China

–

Product

Capacity (t/year) Notes

Polyhydroxy- 50,000 alkanoate (PHA) or Mirel

Polyhydroxy- 10,000 alkanoate (PHA)

Joint venture between Metabolix and Archer Daniels Midland, fermented withK-12 strain of Escherichia coli genetically modified to produce PHA directly. (about 3.5% lower energy consumption compared to conventional plastics), biodegradeable of PHA. Cereplast working with PLA from NatureWorks to make it more heat resistant comparable to polypropylene or polystyrene 80% industrial starch and 8% cellulose mixed with sodium stearate, oleic acid and other ingredients. It can be processed like a petrochemical plastic, can withstand moisture and is heat tolerant PLA technology developed by Dutch lactic acid maker Purac and Swiss process engineering firm, Sulzer DSM has invested in this firm

Soybean oil can also be introduced in unsaturated polyester resins to make composite parts. Soybean oil–based polyols has the potential to replace petrochemical-based polyols derived from propylene oxide in polyurethane formulations [66]. The annual market for conventional polyols is 3 billion pounds in the USA and 9 billion pounds globally.

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Biomass

Wood and Natural Fibers

Isolated and Modified Biopolymers as Biomaterials

Agromaterials, Blends, and Composites

Biodegradable Plastics

Wood, and plant fibers such as cotton, jute, linen, coconut fibers, sisal, ramie and hemp

Cellulose, cellulose esters, cellulose ethers, starch, chitin and chitosan, zein, lignin derivatives

Agromaterials from plant residues, blends of synthetic poleymers and starch, wood plastic composites (WPC), and wood based boards

Polyglycolic acid (PGA), Polylactic acid (PLA), Polycaprolactone (PCL), Polyhydroxyalkanoates (PHA) and cellulose graft polymers

. Fig. 28.22 Biomaterials from biomass [62]

Base oil in lubricants Fatty Acids Natural oils

Surfactants

Methyl soyate from soybean oil

Polymers, Resins and Plasticizers

Polyols Glycerol

Transesterification Epoxidation

Hydroformylation Metathesis

. Fig. 28.23 Natural oil–based chemicals

Established Processes for natural oil feedstock

Processes existing in Petroleum feedstocks, need research for natural oil feedstock

Solvents

Adhesives

Chemicals from Biomass

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Dow Chemicals, the world’s largest manufacturer of petrochemical polyols, also started the manufacture of soy-based polyols [66]. Dow uses the following process for the manufacture of polyols. The transesterification of triglycerides give methyl esters which are then hydroformylated to add aldehyde groups to unsaturated bonds. This is followed by a hydrogenation step which converts the aldehyde group to alcohols. The resultant molecule is used as a monomer with polyether polyols to build a new polyol. Urethane Soy Systems manufactures soy-based polyols at Volga, South Dakota, with a capacity of 75 million pounds per year and supplies them to Lear Corp., manufacturer of car seats for Ford Motor Company. The company uses two processes for the manufacture of polyols: an autoxidation process replacing unsaturated bonds in the triglycerides with hydroxyl groups and a transesterification process where rearranged chains of triglycerides are reacted with alcohols. BioBased Technologies® supply soy polyols to Universal Textile Technologies for the manufacture of carpet backing and artificial turf. Johnson Controls uses their polyols to make 5% replaced foam automotive seats. The company has worked with BASF and Bayer Material Science for the conventional polyurethanes and now manufactures the polyols by oxidizing unsaturated bonds of triglycerides. The company has three families of products with 96%, 70%, and 60% of biobased content. Soybean oil can be epoxidized by a standard epoxidation reaction [67]. The epoxidized soybean oil can then be reacted with acrylic acid to form acrylated epoxidized soybean oil (AESO). The acrylated epoxidized triglycerides can be used as alternative plasticizers in polyvinyl chloride as a replacement for phthalates. Aydogan et al. [68] gives a method for the potential of using dense (sub/supercritical) CO2 in the reaction medium for the addition of functional groups to soybean oil triglycerides for the synthesis of rigid polymers. The reaction of soybean oil triglycerides with KMnO4 in the presence of water and dense CO2 is presented in this paper. Dense CO2 is utilized to bring the soybean oil and aqueous KMnO4 solution into contact. Experiments are conducted to study the effects of temperature, pressure, NaHCO3 addition, and KMnO4 amount on the conversion (depletion by bond opening) of soybean-triglyceride double bonds (STDB). The highest STDB conversions, about 40%, are obtained at the near-critical conditions of CO2. The addition of NaHCO3 enhances the conversion; 1 mole of NaHCO3 per mole of KMnO4 gives the highest benefit. Increasing KMnO4 up to 10% increases the conversion of STDB. Holmgren et al. [69] discusses the uses of vegetable oils as feedstock for refineries. Four processes are outlined as shown in > Fig. 28.24. The first process is the production of fatty acid methyl esters by transesterification process. The second process is the UOP/Eni Renewable Diesel Process that processes vegetable oils combined with the crude diesel through hydroprocessing unit. The third and fourth processes involve the catalytic cracking of pretreated vegetable oil mixed with virgin gas oil (VGO) to produce gasoline, olefins, light cycle oil, and clarified slurry oil. Petrobras has a comparable H-Bio process where vegetable oils can also be used directly with petroleum diesel fractions.

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Application

Biodiesel

Feed

Process

Product

Biodiesel

Biodiesel (FAME), Glycerol

Methanol Vegetable oil and grease

Green diesel

Diesel Vegetable oil and grease

Green gasoline

Diesel Hydrotreater

VGO Vegetable oil and grease

Green olefins

Diesel, green diesel, propane, CO2, H2

Catalytic Cracker

Gasoline

Catalytic Cracker

Light olefins

VGO Vegetable oil and grease

. Fig. 28.24 Processing routes for vegetable oils and grease [69]

Conclusion As in petroleum and natural gas, various fractions are used for the manufacture of various chemicals, biomass can be considered to have similar fractions. All types of biomass contain cellulose, hemicellulose, lignin, fats, and lipids and proteins as main constituents in various ratios. Separate methods to convert these fractions into chemicals exist. Biomass containing mainly cellulose, hemicellulose, and lignin, referred to as lignocellulosics, can also undergo various pretreatment procedures to separate the components. Steam hydrolysis breaks some of the bonds in cellulose, hemicellulose, and lignin. Acid hydrolysis solubilizes the hemicellulose by depolymerizing hemicellulose to 5 carbon sugars such as pentose, xylose, and arabinose. This can be separated for extracting the chemicals from 5 carbon sugars. The cellulose and lignin stream is then subjected to enzymatic hydrolysis where cellulose is depolymerized to 6 carbon glucose and other 6 carbon polymers. This separates the cellulose stream from lignin. Thus, three separate streams can be obtained from biomass. The cellulose and hemicellulose monomers, glucose, and pentose can undergo fermentation to yield chemicals like ethanol, succinic acid, butanol, xylitol, arabinitol, itaconic acid, and sorbitol. The lignin stream is rich in phenolic compounds which can be extracted, or the stream can be dried to form char and used for gasification to produce syngas.

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Biomass containing oils, lipids, and fats can be transesterified to produce fatty acid methyl and ethyl esters and glycerol. Vegetable oils can be directly blended in petroleum diesel fractions and catalytic cracking of these fractions produce biomass-derived fuels. Algae have shown great potential for use as source of biomass, and there have been algae strains which can secrete oil, reducing process costs for separation. Algae grow fast (compared to food crops), fix atmospheric and power plant flue gas carbon sources, and do not require freshwater sources. However, algae production technology on an industrial scale for the production of chemicals and fuel is still in the research and development stage. Growth of algae for biomass is a promising field of research. The glycerol from transesterification can be converted to propylene glycol, 1,3propanediol and other compounds which can replace current natural gas–based chemicals. Vegetable oils, particularly soybean oil, have been considered for various polyols with a potential to replace propylene oxide–based chemicals.

Future Directions These technologies outlined above can be further developed to produce a wide array of chemicals, and further research is needed for the commercialization of these chemicals. Nearly 5.6 billion metric tons of carbon dioxide was emitted to the atmosphere in 2008 from utilization of fossil resources [3]. The world production of polymers from biomass was 13 billion metric tons. There is opportunity to further convert biomass to chemicals and materials, and further research is required in that direction. The derivatives and market penetration of new chemicals from biomass are needed. The lignin stream from cellulosic biomass is an important source of aromatic chemicals such as benzene, toluene, xylene, etc., and can contribute to the BTX chain of chemicals. This chapter outlined the various chemicals that are currently produced from petroleum based feedstock that can be produced from biomass as feedstock. New polymers and composites from biomass are continually being developed which can replace the needs of current fossil feedstock–based chemicals.

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52. CEP (2007) $100-million plant is first to produce propanediol from corn sugar. Chem Eng Prog 103(1):10 53. Moreira AR (1983) Acetone-butanol fermentation. In: Wise DL (ed) Organic chemicals from biomass. The Benjamin Cummind Publishing Company, Menlo Park. ISBN 0-8053-9040-5 54. D’Aquino R (2007) Cellulosic ethanol – tomorrow’s sustainable energy source. Chem Eng Prog 103(3):8–10 55. Zelder O (2006) Fermentation – a versatile technology utilizing renewable resources. In: Raw material change: coal, oil, gas, biomass where does the future lie? http://www.basf.com/ group/corporate/en/function/conversions:/publish/ content/innovations/events-presentations/rawmaterial-change/images/BASF_Expose_Dr_Zelder. pdf. Ludwigshafen, Germany, November 21–22, 2006. Accessed 8 May 2010 56. Ondrey G (2007) A sustainable route to succinic acid. Chem Eng 114(4):18 57. Guettler MV, Jain MK, Soni BK (1996) Process for making succinic acid, microorganisms for use in the process and methods of obtaining the microorganisms. US Patent No. 5,504,004 58. Kamm B, Kamm M, Gruber PR, Kromus S (2006) Biorefinery systems – an overview. In: Kamm B, Gruber PR, Kamm M (eds) Biorefineries – industrial processes and products, vol. 1. Wiley-VCH, Weinheim, Germany. ISBN 3-527-3102 59. Ritter S (2006) Biorefineries get ready to deliver the goods. Chem Eng News 84(34):47 60. Hayes DJ, Fitzpatrick S, Hayes MHB, Ross JRH (2006) The biofine process – production of levulinic acid, furfural and formic acid from lignocellulosic feedstock. In: Kamm B, Gruber PR, Kamm M (eds) Biorefineries – industrial processes and products. Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany. ISBN 3-52731027-4 61. Tullo AH (2008) Growing plastics. Chem Eng News 86(39):21–25

62. Vaca-Garcia C (2008) Biomaterials. In: Clark JH, Deswarte FEI (eds) Introduction to chemicals from biomass. Wiley, Chichester. ISBN 978-0470-05805-3 63. Rossell CEV, Mantelatto PE, Agnelli JAM, Nascimento J (2006) Sugar-based biorefinery – technology for integrated production of Poly (3-hydroxybutyrate), sugar, and ethanol. In: Kamm B, Gruber PR, Kamm M (eds) Biorefineries – industrial processes and products, vol 1. Wiley-VCH, Weinheim. ISBN 3527-31027-4 64. Snell KD, Peoples OP (2009) PHA bioplastic: a valuez-added coproduct for biomass biorefineries. Biofuels, Bioprod Biorefin 3(4):456–467 65. Osipovs S (2008) Sampling of benzene in tar matrices from biomass gasification using two different solid-phase sorbents. Anal Bioanal Chem 391(4):1409–1417 66. Tullo AH (2007) Firms advance chemicals from renewable resources. Chem Eng News 85(19):14 67. Wool RP, Sun XS (2005) Bio-based polymers and composites. Elsevier Academic, Amsterdam. ISBN 0-12-763952-7 68. Aydogan S, Kusefoglu S, Akman U, Hortacsu O (2006) Double-bond depletion of soybean oil triglycerides with KMnO4/H2 in dense carbon dioxide. Korean J Chem Eng 23(5):704–713 69. Holmgren J, Gosling C, Couch K, Kalnes T, Marker T, McCall M, Marinangeli R (2007) Refining biofeedstock innovations. Petrol Tech Q 12(4):119–124 70. Smith RA (2005) Analysis of a petrochemical and chemical industrial zone for the improvement of sustainability, M. S. Thesis. Lamar University, Beaumont, TX 71. DOE (2010a) Biomass multi-year program plan March 2010. Energy efficieny and renewable energy (US DOE). http://www1.eere.energy. gov/biomass/pdfs/mypp.pdf. Accessed 8 May 2010

29 Hydrogen Production Qinhui Wang Institute for Thermal Power Engineering, Zhejiang University, Hangzhou, Zhejiang, China Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1093 Hydrogen Production from Fossil Fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1094 Steam Methane Reforming (SMR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1094 Desulfurization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1095 Steam Reforming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1096 Water–Gas Shift (WGS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1097 H2 Purification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1097 Oil Reforming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1098 Steam Reforming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1098 Partial Oxidation (POX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1099 Autothermal Reforming (ATR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1099 Pyrolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1100 Coal Gasification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1100 Moving Bed Gasification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1101 Fluidized Bed Gasification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1102 Entrained Flow Gasification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1103 Underground Coal Gasification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1104 Hydrogen Production from Biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1105 Thermochemical Conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1105 Pyrolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1106 Gasification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1107 Supercritical Water Gasification (SCWG) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1109 Biological Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1110 Photosynthesis Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1110 Fermentative Hydrogen Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1111 Biological Water–Gas Shift Reaction (BWGS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1112 Hydrogen Production from Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1113 Water Electrolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1114 Alkaline Electrolyzer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1114 PEM Electrolyzer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1115 Solid Oxide Electrolysis Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1115 Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_29, # Springer Science+Business Media, LLC 2012

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Water Thermochemical Splitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1116 Water Photoelectrolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1118 Sorption-Enhanced H2 Production with In Situ CO2 Capture Using Carbon-Containing Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1120 Sorption-Enhanced H2 Production from Solid Fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1122 Sorption-Enhanced H2 Production from Natural Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . 1124 Reactivity of CaO Sorbents Throughout Cyclic Calcination–Carbonation (CC) Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1125 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1126

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Abstract: Hydrogen (H2) is mainly used in chemical industry currently. In the near future it will also become a significant fuel due to advantages of reductions in greenhouse gas emissions, enhanced energy security, and increased energy efficiency. To meet future demand, sufficient H2 production in an environmentally and economically benign manner is the major challenge. This chapter provides an overview of H2 production pathways from fossil hydrocarbons, renewable resources (mainly biomass), and water. And high purity H2 production by the novel CO2 sorption-enhanced gasification is highlighted. The current research activities, recent breakthrough, and challenges of various H2 production technologies are all presented. Fossil hydrocarbons account for 96% of total H2 production in the world. Steam methane reforming, oil reforming, and coal gasification are the most common methods and all technologies have been commercially available. However, H2 produced from fossil fuel is nonrenewable and results in significant CO2 emissions, which will limit its utilization. H2 produced from biomass is renewable and CO2 neutral. Biomass thermochemical processes such as pyrolysis and gasification have been widely investigated and will probably be economically competitive with steam methane reforming. However, research on biomass biological processes such as photolysis, dark fermentation, photo-fermentation, etc., are in laboratory scale and the practical applications still need to be demonstrated. H2 from water splitting is also attractive because water is widely available and very convenient to use. However, water-splitting technologies, including electrolysis, thermolysis, and photoelectrolysis, is more expensive than using large-scale fuel processing technologies and large improvement in system efficiency is necessary. CO2 sorption-enhanced gasification is the core unit of zero emission systems. It has been thermodynamically and experimentally demonstrated to produce H2 with purity over 90% from both fossil hydrocarbons and biomass. The major challenge is that the reactivity of CO2 sorbents decays through multi calcination–carbonation cycles.

Introduction Fossil fuels (i.e., petroleum, natural gas, and coal), which meet most of the world’s energy demand today, are being depleted fast. Also, it is now widely acknowledged that combustion of fossil fuels contributes to the buildup of CO2 in the atmosphere, which in turn contributes to the greenhouse effect, causing the well-known global warming. Many engineers and scientists agree that the solution to this problem would be to replace the existing fossil system by the hydrogen energy system. The idea of a hydrogen economy with decarbonizing energy supply has merit. Additional drivers for the switch to a H2 energy economy can include opportunities for increased energy security through greater diversity of resources for supply and greater efficiency and versatility with the mastery of hydrogen fuel cell technology. Hydrogen is the simplest element known to man. It is also the most plentiful gas in the universe. Hydrogen gas is the lightest gas thus it rises in the atmosphere.

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Therefore, hydrogen as a gas (H2) is not found by itself on earth. It is found only in compound form with other elements. Hydrogen combined with carbon forms different compounds such as methane (CH4), coal, and petroleum. Hydrogen combined with oxygen forms water. And hydrogen is also found in growing things – biomass. The amount of energy produced during hydrogen combustion is higher than released by any other fuel on a mass basis, with a lower heating value (LHV) 2.4, 2.8, and 4 times higher than that of methane, gasoline, and coal, respectively. The product of hydrogen combustion is only water and thus the utilization of hydrogen is pollutant zero emission. An idyllic vision of a ‘‘hydrogen economy’’ is one in which H2 and electricity are the sole energy carriers and both are produced without harmful emissions, from renewable resources. H2 would be used in transport, industrial, commercial, and residential applications, where fossil fuels are currently used. As hydrogen is not an energy source, but a carrier, so it must be produced from other natural sources, not only fossil fuels, but also biomass and water. Sufficient H2 production to meet future demand is the major challenge in moving toward a H2 energy economy.

Hydrogen Production from Fossil Fuel At the present time, H2 is mainly used in chemical industry, for example, to upgrade crude oil and synthesize methanol and ammonia in the petroleum and chemical reactors. Fossil fuel is the major source to produce hydrogen, which amounts to 96% of total hydrogen production in the world. The most common hydrogen production methods are (1) steam methane reforming (SMR) (48%), (2) oil reforming (30%), and (3) coal gasification (18%) [1]. Although ammonia and methanol are also used for H2 production, the proportion is minor. During the transition phase to a sustainable hydrogen economy, hydrogen from fossil fuel will continue to be paid large attention due to the need of considerable cost reduction and technology improvement throughout the entire hydrogen system (production, delivery, storage, conversion, and application).

Steam Methane Reforming (SMR) The dominant industrial process used to produce hydrogen is the SMR process. The first industrial application of SMR was implemented in 1930 [2]. And it is a mature technology which has been in use for several decades as an effective means for hydrogen production. The SMR process is characterized by multiple-step and harsh reaction conditions. Typically, four steps are necessary: (1) desulfurization, (2) steam reforming, (3) water–gas shift (WGS), and (4) H2 purification. > Figure 29.1 shows the diagram of a typical SMR process.

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. Fig. 29.1 A diagram of a typical SMR process

Desulfurization Sulfur that is contained in raw natural gas will lead to catalyst deactivation and facility destruction during H2 production; thus, desulfurization from natural gas to keep the sulfur content in a very low level is a primary and necessary procedure. Typically the desulfurization proceeds by two steps. The first step is wet desulfurization, which is usually performed by the natural gas provider. In this step, natural gas reacts with monoethanolamine (MEA) to remove most sulfur content. The reaction can be expressed by two equations: 2CH3 CH2 OHNH2 þ H2 S !  ðCH3 CH2 OHNH3 Þ2 S ðCH3 CH2 OHNH3 Þ2 S þ H2 S !  2ðCH3 CH2 OHNH3 ÞHS The MEA solvent can be recovered through heating to a higher temperature (>105 C). After wet desulfurization, the sulfur concentration in the raw natural gas will be lowered to approximately 200 ppm. The second step, dry desulfurization, is conducted just prior to the SMR reactor. The aim of dry desulfurization is to realize organic sulfur removal and reach a very low sulfur concentration (2–3 kWe units. The most common catalyst for WGS is Cu based, although some interesting work is currently being done with molybdenum carbide, platinum-based catalysts, and Fe–Pd alloy catalysts. To further reduce the carbon monoxide, a preferential oxidation (PrOx) reactor or a carbon monoxide selective methanation reactor can be used. The PrOx and methanation reactors each have their advantages and challenges. The preferential oxidation reactor increases the system complexity because carefully measured concentrations of air must be added to the system. However these reactors are compact and if excessive air is introduced, some hydrogen is burned. Methanation reactors are simpler in that no air is required; however, for every molecule of carbon monoxide reacted, three hydrogen molecules are consumed. Also, the carbon dioxide reacts with the hydrogen, so careful control of the reactor conditions need to be maintained in order to minimize unnecessary consumption of hydrogen. Currently, preferential oxidation is the primary technique being developed. The catalysts for both these systems are typically noble metals such as platinum, ruthenium, or rhodium supported on Al2O3.

H2 Purification The effluent gas from WGS reactors still contains considerable amounts of CO2, CO, and CH4 gases. In order to obtain H2 with purity higher than 99%, pressure swing adsorption

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(PSA) processes are designed and conducted after WGS reactors. Production of pure hydrogen by using PSA processes has become the state-of-the-art technology in the chemical and petrochemical industries. Several hundred PSA-H2 process units have been installed around the world. In the PSA units, impurity gases with high boiling points are absorbed on the absorbents (zeolites or active carbon) bed at high pressures; however, H2 can pass through the absorbents bed due to the fact that it has the lowest boiling point. The absorbents are then regenerated by lowering down the unit pressure to release the absorbed impurities. In this way, pure H2 is separated from the impurities and fed into the plant’s H2 grid. The released impurities (tail gases) are recycled to the steam reformer burners to provide the necessary heat for the endothermic reforming reactions. Currently, the research goals consisted of developing new H2-PSA processes for (a) increasing the primary and secondary product recoveries while maintaining their high purities, and (b) reducing the absorbent inventory and the associated hardware costs. A considerable effort was also made to develop new absorbents or to modify existing absorbents in order to achieve these research goals. It became a common practice to use more than one type of absorbents in these PSA processes (as layers in the same absorbent vessel or as single absorbents in different vessels) in order to obtain optimum absorption capacity and selectivity for the feed gas impurities while reducing the coabsorption of H2, as well as for their efficient desorption under the operating conditions of the PSA processes.

Oil Reforming Oil reforming is another significant commercial H2 production technology. Light oil with relatively low molecular weight is much favorable to produce H2 comparing with heavy oil such as bitumen or residual oil, as heavy oil is easier to suffer from coke formation which will cause catalyst deactivation. Generally, four reforming techniques, namely, steam reforming, partial oxidation (POX), autothermal reforming (ATR), and pyrolysis, are used to produce hydrogen from oil [3]. In fact, these techniques can also use methane as raw material and all should proceed with the similar four steps as mentioned in steam methane reforming (> section ‘‘Steam Methane Reforming (SMR)’’: desulfurization, (steam) reforming, water–gas shift (WGS), and purification (not necessary for pyrolysis). This section will mainly focus on the distinction among each technology.

Steam Reforming Steam reforming is typically the preferred process for hydrogen production in the industry, using either natural gas or oil. The mechanism can be expressed by the following equation: Cm Hn þ mH2 O ! mCO þ ðm þ n=2ÞH2

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Oil steam reforming is an endothermic reaction and requires an external heat source. It has advantages of not requiring oxygen, having a lower operating temperature than POX and ATR, and producing syngas with a high H2/CO ratio (3:1) which is beneficial for H2 production. However, it does have the highest emissions of the three processes. The catalysts used for oil steam reforming are similar to those in the SMR process. Developing improved and economically available catalysts with high resistance to coke formation is the main research goal.

Partial Oxidation (POX) Partial oxidation (POX) of hydrocarbons and catalytic partial oxidation (CPOX) of oil have been proposed for use in hydrogen production for automobile fuel cells and some commercial applications. It converts oil to hydrogen by partially oxidizing (combusting) the material with oxygen, as shown in the equation: Cm Hn þ m=2O2 ! mCO þ n=2H2 Partial oxidation has advantages of minimal methane slip, higher sulfur tolerance, and beneficial H2/CO ratio (1:1 to 2:1) favored for the feeds to hydrocarbon synthesis reactors such as Fischer–Tropsch. However, in order to reduce coke formation the non-catalytic partial oxidation process needs operating at high temperatures (1,300–1,500 C). Although catalysts can be added to the partial oxidation system to lower the operating temperatures, it is proving hard to control temperature because of coke and hot spot formation due to the exothermic nature of the reactions. Recently, Krummenacher et al. [5] have had success using catalytic partial oxidation for decane, hexadecane, and diesel fuel. But the high operating temperatures (>800 C and often >1,000 C) [5] and safety concerns may make their use for practical, compact, portable devices difficult due to thermal management [6]. In addition, this process requires an expensive and complex oxygen separation unit in order to feed pure oxygen to the reactor.

Autothermal Reforming (ATR) Autothermal reforming adds steam to catalytic partial oxidation (CPOX). The reaction mechanism can be expressed as: Cm Hn þ m=2H2 O þ m=4O2 ! mCO þ ðm=2 þ n=2ÞH2 Autothermal reforming is typically conducted at a lower pressure than POX reforming and has a low methane slip. It consists of a thermal zone where POX or CPOX is used to generate the heat needed to drive the downstream steam reforming reactions in a catalytic zone. The heat from the POX negates the need for an external heat source, simplifying the system and decreasing the start-up time. A significant advantage for this process over steam reforming is that it can be stopped and started very rapidly while producing a larger

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amount of hydrogen than POX alone. There is some expectation that this process will gain favorability with the gas-liquids industry due to favorable gas composition for the Fischer–Tropsch synthesis, ATR’s relative compactness, lower capital cost, and potential for economies of scale [7]. However, for ATR to operate properly both the oxygen to fuel ratio and the steam to carbon ratio must be properly controlled at all times in order to control the reaction temperature and product gas composition while preventing coke formation. Similar to POX, this process also needs an expensive oxygen separation unit.

Pyrolysis Pyrolysis is another H2 production technology where the raw oil is decomposed (without water or oxygen present) into hydrogen and carbon. The reactions can be written in the following form: Cm Hn ! mC þ n=2H2 Since no water or air is present, no carbon oxides (e.g., CO or CO2) are formed, eliminating the need for secondary reactors (WGS, PrOx, PSA, etc.). Thus this process offers significant emissions reduction. Among the advantages of this process are fuel flexibility, relative simplicity and compactness, clean carbon by-product, and reduction in CO2 and CO emissions. One of the challenges with this approach is the potential for fouling by the carbon formed, but proponents claim this can be minimized by appropriate design [8]. Pyrolysis may play a significant role in the future. In Norway, the Kverrner Oil & Gas Company has developed an attractive technique to simultaneously produce carbon and H2 by oil plasma pyrolysis. It is said that this technique has an energy efficiency of 1.1 kW h m3 H2, and the commercial operation is feasible now.

Coal Gasification Coal is an abundant energy source in many parts of the world. H2 production by coal gasification is considered to be a promising option before economical H2 production pathways from renewable energy sources are developed. Coal gasification can be defined as the reaction of solid fuels with air, oxygen, steam, carbon dioxide, or a mixture of these gases at a temperature exceeding 700 C, to yield a gaseous product suitable for use either as a source of energy or as a raw material for the synthesis of chemicals, liquid fuels, or other gaseous fuels. > Figure 29.2 shows the diagram of a typical gasification process. Coal gasification is currently used to produce H2 as an intermediate for the synthesis of chemicals. However, large-scale H2 production project mainly for power generation is also under development. A well-known example is the FutureGen project sponsored by the department of energy (DOE) in USA, which is a 10-year, US $1 billion, demonstration project started from February 2003 [9]. This section shows not only the three main

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Coal Pet coke Oil residue Biomass Industial wastes H2O

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G a s i f i e r

H2O and CO shift to H2 and CO2

H2 (with high purity)

H2S Removal Marketable byproducts: SULPHUR RECOVERY

Sulfur & Slag

. Fig. 29.2 A diagram of a typical gasification process

conventional coal gasification technologies, moving bed gasification, Fluidized bed gasification, and entrained flow gasification, but also an alternative method, denoted underground coal gasification (UCG).

Moving Bed Gasification Moving bed gasification is only suitable for solid fuels with a particle size in the range of 5–80 mm. Typically a mixture of steam and oxygen is introduced at the bottom of the reactor and runs counter-flow to the coal. Coal residence times in moving bed gasifiers are of the order of 15–60 min for high pressure steam/oxygen gasifiers and can be several hours for atmospheric steam/air gasifiers. The pressure in the bed is typically of the order of 3 MPa for commercial gasifiers with tests realized at up to 10 MPa. Maximum temperatures in the combustion zone are typically in the range of 1,500–1,800 C for slagging gasifiers and 1,300 C for dry ash gasifiers. Although moving bed gasifiers are presently less used than entrained flow gasifiers for the construction of new power plants, moving bed gasification present the advantage of being a mature technology. The main requirement of moving bed gasifiers is good bed permeability to avoid pressure drops and channel burning that can lead to unstable gas outlet temperatures and composition as well as risk of a downstream explosion. A typical advanced moving bed technique is the British Gas Lurgi (BGL) technology [10]. It is said that this technology will be adopted in the Kentucky Pioneer Energy project, which is an Integrated Coal Gasification Combined Cycle (IGCC) project cosponsored by Global Energy Inc. and DOE of USA. > Table 29.1 shows the process characteristics of BGL technology.

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. Table 29.1 Process characteristics of BGL technology [9, 11] Feeding mode and Lumped coal together with a flux is discharged at the top of the gasifier operating conditions as a sequence of batches. A distributor plate slowly rotates to ensure even distribution of the coal Gasifier Double-walled cylindrical reactor surrounded by a steam jacket. O2 and steam are added toward the bottom of the bed through tuyeres, resulting in high internal temperature within the gasifier (2,000 C) Ash removal system Slagging gasifier. Molten ash is tapped off and quenched with water Cooling and Tars, high boiling point hydrocarbons, and particulates are removed in cleaning modes a quench vessel and re-injected in the bed near the tuyeres. The gas (450–500 C) is cooled and cleaned by a water quench and scrubbed to remove H2S Remarks It is a slagging gasifier modified from the Lurgi dry ash Gasifier and not suitable for high reactive coals. O2 consumption is higher than Lurgi dry ash Gasifier. It is still difficult to develop very large commercial unit meeting the demand for large-scale industrial gasifier

Fluidized Bed Gasification Fluidized bed gasification can only operate with solid crushed coals in the range of 0.5–5 mm. Coals are introduced into an upward flow of gas (either air or oxygen/steam) that fluidizes the bed of fuel while the reaction is taking place. The bed is either formed of sand, coke, char, sorbent, or ash. Residence time of the feed in the gasifier is typically in the order of 10–100 s but can also be much longer, with the feed experiencing a high heating rate from the entry in the gasifier. High levels of back-mixing ensure a uniform temperature distribution in the gasifier. Fluidized bed gasifiers usually operate at temperatures well below the ash fusion temperatures of the fuels (900–1,050 C) to avoid ash melting, thereby avoiding clinker formation and loss of fluidity of the bed. The low operating temperatures may lead to incomplete carbon conversion of coal, but this can be overcome by char recirculation into the gasifier. Advanced Fluidized bed gasifiers are also operated at elevated pressures. Among the main advantages of this type of gasifier are that they can operate at variable loads and are more tolerant to coals with high sulfur content. But for Fluidized bed gasification it is necessary to process coals with a higher ash fusion temperature than the operating temperature of the gasifier to avoid ash agglomeration (which causes uneven fluidization in dry ash, Fluidized bed gasifiers). Two types of Fluidized bed gasification technologies have been operated at commercial scale. They are High Temperature Winkler (HTW) and Kellogg Rust Westinghouse (KRW) gasification technologies, respectively, both of which can be used in IGCC plants. > Table 29.2 gives the process characteristics of HTW and KRW technologies.

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. Table 29.2 Process characteristics of HTW and KRW technologies [9, 11] HTW Feeding mode and Coal dropped from a bin via a gravity pipe into the gasifier. Operating operating conditions pressure is 1–3 MPa Gasifier Bed is formed of particles of ash, semi-coke, and coal and is maintained at 800 C Ash removal system Dry ash removal through a discharge screw Cooling and cleaning modes Remarks

Using cyclone to remove particulates, water or fire tube cooling system Plan to replace old Lurgi dry ash reactors at Vresova IGCC plant in Czech republic. It is promising due to the elevated operation temperature and pressure compared to the conventional Winkler gasifier

KRW Feeding mode and Lock hoppers, operating pressure is up to 2 MPa operating conditions Gasifier Coal partial combustion around the feed nozzle forming 1,150–1,260 C high temperature zone Ash removal system Ash agglomerating to large particles then separated from the remaining coal char Cooling and Raw gas is cooled from 900 C to 600 C and enters a hot gas cleaning cleaning modes system. A portion of the gas is recycled to the gasifier Remarks

Used in the Pinon Pine IGCC plant. Carbon content in the ash can be greatly lowered down

Entrained Flow Gasification In entrained flow gasifiers, coal particles concurrently react at high speed with steam and oxygen or air in a suspension mode called entrained fluid flow. Short gas residence times (seconds) give them a high load capacity but also require coal to be pulverized. Coal can either be fed dry (commonly using nitrogen as a transport gas) or wet (carried in slurry water) into the gasifier. They usually operate at high temperatures of 1,200–1,600 C and pressures in the range of 2–8 MPa. Although entrained flow gasifiers are the most widely used gasifiers, more critical operational requirements are needed compared to moving bed and Fluidized gasifiers, such as significant cooling of the raw syngas before being cleaned; controlling the coal/oxidant ratio within narrow limits through the entire operation in order to maintain a stable flame close to the injector tip; and strict requests on coal properties including a minimum ash content required for gasifiers with slag self-coating walls, a maximum ash content fixed for each type of entrained flow gasifier, ash composition (SiO2, CaO, iron oxides) limitations to avoid the refractory cracking, optimum ash fusion temperature and critical temperature viscosity recommended for smooth slag

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. Table 29.3 Process characteristics of Texaco and Shell technologies [9, 11] Texaco Feeding mode and operating conditions Gasifier Ash removal system Cooling and cleaning modes Remarks

Shell Feeding mode and operating conditions Gasifier Ash removal system Cooling and cleaning modes Remarks

Slurry-fed through burners at the top of the gasifier. Operate at temperatures in the range 1,250–1,450 C and 3–8 MPa pressures Pressure vessel with refractory lining The molten slag flows out toward the bottom of the gasifier with the raw gas and is water quenched and removed through a lock hopper Raw gas can either be cooled or cleaned from slag by water quenching or radiant cooler There are six Texaco-owned gasification facilities worldwide that produce power, chemicals, and H2 from coal. It has wide applicability to various coal types Coal powders are transported by N2 gases, operation at 2–4 MPa, at 1,500 C and above A carbon steel vessel enclosed by a non-refractory membrane wall Molten slag is removed through a slag tap and water quenched Syngas is quenched with cooled recycled product gas and further cooled in a syngas cooler. Raw gas is cleaned in ceramic filters; 50% gas is recycled to act as a quenching medium There are five gasification plants using the Shell gasification technology till 2006. Only the Nuon Power Buggenum IGCC plant in the Netherlands is fed with coal. More plants are planned to be built in China and USA

tapping, etc. Entrained flow gasification is the most widely used technology. > Table 29.3 shows the process characteristics of Texaco and Shell technologies, representing the wet feed and dry feed entrained flow gasification, respectively.

Underground Coal Gasification Underground coal gasification does not need the construction of surface plants. In the process, injection and production wells are drilled from the surface and linked together in a coal seam. Once the wells are linked, air or oxygen is injected, and the coal is ignited in a controlled manner. Water present in the coal seam or in the surrounding rocks flows into the cavity formed by the combustion and is utilized in the gasification process. The produced gases (primarily H2, CO, CH4, and CO2) can be used to generate electric power or synthesize chemicals after being cleaned. The former Soviet Union (FSU) performed intensive research on UCG from the 1930s to the 1960s; over 15 Mt of coal have been gasified underground in the FSU, generating 50 Gm3 of gas. Due to the discovery of extensive natural gas in Siberia in 1970s, FSU declined the usage of UCG. As a result of the increasing energy needs in recent years, interest in UCG has been

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rejuvenated all over the world [12]. It is said that China is generally believed to have the largest UCG program currently underway. A pilot industrial UCG plant at the Gonggou coal mine, Wulanchabu, Northern Inner Mongolia Autonomous Region is under construction. This $112 million project is a joint venture between the China University of Mining and Technology and the Hebei Xin’ao Group. The UCG process has several advantages over surface coal gasification such as lower capital investment costs (due to the absence of a manufactured gasifier), no handling of coal and solid wastes at the surface (ash remains in the underground cavity), no human labor or capital for underground coal mining, minimum surface disruption, no coal transportation costs, and direct use of water and feedstock available in situ. In addition, cavities formed as a result of UCG could potentially be used for CO2 sequestration. However, construction of a UCG process is quite complex as lots of criteria should be strictly considered, such as the coal seam conditions (thickness, depth, coal seam dip, coal amount, and ranks), groundwater protection, and land-use restrictions.

Hydrogen Production from Biomass Biomass comprises all the living matter present on earth. It is derived from growing plants including algae, trees, and crops or from animal manure. The biomass resources are the organic matters in which the solar energy is stored in chemical bonds. It generally consists of carbon, hydrogen, oxygen, and nitrogen. Sulfur is also present in minor proportions. Some biomass also consists of significant amounts of inorganic species. Biomass is the fourth largest source of energy in the world, accounting for about 15% of the world’s primary energy consumption and about 38% of the primary energy consumption in the developing countries [13]. Since biomass is renewable and consumes atmospheric CO2 during growth, it can have a small net CO2 impact compared to fossil fuels. Biomass can be converted into useful forms of energy products using a number of different processes. Generally there are two routes for biomass conversion into hydrogen-rich gas: (1) thermochemical conversion and (2) biochemical/biological conversion. The yield of hydrogen is low from biomass since the hydrogen content in biomass is low to begin with (approximately 6% versus 25% for methane) and the energy content is low due to the 40% oxygen content of biomass. Thus hydrogen from biomass has major challenges. There are no completed technology demonstrations [14]. However, biomass still has the potential to accelerate the realization of hydrogen as a major fuel of the future.

Thermochemical Conversions Thermochemical conversion involves a series of cyclical chemical reaction for releasing hydrogen. There are three main methods for biomass-based hydrogen production via thermochemical conversions: (1) pyrolysis, (2) conventional gasification, and (3) SCWG (supercritical water gasification), respectively.

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Pyrolysis Pyrolysis is the heating of biomass at a temperature of 650–800 K at 0.1–0.5 MPa in the absence of air to convert biomass into liquid oils, solid charcoal, and gaseous compounds. Pyrolysis can be further classified into slow pyrolysis and fast pyrolysis. As the products are mainly charcoal, slow pyrolysis is normally not considered for hydrogen production. Fast pyrolysis is a high temperature process, in which the biomass feedstock is heated rapidly in the absence of air, to form vapor, and is subsequently condensed to a dark brown mobile bio-liquid. The products of fast pyrolysis can be found in all gas, liquid, and solid phases: 1. Gaseous products include H2, CH4, CO, CO2, and other gases depending on the organic nature of the biomass for pyrolysis. 2. Liquid products include tar and oils that remain in liquid form at room temperature like acetone, acetic acid, etc. 3. Solid products are mainly composed of char and almost pure carbon plus other inert materials. Although most pyrolysis processes are designed for biofuel production, hydrogen can be produced directly through fast or flash pyrolysis if high temperature and sufficient volatile phase residence time are allowed as follows: Biomass þ heat ! H2 þ CO þ CH4 þ other products Methane and other hydrocarbon vapors produced can be steam reformed for more hydrogen production: CH4 þ H2 O ! CO þ 3H2 In order to increase the hydrogen production, water–gas shift reaction can be applied as follows: CO þ H2 O ! CO2 þ H2 Besides the gaseous products, the oily products can also be processed for hydrogen production. The pyrolysis oil can be separated into two fractions based on water solubility. The water-soluble fraction can be used for hydrogen production while the water-insoluble fraction for adhesive formulation. Experimental study has shown that when Ni-based catalyst is used, the maximum yield of hydrogen can reach 90%. With additional steam reforming and water–gas shift reaction, the hydrogen yield can be increased significantly. Temperature, heating rate, residence time, and type of catalyst used are important pyrolysis process control parameters. In favor of gaseous products especially in hydrogen production, high temperature, high heating rate, and long volatile phase residence time are required. These parameters can be regulated by selection among different reactor types and heat transfer modes, such as gas–solid convective heat transfer and solid–solid conductive heat transfer. Fluidized bed reactor exhibits higher heating rates and thus it appears to be the promising reactor type for hydrogen production from biomass pyrolysis.

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Some inorganic salts, such as chlorides, carbonates, and chromates, exhibit beneficial effect on pyrolysis reaction rate. As tar is difficult to be gasified, extensive studies on the catalytic effect of inexpensive dolomite and CaO on the decomposition of hydrocarbon compounds in tar have been conducted [15]. The catalytic effects of other catalysts (Nibased catalysts, Y-type zeolite, K2CO3, Na2CO3, and CaCO3) and various metal oxides (Al2O3, SiO2, ZrO2, TiO2, and Cr2O3) have also been investigated. Among the different metal oxides, Al2O3 and Cr2O3 exhibit better catalytic effect than the others. Among the catalysts, Na2CO3 is better than K2CO3 and CaCO3. Although noble metals Ru and Rh are more effective than Ni catalyst and less susceptible to carbon formation, they are not commonly used due to their high costs [16]. In order to evaluate hydrogen production through pyrolysis of various types of biomass, extensive experimental investigations have been conducted in recent years. Agricultural residues; peanut shell; post-consumer wastes such as plastics, trap grease, mixed biomass, and synthetic polymers; and rapeseed have been widely tested for pyrolysis for hydrogen production. In order to solve the problem of decreasing reforming performance caused by char and coke deposition on the catalyst surface and in the bed itself, Fluidized catalyst beds are usually used to improve hydrogen production from biomass-pyrolysis-derived biofuel. Yeboah et al. [17] constructed a demonstration plant for hydrogen production from peanut shells pyrolysis and steam reforming in a Fluidized bed reactor and the production rates of 250 kg H2/day was achieved. Padro and Putsche [18] estimated the hydrogen production cost of biomass pyrolysis to be in the range of US $8.86/GJ to US $15.52/GJ depending on the facility size and biomass type. For comparison, the costs of hydrogen production by wind-electrolysis systems and PV-electrolysis systems are US $20.2/GJ and US $41.8/GJ, respectively. It can be seen that biomass pyrolysis is a competitive method for renewable hydrogen production.

Gasification Gasification is the conversion of biomass into a combustible gas mixture via the partial oxidation at high temperatures, typically varying from 800 C to 900 C. It is applicable to biomass having moisture content less than 35%. Biomass is converted completely to CO and H2 in an ideal gasification although some CO2, water and other hydrocarbons including methane also exist in practice. The char compositions occurred by the fast pyrolysis of biomass can be gasified with gasifying agents. Air, oxygen, and steam are widely used gasifying agents. Reaction conditions along with heating values are mentioned as follows: 1. Oxygen gasification: It yields a better quality gas of heating value of 10–15 MJ/Nm3. In this process, the temperatures between 1,000 C and 1,400 C are achieved. O2 supply may bring a simultaneous problem of cost and safety. 2. Air gasification: It is the most widely used technology as it is cheap, single product is formed at high efficiency, and does not require oxygen. A low heating value gas is produced containing up to 60% N2 having a typical heating value of 4–6 MJ/Nm3 with

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by-products such as water, CO2, hydrocarbons, tar, and nitrogen gas. The reactor temperatures between 900 C and 1,100 C have been achieved. 3. Steam gasification: Biomass steam gasification converts carbonaceous material to permanent gases (H2, CO, CO2, CH4, and light hydrocarbons), char, and tar. This method has some problems such as corrosion, poisoning of catalysts, and minimizing tar components. Hydrogen can be produced from the gasification gaseous products through the same procedure of steam reforming and water–gas shift reaction as discussed in the pyrolysis section. As the products of gasification are mainly gases, this process is more favorable for hydrogen production than pyrolysis. In order to optimize the process for hydrogen production, a number of efforts have been made by researchers to test hydrogen production from biomass gasification with various biomass types and at various operating conditions. Using a Fluidized bed gasifier along with suitable catalysts, it is possible to achieve hydrogen production about 60 vol%. Such high conversion efficiency makes biomass gasification an attractive hydrogen production alternative. In addition, the costs of hydrogen production by biomass gasification are competitive with natural gas reforming. Taking into account the environmental benefit as well, hydrogen production from biomass gasification should be a promising option based on both economic and environmental considerations. One of the major issues in biomass gasification is to deal with the tar formation that occurs during the process. The unwanted tar may cause the formation of tar aerosols and polymerization to a more complex structure, which are not favorable for hydrogen production through steam reforming. Currently, three methods are available to minimize tar formation: (1) proper design of gasifier, (2) proper control and operation, and (3) additives/catalysts. The operation parameters, such as temperature, gasifying agent, and residence time, play an important role in formation and decomposition of tar. It has been reported that tar could be thermally cracked at temperature above 1,273 K [19]. The use of some additives (dolomite, olivine, and char) inside the gasifier also helps tar reduction. When dolomite is used, 100% elimination of tar can be achieved [20]. Catalysts not only reduce the tar content, but also improve the gas product quality and conversion efficiency. Dolomite, Ni-based catalysts, and alkaline metal oxides are widely used as gasification catalysts. Process modifications by two-stage gasification and secondary air injection in the gasifier are also useful for tar reduction. Another problem of biomass gasification is the formation of ash that may cause deposition, sintering, slagging, fouling, and agglomeration. To resolve the ash-associated problems, fractionation and leaching have been employed to reduce ash formation inside the reactor. Though fractionation is effective for ash removal, it may deteriorate the quality of the remaining ash. On the other hand, leaching can remove biomass’ inorganic fraction, as well as improve the quality of the remaining ash. More recently, gasification of leached olive oil waste in a circulating Fluidized bed reactor was reported for gas production that demonstrated the feasibility of leaching as a pretreatment technique for gas production [21].

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Supercritical Water Gasification (SCWG) The properties of water displayed beyond critical point plays a significant role for chemical reactions, especially in the gasification process. Below the critical point, both the liquid and gas phases exhibit different properties, although it is apparent that these properties become increasingly alike as the temperature rises. Ultimately, when it reaches the critical point (temperature >374 C, pressure >22 MPa), the properties of both liquid and gas become identical. Over the critical point, the properties of this SCW vary between liquidlike and gas-like conditions. SCW is completely miscible with organic substance as well as with gases. When biomass has high moisture content above 35%, it is likely to gasify biomass in a supercritical water condition, where biomass can be rapidly decomposed into small molecules or gases in a few minutes at a high efficiency. Supercritical water gasification is a promising process to gasify biomass with high moisture contents due to the high gasification ratio (100% achievable), high hydrogen volumetric ratio (50% achievable), and avoiding biomass drying. In recent years, extensive research has been carried out to evaluate the suitability of various wet biomass gasification in supercritical water conditions. However, the works have been mostly on a laboratory scale and in an early development stage; hence, the principles and basic mechanisms are not well understood yet. The solubility of biomass components in hot compressed water has been first studied by Mok et al. [22]. The results show that, in hot compressed waters, about 40–60% of the biomass sample is soluble, though the reaction is maintained slightly below the critical water condition. Minowa et al. [23] reported hydrogen production from cellulose gasification in hot compressed water (subcritical) using nickel catalyst. Yu et al. [24] reported that the gasification of glucose at supercritical water condition, such as 873 K and 34.5 MPa, was different from the nonsupercritical water condition. One advantage is that, during gasification, neither tar nor char formation occurs. This early finding stimulated extensive interests in supercritical water research. Using glucose as a model compound, hydrogen yield of more than 50 vol% can be achieved with the use of proper catalysts in supercritical water condition. Tubular reactors are widely used in supercritical water gasification because of their robust structures to withstand high pressure. Although supercritical water gasification is still at its early development stage, the technology has already shown its economic competitiveness with other hydrogen production methods. Spritzer and Hong [25] have estimated the cost of hydrogen produced by supercritical water gasification to be about US $3/GJ (US $0.35/kg). Hydrogen production from biomass thermochemical processes has already been shown to be attractive economically and demonstrated to be a feasible option. However, it should be noted that hydrogen gas is normally produced together with other gas constituents. Thus, separation and purification of hydrogen gas are required. Nowadays, several methods, such as CO2 absorption, drying/chilling, and membrane separation, have been successfully developed for hydrogen gas purification. It is expected that biomass thermochemical conversion processes will be available for large-scale hydrogen production in the near future.

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Biological Conversion Another method for biomass-based hydrogen is biological conversions. These are summarized as photosynthesis process, fermentative hydrogen production, and hydrogen production by BWGS (biological water–gas shift reaction). All processes depend on hydrogen production enzymes.

Photosynthesis Process Many phototropic organisms, such as purple bacteria, green bacteria, Cyanobacteria, and several algae, can be used to produce hydrogen with the aid of solar energy. Microalgae, such as green algae and Cyanobacteria, absorb light energy and generate electrons. The electrons are then transferred to ferredoxin (FD) using the solar energy absorbed by photosystem. However, the mechanism varies from organism to organism but the main steps are similar. Direct Biophotolysis

Direct biophotolysis of hydrogen production is a biological process using microalgae photosynthetic systems to convert solar energy into chemical energy in the form of hydrogen: 2H2 O

solar energy

!

2H2 þ O2

Two photosynthetic systems are responsible for photosynthesis process: (1) photosystem I (PSI) producing reductant for CO2 reduction and (2) photosystem II (PSII) splitting water and evolving oxygen. In the biophotolysis process, two photons from water can yield either CO2 reduction by PSI or hydrogen formation with the presence of hydrogenase. In green plants, due to the lack of hydrogenase, only CO2 reduction takes place. On the contrary, microalgae, such as green algae and Cyanobacteria (blue-green algae), contain hydrogenase and, thus, have the ability to produce hydrogen. In this process, electrons are generated when PSII absorbs light energy. The electrons are then transferred to the ferredoxin (Fd) using the solar energy absorbed by PSI. Since hydrogenase is sensitive to oxygen, it is necessary to maintain the oxygen content at a low level under 0.1% so that hydrogen production can be sustained. This condition can be obtained by the use of green algae Chlamydomonas reinhardtii that can deplete oxygen during oxidative respiration. However, due to the significant amount of substrate being respired and consumed during this process, the efficiency is low. Recently, mutants derived from microalgae were reported to have good O2 tolerance and thus higher hydrogen production. The efficiency can be increased significantly using mutants for hydrogen production. Benemann [26] estimated the cost of direct biophotolysis for hydrogen production to be $20/GJ assuming that the capital cost is about US $60/m2 with an overall solar conversion efficiency of 10%. Hallenbeck and Benemann [27] performed similar cost

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estimation and reported the capital cost of US $100/m2. However, in their estimation, some practical factors were neglected, such as gas separation and handling. Indirect Biophotolysis

The concept of indirect biophotolysis involves the following four steps: (1) biomass production by photosynthesis, (2) biomass concentration, (3) aerobic dark fermentation yielding 4 mol hydrogen/mol glucose in the algae cell, along with 2 mol of acetates, and (4) conversion of 2 mol of acetates into hydrogen. In a typical indirect biophotolysis, Cyanobacteria are used to produce hydrogen via the following reactions: 12H2 O þ 6CO2 ! C6 H12 O6 þ 6O2 C6 H12 O6 þ 12H2 O ! 12H2 þ 6CO2 Markov et al. [28] investigated the indirect biophotolysis with Cyanobacterium Anabaena variabilis exposed to light intensities of 45–55 and 170–180 A mol1 m2 in the first stage and second stage, respectively. Photoproduction of hydrogen at a rate of about 12.5 mL H2/g cdw h (cdw: cell dry weight) was found. In the study on indirect biophotolysis with Cyanobacterium Gloeocapsa alpicola by Troshina et al. [29], it was found that maintaining the medium at pH value between 6.8 and 8.3 yielded optimal hydrogen production. Increasing the temperature from 30 C to 40 C can increase the hydrogen production twice as much. The hydrogen production rate through indirect biophotolysis is comparable to hydrogenase-based hydrogen production by green algae. The estimated overall cost is US $10/GJ of hydrogen [27]. However, it should be pointed out that indirect biophotolysis technology is still under active research and development. The estimated cost is subject to a significant change depending on the technological advancement.

Fermentative Hydrogen Production Bio-hydrogen production can be realized by anaerobic (dark fermentation) and photoheterotrophic (light fermentation) microorganisms using carbohydrate-rich biomass as a renewable resource. The first step is the acid or enzymatic hydrolysis of biomass to highly concentrated sugar solution which is further fermented by anaerobic organisms to produce volatile fatty acids (VFA), hydrogen, and CO2. The organic acids are further fermented by the photoheterotrophic bacteria (Rhodobacter sp.) to produce CO2 and H2 which is known as the light fermentation. Combined utilization of dark and photo-fermentations was reported to improve the yield of hydrogen formation from carbohydrates. Dark Fermentation

Fermentation by anaerobic bacteria as well as some microalgae, such as green algae on carbohydrate-rich substrates, can produce hydrogen at 30–80 C especially in a dark condition. Unlike a biophotolysis process that produces only H2, the products of dark fermentation are mostly H2 and CO2 combined with other gases, such as CH4 or H2S,

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depending on the reaction process and the substrate used. With glucose as the model substrate, maximum 4 mol H2 is produced per mole glucose when the end product is acetic acid: C6 H12 O6 þ 2H2 O ! 2CH3 COOH þ 4H2 þ 2CO2 When the end product is butyrate, 2 mol H2 is produced: C6 H12 O6 þ 2H2 O ! CH2 CH2 CH2 OOH þ 2H2 þ 2CO2 However, in practice, the 4 mol H2 production/mol glucose cannot be achieved because the end products normally contain both acetate and butyrate. The amount of hydrogen production by dark fermentation highly depends on the pH value, hydraulic retention time (HRT), and gas partial pressure. For the optimal hydrogen production, pH should be maintained between 5 and 6. Partial pressure of H2 is yet another important parameter affecting the hydrogen production. When hydrogen concentration increases, the metabolic pathways shift to produce more reduced substrates, such as lactate, ethanol, acetone, butanol, or alanine, which in turn decrease the hydrogen production. Besides the pH value and partial pressure, HRT (hydraulic retention time) also plays an important role in hydrogen production. Ueno et al. [30] have reported that an optimal HRT of 0.5 day could effect maximum hydrogen production (14 mmol/g carbohydrate) from wastewater by anaerobic microflora in the presence of chemostat culture. When HRT was increased from 0.5 to 3 days, hydrogen production rate was reduced from 198 to 34 mmol L1 day1, while the carbohydrates in the wastewater were decomposed at an increasing efficiency from 70% to 97%. Due to the fact that solar radiation is not a requirement, hydrogen production by dark fermentation does not demand much land and is not affected by the weather condition. Hence, the feasibility of the technology yields a growing commercial value. Photo-Fermentation

Photosynthetic bacteria have the capacity to produce hydrogen through the action of their nitrogenase using solar energy and organic acids or biomass. In recent years, some attempts have been made for hydrogen production from industrial and agricultural wastes to effect waste management. Hydrogen can be produced by photo-fermentation of various types of biomass wastes. However, these processes have three main drawbacks: (1) use of nitrogenase enzyme with high-energy demand, (2) low solar energy conversion efficiency, and (3) demand for elaborate anaerobic photobioreactors covering large areas. Hence, at the present time, the photo-fermentation process is not a competitive method for hydrogen production.

Biological Water–Gas Shift Reaction (BWGS) The BWGS is a relatively new method for hydrogen production. Some bacteria (certain photoheterotrophic bacteria), such as Rubrivivax gelatinosus, are capable of performing

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water–gas shift reaction at ambient temperature and atmospheric pressure. Such bacteria can survive in the dark by using CO as the sole carbon source to generate adenosine triphosphate (ATP) coupling the oxidation of CO with the reduction of H+ to H2: CO þ H2 O $ CO2 þ H2 ; DG0 ¼ 20:1 kJ=mol In equilibrium, the dominating products are CO2 and H2. Therefore, this process is favorable for hydrogen production. Organisms growing at the expense of this process are the gram-negative bacteria, such as Rhodospirillum rubrum and R. gelatinosus, and the gram-positive bacteria, such as Carboxydothermus hydrogenoformans. Under anaerobic conditions, CO induces the synthesis of several proteins, including CO dehydrogenase, Fe–S protein, and CO-tolerant hydrogenase. Electrons produced from CO oxidation are conveyed via the Fe–S protein to the hydrogenase for hydrogen production. Biological water–gas shift reaction for hydrogen production is still under laboratory scale and only few works have been reported. The common objectives of these works were to identify suitable microorganisms that had high CO uptake and to estimate the hydrogen production rate. Kerby et al. [31] observed that under dark, anaerobic conditions in the presence of sufficient nickel, the doubling time of R. rubrum was less than 5 h by the oxidation of CO to CO2 coupled with the reduction of protons to hydrogen. However, R. rubrum requires light to grow and hydrogen production is inhibited by medium CO partial pressure above 0.2 atm. An alternative new chemoheterotrophic bacterium Citrobacter sp. Y19 was tested by Jung et al. [32] for hydrogen production using water–gas shift reaction. The maximum hydrogen production activity was found to be 27 mmol/g cell h, which is about three times higher than R. rubrum. Recently, Wolfrum et al. [33] have conducted a detailed study to compare the biological water–gas shift reaction with conventional water–gas shift processes. Their analysis showed that biological water–gas shift process was economically competitive when the methane concentration was under 3%. The hydrogen production cost from biological water–gas shift reaction ranged from US $1.75/kg (US $14.6/GJ) to around US $2.25/kg (US $18.8/GJ) for a methane concentration between 1% and 10%. Compared with thermochemical water–gas shift processes, the cost of biological water–gas shift processes are lower due to the elimination of reformer and associated equipment.

Hydrogen Production from Water There is abundant water resource on the earth and it is widely available almost everywhere. Thus hydrogen production from water is a convenient option and the amount can be boundless. Extensive research efforts have focused on this promising hydrogen production route. In fact, its commercial use dates back to the 1890s. Hydrogen production from water splitting consists of three categories: electrolysis, thermolysis, and photoelectrolysis.

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Water Electrolysis Water electrolysis is essentially the conversion of electrical energy to chemical energy in the form of hydrogen, with oxygen as a useful by-product. > Figure 29.3 shows the diagram of a typical water electrolysis process. It is realized by an electrical current passing through two electrodes to break water into hydrogen and oxygen. The most common water electrolysis technology is alkaline based, but more proton exchange membrane (PEM) electrolysis and solid oxide electrolysis cells (SOEC) units are developing.

Alkaline Electrolyzer Alkaline systems are the most developed and lowest in capital cost. They have the lowest efficiency so they have the highest electrical energy costs. Alkaline electrolyzers are typically composed of electrodes, a microporous separator, and an aqueous alkaline electrolyte of approximately 30 wt% KOH or NaOH. In alkaline electrolyzers nickel with a catalytic coating, such as platinum, is the most common cathode material. For the anode, nickel or copper metals coated with metal oxides, such as manganese, tungsten, or ruthenium, are used. The liquid electrolyte is not consumed in the reaction, but must be replenished over time because of other system losses primarily during hydrogen recovery. In an alkaline cell, the water is introduced in the cathode where it is decomposed into hydrogen and OH. The OH travels through the electrolytic material to the anode where O2 is formed. The hydrogen is left in the alkaline solution. The hydrogen is then separated from the water in a gas liquid separations unit outside of the electrolyzer. The Umin = 1.48 V

O2

2OH

1/2O2

2e

Anode

H2

2H2O + 2e 2OH

H2O

Electrolyte

H2

Membrane

. Fig. 29.3 A diagram of a typical water electrolysis process

Cathode

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typical current density is 100–300 mA cm2 and alkaline electrolyzers typically achieve efficiencies 50–60% based on the lower heating value of hydrogen. The overall reactions at the anode and cathode are: Cathode: 2H2 O þ 2e ! H2 þ 2OH Anode: 2OH ! 1=2O2 þ H2 O Overall reaction: H2 O ! H2 þ 1=2O2

DH ¼ 288 kJ=mol

PEM Electrolyzer PEM electrolyzers build upon the recent advances in PEM fuel cell technology. They are more efficient than alkaline, do not have the corrosion and seals issues like SOEC, but cost more than alkaline systems. PEM-based electrolyzers typically use Pt black, iridium, ruthenium, and rhodium for electrode catalysts and a Nafion membrane which not only separates the electrodes, but acts as a gas separator. In PEM electrolyzers, water is introduced at the anode where it is split into protons and oxygen. The protons travel through the membrane to the cathode, where they are recombined into hydrogen. The O2 gas remains behind with the unreacted water. There is no need for a separations unit. Depending on the purity requirements, a drier may be used to remove residual water after a gas/liquid separations unit. PEM electrolyzers have low ionic resistances and therefore high currents of >1,600 mA cm2 can be achieved while maintaining high efficiencies of 55–70%. The reactions at the anode and cathode are: Anode: 2H2 O ! O2 þ 4Hþ þ 4e Cathode: 4Hþ þ 4e ! 2H2 Overall reaction: H2 O ! H2 þ 1=2O2

DH ¼ 288 kJ=mol

Solid Oxide Electrolysis Cells Solid oxide electrolysis cells (SOEC) are essentially solid oxide fuel cells operating in reverse. These systems replace part of the electrical energy required to split water with

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thermal energy. The higher temperatures increase the electrolyzer efficiency by decreasing the anode and cathode overpotentials which cause power loss in electrolysis. It is said that an increase in temperature from 375 to 1,050 K can reduce the combined thermal and electrical energy requirements by close to 35% [34]. Another advantage of SOEC units is the use of a solid electrolyte which, unlike KOH for alkaline systems, is noncorrosive and does not experience any liquid and flow distribution problems. A SOEC operates similar to the alkaline system in that an oxygen ion travels through the electrolyte (typically ZrO2) leaving the hydrogen in unreacted steam stream. The reactions are shown as follows: Cathode: 2H2 O þ 4e ! 2H2 þ 2O2 Anode: 2O2 ! O2 þ 4e Overall reaction: H2 O ! H2 þ 1=2O2

DH ¼ 288 kJ=mol

SOEC electrolyzers are the most electrically efficient, but are the least developed of the technologies. A major challenge of SOEC technology is that the high temperature operation requires the use of costly materials and fabrication methods in addition to a heat source. The materials are similar to those being developed for solid oxide fuel cells (SOFC), yttria-stabilized zirconia (YSZ) electrolyte, nickel-containing YSZ anode, and metal-doped lanthanum metal oxides, and have the same problems with seals which are being investigated.

Water Thermochemical Splitting Water thermochemical splitting is also called water thermolysis, in which heat alone is used to decompose water to hydrogen and oxygen. It is well known that water will decompose at 2,500 C, but materials stable at this temperature and also sustainable heat sources are not easily available. Thus chemical reagents have been proposed to lower the temperatures. Research in this area was prominent from the 1960s through the early 1980s. However, essentially all research and development stopped after the mid-1980s, until recently. There are more than 300 water-splitting cycles referenced in the literature [35]. All of the processes have significantly reduced the operating temperature. In choosing the process there are five criteria which should be met. (1) Within the temperatures considered, the △G (differential Gibbs free energy) of the individual reactions must approach zero. This is the most important criterion. (2) The number of steps should be minimal. (3) Each individual step must have both fast reaction rates and rates which are similar to the other steps in the process. (4) The reaction products cannot result in chemical-by-products, and any separation of the reaction products

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must be minimal in terms of cost and energy consumption. (5) Intermediate products must be easily handled. Currently, there are several processes which meet the five criteria, such as the UT-3 process, and the sulfuric acid decomposition process. The mechanisms of these two processes are shown as follows: (1) Iodine–Sulfur Process 2H2 OðlÞ þ I2 ðgÞ þ SO2 ðgÞ ! 2HIðlÞ þ H2 SO4 ðlÞ

(100–120 C, exothermic)

2HIðgÞ ! H2 ðgÞ þ I2 ðgÞ

(400–500 C, exothermic)

H2 SO4 ðlÞ ! H2 OðgÞ þ SO2 ðgÞ þ

(850 C, endothermic)

1 2 O2 ðgÞ

Overall reaction: 1 H 2 O ! H 2 þ O2 2 Figure 29.4 gives the diagram of a typical water thermochemical splitting process for hydrogen production using the Iodine–Sulfur Process. >

(2) UT-3 Process CaBr2 ðsÞ þ H2 OðgÞ ! CaOðsÞ þ 2HBrðgÞ

(700–750 C, endothermic)

CaOðsÞ þ Br2 ðgÞ ! CaBr2 ðsÞ þ

(500–600 C, exothermic)

1 2 O2 ðgÞ

Fe3 O4 ðsÞ þ 8HBrðgÞ ! 3FeBr2 ðsÞ þ 4H2 OðgÞ þ Br2 ðgÞ

(200–300 C, exothermic)

3FeBr2 ðsÞ þ 4H2 OðgÞ ! Fe3 O4 ðsÞ þ 6HBrðgÞ þ H2 ðgÞ

(550–600 C, endothermic)

O2

1000°C H2SO4 = H2O + SO2 + 0.5O2

Introduction of heat (such as nuclear)

800°C

600°C

400°C

200°C

0°C

HI

H2O

2HI = H2 + I2

SO2 H2SO4 I2 + SO2 + 2H2O = 2HI + H2SO4

Separation I2 H2O

. Fig. 29.4 A diagram of the iodine–sulfur water thermochemical splitting process

H2

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Overall reaction: 1 H 2 O ! H 2 þ O2 2 However, water thermochemical splitting is still not competitive with other hydrogen generation technologies in terms of cost and efficiency which is the major focus of research in those processes [36]. In addition, these processes require large inventories of highly hazardous corrosive materials. The requirements of high temperature, high pressure, and corrosion result in the need for new materials. The US DOE has active projects investigating several of these processes focused on improving materials, lowering cost, and increasing efficiency [35]. Current research and development on hydrogen from water thermochemical splitting is ongoing in Canada on technologies that couple synergistically with Canada’s present and future nuclear reactors. Also, several countries (Japan, USA, France) are currently advancing nuclear technology and corresponding thermochemical cycles. Sandia National Laboratory in the USA and CEA in France are developing a hydrogen pilot plant with a sulfur–iodine (S–I) cycle. The KAERI Institute in Korea is collaborating with China to produce hydrogen with the HTR-10 reactor. The Japan Atomic Energy Agency plans to complete a large sulfur–iodine plant to produce 60,000 m3/h of hydrogen by 2020, an amount sufficient for about one million fuel cell vehicles. It is believed that scaling up the processes may lead to improved thermal efficiency overcoming one of the principle challenges faced by this technology. In addition, a better understanding of the relationship between capital costs, thermodynamic losses, and process thermal efficiency may lead to decreased hydrogen production costs [37]. The current processes all use four or more reactions, and it is believed that an efficient two-reaction process as shown in the following equations may make this technology viable [37]. ZnOðsÞ ! ZnðgÞ þ 12 O2

(2,300 K, endothermic)

ZnðlÞ þ H2 O ! ZnOðsÞ þ H2

(700 K, exothermic)

Water Photoelectrolysis Photoelectrolysis uses sunlight to directly decompose water into hydrogen and oxygen, and uses semiconductor materials similar to those used in photovoltaics. In photovoltaics, two doped semiconductor materials, a p-type and an n-type, are brought together forming a p–n junction. At the junction, a permanent electric field is formed when the charges in the p- and n-type of material rearrange. When a photon with energy greater than the semiconductor material’s bandgap is absorbed at the junction, an electron is released and a hole is formed. Since an electric field is present, the hole and electron are

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forced to move in opposite directions which, if an external load is also connected, will create an electric current. This type of situation occurs in photoelectrolysis when a photocathode, p-type material with excess holes, or a photoanode, n-type of material with excess electrons, is immersed in an aqueous electrolyte, but instead of generating an electric current, water is split to form hydrogen and oxygen. The process can be summarized for a photoanode-based system as follows: (1) A photon with greater energy than the bandgap strikes the anode creating an electron–hole pair. (2) The holes decompose water at the anode’s front surface to form hydrogen ions and gaseous oxygen, while the electrons flow through the back of the anode which is electrically connected to the cathode. (3) The hydrogen ions pass through the electrolyte and react with the electrons at the cathode to form hydrogen gas [38]. (4) The oxygen and hydrogen gases are separated, for example, by the use of a semipermeable membrane, for processing and storage. Current photoelectrodes used in PEC (photon-to-electron-conversion) that are stable in aqueous solutions have a low efficiency for using photons to split water to produce hydrogen. The target efficiency is >16% solar energy to hydrogen. This encompasses three material system characteristics necessary for efficient conversion: (1) The bandgap should fall in the range sufficient to achieve the energetics for electrolysis and yet allow maximum absorption of the solar spectrum. This is 1.6–2.0 eV for single photoelectrode cells, and 1.6–2.0/0.8–1.2 eV for top/bottom cells in stacked tandem configurations. (2) It should have a high quantum yield (>80%) across its absorption band to reach the efficiency necessary for a viable device. (3) It should straddle the redox potentials of the H2 and O2 half reactions with its conduction and valence band edges, respectively. The efficiency is directly related to the semiconductor bandgap (Eg), that is, the energy difference between the bottom of the conduction band and the top of the valence band, as well as the band edge alignments, since the material or device must have the correct energy to split water. The energetics are determined by the band edges, which must straddle water’s redox potential with sufficient margins to account for inherent energy losses. Cost efficient, durable catalysts with appropriate Eg and band edge positions must be developed. To achieve the highest efficiency possible in a tandem configuration, ‘‘current matching’’ of the photoelectrodes must be done. Electron transfer catalysts and other surface enhancements may be used to increase the efficiency of the system. These enhancements can minimize the surface overpotentials in relationship to the water and facilitate the reaction kinetics, decreasing the electric losses in the system. Fundamental research is ongoing to understand the mechanisms involved and to discover and develop appropriate candidate surface catalysts for these systems [39]. In addition, it is possible to use suspended metal complexes in solution as the photochemical catalysts [40]. Typically, nano-particles of ZnO, Nb2O5, and TiO2 (the material of choice) have been used [40]. The advantages of these systems include the use of low-cost materials and the potential for high efficiencies. Current research involves overcoming the low light absorption and unsatisfactory stability in time for these systems.

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Sorption-Enhanced H2 Production with In Situ CO2 Capture Using Carbon-Containing Resources It is now widely acknowledged ‘‘decarbonizing’’ energy supply will be essential in the near future due to the well-known global warming. Although utilization of H2 is clean and nonpolluting, the production of H2 from fossil fuels actually produces CO2 emission. A typical SMR hydrogen plant with the capacity of one million cubic meters of hydrogen per day produces 0.3–0.4 million standard cubic meters of CO2 per day. If hydrogen is to be produced by coal gasification, the amount of CO2 emissions would be doubled compared to SMR. Further, with regards to end-use applications of H2, additional costs and process complexity are incurred for gas cleaning. Taking fuel cell applications, for example, the CO content in the product gas must be closely managed – a CO concentration of less than 10 ppm is required for low temperature proton exchange membranes and alkaline fuel cells. The cost of separating H2 from a H2-rich gas with impurities, such as CO, CH4, and tar, incurs major cost penalties. The increasing attentions on global warming and the demands for pure H2 production together result in the great interest in the research on sorption-enhanced gasification system where high purity H2 production and in situ CO2 capture can be realized in one single reactor. > Figure 29.5 shows a simple diagram of the system. It is seen that the core unit of the system is the dual gasification–regeneration reactors. And the system is apparently characterized by the addition of CaO additives to the gasifier. The corresponding introduced influences include the following: (1) the water–gas

Purification

H2 user

Flue gas with high CO2 concentration

Product gas with high H2 concentration

CaO & ash

Refill limestone, dolomite, etc.

Hydrocarbons (coal, biomass, CH4, etc.)

CaO

Gasifier

Regenerator CaCO3 Char & ash

Steam

Slag O2

. Fig. 29.5 A simple diagram of the sorption-enhanced gasification system

External heat resources

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29

reaction and the water–gas shift reaction are both enhanced to produce more hydrogen due to the CO2 absorption by the CaO carbonation reaction; (2) the necessary external energy consumption for hydrocarbons steam gasification can be partially substituted by the releasing heat of carbonation; and (3) the formation of pyrolysis tars in presence of CaO additives could be reduced. The mechanism reactions of the system are as follows: Reactions in the gasifier: Water–gas reaction CðsÞ þ H2 OðgÞ ! COðgÞ þ H2 ðgÞ

(For coal)

CH4 ðgÞ þ H2 OðgÞ ! COðgÞ þ 3H2 ðgÞ

(For natural gas)

CH1:5 O0:7 ðsÞ þ 0:3H2 OðgÞ ! COðgÞ þ 1:05H2 ðgÞ

(For typical biomass)

Water–gas shift reaction COðgÞ þ H2 OðgÞ ! CO2 ðgÞ þ H2 ðgÞ Carbonation reaction CaOðsÞ þ CO2 ðgÞ ! CaCO3 ðsÞ The global reaction in the gasifier can be summarized as: CðsÞ þ 2H2 OðgÞ þ CaOðsÞ ! CaCO3 ðsÞ þ 2H2 ðgÞ

(For coal)

CH4 ðgÞ þ 2H2 OðgÞ þ CaOðsÞ ! CaCO3 ðsÞ þ 4H2 ðgÞ

(For natural gas)

CH1:5 O0:7 ðsÞ þ 1:3H2 OðgÞ þ CaOðsÞ ! CaCO3 ðsÞ þ 2:05H2 ðgÞ

(For typical biomass)

Reactions in the regenerator: Combustion reaction CðsÞ þ O2 ðgÞ ! CO2 ðgÞ Calcination reaction CaCO3 ðsÞ ! CaOðsÞ þ CO2 ðgÞ It should be noted that beside Ca-based oxides, a number of candidate CO2 sorbents have been also studied including potassium promoted hydrotalcite (K-HTC) and mixed metal oxides of Li and Na [41]. HTCs are members of the family of double-layered hydroxides that, when doped with K2CO3, can serve as high temperature CO2 sorbents. They react rapidly and the sorbent regeneration is possible with less external energy input. But HTCs have much lower CO2 capacity than Ca-based sorbents and are also considerably more expensive. Mixed metal oxide sorbents of Li and Na such as Li2ZrO3, Li4SiO4, and Na2ZrO3 was spawned, on the one hand, by the desire to find a replacement for Cabased sorbents that could be regenerated at lower temperature, and, on the other hand, would have considerably higher CO2 capacity than HTC. However, because of less favorable thermodynamic properties associated with these sorbents, the equilibrium CO2 pressures are higher and product H2 concentrations must be lower than can be

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obtained using Ca-based sorbents at equivalent reaction conditions. Anyway, Ca-based sorbents are considered to be the most promising option. As a result, current studies on sorption-enhanced H2 production are mostly being conducted using CaO. This section also just discusses sorption-enhanced gasification using Ca-based sorbents. Different feedstocks including both solid fuels (coal, biomass) and natural gas are all summarized.

Sorption-Enhanced H2 Production from Solid Fuels A new near-zero emissions coal (also biomass) utilization technology with combined gasification and combustion has been proposed by Zhejiang University in China [42–45]. > Figure 29.6 displays the diagram of the system. In this system, solid fuels are partly gasified with steam in a pressured circulation Fluidized bed gasifier, producing H2, CO, and CO2. As CaO is used as the CO2 acceptor to absorb CO2 and release the heat for the gasification processes in the gasifier, CO is depleted from the gas phase by the water–gas shift reaction. The H2-rich gas stream produced in the gasifier is oxidized in the solid oxide fuel cell. The remained char with low reaction activity are transferred in a circulating Fluidized bed combustor together with the carbonated CaCO3. The char and the unreacted H2, in the hot off-gas from the fuel cell, are oxidized in the combustor to supply the heat for the CaCO3 calcination. The CO2-rich gas stream produced in the combustor is suitable for disposal after recovering the heat by a gas steam combined cycle. The authors firstly examined the influences of gasifier operation temperature, pressure, and fuel type (coal and biomass), H2O/C on hydrogen production based on chemical equilibrium calculation [43, 44].The results showed that

H2 Purifier

H2 users Electric power Gas turbin Heat recovery

DeAsh Air

Electric power Fuel cell

CaO Coal

Regener Gasifier Char,Ash ator CaCO3

Electric

Water

Steam turbine

CaCO3 H2O H2

Steam

CO2 seperation

Stack

1122

Oxygen separator O2

Air Air preheater

Ash Air

. Fig. 29.6 The near-zero emissions system proposed by Zhejiang University

Exhaust

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29

the increase of CaO addition can obviously increase H2 mole fraction in C/H2O reaction products. The process may achieve high conversion efficiency form coal energy to electrical energy (around 65.5%) with near-zero gaseous emissions. A latest study by these authors [45] also showed that the CaO additives can not only absorb CO2 gases but also enhance the tar reduction reactions in biomass steam gasification with in situ CO2 capture. Sorption-enhanced biomass gasification in Fluidized bed reactor is also being performed in Zhejiang University. In Japan, the hydrogen production by the reaction-integrated novel gasification (HyPr-RING) process is under development [46]. The mechanism of this process is very similar to the system proposed by Zhejiang University. HyPr-RING process has been conducted for both coal and biomass. For coal, conditions in the gasifier of 873–973 K and 3 MPa are reported to result in slightly over 50% carbon conversion with about 90% H2 in the product gas. The remainder of the product gas is predominantly CH4 with less than 0.4% (CO + CO2). The regenerator operates at 1,073 K and 0.1 MPa. For biomass Lin et al. [47] examined the H2 production from woody biomass by steam gasification using CaO as a CO2 sorbent. Firstly, it is said that in the absence of CaO, the product gas contained CO2. On the other hand, in the presence of CaO ([Ca]/[C] = 1; 2, and 4), no CO2 was detected in the product gas. And at a [Ca]/[C] of 2, the maximum yield of H2 was obtained. Secondly, they reported that the H2 yield and conversion to gas were largely dependent on the reaction pressure, and exhibited the maximum value at 0:6 MPa, which indicated a much lower pressure compared to other carbonaceous materials such as coal (>12 MPa) and heavy oil (>4.2 MPa) in steam gasification using a CO2 sorbent. As a result, they concluded that woody biomass is one of the most appropriate carbonaceous materials in H2 production by steam gasification using CaO as a CO2 sorbent, taking the reaction pressure into account. A further kinetic study conducted at 923 K and pressure of 6.5 MPa using a batch reactor with 50 cm3 capacity also demonstrated the complete absorption of CO2 from the gasification syngas [48]. Another significant sorption-enhanced gasification process is the absorptionenhanced reforming (AER) developed within the frame of EU Project AER-Gas II. The atmospheric dual Fluidized bed technology developed at Vienna University of Technology realizes the steam gasification through circulation of hot bed material. The technology has been realized in pilot plant scale of 100 kW fuel input (at Vienna University of Technology) as well as in industrial scale at the combined heat and power plant (CHP) guessing in an industrial scale of 8 MW fuel input in Austria. A comparison of dual Fluidized bed gasification of biomass with and without selective transport of CO2 from the gasification to the combustion reactor is performed by using the facility with 100 kW fuel input. In the case of convention gasification, the hydrogen content in the product gas of gasifier is about 40 vol% (dry basis). However, in the case of carbonates addition to the bed material, much higher hydrogen content up to 75 vol% (dry basis) can be achieved at lower gasification temperatures [49]. The first time application of the AER process on the 8 MW industrial facility also realizes the continuous CO2 removal by cyclic carbonation of CaO and calcination of CaCO3. Results obtained in the industrial facility are presented to be comparable with those obtained at pilot plant scale [50].

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In addition, other similar sorption-enhanced gasification processes for solid fuels are also under development. One is the ZEC process developed at Los Alamos National Laboratory [51]. It is designed to first hydrogasified coal to produce CH4, which is then reformed to H2 using the calcium-based sorption-enhanced process. A systems analysis performed by Nexant Corp. [52] estimated coal to electricity conversion efficiency on the order of 70%. Research on this concept is continuing in a joint study at Cambridge University and Imperial College in the UK [53]. The other is the innovative fuel-flexible advanced gasification-combustion (AGC) process developed by General Electric Energy and Environmental Research Corporation (GE EER) [54]. The R&D on the AGC technology is being conducted under a Vision-21 award from the US DOE NETL with cofunding from GE EER, Southern Illinois University at Carbondale (SIU-C), and the California Energy Commission (CEC). The AGC technology converts coal and air into three separate streams of pure hydrogen, sequestration-ready CO2, and high temperature/ pressure oxygen-depleted air to produce electricity in a gas turbine. The program integrates lab-, bench-, and pilot-scale studies to demonstrate the AGC concept. Besides, research on lab-scale H2 production from sorption-enhanced solid fuels gasification were also performed by Madhukar [55] and Wei [56].

Sorption-Enhanced H2 Production from Natural Gas The effectiveness of both sorption-enhanced steam methane reforming (SE-SMR) and the use of calcium-based CO2 sorbents have been demonstrated in previous works. In particular, Rostrup-Nielsen [57] reports that the first description of the addition of a CO2 sorbent to a hydrocarbon-steam-reforming reactor was published in 1868. Williams [58] was issued a patent for a process in which steam and methane react in the presence of a mixture of lime and reforming catalyst to produce hydrogen. A Fluidized bed version of the process was patented by Gorin and Retallick [59]. Brun-Tsekhovoi et al. [60] published limited experimental results and reported potential energy saving of about 20% compared to the conventional process. Recently, Kumar et al. [61] reported on a process known as unmixed combustion (UMC), in which the reforming, shift, and CO2 removal reactions are carried out simultaneously over a mixture of reforming catalyst and CaO-based CO2 sorbent. In a related work, Hufton et al. [62] reported on H2 production through SE-SMR using a K2CO3-treated HTC sorbent, in spite of the extremely low CO2 working capacity above discussed. Average purity of H2 was about 96% while CO and CO2 contents were less than 50 ppm. The methane conversion to H2 product reaches 82%. The conversion and product purity are substantially higher than the thermodynamic limits for a catalyst-only reactor operated at these same conditions (28% conversion, 53% H2, 13% CO/CO2). In an earlier work, Balasubramanian et al. [63] showed that a gas with a H2 content up to 95% (dry basis) could be produced in a single reactor containing reforming catalyst and CaO formed by calcination of high purity CaCO3. The reported methane conversion was 88%.

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One process that utilizes natural gas is designated Zero Emission Gas Power Project (ZEG), and is being led by the Institute of Gas Technology in cooperation with Christian Michelsen Research AS and Prototech AS in Norway. A brief discussion of the process may be found on the Internet, and an update on the status of the project was recently presented by Johnsen [64]. A number of candidate sorbents have been considered with Arctic dolomite, which does not require pretreatment for sulfur removal, receiving the most attention. H2 is to be used to produce electricity in a high temperature solid oxide fuel cell with the exhaust heat used for sorbent regeneration. Electrical efficiencies from 50% to 80% based on the net power output (LHV) of four process configurations having varying degrees of heat integration are reported. The other sorption-enhanced H2 production process from natural gas is the Pratt and Whitney Rocketdyne (PWR) process. It is now in the pilot stages. While few details have been released, the company claims a 90% size reduction, 30–40% reduction in capital costs, 5–20% higher H2 yield, and reduced product purification requirements that will lead to a smaller PSA system. The comparisons are relative to a standard steam methane reforming process with PSA purification. Upon completion of the current pilot tests, PWR plans to construct a 5 MMscf/day commercial demonstration plant [65].

Reactivity of CaO Sorbents Throughout Cyclic Calcination–Carbonation (CC) Reactions A critical challenge for applications of the sorption-enhanced gasification process is the activity durability of CaO sorbent [66]. It is estimated that the CO2 capture process would not be economical unless the value of CaO conversion after 20 cycles increased to a value of at least 0.45. However, previous studies show that CaO sorbents lose activity dramatically during cyclic CC reactions, which would increase both consumption of fresh sorbents and storage of spent sorbents, and consequently, reduce process economic and result in environment problem. Reasons that are responsible for the calcium-based sorbents reactivity loss can be summarized as follows: (1) Thermodynamic equilibrium limitation. Higher temperatures are favorable for H2 generation; however, increasing the temperature at a constant total pressure will limit the capture of CO2 by CaO sorbents. (2) Tars and coke formation. Interaction between CaO and the tar and coke is expected to hamper CO2 capture [67]. There is a tradeoff between the optimal temperatures for eliminating tar and decomposing coke and maximizing CO2 capture by CaO. (3) Sintering of sorbents. Sintering leads to a reduction in both surface area and pore volume, which in turn affects the rate and extent of gas–solid reactions. (4) Decay in reactivity through multiple CO2 capture and release cycles. Abanades et al. [68] concluded that the decay in activity throughout CC cycles was due to a decrease in microporosity and an increase in meso-porosity. They proposed a simple equation to estimate the CaO conversion, XN, after the Nth CC cycles, claiming that values of fm = 0.77 and fw = 0.17 fit most experimental data of both previous researchers and themselves well.

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XN ¼ fmN ð1  fw Þ þ fw In order to improve the reactivity of calcium-based sorbents, various methods have been proposed, including: (1) Using mild calcination conditions. The use of mild calcination conditions, that is, inert atmospheres (N2 or Ar) and low temperatures (700 C) were reported to produce a more reactive sorbent [69]. However, it may be necessary to use steam as a diluent gas in the regenerator to lower down the CO2 partial pressure, while simultaneously obtaining high purity CO2 gases. (2) The introduction of a water hydration step, or the utilization of steam as a ‘‘carbonation-catalyst,’’ has been reported to enhance CO2 capture through multiple reaction cycles [69–71]. (3) The use of nano-sized sorbent particles. Barker [72] hypothesized that if the particle size (diameter) of CaO is smaller than the product layer thickness that may form on a single particle, then 100% conversion could be achieved. Barker reported a conversion of 0.93 after 24 h of carbonation, maintained for 30 reaction cycles. In conclusion, the development of a CO2 sorbent, which is resistant to physical deterioration and maintains high chemical reactivity through multiple CO2 capture and release cycles, is the limiting step in the scale-up and commercial operation of the sorption-enhanced H2 production process.

Future Directions Given the advantages inherent in fossil fuels, such as their availability, relatively low cost, and the existing infrastructure for delivery and distribution, they are likely to play a major role in energy and H2 production in the near- to medium-term future. However, H2 production from fossil fuels produces large CO2 emission to the atmosphere, which may diminish the environmental appeal of H2 as an ecologically clean fuel. As a result, H2 production from fossil fuels must consider the CO2 capture problem in long-term future. Biomass is potentially a reliable energy resource for hydrogen production. Biomass is renewable, abundant, and easy to use. Over the life cycle, net CO2 emission is nearly zero due to the photosynthesis of green plants. Although the yield of H2 is low from biomass since the hydrogen content in biomass is low to begin with (approximately 6% versus 25% for methane) and the energy content is low due to the 40% oxygen content of biomass, hydrogen production from biomass is still attractive. The thermochemical pyrolysis and gasification hydrogen production methods are economically viable and is said to become competitive with the conventional natural gas reforming method. Biological dark fermentation is also a promising hydrogen production method for commercial use in the future. With further development of these technologies, biomass will play an important role in the development of sustainable hydrogen economy. Hydrogen production from water electrolysis has been commercially available. Regarding the CO2 emission, electricity produced from renewable resources (such as wind, solar, hydro, biomass, tidal, etc.) is favored to be used for water electrolysis.

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Thermochemical water decomposition is one alternative process competitive to water electrolysis. The nuclear power systems have a great potential to be integrated with H2 production from water decomposition. The Advanced High-Temperature Reactor (AHTR) concept, proposed for the US Department of Energy’s Generation IV nuclear plant development program, is specifically designed for H2 production (via high temperature water electrolysis or thermochemical cycles). Thermochemical water-splitting cycles, such as UT-3 cycle and sulfur–iodine cycle, can potentially produce higher overall energy efficiencies (around 50%) compared to electrolysis-based systems (around 24%). However, a major shift away from the negative public perception of nuclear energy would be necessary in order to base a long-term energy scenario on the nuclear-hydrogen option. In addition, for H2 production by direct water splitting, using the solar photocatalysis route could become favorable if conversion efficiencies were increased by a factor of 2–3. It is anticipated that the low cost, environmentally friendly photocatalytic water splitting for hydrogen production will play an important role in the hydrogen production and contribute much to the coming hydrogen economy. However, it is still very far from practical utilization. Sorption-enhanced H2 production with in situ CO2 capture and then CO2 sequestration in geologic formations (e.g., deep coal seams, depleted oil and gas reservoirs, and salt domes), the ocean, aquifers, terrestrial ecosystems, etc., provides a promising solution for the CO2 release during H2 production from fossil fuels. For the future development, challenges for CO2 sequestration such as bringing its cost down and understanding the reservoir options (e.g., size, permanence, and, most importantly, environmental effect) should also be paid significant attention, besides improving the CaO sorbents cyclic reactivity to be practical.

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Hydrogen Production 37. Funk JE (2001) Thermochemical hydrogen production: past and present. Int J Hydrogen Energ 26:185–190 38. Turner J, Sverdrup G, Mann MK et al (2008) Renewable hydrogen production. Int J Hydrogen Energ 32:379–407 39. Licht S (2003) Solar water splitting to generate hydrogen. Fuel: photothermal electrochemical analysis. J Phys Chem B 107:4253–4260 40. Norbeck JM, Heffel JW, Durbin TD et al (1996) Hydrogen fuel for surface transportation. Society of Automotive Engineers, Warrendale, 548 41. Harrison DP (2008) Sorption-enhanced hydrogen production: a review. Ind Eng Chem Res 47:6486–6501 42. Wang QH, Shen X, Luo ZY et al (2003) New near zero emissions coal utilization technology with combined gasification and combustion. Power Eng 23:2711–2715 (in Chinese) 43. Wang ZH, Zhou JH, Wang QH et al (2006) Thermodynamic equilibrium analysis of hydrogen production by coal based on Coal/CaO/H2O gasification system. Int J Hydrogen Energ 31: 945–952 44. Guan J, Wang QH, Cen KF et al (2007) Thermodynamic analysis of a biomass anaerobic gasification process for hydrogen production with sufficient CaO. Renew Energ 32(15): 2502–2515 45. Han L, Wang QH, Ma Q et al (2010) Influence of CaO additives on wheat-straw pyrolysis as determined by TG-FTIR analysis. J Anal Appl Pyrol 88:199–206 46. Lin SY, Suzuki Y, Hatano H, Harada M (2001) Hydrogen production from hydrocarbon by integration of water-carbon reaction and carbon dioxide removal (HyPr-RING method). Energ Fuel 15:339–343 47. Hanaoka T, Yoshida T, Fujimoto S et al (2005) Hydrogen production from woody biomass by steam gasification using a CO2 sorbent. Biomass Bioenerg 28:63–68 48. Fujimoto S, Yoshida T, Hanaoka T et al (2007) A kinetic study of in situ CO2 removal gasification of woody biomass for hydrogen production. Biomass Bioenerg 31:556–562 49. Pfeifer C, Puchner B, Hofbauer H (2009) Comparison of dual fluidized bed steam gasification of biomass with and without selective transport of CO2. Chem Eng Sci 64:5073–5083

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50. Koppatz S, Pfeifer C, Rauch R et al (2009) H2-rich product gas by steam gasification of biomass with in situ CO2 absorption in a dual Fluidized bed system of 8 MW fuel input. Fuel Process Technol 90:914–921 51. Ziock HJ, Lackner KS, Harrison DP (2001) Zero emission coal power, a new concept. In: Proceedings of the first national conference on carbon sequestration, Washington 52. Nawaz M, Ruby J (2001) Zero emission coal alliance project: conceptual design and economics. In: Proceedings of the 26th conference on coal utilization and fuel systems. Coal Technology Association, Clearwater 53. Paterson NA (2005) Study of the reaction chemistry in the production of hydrogen from coal using a novel process concept. Presented at the second international workshop on in-situ CO2 removal (ISCR 2005), Stuttgart 54. Rizeq RG, Lyon RK, Zamansky VM (2001) Fuelflexible AGC technology for H2, power, and sequestration-ready CO2. In: Proceedings of the 26th international technical conference on coal utilization and fuel systems, Clearwater 55. Mahishi MR, Goswami DY (2007) An experimental study of hydrogen production by gasification of biomass in the presence of a CO2 sorbent. Int J Hydrogen Energ 32:2803–2808 56. Wei LG, Xu SP, Liu JG et al (2008) Hydrogen production in steam gasification of biomass with CaO as a CO2 absorbent. Energ Fuel 22:1997–2004 57. Rostrup-Nielsen J (1984) Catalytic steam reforming. In: Anderson JR, Boudart M (eds) Catalysis science and technology. Springer, Berlin 58. Williams R (1933) Hydrogen production. US Patent 1,938,202 59. Gorin E, Retallick WB (1963) Method for the production of hydrogen. US Patent 3,108,857 60. Brun-Tsekhovoi AR, Zadorin AN, Katsobashvili YR et al (1988) The process of catalytic steamreforming of hydrocarbons in the presence of a carbon dioxide acceptor. In: Veziroglu TN, Protsenko AN (eds) Proceedings of the seventh world hydrogen energy conference, Moscow, vol 2, Hydrogen energy progress VII. Pergamon, New York, p 885 61. Kumar R, Cole J, Lyon R (1999) Unmixed reforming: an advanced steam reforming process. Presented at the fuel cell reformer conference, South Coast Air Quality District, Diamond Bar

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Section 4

Alternative Energies (Continued)

30 Nuclear Energy and Environmental Impact K. S. Raja1 . Batric Pesic2 . M. Misra1 Center for Materials Reliability, Chemical and Materials Engineering, University of Nevada, Reno, NV, USA 2 Materials Science and Engineering, University of Idaho, Moscow, ID, Russia

1

Introduction to Nuclear Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1135 Nuclear Fuel Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1136 Uranium Fuel Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1137 Thorium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1141 Fuel Burnup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1142 Types of Nuclear Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1142 Nuclear Reactor Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1146 Radiation Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1146 Probabilistic Risk Assessment (PRA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1147 Nuclear Accidents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1148 Three Mile Island . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1148 The Chernobyl Accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1148 Design Considerations and Life Prediction of Nuclear Components . . . . . . . . . . . . . . . 1149 Fuel and Fuel Cladding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1149 Irradiation Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1150 Environmental Assisted Cracking (EAC) of Austenitic Stainless Steel (SS) in High Temperature Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1150 EAC of Unirradiated Ferritic/Martensitic Steels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1151 Environmental Aspect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1151 Radiolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1151 Flux Dependence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1151 Radiation Water Chemistry and Corrosion Potential . . . . . . . . . . . . . . . . . . . . . . . . 1152 Crack Initiation and Propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1152 Critical Issues on Selection of Candidate Materials for Advanced Nuclear Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1154 High-Temperature Degradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1154 Radiation Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1159 Cost-Benefit Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1162 Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_30, # Springer Science+Business Media, LLC 2012

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Spent Fuel and Reprocessing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1163 Dry Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1164 Transmutation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1165 Reprocessing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1165 Aqueous Reprocessing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1165 Pyroprocessing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1168 Containment of Radionuclides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1176 Nuclear Waste Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1177 Future Direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1178

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Abstract: Nuclear energy is attracting revived interest as a potential alternate for electric power generation in the event of increased concerns about global warming. Compared to energy produced by combustion of a carbon atom in coal, fission of a U-235 atom will produce about ten million times more energy. However, storage of the nuclear waste is an environmental issue. This chapter has four sections with a major focus on introduction of nuclear power plants and reprocessing of spent nuclear fuels. Different nuclear fuel cycles and nuclear power reactors are introduced in the first section and the cost-benefits of different energy sources are compared. Fuel burnup and formation of fission products are discussed along with operational impacts and risk analyses in the second section. Third section discusses about design of nuclear structural components and various degradation modes. Section four discusses reprocessing issues of nuclear spent fuels. Reprocessing of spent nuclear fuel may be an economically viable option, and it reduces high-radioactive load in the nuclear waste repositories as well. However, there is a concern about proliferation of weapons-grade plutonium separated during reprocessing. Containment of radio nuclides in different waste-forms is also discussed in this section.

Introduction to Nuclear Energy Radioactive decay of heavy metals, such as uranium, plutonium, thorium, etc., can be converted into a useful energy form. Radioactivity occurs by emission of charged particles (such as a and b) and electromagnetic wave (g ray). For heavier nuclei (elements with atomic number >40), more neutrons are required for a stable configuration so that the electrostatic repulsion force between the protons can be overcome [1]. When the nucleus has too many or too few neutrons, it will be in a nonequilibrium condition. In order to reach a stable configuration, the nucleus undergoes a spontaneous transformation by rearranging its constituent particles. This is accomplished by the emission of an alpha particle, a beta particle (either b
or b+), a neutron emission, or proton emission. Depending on the energy conservation, gamma radiation may or may not be present during the radioactive decay. In brief, when atoms containing nuclei in the nonequilibrium condition try to reach stable condition, the excess energy of the nuclei is emitted as radiation. In this process, the material disintegrates. According to Einstein’s principle (E = mc2), the disintegrated matter is converted into energy. For example, burning of 1 kg of uranium in a nuclear reactor results in conversion of 0.87 g of matter into energy which amounts to (0.8  10
3 kg)  (3.0  108 m/s)2 = 7.8  1013 J. For comparison, combustion of 1 kg of gasoline will release only 5  107 J of energy, six orders of magnitude smaller than 1 kg of uranium [2]. In addition to high specific energy, the nuclear energy has an advantage of not releasing carbon dioxide into the atmosphere. Combustion of 1 kg of gasoline will release about 3.2 kg of carbon dioxide to the environment. An anthracite coal-based power plant will release about 1.2 kg of CO2 for every KWh electricity generated. Whereas, the lifetime CO2 emission of nuclear power plants, considering the electricity used for mining and processing operations from fossil fuel power plants, will be 100–140 g of CO2/kWh electricity generated [3].

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The major advantages of nuclear energy are ● ● ● ● ●

High specific energy No CO2 emission Spent fuel can be reprocessed and reused, thus conserving natural resources Possibility to produce more nuclear fuel than consumed by using fast breeder reactors Lower operating cost in terms of fuel cost compared to fossil fuel power plants

and disadvantages are ● ● ● ●

Large capital cost and longer construction time of power plants Long-term storage of nuclear waste is an issue Exposure to radioactivity in case of accidents Potential proliferation of weapon’s grade fuel during reprocessing

Nuclear power plants attract more safety and environmental concerns from the public than other power plants. This chapter addresses some of the environmental issues associated with nuclear power generation. The first three sections introduce nuclear fuel cycles, nuclear power reactors, and issues on operational safety. Information on nuclear spent fuels reprocessing, waste management, and long-term storage are given in the last section.

Nuclear Fuel Cycles Conversion of nuclear energy can be achieved by fission or fusion reactions. Most of the commercial nuclear power reactors operate based on nuclear fission reaction. The average energy of neutrons used for power generation is about 0.1 eV, which are called thermal neutrons. Neutrons, those that have energy in the order of 2 MeV are called fast neutrons. Uranium is the most common fissile material used in the nuclear reactors. Naturally mined uranium has 99.24% U-238, 0.72% U-235, and 0.0054% U-234. U-235 is a fissile isotope. Fissile isotopes are the ones that undergo fission reaction upon absorption of slow neutrons (neutron having energy < 0.4 eV). When a neutron is absorbed by U-235, the isotope gains an extra energy and transforms to U-236 in an excited state [2]: 235 92 U

 þ 10 n ! 236 92 U

(30.1)

Since the excited U-236 has a higher mass than U-236 in ground state, the difference in mass is converted into energy of 6.54 MeV. Each fission of U-235 yields about 190 MeV of useful energy. This energy is used for further fission reaction. A continuous and selfsustaining fission chain reaction is required for nuclear power generation. This is achieved by containing a critical mass of uranium, which is about 50 kg of U-235 in the nuclear reactor. 1.3 g of U-235 is consumed for each mega Watt-day of thermal energy [4]. The natural isotope U-235 and artificial isotopes such as Pu-239 and U-233 require only slow (thermal) neutrons to induce fission. On the other hand, U-238 which is abundant in nature can only be activated by fast neutrons of at least 0.9 MeV to initiate fission. If the fission occurs by thermal or slow neutrons, the material is considered as

Nuclear Energy and Environmental Impact

30

‘‘fissile.’’ If a material is converted into a ‘‘fissile’’ material by irradiation, then that material is classified as a ‘‘fertile’’ material. For example, fertile materials such as U-238 and Th-232 can be used for generating ‘‘fissile’’ materials such as Pu-239 and U-233, respectively, by the following neutron reactions [2]: 238 92 U

239 0 239 0 þ 10 n ! 239 91 U ! 93 Np þ
1 e ! 94 Pu þ
1 e

(30.2)

232 90 Th

233 0 233 0 þ 10 n ! 233 90 Th ! 91 Pa þ
1 e ! 92 U þ
1 e

(30.3)

Nuclear fuel cycle describes different stages of preparation, use, safe-storage, and reprocessing of the spent fuel. The fuel cycle starts by mining of fuel ore and ends by reprocessing. If reprocessing is not carried out, then it is called as once-through nuclear cycle. The fuels that can be used in the nuclear power reactors are uranium, plutonium, minor actinides, and thorium. Most of the commercial nuclear reactors use uranium as a fuel with different levels of enrichment depending on the type of reactor. Thorium is also used in some countries at a small scale. This section will focus on only these two fuels.

Uranium Fuel Cycle Mining and Extraction: Uranium ore is mined in several forms, most notably as: Uranite (UO2), pitchblende (UO3 + U2O5), coffinite (U(SiO4)1
x(OH)4x), brannerite (UTi2O6), davidite (REE(Y,U)(Ti,Fe)20O38, REE = rare earth elements), and thucolite (U containing pyrobitumen) [5]. Uranium mining process is similar to mining of other metals such as copper, gold, etc. The mines can be of open pit or underground type. In some cases, in situ leaching of ore is carried out without deep excavating of the earth. Lower-grade ores are concentrated by using a heap leaching process. The excavated ores are collected as heaps and a leaching agent (mostly low concentration of sulfuric acid) is sprayed on the heaps and drained through the ore collection. In this process, uranium is preferentially leached out of the oxide ore and carried by the draining leaching agent. This solution is further processed. In situ leaching process is used by some mining companies. In this process, the surface of the earth is not disturbed by drilling or excavating operations. Instead, a leaching agent (mild acid/alkaline solution containing oxidizers such as hydrogen peroxide) is pumped through the porous surface of the ore deposits. The solution passing through the ore will leach out the uranium. The uranium-containing solution is collected for further processing. During heap leaching and in situ leaching processes, the surrounding ground water is continuously monitored for any contamination. Even after shut down of the mining operation, the monitoring continues. Recent international mining laws require that the mining companies set aside required amount of funds for reclamation of the environment in the neighborhood of the mining operation. This fund will be in place for the required environmental remediation even if the company goes out of business. The uranium rich ore from mill, U3O8, often called as yellowcake, though the actual color is khaki, is purified further either by a solvent extraction or by a ion-exchange process. The U3O8 is dissolved in nitric acid to form uranyl nitrate (UO2(NO3)2), which is

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then treated with ammonia to produce ammonium diuranate ((NH4)2U2O7). This compound is then reduced in a hydrogen atmosphere to form uranite (UO2). It should be noted that this UO2 is not the final form of fuel that can be used in the reactor. It requires enrichment of U-235 isotope to more than 3.5% from 0.7%. In order to accomplish the enrichment process efficiently, the material needs to be in the form of a gas. Therefore, UO2 should be first converted to uranium hexafluoride gas (UF6), gets enriched, and then it is converted back to UO2. In order to form UF6, UO2 is treated with HF which results in UF4. Further fluorination of UF4 renders UF6. Now the UF6 is taken for enrichment process [6]. Enrichment of Uranium

U-235 is a fissile material that utilizes thermal neutrons, which is only 0.7% in the natural uranium source. Stable operation of a critical reactor requires fissile nuclei. Therefore, the ratio between fissile (U-235) and non-fissile (U-238) should be high in a reactor for stable power generation. Typically, the U-235 content in a fuel should be more than 3.5%. This can be achieved by the following enrichment methods [7]: ● ● ● ●

Gaseous Diffusion Gas Centrifuge Jet Nozzle/Aerodynamic Separation Electromagnetic Separation

Gaseous Diffusion

Separation of U-235 isotope by gaseous diffusion process occurs because of the difference in velocity of the gas molecules. The rate of diffusion of a gas through an ideal porous medium is inversely proportional to the square root of the molecular weight of the gas. Therefore, when UF6 is passed through a porous tube, lighter U-235 isotopes will escape the porous container faster than their U-238 counterparts and thus collected separately. > Figure 30.1 schematically illustrates the working principle of a gas diffusion separator. In this arrangement, compressed UF6 gas is contained in a large vessel under pressure and allowed to pass through a porous channel that acts as a diffusion barrier layer. The porous layer is an essential component of the diffusion separator because the efficiency of the U-235 enrichment process in the UF6 stream is determined by the ability of the porous layer permeating the gas molecules. The barrier layer has to withstand the working pressure, be stable in the corrosive UF6 atmosphere, and have pores tiny, in the order of 30–300 times the diameter of a single U atom, around 10 nm and uniformly distributed in the order of billions per square centimeter area. The barrier layer thickness is around 5–6 mm. The material of construction is a classified information because enrichment of U-235 to more than 80% becomes a weapon’s grade material. Plasma-spayed Zr, Ta, Mo coatings of required thickness and porosity can be used as diffusion layer. Silver-Zinc alloy pipes after selective etching with HCl also could serve as a diffusion barrier [8]. Since the velocity of diffusion varies only by 0.4% between U-238 and U-235, multiple stages of gas passage are required to achieve the required enrichment for commercial

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Diffusion barrier layer

235

U

238U

High pressure UF6 feed stock

235U

235U

stream

Depleted stream

235U

stream

Diffusion barrier layer

. Fig. 30.1 Uranium enrichment by gaseous diffusion process

reactors. In the diffusion cascade, the outlet of the depleted stream is bifurcated by redirecting 50% the depleted stream back to the previous stage and the remaining 50% to the inlet of the next stage. This way one may require 4,000 diffusion stages to obtain 99% 235UF6. Gas Centrifuge

In this process, UF6 is passed through rapidly spinning cylinders in series. The centrifugal action drives the heavier 238UF6 molecules to the wall of the rotating container. Lighter 235 UF6 molecules are retained closer to the center of the container. Circulation of the gas from bottom to the top helps separate the heavier and lighter molecules and pass to next separation stages. > Figure 30.2 schematically illustrates the gas centrifuge [9]. The cylinders are heavy in order to impart very high kinetic energy to the gas molecules and rotated at very high speed, in the order of 100,000 rpm. The linear velocity may approach the speed of sound in the material of construction. Therefore, the centrifuges are very sturdy. Nevertheless, this process requires 40–50 times less energy than the gaseous diffusion process to achieve the same level of enrichment. The diffusion process will consume about 4–5% of the energy that the enriched fuel will generate in its cycle time. Furthermore, amount of waste heat generated during UF6 compression for the diffusion process is much higher. This results in utilization of a significant amount of coolants such as Freon-12, etc., in order to cool the gas in the intermediate compression stages. Gas centrifuge process is more advantageous than gas diffusion process considering aforementioned issues. Electromagnetic Isotope Separation

This process can be used as a stand-alone method for enriching uranium from the feedstock of natural uranium or in tandem with the gaseous diffusion process for producing highly enriched uranium from the low enriched stream. It should be noted that commercial reactors do not require highly enriched uranium. The electromagnetic

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Nuclear Energy and Environmental Impact 235U

UF6 feed stock 238U

238U

235U

235U

238U

238U

235U

235U

238U

238U

. Fig. 30.2 Schematic of gas centrifuge for enrichment of U-235

separator works on the principle that the radius of the trajectory of a particle traveling in a magnetic field is determined by its mass. Heavier the particle, larger will be the radius, provided that the particles have the same charge and travel at the same speed. In this process, UCl4 plasma is generated by heating a solid UCl4 material and bombarding it with high energy electrons. This process ionizes uranium. The uranium ions are then accelerated through a strong magnetic field. When these ions complete a half circle, the lighter U-235 ions are nearer to the inside wall of the semicircle channel and heavier depleted U-238 ions are separated at the outer wall of the circular channel. This process requires a large amount of energy to maintain a high magnetic field. However, the rate of U-235 separation is lower than the other processes [4]. Jet Nozzle/Aerodynamic Separation

In this process, UF6 is pressurized with helium or hydrogen gas and sent through a bank of small circular pipes. The curved pipelines ensure that the heavier molecules stay at the outer surface and lighter U-235 stay at the inner surface of the circular path. This process is again energy intensive because compressing lighter gases such He and hydrogen requires more energy. The compression process will be carried out at multiple stages with intercoolers in order to increase the thermal efficiency of the system. Therefore, the entire process results in generation of a significant amount of waste heat, utilization of a large amount of coolants/refrigerants, and both these outcomes lead to environmental concerns [9].

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Conversion of UF6 to UO2

The enriched UF6 gas stream with 3.5% U-235 is taken for fuel rod preparation. The first step is conversion of UF6 back to UO2. Oxide fuels are preferred because of its high melting point that shows resistance for melt down. Metallic fuels (in the form of U or its alloys such as U-Mo, U-Si, U-Zr, etc.) have been used in some experimental fast breeder reactors. Most of the commercial reactors use oxide fuels such as UO2 or mixed oxide fuels such as blend of Pu-239 and depleted uranium [10]. UF6 can be converted to UO2 using three different chemical routes such as: 1. UF6 is reacted with hydrogen and steam to form UO2. 2. UF6 is sent through water and thus hydrolyzed. NH4OH is added to this hydrolyzed solution to precipitate ammonium diuranate. This precipitate is then reduced in hydrogen at 820 C to form UO2. 3. In this method, a gaseous mixture of CO2 and NH3 is hydrolyzed in water to form ammonium uranyl carbonate. This precipitate is then treated with steam and hydrogen at 500–600 C to form UO2. The UO2 is then purified by several washing cycles, dried, and mixed with an organic binder to press as cylindrical pellets. The compacted pellets are sintered at high temperature (1,400–1,700 C). The solid UO2 pellets are machined by fine grinding operation to final dimensions which are typically about 1 cm in diameter and 1.5 cm in length depending on the type of reactor (boiling water (BWR) or pressurized water (PWR)). Fuel Rod Assemblies

The cylindrical fuel pellets are stacked in a fuel clad tube with a nominal diameter of 1 cm and length of 3.6 m. Then the tubes are backfilled with helium at about 3 atm to improve the thermal conductivity and heat transfer. The fuel rods are bundled with a thin encasing tube to prevent density variation that may affect the thermohydraulics of the reactor core. In a typical BWR fuel bundle, there are about 96 fuel rods. The BWR reactor core contains about 360–800 fuel assemblies depending on the capacity of the nuclear reactor. In PWR reactors, the fuel assembly contains a matrix of 14  14 and 17  17 fuel rods. The PWR bundles are about 4 m long. The reactor core contains about 120–193 bundles, depending on the capacity of the reaction. In case of heavy water reactions, U-235 enrichment is not required. Natural uranium (U-238) is loaded into the fuel bundles that have 380 tubes [4].

Thorium The isotope 232Th is about 3–4 times more abundant in earth than uranium. This fertile isotope can be used for producing fissile 233U isotopes. The neutron absorption cross-section of 232Th is also about three times that of U-238 (7.4 b vs 2.7 b, where 1 b = 10
24 cm2). The number of neutrons liberated per neutron absorbed is greater than 2.0 over a wide range of thermal neutron spectrum for the U-233.

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Therefore, the 232Th – 233U fuel cycle can operate in wide spectra of neutrons such as fast, epithermal, and thermal. Thorium oxide is chemically more stable than UO2 and has a low fission product release rate. ThO2 also has a better thermal conductivity than UO2. Furthermore, (Th, Pu)O2 mixed oxide fuel is more attractive than (U, Pu)O2 fuel because Pu is not bred in the (Th, Pu)O2 and presence of 232U makes the spent fuel more proliferation resistant [11]. Some of the limitations of ThO2 fuel include a melting point of 3,350 C. Therefore, the sintering temperature is higher than 2,000 C. Reprocessing requires heavy shielding because of the presence of remitting 232U with 73.6 years of half life. Because of its high chemical stability, ThO2 cannot be easily dissolved in HNO3 for reprocessing. It requires addition of .005 M HF to 13 M HNO3 which makes the stainless steel containers used in reprocessing more prone to corrosion attack even after adding 0.1 M Al(NO3)3 as inhibitor.

Fuel Burnup Fuel burnup gives information about the fuel utilization as how much energy has been extracted from the fuel as a nuclear fuel source. It is expressed as megawatt-days per metric ton (MWd/ton). The generation (II) Commercial reactors were designed for a burnup of 40 GWd/t. During nuclear fission, by products build up and poison the sustainability of the chain reaction. For example, Xenon-135 (cross-section two millions barns), Samarium-149 (75,000 b), and Gd-157 (200,000 b), poison the reactor core which is a serious problem [4]. In order to operate the reactor for longer time/cycle between shutdown for fuel change, excess fuel is added. This high reactivity of the excess fuel needs to be balanced by neutron-absorbing materials in addition to control rods. These are called burnable poisons. Compounds of B and Gd act as burnable poison, whose neutron absorption capacity decreases with fuel burnup. By using neutron poison, the burnup of fuel in a modern reactor can achieve a burnup of 60 GWd/t [2, 4]. Higher enriched fuel in the advanced light water reactors can achieve a burn-up rate of 90 GWd/t. Since the fast neutron reactors can handle fission product accumulation without affecting its performance, the burn-up rate can be around 200 GWd/t. The deep burn molecular helium reactor that utilizes ceramic-coated Plutonium-based fuel can achieve a burn-up rate of around 500 GWd/t [12].

Types of Nuclear Reactors Depending on the coolant and moderator, the reactors can be classified as: 1. Light Water Reactor (LWR) ● Boiling Water Reactor ● Pressurized water

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2. Heavy Water–Moderated Reactor ● CANDU ● Advanced Heavy Water Reactors 3. Graphite-Moderated Reactors 4. Thermal Breeder Reactors ● Molten Salt Breeder Reactor ● Light water Breeder Reactor 5. Fast Neutron Reactors: ● Liquid Metal Fast Breeder Reactor ● Gas-cooled Fast Breeder Reactor Boiling Water Reactors

The original design was developed by the General Electric Company. > Figure 30.3 schematically illustrates the major components of a BWR system. Different power generation capabilities are 200 MWe, 650 MWe, and 1,250 MWe. Here, the subscript ‘‘e’’ in the MWe represents electrical energy as the output. The capacity is also expressed in terms of thermal energy as output. The efficiency of converting thermal energy into electrical energy is around 30%. Therefore, for a given MWe output, the corresponding thermal energy will be at least three times higher. It should be noted that feed-water enters the reactor vessel at a pressure of about 70–85 bar and leaves as steam at 288 C to run the

Steam, 83 bar, 288°C

Reactor Steam Fuel elements

Generator Turbines High purity water, 18.2x 106 Ohm – cm,< 200 ppb dissolved oxygen

Cooling water

Control rods Feed water pump

Condenser

. Fig. 30.3 Schematic diagram of system flow in a boiling water nuclear reactor. Only critical components are shown

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steam turbines. The active core height is about 3–8 m that is placed in a reactor vessel of 22 m height. The bottom of the vessel is occupied by the control rod and drive mechanism. The space above the reactor core is occupied by the steam separator-dryer system components. The inner diameter of the vessel is about 6.4 m (for 1250 MWe reactor). The wall of the reactor is made of 15 cm thick carbon steel cladded with stainless steel. The stainless steel surface is exposed to the water/steam phases [2, 4]. Since a single coolant loop is used for heat transfer and steam generation, the water used in the BWR system is of ultrahigh purity with an electrical resistance of 18.2 MΩ-cm. In order to minimize corrosion, the dissolved oxygen in the water is controlled below 200 parts per billion (ppb) by purging with ultrahigh purity argon or hydrogen. The dissolved oxygen content of water exposed to ambient atmosphere is around 8 parts per million (ppm). Purging with nitrogen could lead to formation of NOx-related compounds by radiolysis. Very high electric resistance of the water and low oxygen content result in low corrosion rates of the pressure boundary components. Pressurized Water Reactors

Pressurized water reactors are developed by Westinghouse Electric Company based on the experience of nuclear submarine reactors. The power generation capability of PWR ranges from 60 to 1,450 MWe. > Figure 30.4 schematically illustrates the major components of the PWR system. The PWR has two coolant circulation loops. The primary loop that

Steam, 150 bar, 325°C

Steam generator

Reactor

Generator Turbines

Fuel elements Primary heat transfer loop

Secondary heat transfer loop

Cooling water

Control rods Feed water pump

Condenser

. Fig. 30.4 Schematic diagram of system flow in a pressurized water nuclear reactor. Only critical components are shown

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removes heat from the reactor core is contained within the reactor vessel and used for transferring heat to a secondary coolant loop. Steam formation takes place in the secondary loop which runs the steam turbine for power generation. The water of the primary loop contains 1,200–1,800 ppm boron in the form of boric acid. Boron is added as moderator/neutron absorber. In order to balance the acidic pH due to boric acid, LiOH is added in the water to maintain a neutral pH at room temperature. The addition of boron and lithium compounds increases the ionic conductivity of the primary loop water. This may lead to increased corrosion rate. Since oxygen reduction reaction is the cathodic reaction in most of the corrosion mechanisms, the dissolved oxygen of the primary water is reduced to less than 5 ppb by purging with ultrahigh purity hydrogen. The primary loop contains lithiated and borated water at a pressure of about 150 bar (atmospheres). The core outlet temperature of the primary loop water is at about 350 C. This primary loop heats the water in the secondary loop to above 290 C and 70–85 bar. The secondary loop conditions are identical to that of BWR steam conditions. The main difference between the PWR and BWR is that the steam entering the turbines of PWR does not contain any radioactivity. A typical PWR reactor vessel is about 13 m tall and 6.2 m in diameter. The wall of the vessel is made of 23 cm thick farritic-bainiric steel with 3 mm stainless steel clad that is exposed to the water/steam environment. The secondary loop, also called the steam generator, is 21 m high and 4.5 m in diameter [2, 4]. Heavy Water–Moderated Reactors

In light water reactors, the water is used as a moderator and coolant. An ideal moderator will have low mass, high neutron scattering cross-section and low neutron absorption cross-section. Light water more rapidly moderates neutrons than heavy water. Therefore, fissile material such as U-235 is required for sustaining the chain reaction. In case of heavy water–moderated reactors, high energy neutrons are available for fission of U-238. Therefore, enrichment of U-235 is not required. However, preparation of heavy water is also a tedious process since deuterium is available in nature with a ratio of 1:7,000 along with regular hydrogen in water. The separation of deuterium from water is an energy intensive process. In CANDU-PHW system, the primary heavy water coolant is pumped through a series of pressure tubes that also house the fuel rods. The heavy water is contained in a vessel called Calendria, which is about 7.6 m in diameter and about 4 m tall. There are about 380 Calendria tubes. Each Calendria tube contains one pressure tube through with the coolant flows [13]. Graphite-Moderated Reactors

These reactors are fueled by natural uranium, moderated by graphite, and the coolant is an inert gas. Advanced gas-cooled reactors use helium as a heat transfer medium. Helium flows through the reactor core and exits at 740 C with a pressure of about 50 bar. The heated gas is fed through the steam generator which produces superheated steam at 510 C under a pressure of 170 bars. The reactor vessel is of prestressed concrete strengthened with vertical and circumferential prestressing steel cables. The dimensions of the vessel are

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28 m high  30 m in diameter. The reactor core size is about 6.3 m  8.5 m. There are six sets of helium loops and steam generators that produce about 1,160 MWe power. Running the generators by gas turbines using the helium is possible [2, 4].

Nuclear Reactor Safety Radiation Effect Three types of radiation damage can occur when high energy particles impinge on a target. These are [14]: ● Transmutation of the constituent atoms of the target to new atoms of new material ● Displacement of atoms from their normal lattice positions in the structure of materials ● Ionization-removal of electrons of atoms that are present in the trajectory of the charged particles and formation of ion pairs Alpha and beta particles have only low penetrating power and can be stopped by very thin layer of materials. Alpha particles produce a linear path with a specific ionization per unit length of travel because of its high mass and charge. Smaller path and charge of particles result in a nonlinear path and very low specific ionization. Gamma rays have higher penetrating power than the alpha and beta particles. Therefore, a heavy shielding is required to stop gamma radiation. Accumulation of fission products in the core of the nuclear reactor poses a potential safety threat among the public. Therefore, integrity of the fuel is important throughout the operating cycle. A set of specified operating parameters limits is determined for every reactor to assure safety of operation. These limits are generally the upper limitation on total reactor power which determines the maximum reactor core temperature that will not result in a meltdown. Fuel integrity is ensured by avoiding hot spots in the core. This is carried out by controlling the ratio of peak power to average power. The other important parameters that control the safe operation of the nuclear reactor core are as follows: limit on the control rod position; the difference between the power generation in the bottom half of the core and the top half; symmetry of power generation across the core; maximum reactor coolant temperature; minimum coolant flow; and maximum system pressure. Under normal operating conditions, a negligible amount of radioactivity will get into the coolant [2]. Since abnormal conditions can exist, a design basis accident is postulated. In this hypothetical accident condition, a loss of coolant is assumed. Loss of coolant can occur either by a breakage of coolant piping or a failure of jet pumps supplying the coolant. Loss of coolant would result in an increase in the temperature of the nuclear core. When the temperature exceeds the melting point of fuel and cladding, the fuel tubes will be damaged and fission products will be released. The reactors are provided with safety measured such as safety rods and emergency core cooling system (ECCS) to safeguard the reactor against loss of coolant accident. The safety rods reduce the reactor power immediately upon loss of coolant flow through the reactor core.

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The emergency core cooling system consists of auxiliary pumps that supplies cooling water to bring down the temperature. In order to minimize the effect of radiation, the nuclear plant is normally located several kilometers away from any population centers. The fission products that might be released, in case of an accident, will be contained within the steel-reinforced concrete reactor building. The concrete building can withstand high internal pressures and is designed to have a very minimal rate of leak. Another fault may occur due to loss of pressure: If there is a leak in the PWR system, the vessel pressure may drop from nominal 2,250 psi to lower values. The safe system in the PWR is activated which pumps water from the borated water storage tank. A large rupture in the coolant system will significantly decrease the vessel pressure and increase the concrete containment pressure. When the vessel pressure drops to 600 psi, water from the core flooding tank will be pumped to the core by a pressurized nitrogen gas stream. If the primary loop pressure drops below 500 psi, then water from the borated water storage tank is pumped to the core by the low-pressure injection pumps [4].

Probabilistic Risk Assessment (PRA) One objective of PRA is to find the chance of an undesired event occurring in a nuclear reactor and analyze its potential causes [15]. The event can be damage in the core, breach of containment, release of radioactivity, etc. The first step in the risk assessment is to investigate all of the possible failure modes of equipment and/or processes. Event trees are constructed to study the process flow. Fault trees are constructed using the principles of Boolean algebra that trace causes of failures and their effects mathematically. The ultimate objective of the probability risk assessment is to determine risks to people by calculating using the relation: Risk ¼ Frequency  Consequences; where frequency is the number of times per year of operation of a reactor that an undesired incident is expected to occur, and consequences refers to quantifications of fatalities related directly or indirectly to the event. Each nuclear power plant and the local government are required to have plans in place for emergencies such as any accident potentially releasing radioactivity. Mock accident drills are carried out periodically that resemble actions to be taken in a real accident. Many organizations also involve in such drills to make a coordinated effort to safeguard the life of residents in case of an accident. These organizations include radiation protection staff, police and fire departments, highway patrol, public health officers, and medical response personnel. If the members of the public suffer loss due to accidents involving reactors or transportation of fuel, they are then compensated by nuclear insurance. The nuclear utilities pay the insurance premium to private insurance companies to cover any accidents to the public.

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Nuclear Accidents Safety goals are set either by regulatory authorities or by the utilities for safe operation of nuclear power plants. The probabilistic design targets for LWR nuclear power plants are: [16] ● A frequency of occurrence of severe core damage that is below about 10–4 events per plant operating year for existing nuclear plants ● Achievement of an improved goal of not more than 10–5 severe core damage events per plant operating year for future reactors ● Practical elimination of accident sequences that could lead to large early radioactive releases In spite of strict safety regulations, there were accidents in the nuclear power plants. Postaccident analyses clearly indicated that these accidents were the results of severe violations of specifications and regulatory instructions.

Three Mile Island A nuclear reactor at the Three Mile Island (TMI) facility failed on March 28, 1979, due to an accident. The accident was considered the result of a combination of design deficiencies, equipment failure, and operation error. The accident was first triggered by a valve failure in the feed water system. Since the feed water system malfunctioned, the turbine generator automatically tripped and the control rods were driven into the reactor to reduce its power. At this stage, water could have been supplied to the reactor by three backup feed water pumps. However, there was an operator error as the valve to the steam generator was left closed by mistake. Therefore, the steam generators went dry, increasing the temperature and the pressure of the primary water coolant to 2,355 psi. This increase in the pressure set the relief valve on. This valve was stuck open due to a mechanical failure. The open valve let the coolant drain off from the primary system that led to a series of malfunctions and the meltdown of the core. The escape of the coolant water also resulted in spillage of some radioactivity. However, it was estimated that the highest possible dose of exposure was only 100 mrems or 1 m Sv, where 1 Sv is equivalent to 1 J/kg of energy release. It should be noted that a person taking a flight from the East Coast to the West Coast in the USA will have a radiation dose of 5 mrems due to cosmic rays.

The Chernobyl Accident The Chernobyl accident occurred not because of operational abnormality but because of gross violation of operating rules and regulations. People who were in the vicinity of the damaged reactor received a radiation dose of 100–1,500 rems. More than 135,000 people were evacuated from a 30 km zone.

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Design Considerations and Life Prediction of Nuclear Components In nuclear reactors, passive components such as pressure vessels and piping systems show very low failure probabilities. Therefore, failures of these components only have limited contributions to plant risk. On the other hand, components within a reactor core must tolerate high temperature water, stress, vibration, and an intense neutron field. Degradation of materials in this environment can adversely affect the performance, and in some cases, lead to sudden failure. Degradation of materials in a nuclear power plant is very complex. There are over 25 different metal alloys within the primary and secondary systems. In addition, there are additional systems with complex nature such as the concrete containment vessel, instrumentation and control, and other support facilities. The combination of diverse set of materials, complex and harsh environment, and load conditions make the degradation process very complicated. The service failures of passive components occur because of the following mechanisms: ● ● ● ● ● ● ● ●

Corrosion fatigue Thermal fatigue Stress corrosion cracking Corrosion attack Erosion and cavitation Flow-accelerated corrosion, i.e., erosion corrosion High-cycle vibration fatigue Water hammer

The in-core components are subjected to radiation assisted failure mechanisms such as radiation-induced segregation, swelling, radiation creep relaxation, radiation-induced hardening, etc. The degradation of materials by radiation is considered first.

Fuel and Fuel Cladding The fuel cladding helps contain the radioactive fission products. If the integrity of the cladding is maintained intact without cracking, rupturing, or melting during a reactor transient, the radioactive fission products are contained within the fuel rod. Transients in reactor operation or hypothetical accidents could weaken the cladding because of a temperature increase, embrittlement by oxidation, or over stressing by swelling of the fuel because of mismatch in thermal expansion (pellet-clad mechanical interaction) or high fission gas pressure. These events alone or in combination can cause cracking or rupture of the cladding and release of the radioactive products to the coolant. The fuel cladding failure models consider several mechanisms: cracking due to hydride formation; swelling of the clad because of differential pressure between the fuel rod gap and the coolant, thermal expansion of the fuel and clad, elastic and plastic straining of the clad,

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interference between adjacent ballooning rods, the effect of grids and azimuthal variations in temperature and straining caused by pellet eccentricity; and stress corrosion cracking induced by pellet–clad interaction in the presence of corrosive fission products such as iodine.

Irradiation Effects Irradiation Assisted Stress Corrosion Cracking (IASCC) has been drawing more attention over the years and has become potentially a critical phenomenon for core internals in light water reactors (LWRs). Alloys of iron and nickel base with oxygen free copper are the materials found to be affected by IASCC. It is widely recognized that IASCC is a result of the interaction of irradiation, material, environment, temperature, and stress. The complexity of IASCC arises from the fact that irradiation has an impact on all the other variables listed above so that the knowledge available on SCC of materials in nonirradiated environmental conditions is not sufficient to solve the IASCC problem. Irradiation can alter the microstructure and microchemistry of the material, can affect the aggressiveness of the environment by water radiolysis, can increase the temperature of the parts by gamma heating, and can change the component stresses through relaxation of creep or by radiation hardening. Interpretation of wide range of issues influencing IASCC requires specialized knowledge covering fracture mechanics, electrochemistry, physical metallurgy, and core neutronics. IASCC may have a higher potential to occur in fusion reactor components because of the higher dose rate of neutron irradiation than in LWRs. Components of the blanket and first wall cooling system, divertor cooling system, and vacuum vessel cooling system are potential problem sites where IASCC could occur. Though the mechanism of IASCC is not fully understood, factors affecting it are well documented, especially the effect of radiation on environment and on material properties. Among the radiation effects, some are fluence dependent and some are flux dependent, while both fluence and flux cause joint effects. Radiation-induced segregation (RIS), radiation-induced microstructures, and radiation creep relaxation are fluence dependent, while radiolysis and to some extent RIS are flux dependent. The ratio of thermal to fast neutron flux affects transmutation.

Environmental Assisted Cracking (EAC) of Austenitic Stainless Steel (SS) in High Temperature Water EAC of stainless alloys in high temperature water occurs due to the synergistic interaction of stress, environment, and material. Generally, active path corrosion cracking and hydrogen cracking are the mechanisms involved in EAC. Crack initiation and crack propagation are two distinct events, which are controlled by environmental, mechanical, and material variables. Water chemistry and microchemistry of the material play a vital role in initiating the SCC. Dissolved oxygen and CO2 and presence of Cl
and SO42
are

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deleterious from an environmental point of view and inclusions such as MnS, segregation of Si and P, sensitized microstructure, and the presence of secondary phases such as sigma, laves, chi, etc., are detrimental from a material point of view.

EAC of Unirradiated Ferritic/Martensitic Steels Ferritic stainless steels (>17% Cr) are considered to have better SCC resistance than austenitic stainless steels. This is true only when the Ni, Cu, and Co contents are below certain levels [17]. However, 8–12% Cr steels are subjected to both SCC and hydrogen embrittlement. Apart from the environmental factors such as dissolved oxygen, presence of sulfate and chloride, ions, etc., microstructural condition of the material also control the cracking behavior. Untempered martensite and acicular bainite phases are found to be more prone to hydrogen cracking than tempered martensite and bainite + ferrite phases [18]. Generally, it is observed that pitting is associated with the initiation of SCC or corrosion fatigue in this type of material. Mostly intergranular cracking is observed along the prior austenite grain boundaries. However, it is not very clear why only the prior austenite grain boundaries are the most preferred site for cracking and not other boundaries such as interlath boundaries or interfaces between two martensite packets. Probably certain solute elements segregated in the austenite grain boundaries may have more affinity to hydrogen, as discussed by Leslie [19]. But, Auger electron spectroscopy carried out on these fracture surfaces did not throw much light on this aspect. Hydrogen cracking resistance of ferritic/martensitic steel is significant for fusion wall application because direct transmutation, water lithium interactions, radiolysis of water, and corrosion could charge hydrogen into the steel. Hydrogen cracking could be enhanced by other irradiation damage mechanisms such as RIS, increased defect density, etc.

Environmental Aspect Radiolysis Radiolysis is a complex issue affected by water chemistry, neutron flux (not fluence), flow rate, temperature, etc. Radiation causes decomposition of water into many species which affect the corrosion potential. At high hydrogen levels (>1 ppm), radiolysis is sufficiently suppressed so that it has very little effect on changing the corrosion potential [20]. The interior of the cracks were not found to be polarized by radiation, as the corrosion potentials of cracks and tight crevices were not altered.

Flux Dependence The structural materials are exposed to temperatures of 290–350 C in water reactors. In the case of a BWR, the temperature is constant at 288 C, whereas in a PWR, the

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temperature varies with location to a maximum of 400 C in the baffle plates. The fast flux in a BWR is around 7  1017 n/m2 s (E > 1 MeV), and in a PWR it is 20–30% higher. Radiation damage in materials is quantified in terms of displacements per atom (dpa) as calculated by approved methods. Empirically, 1.4 dpa per 1025 neutrons (n)/m2 (E > 1 MeV) is used for LWRs. From this, the fast flux can be back calculated to be 10
7 dpa/s in the core of LWRs and 1.5
4  10
7 dpa/s in test reactors. In fast reactors, the fast flux is given approximately as 10
6 dpa/s, and the temperature also is higher (>370 C) in fast reactors. So, the data generated in fast reactors cannot be compared with those of LWRs. The thermal to fast flux ratio also is an important issue. The thermal neutrons are those which are in thermal equilibrium with neighboring atoms and with energies below 0.5 eV.

Radiation Water Chemistry and Corrosion Potential Radiation causes break down of water into primary species (H+, eaq
) and molecules such as H2O2, O2, H2, etc. The concentration of species is proportional to the square root of the radiation flux. Fast neutron radiation has a stronger effect on water chemistry than other types of radiation such as thermal neutrons, beta particles, and gamma radiation [21]. This feature is because of the higher linear energy transfer (LET) and the higher neutron flux of fast neutrons. It is generally believed that the corrosion potential has more influence than the concentration of oxidizing and reducing species in controlling SCC. The initial concentrations of oxygen and hydrogen are found to be important in determining the final corrosion potential after irradiation. Though a large increase in concentration of some species occurs after irradiation, the change in corrosion potential is not drastic. When hydrogen is present at more than 200 ppb and at 0 ppb O2, there is no radiation-induced elevation of corrosion potential, whereas the presence of H2O2 increases the corrosion potential.

Crack Initiation and Propagation It is generally observed that SCC initiation preferentially occurs at sites like pits and second-phase particles. Preferential dissolution of secondary phases or inclusions creates a crevice where the local electrolyte chemistry and local strain level become more favorable for SCC initiation by a slip dissolution mechanism. In the case of IASCC, irradiated microstructural features (like Cr depletion, Si and P segregation, etc.) and the presence of hard phases such as oxides make the crack initiation process much easier. Oxide particles effectively participate in IASCC initiation by two proposed mechanisms as follows: (1) Oxides are hard to deform. So, under load, the shear stress at the interface of the oxide-matrix increases to very high levels as the ductile matrix around the particle

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deforms. This results in failure in the bonding, creating a crevice where the local chemistry of the electrolyte changes to more a conducive condition for promoting SCC. (2) Alternately, the oxide could fracture, creating a microcrack which can either extend into the matrix or create a very high stress intensity for easy SCC initiation. Strain at crack initiation (SCI) was proposed as the definition for IASCC initiation in slow strain rate tensile testing (SSRT) at 10
7 s
1 strain rate. It was defined as the strain at which the stress–strain curve of SSRTs began to depart from that of tensile tests, when plotted using the same coordinates. Higher SCI means SCC initiation starts at higher strain. Though the intergranular (IG) fracture ratio decreases with decreasing dissolved oxygen (DO), it increases inversely below 10 ppb of DO. This phenomenon may indicate the continuum of initiation of IASCC from BWR conditions to PWR conditions. Gamma ray irradiation is not expected to affect the microstructure or microchemistry of the material. However, it decomposes water into many kinds of radiolytic products of which hydrogen peroxide (H2O2) is very important to IASCC. In the 288 C BWR environment, gamma irradiation accelerated the crack growth to varying degrees depending on the water chemistry, flux, etc. For example, the average crack growth rates in unirradiated, irradiated with gamma ray for fluxes of 5  106, and 9  106 R/h were 7.2  10
10, 1  10
9 and 1.3  10
9 m/s, respectively. From these values, the crack growth rates in low conductivity pure water could be observed to be marginally affected by gamma ray irradiation. The effect of dissolved oxygen (DO) on crack velocity with additions of Na2SO4 is similar in both irradiated and unirradiated test conditions. Addition of sulfate ions showed more effect in accelerating the crack growth than did irradiation. DO also had a similar effect. Suppressing the DO content decreased the crack growth rate. Though crack velocity increased with sulfate ions as in the case of the unirradiated condition, DO had a major effect in controlling the crack behavior in the irradiated condition also. Nitrate additions were found to be less aggressive than sulfate additions in a BWR environment for 304 SS. Dissolved hydrogen showed greater beneficial effect in suppressing crack growth. The mechanism of crack growth mitigation by hydrogen injection could be explained by analyzing the corrosion potential of the system. The presence of molecules like H2O2 and O2 increases the free corrosion potential which falls into the cracking range and, hence, the crack velocity is enhanced following the slip dissolution model and Faraday’s law. Whereas, when hydrogen is introduced into the environment, it helps the recombination of species and thus reduces the corrosion potential well below the cracking range. IASCC tests were carried out on irradiated stainless steel samples under BWR condition using the slow strain rate testing method. They presented average crack growth data by dividing the maximum crack depth by total test duration. The maximum crack growth rate divided by the test time was suppressed by hydrogen water chemistry (HWC) below 3  1021 neutrons (n)/cm2, but not above 3  1021 n/cm2. It was observed that variations in either fluence level (3  1020– 9  1021 n/cm2, E > 1 MeV) or flux level (1.5  1013–7.6  1013 n/cm2 s) did not affect the crack velocity drastically (a maximum of a factor of two).

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Critical Issues on Selection of Candidate Materials for Advanced Nuclear Reactors Advanced systems selected for Generation IV reactors require high operating temperatures in the range of 500–1,000 C, depending on the coolant and longer service life. The fuels of the advanced reactors will have very high burnup capabilities and fast neutron spectra. The construction materials of Generation IV reactors will be exposed to severe environmental conditions in combination with increased radiation damage. Therefore, selection of structural materials for advanced reactors requires a thorough understanding of materials behavior in the extreme service conditions. The structural materials of advanced nuclear reactors will undergo degradation primarily due to three factors, namely, (1) exposure to high temperature and service stresses (high temperature degradation), (2) irradiation damage, and (3) interaction with service environments. The first two factors are common among all the types of reactors and therefore the data generated at high temperatures and irradiation levels relevant to the service conditions can be used for materials qualification for different type of reactors, as the operating temperature of most of the advanced reactors is in the range of 500–800 C. However, the third factor, interaction with environment is reactor specific. The material should possess higher resistance to corrosion attack in the service environment. Among the various types of advanced reactors, liquid metal (particularly, liquid sodium and leadbismuth eutectic) cooled fast reactors are considered in this study. Some of the critical issues pertaining to each major degradation modes will be discussed in this presentation. The materials considered for advanced reactor structural applications can be classified into three major categories namely, (1) ferritic-martensitic type Fe-Cr alloys, (2) austenitic alloys (stainless steels and Ni-Cr-Mo alloys), and (3) Oxide Dispersion Strengthened (ODS) alloys. Refractory metal–based alloys are not considered in this work. Merits and disadvantages of first two categories of the materials will be analyzed based on the critical degradation issues.

High-Temperature Degradation Major Issues and Temperature Limits

The major issues of high-temperature degradation are phase stability, oxidation, and creep–fatigue interaction. It is widely believed that thermal effects will offset the irradiation effects at high temperatures because of increased diffusivities and stress relaxation effects. This may be true for annihilation of point defects. However, effect of radiationinduced segregation could be aggravated at high temperatures. Available literature data indicate that the maximum service temperatures of different alloys are limited by chemistry and microstructure. For example, ferritic-martensitic steel with a maximum Cr content of 12% can service up to 650 C, and austenitic stainless steels up to 800 C, nickel base alloys up to 900 C and ODS alloys up to 1050 C. The interaction of creep–fatigue is considered to be of primary importance.

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Fatigue, Creep, and Creep–Fatigue Interaction

Creep or creep–fatigue interaction of structural materials at elevated temperatures over a long period of time in advanced reactor environments is a critical issue. High temperature and the temperature gradient during start-ups, in-services, and shutdowns induce both static and cyclic thermal stresses. These constitute the stress factors that generate creep and creep–fatigue interaction. In addition, components such as thread roots in steam turbine casing bolts, pipe, and branch connections in reactors endure multiaxial stresses. The earlier studies [22] investigated effect of heat-to-heat variation on fatigue and creep-fatigue resistance of type 304 stainless steel at 593 C. Carbides precipitation was considered as the reason of increasing Low Cycle Fatigue (LCF) resistance. Additionally, a fairly uniform distribution of inter- and intragranular carbides M23C6 was considered to increase the resistance to the tensile hold time effect. Generally, zero hold time tests revealed transgranular fracture surfaces, while intergranular features were obtained even with hold times as short as 0.01 h. This is also illustrated by the studies of Schaaf [23] (> Fig. 30.5). The creep-fatigue failure can be categorized in three modes: fatigue dominated failure with almost transgranular features, creep-fatigue interaction (both transgranular and intergranular), and creep-dominated failure with mainly intergranular cracks. In recent years, creep-fatigue properties of Liquid Metal Fast Breeder Reactor (LMFBR) candidate structural materials, such as austenitic 304L, 304NG, 316LN, and AISI 321, were investigated at 600 C [24–26]. It was observed that nitrogen addition improved fatigue life under creep–fatigue condition. The density of Cr-rich carbides formed at the grain boundary of 304NG (0.08% N) was lower than that of 304L (0.03% N). Planar slip planes of 316 LN initiated under creep–fatigue interaction probably enhanced stress concentration immediately next to grain boundaries and promoted intergranular fatigue fracture. In the case of AISI 321, it was observed that the creepfatigue life of TiC aged specimen was 40% longer than that of Cr23C6 aged, although the two carbide densities at grain boundaries were similar. It is suggested that the interfacial

Fatigue dominated-transgranular cracking

Creep dominated-intergranular cracking

Fatigue – creep interaction

. Fig. 30.5 The three failure modes: fatigue dominated (left), creep-fatigue interaction (left), creep dominated (middle) [23]

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free energy between TiC and grains is lower than that between Cr23C6 and grains in AISI 321. In addition, irradiation creep accumulates in reactor materials. It is known that irradiation creep has very weak temperature dependence. However, creep remains high at temperatures as low as 60 C [27]. It is postulated that migration of vacancies and migration of interstitials are two independent mechanisms of irradiation creep. The effect of irradiation is to lower the endurance of plastic strain range. So far, most of the experimental studies on creep-fatigue interaction were conducted by using low-cycle fatigue tests with and without tensile strain hold in air at temperatures ranging from 400 C to 600 C. The accumulated data in simulated reactor environments at high temperature up to 800 C is inadequate for a better understanding of the creepfatigue interaction mechanism. For example, oxidation and solubility of alloying elements in high-temperature liquid metal have to be considered as possible factors affecting creepfatigue behavior. Also, carbides precipitation at component weld joints and Heat Affected Zone (HAZ) may have different behaviors from base metals. Creep–Fatigue Life Prediction

In this section, selected creep-fatigue life prediction methods are reviewed without considering the irradiation effects. Suauzay et al. [28] analyzed their experimental results of creep–fatigue behavior of 316LN at 500 C using linear damage accumulation model. This model is based on Miner’s rule, expressed as: NF pf NF

þ

tF ¼1 tFrelax

(30.4)

NF: number of cycles to failure for a th hold time (tn > 0) NFpf: number of cycles to failure in pure fatigue, based on Coffin-Manson relation (tn = 0) tF = NFth tFcreep: Failure time in pure creep condition given as tFcreep = H/sr, where, H and r are creep coefficients Z th dt tFrelax ¼ NF (30.5) creep sðtÞ 0 tF Tsuji and Nakajima [29] evaluated the damage accumulation of Hastelloy-XR in HTGR environment at 700–950 C by applying life-fraction rule and ductility-exhaustion rule. The creep damage during strain holding time was given as: X DCL ¼ ðDti =DtRi Þn (30.6) i

DCL: creep damage by life fraction rule Δti: strain holding period for particular temperature and stress tRi: rupture time based on Larson–Miller parameter

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n: number cycles for failure in the experimental condition with trapezoidal strain wave form (creep–fatigue components) The Ductility–Exhaustion rule is given as: X Dcd ¼ ð_emin Dti =eRi Þn

(30.7)

i

Dcd : creep damage by ductility-exhaustion rule Δti: strain-holding period for particular temperature and stress e_ min: minimum creep rate calculated from Larson–Miller parameter eRi : strain at rupture It was observed that the ductility-exhaustion rule predicted the fatigue life under the effective creep condition more successfully than the life fraction rule. Most of the creep-fatigue life prediction models are based on phenomenology of failures. For example, ferritic/martensitic steels and nickel-base superalloys showed damage accumulation at the crack tip or crack process zones. In these materials, even compressive stress hold times were found to affect the damage accumulation. In case of austenitic stainless steels, creep–fatigue damage occurs by grain boundary cavitation and tensile hold time are considered to be more important. The proposed damage accumulation function based on grain boundary cavitation phenomenon is given as [30]:  DC
F ¼ Dem p

expð
Qg =RT Þ T

Z

t

2=3 sðtÞdt

(30.8)

0

Δep: plastic strain range m: Strain exponent Qg: activation energy for grain boundary diffusion R: gas constant T: temperature When the damage function is plotted against experimental creep-fatigue life, as shown in > Fig. 30.6, a linear relationship was observed with a slope of
1.66. Consideration of creep-fatigue life of different types of austenitic stainless steels at 600–700 C, revealed that the slope varies from
1.62 to
1.66. Therefore, the proposed damage function can be used for life prediction in the given experimental conditions. It should be noted that most of the life prediction methodologies are based on the data generated using smooth tensile specimens. In these cases, the events of crack initiation and crack propagation were not distinguished. In service conditions, inspection and monitoring methods require data on crack initiation time and crack velocity to evaluate the integrity of the components. Yokobori [31] considered the crack initiation and crack propagation issues for creepfatigue interaction based on critical notch opening displacement criterion. According to these authors, the crack initiation event is complete when the defect size reaches 5 mm,

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1.E-05

Damage Function

1158

1.E-06

1.E-07

1.E-08 100

1000

10000

Creep-Fatigue Life (cycles)

. Fig. 30.6 Normalized Coffin–Manson plot for AISI 316 stainless steel [30]

a dimension that can be resolved by optical microscopy. Crack initiation is considered to occur when a critical strain is reached by some atomistic rearrangement by timedependent plastic flow. This process in creep–fatigue interaction is thermally activated and aided by stress field. Based on these considerations, the time for crack initiation was given as:  
DH
Fðsg Þ A1 1=ti ¼ exp (30.9) RT ec ti: time for crack initiation ec: critical strain required for crack initiation A1: material constant ΔH: activation energy for plastic flow

  KI Fðsg Þ ¼ Df ln pffiffiffi G b

(30.10)

Δf: energy coefficient KI: Stress intensity factor = a a1/2 sg, where a is crack length G: Modulus of Rigidity b: burgers vector Similar expressions can also be written for crack propagation. The expression for crack propagation is:  o3 2 n
DHg
Df ln GKpI ffiffib da n4 5 ¼ Bsm (30.11) g KI dt RT

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The major advantage of the above approach is its ability to take various boundary conditions, such as environmental degradation (reduction in ΔHg due to liquid metal) and irradiation effects, into account.

Radiation Damage Radiation Damage of Microstructure

Among the radiation effects, some are fluence dependent and some are flux dependent, while both fluence and flux cause joint effects. Radiation induced segregation (RIS), radiation induced microstructures and radiation creep relaxation are fluence dependent while RIS is flux dependent to some extent. > Figure 30.7 illustrates schematically the collision of an energetic particle (either a neutron, electron, or proton) with a lattice atom generating radiation damage [32]. If the energy transfer of the elastic collision is greater than the displacement threshold (Ed), a primary knock on atom (PKA) is generated. PKA can displace additional atoms through the lattice if it has sufficient energy until the energy of all the atoms has been reduced below Ed [14]. The Frenkel pair, consisting of a vacancy and self interstitial atom (SIA) could be considered as the fundamental component of radiation damage [15]. The extent of radiation damage is a function of temperature. Several extensive reviews on microstructural evolution in irradiated austenitic stainless steels are available, which report a transition of microstructural damage approximately at 300 C. At high temperatures (>300 C), vacancy clusters in austenitic stainless steels become thermally unstable. The presence of voids and swelling are observed at higher temperatures. Under certain conditions, small gas-filled bubbles can grow to form voids, referred to as swelling, as the volume of material increases beyond the size limitation dictated by the thermodynamic equilibrium of gas. Both hydrogen and helium play an important role in swelling of a material.

Incoming neutron Interstitial

vacancy

PKA

. Fig. 30.7 Schematic illustration of generation of a primary knock-on atom (pka) [32]

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A swelling rate of 1% per dpa is maintained at temperatures above 425 C. The lower limit of temperature for swelling is observed to be affected by displacement rate. Radiation-Induced Microchemistry

In austenitic stainless steels, depletion of Cr and Fe and enrichment of Ni have been observed. The Cr and Fe have higher diffusivity than Ni. Therefore, they migrate away from the interface, enriching the boundary with Ni. This could be attributed to the Inverse Kirkendall segregation. Segregation of Si and P at grain boundaries is observed by an uphill diffusion process. Along with Cr and Fe, minor alloying elements such as Mn, Ti, and Mo also get depleted at grain boundaries. Mn levels drop to 0.5 % at grain boundaries in type 304 SS. In type 316 SS, more than 50% depletion of Mo after irradiation to 3 dpa has been reported [33]. For the same level of irradiation, enrichment of Si occurred to levels of about 6–8 %. Nickel-silicide precipitation also has often been reported to form at dislocation loops at temperatures >380 C and at higher doses (>20 dpa) [33]. At higher doses (PWR relevant, >10 dpa), sulfur segregation can be expected due to the burnup of Mn in MnS inclusions and subsequent release of S. Radiation-induced Cr depletion could retard carbide formation at grain boundaries. Radiation-induced segregation of Ni and Si could lead to formation of g ’ or G phase at higher temperatures [34]. Mechanical Properties

In general, it is observed that with increases in irradiation dose, the yield strength of the material increases. The ultimate tensile strength also increases, but the increase is not as great as for the yield strength. Formation of higher densities of vacancies and interstitials is attributed as the cause for this increase. Suzuki et al. [21] reported increases in strength for various grades of austenitic stainless steels with increase in neutron fluence as shown in > Fig. 30.8. However, a saturation level is reached at the 3  1025 n/m2 fluence level (E > 1 MeV) beyond which no significant increase in strength could be observed. The increase in yield strength (Ds) of the 304 SS irradiated in BWR environment at 288 C showed a relation of Ds = 1.1  10
3  (neutron fluence, n/m2)0.27. It was observed that type 304 SS was more prone to irradiation hardening than was type 316. Composition has two effects, namely, (1) certain alloy elements help nucleate Frank loops and (2) Stacking Fault Energy (SFE) is altered. Low SFE results in more hardening. Also a low SFE can lead to nucleation of twins as an alternative deformation mechanism to dislocation glide. Alloying elements such as Ni, Mo, and C increase the SFE in austenitic stainless steel and Cr, Si, Mn and N tend to decrease the SFE. Loss of work hardening and uniform elongation is observed after irradiation. The elongation decreases significantly with increasing dose. This kind of loss in work hardening and hence uniform ductility could be attributed to the irradiated microstructure, where annihilation of barriers occurs due to their interaction with dislocation. Interacting with obstacles, dislocations multiply in unirradiated material which results in development of back stresses and hence work hardening of the material. However, in irradiated conditions, the obstacles such as loops and voids can be destroyed when they interact with moving dislocations, resulting in work softening. This behavior causes flow localization,

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Increase in yield strength, MPa

1000

100 1.E+23

1.E+24

1.E+25

1.E+26

Neutron fluence (E > 1 MeV), n/m2

. Fig. 30.8 Typical relation between the increase of the 0.2% yield stress of austenitic stainless steels and neutron fluence (E > 1 MeV) after irradiation in BWR environment at 288 C [35]

and hence the slip band spacing increases, ultimately reducing the macroscopic deformation. At higher temperatures (above 600 C), the ductility is observed to be severely affected by He embrittlement. When a large void population develops near 400 C, the fracture mode is observed to be transgranular channel. The reduction of fracture toughness of irradiated SS can be attributed to the higher population of voids so that fracture occurs at an early stage by dislocation channeling or highly heterogeneous deformationdecohesion ahead of the crack tip [23]. RIS of Ni at voids also results in brittle behavior of a material. This preferential segregation of Ni at voids results in matrix depleted of Ni and hence destabilizes the austenite. The strain-induced martensite transformation, possible in the destabilized austenite, acts as low energy path for crack propagation [24]. This mechanism for cracking resulted in quasi-cleavage fracture with an overall fracture toughness of 80 MPa m1/2 after the austenitic material has been irradiated to high dose (1.6  1023 n/cm2) at 425 C. Irradiation hardening and softening are important factors in determining the fusion reactor life limits as creep properties are affected by these changes. In ferritic steels, the irradiation hardening is attributed to the formation of small defect clusters and dislocation loops, with associated precipitation of small carbides such as M2C, M6C, etc. Kimura et al. [36] studied the irradiation hardening behavior of 9Cr-2W-V steel and reported saturation of irradiation hardening at a dose level of about 10–15 dpa. Irradiating at above 430 C resulted in softening at dose levels of 40–60 dpa. Swelling was found to be associated only with hardening, in this study. Shiba et al. [37] investigated the response of F82H steel to irradiation at low damage levels ( Table 30.1. This includes cost of fuel, operation, and maintenance. Capital cost is not considered. The capital cost includes: ● Bare plant – engineering, procurement, and construction (EPC) ● The owner’s cost (land, cooling infrastructure, administration and associated buildings, site works, switch yard, transmission, project management, license, etc.) ● Cost escalation due to increased labor and materials ● Inflation ● Financing and interest on financing Typical construction period of a nuclear power plant is about 48–54 months. Decommissioning cost is about 9–15% of initial capital cost, which is about 0.1–0.2 cent per kWh of energy generated in the USA. The EPC cost in the year 2008 was about $3,000/kW.

Spent Fuel and Reprocessing When the spent fuel assembly is removed from the reactor, it is stored at the reactor site and allowed to cool before reprocessing or disposal. Typical compositions of fresh and spent fuels are listed in > Table 30.2. Most of the commercial reactor spent fuels are stored in water filled swimming pool– type structures. This type of arrangement is chosen because water is inexpensive, has good heat transfer coefficient by convection, provides shielding, and gives a visible opportunity

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. Table 30.2 Typical composition of nuclear fuel and spent nuclear fuel Fresh nuclear fuel

Spent nuclear fuel

235 U

3.3

0.81

238 U 236 U 239 Pu 240 Pu

96.7

94.30 0.51 0.52 0.21

241 Pu 242 Pu Fission Product

0.10 0.05 3.5

to detect undesired events, if any. The limitations of water as a cooling medium in spent nuclear fuel are that water is a neutron monitor and active electrolyte for corrosion reactions. A typical PWR operating cycle is about 1 year when 1/3 of the core is replaced with new fuel. After 1 year of operation, the fuel assembly, which weighs about 1,300 lbs, is removed from the core and transferred to an interim storage facility. The radiation levels of the unshielded fuel assembly is more than millions of rems per hour. The spent fuel assemblies are placed in vertical stainless steel racks. In order to prevent reaching critical conditions of the spent nuclear fuel assemblies, these are stored in wellseparated conditions. Furthermore, neutron absolving materials such as boron carbide or boron rods are inserted to inhibit neutron multiplication. The pool storage facility is designed only for interim storage – until the spent fuel is cooled down to low temperature. The remnant radioactive decay is subsided. Afterward, the spent fuel will be taken for reprocessing or in the absence of reprocessing to a long-term storage facility.

Dry Storage As an alternate to wet pool storage, dry storage using metal casks and concrete modules is practical. The heat generated during radioactive decay of the spent fuel is removed by the forced convection of air, in case of modular concrete vault storage. Metal casks are provided with fins for faster heat transfer. These metal casks, if properly designed, can also be used for transportation of spent nuclear fuels. For transportation of spent nuclear fuel, the metal casks are provided with (1) protection against direct radiation exposure to workers and the public, (2) provision for radioactive heat removal, and (3) neutron absorbers to prevent criticality. The metal casks can contain about 7 PWR assemblies or 18 BWR assemblies. The body of the cask is made of stainless steel of 5 m long and 1.5 m wide. Shielding is provided by depleted

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uranium or lead metal. It has an outer stainless steel shell and a corrugated stainless steel jacket that circulates water as neutron shielding fins are provided for external air forced cooling and minimal impact damage. The spent fuel casks for transportation are constructed so sturdily that it can withstand the impact of being dropped from a height of 10 m onto an unyielding surface (metal anvil) and pass the crash test of a 130 km/h locomotive crash on a stationary cask-loaded tractor-trailer rig. It can also withstand fire for up to a 125 min burn in JP-4 fuel at 980–1,150 C.

Transmutation Transmutation of transuranic elements such as plutonium, neptunium, americium, and curium can be conducted by irradiating with fast neutrons. In this process, the original actinide isotopes are transformed to radioactive and nonradioactive fission products. This process is important for nuclear waste management. Since the isotopes of actinides have half-lives of thousands of years and alpha emitters. By transmuting these isotopes to short lived fission products help eliminate the radioactive hazardous associated with long-lived radionuclides.

Reprocessing The spent fuel contains about 3.5% fission products that predominantly contain neutron poisons such as Xe135 and I-137. Accumulation of fission products and depletion of fissile U-235 in the nuclear fuel make the sustainability of the nuclear chain reaction very difficult. Therefore, the nuclear fuel is removed from the reactor core. Currently, about 10,500 t (of heavy metal) of spent fuel are disposed every year from nuclear reactors. The purpose of reprocessing is to separate the actinides from the fission products so that it can be reused as nuclear fuel. This decreases the burden on uranium mining and results in a more sustainable use of nuclear energy as a renewable energy source. Reprocessing can be carried over using aqueous or nonaqueous processes.

Aqueous Reprocessing The aqueous process is based on the solvent extraction. > Figure 30.9 illustrates the process flow. First the spent nuclear fuel is dissolved in nitric acid. The Zircoloy cladding is removed separately. The aqueous solution containing dissolved spent fuel is taken for the solvent extraction in an organic solution of kerosene-containing tributyl phosphate (TBP). When the aqueous solution comes in contact with the organic TBP, hexavalent uranium (U6+) and tetravalent plutonium (Pu4+) are extracted by TBP. Almost all the fission products remain in the nitric acid solution which in extracted as high-level liquid waste. In the solvent extraction partitioning step, Pu4+ is reduced to Pu3+ by adding Li+ as

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Spent Fuels

Mechanical Disintegration Off-Gas Treatment Dissolution in Nitric acid Acid Recovery

High Level Liquid Waste

Solvent Extraction using tri-n-butyl phosphate (TBP) in kerosene

Solvent Treatment

Addition of U(IV) Partitioning of Pu and U

Conversion to PuO2

UO2 conversion

Reprocessed Uranium

Reprocessed Plutonium

. Fig. 30.9 Flow diagram of PUREX process of reprocessing spent nuclear oxide fuels

a reductant. The Pu3+ is removed by dissolving in nitric acid solution. The recovered Pu can be used as a raw material for Fast Breeder Reactor fuels in the future. The uranium species remaining in the solution can be recovered by processing through a series of scrubbing columns and purification columns. The purified uranium can be enriched and used as a fuel after converting to UO2. The ability to separate plutonium from uranium is considered a potential proliferation concern. Therefore, modifications are made in the PUREX process to avoid separation of plutonium. In the modified processes, uranium is separated while keeping Pu, minor actinides, and fission products in the waste solution. Later, the actinides are separated as a group. Another modification of PUREX process is coprocessing. If the intent of reprocessing of spent fuel is to use the recovered actinides for producing mixed oxide fuel (MOX), then coprocessing is the right method. In this process, partitioning of U or Pu does not take place. Therefore, proliferation of Pu for weapon is not a concern. In the coprocessing method, 30 vol.% TBP in n-dodecane is used as solvent and a 2.5M HNO3 solution is used as scrub solution. The aqueous feed solution containing 4.2M HNO3 2M UO2 + Pu and 1.25M FP is fed through solvent extraction column of TBP in n-dodecane. Uranium and plutonium is complexed with the TBP and thus fission products are separated. The U + Pu

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complexed with organic phase is washed with dilute nitric acid. The resulting nitrate solution of U + Pu is treated with peroxides or oxalates to form precipitates of U + Pu peroxide or oxalate. These oxalate precipitates are calcined to form UO3 or U3O8 reduced in hydrogen atmosphere to form UO2. There are several variations in the PUREX process. > Table 30.3 lists these modified PUREX processes. . Table 30.3 Variations of aqueous-organic reprocessing of nuclear spent oxide fuels. (Adopted from the Nuclear Technology Review Supplement, International Atomic Energy Agency, Vienna, 2008) Process

Purpose

Special aspects

DIAMEX

Extraction of Minor actinides and lanthanides from HLLW

Diamide Extraction Process Solvent based on amides as alternate to phosphorous reagent Generates minimum organic waste as the solvent is totally combustible

TOGDA

Extraction of Minor actinides and lanthanides from HLLW

TRUEX

Transuranic elements (TRU) Extraction from HLLW

SANEX-N

Selective Actinide Extraction process for group separation of actinides from lanthanides

Tetra-octyl-diglycol-amide Amide similar to DIAMEX Extraction by using Carbamoyl Methyl Phosphine Oxide (CMPO) together with TBP Process for separating actinides from lanthanides from HLLW by using neutral N-bearing extractants, namely, Bis-triazinyl-pyridines (BTPs) Use of acidic S-bearing extractants, for example, synergistic mixture of Cyanex-301 with 2,2-bipyridyl Trivalent Actinide Lanthanide Separation by Phosphorus Extractants an Aqueous Komplexes. Use of HDEHP as extractant and DRPA as the selective actinide complexing agent

SANEX-S

Selective Actinide Extraction process for group separation of actinides from lanthanides TALSPEAK Selective Actinide Extraction process for group separation of actinides from lanthanides

ARTIST

SESAME

Selective Actinide Extraction process Amide-based Radio-resources Treatment for group separation of actinides from with Interim Storage of Transuranics. This lanthanides process is made up of: (1) Phosphorusfree branched alkyl monoamides (BAMA) for separation of U, Pu; (2) TOGDA for actinide and lanthanide recovery; and (3) N-donor ligand for actinide/ lanthanide separation Selective Extraction and Separation of Process for separating Am from Cm Americium by Means of Electrolysis by oxidation of Am to A (VI), subsequent extraction with TBP for separation from Cm

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. Table 30.3 (Continued) Process

Purpose

Special aspects

CSEX CCD-PEG

Cs Extraction Extraction of Cs and Sr from raffinate

Using Calix-crown extractants Chlorinated cobalt dicarbollide and Poly-ethylene glycol (CCD-PEG) in sulfone-based solvent is planned for extraction of Cs and Sr from UREX raffinate

SREX GANEX

Sr Extraction Using dicyclohexano 18-crown-6 ether Uranium Extraction + other processes A series of five solvent – extraction for further separation flow sheets that perform the following operations: (1) recovery of Tc and U (UREX); (2) recovery of Cs and Sr (CCD-PEG); (3) recovery of Pu and Np (NPEX); (4) recovery of Am, Cm, and rare-earth fission products (TRUEX); and (5) separation of Am and Cm from the rare earth fission products (Cyanex 301)

Pyroprocessing Pyrochemical or pyrometallurgical processing using LiCl-KCl molten salt systems is considered one of the most feasible alternatives to the PUREX process for safe and proliferation resistant recovery of nuclear fuel elements from the spent fuels. This technology may also be useful for separating actinides from the high level waste generated by the PUREX process. Pyrometallurgical process is preferred because of the stability of the molten salts to high radiation and shorter cooling times [39]. Reprocessing of metallic fuels involves separation of actinides from the fission products by electro-transport in a molten salt electrolyte. Since rare earth elements (as part of fission products) have similar chemical properties as that of actinides and show neutronic poison effect, separation of fission products is important for efficiently recycling the actinides. Spent oxide fuels also can be reprocessed by the pyrometallurgical electrorefining method. In this case, the spent oxide fuel is reduced to metal form by lithium [35] or chlorinated in the presence of a reductant such as carbon [40] before anodic dissolution or direct dissolution in presence of an oxidizer such as CdCl2 into the molten salt [41]. The major advantages of the pyroprocessing spent fuel are as follows: ● The process is proliferation resistant since Pu is not separated from minor actinides. ● Interim storage of spent nuclear fuel may not be required since the pyroprocessing is capable of handling spent fuels in hot conditions as the process takes place in temperatures greater than 500 C. ● No liquid wastage is generated for disposal. Therefore, waste management becomes easy. ● The process can be adopted for in-line reprocessing at the reactor site.

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● This process can accept several forms of fuel such as uranium oxide, carbide, nitride, mixed oxides, and pure heavy metals. ● Very short turn-around time results in cost saving. ● Generation of minimum transuranic waste. The limitations of the process are requirements of facilities with oxygen and moisture free environment, arid construction materials that withstand very high temperature, and highly corrosive molten halide environment. Reprocessing of Spent Metallic Fuel

Metallic fuels are used in experimental fast breeder reactors with liquid sodium as coolant. Reprocessing of this spent fuel (U-Zr, U-Pu + Zr alloys) is carried on by first chopping them into small pieces, loaded onto an anode basket made of SS, and dissolving them by applying anodic potential in an electrorefining cell. The electrolyte is typically an eutectic of LiCl-KCl at 500 C. By applying an anodic potential to the stainless steel basket containing the chopped fuels, the pellets are oxidized and dissolved in the molten salt. Dissolved actinides are present as chlorides in the molten salt. Lanthanides in the fission product are converted to lanthanide chlorides and dissolved in the molten salt. Addition of CdCl2 to the LiCl-KCl mixture helps transfer most of the actinides and lanthanides as chlorides in the molten salt bath. Gaseous fission products are outgassed. Undissolved cladding materials and noble fission products will be recovered as solids from the reprocessing cell. During the electrorefining process, uranium is recovered from the molten salt by application of a constant cathodic current density to a steel cathode in a shape of a cylindrical rod, as shown in the > Fig. 30.10. The resultant cathodic potential is just sufficient to electrodeposit only uranium on to the steel cathode. After depositing uranium, when the ratio of plutonium to uranium is greater than 2 (Pu/U > 2), now the electrodeposition process is continued with liquid cadmium as cathode. In this step, plutonium is recovered along with americium(Am) in the form of Pu1-xAmxCd6 compound. More than 10 wt.% of Pu collected using this method. A high separation factor between actinides and rare earths within a MClx-LiCl-KCl system has also been reported when liquid bismuth is used as liquid cathode. After the actinide recovery, the molten salt is solidified and scrubbed to remove fission products through a zeolite column. The redox potentials of actinides and lanthanides are given in > Tables 30.4 and > 30.5, respectively. The lanthanides show more negative potentials than actinides. Among the actinides, uranium show less negative reduction potential than plutonium and americium. Therefore, under a sufficient cathodic polarization, uranium will be reduced first. Electrodeposition of the uranium on the solid steel cathode decreases the concentration of the uranium (III) ions in the melt. Therefore, the redox potential of U(III) will move to more negative potentials with continuation of the electrorefining process. The electrorefining process is switched to liquid cadmium cathode because of the following reasons: (1) Liquid cadmium as cathode decreases the activity of actinides other than

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Anode +

Liquid Cd cathode (–) Solid cathode (–)

U3+

Liquid Cd

Anode fuel basket Dissolution U

3+,

Pu3+,

MA.

MA3+

U deposit on solid steel REE3+ LiCl-KCl eutectic

U3+

Pu3+

. Fig. 30.10 Schematic arrangement of electrorefining cell for pyroprocessing of spent nuclear fuel in molten LiCl–KCl

. Table 30.4 Redox potentials and activity coefficients of actinides in LiCl–KCl eutectic melt at different temperatures [42] Potential at different temperatures of LiCl-KCl (V vs Cl
/Cl2) (g = activity coefficient) Actinide system

673 K

723 K

773 K

823 K

U(III)/U


2.53 (g = 2  10
3)


2.49 (g = 3.1  10
3)


2.45


2.42

Pu(III)/Pu


2.845 (g = 1  10
3)


2.808 (g = 2.3  10
3)
2.843


2.775 (g = 4.1  10
3)

Am(II)/Am

uranium as shown in > Table 30.6; (2) the lower activity coefficient brings the redox potentials of all actinides closer so that these elements can be deposited together; and (3) recovery of Pu along with other minor actinides gives better proliferation resistance. The five orders of magnitude smaller activity coefficient of Pu as compared to that of U could be attributed to formation of PuCd6 compounds in the liquid Cd cathode [49]. When Pu is electrodeposited onto liquid cadmium cathode, the reduction potential is shifted by 0.3 V in the positive direction as compared to the electrodeposition onto a solid surface. This shift in the positive direction brings the reduction potential of Pu closer to

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. Table 30.5 Redox potentials of lanthanides dissolved in LiCl–KCl eutectic at 450 C Redox couple

Reduction potential at 450 C, V versus Cl
/Cl2

La3+/La


3.1 [43]

Ce /Ce Nd3+/Nd Dy3+/Dy2+ Dy2+/Dy


3.26 [44]
3.02 [45]
3.32 [46]
3.36 [16]

Gd3+/Gd Pr3+/Pr


3.15 [47]
3.41 [48]

3+

. Table 30.6 Activity coefficients of actinides in liquid cadmium at 450 C Element

Activity coefficient in liquid cadmium at 450 C

U

15

Np Pu Am

2.8  10
3 3.1  10
5 1.1  10
4

the reduction potential of U(III). The shift in the reduction potential of PU(III) in liquid cadmium cathode can be explained by using the Nernst equation: Pu3þ þ 3e
! Pu E1 ¼ E0 þ

(30.12)

2:3RT ½Pu  log 3F ½gPu 3þ

(30.13)

Since the value of g is 3.1  10
5 in the liquid cadmium, the redox potential is shifted almost by 0.25 V in the positive direction. Sustained operation of the electrometallurgical reprocessing cell results in accumulation of fission products in the electrolyte and depletion of the uranium ions in the salt. The variation in composition of the electrolyte could potentially alter the operating conditions of the cell because of the significant changes in the thermophysical properties and interfacial electrochemical behavior of the molten salt systems. For better process control, a detailed database of the electrochemical properties of the molten salt system is required. When multiple fission product elements are present in the electrolyte, the reduction behavior of the actinides could significantly be altered because of possible under potential reduction of lanthanides and slower diffusion kinetics of actinides. This is important for determining limits on use of the molten salt electrolyte before it needs to be purified or disposed.

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Thermodynamic and transport properties of binary LnX3-MX systems have been investigated widely [50–52], where Ln = La, Ce, Pr, Nd, Gd, Tb, and Eu; M = Li, L, Na, Cs, and Rb; and X = F, Cl, I, and Br. Addition of lanthanide chloride to alkali metal chloride results in formation of variety of stoichiometric compounds such as M3LnCl6, MLn2Cl7, M2LnCl5, M3Ln5Cl18, etc. Formation of compounds and complexes in the molten salt system affects the electrical conductivity and other thermophysical properties. Stoichiometric compounds show minimum electrical conductivity. Structural disordering increases the number of current carriers and improves the conductivity. The specific electrical conductivity of LnCl3 ranged from 0.11 to 0.4 Sm
1 at 1,000–1,250 K. The activation energy for electrical conduction was about 28–30 kJ/mol. Polymerization of the melt was reported to play a significant role in increasing the electrical conductivity of the molten salt system [2]. Existence of octahedral complex anions of LnCl63
in the LnCl3 melts and formation of dimers has been proposed by the following reaction: [53] 2LnCl6 3
! Ln2 Cl11 5
þ Cl


(30.14)

Since free Cl
ions are produced by the above dimerization reaction, the conductivity of the melt increase. Both polymerization of melt and presence of free chloride ions could affect the activity and mobility of the cations and, in turn, the separation kinetics could be altered. Standard potentials of actinides in LiCl-KCl eutectic salt and separation of the actinides from rare earths by electrorefining have been widely reported by many research groups [42, 54, 55]. Recently, Castrillejo and coworkers [56] reported electrochemical behavior of a series of lanthanide elements in LiCl-KCl eutectic melt in the temperature range of 400–550 C. Cyclic voltammetry results of binary, ternary, and quaternary LnCl3-(LiCl-KCl)Eutectic systems at 500 C indicate that the incipient potentials of cathodic reduction waves shifted to less negative values with increased additions of lanthanide components. The positive shift in the potential of reduction wave is, in general, associated with two phenomena, namely, (1) under potential deposition, where the interaction of reducing species (R) with the substrate (S) is energetically more favorable than the species-species (R-R) interaction; and (2) when two species (A and B) are present in the electrolyte, formation of a compound (AnBm) is more favorable by having a negative free energy (
DG) and the deposition potential is positively shifted from the redox potential of the more negative species by an amount (
DG/nF) [57]. The CV results of binary system (single component lanthanide addition) do not show any underpotential deposition of pure lanthanide elements. However, in this investigation, addition of more than one lanthanide chloride in the LiCl-KCl eutectic resulted in considerable shift in the incipient potential of the cathodic wave. According to Hume-Rothary principles, atoms having similar size (size difference < 15%) and electronegativity will preferentially form solid solutions and not compounds. Therefore, elements of lanthanide series will not form compound within them but can form solid solutions. The commercially available mischmetal is such an extended solid solution of various lanthanide elements that is separated from naturally occurring monazite mineral. Easy formation of solid solution of lanthanide elements indicates that

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this is a thermodynamically more favorable process. Therefore, any change in the free energy of formation of solid solution will be reflected in shifting the cathodic wave potential to positive direction with reference to the individual elements reduction potential. The other possible reason for the positive shift in the reduction potential of multicomponent lanthanide system could be because of lowered stability of the lanthanide clusters in the molten alkali salt. Generally, solvation of Ln(III) in LiCl-KCl eutectic mixture forms clusters of [Ln(KCl)n]3+, and [Ln(LiCl)n]3+, with the coordination number, n, varying from 4 to 9. Presence of a single lanthanide component in the alkali molten salt results in coordination number 6–9. Model calculations of Hazebroucq et al. [58] indicated that the stable coordination number for Gd (III) was 6 and for La (III) it was 7–8. When multiple lanthanide components are present, the coordination of the solvated clusters is significantly affected and their stability is reduced. Therefore, the positive shift in the reduction potential for multicomponent system could be attributed to the change in stability of the solvated clusters in the molten salt. Recovery of Rare Earth Elements (REE) from Fission Products

Rare earth elements are part of strategic materials used in various important energy and defense applications. Separation of rare earth elements from fission products could help reduce the burden on nuclear waste management and reduce the impact on environment during mining operation of extraction of these strategic materials. Rare earth elements such as neodymium and samarium are used in producing high strength permanent magnets that are used in various applications such as motors, and electronic components. Rare earth oxides are used in laser applications. Almost 38% of REEs find application as phosphors and solid state lighting device. Mischmetals are used for manufacturing AB5 type nickel-cobalt hydrides that are used as cathodes for metal hydride batteries and hydrogen storage for electric vehicle applications. Rare earth oxides are extensively used as catalysts for various chemical processes such as methane reformation, fluid cracking, oil refining, and water–gas shift reactions. Furthermore, rare earth oxides are used in fuel cell and high temperature battery applications as catalysts and membranes. Rare earth elements are used in thermal barrier coatings and strategic alloys as well. Therefore, separation of lanthanide elements from fission products is important from both strategic and environmental points of views. It is observed that addition of multicomponent lanthanides (more than 5 wt.%) to the LiCl-KCl eutectic shifted the reduction potential to less negative values which might hinder the effective separation of actinides from the lanthanides. One possible way of minimizing this effect is to remove the lanthanides as the electrorefining progresses so that accumulation of lanthanide is minimized. Separation of lanthanide can be made possible by using a bipolar cell and a bipolar membrane that has a high diffusion coefficient to lanthanide series. The design of the cell is given in > Fig. 30.11. > Figure 30.11 schematically illustrates the construction of the bipolar cell. Two compartments are connected by a thin metal diaphragm. This metal diaphragm will preferentially alloy with a particular lanthanide element, for example, neodymium. The right-side compartment will contain molten salt of multicomponent additions that needs to

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–ve

REF

+ve

–ve

REF

+ve

Diaphragm

Electrolyte containing diffused and oxidized lanthanide

Electrolyte containing mixed elements

. Fig. 30.11 Schematic of bipolar cell with metal diaphragm that preferentially alloys with select lanthanide(s) and allows diffusion of lanthanide elements to the other side

be electrolyzed. The diaphragm as a cathode, an inert electrode as an anode, and Ag/AgCl as a reference electrode will complete the electrical circuit. Depending on the applied potential, a particular lanthanide element that has a higher alloying affinity with the diaphragm metal will deposit onto the diaphragm and diffuse out to the left compartment because of a concentration gradient and a small electric field across the diaphragm. In the left compartment, the diaphragm is connected to a positive terminal of another electric circuit. Therefore, depending on the anodic potential applied to the diaphragm, the diffused lanthanide element will dissolve into the electrolyte of the left-side compartment. The oxidized lanthanide species will get reduced at the cathode of the left side compartment and thus separated from the other species. The main issue of this design is construction of a stable diaphragm that is thin enough to allow a required flux of the lanthanide. Aluminum diaphragms can be used for separating Nd. Nickel diaphragm also can be used. A thin diaphragm of Ni can be prepared by electroless deposition onto an organic substrate. Pyroprocessing of Spent Oxide Fuels

Spent nuclear oxide fuels also can be reprocessed using molten salt refining technique as that of metal oxide fuels. The electroreduction technique used for directly reducing

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30

uranium oxide to uranium is similar to the technique of FCC- Cambridge process proposed for directly reducing TiO2 to Ti [59]. Alternately, the oxide fuels can be reduced by using lithium. The first step in chemical reduction of UO2 is to convert the material to U3O8. Similarly, PuO2 is also converted to Pu2O3 before reacting with lithium. The proposed reactions are: U3 O8 þ 16Li ! 3U þ 8Li2 O

DG ¼
871:8 kJ

(30.15)

Pu2 O3 þ 6Li ! 2Pu þ 3Li2 O DG ¼ 18:8 kJ

(30.16)

Am2 O3 þ 6Li ! 2Am þ 3Li2 O DG ¼ 23:18 kJ

(30.17)

Mixed oxide spent fuels can be electrochemically reduced more easily than UO2 in a LiCl bath at 650 C. In the uranium oxide electroreduction cell as presently conceived, a platinum (Pt) wire is used as the anode [1]. The Pt wire is slowly etched away as the electrolytic reduction proceeds because of the highly oxidizing conditions and attack by lithium (Li). The cell is operated at 650 C with a LiCl–Li2O electrolyte. The overall cell reaction is as follows: UO2 ! U ðcathodeÞ þ O2 " ðanodeÞ

(30.18)

The Li2O content varies from 1 to 8 wt.% for the Li assisted chemical reduction of UO2 by participating in the following reactions: 2Li2 O ! 4Li þ O2 "

(30.19)

4Li þ UO2 ! U þ 2Li2 O

(30.20)

Although the reduction of Li2O to Li increases the reduction rate of the spent oxide fuel, the Li diffuses through the salt electrolyte and attacks Pt, thereby degrading the anode. To decrease degradation of the Pt anode, a secondary electric circuit is provided to oxidize the Li to Li(I). Provision of a more refractory anode that withstands the highly oxidizing conditions and attack by Li would greatly simplify operation of the cell. Therefore, finding an alternative anode material is vital before the electrolytic cell is put into production. Platinum metal is highly resistant to oxidation under normal conditions, but not under high anodic potential at 650 C in a corrosive Li-containing molten chloride electrolyte. Several materials are worthy of consideration as inert anodes. Various nickel-based super alloys such as Haynes 263, Haynes 75, Inconel 718, Inconel X-750, Inconel 713 LC, Inconel MA 754, Nimonic 80A, and Nimonic 90 have been investigated by KAERI [2]. It was noted that increasing the chrome (Cr) contents of the above alloy increased the stress on the surface layer and increased the corrosion rate. Elements such as aluminum (Al) and titanium (Ti) improved the corrosion resistance by forming a more protective layer. It should be pointed out that these test conditions did not include metallic Li in the electrolyte. The solubility of Li in LiCl was more than 0.6 mol%. Oxidizing environment was created by purging argon +10% O2 gas into in LiCl + 3 wt.% Li2O electrolyte at 650 C. Boron-doped diamond as a potential anode material has also been reported [3].

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Inert anode material for electrolytic reduction of the spent fuel in LiCl + Li2O electrolyte should satisfy the following requirements: ● The material should have comparable electrical conductivity to that of platinum. ● The material should not be consumed by the electrochemical/chemical reaction so that the dimensions remain stable throughout the electrolytic process without altering the cell voltage significantly. ● The material should be resistant to corrosion by lithium in the molten salt. ● The protective oxide layer of the material must not dissolve in the basic flux of Li2O present in the molten salt. ● The material must be stable in the highly oxidizing potentials encountered at 650 C in LiCl + Li2O electrolyte. ● The material should possess sufficient mechanical properties (such as creep strength and fracture toughness) in order to withstand thermal shock and service related stresses. The material fulfilling the above requirements can be a metal or an alloy with high electronic conductivity. The material can also be a composite (cermet) or made of metal/ alloy-coated with external oxide/carbide/nitride coating. This article describes the investigation of inert anode materials for use in an electrochemical cell by simulating the corrosive environment of the spent nuclear fuels with LiCl and LiCl + Li2O molten mixtures.

Containment of Radionuclides Development of next generation nuclear waste forms capable of reliable and safe immobilization of radionuclide is a significant challenge that limits the imminent nuclear renaissance to meet the energy demands. Among the nuclear wastes, Cs and Sr are considered critical because of the high activities of 134Cs (half-life: 2 years), 137Cs (half-life: 30.17 years), and 90Sr (half-life: 28.8 years). Removal of these isotopes will significantly reduce the radioactive load on a geologic repository [60]. These radionuclides are separated from the low level nuclear wastes using an ion-exchange process and combined with high level waste fraction and then immobilized in a glass or ceramic form. The following transmutation reactions take place during radioactive decay of 137Cs and 90Sr: 137

Cs!137 Ba þ bðhalf life : 30:17 yearsÞ ! 137 Ba þ gð2:55 minÞ 90

Sr!90 Y þ bðhalf life : 30:17 yearsÞ!90 Zr þ bð64:1 hÞ

(30.21) (30.22)

The decay of 137Cs emits beta particles with energy ranging from 0.089 to 1.454 MeV and gamma rays with 0.475–1.168 MeV energy [61]. The beta and gamma decays of the radionuclides could detrimentally affect the stability of the host material. Furthermore, formation of the transmuted elements in the host materials alters the electronic structure

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and chemical composition of the waste form. Most of the investigations so far have concentrated on the effect of radiation damage such as swelling, bubble formation, and leachability on the structural stability of the waste form. Very little attention has been paid on the effect of electronic structure changes during the decay of constituent radio isotopes in the waste form. For example, when the Cs+ transmutes to Ba2+ + e
(b) + g, the single valent Cs is replaced with divalent Ba. Therefore, the host material should be able to accommodate the valence and associated ionic radius changes. Recently, Jiang et al. [62] from LANL reported for the first time the modeling of the chemical evolution of CsCl to BaCl due to radioactive decay using ab initio calculations. In the modeling calculations, these authors considered CsCl crystal as a representative waste form. Crystalline silicotitanate (CST) and (Ba,Cs) hollandite ceramics are considered potential candidates for the specific immobilization of Cs. The sodium silicotitanate (Na2SiTi2O7. 7H2O) is ion-exchanged to form hydrogen-silicotitanate (H2SiTi2O7.1.5H2O). This material effectively sequesters both Cs and Sr [63]. The hollandite for Cs sequestration has a formula of (BaxCsy)(M2x+yTi8
2x
yO16), where M is trivalent cations such as Fe3+, Al3+ and Ti3+, and x + y < 2. Celestian et al. [4] showed that selective ion-exchange of Cs in the H-silicotitanate (H-CST) is achieved by repulsive forces between the Cs+ and H2O dipole that lead to a series of events at the molecular-scale level such as rotation of H2O by 159 followed by bending away of hydroxyl group by 0.055 nm displacement which makes TiO6 to rotate about 5.6 . The rotation of the TiO6 columns results in a structural transformation that changes the initial P42/mbc space group of the H-CST to P42/mcm of Cs-CST. During this transformation, an initial elliptical eight-member-ring (8MR) channel becomes a circular one that opens up a new site for Cs+ occupancy at the center of the channel (known as Cs1 site) in addition to the initial Cs2 site which is outside the 8MR window. A minimum occupancy of 0.15 at the Cs2 site is required to initiate the structural transformation and formation of the new Cs1 sites. The above hypothesis for the selective ion-exchange mechanism of Cs in the H-CST material indicates that the interaction of Cs+ and H2O dipole/hydroxyl groups is very important not only for the site selectivity but also for the stability of the Cs-CST structure. It is not clear how the radioactive transmutation of Cs+ to Ba2+ will affect the stability of the Cs-CST structure over an extended period of time. In case of the hollandite, structural transformation from tetragonal to monoclinic at room temperature is reported with increased Ba occupancy in BaxFe2xTi8
2xO16 [64].

Nuclear Waste Management All types of radioactive waste can be disposed of if the disposal method provides protection for the health and safety of people and the environment. Members of European Union (EU) produce about 7,000 m3 of high level waste from 143 nuclear power plants. Disposal in deep underground-engineered facilities is considered the best solution for managing high level and long lived radioactive wastes. High-level waste is mixed with glass and vitrified. The vitrified waste is stored for 30–50 years and allowed to cool.

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After cooling, the waste is placed in a iron shell container. The iron container is placed inside a copper shell, which is evacuated and backfilled with an inert gas and sealed. The copper canister is buried in a deep permanent repository with engineered barriers. Swedish and Finnish nuclear waste repository models are based on copper canisters since copper is considered to be stable in clay environments devoid of oxygen. Several countries plan to use this approach of permanent storage of the high level radioactive waste. When the amounts of radioactive waste in surface storage increase, the sustainability of storage in the long term and the associated safety and security implications is of concern. Geological disposal promises to provide containment and isolation of radioactive waste from the human environment for the very long periods required. Safety concerns due to possible human intrusion into the waste are very much reduced as compared to surface storage, owing mainly to the significant depths under the surface at which geological repositories will be located. In the USA, long-term storage of nuclear waste in Yucca Mountain was considered an option. The Yucca Mountain repository was based on different layers of engineered barriers to nuclear waste storage such as 300 m deep geological barrier, Ti-alloy drip shield to prevent water seeping through rock faults falling on the canister surface, an outer wall of canister made of Ni-22Cr-13Mo-3Fe alloy, and a thicker inner wall of canister made of type 304 stainless steel. Recently, the US Department of Energy filed a motion with Nuclear Regulatory Commission to withdraw the license application for a high-level nuclear waste repository at Yucca Mountain. Therefore, the spent fuel assemblies from the nuclear power plants will be stored on-site in the utility facilities for longer time.

Future Direction Meltdown of the nuclear core is considered the severest form of nuclear accident since the probability of release of radioactivity is high in this condition. In order to prevent core meltdown, western nuclear power plants are provided with two or four emergency core cooling systems (ECCS). This system consists of high-pressure coolant injection system, de-pressurization system, low-pressure coolant injection system, core spray system, containment spray system, isolation cooling system, and emergency electrical system. The emergency electrical system consists of diesel generators, motor generator flywheels, and batteries. In case of an emergency situation, the control rods are moved completely inside the reactor core and the power is reduced considerably. Any loss of coolant will trigger the ECCS. There are two are four ECCS in a reactor to ensure that at least one will respond and meltdown will be avoided. However, if all ECCS fail as in the case of Fukushima Nuclear Plants in March 11, 2011, meltdown of the core is initiated. It should be noted that the Fukushima nuclear disaster is not due to operator error or gross violation of safety regulations unlike the accidents reported in Three Mile Island or Chernobyl. The plant suffered a major damage because of an earthquake of 9.0 in a Richter scale. The reactors were designed for a maximum ground acceleration of 0.18 g (1.74 m/s2), whereas the earthquake caused a ground acceleration of 0.35 g (3.43 m/s2).

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Therefore, the reactors were shut down automatically. This would have triggered the insertion of control rods and ECCS. However, a tsunami of 20 m tall waves followed the earthquake and flooded the power plant. The plant was designed only for a tsunami of 5.7 m. The flooding situation knocked down the emergency power and prevented any assistance reaching the power plant. The batteries provided in the emergency electrical system was not adequate to pump required volume of coolant to the core. The power required for running coolant pumps or other electrical systems triggered a cascade of accidents in the Fukushima nuclear plant that released radioactive gases into the environment causing displacement of several 1,000 people living around the power plant. In order to cool the core, several measures were taken by the Fukushima power plant officials. Adding water to the degraded core can result in several consequences such as [65]: ● ● ● ● ●

Hydrogen production Change in the geometry of core Pressurization of the system due to high rate of steam generation Steam explosion Re-criticality of the core when enough neutron absorbers are not present

The core damage occurs in several stages as explained below [65]: Pre-damage stage: If the core is not fully immersed in water, then the upper portion of the core will be exposed to steam in the reactor. Now the core will start to heat up at a rate of 0.3–1 C/s. Ballooning and bursting of fuel rods: When the temperature reaches >1,100 K, the zircoloy cladding will balloon up because of the rapid heating and burst. This altered geometry of the fuel rod will affect the geometry of the coolant flow channels in the core. Some locations will have restricted access to the coolant because of the ballooning effect. If sufficient water is added, core damage can be suppressed at this stage. Rapid oxidation: This stage is initiated at 1,500 K. When zircoloy reacts with steam, hydrogen is produced as given by the following reaction and a large amount of heat is released: Zr þ 2H2 O ! ZrO2 þ 4H2 þ 6:5 MJ=kg of Zr If water is added at sufficient rate and volume, the core will be quenched and progression of damage could be stopped. If the water is not sufficient or the rate of heat removal is less than the rate of heat generated, the damage propagates to the next stage. Debris bed formation: When the temperature reaches 1,700 K, the molten control materials will flow to the lower part of the core (which is submerged in the water) where the temperature is low and solidify. At 2,150 K melting of zircoloy occurs. Molten zircoloy along with dissolved UO2 may flow downward and solidify at the lower portion of the core. These solidified debris will form a cohesive bed leading to restricted flow of coolant in the lower region of the core. Relocation of lower plenum: When molten core material (that are experiencing 1,500– 2,150 K) fall to the lower region of the core which is at 550 K, steam is generated rapidly leading to occurrence of steam explosion. Furthermore, this steam oxidizes any

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unoxidized molten zircoloy, which generates hydrogen at a faster rate. These recations lead to over pressurization of the system. Re-criticality also may occur in the relocated core debris when the control materials are not present in the required concentration. Understanding of the sequence of core damage is necessary to design preventive measures of core meltdown. Future work on nuclear safety should concentrate on a reliable ECCS that can be operated even in the worst case scenario as experienced in Tohoku Tsunami. Future work also should focus on a reliable system, with public acceptance, for a long-term safe storage of nuclear spent fuel.

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13. CANDU Reactors. http://www.aecl.ca/Reactors. htm 14. Shapiro J (1990) Radiation protection, 3rd edn. Harvard University Press, Cambridge, MA 15. Fullwood RR, Hall RE (1988) Probabilistic risk assessment in the nuclear power industry: fundamentals and applications. Pergamon Press, Oxford 16. IAEA (2001) Safety assessment and verification for nuclear power plants – a safety guide. Safety Standards Series, No. NS-G-1.2, ISBN 92-0101601-8 17. Bond AP, Dundar HJ (1977) In: Staehle RW, Hochmann J, MdRight RD, Slater JE (eds) Stress corrosion cracking and hydrogen embrittlement of iron base alloys. NACE, Houston, p 1136 18. Kerr R, Solana F, Bernstein IM, Thompson AW (1987) Metall Trans A 18A:1011 19. Leslie WC (1977) Stress corrosion cracking and hydrogen embrittlement of iron base alloys. NACE, p 52 20. Maziasz PJ, McHargue CJ (1987) Int Metals Rev 32:190 21. Suzuki S, Saito K, Kodama M, Shima S, Saito T (1991) SmiRt 11 Trans D, Tokyo 22. Brinkman CR, Korth GE (1973) Heat-to-heat variations in the fatigue and creep – fatigue behavior of AISI Type 304 Stainless Steel at 593 C. J Nucl Mater 48(3):293–306 23. van der Schaaf B (1988) The effect of neutron irradiation on the fatigue and fatigue-creep behaviour of structural materials. J Nucl Mater 155–157:156–163 24. Rho BS, Nam SW (2002) Heat effects of nitrogen on low-cycle fatigue properties of type 304L

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25. 26.

27.

28.

29.

30.

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32.

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34. 35.

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austenitic stainless steels tested with and without tensile strain hold. J Nucl Mater 300:65–72 Nilsson JO (1988) ASTM STP 942, 543. American Society for Testing Materials, Philadelphia Min KS, Nam SW (2003) Correlation between characteristics of grain boundary carbides and creep-fatigue properties in AISI 321 stainless steel. J Nucl Mater 322:91–97 Grossbeck ML, Ehrlich K, Wassilew C (1990) An assessment of tensile, irradiation creep, creep rupture, and fatigue behavior in austenitic stainless steels with emphasis on spectral effects. J Nucl Mater 174(2–3):264–81 Suauzay M et al (2004) Creep-fatigue behaviour of an AISI stainless steel at 550 C. Nucl Eng Design 232:219–236 Tsuji H, Nakajima H (1994) Creep-fatigue damage evaluation of a nickel-base heat-resistant alloy Hastelloy XR in simulated HTGR helium gas environment. J Nucl Mater 208:293–299 Nam SW (2002) Assessment of damage and life prediction of austenitic stainless steel under high temperature creep-fatigue interaction condition. Mater Sci Eng A322(1–2):64–72 Yokobori T, Yokobori AT Jr (2001) High temperature creep, fatigue and creep-fatigue interaction in engineering materials. Int J Press Vessel Pip 78:903–908 Maziasz PJ (1993) Overview of microstructural evolution in neutron-irradiated austenitic stainless steels. J Nucl Mater 205:118–45 Cookson JM, Was GS (1995) Proceedings of the seventh international conference on environmental degradation of materials in nuclear power systems water reactors. NACE, Breckenridge, p 1109 Economics of nuclear power. Reported in http:// www.world-nuclear.org/info/inf02.html Koyama T, Hijikata T, Usami T, Inoue T, Kitawaki S, Shinozaki T, Myochin M (2007) Integrated experiments on electrometallurgical processing using PuO2. J Nucl Sci Tech 44(3):382–392 Kimura A et al (1996) Irradiation hardening of reduced activation martensitic steels. J Nucl Mater 233–237(Pt A):319–325 Shiba K et al (1996) Irradiation response on mechanical properties of neutron irradiated F82H. J Nucl Mater 233–237(Pt A):309–12 Klueh RL, Alexander DJ (1996) Impact behavior of reduced-activation steels irradiated to 24 dpa. J Nucl Mater 233–237(Pt A):336–341

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39. OCDE (2002) OCDE/NEA report: acceleratordriven systems (ADS) and fast reactors (FR) in advanced nuclear fuel cycles. A comparative study. OCDE, Paris, p 1 40. Yang YS, Kang YH, Lee HK (1997) Estimation of optimum experimental parameters in chlorination of UO2 with Cl2 gas and carbon for UCl4. Mater Chem Phys 50:243–247 41. Koyama T, Iizuka M, Shoji Y, Fujita R, Tanaka H, Kobayashi T, Tokiwai M (1997) An experimental study of moltensalt reprocessing. J Nucl Sci Tech 34(4):384–393 42. Serrano K, Taxil P (1999) J Appl Electrochem 29:505 43. Kuznetsov SA, Hayashi H, Minato K, GaunoEscard M (2005) Determination of U and RE metals separation coefficients in LiCl-KCl melt. J Nucl Mater 344:169–172 44. Castrillejo Y, Bermejo MR, Pardo R, Martinez AM (2002) Use of electrochemical techniques for study of solubilization of cerium compounds in molten chloride. J Electroanal Chem 322:124–140 45. Hamel C, Chamelot P, Taxil P (2004) Nd cathode process in molten fluoride. Electrochim Acta 49:4467–4476 46. Castrillejo Y et al (2005) Electrochemistry of Dy in LiCl-KCl. Electrochim Acta 50:2047–2057 47. Caravaca C, de Cordoba G, Tomas MJ, Rosado M (2007) Electrochemical behavior of Gd in molten LiCl-KCl. J Nucl Mater 360:25–31 48. Castrillejo Y et al (2005) Electrochemical behavior of Pr(III) in molten chlorides. J Electroanal Chem 575:61–74 49. Shirai O, Iizuka M, Iwai T, Suzuki Y, Arai Y (2000) J Electroanal Chem 490:31–36 50. Gaune-Escard M, Bogacz A, Rycerz L, Szczepaniak W (1994) Thermochim Acta 236:67–80 51. Takagi R, Rycerz L, Gaune-Escard M (1997) J Alloys Compd 257:134–136 52. Gong W, Gaune-Escard M, Rycerz L (2005) J Alloys Compd 396:92–99 53. Ikeda M, Miyagi Y, Igarashi K, Mochinaga J, Ohno H (1988) The 20th Symposium on molten salt chemistry, C303, Yokohama, 10 Nov, 1988 54. Sakamura Y et al (1998) J Alloys Compd 271–273:592–596 55. Roy JJ et al (1996) J Electrochem Soc 143:2487 56. Castrillejo Y et al (2005) Electrochim Acta 50:2047; (2006) 51:1941; (2008) 53:5106; (2005) J Electroanal Chem 575:61–74 57. Cohen U (1983) J Electrochem Soc 130:1480

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58. Hazebroucq S, Picard GS, Adamo C (2005) A theoretical investigation of Gd(III) salvation in molten salts. J Chem Phys 122:224512 59. Chen GZ, Fray DJ, Farthing TW (2000) Nature 407(6802):361–364 60. Wigeland RA et al (2006) Nucl Technol 154:95 61. Lide DR (1997) Handbook of chemistry and physics, 78th edn. CRC Press, Boca Raton

62. Jiang C et al (2009) Phys Rev B 79:132110 63. Celestian AJ et al (2008) J Am Chem Soc 130:11689 64. Carter ML (2004) Mater Res Bull 39:1075 65. Kuan P, Hanson DJ (1991) INL report EGG-M91375

31 Fusion Energy Hiroshi Yamada Department of Helical Plasma Research, National Institute for Fusion Science, Toki, Gifu, Japan Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1184 Why Fusion for Global Warming Suppression? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1185 What is Fusion? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1188 Fusion Reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1188 Difference Between Fusion and Fission Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1192 Core of Fusion Reactor: Burning Plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1193 Characteristics of Plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1193 Magnetic Confinement of Plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1196 Engineering Elements of Fusion Reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1200 Structure of a Fusion Reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1200 Plasma Facing Component and Structure Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1201 Blanket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1203 Superconducting Magnet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1204 Present Status and Future Direction of Nuclear Fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1206 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1213

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_31, # Springer Science+Business Media, LLC 2012

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Abstract: Nuclear Fusion is the power of the sun and all shining stars in the universe. Controlled nuclear fusion toward ultimate energy sources for human beings has been being developed intensively worldwide for this half a century. A fusion power plant is free from concern of exhaustion of fuels and production of CO2. Therefore it has very attractive potential to be eternal fundamental energy sources and will contribute to resolving problems of climate change. On the other hand, unresolved issues in physics and engineering still remain. It will take another several decades to realize a fusion power plant by integration of advanced science and engineering such as control of hightemperature plasma exceeding 100 million degrees in Celsius and breeding technology of tritium by generated neutrons. The research and development has just entered the phase of engineering demonstration to extract 500 MW of thermal energy from fusion reaction in the 2020s. The demonstration of electric power generation is targeted before 2040.

Introduction Nuclear Fusion is the power of the sun and all shining stars in the universe. An artificial sun on the earth, that is controlled nuclear fusion, has a very attractive potential to offer an environmentally friendly and intrinsically safe energy source. Tremendous efforts have been paid globally in these 50 years toward realization of controlled nuclear fusion [1, 2]. Hereafter, Nuclear Fusion is simply referred as fusion. At this moment, there still remain unresolved issues for a fusion reactor even with state-of-the-art science and technology. It would be said that it will still take another 30 years to realize the first fusion reactor. Nonetheless, fusion is no longer a dream or a mirage and the targeted goal and a roadmap to reach the goal can be defined clearly. Symbolically, the construction of ITER (International Thermonuclear Experimental Reactor) [3, 4], which plans to produce more than 500 MW of heat by fusion, has been just started by international collaboration. The fuel for nuclear fusion is isotopes of hydrogen: deuterium and tritium. Deuterium can be extracted from water and tritium can be transmuted from lithium, which is abundant, in a fusion reactor. Therefore fusion is an inexhaustible energy source. When these fuels are heated up beyond 100 million degrees in Celsius, fusion reaction occurs. At this extremely high-temperature state, fuels become plasma which is ionized gas consisting of ions and electrons [5]. High temperature means that ions and electrons have large kinetic energy. It is necessary to put nuclei (ions) sufficiently close to each other to drive fusion reaction. Large kinetic energy is required to overcome the repulsive force between nuclei with positive electric charge. The product of fusion reaction is helium. To control fusion reaction, it is required to integrate advanced science and technology such as deep understanding of complex plasma physics, development of materials against high heat and neutron loads, and critical engineering related to superconductivity, vacuum, and electricity. Nuclear fusion was discovered in 1932, which is earlier than nuclear fission in 1939. Although the physics study was initiated almost at the same time, these two nuclear

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reactions have traced different history. Nuclear fission was used for an atomic bomb in 1942 when it was only 3 years later since its discovery. The fission reactor started power generation in 1951 and more than 400 fission power plants are operated to provide base load of electricity worldwide now. In contrast, nuclear fusion was used for a hydrogen bomb in 1952 and its peaceful use for power generation awaits for another couple of decades. These two nuclear reactions are quite different and consequently they contrast with each other from the aspect of their engineering control. Nuclear fission occurs in heavy atoms such as uranium and plutonium. Some isotopes of these heavy atoms are unstable and break apart easily or spontaneously. Although purification of fuels of nuclear fission requires a huge facility and operating cost, it has been industrialized. The control of nuclear fission means suppression of runway of reactions. In contrast, nuclear fusion does not occur easily. Since the reaction occurs between light nuclei which have positive electric charge, extremely high energy is required to bring nuclei closely enough to fuse. This reaction only occurs naturally only in the sun and stars. The required temperature is in the millions of degrees in Celsius. Therefore the control of nuclear fusion means how to heat the fuels to this extremely high temperature and keep them. The scientific assessment of a fusion reactor has been almost completed by more than 50-year research and the development stage is shifting to the assessment of engineering and technological feasibility. A fusion reactor is not a dream but a target within hailing distance. While another couple of decades of research and development is necessary to realize fusion energy, its realization will be able to resolve global issues related to environment and energy, and change social structure. Patient long-term research and development should be conducted with global social endorsement of this highly innovative technology. Then, steady progress will enable commercial reactors to deliver 1 million kW of electric power to the grid in 2050. The fusion power plant has promising potential provide the base load of electricity in the later half of this century. Two methodologies which are magnetic confinement fusion [6] and inertia confinement fusion [7] are being developed in parallel worldwide. This chapter is devoted to the present status and prospect of magnetic confinement fusion which is now stepping up to engineering demonstration from successful scientific demonstration.

Why Fusion for Global Warming Suppression? Fusion is on the stage of research and development, and it will take another half century to commercialize a fusion reactor. Nonetheless, fusion offers attractive advantages to other energy sources in terms of waste, fuel, and safety. 1. Waste Fusion does not emit CO2. The effect of power plants on global warming is assessed by CO2 emission intensity with consideration of construction and operation of a plant, consumed fuel, and release of methane in digging, etc. > Figure 31.1 shows the CO2

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300 250

Hydroelectric

Light Water Fission

Fusion

Wind

CCS LNG

fuel fuel fuel fuel fuel

Photovoltanics

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100

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150

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CO2 Emission Intensity (Cg/kWh)

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. Fig. 31.1 Carbon dioxide emission intensity of fired (coal, oil, LNG), renewable (solar, wind), fusion, fission, and hydroelectric power plants. CCS stands for carbon capture and storage. Each bar is separated to the contributions from fuel and construction of a power plant

emission intensity of thermal power plants, a fission reactor and a fusion reactor [8]. Coal-fired, oil-fired, and LNG-fired thermal stations emit much larger amount of CO2 than other power stations. Although the CO2 emission intensities are reduced to one third by employing CO2 collection, they are still major players to emit CO2. Fusion power plant does not emit CO2 in operation and its CO2 emission intensity is a little bit larger than hydraulic and nuclear fission power plants. Fusion power is produced by nuclear reaction and fusion is not free from nuclear waste. However, a product fusion reaction is helium, which is not radioactive at all, and nuclear waste is limited to structure materials with neutron induced activation. Absence of very long-lived radioactive waste promises annihilation of radio toxicity in the order of 100 years (see > Fig. 31.2) [9]. This property would ease the management of radioactive wastes compared with fission reactors. Hazard potential due to radioactivity of a fusion reactor is one thousandth of a fission reactor. 2. Fuel Fuels of fusion are abundant atoms: deuterium and lithium. They are substantially inexhaustible and widely distributed on earth. Thirty-three grams of deuterium exists in 1 m3 of water, which means 4.5
1013 ton in oceans and is still tiny amount of water itself. The amount of lithium as a mineral resource is estimated 940 million ton and that in oceans is 230 billion ton. Compared with these abundant fuels, a fusion power station producing 1 million kW of electricity only consumes 0.1 t of deuterium and 10 t of lithium a year. Readers can evaluate sustainability of fusion energy in terms of fuels easily. 3. Safety Fusion reaction occurs in very high-temperature gas; plasma and fuels are supplied to a reactor like a gas burner. There is no more than a minute of burn of fuels in a reactor.

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1.00E+00

Fission 1.00E−01 Coal PWR EFR A EFR B Model 1 MINERVA-W MINERVA-H Model 4 Model 5 Model 6

1.00E−02

1.00E−03

1.00E−04

Fusion

1.00E−05

Coal 1.00E−06 0

100

200 300 Years after shutdown

400

. Fig. 31.2 Relative radio toxicity of fission and fusion reactors versus time after shutdown. The bands correspond to differences in the fuel cycle (reprocessing) for fission and to the choice of structural material for fusion. The bottom black line is the radio toxicity of coal (Reproduction of > Fig. 31.1 in Ref. [9])

The fusion reaction is intrinsically quenched by any accident to disturb the burning condition. Unlike the fission reaction, which is essentially a chain reaction in massive fuels, the fusion reaction does not run away in principle. Since fusion itself is completely unrelated to uranium and plutonium, it does not cause proliferation of nuclear weapons. Extreme temperature as high as 100 million degrees in Celsius is required to make fusion happen. Even if fuels of fusion (deuterium and tritium) are available, fusion does not take place. Therefore it is emphasized that fusion does not strictly adhere the non-proliferation treaty unlike fission. Also, it should be noted that there is a fusion-fission hybrid which utilizes neutrons generated by fusion reaction to drive fission reaction. This concept is not free from a proliferation issue.

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What is Fusion? Fusion Reaction Solar energy, which not only human kind but also almost all lives on the earth enjoy, is delivered as light from the sun. The energy of light originates from fusion reaction taking place in the core of the sun. Four nuclei of hydrogen are fused into a nucleus of helium there. This fusion reaction has been taking place continuously, and the sun has been burning stably in these 5 billion years and will continue to burn in another 5 billion years. Physical process of this fusion reaction in the sun was identified in late 1930 after establishment of quantum mechanics [10]. Studies to realize this reaction in a laboratory and utilize this reaction as energy source were launched soon after this discovery. The special theory of relativity by Einstein gives a famous formula E = mc2, where E, m and c are energy, mass, and velocity of light. This formula means energy and mass are equivalent. It is known that total rest mass of nuclei changes when combination of nuclei is reorganized by nuclear reaction. If the rest mass after reaction is smaller than that before the reaction, loss of mass is transformed to energy. This relation is not only limited to nuclear reactions but applicable to chemical reactions as well. However, while the loss of mass is usually amounted to one thousandth in the case of nuclear reaction, that in the case of chemical reaction is only in the order of 100 millionth. This is the reason why a nuclear reaction produces 100,000 to 1 million times larger power than a chemical reaction. > Figure 31.3 shows the mass per one nucleon (proton or neutron) which composes an atomic nucleus from the lightest elements, hydrogen, to the heaviest element in nature, uranium. Even at the nuclear reaction, the number of nucleon is conserved. Therefore, this figure indicates that mass is lost when combination (fusion) of lighter elements like hydrogen generates a heavier element like helium. Mass is also lost at the breakup of a heavier element like uranium to lighter elements. This is fission reaction has been already used in nuclear power plants. The mass of a composing nucleon is lightest as iron thus the most stable element. In stars like the sun, fusion reaction proceeds stage by stage and ultimately generates iron. Heavier elements than iron are generated by another process, such as neutron capture at a supernova explosion. The fact that heavier elements than iron exist on the earth means that the solar system is on and after the second generation which experienced a supernova explosion since the initiation of the universe. There are a variety of fusion reactions and each has its own specific probability of reaction. Since this probability of nuclear reaction between particles has the dimension of area (m2), it is referred to as cross section and expressed by s. Probability of fusion reaction between two particles has been well investigated and quantified by various kinds of experiments using accelerators. The probability of the reaction of four hydrogen nuclei to a helium nucleus, which takes place in the core of the sun, is extremely low. The sun is so huge (100 times larger diameter than that of the earth) that it can keep burning by this fusion reaction with very low probability. Therefore another fusion reaction of hydrogen isotopes (see > Fig. 31.4) which has the largest probability is required to realize a fusion

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Mass per one nucleus

1.008

31

hydrogen deuterium

1.006 tritium 1.004 lithium

1.002

helium carbon

1.000 0.998

0

50

iron

gold

silver 100 150 Mass number

uranium

200

250

. Fig. 31.3 Change of mass per one nucleus composing an atom

Hydrogen

Proton

Electron

Deuterium

Neutron

Tritium Neutrons

. Fig. 31.4 Isotopes of hydrogen

reaction in a plant size on the earth. This reaction is combination of deuterium D and tritium T. In the case of the fusion reaction between D(deuterium) and T(tritium), the probability has the maximum at the relative speed of these two particles of 3
106 m/s. In order to use fusion reaction for energy production beyond a basic experiment of elementary particle physics by an accelerator, massive number of fusion reaction should be controlled. Cluster of particles with this speed forms very high-temperature gas: plasma. Then, the

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ensemble average of probability over distribution functions of all particles is more meaningful to evaluate released power. While the cross section is a function of the energy of particles, reaction rate (the number of reactions per unit volume and unit time) expressed by with the unit of m3/s at the specific temperature is calculated by the integration of the cross section with regard to the velocity space. The reaction rate of representative fusion reactions is shown in > Fig. 31.5 [11]. In the case of D(deuterium) and T (tritium), the cross section has the peak around several tens keV (1,000 million degrees in Celsius. Note that 1 eV (electron volt) corresponds to 11,600 K). Its rate equation is described as D þ T ! He þ n Consequently, helium and neutron are generated and simultaneously the energy of 17.6 MeV (2.8
1012 J) is released. From the momentum conservation law, the kinetic energy delivered to helium and neutron is 3.5 MeV and 14.1 MeV, respectively.

10−21

e - 3H He

3

T-T

D- 3H e DD

D-T

10−22

10−24

p-T

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T- 3He

(s v) (m3 sec−1)

1190

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10−26

1

10 102 Kinetic temperature (keV)

103

. Fig. 31.5 Fusion reaction rate between light atoms (Reproduction from Ref. [11])

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Fusion power density Pfusion is expressed by Pfusion ¼ nD nT DT QDT ;

(31.1)

where nD , nT , DT and QDT are particle density of deuterium, particle density of tritium, rate of DT fusion reaction, and released energy by one DT fusion reaction (17.6 MeV = 3.5 MeV + 14.1 MeV). For example, a typical presumed condition of fusion reactor with nD = nT = 1
1020/m3 and the temperature of 20 keV (230 million degrees of Celsius) gives fusion power of 11 MW/m3. While deuterium exists as 1/7,000 (0.015%) in hydrogen, abundance of tritium is quite low in nature. Therefore, a fusion reactor produces tritium in itself through the reaction of lithium with neutron which is generated by the following two reactions; n þ 6 Li ! 4 He þ T þ 4:8MeV n þ 7 Li ! 4 He þ T þ n  2:5MeV: Natural lithium is composed 6.4% of 6Li and 92.6% of 7Li. While the reaction between a neutron and 6Li releases 4.8 MeV, the 7Li reaction only occurs with neutron fast enough to absorb 2.5 MeV of energy. Therefore, enriched 6Li to several tens% is placed around the fusion reactor core like a blanket to breed tritium (see > Fig. 31.6). Various forms of breeding material have been proposed, such as ceramics like Li2O and Li2TiO3, liquid metals like Li and LiPb, etc. Techniques for isotope separation of lithium have been established as the column exchange separation method which uses the difference in affinity for mercury and the vacuum distillation method which uses the difference in the mean free path of the evaporated isotopes. Fuels from the amount of lithium in a single cellular phone (around 0.3 g) and deuterium extracted from only 3 l of ordinary water produce energy of 78,000 MJ which is equivalent to electricity of 22,000 kWh. A typical family in developed countries can be furnished with this electricity for a year.

. Fig. 31.6 Major nuclear reactions in a fusion reactor

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A fusion power plant with electric power production of one million kW consumes 0.1 t of deuterium and 10 t of lithium a year as fuel. Needless to say, deuterium is truly abundant in seawater. Technology extracting heavy water (D2O) is available as an industrial process. Since the fusion energy is one million times larger than the chemical binding energy, the cost for electrolysis of heavy water to get deuterium is easily recovered. Lithium is abundant mineral resources and also available from seawater. Collection of lithium from seawater has not been industrialized yet; however, promising technologies are being developed. The increasing demand of lithium for batteries accelerates these technologies. Therefore, a fusion reactor is free from the issue of fuel.

Difference Between Fusion and Fission Reactors While both fusion and fission accompanies huge energy released by loss of mass at the change of nuclei, there exist contrasting features between them. The first difference can be seen in the way how the reaction is controlled. The fission reaction that has been already employed in a power plant is driven by absorption of neutrons into uranium 235. One fission reaction releases two or three neutrons, and consequently a chain reaction takes place. This means only one neutron can trigger a continuous and even explosive reaction within a certain amount of uranium 235, in principle. In a fission power plant, uranium fuel for several-year long operations is mounted in a reactor and burned gradually by applying the brake with control rods absorbing neutrons. In a fusion reactor, in contrast, hydrogen isotope fuel is fed continuously into a reactor like a gas burner. Therefore when the refueling is stopped, fusion reaction stops immediately. Burning takes place in plasma state which will be described in detail later. A very high temperature more than 100 million degrees in Celsius is required to give rise to a fusion reaction. This necessary condition is broken so easily since fusion is free from chain reaction in principle. For example, too much amount of fuel drops the temperature and quickly stops the fusion reaction since fusion power cannot keep the sufficiently high temperature of the inlet fuel. The second difference is distinguished by products of reaction. In case of fission, elements with the mass number around 90–100, such as strontium and yttrium, and elements with the mass number around 130–140, such as iodine and barium, are produced as ash. Major of these have large radioactivity and needs a careful treatment as high-level radioactive waste. Also unburnable uranium 238 is converted to plutonium 239. While this plutonium can be used as fission fuel in a reactor, it is a long-lived radioactive element and has very high toxicity. Plutonium can be used to make nuclear weapons and must be controlled strictly under the Nuclear Non-Proliferation Treaty. On the other hand, the product from fusion reaction is a stable element: helium. Simultaneously produced neutrons are used to make tritium by reacting with lithium in a surrounding blanket. Neutrons are also absorbed in peripheral components of a reactor and may activate them. Tritium is also a radioactive element with a half-life of 12 years and changes to helium 3 by the b decay. Therefore, it should be noted that a fusion reactor is

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not free from issues related to radioactivity. However it is much mitigated. Its hazard potential can be compared by a potential radioactive risk factor. This factor assesses the risk of the maximum accident of reactors by how much air is required to dilute released radioactive elements to the tolerable level to human body. When iodine 131 and tritium, which are easily absorbed in human body in fission and fusion reactors, respectively, compared, the risk of a fusion reactor is less than that of a fission reactor by a factor of 1,500. The risk of a whole activated materials of a reactor is about one hundredth at the operation, and the risk of fusion reactor decays quickly after shutdown since a majority of produced radioactive elements have short half-lives. The present material design of a fusion reactor aims at reuse of materials after 100-year cooling phase. Both fission and fusion power stations need fuel processing; however, the level of risks related to proliferation and radioactive wastes in the processing is much mitigated for a fusion power station. In the case of a fission power station, used fuels contain high-level radioactive wastes as a fission product, and plutonium is transformed from uranium-238. High-level radioactive wastes are hazardous and should be controlled safely for an extremely long time. Reprocessing of used fuels breeds fuels (plutonium), which is, in turn, concerned for proliferation. It should be also pointed out that this fuel processing is done in a fuel-cycle factory which is usually located apart from a fission power station. Tight security in transportation of used fuels and new fuels between a fission power station and a fuel-cycle factory should be in force. In the case of a fusion reactor, in contrast, tritium is bred in a fusion power station through the reaction between lithium and neutrons as described in the previous chapter. This process is confined in a fusion power station. Therefore, transportation of radioactive tritium outside a fusion power station is not required.

Core of Fusion Reactor: Burning Plasma A schematic diagram of a fusion reactor is shown in > Fig. 31.7. The energy source of a fusion reactor is the burning plasma in the core. In this chapter, the principle to confine the plasma leading to burning is described.

Characteristics of Plasma The fusion reaction requires temperature beyond 100 million degrees in Celsius, which is higher than in the core of the sun by more than one order of magnitude. At this high temperature, all material becomes plasma, which is ionized gas. It is well known that the state of material has three phases: solid, liquid, and gas. And when material is heated to 10 thousand degrees in Celsius, molecules composing gas dissociates into atoms and then electric restraint between nucleus with positive electric charge and electrons with negative electric charge is unbounded. This state is the fourth state of matter, plasma (see > Fig. 31.8). All fixed stars shining in the sky including the sun are a mass of plasma.

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Superconducting magnet

Heat exchanger

Blanket

Electric power

neutrons Li

Steam D-T Plasma

T

Turbine-Generator

Plasma facing components

Condenser

Coolant

Helium ash pumping

Sea water Deuterium extractor

Tritium extractor

. Fig. 31.7 Conceptual schematic view of a fusion power plant

Nucleus Electron Molecules

Solid (ice)

Liquid (water)

Gas (steam)

Plasma

. Fig. 31.8 Four states of matter

On the earth, a flash of lightning and aurora are natural plasma, and plasma is used for neon lights and plasma displays. It is necessary to confine high-temperature plasma to ignite fusion reaction and maintain burning. Here it should be noted that confinement does not mean absolute confinement so as not to release anything. To prevent fuel cooling, thermal insulation is needed like in a fireplace to keep burning. It is also necessary to supply new fuels continuously. Therefore, confinement here is defined as sustainment of the phase with sufficient condition of burning and continuous replacement of fuels. The temperature should be kept beyond 100 million degrees in Celsius. Usual materials such as metal used for a gas cylinder cannot withstand high temperature of plasma. In other words, plasma is cooled down by the cylinder wall.

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In addition to temperature, appropriate density as high as 1
1014 ions per 1 cc (1
1020 ions/m3) is also required to keep burning. This density is one over 200,000 of air’s, which means burning plasma is very rare. It should be noted, however, that the pressure of burning plasma reaches 10 atmospheres because of high temperature of 100 million degrees. Balancing force against this pressure is required to confine the plasma. In the case of the sun, its own gravity balances the expansion due to the plasma pressure. Since gravitation is, unfortunately, not large enough to realize the fusion burning condition by the same scheme on the earth. There are two alternative potential concepts to realize and control fusion reaction, which are inertial confinement and magnetic confinement. Very fast compression and heating of a small D/T fuel cell can be achieved by highly intensive laser reaching several hundreds terawatt or even petawatt. This has been investigated to realize the required condition for fusion in very short-time scale as long as the inertia confines the fuels [12]. The outer layer of the fuel cell (typically a few millimeters in diameter) is heated by intensive laser itself or converted X-ray, and explodes outward. This ablation produces the force to compress the inner part of the fuel cell. This implosion energy leads the D/T fuel to ignition. The other method to keep the burning plasma is magnetic field confinement. Magnetic field forms invisible bottle to contain plasma apart from material wall in steady state. Since the plasma is composed by charged particles (ions and electrons), the invisible bottle made by magnetic field can confine the plasma. Charged particles rotate around the field line by the Lorentz force and consequently their motion is restricted by a magnetic field line as shown in > Fig. 31.9. It should be noted that the rotating directions of positively charged ions and negatively charged electrons are opposite to each other. This is the principle of magnetic confinement of plasmas in a microscopic (particle) view. In a macroscopic (fluid) view, the expanding pressure of the plasma is pushed back by the pressure of magnetic field which is usually 20 times larger than the pressure of the plasma.

Magnetic field line

v Ion (nucleus)

B

F

Lorentz force F = qv⫻B

Electron

. Fig. 31.9 Motion of an ion and an electron restricted by a magnetic field line

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Magnetic Confinement of Plasma If the magnetic field line intersects the material, the charged particles hit the material along the magnetic field line. Therefore, circulating magnetic field lines without end is required to avoid interaction with the material wall. > Figure 31.10 shows the basic concept, where electric current on the major axis generates the circulating magnetic field lines. An important point here is that the strength of magnetic field is inversely proportional to the distance from the major axis. The charged particles rotate around the magnetic field lines and its rotating radius, which is called the Larmor radius, is inversely proportional to the strength of magnetic field. Therefore, the rotating radius is becomes small in approaching the major axis and large in going away from the major axis. Combination of this change and rotating motion results in the vertical motion of particles. Remembering the difference of rotational direction of ions and electrons, these two kinds of particles are separated upside-down (see > Fig. 31.11a). This separation of charged particles generates vertical electric field, which accelerates or decelerates the charge particles. Since the rotating radius is proportional to the velocity of the charged particle, rotating motion is affected by the electric field as shown in > Fig. 31.11b). In this case, both ions and electrons go away from the major axis and are lost eventually. In result, simple circulating magnetic field lines cannot confine charged particles. By twisting magnetic field lines in a torus, the upper part and the lower part can be short-circuited and consequently unfavorable charge separation can be avoided. In reality, sophisticated modification of simple circulating magnetic field lines is required to keep high temperature plasma stable. One element twists the magnetic field lines and another element forms nested magnetic surfaces composed by numerous turns around a doughnut. Most simply speaking, centrifugal force driven by the motion along the bended magnetic field line and electric field generated by charge separation are compensated by the geometrical arrangement. I B ∝ 1/R

B

∇B

R

. Fig. 31.10 Generation of circulating magnetic field line without an end. Electric current I generates magnetic field B

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. Fig. 31.11 Drift motion of charged particles in a nonuniform magnetic field. E and B denote an electric field and magnetic field, respectively. (a) A drift by the gradient of magnetic field. (b) A drift by resultant electric field due to the gradient of magnetic field

Plasma

Toroidal field coil

a

Plasma currents

Helical coil

b

. Fig. 31.12 Concepts of magnetic confinement fusion. (a) Tokamak, (b) helical system

There are two ways to form a magnetic bottle with fulfillments of these requirements. One is called ‘‘tokamak’’ [13] which was invented by Sakharov [14] and Tamm in the former Soviet Union in the 1950s. This concept is based on combination of externally generated circulating magnetic field and the magnetic field generated by circulating currents in the plasma (> Fig. 31.12a). Circulating magnetic field looking like a doughnut can hold the plasma apart from the material wall. A set of planar coils arranged around a doughnut generates simple circulating magnetic field and circulating currents in the plasma is driven by the principle of transformer. This concept is axisymmetric and simple in machine construction as well as theoretical analysis of plasma physics. Another concept is a helical system. Only twisted (helical) coils generate the magnetic field to confine the plasma (see > Fig. 31.12b). An American physicist Spitzer Jr. [15] and a Japanese physicist Uo [16] are pioneers in this concept. Their inventions are called stellarator and heliotron, respectively. A helical system does not require the currents in the plasma to generated twisted magnetic field. Therefore a helical system is free from issues

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related to the plasma currents, which are critical in a tokamak. A helical system has an intrinsic advantage of steady-state and stable operation. Although the complicated threedimensional geometry has prevented the progress of this concept both experimentally and theoretically, the development is being accelerated by the first large-scale experiment (Large Helical Device: LHD [17] in Japan) and large-scale simulations. Confinement capability has been proved to be equivalent to a tokamak. Although the physical picture of particle confinement is well documented, plasma behaves as fluid as well. Dynamics of plasma is highly nonlinear and the modeling of plasma motion is still a challenging issue. Heat loss due to turbulence in the plasma has not been fully understood yet. The confinement capability of plasma is compared to containment of water in a bucket with holes (see > Fig. 31.13a). Supply of water from an external faucet P is balanced with the leak from holes L and consequently the water level W is kept. When the faucet is closed, the water level goes down exponentially with a specific time constant t. In the case of fusion plasma, the plasma stored energy W is modeled by dW =dt ¼ Pin W =tE ;

(2)

where Pin is input heating power and tE is called an energy confinement time. If there is no external heating, the plasma stored energy decays with exp(t/tE) as shown in > Fig. 31.13b. Power balance in a fusion reactor is schematically shown in > Fig. 31.14. It should be noted that the fusion energy carried by fusion-producing helium contributes to heating of the plasma. Another fusion product, neutrons, is not confined by the magnetic field because of no electric charge. The energy multiplication factor Q of a fusion reactor is defined based on this picture by Q ¼ Pfusion =Pin :

P

(3)

1.0

W

1198

0.5

W 0

a

L

0

0.5

1.0 t /τ

1.5

2.0

b

. Fig. 31.13 (a) Concepts of confinement. Water is compared to energy. (b) Level (volume) of water decreases exponentially

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Pout

Pin

Ploss

Fusion Palpha

Pneutron Pfusion

. Fig. 31.14 Conceptual diagram of power balance in a fusion reactor

This Q value should be larger than 50 to establish a fusion reactor as an energy source and the condition of Q = 1 is called breakeven. In steady state, > Eq. 31.2 gives Pin ¼ W =tE :

(4)

Combination of > Eq. 31.1 in > section ‘‘Fusion Reaction’’ and > Eq. 31.4 yields, Q /< nD ; nT ; DT > =ðW =tE Þ;

(5)

where the bracket means the volume averaged value. The cross section < sv > DT > can be approximated well by the temperature T squared in the targeted temperature range around 10 keV, and nD and nT are ideally the same. Also the plasma stored energy W can be rephrased by , where n is the representative particle density. Consequently, Q is expressed approximately by < n 2T 2>/ tE and then < n > tE. More simply, nTtE is called a fusion triple product and the most important parameter to describe the performance of fusion plasma. In early stage of fusion energy development, J.D. Lawson defined the condition to produce net energy [18] and indicated that the breakeven condition corresponds to of 1
1021 m3 keV s. More specifically, a typical target is simultaneous achievement of the density of 1
1020 m3, the temperature of 10 keV (around 120 million degrees in Celsius) and the energy confinement time of 1 s. Although the plasma turbulence predominating the energy confinement has not been understood from the first principle yet, empirical scaling tolerable enough to foresee

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101

100 τE in experiments (s)

1200

10−1

10−2

10−3 10−3

10−2

10−1

100

101

τE predicted by scaling (s)

. Fig. 31.15 Comparison of an energy confinement time in experiments with prediction from the scaling

a reactor has been already available [18, 19]. The energy confinement time is described by the power laws with plasma and operational parameters, for example [19], 0:69 1:39 0:58 0:78 0:19 0:41 tE ¼ 0:0562I 0:93 B 0:15 n R a k M ; 19 P

where I is the circulating current in tokamak plasma in MA, B is the magnetic field in T, 19 is the line averaged density in 1019 m3, P is the heating power in MW, R is the major n radius of the torus in m, a is the minor radius of the torus in m, k is the elongation of the poloidal cross section of the plasma (the plasma cross section is usually vertically elongated prolate shape, k is the ratio of the height and the breadth of the plasma crosssection) and M is the mass number (1 for hydrogen and 2 for deuterium). For helical systems, another scaling expression has been proposed [20] and both scaling expressions share large commonality in physics. As shown in > Fig. 31.15, the scaling fits the experimental observation by factor of 2 in 3 orders of magnitude.

Engineering Elements of Fusion Reactor Structure of a Fusion Reactor As shown in > Fig. 31.7, fundamental components in the core are (1) confined plasma as energy source due to fusion reaction, (2) plasma facing components surrounding the plasma, (3) blanket to receive neutrons and generate heat and tritium, and (4) superconducting magnets to generate confining magnetic field. Heat generated

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in the blanket is transferred by coolant like water. The consequent process of electric power generation is the same as a fission power plant and a thermal power plant. In addition, affiliate facilities which are not seen in other power plants are vacuum pumping system and heating system to bring the plasma to ignition. A fusion reactor is basically a large-scale electromagnetic and nuclear device which requires extremely high-level integration of engineering and physics. Steady-state control of the plasma is a primary demand. Safety and materials are also key issues. Damage on plasma facing components by high energy (14 MeV) neutrons and helium irradiation should be assessed precisely to guarantee safety over their lifetime. For safe steady-state operation, peak heat loads exceeding 10 MW/m2 should be managed safely. Also, an economically competitive power station must minimize the internal circulating power consumed in the plant. A fusion reactor needs a variety of large-scale electric facilities such as vacuum and cooling pumps, cryogenic system, magnets, heating and control system. This internal circulating power in the present fission power station is only 3–4% of the generated electric power. If the circulating power becomes significantly large to operate a fusion reactor, a fusion reactor cannot gain economical attractiveness. The above mentioned major three components beside the core plasma is explained in detail in the following sections.

Plasma Facing Component and Structure Material When the plasma is contaminated by impurities other than deuterium and tritium, radiation loss is enhanced to cool the plasma and fuels are diluted. Therefore, the plasma is generated in an airtight vacuum vessel. Although the plasma is held apart from the wall of the vacuum vessel by the magnetic field, a part of highly energetic particles and particles neutralized by the charge exchange process bombard the plasma facing components located on the wall. Here it should be noted that the plasma with the pressure as high as 10 atmospheres is pressed down by the magnetic field and that the space between the plasma and the wall of the vacuum vessel is almost vacuum with very rare neutral gas. While the temperature of the burning plasma exceeds 100 million degrees in Celsius, the direct interaction between the burning plasma and the plasma facing component is avoided by the magnetic field. Even this thermal insulation, the heat load to the plasma facing component reaches 10 MW/m2 due to radiation and the fluxes of neutrons and charge exchanged neutrals. The operational temperature of the plasma facing component is evaluated up to 900 in Celsius and the first planned material is tungsten which has high-melting temperature (3,380 in Celsius). Although carbon is widely used as the plasma facing component in the present fusion experiment devices, it is not compatible with the reactor condition due to large erosion and retention of tritium. Neutrons generated by fusion reaction are not confined by the magnetic field and penetrate into the structure materials. Therefore, the plasma facing components and structure materials are required to have sufficient tolerance against the heat and neutron loads. Relatedly, employed materials should have good heat removal property

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and reduced activation. Also it is preferable to keep sufficient tightness and mechanical strength during a lifetime of a plant. Alloys such as stainless steel have been usually used in the current experimental devices, but these alloys do not fulfill the requirement of a reactor. Ferritic steel is a promising material for the first generation of a reactor and advanced materials using vanadium silicon carbide are being developed. In addition to heat and neutron loads, helium generates bubbles in the plasma facing components and causes swelling and consequent blistering. Since falling flakes deteriorate plasma performance, materials should suppress this effect in addition to securing soundness of components themselves. In general, materials show degradation of its properties, such as dimensional instabilities, yield strength, ductility, creep rate, fatigue life, and fracture toughness. Neutron radiation often accelerates this process [21]. The standard to assess irradiation damage is displacements per atom (dpa) [22]. The dose of 1 dpa corresponds to a 14 MeV neutron wall loading of 0.1 MW year/m2 in steels. The structure component of a fusion power plant is expected to have a neutron dose of 100–150 dpa around temperatures of 500–600 in Celsius. While stainless steel can be used in the experimental reactor level (ITER) where the neutron fluence is limited to 3 dpa, development of new material is prerequisite for a fusion reactor as a power plant. The promising material for the first generation of a fusion reactor is low-activation ferritic steel, which has been used in fuel tubes for a fast breeder fission reactor and evaluated to be used up to 40 dpa by 14 MeV neutron radiation. This tolerance corresponds to 1-year operation of a fusion reactor. Innovative and attractive materials such as vanadium alloy (V-4Cr-4Ti) [23] and silicon carbide (SiC/SiC) [24] are also under development. In addition to mechanical properties, physical properties such as electric conductivity changes due to neutron irradiation. These complicated phenomena depend on energy and dose of neutrons, and operating temperature. A new neutron irradiation facility is planned to evaluate irradiation property of materials precisely for reliable design of a fusion reactor. This facility is called International Fusion Material Irradiation Facility (IFMIF) [25] and simulates 14 MeV neutrons at the maximum capability of 50 dpa/year. The schematic view of IFMIF is shown in > Fig. 31.16. The report of Ref. [25] defines the mission of IFMIF as to provide an accelerator-based, D-Li neutron source to produce high energy neutrons at sufficient intensity and irradiation volume to test samples of candidate materials up to about a full lifetime of anticipated use in fusion energy reactors. IFMIF would also provide calibration and validation of data from fission reactor and other accelerator-based irradiation tests. It would generate an engineering base of material-specific activation and radiological properties data as well as support the analysis of materials for use in safety, maintenance, recycling, decommissioning, and waste disposal systems. A deuterium beam with 40 MeV and 250 mA irradiates a lithium target and generates neutrons with the energy peak at 14 MeV through the D-Li stripping reaction. The Engineering Validation and Engineering Design Activities (EVEDA) for IFMIF are now being conducted by Japan-EU cooperation in Rokkasho, Japan [26].

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Test Cell: Target & Test Modules

31

PIE Facilities

Ion Source RFQ

High Energy Beam Transport

Li Loop

0

20

40m

. Fig. 31.16 Schematic view of International Fusion Material Irradiation Facility (IFMIF). PIE and RFQ stand for Post Irradiation Examination and Radio Frequency Quadrupole, respectively

Blanket The blanket surrounds the plasma with protection by the plasma facing components. The function of blanket is to produce tritium and extract heat from neutrons generated by the fusion reaction. Tritium Breeding Ratio (TBR) is a critical parameter for a fusion reactor. TBR is a measure of breeding capability of the blanket and is defined as, TBR ¼ Rate of tritium production in the blanket=Rate of burning tritium in the plasma Since the abundance of tritium in nature is tiny, a fusion reactor is required to produce more tritium than burned tritium, which means TBR >1. The blanket consists of breeding material for tritium, multiplier of neutrons and coolant which are designed to fulfill three major specifications: (1) sufficient tolerance against heat, neutrons, and electromagnetic forces due to confining magnetic field, (2) the breeding ratio of tritium with more than 1, and (3) sufficiently high efficiency of heat removal. Tritium breeding material produces more tritium than consumed tritium by using the reaction between lithium and neutron described in > section ‘‘Fusion Reaction.’’ There are two major categories in the form of lithium. One is a solid-breeding scheme in ceramic made of lithium and another is a liquid-breeding scheme of pure lithium(Li), lithium lead (LiPb), or molten salt (FLiBe). Solid breeding is progressing faster due to the advantages of easy handling and chemical stability. Liquid breeding has advantages in much reduction of radiation damage, simple design for easy maintenance and potentially high TBR.

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However, liquid-breeding material is chemically active in general. In particular, careful attention should be paid to a chemical reaction with water which is the secondary coolant and corrosion of the cooling channel. Also liquid metal is a electrically conducting fluid and the electromagnetic force under the strong magnetic field prevents efficient flow. Therefore, research and development have been being conducted to resolve these issues. One neutron is generated by one fusion reaction between deuterium and tritium, and a fusion reactor must produce more than one tritium by this one neutron. Since some neutrons are absorbed in surrounding structure and lost, all neutrons cannot be used to breed tritium. Therefore, it is needed to multiply neutrons by the reaction using beryllium such as, 9

Be þ n ! 2n þ 24 He:

This kind of neutron multiplier is inserted between the plasma facing component and tritium breeding material. Also the shield is located behind the breeding material to reflect neutrons back to use them efficiently and protect superconducting magnet is located behind the breeding material. Coolant should be compatible with tritium breeding material and have sufficient heat removal capability. The most conservative combination is to use solid breeding and water or helium as coolant. Operating temperatures are around 300 and up to 500 in Celsius for water cooling and helium gas cooling, respectively. The blanket must hold a critical compound role in a fusion reactor. In addition, constraints due to configuration of magnets and economical viewpoints require the thickness of blanket limited to around 1 m. In spite of limited availability of neutron fluence on ITER (around 3 dpa), the ITER project definition states ‘‘ITER should test tritium breeding module concepts that would lead in a future reactor to tritium self-sufficiency and to the extraction of high-grade heat and electricity production’’ [27]. Toward this goal, several fusion reactor relevant Test Blanket Modules (TBM) [28] are proposed.

Superconducting Magnet To confine the burning plasma described in Core of Fusion Reactor: Burning Plasma, the strong magnetic field exceeding 10 T at the magnets is needed. Since the volume of the plasma is around 1,000 m3, magnets produce this strong magnetic field with sufficient accuracy to cover the large volume. It is well known that Joule heating due to resistivity is accompanied by currents. The loss of this energy is critical in a fusion power plant. Therefore, superconducting magnets are inevitable since they are free from energy loss due to Joule heating because of no resistivity at cryogenic temperature. Superconducting magnets in a fusion power plant are characterized by large-scale, sufficient tolerance and preservation of accuracy against the large electromagnetic force and tolerance against nuclear heating and activation. Superconducting magnets using alloys such as NbTi and a compound such as Nb3Sn have been developed to fulfill these specifications.

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100

31

DEMO

Magnetic Energy (GJ)

ITER 10 Normal JT-60 JET 1

TFTR

ToreSupra

0.1 1980

LHC

LHD

JT-60SA

LCT KSTAR EAST

W7-X

TRIAM-1M 1990

2000 Year

2010

2020

. Fig. 31.17 Development of large-scale superconducting magnets in terms of magnetic energy. Three large tokamaks employing normal conductors and the superconducting magnets for the Large Hadron Collider (LHC) are also plotted as references (Reproduction of > Fig. 31.4 in Ref. [29])

> Figure 31.17 shows the development of large superconducting magnets in fusion devices [29]. The largest operating magnet system for fusion is the Large Helical Device (LHD) [30] and its magnetic stored energy is close to 1 GJ. The Large Hadron Collider (LHC) employs two large detectors with large-scale superconducting magnets: ATLAS and CMS and each magnetic stored energy exceeds 1 GJ. The total stored magnetic energy of LHC reaches 15 GJ [31]. The stored magnetic energy of the superconducting magnet system in ITER is 50 GJ [32], which is well beyond the achievements so far. The specification of the magnets for ITER requires the mechanical tolerance against 1 GPa, the withstanding voltage of 10 kV and irradiation dose on electric insulation of 10 MGy, which are the present technological limits. The prototype magnet employing Nb3Sn conductors have demonstrated 13 T [33] and fabrication of real components has started. The specification required for a fusion reactor would be higher than that of ITER. Since Nb3Sn has an issue that the critical current density degrades by strain, solution of this issue is inevitable to achieve higher magnetic field for a fusion reactor than in ITER. A strong candidate is Nb3Al because of its outstanding property of critical current density against strain and magnetic field [34]. Although basic engineering advantage has been already established for Nb3Al, R&D to mitigate difficulty in mass production and cost is still required for its application to a fusion reactor. Further development of conductors is being conducted to pursue capability to carry higher currents under higher magnetic field than these established conductors. In particular, a high-temperature superconductor which does not need cryogenic operation by liquid helium will have a big impact on a design of a fusion reactor.

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Present Status and Future Direction of Nuclear Fusion Fusion research was started as classified military research about 60 years ago. Then, global scientific research activity toward a peaceful use of fusion energy was launched by declassification at the second United Nations Conference on the Peaceful Uses of Atomic Energy in Geneva in 1958. Table-top size experiments demonstrated proof-of-principle of physical ideas, and medium-sized experiments with the major diameter of up to 3 m extended plasma parameters to the order of ten million degrees. Then three large-scale tokamaks, TFTR [35], JET [36, 37], and JT-60U [38] with the diameter of about 6 m and the plasma volume of several tens to more than 100 m3 were constructed in the 1980s to demonstrate scientific feasibility of fusion. As an alternative line, a helical system is catching up with tokamak by large facilities, LHD [17, 29, 39] and Wendelstein 7-X [40, 41]. In parallel with convergence to the first demonstration of burning plasma on ITER, a variety of experimental project are being conducted to resolve unresolved issues and create innovation by worldwide efforts as shown in > Fig. 31.18. Although the fusion power plant has not been realized like a fission power plant, the progress in these 50 years is remarkable [1]. For example, the most typical index to describe performance of fusion plasma, the fusion triple product of temperature, density, and energy confinement time, has been improved in the same speed of the density of an integrated circuit, which refers to the famous Moore’s law (doubled in 18–24 months) (see > Fig. 31.19) [42]. > Figure 31.20 is the so called Lawson diagram, which shows the performance of fusion plasmas on the plane of the product of density and energy confinement time, and temperature. Recent experiments on JET [43] and JT-60U [44] achieved the breakeven condition Q = 1 in the 1990s. It should be noted that the breakeven conditions have been equivalently satisfied by using only deuterium. Also more than 10 MW of real fusion power generation has been demonstrated using deuterium and tritium on TFTR [45] and JET [46] even for a short-time period as long as a few seconds (see > Fig. 31.21). These two major achievements, breakeven and DT burning, have motivated the next generation of a tokamak experimental reactor. Based on accumulated achievements by worldwide tokamaks [47], fusion power development is stepping up the stage. Seven leading parties of fusion research; China, EU, India, Japan, Korea, Russia, and USA have jointly started construction of the International Thermonuclear Experimental Reactor (ITER) [3] in Cadarache, France. For this distinguished international project, the ITER Organization was formally established on October 24, 2007 after ratification of the ITER Agreement in each Member party. ITER will be built largely (90%) through in-kind contribution by the domestic agencies of seven parties. ITER is the largest tokamak ever built. Its plasma volume is close to 1,000 m3 (see > Fig. 31.22) and the total weight reaches 23,000 t. The goal of ITER is the demonstration of control of burning plasma and engineering feasibility of a fusion reactor. ITER plans to demonstrate 500 MW of fusion power production by DT fusion reaction at the temperature of 150 million degrees in Celsius for 500 s in the 2020s. This amount of fusion power is expected to be ten times larger than the external heating power put into the plasma, which means Q = 10. > Figure 31.23 is the schedule of ITER [48].

CEA, France

Tore Supra

CNR, Italy

RFX

Plasma Physics Research Centre, Switzerland

ITER Int. Org.

loffe Institute, Russia

Globus-M

LHD

EAST Institute of Plasma Physics, China

Australian National University, Australia

General Atomics, USA

DIII-D

University of Wisconsin, USA

HSX

Princeton Plasm Phys Lab., USA

NSTX

Massachusetts Institute of Technology, USA

Alcator C-mod

Japan Atomic Energy Agency Japan

JT-60SA 2016-

H-1NF Heliac

National Fusion Research Center, Korea

KSTAR

Kurchatov Institute, National Institute for Fusion Russia Science, Japan

T-10

Southwestern Institute of Physics, China

HL-2A

Max. Planck Institute for Plasma Phystics, Germany

W7-X 2015-

ITER

ENEA, Italy

FTU

Max Planck Institute for Plasma Physics, Germany

ASDEX-Upgrade

. Fig. 31.18 Experimental facilities for magnetic confinement of fusion plasma in the world

Kharkov, Ukraine

URAGAN

CIEMAT, Spain

TJ-II

Forschungszentrum Jülich, Germany

TCV

European Fusion Development Agreement, EU

EURATOM/UKAEA, UK

TEXTOR

JET

MAST

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. Fig. 31.19 The rapid progress toward harnessing fusion as a power source compares very favorably with progress in other high technologies such as computing performance and particle accelerators. This figure was originally produced by J B Lister, CRPP Lausanne (crppwww. epfl.ch), and M Greenwald, MIT (www.psfc.mit.edu) (Reproduction of > Fig. 31.3 in Ref. [42])

The latest argument suggests an updated schedule that is a bit behind. The first plasma with hydrogen is planned to be ignited in 2019, and the experimental campaign of DT burning will start in 2027. ITER will also be a test bed for blanket technology as discussed in > section ‘‘Blanket.’’ The goal of ITER is defined as engineering demonstration of fusion energy. However, it should be noted that ITER does not have a plan to generate electric power. Then, a demonstration reactor which fulfills the requirement of a power plant including economical validity to some extent will come in the next. ITER is certainly the necessary condition to proceed to a demonstration fusion reactor but not sufficient for a demonstration fusion reactor. In particular, material development should be conducted by an intensive neutron irradiation facility (IFMIF) [25] in parallel to assess property of materials, in particular lifetime.

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JAEA 101

ni(0)τE (1020 m−3 s)

100 10−1 10−2 10−3 10−4 10−1

‘58

101

1

102

Plasma Temperature (keV)

. Fig. 31.20 Lawson diagram for magnetic fusion illustrating progress over 50 years (Courtesy of the Japan Atomic Energy Agency: Naka Fusion. Reproduction of > Fig. 31.10 in Ref. [1])

JET (1997)

15

10

JET (1997)

5

Q~0.2

JET (1991) 0

0

1.0

2.0

3.0

4.0

JG01.326-10c

Fusion power (MW)

Q~0.65 TFTR (1994)

5.0

6.0

Time (s)

. Fig. 31.21 Progress in fusion power and energy in time, from JET and TFTR which are capable of DT operation (Reproduction from http://figures.jet.efda.org/JG01.326-10c.eps)

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MANY HANDS Multiple members will build each piece of ITER

Central solenoid: US, Japan

Vacuum vessel: EU, India, Korea, Russia

Neutral-beam heating: EU, Japan, India

Blanket: China, Russia, US, Japan, Korea, EU

RF heating: EU, US, India, Japan, Russia

Reinforced concrete bindings: EU

Toroidal-field coils: Japan, US, EU, Russia, Korea, China

Diverter:

Poloidal-field coils:

EU, Japan, Russia

EU, Russia, China

. Fig. 31.22 A cutaway view of ITER (courtesy of the ITER Organization). The major diameter of a doughnut-shaped plasma is 12.4 m. Duplication from Nature 459: 488–489, 2009. Seven parties in the world share the responsibility of construction

ITER adopts the tokamak concept described in > section ‘‘Magnetic Confinement of Plasma.’’ Tokamak is the most promising concept to demonstrate controlled burning plasma from the presently available knowledge. However, when the system is assessed from the viewpoint of a fusion power plant, it is serious and critical to overcome the issues related to the control of huge currents in the plasma. In the case of ITER, electric current of 15 MA (1.5
107A) flows in very rare gas (plasma) with weight of less than 1 g. This plasma current should be stably held in steady state. This requirement poses two critical issues. One is avoidance of current disruption. Since a huge plasma current has huge electromagnetic energy, abrupt destruction of the plasma current called disruption occurs when stability of the current is lost. This phenomenon happens in the order of 1 ms, huge transient electromagnetic forces are generated in the machine component. Therefore

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First Plasma ITER Construction

2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 Tokamak Baslc Machlne 1*TF Coil at Site

Issue TF Coils PAs Issue PF Coil PAs Issue VV PAs

Last TF Coil at Site

1*PF Coil at Site 1*VV Sector at Site

Last PF Coil at Site Last VV Sector at Site

Bulldings & Site Site Leveling & Pre Excavation* Issue Construction PA Construction Contract AE Contract & Design

* Site Leveling Was Completed in June 09

Tokamak Complex Excavations Seismic Isolation Basemat

Tokamak Bidg II RFE Tokamak Building Construction Remaining Construction

Tokamak Assembly Start Sub Assemble VV Tokamak Basic Machine Assembly Start Install CS Start Cryostat Closure Ex Vessel Assembly In Vessel Assembly Assembly Phase 2 Assembly Phase 3

ITER Operations Pump Down & Integrated Commissioning Plasma Operations

. Fig. 31.23 Schedule of ITER (Reproduction of > Fig. 31.13 in Ref. [48])

the control and mitigation of disruption is prerequisite for a tokamak fusion reactor. Another requirement is current drive. In addition to transient induction as in a transformer, a reliable and efficient current-drive scheme should be established. Fortunately, to some extent, high temperature plasma in a doughnut shape has a physical mechanism to drive the circulating currents spontaneously, called bootstrap currents. However these currents are not sufficient to sustain the burning plasma, and an external source to drive the sufficient current. This means that some amount of produced electric power in a tokamak fusion power plant is consumed to drive the plasma currents. Simultaneous achievements of spontaneous current fraction of 70% and efficiency of current drive from the plug of 50% are required to deliver electric power to the grid economically. This requirement is very demanding, and ITER will not be able to resolve this issue. Therefore a new tokamak facility JT-60SA [49] to explore the steady-state tokamak operation is now under construction by bilateral collaboration of EU and Japan. Since a helical system which is alternative to a tokamak does not need plasma currents to confine the plasma and is free from challenging issues related to the plasma current, it is an extremely attractive concept of a steady-state stable reactor. Nonetheless, complex shape of magnets has caused troubles and difficulties in both experimental and theoretical approaches, and the progress of research and development lagged behind tokamak by one generation. However, the first large-scale helical device, LHD (see > Fig. 31.24), has been

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. Fig. 31.24 Photograph of the plasma vacuum vessel of LHD: the Large Helical Device (courtesy of the National Institute for Fusion Science, Japan). The major diameter of a twisted doughnutshaped plasma is 7.8 m

in operation since 1998, and remarkable progress has been achieved recently [39]. LHD employs superconducting magnets and has capability of steady-state operation in both physics and engineering aspects. LHD has achieved the comparable plasma parameters such as temperature of 75 million degree and already demonstrated 1 hour long operation of high temperature plasma with 12 million degrees in Celsius. Another helical device, Wendelstein 7-X, is now under construction in Germany and will be operational in 2015 [41]. In the coming couple of decades, physical study and engineering demonstration of burning plasma will be conducted in ITER in parallel with research and development of steady-state operation by advanced tokamaks and helical systems. Reactor engineering, in particular material development, should be also pursued toward establishment of an economical fusion reactor. Integration of all this knowledge will lead to the first demonstration fusion reactor which produces electric power of 1 million kW in the 2030s (see > Fig. 31.25). Establishment of fusion as energy source is targeted in the mid of this century [50]. The National Ignition Facility [51] in the USA plans to demonstrate ignition by the completely different inertia confinement scheme in 2011. Operation is limited to a single shot basis due to availability of highly intensive laser, and the inertia confinement is in the stage of scientific demonstration.

Fusion Energy

JET

ITER

80 m3

800 m3

~16 MWth

~500 MWth

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DEMO ~1000–3500 m3 ~2000–4000 MWth - Dominant self heating ---------------------------->

. Fig. 31.25 The growth in scale of tokamak devices from JET, which produced the first DT fusion power, through ITER, aiming for Q = 10 at 500 MW thermal, to a DEMO reactor producing 1GW electrical (Reproduction of > Fig. 31.15 in Ref. [48])

Summary Fusion is an energy source of the sun, and controlled fusion as energy sources for human beings has been being developed intensively worldwide for this half a century. A fusion power plant is free from concern of exhaustion of fuels and production of CO2 and has an advantage to a nuclear fission power plant in terms of high-level radioactive waste. Therefore it has very attractive potential to resolve global warming and to be eternal fundamental energy sources. On the other hand, unresolved issues still remain. It will take another several decades to realize a fusion power plant by integration of advanced science and engineering such as control of high-temperature plasma exceeding 100 million degrees in Celsius and breeding technology of tritium by generated neutrons. The research and development has just entered the phase to start the project to extract 500 MW of thermal energy from fusion reaction in the 2020s. The demonstration of electric power generation is targeted before 2040. Even the first-generation fusion demonstration reactor will produce electricity of 1 million kW. Fusion reaction itself has been already demonstrated in an unpeaceful manner as a hydrogen bomb which is ignited by an atomic bomb. In peaceful use of fusion energy, a fusion power plant employs completely different principle that the fusion reaction in plasma is controlled stably in steady state. Since fusion energy is free from nuclear proliferation and unfair distribution of fuels, geopolitical issues can be much mitigated

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by its realization. Fusion energy, a sun on the earth, has attractive and critical potential to resolve diversified issues related to energy and to change global social structure. Lastly, the further sources about Fusion can be found in books as cited by Ref. [52–55].

References 1. Meade D (2010) 50 Years of fusion research. Nucl Fusion 50:014004 2. Braams CM, Stott PE (2002) Nuclear fusion: half a century of magnetic confinement fusion research. IOP, London 3. http://www.iter.org/ 4. Green BJ (2003) ITER: burning plasma physics experiment. Plasma Phys Cont Fusion 45:687–706 5. Eliezer S, Eliezer Y (2001) The fourth state of matter: an introduction to plasma science. IOP, London 6. Lie J, Zhang J, Duan X (2010) Magnetic fusion development for global warming suppression. Nucl Fusion 50:014005 7. Mima K (2010) Inertial fusion development: the path to global warming suppression. Nucl Fusion 50:014006 8. Report of Japan Atomic Energy Commision in 2005. Japanese, available at http://www.aec.go.jp/ jicst/NC/senmon/kakuyugo2/siryo/kettei/houkok u051026/index.htm 9. Jacquinot J (2010) Fifty years in fusion and the way forward. Nucl Fusion 50:014001 10. Bethe H, Peierls R (1935) Quantum theory of the diplon. Proc R Soc London A 148:146–156 11. Kaye and Laby Online (2005) Tables of physical & chemical constants, 16th edn. 2.1.4 Hygrometry version 1.0. Available at http://www.kayelaby.npl. co.uk/ 12. Atzeni S, Meyer-Ter-Vehn J (2004) The physics of inertial fusion. Clarendon, Oxford 13. Wesson J (2004) Tokamaks (The international series of monographs on physics). Oxford University Press, Oxford 14. Sakharov AD, Leontovitch MA (eds) (1961) Plasma physics and the problem of controlled thermonuclear reactions, Vol. 1. Pergamon, London, p 21 15. Spitzer L Jr et al (1954) Problems of the stellarator as a useful power source. PM-S-14, USAEC NYO-6047

16. Uo K (1961) The confinement of plasma by the heliotron magnetic field. J Phys Soc Jpn 16:1380–1395 17. http://www.lhd.nifs.ac.jp/en/ 18. Lawson JD (1957) Some criteria for a power producing thermonulear reactor. Proc Phys Soc Section B 70:6–10 19. ITER Physics Basis Editors (1999) ITER Physics Basis. Nucl Fusion 39:2137–2638 20. Dinklage A et al (2007) Physics model assessment of energy confinement time scaling in stellarators. Nucl Fusion 47:1265–1273 21. Zinkle SJ (2005) Fusion material science: overview of challenges and recent progress. Phys Plasmas 12:058101 22. Norgett MJ et al (1975) A proposed method of calculating displacement dose rates. Nucl Eng Design 33:50–54 23. Muroga Tet al (2002) Vanadium alloys – overview and recent results. J Nucl Matter 307–311:547–554 24. Katoh Y et al (2007) Current status and critical issues for development of SiC composites for fusion applications. J Nucl Matter 367–370:659– 671 25. Martone M (ed) (1996) IFMIF-international fusion materials irradiation facility conceptual design activity, Final report. ENEA frascati report, RT/ERG/FUS/96/11 26. Garin P et al (2009) Main baseline of IFMIF/EVEDA project. Fusion Eng Design 84:259–264 27. Aymar R (2001) Summary of the ITER final design report. ITER document G A0 FDR 4 01-06-28 R 0.2, Garching ITER joint work site, 9 July 2001 28. Giancarli L et al (2006) Breeding blanket modules testing in ITER: an international program on the way to DEMO. Fusion Eng Design 81:393–405 29. Yamada H et al (2009) 10 years of engineering and physics achievements by the large helical device project. Fusion Eng Design 84:186–193

Fusion Energy 30. Imagawa S et al (2010) Overview of LHD superconducting magnet system and its 10-year operation. Fusion Sci Tech 58:560–570 31. Ross L (2010) Superconductivity: its role, its success and its setbacks in the large hadron collider of CERN. Supercond Sci Tech 23:034001 32. Mitchell N et al (2010) Status of the ITER magnets. Fusion Eng Design 84:113–121 33. Kato T et al (2001) First test results for the ITER central solenoid model coil. Fusion Eng Design 56–57:59–70 34. Koizumi N et al (2005) Development of advanced Nb3Al superconductors for a fusion demo plant. Nucl Fusion 45:431–438 35. Hawryluk RJ et al (1998) Fusion plasma experiments on TFTR: a 20 year retrospective. Phys Plasmas 5:1577–1589 36. http://www.jet.efda.org/ 37. Pamera J, Solano ER (2001) From JET to ITER: preparing the next step in fusion research. EFDAJET-PR(01)16, EFDA, Culham Science Centre, Abington, Oxon 38. Ohyama N et al (2009) Overview of JT-60U results towards the establishment of advanced tokamak operation. Nucl Fusion 49:104007 39. Komori A et al (2010) Goal and achievements of large helical device project. Fusion Sci Tech 58:1–11 40. http://www.ipp.mpg.de/ippcms/eng/pr/forschung/ w7x/ 41. Bosch HS et al (2010) Construction of wendelstein 7-X engineering a steady-state stellarator. IEEE Trans Plasma Sci 38:265–273 42. Webster AJ (2003) Fusion: power for the future. Phys Educ 38:135–142

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43. Team JET (1992) Fusion energy production from deuterium-tritium plasma in the JET tokamak. Nucl Fusion 32:187–203 44. Ishida S et al (1999) JT-60U high performance regime. Nucl Fusion 39:1211–1226 45. Bell M et al (1995) Overview of DT results from TFTR. Nucl Fusion 35:1429–1436 46. Gibson A (1998) Deuterium-tritium plasmas in the Joint European Torus (JET): behavior and implications. Phys Plasmas 5:1839–1846 47. Ikeda K et al (2007) ITER progress in the ITER physics basis. Nucl Fusion 47 E01, S1–S414 48. Ikeda K (2010) ITER on the road to fusion energy. Nucl Fusion 50:014002 49. Ishida S et al (2010) Status and prospect of the JT-60SA project. Fusion Eng Design 85:2070–2079 50. Masionnier D et al (2005) A conceptual study of commercial fusion power plants, final report of the European fusion power plant conceptual study (PPCS). European fusion development agreement, EFDA(05)-27/4.10 available at http://www.efda. org/eu_fusion_programme/downloads/scientific_ and_technical_publications/PPCS_overall_report_ final.pdf 51. http://lasers.llnl.gov/ 52. McCraken G, Stott P (2005) Fusion: the energy of the universe. Elsevier Academic, London 53. Stacey WM (2010) Fusion: an introduction to the physics and technology of magnetic confinement fusion. Wiley-VCH, Weinheim 54. Kikuchi M (2011) Frontiers in fusion research. Springer, London 55. Chen FF (2011) An Indispensable truth, how fusion power can save the planet. Springer, London

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32 Harvesting Solar Energy Using Inexpensive and Benign Materials Susannah Lee1 . Melissa Vandiver1 . Balasubramanian Viswanathan2 . Vaidyanathan (Ravi) Subramanian1 1 Department of Chemical and Metallurgical Engineering, Chemical and Materials Engineering Department, LME 310, MS 388, University of Nevada, Reno, NV, USA 2 National Center for Catalysis Research, Indian Institute of Technology Madras, Chennai, India Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1221 Importance of Energy in Human History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1221 Present Sources of Large-Scale Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1221 Issues with Large-Scale Usage of Fossil Fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1222 Need for an Alternate Energy Focus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1222 Options Available to Us . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1222 Wind Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1223 Biomass Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1224 Geothermal Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1225 Solar Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1225 Solar Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1225 What Is Solar Energy? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1226 Advantages/Disadvantages of Solar Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1226 Applications of Solar Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1226 Principles of Solar Energy Utilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1228 Space and Water Heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1228 Water Purification Using Solar Stills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1228 Food Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1230 Solar-Assisted Biofuel Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1230 Solar Photovoltaics (PV) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1231 Photocatalytic Oxidative (Water Splitting) and Reductive (CO2 ! Fuel) Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1233

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_32, # Springer Science+Business Media, LLC 2012

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Toolkit for Characterization of Photoactive Materials (PMs) . . . . . . . . . . . . . . . . . . . . . . 1233 Photoelectrochemical Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1234 Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1235 Transient Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1235 Materials for Solar Energy Utilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1237 What Is the Holy Grail in Photocatalysis? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1237 Review of Synthesis Procedures for Photocatalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1238 System Integration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1238 Previous Attempts in Materials Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1239 Materials for Photovoltaics, Water Splitting, and CO2 Reduction . . . . . . . . . . . . . . . 1239 Photovoltaics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1240 Water Splitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1240 CO2 Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1240 Challenges and Limitations to Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1240 Integrating Tested Concepts of Solar Energy Utilization to Produce Fuels in an Effective Way . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1244 Example 1: Integrated Organic Waste Treatment and Fuel Cell System . . . . . . . . . 1245 Example 2: A Hybrid Photocatalytic–Photovoltaic System (HPPS) . . . . . . . . . . . . . 1245 Example 3: Bio-processes to Convert Waste to Energy Using Algae . . . . . . . . . . . . . 1246 Example 4: Solar-Powered Biomass Gasification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1248 Commercial Ventures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1248 Konarka® Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1249 Unique Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1249 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1250 Cost per Watt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1250 Future Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1251 Dyesol® . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1251 Unique Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1252 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1252 Cost per Watt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1252 Future Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1253

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Inventux Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Unique Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cost per Watt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Commercial Venture That Employs Tested Concepts of Solar Energy Utilization to Produce Fuels in an Effective Way . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Other Types of Solar Companies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1253 1254 1254 1254 1255 1256

Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1256 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1257

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Abstract: Historically, the growth and prosperity of human civilization has mainly been propelled by fossil energy (coal and petroleum) usage. Decades of tested and proven technologies has led to a continuous increase in demand for fossil-based fuels. As a result, we are now finding ourselves at the threshold of a critical tipping point where environmental consequences and global climate can be irreversibly affected and hence cannot be ignored. More than ever before, our unending and rapidly growing need for energy has necessitated urgent action on efforts to examine alternative forms of energy sources that are eco-friendly, sustainable, and economical. There are several alternatives to fossil-based fuels. These include biomass, solar, wind, geothermal, and nuclear options as prominent and possible sources. All these options can assist us with reducing our dependence on fossil fuels. Solar energy, being one of them, has the unique potential to meet a broad gamut of current global energy demand. These include domestic applications such as solar-assisted cooking, space, heating, as well as industrial processes such as drying. Solar energy utilization in several key areas such as electricity generation (photovoltaics), clean fuel production (hydrogen), environmental remediation (photocatalytic degradation of pollutants), and reduction of greenhouse gases (CO2 conversion to value-added chemicals) is also of great interest. A key challenge that must be addressed to boost commercialization of solar energy technologies, and common to these applications, is material properties and solar energy utilization efficiency. To realize large-scale and efficient solar energy utilization, application-based materials with a unique combination of properties have to be developed. The material has to absorb visible light, be cost competitive, composed of earth abundant elements, and nontoxic, all at the same time. This chapter consists of ten sections. The first introduction section consists of a detailed discussion on the importance of energy in human activity, the effects of fossil fuels on climate and human lifestyle, and materials that meet many of the above criteria. The second section provides a short and critical comparison of solar energy with other alternatives. The third section provides a quick review of the basic concepts of solar energy. The commonly employed toolkits used in the characterization of materials for solar energy conversion are discussed in section four. Some of these tools can be used to evaluate specific optical, electronic, and catalytic properties of materials. Section five discusses the main categories of materials that are either commercialized or under development. The challenges to developing new materials for solar energy conversion are addressed in section six. Section seven outlines some of the main strategies to test the promising materials before a large-scale commercialization attempt is initiated. Section eight profiles companies and institutions that are engaged in efforts to evaluate, improve, and commercialize solar energy technologies. This segment provides information about the product from a few representative companies around the world and their niche in the commercial market. Section nineprovides a general outlook into the trend in solar energy utilization, commercialization, and its future. Finally, section ten provides the authors’ concluding perspective about the solar energy as a pathway for reducing our dependence on fossil fuels. At the conclusion of this chapter, we have also provided over 100 references that are highly recommended for further in-depth study into various aspects of solar energy.

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Introduction Importance of Energy in Human History Energy has been one of the basic requirements for human activity and has played a pivotal role in human history. Research has been undertaken that correlates the increased availability of energy within a society to its citizens to an increase in the standard of living conditions. The nineteenth century saw the ushering of a technology revolution, a period in time that contributed to a significant improvement in the quality of human life while witnessing an increasing demand for energy in order to maintain these improved standard living conditions. Fossil fuels were critical to the industrial revolution that accompanied technological development during this era. The latter twentieth century saw a rapid increase in the demand for various other forms of energy in different parts of the world. Moreover, it is anticipated that this voracious demand for energy will only increase in the foreseeable future as many more countries of the world strive to improve quality of life for their citizenry [1–3].

Present Sources of Large-Scale Energy The US Department of Energy’s 2003 Annual Energy Report divides US energy usage into four main categories with a percentage of the total US 98.3 QBtu/year usage: Residential usage (21.23%), Commercial (17.55%), Industrial (32.52%), and Transportation (26.86%). This same report then proceeds to break down the 2003 US Energy Consumption which is shown in > Table 32.1. As is evident from > Table 32.1, fossil fuels (coal, petroleum, and natural gas) make up 85.7% of the US energy consumption, making them the first and by far the predominantly used sources [4]. The reason for a predominantly fossil-fuel-based economy is that (1) the technologies and infrastructure using fossil-based fuels have been well developed over several decades and (2) the comparatively lower cost of fossil fuels in relation to other types of energy sources. . Table 32.1 2003 US energy consumption Source

Amount

QBtu

Coal Natural gas

1.08  10 t 21.8  1012 ft3

22.6 22.5

23.0 22.9

Petroleum Nuclear Renewable Total

6.72  109 bbl 757  109 kWh 578  109 kWh

39.1 7.97 6.15 98.3

39.8 8.1 6.3 100

9

Percent

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The next highest US energy consumption after the fossil fuel is nuclear energy. Nuclear energy has been extensively exploited as an energy source in several developed countries as an alternate to fossil fuels and is a promising eco-friendly energy source for large-scale applications [5, 6]. However, nuclear energy has a high capital cost, vulnerability to manmade disruption, and the potential to be used for destructive purposes. Furthermore, a tremendous challenge lies in changing negative public perception about nuclear technology, stemming from perceived danger due to prior unfortunate nuclear-related incidents in Chernobyl, USSR, and Three Mile Island, USA. It is to be noted that the trend in the United States’ energy consumption has been reflected in several developed countries as well.

Issues with Large-Scale Usage of Fossil Fuels In spite of the availability of several energy sources for large-scale usage, fossil fuels have been one of the most cost competitive, easily accessible, widely available, and therefore a more attractive option. It continues to be the primary form of cheap energy source in many countries with wide-ranging economic portfolios. However, with the continued use of fossil fuels coupled with a demand, their detrimental impact on climate and environment has forced us to reexamine the viability of relying further on this form of energy as mankind’s primary resource for the future. Speculated major concerns are climate change, health hazards, and potential for economic chaos. The details of some leading concerns regarding continued dependence on fossil fuel as a primary resource are listed in > Table 32.2.

Need for an Alternate Energy Focus A closer look at other alternatives to meet mankind’s demand for energy is urgently needed. The reasons cited in > Table 32.2 highlight the need for a serious reexamination of mankind’s approach to identifying, researching, and implementing possible options of energy resources. The key criteria for choosing an alternative energy form are: (a) sustainability, (b) eco-friendliness, (c) availability, (d) cost (capital and operating), (e) political will to change status quo by modifying governmental public policies, (f) population support, (g) technological reliability, and (h) safety aspects. It has to be first understood that no single form of energy can offset fossil fuel usage completely and continue to meet the rising demands globally. It is also perhaps a smart decision to avoid focusing on just one form of alternate energy, but explore a diversified energy portfolio. It is generally agreed that an energy portfolio containing a mix of various forms of non-fossil-based alternative ranked using the above criteria should be tailored based on region- or country-specific needs.

Options Available to Us There are several non-fossil-fuel-based alternatives that have been examined as possible energy sources [7]. The United States and Europe are leading the effort in examining

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. Table 32.2 Issues with continued reliance on fossil fuels as a primary resource for mankind’s energy needs Problem areas for fossil fuels

Specifics

Description

Climate Global warming change issues

Health hazard

Economic risks

Others

Emission of greenhouse gases such as CO2 traps solar heat which raises atmospheric temperature Sea level rise Rise in sea levels due to global warming can lead to flooding of low-lying areas Alternation of weather pattern Draughts, floods, hurricanes, and tornados resulting from temperature can critically impair local/regional economic change activities such as agriculture and even lead to displacement of the population Tailpipe/stack emissions SOx, NOx, and particulates in emissions can reduce air quality by promoting smog formation which may lead to health hazards such as lung cancer Unsteady supply of increasingly Increasing demand for finite resources can finite resources lead to spiraling prices (price fluctuations) that can hurt or even stunt economic growth Geopolitical instability Extreme reliance on very few sources where political situation can become unfavorable Man-made disruption Disruption of stable supply of energy due to activities such as terrorism Land destruction Environmental impact on local animal and plant life

the induction of non-fossil alternatives into mainstream energy sector. However, there is still a long way to go in this direction. For example, current US consumption of renewable energy forms – wind, biomass, geothermal, and solar – is 6.3%, a very small fraction of the total 98.3 QBtu of energy used by the United States. Some of the pros and cons of these green alternatives are discussed next.

Wind Energy Wind power is broadly defined as the conversion of wind energy into a useful form of energy utilizing machinery such as sailing vessels, windmills, and wind turbines (> Scheme 32.1). Wind energy shows promise as a replacement for fossil fuels as an energy source; theoretical estimates indicate that global output from wind can be the equivalent

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Green options

Biomass

Solar

Wind

Geothermal

. Scheme 32.1 Green energy options that have potential to meet global energy needs

of 5,800 quads of energy per year [8] (1 quad = 172 million barrels of oil = 425 million tons of coal). Moreover, wind power has certain advantages over other renewable forms of energy such as solar energy, for the wind can blow day and night, sunny or cloudy, and often is strongest during dark, overcast winter storms when energy is needed for heating and getting solar energy is not possible. However, wind power also has its limitations. Many devices that convert wind energy need specific wind velocities to work efficiently and as a result these specific wind velocities are often location specific, limiting the areas in which wind energy conversion devices can be used. Furthermore, contentious issues such as potential harm to endangered birds due to the rotating blades, noise concerns, health concerns, and the effects on aesthetics of the landscape due to the presence of several hundred windmills in a farm need to be resolved. Countries such as the United States [9] and England [10] are seriously considering or have projects underway to harvest wind energy. The data from such case study locations should be carefully examined and appropriate changes have to be made to address the aforementioned concerns to exploit wind energy on a larger scale.

Biomass Energy Biomass is a renewable energy source because the energy it contains comes from the sun. Plants capture the sun’s energy via the process of photosynthesis. Photosynthesis converts carbon dioxide from the air and water from the ground into carbohydrates, complex compounds composed of carbon, hydrogen, and oxygen. Later when these carbohydrates are combusted, fermented, or gasified for energy utilization, they turn back into carbon dioxide and water and release the sun’s energy that they contain. Through this cyclic process, biomass functions as a sort of natural and potentially infinite battery for storing solar energy. Depending on the biomass source and method used for releasing the captured energy, biomass energy can have the potential to supply 79 QBtu of energy (this is 80% of the US energy consumption). However, in order to reach this output, the current 350  106 acres of land being harvested in the USA would have to be used solely for biomass production. This leads to the main disadvantage of biomass – the land needed to produce the biomass often leads to competition with land for food, destruction of forests, and with some biomass technologies, such as ethanol, food crops are used directly [11]. However, biomass from solid maniple waste and new research investigating biomass

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produced from nontraditional sources such as coffee waste or algae-based biofuel production possibly positively influence technological and commercial advances within this field [12, 13].

Geothermal Power Geothermal power utilizes the continuous flow of heat energy from the hot interior of the earth to its surface, by means of space heating and the generation of electricity. Unlike fossil fuels, biomass, wind, and solar, geothermal has the capacity to sustain itself in a continuous closed-loop system using heat from the earth’s crust. Moreover, the world’s geothermal energy reserve is recorded at 108 QBtu, a million times the total yearly US energy consumption. Unfortunately, current geothermal energy is limited by locations where natural reserves occur and the heat energy can be tapped in a commercially viable manner; however, there are new technologies being researched, such as the Normal Geothermal Gradient and Hot Dry Rock technologies, which would expand geothermal usage tremendously.

Solar Power It is to be noted that solar energy can be considered as the indirect source for wind (solardriven temperature changes cause wind movement) and biomass (chlorophyll pigments absorbing sunlight to grow plants/biomass). However, we do not focus on that aspect often when we talk about solar power. Solar power harnesses the radiant light and heat given off by the sun and is unquestionably the most universally available and least utilized form of renewable energy resource. It is estimated that the earth receives 162,000 TW of energy from the sun [14]. If one assumes that earth has a land mass of approximately 20%, the fraction of energy reaching land is 32,400 TW, a fraction of the world’s yearly energy consumption! If it is possible to build systems that can harness this solar energy, it could solve mankind’s energy problems. However, the biggest challenge is the development of materials that can economically and efficiently convert solar energy into useful forms at a commercially viable efficiency. This chapter focuses on solar energy and some of the factors that are pivotal to using solar energy as a resource for meeting global energy needs. For further details on these topical areas, the readers are referred to four chapters on biomass and one chapter on wind energy in this text.

Solar Energy The following sections assume that the reader already has a fundamental knowledge of solar energy. For a review of these concepts, there are numerous publications in circulation that cover these fundamentals in greater detail.

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What Is Solar Energy? Solar radiation consists of light of different wavelengths (energy). The energy associated with each wavelength can be estimated using the equation E ¼ h lc , where E = energy (eV), h = Planck’s constant (6.6  1034 J s), l = wavelength of light (nm), and c = velocity of light (3  108 m/s). As the wavelength of light increases, the energy associated with that wavelength decreases. Solar energy received at the surface of the earth also depends on the location (zenith angle) and effects of atmospheric interference (pollution or turbidity). In general, the irradiance at the surface reduces toward the poles and increases with atmospheric pollution. The solar spectrum can be divided into several regions. These include far-UV (1,400 nm). The distribution of energy associated with sunlight can be identified to different regions and may be approximated as UV Table 32.3.

Applications of Solar Energy Traditionally, the most common forms of solar energy usage have been harvesting the heat associated with the solar radiation, which is later utilized in applications such as cooking, space heating, and drying. Many of these applications have undergone technical refinement over time leading to cost competitive, efficient, and wide-scale usage. A brief discussion on some of these applications is presented in > section ‘‘Principles of Solar Energy Utilization.’’ > Figure 32.1 shows the breadth of applications that employ various aspects of solar power. Since the 1900s, efforts to use solar energy for energy generation involved focusing on the direct production of electricity, liquid, and gaseous fuels utilizing solar energy. Of particular interest, and also a great challenge, is using solar energy to sequester CO2 for producing value-added products such as fuels and control its emissions into the environment at the same time. The objective is to address two of mankind’s fundamental challenges: provide sustainable energy and reduce impact on climate. Due to the criticality of these challenges, CO2 control using solar energy is an emerging area of research.

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. Table 32.3 Advantages and disadvantages of solar energy Advantages

Disadvantages

Large area required to produce sizeable power (may not be possible to harvest solar energy in densely populated areas) Some materials used currently in solar energy conversion can be expensive and toxic and may require carefully planned disposal protocols 3. Sustainable and free of geopolitical Weather patterns can be a source of instabilities. No security issues unpredictable interference 4. Political support and incentives to switch to Public awareness about incentives (rebates) and education is still low and needs solar energy systems is favored in many a significant boost countries 5. Solar energy usages range from food Solar conversion efficiencies in most processing (solar cookers) to large-scale applications are low. Efficiency improvement electricity generation via materials development is a key challenge 1. Universally available, infinite energy source, and free. Complementary technologies ensure continuous availability 2. Clean eco-friendly, very low maintenance, supports local economy ‘‘green jobs,’’ and does not contribute to global warming

• Heating –water and air • Heat Storage • Air conditioning

• Crop drying • Cooking –ovens • Distillation

• Furnaces • PV • Fuels –biofuels

Food Processing

Temperature Control

Energy Consumption

Environment

• Photocatalytic pollutant removal • CO2 Conversion

. Fig. 32.1 Solar energy can be utilized in a wide range of applications from processing of agricultural precuts to energy generation to environmental remediation

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From an environmental perspective, the applications of solar energy in waste treatment cannot be ignored. Photocatalytic degradation of a wide variety of gas-phase and liquid-phase pollutants assists in keeping the atmosphere and water bodies clean. This process involves the destruction of potentially toxic materials through a series of steps into relatively benign intermediates and later into CO2 and water. Depending on the nature of the pollutant(s), the application of solar energy for environmental protection can therefore be a simple and cost-effective method to treat recalcitrant materials. A limited discussion of this aspect of solar energy utilization is provided later (> sections ‘‘CO2 Conversion,’’ > ‘‘Example 1: Integrated Organic Waste Treatment and Fuel Cell System,’’ and > ‘‘Example 3: Bio-processes to Convert Waste to Energy Using Algae’’).

Principles of Solar Energy Utilization This section discusses the principles of solar energy utilization in commonly used applications such as water purification, residential heating, food processing, biofuel production, photovoltaics, water splitting, and CO2 conversion to hydrocarbons.

Space and Water Heating Space heating is often used in residential and commercial areas [17–22]. The process involves utilizing heat from the sun in order to provide comfortable living conditions in an eco-friendly manner. Space heating involves careful planning of the design of structures based on the orientation of the sun. The differences in the densities of warm and cold air are exploited to cause an artificially induced circulation in a confined space. The roof can be slanting or flat and made of partially transparent glass, permitting natural illumination. The principle design of one form of a well designed space heating system, including the general steps involved, is schematically illustrated in > Fig. 32.2a. A slight variation of this concept can also be used in heating water. A typical setup may include off-the-shelf metallic heat conducting tubes that carry water through a blackened enclosure exposed on one side to solar radiation. This produces water fit for domestic use. > Figure 32.2b shows the pictures of solar water heating apparatus on the roofs of buildings in China. Benefits of employing such eco-friendly approaches may include significant cost savings in utility bills, reduced illumination costs, reduced dependence on fossil-based fuels, and protected earth’s climate by minimization of carbon footprint.

Water Purification Using Solar Stills Solar stills (or solar distillation) are used for producing portable water from impure and/ or scarce water resources [23–26]. A solar still can be used in places with little or no infrastructure such as deserts, regions with mines that have potential ground water

. Fig. 32.2 The use of solar energy in several applications has been studied extensively. Here are some examples where solar energy is utilized in (a) large-scale and (b) small-scale portable water heater, (c) solar still, and (d, e) solar cooker. Refer > section ‘‘Principles of Solar Energy Utilization’’ for details (Reprinted with permission from Elsevier)

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contamination, in areas that have frequent disruptions in utilities (power and water supply), and as an emergency survival kit. The principle of operation of a solar still is shown in > Fig. 32.2c. Heat energy from the sun facilitates evaporation followed by condensation of water. The still consists of a lower darkened region with a transparent cover (glass or polymer) placed at an inclination that allows solar radiation to pass through. The bottom of the still often houses the impure water and can be maintained dark if needed to maximize absorption of heat from the sun. The source of this water can be groundwater, industrial effluents, agricultural runoffs, wastes from poultry/diary, or other sources. The absorbed heat is transferred to the water which evaporates and then condenses on the inner side of the cover. The condensate trickles down along the slope of the cover and collects in a separate reservoir, providing water fit for consumption. Since water has to be boiled to kill microorganisms such as bacteria, a solar still may not be able to do this effectively as boiling is not always achieved at the still operating temperatures. One can fabricate a crude still using materials such as transparent plastic, a water-resistant darkened polystyrene sheet, and stones.

Food Processing Solar energy can be used in cooking, drying of organic matter, and in the elimination of pests that threaten crops [27–30]. Solar cookers are the simplest form of food processing equipment. The concept is similar to a solar still or solar water heater. Incident as well as reflected sunlight is absorbed by a dark vessel that contains the food material that has to be cooked. A simple solar cooker can be made of a wooden box, with a glass wool liner and aluminum reflector sheets. A schematic representation of a solar cooker is shown in > Fig. 32.2d. > Figure 32.2e shows a photograph of a household solar cooker. Solar cookers can be especially effective in countries along the equator since they receive significant amounts of solar radiation for a better part of the day peaking right around the midday periods. Therefore, solar radiation can be easily used to cook a midday lunch in a reasonable time. Larger area solar dryers consist of wooden boxes with ventilation holes in the sides. These holes assist in air circulation. Dry air carries the moisture generated from the organic matter outside. The top of the box is covered with glass or flexible polymeric materials at a latitude-based angle to allow maximum sunlight. These boxes can be used to dry organic matter: fruits, vegetables, or fish.

Solar-Assisted Biofuel Production Fuels obtained from a biological source such as an organic matter (plants and waste matter) are called biofuels: [31–33] vegetable oil (biodiesel), bioalcohols (ethanol), and biogas (methane) are common examples [31–34]. The principles involved in the production of these biofuels vary vastly depending on the type of approach used for the biofuel production. However, common to all these processes is the (1) cyclic nature of CO2 from

Harvesting Solar Energy Using Inexpensive and Benign Materials

(I) Vegetable

Catalyst

(II) Corn (III) CO2+nutrients

(IV) CO2+H2O

32

Biodiesel

Ethanol Higher alcohol

Methane

. Fig. 32.3 The production of biofuels can be carried out using different raw materials in the presence of a catalyst

the sunlight being utilized by a plant to the utilization of this stored energy and (2) the requirement that a catalyst drive this reaction. > Figure 32.3 illustrates the different types of catalyst-driven reactions. Among the four pathways shown in > Fig. 32.3, pathways I and II are benefited due to solar energy usage in the left side. Solar energy is absorbed by catalysts such as chlorophyll to form chemical energy in vegetables and plants. This in turn can be converted using appropriate catalysts to biodiesel and/or ethanol. The carbon cycle for an energy crop produced from the Rape plant is shown in > Fig. 32.4a. Solar energy is utilized in pathways III and IV to drive products in the right side. Path III utilizes microorganisms such as algae which drive the photoconversion of CO2 to value-added fuels. In pathway IV, redox chemistry at the photocatalyst surface is central to the conversion of CO2 to value-added chemicals. The development of biofuels using solar energy is very promising, and this approach to solar energy conversion can be a major player in the energy mix for the future.

Solar Photovoltaics (PV) A photovoltaic device converts solar energy to electricity through two main steps: the energy from the solar radiation is absorbed by the photoactive material(s) to produce excited electrons and these electrons then tunnel through the material to the external circuit to generate a photocurrent [35–39]. > Figure 32.4b shows the operating principle of a solar cell based on a combination of an inorganic material called titanium dioxide (TiO2) and a visible light absorbing dye. > Figure 32.4c shows the parts of a dye-sensitized solar cell. In this system, electron–hole pairs are generated due to the light absorbed by the dye, and it tunnels though an underlying TiO2 layer to a collecting conducting glass substrate. An electrolyte is present between the anode (conducting glass) and the cathode of a PV device. The role of the electrolyte is to function as a redox couple and facilitate replenishing of the charges at the photoanode. Composite systems are often used to (1) improve light absorbance, (2) promote charge separation, and (3) increase the overall performance efficiency of the solar cell. Tandem cells, inorganic composite–based

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. Fig. 32.4 (a) Schematic of the steps involved in biofuel cycle, (b) the process of solar energy conversion to electricity using a PV device, (c) the exploded view of a dye-sensitized solar cell, (d) mechanism of redox processes in a photocatalyst, and (e) CO2 photocatalytic reduction using solar energy over a semiconductor oxide photocatalyst (Reprinted with permission from Elsevier)

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solar cells, and dye-sensitized solar cells are some examples of popular photovoltaic devices. An ideal solar cell is one which is able to absorb most of the solar radiation (usable parts of the solar radiation are ultraviolet, visible, and infrared) and generate electricity with a high level of solar-to-electric power conversion efficiency (Z). Investments in the area of solar photovoltaics have been growing at an incredible rate in the last decade [40]. Improvement in technology, low material and processing costs, and political incentives have been identified as the major factors contributing to solar PV growth in developed as well as developing countries.

Photocatalytic Oxidative (Water Splitting) and Reductive (CO2 ! Fuel) Reactions Solar energy can be used to drive different types of chemical reactions yielding many value-added products [41–46]. Water splitting, CO2 control, and environmental remediation are popular examples of such solar-driven reactions. The principle behind these different reactions is essentially the same. In a photocatalyst surface, both oxidative (electron liberating) and reductive (electron gaining) reactions can occur simultaneously as shown in > Fig. 32.4d. In either type, the photocatalyst driving the reaction has to straddle the reaction of interest if it were to be performed without the application of an external electric field or bias. In photooxidative reactions such as water splitting and environmental remediation using oxidation, hole or hydroxyl radicals generated at the valence band of the semiconductor are often the main participating agents. Photocatalytic water splitting involves the hydrogen formation at the cathode and oxygen formation at the anode. Reduction reactions are performed by the electrons at the conduction band. Examples of reductive reactions include CO2 reduction to hydrocarbons such as methane, methanol, or methyl formate (> Fig. 32.4e) and reductive precipitation of toxic heavy metals such as mercury and cadmium from waste streams. For a detailed discussion on the mechanistic aspects of the redox reactions on a photocatalyst surface, readers are referred to a few representative reviews in the literature [15, 16, 47–52].

Toolkit for Characterization of Photoactive Materials (PMs) Photoactive materials or PMs for solar-to-energy conversion can be simple (consisting of one element or compound) or complex (consisting of several materials in the form of a composite). Often, synthesis procedures for complex PMs employ preformed materials as building blocks. To improve the performance of the PMs, one has to examine surface, optical, electronic, and catalytic properties of the material(s) as they start to take the desired shape or form. There are several tools that can be employed to evaluate material properties at various stages of synthesis. Some of these stages include formation, phase transformation, growth, photoactivity before and after integration with other materials, and performance after the entire device has been fabricated. > Table 32.4 is a list of some

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. Table 32.4 Optical, surface, and electrochemical measurements that can be performed to determine the properties of photoactive materials Category Instrument

Purpose

Optical

Spectrometer FT IR

UV–vis absorption Interaction with other materials (composite formation), synthesis progress

Surface

SEM, TEM, HRTEM

Surface morphology (shape, size, aspect ratio), crystallinity, size distribution Surface area Thermal stability, phase transition properties

BET TGA-DSC XRD AFM Electronic VOC, I/t, V/t, I/V

Incident photon to current efficiency

Crystallinity, compound formation Surface properties (morphology, roughness) of films Photoelectrochemical properties (of interest in, e.g., PV, photoelectrocatalytic water splitting), Mott–Schottky, band edges Effectiveness of materials to convert solar to electric energy

FT IR Fourier transform infrared spectrometer, SEM scanning electron microscope, HR(TEM) high resolution (transmission electron microscope), TGA-DSC thermogravimetric analyzer–differential scanning calorimeter, XRD X-ray diffraction, AFM atomic force microscope, Voc open circuit potential, I/t current-time, V/t voltagetime, I/V current-voltage

common tools used to evaluate material performance. A detailed description of some of these tools is also provided below. (Note: For brevity, only commonly used tools representing each of the three categories below are discussed.)

Photoelectrochemical Measurements PMs produce charge carriers such as electrons and holes on photoillumination. These charge carriers are the basis of any activity involving the PMs. A knowledge of electron– hole transport in photoelectrochemical systems is critical to designing nanostructured materials (especially composites) with high efficiency. Factors that may contribute to altering this efficiency of charge generation are the composition of the nanostructure, film thickness (if it is a film), light intensity, electrolyte and its concentration. An essential requirement in a photoactive system is the need to maximize the separation between the photogenerated charges. Careful consideration of other aspects such as mode of illumination (front and back faces for films), which depends on the film thickness, decides the extent of light conversion. Photoelectrochemical techniques provide the necessary means for the evaluation of a nanostructured photoactive composite to maximize light energy conversion and its application in energy production. In the case of films, the commonly used setup for the electrochemical measurements involves a light source (solar simulator), appropriate

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filters to control light intensity and wavelength, and a cell consisting of three electrodes. The PM to be analyzed is deposited as a film on a conducting medium and is called the working electrode. It is flanked with a reference and counter electrode. The activity of the PM can be determined in the presence of white light and/or light of different wavelengths. Electrochemical measurements typically involve the estimation of the open circuit potential (Voc), current–voltage characteristics (cyclic voltammetry), and the estimation of efficiency. These measurements can provide information on the effectiveness of the photoelectrode to perform solar-to-electric power conversion, water splitting, or fuel production (CO2 to value-added chemical). Efficiency is calculated in the form of incident photon to current conversion efficiency (IPCE). IPCE and other optical tools can provide information about what material is contributing to photoactivity and which region of the solar spectrum is effectively utilized. Further details of these types of analysis and the features of the plots obtained in these measurements are discussed in an earlier work [53].

Spectroscopy Spectroscopy chiefly involves absorption and fluorescence measurements [54, 55]. Most of the materials participating in solar-assisted energy production can include metals, semiconductors, insulators, polymers, organic dyes, and composites of materials from these groups. These materials can exhibit absorption to varying degrees and in different regions of the light spectrum. Absorption spectroscopy is therefore an invaluable tool to probe the optical properties of the photoactive material. In the nanometer size, materials demonstrate interesting optical properties. For example, noble metals exhibit unique properties due to the development of plasmon band. Semiconductors exhibit sizedependent optoelectronic properties called quantization effect. While most of the materials exhibit absorbance, a few materials demonstrate fluorescence. Fluorescence involves energy liberated by a photoactive system when charge/energy exchange between a material and surroundings leads to the material transitioning to a steady base (unexcited state). If a material is fluorescent, conventionally both fluorescence and absorption spectroscopy is used. The layout of a fluorescence measurement system is shown in > Scheme 32.2. Typically, the material absorbs light of a higher energy, and the emission from the material, usually of lower energy, is probed at an angle of 90 to the incident beam. Complementary usage of fluorescence and absorption for probing interactions in composites (such as TiO2–Au) is generally applied for photoactive materials and enables a deeper understanding of the interactions in the composite. Charge transfer processes, ground and excited state interactions’ bonding, and complexations between interacting molecules are some of the aspects studied using these optical techniques.

Transient Studies Several composites can display interactions in the sub-second time domain. These interactions usually take place by charge and energy transfer and could be in the order

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of micro-, nano-, pico-, and femtosecond time domains. A flash photolysis study which is primarily carried out to elucidate this mechanism involves an elaborate setup consisting of an array of optics (lens, filters, photomultipliers, and monochromators) and a light source. While the source is a laser beam of known wavelength which initiates the materials in the composite to excited state, a probe beam (usually from a xenon lamp) is used to investigate the changes due to the incident monochromatic light. > Scheme 32.3

Monochromator I

shutter Filter

Light Source PMT Monochromator II

Sample chamber

PMT converts light to electrical signal which is fed to the data processor

Data processor

. Scheme 32.2 Simplified layout of a general spectrofluorometer

N2 Trigger

FR

Laser source

Probe light (Xenon Lamp)

B

• Convex lens (L) focus light on cell (C), slit (S)

A

• Shutters A & B are triggered in unison with precise intervals

C

FR L L

L F

• Filter reflectors (FR) direct laser after calculated delay on cell (C)

S

D

• Detector (D) can be IR or UV • Filter (F) to cut off light from passing into Monochromator

Monochromator Signal to processor and computer

. Scheme 32.3 Schematic of the laser flash photolysis setup for probing charge transport dynamics in the sub-second timescale using a nitrogen excitation laser (337 nm)

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shows a typical laser flash photolysis setup. Transient study plots are designated as difference absorption spectra [56, 57] and help one to shed light on the dynamics occurring in the sub-second timescales. Pulse radiolysis (for steady state one can use g-radiolysis) is employed to observe the effect of highly reactive species such as hydroxyl radicals and aqueous electrons on a composite system. Bombardment of water with high-energy ionizing radiation produces reductive and oxidizing species as shown below. H2 O ! eaq  ; H ; OH ; H2 ; H2 O2 ; H3 Oþ ; OH Reactivity of a certain radical with the semiconductor–metal composite can be observed by selectively scavenging out other radicals from the system using different agents. The above section provides an overview of different techniques that can be used to determine the photoelectrochemical properties of materials. Several of these techniques can be performed by a reasonable well trained student. These techniques can be used as a screening step to determine the use of a material for a certain application.

Materials for Solar Energy Utilization Photoactive compounds or composites have to pass a set of very stringent criteria to qualify as a material for solar energy utilization. This section discusses some of these criteria. A brief overview of the methods that can be used for the synthesis of photoactive materials and device fabrication is discussed. This is followed by a summary of the state of various popular photoactive materials and their limitations. The materials used in PV, water splitting, and CO2 conversion applications are discussed in detail toward the end of this section.

What Is the Holy Grail in Photocatalysis? The properties that one has to look for in materials for photocatalytic applications include: solar response, availability, toxicity, processability, compatibility, stability, cost, and recyclability. Specific details of these aspects are listed below: ● Response to wide range of wavelengths in solar radiation (ability to effectively utilize maximum parts of the solar spectrum) ● Availability (large supply of materials) ● Process ability (amenable to large processing techniques and preferably cost effective) ● Absence of any toxic effects (preference is minimal environmental and/or health hazard) ● Compatibility (flexibility to couple with other materials with the intent to improve optical, electronic, and/or catalytic properties)

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● Stability (providing consistent performance without significant deterioration over time) ● Cost competitive (this is directly related to availability). These are the major criteria that a material must fulfill to be considered as a promising candidate in photocatalysis. It is not possible to rank all known materials based on all these aspects. In this work, the authors have therefore focused on a select few materials based on applications and which meet several of the aforementioned selection criteria.

Review of Synthesis Procedures for Photocatalysts There are several methods that can be used for the synthesis of materials for solar energy conversion. These include wet chemical methods (such as solgel and reverse micelle techniques) and chamber-based methods (such as chemical vapor deposition and atomic layer deposition). Wet chemical methods usually involve using precursors of the materials that form the photoactive material, agents that participate in the transformation of the precursor to the desired final product (this may include complexing agents, stabilizers, and initiators). Detailed description of the merits of different wet chemical methods can be found in reviews by several authors [58–61] including one from the authors’ group [62]. Chamber-based methods can be expensive initially due to higher capital cost and the need for possible sophisticated materials handling. In contrast to the wet chain methods, they do not require several agents and can oftentimes lead to a product that is much purer. Anodization and layer-by-layer self-assembly (or Successive Ionic Layer Adsorption and Reaction – SILAR) process are often used to prepare composite particles using preformed materials as building blocks. They are rather simple, generic protocols customizable to the synthesis of different materials. Oftentimes these methods are used to prepare the anode and/or the cathode of a solar energy harvesting device separately, and then a different method has to be used to integrate these elements to form the device (PV or photoelectrochemical (PEC) cell).

System Integration The fabricated materials have to be integrated to form a device prior to its application in solar energy conversion. A film-based PEC device is often used in water splitting reactions. A PEC system consists of an anode, cathode, and an electrolyte. The electrolyte is often the source of the fuel (e.g., aqueous solution of an alcohol produces hydrogen by splitting water in the electrolyte). A slurry-based PEC system does not have a clear separation of the anode and cathode since the catalyst acts as a center where both redox activities occur simultaneously. Whereas a dye-sensitized solar cell device consists of an anode, cathode, and electrolyte that are clearly separate from one another. On the other hand, a slurry system has no distinct anode-cathode; the particles itself act as PEC, as referred to in Bard’s concept [63].

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Previous Attempts in Materials Development A list of different materials that can be used as a photocatalyst is provided in > section ‘‘Materials for Photovoltaics, Water Splitting, and CO2 Reduction.’’ Titanium dioxide (TiO2) has been the most popular and extensively studied photocatalyst for its ability to harvest solar energy, and hence it is first discussed here [64]. It demonstrates good stability over a wide pH range, compatibility with other materials, environmental friendliness, and low cost. Its applications include solar energy conversion (photovoltaics) [65, 66] and hydrogen production (by photocatalytic water-splitting) [42]. However, TiO2 has some significant limitations. For example, TiO2, by itself, has high charge recombination rates compared to its combination with other materials such as dyes or semiconductors. TiO2 alone has very limited light harvesting ability (it only absorbs UV light) [67]. Several reviews have discussed the photoactivity of TiO2 and its composites for different applications [52, 68–72]. The photoactivity of TiO2 can be significantly improved by dye sensitization [68], altering its composition (such as doping) [69, 73] and/or combining TiO2 with other materials [52, 70, 71]. These efforts have been reasonably successful in improving the performance of TiO2 composites. With respect to photovoltaic applications, the efficiency of light absorbance and improvement in charge separation of TiO2-based nanocomposites still remains low (10–12%). The limitations of TiO2-based materials can be attributed to the absence of flexibility for altering the inherent photoactivity of TiO2 itself (because there is just one cation site (Ti) available for manipulation of electronic properties). In this context, a photoactive material, whose inherent electronic properties can be altered with greater flexibility, is needed. Silicon-based solar cells are probably the most reliable, with proven high efficiencies (Z = 10–20%) based on the nature of crystallite size and manufacturing methods [74–77]. However, silicon for high-efficiency applications is becoming increasingly expensive. Complex processing routines also drive manufacturing costs high. Chalcogenide films made of various combinations of Cu, In, Ga, As, Cd, Se, and Te can be tuned to absorb significant visible light and show near optimal photovoltaic performance (Z  20%) [78] but pose toxicity concerns to environment, can require expensive reagents, and processing cost is high [35, 79]. Multi-junction devices can produce very high efficiencies (>35%) [80], but one of the issues is the transparency required to activate underlying layers. Photoactive polymers with fullerenes as the electron transport agent are significantly simple to process compared to Si-based devices but are limited in their stability during long-term operations [81, 82].

Materials for Photovoltaics, Water Splitting, and CO2 Reduction The following section provides a list of materials for photovoltaic, water splitting, and CO2 reduction applications. The selection of materials is based on meeting one or more of the following criteria: cost effectiveness, eco-friendly, and ease of synthesis.

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Photovoltaics Solar cells can be distinguished on the basis of their overall solar-to-electric conversion efficiency into several categories. Several reviews have discussed different aspects of PV [35, 83–87]. > Table 32.5 provides a comparison of the different technologies available today and how these technologies rank with respect to each other. Many of the materials identified here either have been commercialized and/or offer promise for commercialization due to aspects such as cost competitiveness or eco-friendliness, or ease of process ability. In general, all solar cell technologies known today are designed for niche applications and come with advantages and disadvantages. Therefore, the choice of a solar cell technology is usually made based on the type of application and the length of time the cell is expected to be in service. A summary of the advantages and disadvantages of the different types of cells is provided in the following sections. (Chemical formulas are shown in the table for brevity. Readers are referred to citations for details.)

Water Splitting Water splitting can be performed in the presence or absence of sacrificial agents. Based on the approach employed, several reviews have discussed the materials [41, 42, 58, 59, 113, 114]. The following segments list some of the popular materials that have been used successfully for water splitting. Properties of the materials are listed in column 2. Oxides, oxide composites, and non-oxides are common materials for driving water splitting reactions. Other materials such as perovskites, sillenites, and pyrochlores are also promising families of compounds that demonstrate water splitting. However, these materials may be difficult to synthesize and more research has to be performed to determine the applicability of such materials for water splitting reactions (> Table 32.6).

CO2 Conversion Due to global environmental concern, the research in utilization of solar energy for CO2 conversion and/or control is gaining momentum. Several articles [135–140] have addressed this topic and readers are directed to these articles for further information. > Table 32.7 lists some of the articles that demonstrate the application of a few leading and representative materials for CO2 conversion.

Challenges and Limitations to Materials Mathematical models that consider thermodynamic limits and the near impossibility to convert solar energy to other forms of energy without generating entropy pins the maximum attainable theoretical efficiency of conversion of solar energy at 85% [154].

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. Table 32.5 Materials for photovoltaic applications Material

Reason

Ref

CdTe

Low-cost preparation technique, high conductivity, appropriate band gap, recycling methods developed Low-cost, non-vacuum preparation technique

[88–90]

Combination rapid thermal process and layer-by-layer spin coating preparation TiO2 nanotube array in ionic liquid electrolyte cell TiO2 nanorod assembly

[94]

Low-cost encapsulation method Low-cost vapor deposition preparation Low-cost, non-vacuum preparation technique with solution coating and reduction-sulfurication technique Synthesized hollow nanospheres from common inorganic metal salts using surfactant-assisted chemical route Thin-film reduced cost

[97] [98] [99]

Cheaper hybrid PV cells High efficiency, low-cost thin film Charge transport material to be used with ZnO or CdTe

[102] [90] [103]

CuInSe2 TiO2

a-Si CuInS2

Thin crystalline silicon ZnO/Al2O3 CuGaInSe2 Nafion

[88, 91, 92] Continuous non-vacuum process by simple printing techniques [93]

[95] [96]

[100] [87, 101]

Organic PV cell, low-cost, experiment with rubrene doping ZnPc/C60 PbSe Lower cost, high-efficiency semiconductor material Carbon nanotube Alternative to platinum as a counter-electrode in DSSCs (w/TiO2)

[104] [105] [106, 107]

P3HT/PCBM

[108] [109]

FeS2

FeS and FeS2

BJH cell that is lightweight, flexible, low-cost production Preparation by low-cost quick drying technique, improved efficiency over other techniques P3HT nanowires and PC61BM or PC71CM

[110]

Lower cost due to abundance and production than silicon [111] and > or = efficiency Nanosheet films from reaction of iron foil and sulfur powder, for [112] photocathodes in tandem solar cell with TiO2 as photoanode

Specific to photovoltaics, silicon (Si) solar cells (both single and polycrystalline) have been by far the most studied devices with the greatest market penetration and demonstrate the highest efficiencies (10–25% for wafers, 4–20% for modules) [85, 155]. However, increasing demand for Si, material processing, and device manufacturing costs have led to the opportunity for other non-Si-based technologies to enter the commercial market [85, 86]. Thin-film processing technologies that use amorphous silicon (a-Si) is less expensive if

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. Table 32.6 Materials for photocatalytic water splitting to produce hydrogen Material

Properties

Ref

a-Si

Relatively high conversion efficiency, no catalyst degradation, low-cost hydrogen production Inexpensive, efficient, and renewable hydrogen source Surface engineering to increase active sites for reaction Carbon-doped TiO2 increases efficiency of water splitting

[115]

TiO2

Si/TiO2 Fe2O3

ZnO SrTiO3 WO3 CuInS2 Cu2O

In2O3

Nano-size photocatalyst, low cost, environmentally friendly Nanostructured photocatalyst to reduce material cost Nanotube and nanowire arrays for improved efficiency Carbon modified n-type TiO2 photoelectrodes to increase conversion efficiency Efficient photocatalyst prepared by environmentally friendly microwaveassisted hydrothermal process Si doping improves efficiency, low-cost solar-to-chemical conversion

[116] [117] [118] [67] [119] [120] [121] [122] [123]

Require smaller overpotential to oxidize water, single solar cell power, lower production costs Ag-Fe2O3 nanocomposite photocatalyst as efficient, low-cost PEC Doping to improve efficiency

[117]

Thin layer of Fe2O3 using nanostructured host scaffold of WO3 Low-cost oxide semiconductor Low-cost oxide semiconductor Fe3+/Fe2+ redox over WO3, efficient photocatalyst, low-cost option

[126] [42] [42] [127]

Nanoporous WO3 for improved efficiency High H2 evolution in presence Na2S/Na2SO3 as sacrificial electron donors under visible light radiation Cheaper synthesis than similar photocatalyst

[128] [129]

[124] [125]

[130]

Cu2O powders in coupled with WO3 in suspension had good H2 evolution [149] High absorption efficiency, non-toxic, elements abundant [122] Nitrogen doping shows better photoelectrochemical activity for water [131] splitting than N-doped TiO2

High purity, low-cost, environmentally friendly production [132] SnO2/ a-Fe2O3 CdS CdS glass composite to reduce photocorrosion of powder form [133] (CdS/TiO2) CdS/TiO2 nanotubes showed greater efficiency than either material alone [134]

single junction solar cells are of interest. However, single junction a-Si solar cells have low efficiencies (3–4%), and employing amorphous thin films in a multijunction type cell (for example, using a-Si and a-SixGe1x) can improve efficiencies up to 6–8% [85] and make them commercially viable [156] but again increases cost. Comparative efficiencies of silicon-based and non-silicon-based solar cells are discussed at length in literature [78].

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. Table 32.7 Materials for photocatalytic reduction of CO2 Material

Reason

TiO2

TiO2 anchored on glass act as active photocatalyst for reduction of [141] CO2 with H2O Highly dispersed anchored TiO2 to reduce CO2 to CH4, Cu loading [45] increased CH3OH [136] TiO2 nanoparticles, found 14 nm to be optimum photocatalyst

CdSe CdS Ti-Si Titanium silicalite

Simple synthesis methods to form highly active nanocomposite photocatalyst TiO2 pellets reduced CO2 in the presence of water vapor under UV irradiation Cu-loaded TiO2 increases photoreduction CO2, shown Cu(I) as primary active site Cu-TiO2 optical fibers transform CO2 to hydrocarbons at higher efficiencies Highly dispersed TiO2 within zeolite cavities for efficient CO2 reduction TiO2 on a SnO2 glass substrate to form bilayer catalyst, high photocatalytic activity Effect of metal depositing on TiO2, improved efficiency CdSe/Pt/TiO2 photocatalyst producing high yield of CH4 with CH3OH, H2, and CO as minor products Effective photocatalytic reduction, increased efficiency with excess Cd2+ Ti-containing silicon thin films higher reduction than powdered photocatalyst UV irradiation reduction of CO2 with H2 to CH4, Ti believed to provide active site Photocatalyst in presence of phenol to produce salicyclic acid

Poly (3-alkylthiophene) Photocatalytic ethanol production under visible light BiVO4 CaFe2O4 Non-poisonous, cheap, p-type semiconductor with small band gap Ga2O3 Photoreduction of CO2 with H2 at room temperature and ambient pressure Common water splitting semiconductor, now tested CO2 InTaO4 reduction. Reduction potential increased by adding NiO cocatalyst Photocatalytic reduction of CO2 to CO in presence of H2 (K,Na, Li)TaO3

Ref

[137] [142] [139] [140] [143] [144] [145] [138] [146] [147] [148] [149] [150] [151] [152] [153] [44]

Alternate to Si cells are compound semiconductor solar cells; GaAs, InGaP, and copper indium gallium selenides (CIGS) are popular examples that have tremendous commercial potential but are presently limited by processing cost and hence used only in niche areas

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such as space applications [157]. Using these in a multijunction format to boost efficiencies to the order of 6–8% and possibly reducing processing cost could bring the technology for terrestrial use (application in on-demand and on-site power generation) [157]. Alternate concepts on how to overcome efficiency limitations using tandem cells, intermediate band gap solar cells, and Quantum dot (QD) solar cells as discussed in this review, have to be explored [158]. Dye-sensitized solar cells (DSSC) may be a cost-effective option, a significant limitation being dye cost and stability, and corrosion of metal components of the cell due to usage of the popular iodine-iodide-based, charge shuttling electrolyte [159]. Recombination of photogenerated charges, mainly due to irregularity in the periodicity of the materials, has to be addressed or the performance of a solar cell improved [72]. To improve the application of low-cost, high-efficiency solar cells, low-cost ink technologies need to be developed to make it possible to develop a sort of spray paint methodologies to prepare bulk high-efficiency solar cells [160]. International standardization of cost for solar cell fabrication is being developed and tested [161]. Organic material-based solar cells are relatively new and far from becoming state-ofthe-art devices. However, they are gaining popularity and there is some market activity with devices offering efficiencies of 4–6% [162]. Due to the fact that solar systems are open to the elements and the moving nature of the sun, issues such as tracking to maintain efficiency of the system and protection against dust and minimizing the impact of cloud interference have to be considered for reliable operation of the system. One has to explore the development of new materials and applications for solar energy utilization and minimize the use of environmentally toxic materials such as Cd [163]. Other emerging areas such as band gap engineering and multilayered systems (high-efficiency tandem cells) for solar energy utilization have to be examined as well [164, 165].

Integrating Tested Concepts of Solar Energy Utilization to Produce Fuels in an Effective Way One method to improve solar energy utilization is to develop ‘‘smart and integrated systems’’ that can perform several solar-driven processes that are complementary in nature. The benefits of such an approach are as follows: 1. Maximizing solar energy utilization 2. A one-stop system for multiple applications 3. Improved utilization of land (this benefit can be a significant advantage in places with costly real estate and where limited land may be available for solar energy) 4. Potential for improved energy efficiency, reduced ecological impact, and greater benefits for human activity Three examples are presented below that illustrate these aspects.

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32

Example 1: Integrated Organic Waste Treatment and Fuel Cell System An interesting concept that combines two traditional applications of photocatalysis, environmental remediation and energy generation, to form a photo-fuel cell device is discussed below [166]. Photocatalytic degradation of organic environmental waste results in the formation of hydrogen ions which can be tapped to produce hydrogen molecules in order to use them as a clean fuel. The organic ‘‘fuel’’ wastes can be a part of a photoelectrochemical device that is comprised of two electrodes, (1) a photoanode that essentially consists of the photocatalyst where holes oxidize the organics to liberate H+ ions, (2) a cathode where the ions are reduced to form hydrogen, and (3) an electrolyte consisting of water, organics, and some salt (essential for ionic conductivity). A schematic of the setup and a prototype of the device is shown in > Fig. 32.5 TiO2 coated on a fluorine-doped tin oxide (FTO) substrate is used as a photoanode for oxidation of organics. One can expand on this concept a step further by (1) matching the pollutants in a manner that maximizes photooxidation on the basis of redox properties of the materials involved, (2) mechanism of degradation, or (3) potential for H+ ion generation to improve the yield of hydrogen.

Example 2: A Hybrid Photocatalytic–Photovoltaic System (HPPS) A research group from Switzerland has pioneered the development of an autonomous eco-friendly HPPS system which utilizes solar energy to perform photodegradation of

e– FTO

hν

Glass support

Pt R’+2H+ H2O

R+2h+

n-TiO2

2H++1/2O2+2e–

Nafion Membrane

. Fig. 32.5 Schematic representation of a two-compartment PEC cell. The openings at the upper part represent gas inlets and outlets. The chemical reactions shown are only indicative examples. The system can be used with other combination of pollutants to produce energy (Reprinted with permission from Elsevier)

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. Fig. 32.6 Schematic representation of a hybrid photocatalytic-photovoltaic system powered using internally generated energy (Reprinted with permission from Elsevier)

pollutants and a PV system to generate power for operating the system simultaneously [167]. This three-tiered system consists of (1) a sun-facing top layer where UV-assisted photodegradation of pollutants is performed, (2) an intermediate water layer which functions as an IR filter to regulate temperature, and (3) a visible light absorbing PV device that produces electricity at the bottom to power a recirculation pump associated with the system. A schematic of the system is shown in > Fig. 32.6. The system thus does not draw any external power for performing the waste treatment. The system consists of four PV modules, and has an overall volume of 25 L. This is an example of a smart integrated system that utilizes UV, visible, and IR parts of the solar spectrum to combining photodegradation of pollutants and producing electricity. A possible direction to further improve the efficiency of such systems may be to focus on trying to harvesting IR photons to produce electricity using new photocatalysts.

Example 3: Bio-processes to Convert Waste to Energy Using Algae Man-made emissions such as CO2 from industries have adverse effects on the environment; the realization of the negative effects of such emissions has led to international protocol and policy changes such as cap-and-trade agreements to control environmental impact [168–170]. On the other hand, the shortage of transportation fuels has necessitated the need to develop alternate sources of energy. These two challenges can potentially be addressed simultaneously using algae. Algae-based systems can assist in green house gas control by consuming CO2 to produce a variety of useful products. Algae in the presence of sunlight, water, and CO2 nutrients produce biofuels (for transportation), solid biomass (burned to produce heat or electricity), hydrogen, or oxygen. A schematic of the pathway for some of these products is

Harvesting Solar Energy Using Inexpensive and Benign Materials

32

shown in > Fig. 32.7. This approach is considered a promising solution to global environmental and energy needs. Photobioreactors or raceway ponds are two common methods to contact algae with light, CO2, and nutrients. An example of a raceway pond is shown in > Fig. 32.7. In a generic parlance, these examples help reinforce the old adage – One man’s junk is another man’s treasure.

Wastewater including nutrients

Spare electricity Exhaust CO2 Power generator

High-rate algal pond

Sunlight

Harvesting pond

Purified water

Electricity

Bio-gas Bio-oil

Biomass collection + chemical conversion

Lipid extraction + transesterification

Spare biofuel

Biodiesel

Harvest Food Paddlewheel

Baffle

Flow

Baffle

. Fig. 32.7 The steps involved in biodiesel production using waste water, solar energy, and CO2, and the picture of an actual raceway facility implementing about process (Top) (Reprinted with permission from Elsevier and ACS)

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Example 4: Solar-Powered Biomass Gasification Biomass gasification is the process of converting organic material to syngas, primarily carbon monoxide and hydrogen, which can be used to produce various forms of energy and fuels [171, 172]. Organic biomass is reacted at high temperatures with a specific amount of oxygen and water to produce syngas. The syngas is then purified and can be used for electricity generation, production of liquid fuels, or production of hydrogen gas. The problem with traditional gasification processes is that a large amount of energy is required to generate the high temperatures necessary for gasification. This energy is typically supplied by coal-fired power plants or by burning part of the biomass feedstock. Researchers at several Colorado universities in collaboration with the National Renewable Energy Laboratory have developed a rapid solar-thermal reactor that can be used for biomass gasification. In this process, a number of mirrors are used to concentrate solar energy to a single point producing extremely high reactor temperatures, in excess of 2,000 C. Sundrop Fuels has applied this technology at their solar-driven biomass gasification facility in Louisville, Colorado. Sundrop Fuels uses thousands of solar heliostat mirrors on the ground to direct concentrated solar energy to a thermochemical reactor atop a high tower. Feedstock entering the reactor is converted to syngas at 1,300 C. > Figure 32.8 shows a schematic representation of the solar-driven gasification process. The syngas is then cleaned and processed to create ‘‘green’’ gasoline, diesel, and aviation fuels. Biomass gasification is a promising technology for producing a number of fuels, and the use of concentrated solar energy eliminates traditional energy losses during thermal energy generation.

Commercial Ventures The progress in the development of materials for solar energy utilization in the last few decades has permitted a wide variety of solar cell-based commercial ventures to fulfill

. Fig. 32.8 Schematic of Sundrop Fuels® system to concentrate solar energy onto the thermochemical reactor for gasification, and the ground view of heliostat mirrors used to concentrate solar energy

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. Table 32.8 Commercial companies involved in the design of solar energy conversion systems Company Konarka Technologies Dyesol Inventux Technologies

Headquarter’s location

Solar cell technology

Website

Lowell, MA

Power plastics

Queanbeyan, NSW, Australia Berlin, Germany

High purity dye solar cell

http://www. konaraka.com http://www.dyesol. com http://www. inventux.com

Solar micromorph thin-film modules

contemporary specific niches and markets. Furthermore, solar companies are constantly researching and refining their manufacturing processes to discover more economical and eco-friendly solar cells that will satisfy emerging markets and cliental needs. Within this section, we will profile three solar companies: Konarka Technologies, Dyesol, and Inventux Technologies. > Table 32.8 briefly introduces these companies.

Konarka® Technologies Konarka Technologies is an international solar company receiving recognition worldwide for developing a third-generation organic photovoltaic technology–based solar cell [173]. An organic photovoltaic cell utilizes conductive polymers or small carbon-based molecules for light absorption and charge transport, respectively, while traditional electronics use inorganic conductors such as copper. Konarka’s chief technology, Power Plastic, was invented by the company’s cofounder and Nobel Prize laureate, Dr. Alan Heeger. Power Plastic is a photo-reactive polymer material and can be printed or coated inexpensively onto flexible substrates using roll-to-roll manufacturing; it is comprised of several thin layers: a photo-reactive printed layer, a transparent electrode layer, a plastic substrate, and a protective packaging layer, as illustrated in > Fig. 32.9.

Unique Features Konarka’s Power Plastic has several advantages over other organic photovoltaic technologies. These include: ● Tunable cell chemistry to absorb specific wavelengths of light as well as broad spectrum ● To capture both indoor and outdoor light and convert it into direct energy in the form of electric current ● To perform its function using all recyclable materials ● Being thin, lightweight, and flexible

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Transparent Packaging Transparent Electrode

Printed Active Material Primary Electrode Substrate

Light

Transparent Packing

Electrons

Transparent Electrode Printed Active Material

External Load

Primary Electrode Substrate

. Fig. 32.9 Illustration of power plastic layers (modified from the Konarka® website)

Applications Konarka’s Power Plastic has four major end-product applications. These include: ● ● ● ●

Microelectronics: Powering sensors, smart cards, and low power applications Portable power: Solar-powered sensors, backpacks, cell phone chargers Remote power: Accessing renewable power at stadiums, carports, airports Building integrated applications (BIPV): Custom-manufactured applications roof, windows, and walls

Cost per Watt Konarka’s Power Plastic technology has already reduced the cost of manufacturing solar cell so that it is less than $1 per watt; moreover, Konarka states that through mass production this cost will be further reduced to approximately $0.10/W.

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Future Plans Konarka is currently developing two future applications for Power Plastic which are under development by Konarka and Arch Aluminum & Glass: ● Manufacturing transparent and opaque solar cells for integrated curtain walls and windows components ● The ability for this technology to work off-angle permitting the technology to expand to other niches Konarka’s ongoing research involves conducting advanced research in power fibers, bifacial cells, and tandem architecture. The resulting products of this ongoing research would permit Konarka to expand solar power technology to woven textiles via power fibers. Bifacial cells being transparent in nature would permit the solar cells to generate electricity from inside and outside light while allowing the technology to double as a seethrough window. Tandem architecture would increase the efficiency of organic photovoltaic devices to 15% through the process of stacking series-connected sub-cells.

Dyesol® Dyesol manufactures and sells high purity dye solar cell (DCS) materials, titania pastes, sensitizing dyes, electrolytes, and electrode catalysts [174]. As seen in > Fig. 32.10, the DSC structure consists of a layer of nanoparticulate titania (titanium dioxide) which is formed on a transparent electrically conducting substrate and photosensitized via a single ruthenium (Ru)-based dye layer. An iodide-tri-iodide-based electrolyte redox system is placed between a layer of photosensitized titania and a second electrically conducting catalytic substrate.

Glass

h Lig

Conductive Layer

t

Working Electrode –ve

e–

Titania (TiO2)

–

Dye Electricity I– Counter Electrode +ve

Electrolyte Catalyst

+

Conductive Layer Glass

. Fig. 32.10 The fundamental DSC structure design consideration (taken from the Dyesol® website)

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Unique Features Some advantages of using DSC technology versus other contemporary silicon-based photovoltaic technology are that they: ● Are much less sensitive to angle of incidence of radiation – It is a ‘‘light sponge’’ soaked with dye ● Perform over a wide range of light conditions ● Have low sensitivity to ambient temperature changes ● Are much less sensitive to shadowing and can be diode free ● Are an option for transparent modules thus enabling wider applications ● Are truly bifacial: They absorb light from both faces and can be inverted ● Are versatile: DSC power can be amplified by tandem and optical techniques without use of concentrators The resulting DSC panels are more versatile because they are less sensitive to the angle of the solar radiation, allowing them to be installed on vertical walls and in low light areas; moreover, they can be transparent and can be designed in various color schemes permitting more attractive architectural integration options than those available for silicon.

Applications Dyesol’s patented products and their applications are listed below: ● Interconnected Glass Module: This design is for applications where longest lifetime is needed for exposed mounting and to be isostructural to and replacing the existing structure. Electrical interface can be typically via a short DC bus to a local area network for distribution or inversion to AC. ● SureVolt Solar Range: Maintain voltage at all light levels, and have high resistance to damage through impact, bending, tension, torsion, and compression. The range is ideally suited for use in portable consumer electronics, military and indoor applications, as well as developed landscape infrastructure. Dyesol’s dye solar cells (DSC) are marketed to low light, dappled light, and indoor light markets, a market that only DSC can address.

Cost per Watt The Photovoltaic World May/June 2009 magazine stated at the anticipated 7% Dyesol efficiency, the resulting cost of DSC technology was $1.00/W.

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Future Plans Dyesol appears to have two major future goals: 1. To outsource to working in collaboration with wireless technology and tandem products 2. To enhance power out devices to direct chemical production and complete building solutions

Inventux Technologies Inventux is a solar energy company that specializes in the development, production, and marketing of environmentally friendly, silicon-based thin-film solar (micromorph thinfilm) modules [175]. The combination of an amorphous with a microcrystalline cell is termed a micromorph cell. Micromorph cells thus represent the most consistent advancement of amorphous silicon-based tandem cell technology. > Figure 32.11 illustrates the thin film photovoltaic modules layer composition. The glass serves both as a substrate for the thin-film PV cell and a component of the later encapsulation of the element. The various layers are successively deposited on the front glass. To produce the absorber layers, the plasma enhanced chemical vapor deposition (PECVD) using gaseous silicon hydrogen compounds became generally accepted. The production of the front and back contact layers (transparent conductive oxide – TCO) takes place by applying low pressure chemical vapor deposition (LPCVD).

Front Glass TCO Front Contact a-Si μc-Si TCO Bank Contact Back Glass

. Fig. 32.11 Thin-film photovoltaic modules layer composition (taken from the Inventux® website)

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Unique Features Inventux’ solar modules contain absorbers made of amorphous and microcrystalline silicon. Amorphous and microcrystalline silicon are suitable to be combined in a tandem solar cell, since the different band gaps facilitate an enhanced utilization of solar radiation and manufacturing can be done using the same technology. Several of the advantages and benefits of using Inventux Solar Technologies PV modules are: ● The extremely thin 0.002-mm absorber layer requires only a minimum amount of raw material (silicon); the layer thickness is just one-hundredth of that of conventional photovoltaic technology. ● Exploitation of a broader light spectrum as well as fewer shading losses as with crystalline modules, up to 30% higher yield during inhomogeneous light conditions compared to crystalline modules and a wider range of applications possible. ● By far better temperature behavior at good solar radiation conditions as with crystalline technology, higher yields at full load conditions. ● Monolithic module configuration, as opposed to crystalline cell configuration – with its electrically required spacing, only very little inactive module surface exists. ● Monolithic wiring during the process makes subsequent manual production steps superfluous. ● Series connection of solar cells leads to a relatively high open circuit voltage of the modules, minimized conduction losses, and reduced cabling work. ● Due to the very high spectral acceptance, they have the highest efficiency potential in the area of silicon-based thin-film photovoltaics.

Applications Inventux thin-film photovoltaic modules are particularly suitable for large, grid-connect photovoltaic systems; moreover due to the micromorph tandem structure wide light spectrum absorption capabilities, Inventux technologies can be used during inhomogeneous light conditions and climate conditions.

Cost per Watt Inventux Solar Technologies implements Oerlikon Solar’s micromorph technology in the company’s manufacturing processes. Oerlikon claims that through the incorporation of

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32

advanced fabrication designs, the company’s turnkey tandem junction technology would be capable of producing modules for $0.70/W by the end of 2010.

Commercial Venture That Employs Tested Concepts of Solar Energy Utilization to Produce Fuels in an Effective Way Algenol® [176] is a US-based firm that proposes sequestering CO2 from power plant exhausts and producing transportation fuel from it. The company plans to use water and sunlight to produce value ethanol (an additive to gasoline). A schematic of their proposed flow sheet is shown in > Fig. 32.12. The firm focuses on the production of ethanol from algae without destroying the algae. A unique highlight of their system is the possibility of growing the algae in land areas that may be deemed unfit for agricultural activities, for example, a desert-like environment. They are planning to build commercial facilities in the United States and Mexico in the near term for large-scale ethanol production. The company plans to sell ethanol at a price of $3.00/gal and is expected to be a major player in the value ethanol market in the near future.

Nutrients

Solar Radiation

Exhaust Gas from Power Plant CO2 Gas Treatment

Seawater

Oxygen

Blue-green Algae

Unproductive Land

Separation Process

Bio-ethanol

(Fresh Water)

. Fig. 32.12 An artistic rendition of a plant showing CO2 capture from exhaust of a power plant and its utilization in a biofuel production facility. http://www.treehugger.com/files/2008/06/ algenol-algae-biofuel-race-process-economics-advantage.php

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Other Types of Solar Companies A list of other solar companies from different regions around the world is provided next. These companies are involved in manufacturing products that utilize solar energy in different processes. The reader is referred to the links provided for further information.

Company

Headquarter’s location

Solar cell technology

Website

Auria Solar

Taiwan

Amorphous silicon thin film

First Solar

Phoenix, AZ

Cadmium telluride

http://www.auriasolar. com/ http://www.firstsolar. com

Evergreen Solar Inc Marlboro, MA OriginOil

Los Angeles, CA

Schu¨co

US location Union City, CA Queensland, Australia Winnipeg, MB Canada Ithaca, NY

Solar Biofuels Northern Lights Solar Solutions Silicon Solar DesignLine

Christchurch, New Zealand

String ribbon crystalline silicon http://evergreensolar. com/en/ Biofuel with solar http://www.originoil. com/ Solar cooling http://www.schueco. com/web/com Solar hot water Solar biofuels (biomass) http://www. solarbiofuels.org/ Solar heating http://www.solartubs. com/ Portable solar power solutions http://www.siliconsolar. com/index.html Solar-powered bus (Tindo in http://www. Adelaide, Australia) designlinecorporation. com/

Future Work Solar research is no longer considered as a small blimp in the energy field. The last three decades of work has in fact brought it to a position where it has been accepted as a serious competitor to many traditional/nontraditional sources of energy. This is evident from the skyrocketing growth rate for solar-based technologies in the world. However, much needs to be done. Several critical areas require further development to cement the status of solar as a reliable, large-scale, and everlasting source of energy for mankind. To make solar commercial, economical, and lasting, development has to be simultaneously realized along three fronts: scientific, pilot-scale testing and processing, and rapid evaluation and commercialization of promising technologies. A brief insight into future directions along these lines is provided. The scientific step is the most important aspect of all the three stages. Materials properties, or rather constraints, is an area that clearly is the limiting factor and greatest challenge to solar energy commercialization. Since solar energy harvesting requires a close interaction of materials with

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elements and in some instances requires operation under extreme conditions, materials stability is of paramount importance. Solar-to-electric conversion technologies have the potential to transform mankind’s energy needs. However, materials that demonstrate stable performance without undergoing chemical transformations and consisting of earth abundant elements are urgently needed. Researchers have to focus on developing lowcost, wide-spectrum solar energy harvesters. The improvement of solar conversion or utilization efficiency is critical. To achieve efficiency improvements, fundamental understating of materials properties such as charge transport, recombination dynamics, and thermal management is needed. One approach to accelerate materials identification and its testing is to employ a combinatorial analysis method. There have been some efforts in this direction but more is needed. Past research has abundantly shown that multielement/multi-compound systems as light harvesters are the correct way to move toward realizing efficient solar harvesters. Stacking different materials built on-site or assembling prefabricated compound(s) is required to improve light absorbance as well as efficient transformation of absorbed energy. Combinatorial techniques have to be developed to analyze libraries of possible compounds and to expedite the identification of formulations for maximizing light absorbance and its testing. In stage II, one really needs to focus on the techniques to synthesize solar energy harvesters and convertors on a large scale. Issues such as reliable scale-up material properties (identical and reproducible product) and cost competitiveness have to be addressed at the pilot scale. Approaches such as screen or inkjet printing have been considered to be very promising techniques to reproduce lab-scale results on a commercial scale. These techniques have to be tested and perfected before further large-scale ventures. Performance data of extended use of solar energy convertors is still limited. Therefore, such data along with weather patterns and its influence on solar energy transformation has to be obtained. Realistic modeling predictions and long-term solar energy outputs have to be generated before using solar as the alternative source of energy for human activity. Stage III will require a large-scale effort on the part of governments (policy makers), green technology companies (research entities and venture capitalists), and public at large to come together to make solar energy a lasting and impacting form of alternate energy source. There are several evidences of governments getting sensitized to such needs, and short-term incentives are provided to test the people’s acceptance of the technologies and market reactions. However, there is still no leading technology within the solar energy conversion technologies that can be considered as the one solution for mankind’s energy needs. Therefore, the search has to go on.

Conclusion Solar energy utilization has immense potential due to the range of applications in which it can be utilized. The core issue with solar energy is materials development. There has been significant progress in this area thanks to cutting edge research in different parts of the world. Market penetration–driven favorable incentives now have to drive the commercialization of promising technologies. The authors are of the opinion that it is no longer

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necessary to follow a wait and watch approach for solar energy systems as many of these systems have passed that stage. One has to take concerted efforts to (1) customize systems based on geographical needs, (2) cost considerations, (3) long-term goals, and (4) institutional support. Solar energy systems are going to play a significant role in future energy portfolios regardless of the applications.

Acknowledgments The authors thank Prof. Wei-Yin Chen for the opportunity to make this contribution. Vaidyanathan Subramanian would like to thank the representatives of Konarka®, Dyesol®, and Inventux Technologies® for their time and contributions. He would also like to thank Prof. Misra and York Smith for their insights as well as the Department of Energy (Grant # DE-EE0000272) for the financial support.

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33 Solar Concentrators Anjaneyulu Krothapalli1 . Brenton Greska2 1 Department of Mechanical Engineering, Florida State University, Tallahassee, FL, USA 2 Sustainable Energy Technologies, LLC, St. Cloud, FL, USA Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1264 Solar Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1266 CSP Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1269 Parabolic Trough Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1269 Linear Fresnel Reflector Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1276 Dish-Stirling Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1279 Power Tower Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1282 Solar Chimney Power Plant Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1286 Nonimaging Concentrator Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1289 Concentrating Solar Power (Thermal) Systems Economics . . . . . . . . . . . . . . . . . . . . . . . . 1289 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1292

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_33, # Springer Science+Business Media, LLC 2012

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Abstract: In spite of several successful alternative energy production installations in recent years, it is difficult to point to more than one or two examples of a modern industrial nation obtaining the bulk of its energy from sources other than oil, coal, and natural gas. Thus a meaningful energy transition from conventional to renewable sources of energy is yet to be realized. It is also reasonable to assume that a full replacement of the energy currently derived from fossil fuels with energy from alternative sources is probably impossible over the short term. For example, the prospects for large-scale production of cost-effective renewable electricity remains to be generated utilizing either the wind energy or certain forms of solar energy. These renewable energies face important limitations due to intermittency, remoteness of good resource regions, and scale potential. One of the promising approaches to overcome most of the limitations is to implement many recent advances in solar thermal electricity technology. In this section, various advanced solar thermal technologies are reviewed with an emphasis on new technologies and new approaches for rapid market implementation. The first topic is the conventional parabolic trough collector, which is the most established technology and is under continuing development with the main focus being on the installed cost reductions with modern materials, along with heat storage. This is followed by the recently developed linear Fresnel reflector technologies. In two-axis tracking technologies, the advances in dish-Stirling systems are presented. More recently, the solar thermal electricity applications in two-axis tracking using tower technology is gaining ground, especially with multitower solar array technology. A novel solar chimney technology is also discussed for large-scale power generation. Non-tracking concentrating solar technologies, when used in a cogeneration system, offer low cost electricity, albeit at lower efficiencies – an approach that seems to be most suitable in rural communities.

Introduction Solar thermally generated electricity is a low cost solar energy source that utilizes complex collectors to gather solar radiation in order to produce temperatures high enough to drive steam turbines to produce electric power. For example, a turbine fed from parabolic trough collectors might require steam at 750 K and reject heat into the atmosphere at 300 K, thus having an ideal thermal (Carnot) efficiency of about 60%. Realistic overall conversion (system) efficiency of about 35% is feasible with intelligent management of waste heat. The solar radiation can be collected by different concentrating solar power (CSP) technologies to provide high-temperature heat. The solar heat is then used to operate a conventional power cycle, such as Rankine (steam engine), Brayton (gas turbine engine), or Stirling (Stirling engine) [1]. While generating power during the daytime, additional solar heat can be collected and stored, generally in a phase-change medium such as molten salt [2]. The stored heat can then be used during the nighttime for power generation. A simple schematic, shown in > Fig. 33.1, describes the main elements of such a system.

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The markets and applications for CSP dictate the category of the system and its components. Typically, the general categories considered by size are small ( Fig. 33.2. The efficiency of a solar collector field is defined as the quotient of usable thermal energy versus received solar energy. The power generation subsystem efficiency is the ratio of net power out to the heat input. The different CSP technologies that will be explored in the following sections are: parabolic trough, central tower receiver, dish-Stirling, linear Fresnel, and solar chimney. CSP technologies require sufficiently large (>5.2 kWh/m2/day) direct normal irradiance

Concentrating Solar Thermal Field

Thermal Energy Storage

Power Block

~

Electricity Waste Heat

. Fig. 33.1 Main components of a Concentrating Solar Power (CSP) system

Collec

Useful Energy Produced

tor sub

system

Power generation subsystem

Combined system

Operating Temperature

. Fig. 33.2 CSP system efficiency variation with operating temperature

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25 Initial SEGS plants 20 Largest SEGS plants

Advanced Concentrating Solar Power

15

10

0 & M cost reduction of SEGS plants Added value for green pricing

5

0 1985

Conventional cost of peak or intermediate power

1990

1995

2000

2005

2010

2015

2020

. Fig. 33.3 Levelized electricity cost (cents/kWh) projections of CSP (Source: SolarPACES)

(DNI), as opposed to PV technologies that can use diffuse, or scattered, irradiance as well [3]. The history of the Solar Electricity Generating Systems (SEGS) in the southwest desert of California [4], where DNI is quite favorable for CSP, shows impressive cost reductions as shown in > Fig. 33.3. These parabolic trough plants have been operating successfully for over 3 decades, thus providing valuable data. As indicated in the figure, the advanced concepts, with large-scale implementation and improved plant operation and maintenance, provide a great opportunity for further reductions in the levelized electricity cost (LEC), a topic that will be discussed later. Life-cycle assessment of emissions and land surface impacts of the CSP systems suggest that they are best suited for greenhouse gas and other pollutant reductions. CSP systems are also best suited, because of the effortless capture of the waste heat, for multigeneration applications, such as the simultaneous production of electricity and water purification. Because of rapid developments occurring both in technology and electricity market strategies, CSP has the greatest potential of any single renewable energy area. It also has significant potential for further development and achieving low cost because of its guaranteed fuel supply (the sun). In this chapter, a succinct review of the current technologies is given together with an assessment of their market potential. While describing some of the recent approaches in some detail, the activity around the world will also be included.

Solar Radiation The potential for CSP implementation in any given geographic location is largely determined by the solar radiation characteristics [3]. The total specific radiant power per unit area, or radiant flux, which reaches a receiver surface, is called irradiance, and it is measured in W/m2. When integrating the irradiance over a certain time period, it becomes solar irradiation and is measured in Wh/m2. When this irradiation is considered over the

Solar Concentrators

33

course of a given day, it is referred to as solar insolation, which has units of kWh/m2/day (= 3.6 MJ/m2/day). However, by assigning a number of useful solar hours in a given day the units simplify to W/m2. As such, the terms irradiance and insolation are typically used interchangeably. Solar radiation consists primarily of direct beam and diffuse, or scattered, components. The term ‘‘global’’ solar radiation simply refers to the sum of these two components. The daily variation of the different components depends upon meteorological and environmental factors (e.g., cloud cover, air pollution, and humidity) and the relative earth–sun geometry. The direct normal irradiance (DNI) is synonymous with the direct beam radiation, and it is measured by tracking the sun throughout the sky. > Figure 33.4 shows an example of the global solar radiation that is measured on two flat plates, one that is stationary and one that is tracking the sun. The measured DNI is also included, and its lower value can be attributed to the fact that it does not account for the diffuse radiation component [5]. In CSP applications, the DNI is important in determining the available solar energy. It is also for this reason that the collectors are designed to track the sun throughout the day. > Figure 33.5 shows the daily solar insolation on an optimally tilted surface during the worst month of the year around the world [6, 7]. Regions represented by darker shades of gray are most suitable for CSP implementation. The annual DNI value will also greatly influence the levelized electricity cost (LEC), which will be discussed later. Typical values

1200

Irradiance (W/m2)

1000

800

600

400 DNI Total Tracked Total Flat Plate

200

0 0

2

4

6

8

10

12

14

16

18

20

22

24

Hour

. Fig. 33.4 Solar irradiance variation within a day measured on a flat plate positioned horizontal and tracking the sun and direct normal irradiance (DNI). (Source: Edith Molenbroek, ECOFYS, 2008)

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of DNI at different latitudes and selected locations around the world are given in > Fig. 33.6 and > Table 33.1. Based on the information presented here, it can be seen that desert and equatorial regions appear to provide the best resources for CSP implementation.

1.0-1.9

2.0-2.9

3.0-3.9

4.0-4.9

5.0-5.9

6.0-6.9 Midpoint of zone value

. Fig. 33.5 The solar insolation (kWh/m2/day) on an optimally tilted surface during the worst month of the year (Source: http://www.meteostest.ch)

3,000 global horizontal irradiation direct normal irradiation DNI

2,500 CSP kWh/(m2 a)

1268

2,000 1,500 1,000 500 0

30

35

40

45

50

55

60

Latitude in °

. Fig. 33.6 Annual global irradiation in Europe and USA. (Source: Volker Quascning, DLR & Manuel Blanco Muriel, CIEMAT, Spain)

Solar Concentrators

33

. Table 33.1 Annual DNI at selected locations Location

Site latitude

Annual DNI (kWh/m2)

United States Barstow, California Las Vegas, Nevada Tucson, Arizona Alamosa, Colorado

35
N 36
N 32
N 37
N

2,725 2,573 2,562 2,491

Albuquerque, New Mexico EI Paso, Texas International Northern Mexico

35
N 32
N

2,443 2,443

26–30
N

2,835

Wadi Rum. Jordon Ouarzazate, Morocco Crete, Greece Jodhpur, India

30
N 31
N 35
N 26
N

2,500 2,364 2,293 2,200

CSP Technologies Parabolic Trough Technology This technology is comprised of relatively long and narrow parabolic reflectors with a single axis tracker to keep the sun’s image in focus on a linear absorber or receiver. This technology uses reflectors curved around the rotation axis (which is typically oriented north-south) using a linear parabolic shape, which has the property of collecting nearly parallel rays from the direct solar beam in a line image. A long pipe receiver can be placed at the focus for heating of heat transfer fluid (> Fig. 33.7). The receiver is normally a tube, which contains a heat transfer fluid or water for direct steam generation. The two major components of the collector subsystem are: the parabolic trough reflector, including its support structure, and the receiver, also referred to as the heat collector element. Important factors for the most-efficient parabolic trough reflector include the stability and accuracy of the parabolic profile, optical error tolerance, method of fabrication, material availability, and strength constraints. The geometry, length of the trough, the aperture, and rim angle will dictate the amount of heat collection. Since there are a large number of collector modules in a typical plant, the cost optimization requires minimizing: the material weight (steel or aluminum), the operations needed to manufacture the structure, and the assembly of the elements that compose the collector [8]. A typical modern structure using aluminum space frame technology to support the reflector is shown in > Fig. 33.8. These are considerably lighter per unit of aperture area compared to standard steel structures.

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All utility-scale parabolic trough installations to date have utilized silvered glass mirrors as reflectors (> Fig. 33.7). These reflectors are limited in size and are typically driven by manufacturing limitations, strength, handling, shipping, and installation issues. These parabolic trough modules will have between 20 and 40 mirrors mounted to a single space frame module. The mirrors are typically 4–5 mm thick and are mounted to the structural frame with bolted connections. Alternatively, a UV-stabilized mirror film (i.e., ReflecTechTM) laminated onto an aluminum substrate (> Fig. 33.8, right) provides a

Steel structure

Parabolic trough reflector Adsorber pipe

. Fig. 33.7 A typical parabolic trough system. (Source: http://www.abengoasolar.com)

. Fig. 33.8 Left: Parabolic trough space frame structure (Source: NREL); right: lightweight trough with reflective thin film mirror [9]

Solar Concentrators

33

reflectance of about 94% [9]. The weight of the modern reflective surface is about 3.5 kg/m2 versus 10 kg/m2 (2.1 lbf/ft2) for glass mirrors and allows for a lower initial cost. The receiver must achieve high efficiency with high solar absorptance, low thermal losses, and minimum shading. The receiver typically consists of a pipe with a solar selective coating encased in a glass tube throughout which there is a vacuum. The most commonly used thermal receiver is the SCHOTT PTR® 70 [10], shown in > Fig. 33.9, which has a highly selective absorber coating on a stainless steel tube that has an outside diameter of 70 mm. The tube is enclosed in a glass cylinder with vacuum insulation to minimize the long wave IR radiation and convection losses. The receiver tube supports are designed to minimize any receiver deflection and sunlight blockage. This particular configuration is in widespread use, but it has a number of drawbacks, which include the fact that it is difficult to maintain the vacuum seals, especially after welding, and, as has been observed, the heat transfer fluid and solar selective coating off-gas hydrogen into the vacuum tube, thus negating the convection reducing effects of the tube. The typical thermal conversion efficiency (net heat collected/incident solar radiation over the trough aperture area) for a parabolic trough is shown in > Fig. 33.10 for the PT-1 concentrator [11]. The efficiency is largely affected by the collector thermal and optical losses. Since the radiation losses are proportional to the fourth power of the temperature, the efficiency decreases rapidly with increasing working fluid temperature. The nominal operating temperature of many plants (e.g., SEGS) is about 400
C (350
C above ambient) operating at a thermal conversion efficiency of about 50% at best. The trend over the last 25 years has been to make larger collectors with higher concentration ratios in order to improve the collector thermal efficiency. However, due to increased material manufacturing and installation costs of the large aperture (>6 m) troughs, the LEC still remains high for widespread implementation. The concentrating parabolic trough systems typically produce power based on the Rankine cycle, which is the most fundamental and widely used steam-power cycle.

Durable glass-to-metal seal material combination with matching coefficients of thermal expansion

AR-coated glass tube ensures high transmittance and high abrasion resistance

New absorber coating achieves emittance ≤10% and absorptance ≥95% Vacuum insulation minimized heat conduction losses Improved bellow design increased the aperture length to more than 96%

. Fig. 33.9 Schott PTRTM 70 receiver (Source: http://www.schottsolar.com)

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Trough Efficiency vs. Operating Temperature

90

Thermal Efficiecny, %

80 70 60 50 40 30 20 10 0 0

50 100 150 200 250 Collector Temperature above Ambient, C⬚

300

. Fig. 33.10 The variation of the thermal efficiency of a parabolic collector with operating temperature [11]

The cycle starts with superheated steam generated by the heat collected from the parabolic trough field. The superheated vapor expands to lower pressure in a steam turbine that drives a generator to convert the work into electricity. The turbine exhaust steam is then condensed and recycled as the feed water for the superheated steam generation to begin the cycle again. The simple steam cycle thermodynamic efficiency can be as high as 35%. Considering that the generator sets are better than 90% efficient in converting the shaft power into electricity, it is expected that the cycle can produce electricity at an efficiency in excess of 30%. As such, the total combined plant efficiency (solar to electricity) is best estimated to be about 15%. The SEGS system experience shows that the annual solar to electric efficiency varies from 10.7% to 14. 6%, with the higher number corresponding to the case where thermal storage is included in the plant. Although the plant efficiency appears low when compared to conventional fossil fuel based plants, the operation and maintenance (O&M) costs are negligible due to the absence of any fuel costs, thus making the LEC largely depend on the capital costs. It is useful to think in terms of the cost/ efficiency ratio to determine the viability of the CSP plant. Although much of the recent effort is on increasing the efficiency of the plant, it is more useful to find ways to reduce capital costs, thereby reducing the LEC. Hence, the following is a discussion assessing the components costs for a parabolic trough plant. > Figure 33.11 gives a breakdown of the investment costs associated with a typical parabolic trough plant utilizing the Rankine steam cycle [12]. As the pie chart indicates, the majority of the initial investment cost is associated with the solar field. Much progress has been made recently with the introduction of lightweight space frame structure designs and the development of efficient highly reflective film [13], such as ReflecTechTM and 3MTM Solar Mirror Film 1100 [14]. The heat transfer fluid (HTF) system moves the heat

Solar Concentrators

33

from the solar field to the power block, and it requires an HTF with the following properties: high-temperature operation with high thermal stability, good heat transfer properties, low energy transportation losses, low vapor pressure, low freeze point, low hazard properties, good material compatibility, low hydrogen permeability of the steel pipe, and economical product and maintenance costs. As a result, synthetic organic HTFs are most suitable for the parabolic trough plants. For example, SYLTHERMTM 800, a high-temperature HTF by Dow Chemical Company, can be used in liquid form up to 400
C and meets many of the requirements delineated above [15]. The last of the major components is the power block, which consists of a conventional steam-turbine-based system, the costs of which are well established and a number of new players from China and India have made the prices quite competitive. Any significant reduction in the cost of any of these three major components will result in a lower LEC for CSP systems. The most recent 64 MW (nominal) installation in Nevada (Nevada Solar One), shown in > Fig. 33.12, uses 5.77 m aperture parabolic troughs with SCHOTT PTR®70 receivers, resulting in a geometric concentration ratio of 26. The total solar field is 357,200 m2, and the plant site area is 1.62 km2. Field inlet and outlet temperatures are 300
C and 390
C, respectively. The solar steam turbine inlet temperature is about 371
C at 86.1 bar.

Solar Field 45% 3%

HTF System Power Block

18%

Balance of Plant 7%

7% 7%

13%

Services Other Site work

. Fig. 33.11 Typical cost breakdown of a parabolic trough SEGS plant

. Fig. 33.12 Left: Parabolic trough field; right: power block at Nevada Solar One power plant (Source: www.acciona-na.com)

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The plant uses a supplementary gas heater to provide 2% of the total heat requirement. The plant produces about 134  106 kWh of electricity annually, which yields a plant capacity factor of about 0.24. Coal power plants have a capacity factor on the order of 0.74, and as such they can produce the equivalent electricity output from a 21 MW plant. The solar to electricity efficiency of the plant (> Fig. 33.13 shows the plant schematic) is estimated to be 14.6% based on the annual DNI of 2,573 kWh/m2. The CO2 emissions reduction (as compared to an equivalent coal plant) is estimated to be about 100,000 MT/year. A typical electricity production in a day is depicted in > Fig. 33.14, where the hourly DNI variation is also displayed. The total installed cost of the project was $266 million resulting in a nominal price of about $4.15/W. With medium temperature (250–300
C) parabolic troughs and advanced receiver designs, it is anticipated that the installed costs may reach as low as $2.50/W, thus making the parabolic trough systems competitive with many other renewable energy solutions. The ability to provide near-firm power through the use of thermal energy storage is gaining prominence. This characteristic differentiates CSP from PV technology, as the utilities can tailor the use of CSP electricity as needed. The thermal storage can also provide more uniform output over the day and increase annual electricity generation, thereby increasing the plant capacity factor. For example, while solar energy availability

Solar collectors

Flow of heat transfer fluid

ed id eat r h fer flu a l So rans tt hea

Supplementary gas heater

Super heated steam

Turbine

Solar superheater Water flow

Steam & water

1274

Steam generator Condenser Cooling tower Cooling water

. Fig. 33.13 Nevada Solar One plant schematic (Source: www.acciona-na.com)

Electric generator and transformer

Solar Concentrators

33

peaks at noon, demand peaks in the late afternoon when the energy from the sun is already going down. > Figure 33.15 shows a parabolic trough plant schematic with molten salt thermal storage incorporated [16]. A high-temperature thermal energy storage option has been developed for parabolic troughs that use molten nitrate salt as the storage medium in 80

1000

70

900 800

60

700 600 JUNE 12, 2007

40

500 400

30

W/m2

M We

50

300

20

200

10

100 0 7:30 PM

0 7:00 AM

9:30 AM

12:00 PM

Production Mwe

12:30 PM

5:00 PM

Directive Normal Incidence

. Fig. 33.14 Nevada Solar One electricity output and DNI for a typical summer day (Source: www.acciona-na.com)

solar collector field

flow of heat transfer fluid

steam steam turbine

htf-salt heat exchanger

hot salt tank

cold salt tank

solar evaporator

condenser

deaerator

. Fig. 33.15 A schematic of a parabolic trough plant with added thermal storage [16]

cooling system

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33

Solar Concentrators

a two-tank system; it has an oil-to-salt heat exchanger to transfer thermal energy from the solar field to the storage system [17]. A more desirable option under development is an advanced heat transfer fluid (HTF) that is thermally stable at high temperatures, has a high thermal capacity, a low vapor pressure, and remains a liquid at ambient temperatures. The effect of storage to follow the utility system demand is clearly depicted in > Fig. 33.16. When compared to the data shown in > Fig. 33.14, where the electricity supply follows closely with the sun’s energy, the storage extends the availability of electricity through evening hours. The performance of SEGS plants, the successful development of Nevada Solar One, and the progress made by industry innovations have greatly increased interest in utilityscale CSP projects in the USA and Europe. Abengoa Solar’s proposed 250 MW Solana parabolic trough plant provides an example of the potential of this technology [18].

Linear Fresnel Reflector Technology

1.8

900

1.6

800

1.4

700

1.2

600

1.0

500

0.8

400

0.6

300

0.4

200

0.2

100 0

0.0 1

2

3

4

5

6

7

8

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Hour Ending

Relative Value of Generation

Trough Plant with 6 hours Thermal Energy Storage Solar Radiation

. Fig. 33.16 The effect of storage on utility load during a typical day [16]

Solar Resources (W/m2)

Fresnel lenses are used as solar concentrators where the reflector is composed of many long row segments of flat mirrors, which concentrate beam radiation onto a fixed receiver, located at few meters height, running parallel to the axis of rotation of the mirrors (> Fig. 33.17). Linear Fresnel follows the principles of parabolic trough technology, but replaces the curved mirrors with long parallel lines of flat, or slightly curved, mirrors. Unlike, parabolic troughs where the aperture is limited to few meters, a large aperture can be achieved by the linear Fresnel reflector at low cost. Although the original idea is quite old [19, 20], only recently has this concept been brought to fruition by two teams in Australia and Belgium. The concentration ratios used in this system are quite similar to

Utility Load, Trough Plant Output

1276

Solar Concentrators

33

those achieved using parabolic troughs (10–80). Hence, the operating temperatures are also in the same range of the parabolic trough systems: 250–400
C. A picture of the Solarmundo prototype system [21] erected in Liege, Belgium, is shown in > Fig. 33.18. The collector area is 2,500 m2 (25 m wide and 100 m long), and the absorber tube has an

Sun rays Second stage reflector Primary fresnel reflectors Absorber tube

. Fig. 33.17 The principle of a typical Fresnel collector [21]

. Fig. 33.18 2,500 m2 reflected area Fresnel concentrator prototype in Belgium [21]

1277

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outer diameter of 18 cm and it is covered with a black nonselective coating. However, in order to achieve satisfactory thermal performance, a highly selective absorber coating that is stable at high operation temperatures must be applied. A 1 MW (peak) thermal pilot plant, similar to the prototype, was built at PSA in Almeria, Spain. In the pilot plant water flows through the absorber tube in order to produce steam (as in a conventional power plant), which is then converted into electrical energy through the use of a steam turbine. A 5 MWe Compact Linear Fresnel Reflector (CLFR) power plant was built by Ausra in California as a demonstration plant [22] (> Fig. 33.19). The solar-field aperture area was 26,000 m2, with three lines, each 385 m length with a mirror width of 2 m. The plant produces 354
C superheated steam at 70 bar. The CLFR utilizes multiple absorbers, which is an alternate solution to the Linear Fresnel Reflector (LFR) where only one linear absorber on a single linear tower is used. This prohibits any option of the direction of orientation of a given reflector. Therefore, if the linear absorbers are close enough, individual reflectors will have the option of directing reflected solar radiation to at least two absorbers. This additional factor gives potential for more densely packed arrays, since patterns of alternative reflector inclination can be set up such that closely packed reflectors can be positioned without shading and blocking. The main advantages of linear Fresnel are its lower investment and operational costs. Firstly, the flat mirrors are cheaper and easier to produce than parabolic curved reflectors and so are readily available from manufacturers worldwide. The structure also has a low

. Fig. 33.19 The Ausra 5 MW Kimberlina solar thermal demonstration plant (Source: http://www.ausra. com)

Solar Concentrators

33

profile, with mirrors just 1 or 2 m above ground. This means the plant can operate in strong winds, and it can use a lightweight, simple collector structure. Although the technology offers a simpler and more cost-effective solution, it has not been tested long enough to determine its viability as an alternative to parabolic trough technologies.

Dish-Stirling Technology Dish-Stirling systems are relatively small units that track the sun and focus solar energy onto a cavity receiver at the focal point of the reflector, where it is absorbed and transferred to a heat engine/generator. The ideal concentrator shape is a paraboloid of revolution (> Fig. 33.20, left). Some concentrators approximate this shape with multiple spherically shaped mirrors supported with a truss structure (> Fig. 33.20, right). An engine based on the Stirling cycle is most commonly used in this application due to its use of an external heat supply that is indifferent to how the heat is generated [23]. Hence, it is an ideal candidate to convert solar heat into mechanical energy. The high-efficiency conversion process involves a closed cycle engine using an internal working fluid (usually hydrogen or helium) that is recycled through the engine. The working fluid is heated and pressurized by the solar receiver, which in turn powers the Stirling engine. Stirling engines have decades of recorded operating history. For over 20 years, the Stirling Energy System [24] dish-Stirling system has held the world’s efficiency record for converting solar energy into electricity with a record of 31.25% efficiency. Their size typically ranges from 1 to 25 kW with a dish that is 5–15 m in diameter. Because of their size, they are particularly well suited for decentralized applications, such as remote stand-alone power systems.

Stirling Engine and Alternator Receiver

Concentrator

. Fig. 33.20 Left: Euro Dish (Source: http://www.sbp.de); right: SAIC-Sandia dish (Source: http://www. energylan.sandia.gov/)

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Solar Concentrators

One of the most advanced dual axis tracking parabolic dish-Stirling systems is manufactured by Stirling Energy Systems (SES), and it produces 25 kWe peak power (at 1,000 W/m2 DNI) [24]. This unique design uses a radial solar concentrator dish structure that supports an array of curved glass mirror facets as shown in > Fig. 33.21. The dish has a diameter of about 11.6 m (glass surface area 90 m2), which results in a concentration ratio of about 7,500. The heat input from the sun is focused onto solar receiver tubes (at a focal length of 7.45 m) that contain hydrogen gas. The solar receiver is an external heat exchanger that absorbs the incoming solar thermal energy. This heats and pressurizes the gas in the heat exchanger tubing, which in turn powers the Stirling engine at a typical operating temperature of about 800
C. A generator that is connected to the engine then provides the electrical output. Waste heat from the engine is transferred to the ambient air via a radiator system similar to those used in automobiles. The gas is cooled by a radiator system and is continually recycled within the engine during the power cycle. The solar energy to electricity peak conversion efficiency is reported as 31.25%. A much smaller 3 kWe advanced parabolic dish-Stirling system is manufactured by Infinia (> Fig. 33.21). The single free piston Stirling engine uses helium in a hermetically sealed system, thereby avoiding maintenance issues generally associated with moving parts. The solar to electric peak efficiency is reported to be around 24%. Dish-Stirling systems are quite flexible in terms of size and scale of deployment. Owing to their modular design, they are capable of both small-scale-distributed power output

. Fig. 33.21 Left: SES Sun CatcherTM (Source: http://www.stirlingenergy.com/); right: Power DishTM by Infinia (source: http://www.infiniacorp.com)

Solar Concentrators

33

and large, utility-scale projects. Although dish-Stirling systems have been tested and proven for over 2 decades with no appreciable loss in the key performance criteria, there were no utility-scale plants in operation until very recently. Within the past year, 60 SES SunCatcherTM systems were installed as part of the Maricopa Solar demonstration plant in Arizona (> Fig. 33.22). The plant is currently operational, and it is capable of producing 1.5 MWe. Two other plants in California, totaling over 1.4 GW, are slated to begin construction soon using thousands of the SES systems. A similar 1 MW system is under construction in Villarobledo, Spain, using the Infinia 3 kW units [25]. The successful installation and operation of these dish-Stirling systems in a scale beyond a handful of units will demonstrate their technical viability for the large-scale utilityscale plants. Unlike steam cycles, this technology uses no water in the power conversion process; a key benefit compared to other CSP plants. Current installed cost for the dish-Stirling systems at demonstration scale, with few units (mostly built in semiautomated manufacturing facilities) is about $6,000/kW. This cost is approximately distributed with 40% in the concentrator and controls, 33% in the power conversion unit, and the remaining 27% of the costs in the balance of plant and installation of the system. Mass production techniques, such as those employed at the automotive scale, will provide great cost benefits to these systems. With the economies

. Fig. 33.22 Top: 1.5 MW Maricopa Solar installation (source: http://www.srpnet.com/ maricopasolar); Bottom: 1 MW solar installation in Villarrobledo, Spain (Source: http://www.infiniacorp.com)

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of scale in their favor and because of higher solar to electricity efficiency (25–30%), the dish-Stirling systems will become competitive with the photovoltaic and parabolic trough systems. However, unlike the parabolic trough systems, the 20-year life-cycle costs of these systems are yet to be determined.

Power Tower Technology The solar central receiver power tower is a concept that has been under study both in the USA and Spain over the last three decades. This technique utilizes a central power tower that is surrounded by a large array of two-axis tracking mirrors – termed heliostats – that reflect direct solar radiation onto a fixed receiver located on the top of the tower. The typical concentration ratio for this approach is in excess of 400. Within the receiver, a fluid transfers the absorbed solar heat to the power block where it is used to generate steam for a Rankine cycle steam engine-generator. Until recently, the largest demonstration plant employing this technology was the 11.7 MWe ‘‘Solar One’’ plant in Barstow, California (> Fig. 33.23) that was constructed and operated in the 1980s. Solar One operated at a nominal temperature of 510
C, and it had a peak solar to electric efficiency of about 8.7%. In the 1990s, Solar One was converted to ‘‘Solar Two’’ through the addition of additional heliostats and a two-tank molten salt storage system to improve the capacity factor of the system [26]. Two important components of the power tower technology are the heliostats and the receiver. Heliostats are the most important cost element of the power tower plant, and they typically contribute to about 50% of the total plant cost. Consequently, much attention has been paid to reduce the cost of heliostats to improve the economic viability of the plant. The most commonly used design is the two-axis sun-tracking pedestalmounted system as shown in > Fig. 33.24. A heliostat consists of a large mirror with the motorized mechanisms to actuate it, such that it reflects sunlight onto a given target throughout the day. A heliostat array is a collection of heliostats that focus sunlight continuously on a central receiver. A 148 m2 ATS glass/metal heliostat has successfully operated for over 20 years at the National Solar Thermal Test Facility in Albuquerque, USA, without much degradation of the beam quality. It has also survived high winds in excess of 40 m/s. Depending upon the production rates, the installed price of the ATS heliostat was estimated to be between $126 and $164 per square meter [27] With increasing installations, the estimated installation price will be around $90/m2. The Sandia study also suggests that large heliostats are more cost efficient than small ones on a cost per square meter basis [27]. A relatively new facility that began operation in 2006 is the PS10 solar power tower in Spain [28]. The main goal of the PS10 project was to design, construct, and operate a power tower on a commercial basis and produce electricity in a grid-connected mode. This 11 MWe facility generates about 23,000 MWh of grid-connected electricity annually at an estimated solar to electricity efficiency of about 15%. However, it should be noted that the plant also uses natural gas for 12–15% of its electricity production. The solar

Solar Concentrators

Hot Salt Storage Task

33

565 °C Cold Salt Storage Task

290 °C

Steam Generator Conventional EPGS

. Fig. 33.23 Top: Solar One/Two central solar tower receiver plant; Bottom: Schematic of the plant’s major components. (Source: USDOE)

radiation is concentrated through the use of 624 reflective heliostats, each of which has a 121 m2 curved reflective surface, arranged in 35 circular rows, as shown in > Fig. 33.25. As a result, the total reflective surface is 75,216 m2. The heliostats concentrate the solar radiation to a cavity receiver that is located at the top of a 115 m high tower. The cavity receiver is basically a forced circulation radiant boiler designed to use the thermal energy supplied by the concentrated solar radiation flux to produce more than 100,000 kg/h of saturated steam at 40 bar and 250
C. The saturated steam is then sent to the turbine where it expands to produce mechanical work and electricity. For cloudy

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Solar Concentrators

. Fig. 33.24 Typical advanced heliostat field (Source: Plataforma Solar de Almeria – PSA, Spain)

transient periods, the plant has a saturated water thermal storage system with a thermal capacity of 20 MWh, which is equivalent to an effective operational capacity of 50 min at 50% turbine workload. This is a relatively short storage time, partially because the tower uses water rather than molten salt for heat storage. The water is held in thermally clad tanks and reaches temperatures of 250–255
C (instead of around 600
C for systems using salt). The investment cost of the PS10 plant was about 35 million Euros, thus resulting in an installed cost of about 3,000 Euros per kWe.. Of this cost, the heliostat cost was reported to be about 140 Euros/m2. From this experience, it appears that about 30% of the total installed cost of a solar power tower goes toward the heliostat expense. A second-generation plant, referred to as PS20, has twice the PS10 output (20 MW), with 1,255 two-axis sun-tracking heliostats. The receiver is located on top of a 165 m tower, and it utilizes the same technology as that of PS10 for electricity generation. The new plant features include control and operational systems enhancements, an improved thermal energy storage system and a higher efficiency receiver. A utility-scale 400 MW solar tower power project, referred to as the ‘‘Ivanpah Solar Power Complex,’’ is being built in California by a consortium led by Bright Source Energy, and it is expected to be operational in 2012 [29]. The heliostats in this project will consist of smaller flat mirrors, termed the LPT 550, each having a reflecting area of 14.4 m2. 50,000 of these LPT 550 heliostats will be required for every 100 MW of installed capacity. The receiver is a traditional high-efficiency boiler positioned on top of the tower. The boiler tubes in the receiver are coated with a solar selective material that maximizes energy absorbance, and there are sections within the receiver for steam generation, superheating, and reheating. This results in the generation of superheated steam at 550
C and 160 bar (unlike the saturated steam that is produced in the PS10 and PS20). The power block

Solar Concentrators

Solar receiver

Steam drum

Steam 40 bar, 250°C

Turbine

33 Generator 11.0 MWe

Steam storage system Condensator 0,06 bar, 50°C Heliostat field

. Fig. 33.25 PS10 11 MW Central Receiver Tower project in southern Spain. Top: plant schematic; Bottom: the PS10 plant aerial picture (Source: Abengoa Solar)

consists of a conventional Siemens steam turbine generator with a reheat cycle, and auxiliary functions of heat rejection, water treatment, water disposal, and grid interconnection capabilities. The technology demonstration plant, as shown in > Fig. 33.26, has 1,641 heliostats (reflecting area 12,000 m2) with each measuring 2.25 m  3.21 m (7.22 m2). The tower height was 75 m (60 m tower plus 15 m receiver), and the thermal energy collected by the receiver was between 4.5 and 6 MWth.. Because of the higher operating temperature, the solar to electrical efficiency of these plants is expected to be about 20%. Although there is not yet any experience with utility-scale plant installations, it appears that the installation cost of these plants may be in the range of $3,000/kWe.

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. Fig. 33.26 The LPT 550 central receiver tower demonstration plant in Israel’s Negev desert. Left: heliostat field with central tower, right: 7.22 m2 heliostat (Source: Brightsource energy)

In an attempt to bring down the installed cost of the solar power plant technology, eSolar, a California company introduced a modular/distributed tower design with a 1-m2 reflected area heliostat [30]. These much smaller heliostats, with fully automated two-axis sun tacking system, are easy to assemble and install in large numbers. Each central tower unit is capable of producing 2.5 MWe through the use of 12,000 mirrors that reflect the radiation onto a 47 m high tower. The thermal receiver in the tower has external evaporator panels for producing superheated steam at 440
C and 60 bar. > Figure 33.27 shows a technology demonstration plant with two-tower system that nominally produces 5 MWe of electricity. Since the performance details of the plant are not disclosed in any public domain, it is difficult to assess the solar to electric efficiency and the installed plant cost. In principle, the smaller heliostats are easy to manufacture, install, and maintain. However, the solar energy collection may involve significant losses due to spillage reaching the thermal receiver. Hence, it is important to study the pilot plant performance characteristics before a utility-scale plant design is considered.

Solar Chimney Power Plant Technology A solar chimney power plant has a high chimney (tower) that is surrounded by a large collector roof made of either glass or resistive plastic supported on a framework

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(> Fig. 33.28) [31]. Toward its center, the roof curves upward to join the chimney, thus creating a funnel. Solar radiation (direct and diffuse) strikes the collector and transmits part of its energy that heats up the ground and the air underneath the collector roof. At the ground surface, part of the transmitted energy is absorbed and the rest is reflected back to the roof, where it is subsequently reflected to the ground. The multiple reflections

. Fig. 33.27 5 MW twin central receiver tower facility with 1 m2 heliostats in California (Source: eSolar)

Sun Solar radiation G

Turbine

Htower Solar chimney SC

Collector area CA

Ground Dcoll

Turbine

Generator coupled to the turbine PCU

. Fig. 33.28 Left: An artist rendering of a 5 MW solar chimney plant (Source: http://www.sbp.de); right: a schematic indicating the main components of the plant [31]

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result in a higher fraction of energy absorbed by the ground. The warm ground surface heats the adjacent air through natural convection. The buoyant air follows the upward incline of the roof until it reaches the chimney, thereby drawing in more air at the collector perimeter. The natural and forced convection set up between the ground and the collector flows at high speed through the chimney and drives wind generators at its bottom. As the air flows from the collector perimeter toward the chimney, its temperature increases, while the velocity remains constant due to the increasing collector height at the center as shown in the schematic (> Fig. 33.28). The pressure difference between the outside cold air and the hot air inside the chimney causes the air to flow through the turbine. The ground under the collector roof behaves as a storage medium and can even heat up the air for a significant time after sunset. The efficiency of the solar chimney power plant is below 2% and depends mainly on the height of the tower. As a result, these power plants can only be constructed on land that is very cheap or free. Such areas are usually situated in desert regions. However, this approach is not without other uses, as the outer area under the collector roof can also be utilized as a greenhouse for agricultural purposes. A 200 m-high solar chimney demonstration plant base was constructed in Manzanares, Spain [32]. The peak power output of this demonstration plant was 50 kW, and it operated for over 8 years without any significant degradation in performance. However, as with other CSP plants, the minimum economical size of the solar chimney power plant is in the several MW range. Although no pilot plant has been built to demonstrate the viability of this technology in the MW range, computer simulations suggest its promise as a low-cost solar thermal technology. > Figure 33.29 shows the results from a simulation of a large-scale solar chimney power plant with a 5,000 m collector diameter ( 20 km2 area), and a chimney height of 1,000 m and inside diameter

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. Fig. 33.29 Simulated results of electrical power output of solar chimney power plant during summer and winter [31]

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. Fig. 33.30 Ray tracing diagrams for the Winston Series CPC. Left – incoming light rays directly overhead; right – incoming light rays at the acceptance angle of the design. (Source: www. soalrgenix.com)

of 210 m [31]. With the vast expanse of unpopulated land in Australia, it may be possible to economically erect a solar chimney plant of this size.

Nonimaging Concentrator Technology All of the concentrating technologies discussed thus far require some type of active solar tracking in order to account for the change in the elevation of the sun on any given day and throughout the year. Nonimaging concentrators, such as the compound parabolic concentrator (CPC), allow for the use of a non-tracking stationary concentrator that can account for the daily and annual excursion in solar elevation [33]. > Figure 33.30 illustrates how the light rays in a commercial CPC collector are concentrated when the source is directly overhead (left), such as solar noon on the equinox, and when it is at the acceptance angle of the CPC design (right), such as would be observed during the solstice. The stationary benefit of the CPC comes at the expense of a concentration ratio of 2 for the design. This is an order of magnitude lower than what can be achieved through the use of a parabolic trough, but it is twice that of a typical flat-plate collector. As such, the CPC design is capable of producing sensible heat at temperatures well in excess of 120
C, thus making it a good candidate for use with an absorption refrigeration system. It can also be paired with a low temperature power cycle, such as an organic Rankine cycle, to generate electricity. The resulting system would be fairly inefficient when compared to a dishStirling system, but it would have a cost-to-efficiency ratio that would make it attractive for use in rural areas.

Concentrating Solar Power (Thermal) Systems Economics The concentrating solar power (CSP) for electricity generation technologies examined in the previous sections are the most dominant and have the greatest potential for

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commercialization. Current projects are targeted so that they meet specific needs at an economic benefit. Once success is achieved, the price points will come down and good economics will drive the CSP projects. The following discussion is included here to indicate that CSP is becoming more economically attractive. Component manufacturers, utilities, and regulators are making decisions now that will determine the scale, structure, and performance of the CSP industry. Since each country’s approaches to the renewable electricity industry is different, only the observations that are more common globally are included here. When considering the economic viability of CSP, often the levelized electricity cost (LEC) is calculated and compared among different technologies. Therefore, in the following, a general method is given for determining LEC. The LEC is dependent on many variables related to the site, technology chosen, and the plant financing. The LEC is defined as [34]: LEC ¼

CRF  KI þ KOM þ KF E

where CRF ¼

k d ð1 þ k d Þn þ ki ð1 þ k d Þn  1

CRF: Capital Recovery Factor; KI: total investment of the plant; KOM: annual operation and maintenance costs; KF: annual fuel costs (any fossil fuel, such as natural gas); E: annual net electricity revenue; kd: debt interest rate; n: depreciation period in years (30); ki: annual insurance rate (1%). The many factors that determine the LEC vary greatly due to government subsidies, tax incentives, and annual net electricity production. One of the key parameters in the above formula is the determination of the annual electricity generation, which depends largely on the available DNI at the plant location. For example, > Fig. 33.31 shows the impact of the annual DNI on the annual power generation and the LEC of a 50 MWe parabolic trough SEGS type power plant with a 375,000 m2 solar field. The economic parameters (e.g., discount rate of 6.5%, solar field costs of 200 Euro/m2, power block costs of 1,000 Euro/kW, and O&M costs of 3.7 million Euro per annum) have been kept constant [35]. Although, some of the financial data may be outdated, the intent here is simply to show that the annual electricity generation is approximately proportional to the DNI. This suggests that a careful analysis needs to be carried out for the determination of an economically optimized project site that not only depends on the solar irradiance (DNI), but on many other influencing parameters. The present evaluation estimates (> Fig. 33.32) from a number of sources is that the LEC for CSP systems, shown here as cost of electricity (COE), will be around $0.15–0.20/kWh, assuming a load demand between 9:00 am and 11:00 pm. However, the absolute cost data on many of the CSP systems considered here, and those planned for commercial deployment around the world, is largely unavailable, so these numbers must be considered with some caution. Cost reductions due to technological improvements, such as the implementation of

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. Fig. 33.31 The variation of annual electricity generation and LEC for a 50 MWe parabolic trough plant with a 375,000 m2 solar field for fifty chosen sites [35] 85

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. Fig. 33.32 The variation of the LEC for concentrating solar thermal power (Source: National Renewable Energy Laboratory, USA)

thermal storage, and large-scale deployment are estimated to be around 10–30% for parabolic trough systems, 20–35% for central receiver systems, and 20–40% for dish-Stirling systems [33]. Given the rapid deployment of CSP systems, it is suggested that within the next 5 years, the LEC will be $0.10–0.15/kWh. With the additional benefit of carbon credits,

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CSP technology is poised to become the dominant solar electricity generating plant development in places where there is good DNI.

Summary and Conclusions Concentrating solar thermal power (CSP) is a proven technology, which has significant potential for further development and achieving low cost. The history of the Solar Electricity Generating Systems (SEGS) in California demonstrates impressive cost reductions achieved up to now, with electricity costs ranging today between $0.10 and $0.15/kWh. Advanced technologies, mass production, economies of scale, and improved operation will allow for a reduction in the cost of solar produced electricity to a competitive level within the next 5–10 years. Hybrid solar-and-fuel plants, at favorable sites, making use of special schemes of finance, can already deliver competitively priced electricity today. With over 2 decades of experience, parabolic trough technology is mature enough that its investment cost estimates can be made with confidence. Given the rapid growth contemplated within the immediate future (mostly in the southwest USA) and medium temperature CSP systems (250–300
C), it is very likely that the LEC price target of $0.10/kWh may well be met within the next 3 years using the parabolic trough technology. When the parabolic trough technology is combined with biomass gasification in a hybrid system, the overall plant efficiency will be substantially increased, thus resulting in a relatively low LEC. This is an approach that is ideally suited for regions of moderate DNI (5.2–5.5 kWh/m2/day) and for distributed power applications (1–5 MW power plants). A greater opportunity lies in the thousands of niche markets that are primed for smaller scale (1–10 MW) parabolic trough projects at a lower cost. The central receiver tower (CRT) systems are being pursued aggressively by a number of companies with approaches that mostly differ in the heliostat size. The distributed approach with multiple towers appears to gain prominence because of their lower installation costs. Both parabolic trough and central tower systems benefit from heat storage, especially when the power demand is during off-peak solar hours. The CRT systems are best suited in areas of good annual solar insolation (>2,000 kWh/m2/year) and utility-scale plant sizes (>50 MW). Because of the steam cycle used in the power block, the water availability can be an issue, especially in desert regions. The problem can be overcome by the use of an air-cooling system, which will have the adverse effect of reducing the overall plant efficiency. The recent advances made in dish-Stirling systems in improving their solar to electric efficiency in the range of 30% make them attractive for utility-scale power plant implementation. Because of their small unit electricity output ( Fig. 34.1) is installed in the USA (25 GW) and in the EU (about 65 GW), followed by China (12 GW) and India (10 GW). Wind energy deployment has been increasing rapidly throughout the past decade, recording growth rates of around 30% since 1996 (> Fig. 34.2). More than half of the 2008 additions occurred in the USA and in China (> Fig. 34.3), with the USA overtaking Germany as the leader in installed wind capacity. Measurements from numerous surface and balloon-launch monitoring stations suggest that the global technical potential from onshore wind energy exceeds current world electricity demand. Using global grid-cell data, Hoogwijk et al. [6] undertake a detailed assessment of: 1. The theoretical potential (the energy content of global wind). 2. The geographical potential of onshore wind. Hoogwijk et al.’s assessment excludes land areas with wind speeds below 4 m/s (if the cutoff point had been 6 m/s, areas with current wind turbine installations would have been excluded). It also excludes areas

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. Fig. 34.1 Installed wind power capacity by region (Compiled from [5, 15]). *Asia excludes China and India

unavailable for turbine installation, such as nature reserves and areas with other functions, and urban areas and high altitudes above 2,000 m with low air density. For further details, Table 1 in [6] provides suitability factors, which shows the percentage of a land area available for wind turbine installation. 3. The technical potential (extrapolating wind data to hub height, considering wake effects and realistic power densities in MW/km2, applying average capacity factors, subtracting downtime). 4. The economic potential, given the cost of alternative sources (calculating rated turbine power optimized for grid-cell wind conditions, regressing capital cost and turbine output as a function of rated power and an economies-of-scale factor). While the theoretical onshore potential exceeds humankind’s energy consumption by a few 100-fold, Hoogwijk et al. [6] estimate the technical potential to be about 100 PWh/ year, and the economic potential at cost below 7 US¢/kWh to be about 20 PWh/year, both of which still exceed current global electricity consumption. This is consistent with previous studies ([7], and references listed by [6] in their Sect. 7.2). However, most

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. Fig. 34.2 Historical development of installed wind power capacity, and annual growth rates (Compiled from [5, 15])

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. Fig. 34.3 Regional shares of added capacity in 2008 (After [5])

of the economic onshore potential – 15 PWh/year – is concentrated in a few remote regions (> Fig. 34.4), namely, the north of Canada (8 PWh/year), Patagonia (4 PWh/year), Siberia (2 PWh/year), and the coastal regions of Australia (1 PWh/year). Only about 5 PWh/year overlaps with regions of significant electricity consumption, the central US

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Excluded areas Costs above 0.25 $/kWh Costs below 0.25 $/kWh Costs below 0.15 $/kWh Costs below 0.10 $/kWh

Costs below 0.06 $/kWh

. Fig. 34.4 The economic potential of onshore wind power (After [6])

(3 PWh/year), Western Europe (1 PWh/year), and Central America (1 PWh/year). Relatively small potential is found in Africa, South Asia, and South East Asia. The regional technical potentials given by Hoogwijk et al. [6] are confirmed in studies on the USA [8], India [9], and China [10]. Hoogwijk et al. [6] do not include any grid integration, transmission, and distribution issues in their assessment, which is instead dealt within their later publication [11]. The resolution of their global assessment is also such that it cannot account for specific circumstances at the small-region geographical level. In India, for example, the technical potential is further limited by transmission capacity of the grid [9]. Offshore potential is estimated to be even higher (see [12]), but reliable wind data are often lacking [6]. Offshore wind power is currently seen as more expensive than onshore wind, but at higher penetration rates in the longer term could offer more benefits than onshore because of its more level output, and its proximity to large coastal cities [13]. The later assessment of wind by Hoogwijk et al. [11] takes into account a whole range of effects occurring with increasing penetration, such as output smoothing and increasing interconnection, depletion of the wind resource, requirements of reliability backup and short-term spinning reserves, and increasingly discarded excess wind energy. The potential of wind power is hence not limited by the resource potential, but instead by how much can be integrated into existing power supply systems without causing major supply and demand imbalances, and at acceptable costs [14]. At a given penetration rate, wind power’s mitigation potential would depend on future electricity demand. Assuming steady increases in turbine size (from 1.5 MW in 2007 to 2 MW in 2030) and capacity

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factor (from 25% in 2007 to 30% in 2030), the GWEC [15] projects a moderate growth scenario to lead to 1,400 GW capacity in 2030 (generating 3,500 TWh), and 1,800 GW in 2050 (4,800 TWh). Assuming a 2030 demand of 30 PWh, this scenario is equivalent to an average penetration rate of just over 11% (compare [15] p. 40). 2050 annual CO2 mitigation would then amount to about 4.4 Gt CO2/year. Extrapolating this trend linearly to 2,100 yields a crude estimate of 350 Gt CO2 total mitigation potential. In addition, the GWEC [15] reference scenario yields about 1.7 Gt CO2/year in 2050, or 150 Gt CO2 until 2100, and the advanced scenario yields about 8.2 Gt CO2/year in 2050, or 650 Gt CO2 until 2100. These scenarios are consistent with estimates by the GWEC [15] (pp. 38 and 45–46). A long-term global penetration rate of around 20% is perhaps realistic (compare estimates of 15–20% in [16]) given that (a) large economic potential is not available in all world regions, and (b) current research indicates substantial difficulties of integrating wind at penetration rates higher than 20% [11]. This corresponds to a total mitigation potential of about 450–500 Gt CO2. For comparison, Hoogwijk et al. [11] arrive at potentially avoided CO2 emissions of 1 Gt CO2/year, just in OECD Europe and the USA, at carbon prices of around US $30–50/t CO2. This figure is in the ballpark of the estimate given above.

Technical Principles of Wind Energy Converters This section discusses modern wind energy conversion systems. However, before setting forth the different types of wind turbines along with their design principles and characteristics, a reminder of the origin of winds, followed by a brief overview of the historical development of wind-powered devices, will first unfold. Wind power is actually a form of solar power as winds result from solar radiation. Sunbeams entering the atmosphere heat the Earth’s surface but not evenly across the surface and over time. Indeed, the equator receives more energy from the sun than the poles and dry land surfaces absorb, retain, and release heat at different rates than the oceans. Consequently, air masses surrounding the Earth’s surface warm and cool at different rates. Since hot air masses are lighter than cold ones, they rise and reduce the atmospheric pressure below them drawing in cooler air masses. This creates a global atmospheric convection system that gives birth to winds. Since these air masses are in motion, they have kinetic energy. Wind energy converters capture this kinetic energy and then convert it into a useful form of energy such as electricity or mechanical power. Sailboats and sailing ships have been using the power of the wind for at least the last 3,000 years. However, the first recorded use of (vertical-axis) windmills to operate irrigational and agricultural projects was in the seventh century BC in the Afghan highlands. The most ancient historical documents pertaining to horizontal-axis windmills technology date from about 1000 AD and were found in the regions of Persia, Tibet, and China. From there, the technology spread westward to Europe where it was later, at the beginning of the twelfth century, extensively used to grind flour [17].

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Another seven centuries or so will pass before the first windmill designed for electricity production is built in Scotland in 1887 by Professor James Blyth. Set up in his holiday cottage, his 10-m high wind turbine charged accumulators engineered by the Frenchman Camille Alphonse Faure to power the lighting of the cottage, thus making it the first residential area in the world to have electricity supplied by wind power [18]. A precursor of modern horizontal-axis wind generators was developed in Yalta, USSR in 1931. This 100 kW generator mounted atop a 30-m tower was reported to have a capacity factor of 32%, quite close to current wind machines [19]. On the eve of the twenty-first century, rising concerns over energy security of supply and global warming paved the way to an expansion of interest in all available forms of renewable energy in general and in wind power in particular. Like this, and boosted in addition by readily available wind resources and economies of scale, worldwide gridconnected wind capacity doubled approximately every 3 years during the 1990s. After the 2003 surge in oil prices due to the geopolitical situation in the Middle East, interest in commercial wind power further expanded.

Modern Wind Energy Conversion Systems Wind power is the conversion of the kinetic energy of winds into another form of energy, either mechanical or electricity. If the useful form of energy is mechanical (to, for instance, pump water or grind stones), the converter is generally referred to as a windmill. In contrast, if the useful form of energy is electricity, the converter is called a wind turbine or a wind energy converter. In the following section, focus will be on the latter technology, that is, to harness the kinetic energy of wind to produce electricity. Before examining modern wind energy conversion systems, it is important to bear in mind that only a given fraction of the (kinetic) energy of wind can effectively be harnessed. If all the energy was to be extracted by a wind turbine, the air mass would come to a stop in the intercepting rotor area jamming the cross-sectional area for the following air masses. The theoretical limit of the kinetic energy of the wind that can be harnessed by a hypothetical ideal wind-energy extraction machine (referred to as Betz’s law and derived by combining the fundamental laws of conservation of mass and energy) is 16/27 (59.3%). Wind energy conversion systems can either depend on aerodynamic drag (force acting in a direction opposite to the oncoming flow velocity) or on aerodynamic lift. Most of modern wind turbines are based on the aerodynamic lift. The resulting force stemming from the blades intercepting the air flow has two components. A (drag force) component in the direction of the flow and a (lift force) component perpendicular to the drag. The lift force is a multiple of the drag force and consequently the main driving power of the rotor, by means of which it produces the necessary driving torque. The orientation of the spin axis of wind turbines based on aerodynamic lift (lift-type wind turbine) can be either vertical or horizontal. However, horizontal-axis machines are more commonly used for large-scale industrial applications [20].

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Horizontal-Axis Wind Turbines Horizontal-axis wind turbines (HAWTs) consist of a tower atop of which a nacelle containing the rotor, the generator, and an optional gearbox is mounted. There exist diverse mechanisms to position the nacelle into or out of the wind. Small turbines are pointed by a wind vane, while large ones most of the time use a wind sensor coupled with a servo-motor to electrically yaw (align) the nacelle toward or away from the wind depending on the signal sent by the wind sensor. Since the power in the wind is a cube of the wind speed, the converted mechanical power must always be controlled at high wind speed. This power output control can be achieved by stall control (the blade position remains unchanged but natural turbulences occurring behind the blades in high wind speed reduce the aerodynamic forces and thus the power output), pitch control (the blade angle of attack is reduced at higher wind speed and so are consequently the aerodynamic forces and the power output), or a combination of the two, active stall regulation (the blade angle of attack is fine-tuned to create stall along the blade). If the wind speed rises above the cutout wind speed threshold (usually varying between 20 and 30 m/s), the turbine is shut off and the rotor is turned out of the wind to avoid potential damage to the primary turbine structure. In so doing, a substantial quantity of energy is wittingly lost. However, equipment capital costs required to strengthen the primary structure to resist wind speeds over the cutout wind speed threshold will likely be larger than the value of the lost energy that could have had otherwise been harvested over the lifetime of the wind turbine. The number of blades of a horizontal-axis wind turbine depends on its purpose. Turbines designed with two or three blades are usually more suited for electricity generation while turbines designed with twenty or more blades are generally more suited for mechanical operations (e.g., water pumping). While most generators are designed to run in the range of 1,200–1,800 rpm (revolutions per minute), large wind turbine rotors most of the time operate at speeds between 10 and 60 rpm. To convert the slow rotational speed of the blades to the higher speeds necessary to drive the electrical generators, gearboxes are therefore used on a majority of large turbines. However, direct mechanical connection (direct-drive) can also be achieved with generators designed to run at very low rpm. Such generators usually consist of many poles (the required rpm of a generator depends on the number of pole pairs) and are very large (large diameter to accommodate the large number of poles) in comparison to generators attached to gearboxes [21]. A fixed-speed turbine technology imposes the rotational rate of the turbine to that of the electric grid whereas a variable-speed turbine technology allows the speed of the rotor to be proportional to the wind speed. In so doing, the former technology forgoes a substantial amount of wind potential, while the latter, in contrast, considerably improves the aerodynamic efficiency in high wind and allows to run at lower speeds so that, everything else being kept equal, a variable-speed technology collects more energy than its fixed-speed counterpart. However, this enhanced energy capture that comes

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at a high price because of the expensive embedded power electronics and control systems can be economically counterbalanced by fixed-speed wind turbines. Drawbacks of HAWTs are that the tall towers and blades, up to 90 m long, are difficult to transport and to erect, necessitating tall and expensive cranes and skilled operators. In addition, their imposing structures make them pointedly visible across large areas, disrupting sceneries and landscapes, sometimes leading to local opposition. In spite of turbulence issues, downwind HAWTs have also been engineered. First, because no additional mechanism for maintaining them aligned with the wind are necessary and second because in high winds, blades can bend, which decreases their swept area and subsequently their wind resistance. However, since turbulences ultimately lead to fatigue failures, horizontal-axis wind turbines are almost exclusively upwind machines.

Vertical-Axis Wind Turbines (VAWT) The main advantage of this disposition, especially at sites where the wind direction is highly patchy, is that the turbine does not need to be pointed into the wind to be effective. In addition, the generating machinery and gearbox can be placed at ground level, easing maintenance and lowering material requirement. However, drawbacks are that the driving torque of the rotor varies more noticeably within each turn, the static torque is rather low, and the rotor has to be started up by using the generator as a motor [22]. In addition, it is difficult to erect vertical-axis turbines atop towers. Consequently they are most of the time erected close to the foundations upon which they rest (ground or building rooftop, for instance). It entails that, for a given installed capacity, less wind energy can be harnessed as wind blows slower at lower altitude. In addition, air masses flowing close to the ground are turbulent, potentially producing vibration, and subsequently noise and bearing wear, increasing the maintenance and/or shortening the equipment lifetime [23]. In contrast, the wind always strikes at a consistent angle the face of a horizontal-axis blade whatever the position in the rotation ensuring a consistent lateral wind loading during a revolution, reducing vibration and audible noise. Moreover, as opposed to HAWTs, blades, which are fixed to the shaft, cannot be adjusted (pitched), so that power output can be controlled only by aerodynamic stall.

Characteristics of a Wind Turbine A wind turbine installation is made up of subsystems to harness the energy from the wind (rotor), to point the turbine into the wind (yaw mechanism), and to convert the mechanical rotation into electrical power (generator), as well as subsystems to start, stop, and control the turbine. Horizontal-axis medium to large size grid-connected wind turbines (>100 kW) currently occupy the biggest market share and are expected to principally account for wind deployment in the near future [17]. This section therefore specifically focuses on their designs that can be divided into three parts [24]:

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– A tower on top of which the nacelle is mounted – The rotor that includes blades – The generator that includes an electrical generator, control electronics, and most of the time a gearbox

The Tower The tower is an important part of a wind turbine primarily because it supports the nacelle and the rotor. The tubular steel tower design is the most widespread technological choice, even though there exist other alternatives like lattice towers or concrete towers. Towers are conical, with their diameter decreasing toward the nacelle, to enhance their strength on the one hand and reduce their material intensity on the other. In areas with a high surface drag it is better to erect tall towers since the wind blows faster farther away from the ground. More specifically, wind speed follows in daytime the wind profile power law, which foresees that wind speed rises proportionally to the seventh root of altitude [25]. Consequently, doubling the altitude of a turbine theoretically increases the expected wind speeds by 10% and the expected power by 34%. However, to avoid buckling, increasing the tower height generally entails enlarging the diameter of the tower as well.

Rotor: Blade Design and Count Turbine blades, sometimes slightly tilted up, are positioned significantly ahead of the tower and made rigid to prevent them from being shoved into the tower by high winds. Most modern large-scale wind turbine rotor blades are therefore made of glass fiberreinforced plastics (e.g., epoxy), which, besides, allows for low rotational inertia and quick accelerations, should gusts of wind occur (variable-speed turbines). In contrast, previous generations of (fixed-speed) wind turbines whose rotational speed is imposed by the AC frequency of the power lines are manufactured with heavier steel blades, and therefore higher inertia [26]. The determination of the number of blades depends on the purpose of the wind turbine as aforementioned. Wind turbines for electricity generation usually use either two or three blades even though two-bladed designs are more the exception than the norm for large-scale grid-connected horizontal-axis wind turbines. The rotor moment of inertia of a three-bladed wind turbine is simpler to comprehend than that of a two-bladed one. In addition, three-bladed wind turbines are often better accepted for their visual aesthetics and are responsible for lower audible noise than their two-bladed counterparts [27]. Furthermore, during the yawing (alignment) of the nacelle in or out of the wind, a cyclic load is exercised on the root end of every blade and whose magnitude is function of the blade position. Three-bladed turbines see their cyclic load symmetrically balanced when combined at the turbine drive train shaft, contributing to smoother maneuvers during yawing.

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On the flip side, two-bladed wind turbines, when equipped with a pivoting teetered hub can also nearly filter out the cyclic loads into the turbine drive shaft and system during yawing. Moreover, the tower top weight is lighter and so consequently is the whole supporting structure, lowering associated costs. In addition, two-bladed turbines can have a higher rotational speed than their three-bladed counterparts. Indeed, the degree of rigidity necessary to avoid hindrance with the tower imposes a lower limit on the thinness of the blades and subsequently (a lower limit) on their mass. However, this is only true for upwind machines as bending of blades enhances tower clearance for downwind ones. Likewise, cheaper gearbox and generator costs can be achieved with two-bladed turbines as faster rotational speeds reduce peak torques in the turbine drive train. Lastly, the fewer the number of blades the higher the system reliability is, chiefly through the dynamic loading of the rotor into the tower and turbine drive train systems.

Electrical Generator The energy captured by the blades is subsequently passed onto the generator via a transmission system consisting of a rotor shaft with bearings, brakes, an optional gearbox, as well as a generator. Whereas the power generation industry resorts almost integrally to synchronous generators because of their variable reactive power production (voltage control), most wind turbines generate electricity through (six-pole induction) asynchronous generators that are directly connected with the electricity grid. However, some designs also use directly driven synchronous generators [17]. Electrical generators produce AC (alternating current) power by definition. While the previous generations of (fixed-speed) wind turbines spin at a constant speed governed by the frequency of the grid they are connected onto, new (variable-speed) ones most of the time rotate at the speed that produces electricity most efficiently being given the actual wind conditions. This can be achieved either using direct AC to AC frequency converters (cycloconverters) or using DC current link converters (AC to DC to AC). Although variable-speed turbines require costly power electronics that in addition generate supplementary power loss, a substantially larger fraction of the wind energy can be harnessed by the rotor [21].

Control Electronics Wind conditions being highly variable across sites and over time, a wind turbine is designed to operate over a large range of wind speeds (usually between 12 and 16 m/s). Therefore, to avoid any potential damage to the primary turbine structure during operation in strong winds while ensuring an optimal aerodynamic efficiency of the rotor in light ones, the rotational speed and torque of the rotor must permanently be monitored and controlled. There are several approaches to successfully achieve this (power output) control.

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Stall Regulation This technique requires the rotor to spin at a constant speed (independent of the wind speed). When a wind stream is intercepted in the rotor area, it creates natural turbulences right behind the blades. This is called the stall effect. As a result, aerodynamic forces (induced drag or drag associated with lift) are reduced and so subsequently is the power output of the rotor [17]. If the stall effect is a complicated dynamic process to comprehend, stalling is an easy power output control to practically implement as the faster the wind blows, the larger the stall effect is (passive regulation). However, stalling increases the (ordinary) drag by increasing the cross section of the blade facing the wind.

Pitch Control Pitching the angle of attack of the blades into (respectively out of) the wind increases (respectively reduces) the aerodynamic forces and subsequently the power output of the rotor. One of the main technical challenges associated with designing pitch-controlled wind turbines is getting the blades to furl (to swing out of the wind) swiftly enough in case of a gust of wind. Seemingly, these systems must be able to adjust the pitch of the blades by a fraction of a degree at a time, depending on the wind speed, to control the power output. The pitching system in medium and large size grid-connected wind turbines is usually based on a hydraulic system, controlled by a computer system. To prevent an eventual hydraulic power failure to furl the blades pitch regulation systems are also spring-loaded. By permanently fine-tuning at an optimum angle the rotor blades (even in low wind conditions) pitch-controlled turbines achieve a better yield at low-wind sites than stallregulated turbines. In addition, the thrust exercised by the rotor on both the tower and the foundation being significantly lower for pitch-controlled turbines than their stallregulated counterparts, the primary structure of the former is less material-intensive, and likely incur lower costs. Moreover stall-regulated (fixed-pitch) turbines must be shut down when the cutout wind speed threshold is reached, whereas pitch-controlled ones can progressively evolve toward a spinning mode as the rotor operates in a no-load mode at the maximum pitch angle (fully furled turbine). On the flip side, once the stall effect becomes effective (in high wind conditions) the power oscillations occurring on stall-regulated turbines and stemming from the wind oscillations are smaller than those occurring on pitch-controlled turbines in a corresponding regulated mode [17].

Active Stall Regulation This regulation system is a combination between and a culmination of pitch and stall approaches. Combination because, to optimize the aerodynamic efficiency of the rotor

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and to ensure a torque large enough to create a turning force in light winds, the rotor blades are pitched like in a pitch-controlled wind turbine, whereas, after the rated capacity is reached, they are pitched in the opposite direction (than that of a pitch-controlled turbine) in order to increase their angle of attack and install them into a deeper stall. Culmination because active stall regulation achieves a power output control smoother than the jerky one associated with pitch-controlled turbines while still preserving at the same time the advantage of pitch-controlled turbines over stall-regulated ones to turn the blades parallel to the airflow (the so-called low-load feathering position) and subsequently reducing the thrust on the turbine structure [17].

Wind Farms Groups of turbines are often combined into wind farms whose installed capacity can range from a few to several hundred MW. The largest wind farm for commercial production of electric power, situated in Texas, USA, combines 421 turbines into a 735 MW plant. Such turbines are usually three-bladed and have high tip speeds (the ratio between the rotational speed of the tip of a blade and the actual velocity of the wind) of 300 km/h. Their supporting structures tower from 60 to 90 m above ground while their associated blades range from 20 to 40 m in length. Wind plants have short construction lead times, even compared to those of transmission infrastructure.

Trends Variable-speed turbines with pitch control using either direct driven synchronous ring generator or double fed asynchronous generators are likely to become the norm, not the exception. However, cost of energy is and will remain the key driving force of wind energy growth. Therefore, if variable-speed turbines are to become a sound economic winner, additional costs incurred by power electronics required by most variable-speed designs must clearly be counterbalanced by the enhanced energy capture.

Capacity and Load Characteristics Wind energy converters are dependent on the wind, and hence turbine output varies over time, across all timescales ranging from seconds to up to years. Measuring, modeling, and understanding this variability is crucial for site selection, and also for integration of wind power into electricity grids. In 2008, the global capacity of wind energy converters was 121 GW, generating about 260 TWh of electricity [5]. This yields a capacity factor of about 24.5% (> Fig. 34.5). Plant outages are not as problematic with wind power as they are with fossil, nuclear or large hydro, because numerous wind plants are usually distributed over a wide

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this study k = 2

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. Fig. 34.5 Average capacity factor as a function of wind speed. Most turbines operate in a range between 2,000 and 3,000 full load hours, which is equivalent to capacity factors between 23% and 34% (after [6]; k is the Weibull wind speed distribution parameter). For wind farms at certain windy sites, average capacity factors of up to 45% are reported [28]

geographical area [28]. Such decentralization in a power supply system reduces the requirements for contingency reserve, since this type of reserve is mostly tied to the largest potential source of failure, which is the largest single generator in the system [29]. Output from wind farms can be expected to be smoother than that of a single turbine, but smoothing effects on larger scales may not be so significant, and may also vary between regions. While smoothing effects are discernible when comparing single turbines with wind farms and regions (> Fig. 34.6, and also a similar figure for the UK in [30]), combining regions as such may not necessarily lead to much additional smoothing because of strong correlations in the wind regime over large distances (> Fig. 34.7). Østergaard [31] artificially combines the wind output of West and East Denmark (which are not connected into a common grid) and obtains only small averaging effects.

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1.0 0.8 0.6 0.4 0.2 Single turbine (Oevenum/Fohr) 225 kW

Normalised power

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0.8 0.6 0.4 0.2 0.0 1.0 All WTs in Germany 14.3–15.9 GW

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. Fig. 34.7 Variability and correlation of wind loads across Ireland, the UK, and Germany (After [30]). On February 2, the electricity demand in Britain reached its peak for 2006

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Oswald et al. [30] uses weather maps to demonstrate the correlation and variability of wind regimes across a large area combining Ireland, the UK, and Germany (> Fig. 34.7). His findings (confirmed for Germany in [32], Sect. 3.1 and Fig. 4) cast doubt on the effectiveness of a trans-channel ‘‘supergrid’’ in smoothing out variations in wind load. Holttinen et al. [33] present a detailed account of variability across geographical and temporal scales. Archer and Jacobson [34] present wind speed data for a single site, and three and eight sites in Kansas, USA, and show how the frequency of low-wind events decreases as the number of included sites increases. However, wind generators cannot – without storage – react to changes in demand because unlike hydropower they cannot follow a fluctuating demand (> Fig. 34.8). Therefore, in the absence of supply-matched end-uses, they require a flexible electricity grid with a sufficient portion of technologies that can react quickly to demand changes, such as hydropower or natural-gas fired plants [15, 35]. The average capacity factor of 24.5% given above does not reflect the circumstance that electricity system planners must meet demand whenever it occurs and not on average. Where a technology is assessed with regard to its ability to supply peak load, the capacity credit describes the fraction of average capacity that is reliably available during peak demand. Capacity credit is also referred to in the literature as demand capacity [36], capacity value [37], or moderation factor [38]. The difference between the average capacity and capacity credit is proportional to the time when wind power cannot meet (peak) demand because of a lack of wind. For example, provided a filled reservoir, the capacity credit of hydropower is virtually equal to its average capacity, but this is not the case for wind power because of its variability and uncertainty. Some generators assign zero capacity credit to wind, however this is unrealistic [39]. Wind can achieve

West Denmark January 2006

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“Ireland ESBNG 5GW” “Ireland ESBNG 6.5GW”

. Fig. 34.9 Capacity credit of wind power as a function of wind penetration (After [33]). Note that as penetration approaches 20%, the capacity credit starts to fall consistently below wind power’s average capacity factor. The results from Mid-Norway show that geographical dispersion improves capacity credit. Decreasing capacity credits have been confirmed theoretically, for example, by [41]

up to 40% capacity credit when penetration is low and times of ample wind coincide with times of high demand [33]. In general however, the higher the penetration of wind power in a system, and the more uncorrelated wind output with demand load, the lower its capacity credit see (Fig. 11 in [40], and > Fig. 34.9). Capacity credit is usually measured by applying probability calculus to hourly data on load, generation capacity, ramp rates, and planned or forced outages, and applying merit orders in which technologies that avoid fuel costs are recruited first [37]. The LossOf-Load-Probability LOLPi = Prob(∑jCj < Li), with Cj being the capacity of generator j in the grid and Li the load at hour i, is the probability that a supply system is not able to meet demand in hour i. Integrating LOLP overall operating hours results in the LossOf-Load Expectation LOLE = ∑i LOLPi, which is expressed in units of hours/year, or days/10 years, and provides a measure of system reliability. A common system LOLE target is 1 day/10 years, in which case the system has to import capacity from elsewhere. This corresponds to a 1 – 1/(10  365) = 99.97% probability that the system will be able to meet demand without having to import capacity. A power supply system is usually made up of a technology mix. A measure that allows characterizing the incremental contribution of any one component to the reliability of the system is the Effective Load Carrying Capability ELCC, which is the new firm (i.e., zerovariance) load that can be added to the system including the incremental capacity increase, without deteriorating the system’s reliability. Adding a new generator G as well as a hypothetical firm load ELCC to a system, hourly LOLP becomes LOLPi = Prob (∑jCj + G < Li + ELCC). ELCC is a hypothetical firm (i.e., zero-variance) load that can be added to a system as a result of the addition of a non-firm (i.e., variable) capacity G, that would not change the system’s LOLE. ELCC is hence calculated by solving ∑i Prob (∑jCj < Li) = ∑i Prob(∑jCj + G < Li + ELCC).

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ELCC depends critically on the ability of a generator to meet demand at top-ranking LOLP hours, which, in the case of wind, is determined by the correlation of wind output with top-ranking LOLP hours. Capacity credit is the ratio of ELCC and rated capacity. Defined as such, capacity credit values are around or lower than average capacity (> Fig. 34.9). However, capacity credit has at times been measured as the ratio of ELCC and average power [41], in which case it varies between 0% and 100%. As a result, where grid operators are required to meet demand at usual loss-of-load expectations, reserve load-carrying capacity or storage has to be secured ([36]; > Fig. 34.10). Similarly, operators also strive to avoid having to curtail surplus wind power at times of high wind, raising different management issues again [14]. Geographical dispersion of wind turbines can help to reduce variability as well as increase predictability of output [29]. Even during a rapidly passing storm front, power from dispersed capacity will take a few hours to change [42]. Depending on the characteristics of the power system, that is, composition and diversity of technologies, demand management, size, demand profile, and the degree of interconnection, low capacity credit poses barriers to the degree of integration of wind energy. In general, the more flexible, load-following capacity there

Area relevant for impact studies Task 25 Balancing System wide 1,000–5,000 km

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. Fig. 34.10 Typology of grid impacts of wind power across temporal and spatial scales (After [33]). Balancing reserves deal with short-term variability in the order of up to 24 h. Adequacy in peak-load situations (i.e., low LOLE) has to be secured long-term, and requires load-carrying reserves to compensate for shortfalls in capacity credit

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is in the existing grid, the higher the potential penetration of wind power. However, operators run either the risk of not meeting demand by committing too much cheap slow-start capacity, or the risk of overrunning cost by committing too much expensive fast-start capacity [43]. Grid integration issues have largely been studied theoretically, except for some European regions. For example, while Denmark receives on average more than 20% of its electricity from wind, it sometimes receives much higher percentages, and sometimes very little, in which case Denmark exports or imports electricity from the European grid, and thus relies on other generation technology for load balancing [36, 44], in particular Norwegian, Swedish, and Finnish hydro reservoirs, and idle peaking plants in Denmark [45]. For higher degrees of integration, the management and/or export of excess wind loads become(s) an issue [43]. So¨der et al. [42] report results from four regional systems with high wind penetration, among which two are connected to a larger outside system, and two are not. Management of wind power variability involves the requirement for flexible interconnection capacity, and the ability to curtail wind power production, respectively. Hoogwijk et al. [11] their (> Fig. 34.9) find that – subject to supply and load correlation – the amount of electricity that has to be discarded grows strongly for penetrations in excess of 20–30%. Lund [38] investigates a scenario for expansion of wind power to cover 50% of Danish demand, and concludes that supplydemand balancing problems would become severe. Similarly, penetration of less than 20% can lead to instabilities if a grid is not well interconnected with other grids, such as in the case of Spain [11].

Life-Cycle Characteristics Lenzen and Munksgaard [46] review and analyze a large body of literature on the life cycle of wind energy converters, comparing bottom-up component analyses with top-down input–output analyses. In their multiple regressions these authors take into account technical features such as scale, vintage year, and load factor, but also scope and methodology of the analysis (> Fig. 34.11). A more recent study by Wagner and Pick [47] confirms the energy payback times between 3 and 7 months, which – assuming a turbine lifetime of 20 years – corresponds to cumulative energy requirements between 0.035 and 0.075 kWhth/kWhel. The cumulative energy requirement  is related to the energy payback time, that is, the time it takes the wind turbine (lifetime T ) to generate the primary-energy equivalent of its energy requirement, via tpayback = 
T
efossil. efossil is the conversion efficiency (assumed to be 35%) of conventional power plants that are to be displaced by wind turbines. Lenzen and Munksgaard [46] found greenhouse gas intensities for the larger, modern turbines to be about 10 g/kWhel, ranging among the lowest values for all electricity generation technologies. Lenzen and Wachsmann [48] found large variations of specific life-cycle emissions of wind turbines between countries where turbine components were produced.

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0.15

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. Fig. 34.11 Cumulative energy requirements of wind energy converters as a function of rated power (After [46]). The multivariate regression line takes into account different scopes and methodologies adopted in case studies. 0.05 kWhth/kWhel is found to be realistic for modern large turbines

Roth et al. and Pehnt et al. [49, 50] take the reduced capacity credit of wind into account in their systems LCA, and conclude that CO2 emissions arising from the need of additional reserves add between 35 and 75 g CO2/kWh, thus outweighing CO2 emissions from the turbine life cycle. However, these values depend strongly on the technology mix of the overall power system. Noise, and impacts on birds are likely to be small from wind farms, compared to other impacts [15]. Snyder and Kaiser [13] provide a detailed account of possible ecological impacts from offshore wind farms. The mitigation potential of wind in a power system represents an optimization problem, because the higher the penetration of wind power, the higher emission reductions, but also the higher the variability cost.

Current Scale of Deployment Due to large economies of scale the scale of single wind energy converters has been increasing steadily (> Fig. 34.12), featuring taller towers and larger rotors. Larger turbines

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with ratings above 3.5 MW are usually dedicated to offshore power generation, while onshore installations are usually rated between 1.5 and 3 MW [15]. In early 2009, the French manufacturer Areva deployed 5 MW turbines for operation 45 km offshore of the German North Sea island of Borkum [51]. 5 MW turbines are also installed at the Beatrice site (40 m depth) off the Moray Forth east of Scotland (http://www.repower.de/ index.php?id=369). In 2007, the average size of operating turbines was 1.5 MW.

Contribution to Global Electricity Supply In 2008, the global capacity of wind energy converters was 121 GW, generating about 260 TWh of electricity, or about 1.5% of global electricity production [5]. Most of the capacity (> Fig. 34.1) is installed in the USA (25 GW, 1% of electricity generation) and in the EU (about 65 GW, 3.7%), followed by China (12 GW) and India (10 GW). However, regional shares of wind power can be much higher in some countries: Denmark (21%), Spain (12%), Portugal (9%), Ireland (8%), and Germany (7%). However, it is worth noting that Denmark at times receives much higher percentages of its electricity from wind, and sometimes very little, in which case Denmark exports or imports electricity from the European grid, and thus relies on other generation technology for load balancing [36, 45]. Wind energy deployment has been increasing rapidly throughout the past decade, recording growth rates of around 30% since 1996 (> Fig. 34.2). More than half of the 2008 additions occurred in the USA and in China (> Fig. 34.3), with the USA overtaking Germany as the leader in installed wind capacity [5]. In the USA, wind power has represented 40% of 2007 national capacity growth [52]. Most of the wind generation is onshore; only about 1.1 GW is presently installed offshore, mainly located in Denmark (420 MW), the UK (300 MW), Sweden (135 MW), and the Netherlands (130 MW) ([53]; www.ieawind.org/Annex_XXIII.html). A further 8 GW were planned in early 2009 [51].

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Cost of Electricity Output Capital costs make up about 80% of total wind energy cost, with the remainder for operation and maintenance, since the wind turbine does not require any fuel input. Blanco [54] presents a detailed breakdown of these costs; in onshore installations, the turbine covers 70% of capital cost, with the remainder for grid connection, civil works, taxes, permits, etc. Within the turbine, the tower and blades make up for half of the costs. Electricity costs vary with site conditions: Assuming a 20-year plant life, 5–10% discount rate, and 23% average capacity factor, Blanco [54] states a levelised cost range for electricity from European 2 MW wind turbines between 6.5 and 13 US¢/kWh. Welch and Venkateswaran and Snyder and Kaiser [13, 55] report US cost estimate between 3 and 5 US¢/kWh, DeCarolis and Keith [43] between 4 and 6 US¢/kWh. Levelised electricity cost is the constant (discounted to present values) real wholesale price of electricity that recoups owners’ and investors’ capital costs, operating costs, fuel costs, income taxes, and associated cash flow constraints. They exclude costs for transmission and distribution. Levelised cost may differ from sales prices, because of profits or losses. The figures reported here are averages over plant types and vintages, and over locations with varying resource endowments and demand profiles. Actual cost for particular plants may be different from the cost given here. Levelised electricity costs are strongly determined by the competitive landscape, in particular the extent and nature of regulation, subsidization and taxation, primary fuel (coal, gas, uranium) prices, and future carbon pricing. While under government regulation operators are able to transfer costs and risk to consumers and taxpayers, this is not the case in deregulated electricity markets, where high interest rates lead to investors favoring less capital-intensive and therefore less risk-prone power options. Electricity cost figures reported here refer to the financial and regulatory environment at the time of publication of the various references. Civil works, and especially the foundations are much more expensive in offshore installations, where they represent 20% of capital cost, leading to higher levelised cost of 9–16 US¢/kWh. This is confirmed in an estimate of 10 US¢/kWh by Snyder and Kaiser [13]. However, technological learning can bring these costs down in the future [53, 56]. Wind energy costs have increased during the past 3 years, mainly driven by supply tightness and price hikes of raw materials [53], which is difficult to control by government fiscal policy. Bolinger and Wiser [52] provide a detailed analysis of most recent upward cost trends. Yet, the analysis of learning curves for the industry suggests that levelised costs will come down through increased efficiency, by about 10% for every doubling of capacity ([54], compare Fig. 14 in [1]). As with other non-fossil electricity generation technologies, wind plant operators expect the competitive landscape to change in favor of wind power, once carbon is adequately priced [15, 43]. In the future, wind energy is also expected to benefit more from not being affected by fuel price volatility. However, depending on the penetration of a power system with variable wind energy, additional indirect cost arise for maintaining LOLE, because wind energy will not be able to meet demand at its average capacity factor, but at a generally reduced rate depending on

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its capacity credit [43]. In addition, the presence of wind power in a power supply system introduces short-term variability and uncertainty, and therefore requires balancing reserve scheduling and unit commitment. Grid operators need to meet peak demand to certain statistical reliability standards even when wind output falls relative to load. During these periods, which range from minutes to hours, electricity markets need to recruit demand-following units (such as gas, hydro, or storage), which at times of sufficient wind remain idle, so that costs arise essentially for two redundant systems [36, 57], and for inefficient fuel use during frequent ramping (see p. 903 in [11], [57, 58]). Both adequacy and balancing cost compare (> Fig. 34.10) are sometimes referred to as intermittency cost, however in this chapter the term variability cost is used because strictly speaking wind energy is variable and not intermittent [39]. Thus, wind energy reduces dependence on fuel inputs, but does not eliminate the dependence on short-term balancing capacity and long-term reliable load-carrying capacity. The impact of wind power on the power supply system is critically dependent on the technology mix in the remainder of the system, because the more flexible and loadfollowing existing technologies, the less peak reserves are needed. It is also dependent on time characteristics of system procedures (frequency of forecasts, etc.) and local market rules [14]. In general, the higher the wind penetration, the higher the variability in the supply system, and the more long-term reserve and short-term balancing capacity has to be committed (> Fig. 34.13) on short-term balancing only. The corresponding cost increases are only partly offset by a smoothing out of wind variability when many turbines are dispersed and interconnected over a wide geographical area [59], but they are more than offset by reduced fuel and operating cost. In specific applications, the cost of additional wind power also depends on the relative locations of turbines, load, and existing transmission lines, and on whether sufficient load-carrying reserve exists in the grid or has to be built.

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As expected, variability costs scatter significantly depending on a large array of parameters. They cannot be derived from capacity credit estimates, since these do not contain any information about to what extent cheap base load and expensive peak load are being displaced by wind [60]. Variability costs are difficult to disentangle from overall cost in real-world grids [43], so that they have largely been estimated for theoretical settings, using statistical models for resource and load fluctuations, and least-cost-optimizing generation and reserve scheduling under given output limits, startup and shutdown cost, ramp-rate restrictions, planned outages, fuel cost, and day-ahead forecasts [29, 59]. They have been quoted between 0.2 and 0.4 US¢/kWh for existing installations [13, 15], but also higher at 1–1.8 US¢/kWh [43, 57, 61] for larger degrees of wind penetration. In a more up-to-date survey, Holttinen, Strbac et al., and Smith et al. [14, 40, 58] report on recent findings about increases in balancing requirements due to the presence of wind, ranging widely between 0.05 and 0.5 US¢/kWh (> Fig. 34.14). Hence, at penetrations of up to 20%, variability cost can be expected to be about equal or less than 10% of generation cost. Hoogwijk et al. [11] see (> Fig. 34.15) run numerical experiments at large-scale penetration rates of up to 45%, and find that beyond 30% penetration the cost incurred by discarded excess electricity becomes comparable to base cost (6 US¢/kWh). The market for wind turbine manufacturing is diverse and competitive, with manufacturers spread across many countries. However, large corporations are entering the market, sometimes assimilating smaller entities [15]. During the recent wind market boom, and the shift to larger turbines, the industry faced a number of supply chain bottlenecks related to gearboxes and large bearings [54], leading to waiting times for turbines of up to 30 months [45].

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. Fig. 34.14 Increase in balancing requirements per kWh of wind power as a function of wind penetration (After [33])

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Future Directions Wind energy faces a number of technical future challenges. The variable and distributed nature of wind energy requires specific grid infrastructure in order to ensure grid stability, congestion management, and transmission efficiency. Significant investment in grid infrastructure has to occur in order to allow for substantial global penetration of wind energy [15]. One of the most significant challenges is hence the integration of wind power into a large grid, and the theoretical modeling of power system behavior at high penetration rates of wind. Recent efforts are also aimed at improving short-term forecasting of wind, which is still less accurate than forecasting of load [33]. With increasing interconnection and geographical dispersion, forecasting errors are expected to decrease see(> Fig. 34.16). Some researchers suggest directing wind power to where it can be most competitive, or where its variability does not create problems. Some industrial applications and also combined heat and power plants can – within limits – adjust their demand to supply [44]. Dedicated load-leveling applications such as desalination, aluminum smelting, space and water heating, or a chargeable hybrid vehicle fleet can deal with hourly variations in wind power since they only require a certain amount of energy over a period of many hours [12, 36]. For example, large-scale vehicle-to-grid technologies can significantly reduce excess wind power at large wind penetration, and replace a significant fraction of regulating capacity, but as Lund and Kempton [62] show in a study for Denmark, electric vehicles would not nearly eliminate excess power and CO2 emissions, even if they had long-range battery storage. Tavner and Smith et al. [58, 63] list improvements in resource, turbine and systems modeling and forecasting, capital cost reduction, lifetime extension, transmission

Wind Energy

34

1

Error reduction

0.8 0.6 0.4 0.2 0

0

500

1,000 1,500 Region size (km)

2,000

. Fig. 34.16 Measured forecast error as a function of spatial range of interconnection (After [68]). The error reduction plotted on the y-axis is the ratio of the root-mean-square error (rmse) of prediction at a regional scale, and the single-site prediction rmse

upgrading, and system integration as the main future research challenges for wind power. Joselin Herbert et al. [64] review past developments and present research needs for wind technologies, such as for resource assessment, site selection, turbine aerodynamics, wake effects, and turbine reliability. Offshore wind deployment faces technical challenges in form of extreme wind conditions that exceed tolerances of current onshore turbines [13, 56]. The IEA Wind offshore subgroup’s tasks include research on ecological issues and deepwater installation. In order to reduce offshore wind costs, turbine concepts, submerged structures and cabling, and remote operation and maintenance will need to undergo further research [54]. Many of the above issues are approached through theoretical modeling, be it turbine structure, system control and balancing, wind conditions, or reliability [63]. Surprisingly, offshore wind power generation shares many of large hydropower and nuclear power’s challenges regarding public opinion. Firestone and Kempton [65] report a case study where the majority of survey respondents opposed offshore wind power development for environmental reasons, and that many of the beliefs were ‘‘stunningly at odds’’ with the scientific literature. Perceived landscape changes also feature in a survey by Zoellner et al. [66], but economic considerations more strongly influenced acceptance.

Summary Wind energy deployment has witnessed a rapid increase throughout the past decade, with annual growth rates around 30%, generating now about 1.5% of global electricity. The technology is mature and simple, and decades of experience exist in a few countries. Due to strong economies of scale, wind turbines have grown to several megawatts per device, and wind farms have now been deployed offshore. In recent years, wind power has become competitive without subsidies, in markets without carbon pricing. The global technical

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potential of wind exceeds current global electricity consumption, however taking into account the temporal mismatch and geographical dispersion of wind energy and demand loads, and requirements for supply–load balance and grid stability, the maximum economic potential appears to be in the order of 20% of electricity consumption. At such rates of wind energy penetration, and without storage and supply-matched demand, the integration of wind power into electricity grids and long-distance transmission begins to present significant challenges for system reliability and loss-of-load expectation. The main issue for future deep penetrations of wind on a global scale is hence how wind plants can be integrated across very large geographical scales and with other variable power sources. For example, there are popular proposals for integrating parts of North African solar power for output-smoothing of large wind supply in Europe. Some commentators remark that these proposals may be difficult to implement because of political and supply security issues; others are more optimistic. Finally, the life-cycle greenhouse gas emissions from wind power are some of the lowest among all electricity-generating technologies, but depending on the remainder of the power supply system, emissions arise because of the use of conventional technologies for supply–demand balancing.

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32. Weigt H (2008) Germany’s wind energy: the potential for fossil capacity replacement and cost saving. Appl Energy 86:1857–1863 33. Holttinen H, Meibom P, Orths A, van Hulle F, Lange B, Malley MO, Pierik J, Ummels B, Olav Tande J, Estanqueiro A, Matos M, Gomez E, So¨der L, Strbac G, Shakoor A, Ricardo J, Charles Smith J, Milligan M, Ela E (2009) Design and operation of power systems with large amounts of wind power, VTT Research Notes 2493. Espoo, Finland 34. Archer CL, Jacobson MZ (2003) Spatial and temporal distributions of U.S. winds and wind power at 80 m derived from measurements. J Geophys Res 108:1–20 35. So¨der L (2004) On limits for wind power generation. Int J Global Energy Issues 21:243–254 36. Pavlak A (2008) The economic value of wind energy. Electricity J 21:46–50 37. Milligan M, Porter K (2008) Determining the capacity value of wind: an updated survey of methods and implementation. Conference Paper NREL/CP-500-43433, Golden, USA, National Renewable Energy Laboratory 38. Lund H (2005) Large-scale integration of wind power into different energy systems. Energy 30:2402–2412 39. Diesendorf M (2007) The base-load fallacy. energyscience.org.au. 40. Strbac G, Shakoor A, Black M, Pudjianto D, Bopp T (2007) Impact of wind generation on the operation and development of the UK electricity systems. Electric Power Syst Res 77:1214–1227 41. Martin B, Diesendorf M (1980) Calculating the capacity credit of wind power. Fourth Biennial Conference of the Simulation Society of Australia. University of Queensland 42. So¨der L, Hofmann L, Orths A, Holttinen H, Wan Y-h, Tuohy A (2007) Experience from wind integration in some high penetration areas. IEEE Trans Energy Convers 22:4–12 43. DeCarolis JF, Keith DW (2006) The economics of large-scale wind power in a carbon constrained world. Energy Policy 34:395–410 44. Østergaard PA (2003) Transmission grid requirements wit scattered and fluctuating renewable electricity-sources. Appl Energy 76:247–255 45. Sovacool BK, Lindboe HH, Odgaard O (2008) Is the Danish wind energy model replicable for other countries? Electricity J 21:27–28

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46. Lenzen M, Munksgaard J (2002) Energy and CO2 analyses of wind turbines – review and applications. Renew Energy 26:339–362 47. Wagner H-J, Pick E (2004) Energy yield ratio and cumulative energy demand for wind energy converters. Energy 29:2289–2295 48. Lenzen M, Wachsmann U (2004) Wind energy converters in Brazil and Germany: an example for geographical variability in LCA. Appl Energy 77:119–130 49. Roth H, Bru¨ckl O, Held A (2005) Windenergiebedingte CO2-Emissionen konventioneller Kraftwerke. lfE-Schriftenreihe Heft 50, Mu¨nchen, Germany, Lehrstuhl fu¨r Energiewirtschaft und Anwendungstechnik 50. Pehnt M, Oeser M, Swider DJ (2008) Consequential environmental system analysis of expected offshore wind electricity production in Germany. Energy 33:747–759 51. Jha A (2009) Brawny wind turbines set for German offshore debut. The Guardian Weekly 30 January 10 52. Bolinger M, Wiser R (2009) Wind power price trends in the United States: Struggling to remain competitive in the face of strong growth. Energy Policy 37:1061–1071 53. IEA (2008b) Wind renewable energy essentials. OECD/IEA, Paris 54. Blanco MI (2008) The economics of wind energy. Renew Sustain Energy Rev 13:1372–1382 55. Welch JB, Venkateswaran A (2008) The dual sustainability of wind energy. Renew Sustain Energ Rev 12(9):2265–2300 56. Smit T, Junginger M, Smits R (2007) Technological learning in offshore wind energy: Different roles of the government. Energy Policy 35:6431–6444

57. Benitez LE, Benitez PC, Van Kooten GC (2008) The economics of wind power with energy storage. Energy Econ 30:1973–1989 58. Smith JC, Milligan M, DeMeo EA, Parsons B (2007) Utility wind integration and operating impact state of the art. IEEE Trans Power Syst 22:900–908 59. Hirst E, Hild J (2004) The value of wind power as a function of wind capacity. Electricity J 17:11–20 60. Martin B, Diesendorf M (1982) Optimal mix in electricity grids containing wind power. Electr Power Energy Syst 4:155–161 61. Ilex X, Strbac G (2002) Quantifying the system cost of additional renewables in 2020. Ilex Energy Consulting, Oxford 62. Lund H, Kempton W (2008) Integration of renewable energy into the transport and electricity sectors through V2G. Energy Policy 36:3578–3587 63. Tavner P (2008) Wind power as a clean-energy contributor. Energy Policy 36:4397–4400 64. Joselin Herbert GM, Iniyan S, Sreevalsan E, Rajapandian S (2007) A review of wind energy technologies. Renew Sustain Energy Rev 11:1117–1145 65. Firestone J, Kempton W (2007) Public opinion about large offshore wind power: underlying factors. Energy Policy 35:1584–1598 66. Zoellner J, Schweizer-Ries P, Wemheuer C (2008) Public acceptance of renewable energies: Results from case studies in Germany. Energy Policy 36:4136–4141 67. Energy&Meteo systems, German forecasting company Ulrich Focken/Matthias Lange (www. energymeteo.de) 68. Fraunhofer Institut fu¨r Windenergie und Energiesystemtechnik IWES, Kurt Rohrig (www. iwes.fraunhofer.de)

35 Geothermal Energy Hirofumi Muraoka North Japan Research Institute for Sustainable Energy (NJRISE), Hirosaki University, Aomori, Japan Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1326 Heat in the Earth’s Interior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1327 Quantity of Thermal Energy Supplied from the Earth’s Interior . . . . . . . . . . . . . . . . . . . 1329 Direct Use of Geothermal Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1329 Geothermal Power Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1330 Category of Geothermal Resource Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1333 Sub-Solidus Magma Penetrated by Well WD-1a in Kakkonda, Japan . . . . . . . . . . . . . 1336 Distribution of Geothermal Resources in the World . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1339 Global Geothermal Resource Potentials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1342 Present State of Geothermal Development in the World . . . . . . . . . . . . . . . . . . . . . . . . . . . 1345 Geothermal Cascade Utilization Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1347 Mitigation of Global Warming by Geothermal Development . . . . . . . . . . . . . . . . . . . . . . 1350 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1351

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_35, # Springer Science+Business Media, LLC 2012

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Abstract: While most renewable energies are, directly or indirectly, derived from the sun, geothermal energy originates in the interior of the earth. Geothermal energy is the most stable of the renewable energies because it can be utilized constantly, regardless of weather or season. Geothermal energy can be used not only for power generation, but also for direct heat application. The development of geothermal power generation entered a phase of rapid growth in 2005, and its total-installed capacity worldwide reached 10.7 GWe in 2010. The capacity of 10.7 GWe appears small when compared with solar and wind power generation; however, the high-capacity factor of geothermal power plants, which is 0.7–0.9, provides several times greater electricity from the same installed capacity than photovoltaic and wind plants. Direct heat application can be used almost anywhere on land. Geothermal resources are classified into two categories: hydrothermal convection resources and thermal conduction resources. Today’s geothermal power capacity is mainly hydrothermal-based and unevenly distributed in volcanic countries. As a borehole is drilled into deeper formations, formation temperature becomes higher but permeability becomes lower. Hydrothermal convection resources have a limit depth. Rock’s brittle-plastic transition gives a bottom depth to permeability, and it is the absolute limit depth for the hydrothermal convection resources. Enhanced or engineered geothermal systems (EGS), in which fractures are artificially created in less-permeable rocks and heat is extracted by artificially circulating water through the fractures, are still at a demonstration stage, but they will extend geothermal power generation to thermal conduction resources and to depths even deeper than the brittle-plastic transition. Assessment of worldwide geothermal resource potential is still under study. However, an estimate shows that potential is 312 GWe for hydrothermal resources for electric power generation to a depth of 4 km, 1,500 GWe for EGS resources to a depth of 10 km, and 4,400 GWth for direct geothermal use resources. Were 70% of hydrothermal resources, 20% of EGS resources, and 20% of direct use resources to be developed by 2050, it could reduce carbon dioxide emission by 3.17 Gton/year, which is 11% of the present worldwide emission.

Introduction While most kinds of renewable energy available are, directly or indirectly, derived from the sun, geothermal energy originates in the interior of the earth. This makes geothermal energy distinct from other kinds of renewable energy, giving it use merits as well as demerits. Geothermal energy is the most stable energy among a variety of renewable energies. The capacity factor, a ratio of working time of the facility, of geothermal power plants is as high as those of thermal power plants, qualifying geothermal power generation as a base load electricity source. Geothermal energy can be supplied constantly from the earth’s interior regardless of time of the day or night, weather, or season. Assessment of the resource potentials of most kinds of renewable energy, such as the wind velocity and solar radiant energy, is not very difficult because they can be directly

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observed. Assessment of geothermal resource potential is not as easy, however, because geothermal resources are stored in the earth’s crust. This makes the initial investment risk for geothermal energy developments higher. For many years, geothermal energy development was only undertaken in volcanic countries such as Italy, New Zealand, Japan, the USA, the Philippines, Iceland, and Indonesia. More recently, however, less volcanic countries, such as Germany, Australia, France, and Switzerland, have begun enthusiastically developing geothermal power plants under a new concept of the enhanced or engineered geothermal system (EGS). Innovation in geothermal energy utilization technology currently aims at a goal that every country can use geothermal energy.

Heat in the Earth’s Interior Enormous heat is stored in the earth’s interior. The simplified thermal structure of the earth’s interior is illustrated in > Fig. 35.1. The deepest hole ever drilled was the SG-3 well in Kola Peninsula, Russia, that reached a depth of 12,262 m in 1989 [3]. The hole reached only 0.2% of the radius of the earth, suggesting that direct temperature measurement of the earth’s interior would be difficult. The temperature of the earth’s interior is estimated from the transmissibility and velocity of seismic waves, high-temperature and highpressure experiments for mineral phase changes, a model calculation of temperature increases by the adiabatic compression of mineral phases, a model calculation of electric conductivity of mineral phases, and many other methods. All of these are indirect estimates and inevitably yield a large opportunity for error. The temperature at the center of the earth is commonly estimated to be 6,000
C, but that may easily yield an error 1,000
C (> Fig. 35.1). Seismological observation delineates that the outer core of the earth consists mainly of molten state iron and nickel, and the mantle of the earth consists of solid state peridotite (ultramafic rocks mostly composed of olivine, Ca-poor pyroxene, and Ca-rich pyroxene). When the melting point temperatures of these are considered at the given pressure, the core-mantle boundary is estimated to be about 4,000
C [4]. The abrupt change of the velocity of seismic waves at a depth of 670 km in the lower and upper mantle boundary is ascribed to the phase changes from g phase of spinel to perovskite + magnesiowu¨stite at 1,600
C [5]. The thickness of lithosphere, a rigid plate, is less than 30 km near the axis of ocean ridges and increases to 100 km away from the ridge. Low-velocity zones of the seismic waves or asthenosphere underlie the rigid plate at a depth between 70 and 250 km. This zone is partially fused and probably reaches 1,000
C because of the wet solidus temperature of peridotite. Therefore, only a thin veneer of the earth’s surface is less than 1,000
C, and the 93% volume of the earth’s interior exceeds 1,000
C (> Fig. 35.1). Thus, the earth is some sort of a thermal engine. The derivation of the heat is mainly attributed to the accretion heat from bombardment of unsorted micro-planet materials and the heat from gravitational

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C

00°

Lower mantle (670–2,900 km)

C

00°

3,0

C 00° 4,0 Outer core (2,900–5,100 km)

3,000 4,000

5,000 6,000 6,371 km

Inner core (5,100–6,371 km) 6,000°C at the center

Sunda n tio subduc zone

1,000 2,000

C

00°

2,0

t ibe –T ya tal ala inen one Himcont on z i llis co

su Ag bd ea uc n tio se n a zo ne

1,0

Up p (35 er ma –67 ntl 0k e m)

Lithosphere (thickness 30∼100 km) S Oc W Ind ea ian n rid ge

E In a n dia n r id g e

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S e Oc

Temperature color scale of Planck’s black-body radiation 0

1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 °C

. Fig. 35.1 Simplified thermal structure of the earth’s interior (Topographic data are taken from [1] and drawing is made with GMT by [2])

differentiation and compression in the initial stage of the earth’s formation history some 4.6 billion years ago [6]. The earth is gradually losing the initial heat with time. Nevertheless, abundant heat is still stored in the earth’s interior, 4.6 billion years after its incipiency. The thermal life of the earth is prolonged by the additional heat generation in radioactive decay. Based on the past 4.6 billion years, the earth’s heat will be probably preserved for another 4.6 billion years. Thus, the earth is some sort of a semipermanent thermal engine.

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Quantity of Thermal Energy Supplied from the Earth’s Interior The earth’s interior constantly supplies heat to the surface. This heat transportation phenomenon is called ‘‘terrestrial heat flow.’’ Terrestrial heat flow can be measured in wells at a depth from 0.3 to 3 km on shore, where the solar radiant heat does not reach. Terrestrial heat flow can be measured in shallower wells on the ocean floor because of no disturbance by solar radiant heat. Terrestrial heat flow is calculated from the observed thermal gradient multiplied by the thermal conductivity of the constituent rocks. An average terrestrial heat flow is 65  1.6 mW/m2 on shore and 101  2.2 mW/m2 offshore [5]. The value of the terrestrial heat flow observed on shore consists of not only heat flow from the earth’s interior, but also heat flow from radioactive decay of elements such as uranium, thorium, and potassium predominantly concentrated in the continental crust. About half of the terrestrial heat-flow value on shore may be derived from radioactive decay. The value of the terrestrial heat flow observed offshore has a negative correlation with the geological age of ocean floor. The younger ocean floor tends to yield the higher terrestrial heat flow [5]. Including both continental and oceanic regions, a global average terrestrial heat flow is 87  2.0 mW/m2. This value 2.1  106 cal/cm2·s (87 mW/m2) multiplied by the entire global area is converted to the annual value, yielding an annual global terrestrial heat-flow energy Ehf = 1.3  1021 J/year or 3.2  1020 cal/year [7]. This heat-flow energy causes a variety of the earth’s internal dynamics, such as mantle convection, plate tectonics, earthquakes, and magma generation. Thermal energy of lava flow and volcanic ash erupted from global volcanoes is estimated to be Ee = 3  1019 J/year or 7  1018 cal/ year [7]. This energy is one or two orders of magnitude lower than the terrestrial heat-flow energy that causes it. Many active volcanoes form high-level magma chambers that heat up ground water to discharge fumaroles (natural vents of steam and volcanic gas) and hot springs. The discharge energy of fumaroles and hot springs on the earth is estimated to be Ew = 2  1018 J/year or 5  1017 cal/year [7]. This energy is also one magnitude lower than the volcanic eruption energy that causes it. The earth seems to be an almost semipermanent thermal engine, where abundant terrestrial heat flow is always being lost from the earth’s surface. Therefore, artificial utilization of the terrestrial heat flow does not seriously affect the dynamic equilibrium of the earth. This is a concept of the environment-friendly geothermal energy utilization.

Direct Use of Geothermal Energy Since the early history of human beings, hot springs, and steaming grounds were utilized for a variety of purposes such as bathing, cooking, balneology, and healing. Direct use of geothermal energy thus has a long history over the last few millenniums. The direct use of geothermal energy is currently extended to the hot-water supply, swimming pools, space heating, snow melting, drying foods or materials, condensing sugar, green house cultivation, and fish cultivation. Geothermal heat pumps for heating and cooling of

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buildings and houses are rapidly spreading in the world. Methods of direct use of geothermal energies are briefly described here. Bathing is one of the most traditional direct uses of geothermal energy. For example, as of March 2010, there are 27,825 hot-spring sources in Japan [8], most of which were developed by drillings for bathing in hot-spring resort hotels. In China, since the China Western Development policy was launched in 2000, many hot springs were developed by 3,000 m class deep drillings to the porous Ordovician limestone strata [9]. In New Zealand, the Maori people have traditionally cooked foods in steaming grounds in Rotorua and Taupo. Large-scale flower cultivation green houses heated by hot springs are found in Monte Amiata, Italy. Shrimp cultivation by hot water from the geothermal power plant is famous in Wairakei, New Zealand. In Iceland, approximately 90% of residences are heated by hot water from geothermal power plants and hot-spring wells. Thus, Iceland has become an almost energy independent nation. Use of geothermal heat pumps, a direct use of geothermal energies, has increased rapidly because they do not require any geothermal anomaly areas and can be utilized almost everywhere on land. The equivalent number of the 12 kW units (typical of US and Western European homes) reached 2.94 million in 2010, over double the number of units in 2005 [10]. Temperature is constant underground. This can be experienced in limestone caves, which feel warm in winter and cool in summer. Only the atmospheric temperature changes from day to night and due to seasonal variation of solar radiant energy. Solar radiant energy reaches the shallower part of the ground, to a depth of 10, 20, or 30 m, depending on the rock species of strata, but does not reach the deeper formations. Therefore, heat can be wasted through a well as shallow as 50 or 100 m underground by a heat pump in summer and can be extracted in winter. Geothermal heat pumps resemble air conditioners (air-sourced heat pumps), but air conditioners waste heat to the atmosphere in summer, causing the heat island phenomenon. Increasing use of geothermal heat pumps for heating and cooling of buildings and houses will effectively mitigate the global warming and the heat island phenomena.

Geothermal Power Generation Geothermal power generation has a relatively short history, beginning only in the last century. Geothermal power generation experiments were successfully initiated at Larderello in Tuscany, Italy, in 1904 [11]. Since then, a variety of methods of geothermal power generation have been developed. These methods of are briefly described here. Geothermal power generation is classified into two categories: steam flash power generation from high-temperature hydrothermal resources of 150–370
C and binary cycle power generation from low-temperature hydrothermal resources of 50–200
C (> Fig. 35.2). In the 1970s, geothermal fluids less than 150
C could not have been economically utilized for electric power generation. The only available method of geothermal power generation in those days was conventional type steam flash power generation, which uses the conventional steam turbine directly rotated by the natural

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Geothermal power generation Binary cycle power generation: suitable for 50–200°C resources, zero emission but low efficiency and small scale

Steam flash power generation: suitable for 150– 370°C resources, non-zero emission but high efficiency and large scale Double flash power generation: secondary steam can also be utilized

Single flash power generation: no secondary flasher

Back pressure power generation: no condenser and cooling tower

Kalina cycle power generation: twocomponent working fluid

Rankine cycle power generation: one-component working fluid

. Fig. 35.2 Classification of geothermal power generation

Turbine Steam

Generator

Steam Cooling tower

Water Separator

Intra-borehole flash

Condenser

Production well

Cooling water pump

Reinjection well

. Fig. 35.3 Illustration of a plant of the single flash geothermal power generation (Modified from [11])

steam from the geothermal production wells (> Fig. 35.3). Even if the subsurface natural fluid is a liquid state under the high-pressure geothermal reservoirs at a depth, a pressure release by the drill hole makes the fluid boil and the steam ascends to the surface automatically. This phenomenon is called ‘‘borehole flash’’ and requires the temperature of water to be at least 150
C (> Fig. 35.3). Therefore, the temperature threshold of 150
C used to be important. This situation changed with the development of binary cycle power generation technology in the 1980s. The binary cycle power generation method uses a secondary working fluid, such as pentane or ammonia, that has a low boiling-point temperature (> Fig. 35.4). When the temperature of subsurface water is around 150
C or lower, the water is not easy to flash. Then, subsurface hot water is pumped up from the production wells. The subsurface water is only used as a heat source for the secondary

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Geothermal Energy

Working fluid

Turbine

Generator

Cooling tower

Water

Heat exchanger (evaporator) Normally pumping up

1332

Production well

Feed pump

Heat exchanger (condenser)

Cooling water pump

Reinjection well

. Fig. 35.4 Illustration of a plant of the binary cycle geothermal power generation (Modified from [11])

working fluid. Today, binary cycle power-generation technology enables use of moderate(150–90
C) to low-temperature ( Fig. 35.4). The most common type of binary cycle power generation is Rankine cycle power generation, which uses one-component working fluid with the fixed boiling-point temperature under a constant pressure. When a hydrocarbon is used for the working fluid, such as pentane and butane, the system is called an organic Rankine cycle (ORC). In 1980, Aleksandr I. Kalina invented a binary cycle power-generation system that uses a twocomponent working fluid of ammonia and water. This system is called Kalian cycle power generation. The boiling-point temperature is continuously changed with the ratio of two components under a constant pressure so that the thermal efficiency is higher than that of the Rankine cycle. The original Kalina cycle is specific to binary cycle power generation with the ammonia-water working fluid, but it seems more useful to extend it to binary cycle power generation with a two-component working fluid (> Fig. 35.2). The most efficient existing cycle of thermal engines converting a given amount of thermal energy into work is expressed by the Carnot cycle. The Carnot cycle is a particular thermodynamic cycle proposed by Nicolas Le´onard Sadi Carnot in 1824, and this theorem contributed to establish the second law of thermodynamics. The most efficient cycle of thermal engines is expressed as follows: ¼

QH  Q L QH

(35.1)

where  is the efficiency of the thermal engine, QH is the thermal energy given from the high-temperature heat source to the working fluid, and QL is the thermal energy wasted

Geothermal Energy

35

from the working fluid to the low-temperature heat source. Any excellent thermal engine cannot exceed the idealistic efficiency expressed by > Eq. 35.1. The > Eq. 35.1 indicates that the temperature difference between high- and low-temperature heat sources is critically important for the efficiency of thermal engines regardless of any species of materials of working fluid. It can be easily estimated from the > Eq. 35.1 that the ideal thermal efficiency of high-temperature steam flash power generation might be close to 0.5 but that of the low-temperature binary cycle power generation might be close to 0.2. In addition, low-temperature binary cycle power generation has large amounts of energy loss in the heat exchangers so that the available thermal efficiency is normally close to the half of the ideal efficiency, as low as 0.1. From the environmental point of view, steam flash power generation releases small amounts of natural steam from the cooling tower that contains small amounts of carbon dioxide. Hence, subsurface hot water in binary cycle power generation is only used as a heat sources for the working fluid, and it can be totally recharged into shallower crust by reinjection wells. Zero-emission operation by a closed-loop system is possible in binary cycle power generation. Therefore, binary cycle power generation is more environmentally friendly, even if the thermal efficiency is low. When high-temperature hydrothermal fluid is unusually high in carbon dioxide, water binary cycle power generation, where relatively pure water is used as the secondary working fluid, is a possible option for zeroemission operation instead of the conventional steam flash power generation.

Category of Geothermal Resource Base The assessment of a geothermal resource requires economic feasibility criteria, the same as other resources. Geothermal resources are one of the ‘‘invisible’’ resources stored in the earth’s interior. Therefore, the confirmation of geothermal resources requires geological assurance processes such as exploration, drilling, and production tests. Based on factors of economical feasibility and geological assurance, geothermal resources are defined on a so-called McKelvy diagram, as shown in > Fig. 35.5 [12]. In 1978, an economically feasible depth for geothermal power developments was considered to be about 3 km [13]. There were not any geothermal wells deeper than 3 km at that time. Today, deep wells, at depths of 3.58 km at Unterhaching, Germany, 4.42 km at Cooper Basin, Australia, and 5 km at Soultz, France, are commonly utilized for geothermal power generation [14]. Likewise, the extent of geothermal resources is rapidly enlarging with time and technological innovation (> Fig. 35.5). The geothermal resource base, including future geothermal resources, is considered here (> Fig. 35.5). A geothermal resource base is classified into three categories by the kind of the heat transportation medium: hydrothermal convection system, thermal conduction system, and high-level magma system (> Fig. 35.6). The hydrothermal convection system is, in a narrow sense, a traditional geothermal resource. Conventional geothermal power generation includes steam flash–type power generation and binary cycle power generation using hydrothermal convection resources. The thermal conduction system is a

1333

35

Geothermal Energy

Geological assurance Identified

Undiscovered

Subeco-nomic

Economic at future time

Resource base

Residual

Accessible

Useful

Economic

Depth

Inaccessible

Economic feasibility

1334

Reserve

Resource

. Fig. 35.5 Definition of geothermal resources on the so-called McKelvy diagram [12]

next-generation geothermal resource and is economically marginal at this time. The highlevel magma system is a remote future geothermal resource. However, the high-level magma systems have already played an important role of sub-volcanic heat sources to form hydrothermal convection systems. Three representative thermal gradients are shown in > Fig. 35.3, where their curvatures arise from the heat generation of radioactive decay mostly generated in the upper granitic crust. The geothermal gradient labeled ‘‘Continent’’ shows an average trend about 30
C/km on the continental regions, ‘‘Volcanic zone’’ shows the higher trend about 40
C/km on active volcanic zone, and ‘‘Older continent’’ shows the lower trend about 18
C/km on the coldest region. In any geothermal gradient regions, if a hole is drilled deeper and deeper, the formation temperature can be higher and higher. Therefore, the greater depth is promising, with more abundant geothermal energy in terms of the temperature regime.

Geothermal Energy

35

. Fig. 35.6 Temperature (left) and permeability (right) with a depth of earth’s crust. In the left diagram, red dots show 6,522 bottom hole temperatures from Japanese wells [15] and BPT indicates the brittle-plastic transition. The right diagram is redrawn from [16]

However, the permeability of crustal rocks is known to rapidly decrease with increasing depth of crust (> Fig. 35.6) [16]. Permeability is hydrological flow efficiency of water or water-dominated fluids in crustal rocks. This parameter depends not only on the porosity of rocks, but also on the density of fractures of the macroscopic rock strata. The depth dependency of permeability indicates that the velocity of hydrothermal convection dramatically decreases with increasing depth of crust. Therefore, hydrothermal reservoirs become rarer with increasing depth of crust. This is a continuous model on the permeability-depth relationship. There is another constraint on the permeability-depth relationship: the concept of the brittle-plastic transition. All rocks will lose permeability at the depth of the brittle-plastic transition, below which all fractures and pores will be closed by the viscous behavior of rocks [17]. Schematic models of the brittle-plastic transitions on upper granitic crust, lower gabbroic crust, and upper peridotite mantle are shown in > Fig. 35.6. The WD-1a well drilled to the depth of 3,729 m in Kakkonda, northeastern Japan, penetrated the brittle-plastic transition at a depth of 3,100 m [18]. The brittleplastic transition on the upper peridotite mantle may coincide with the bottom of lithosphere. This is a discontinuous model on the permeability-depth relationship. The continuous model [16] and discontinuous model [17, 18] on the permeability-depth relationship are probably compatible with each other. When the crust is observed statistically, the continuous model will be valid. When the crust is observed in some specific locality, the discontinuous model is obtained. Based on both continuous and discontinuous models, the permeability-depth relationships suggest that all hydrothermal convection resources have a limit depth.

1335

1336

35

Geothermal Energy

As a borehole is drilled into deeper formations, the formation temperature becomes higher but permeability becomes lower. Therefore, hydrothermal convection resources have a limited depth. Particularly, the brittle-plastic transition of rock property gives a bottom depth to permeability and it gives the absolute limit depth for the hydrothermal convection resources. As a result, the region of the hydrothermal system is confined to the low-temperature and shallow region, as schematically shown in > Fig. 35.6. Enhanced or engineered geothermal systems (EGS), in which fractures are artificially created in less-permeable rocks and heat is extracted by artificially circulating water through the fractures, are still at a demonstration stage. However, they will extend geothermal power generation to the thermal conduction region to a broad depth range even greater than the brittle-plastic transition and to a broad temperature range even higher than the brittle-plastic transition (> Fig. 35.6). Even if the given depth is a plastic region, artificial circulation of water makes the local domain brittle and attains artificial fracturing. Therefore, the EGS technology will open the next generation of geothermal power generation that can be applied anywhere on land [19].

Sub-Solidus Magma Penetrated by Well WD-1a in Kakkonda, Japan The exploration well WD-1a was drilled to a depth of 3,729 m in the Kakkonda geothermal field, northeast Japan, using efficient borehole cooling techniques in July 1995 (> Fig. 35.7) [18, 20]. The well penetrated an entire shallow hydrothermal convection zone, an entire contact metamorphic aureole, and part of a young granitic intrusion called the Kakkonda Granite. The recovered temperature of the well indicates a boiling point– controlled profile up to 380
C to a depth of 3,100 m, and a conduction-controlled profile with a very high gradient from 3,100 m to the bottom of the hole, where the temperature is 500
C (> Fig. 35.8) [18, 20]. The well WD-1a may be the first geothermal well that encountered 500
C, which exceeds the conventional hydrostatic boiling-point curve (> Fig. 35.6). An inflection point of the temperature-depth profile at 3,100 m and about 380
C reflects the brittle-plastic boundary (> Fig. 35.8). The brittle-plastic boundary constrains the maximum depth of fracture formation, and the fracture distribution constrains the maximum depth of hydrothermal convection. The theory of lithosphere strength can be applied to the well WD-1a. The theory consists of Byerlee’s law in a brittle region and a power law creep equation in a plastic region (> Fig. 35.9). The Byerlee’s law in a brittle region is expressed by the following equation [21]:
1 ffi 5 s
3 ; s
3 < 110 MPa s
1 ffi 3:1 s
3 þ 210; s
3 > 110 MPa s where s1 = the maximum principal stress s3 = the minimum principal stress

(35.2)

Geothermal Energy

35

Iwate San

Shimokurayama Nakakurayama Ofukadake Omatsukurayama Mitsuishiyama

Oshiromori Kakkonda River Kakkonda River 1,000 m a.s.l. N55°W

0 −1,000 m −2,000 m −3,000 m

S55°E N55°W Yamatsuda formation Takinoueonsen Torigoenotaki formation dacite WD-1a Kunimitouge formation Obonai formation Pre-tertiary system Kakkonda Granite

1,000 m Takakurayama a.s.l. S55˚E

0 −1,000 m −2,000 m

1,000 m

−3,000 m

. Fig. 35.7 The Kakkonda geothermal field, Iwate Prefecture, Japan, and the well WD-1a [18,20]

Figure 35.9 is only constrained by the upper equation. The power law creep is expressed by the following equation [21]: >

e_ ¼ Aðs1  s3 Þn e ð RT Þ H

(35.3)

where e_ = strain rate, s1 A = material constant specified to the rock or mineral species n = stress exponent H = activation enthalpy, J mol1 R = gas constant, J K-1 mol1 T = temperature, K Most of these parameters are reasonably determined on the well WD-1a. The strain rate e_ is given to be 1012 s1 because of the active compressive tectonic region [17]. Taking the data from quartz diorite close to the Kakkonda Granite, the stress exponent n is given to be 2.4, and activation enthalpy H is given to be 219 kJ mol1. The temperature T is given by the temperature profile of the well WD-1a in > Fig. 35.8. The material constant A varies from 1019 to 1049 according to the given material, and only this parameter cannot be reasonably determined. However, the inflection point of the strength curve by the temperature inflection in the plastic region should coincide with the depth of

1337

35

Geothermal Energy

0

0

100

Temperature (°C) 200 300 400

500

600

Minimum homogenization temperature of fluid inclusions of minerals

Inflection point dividing the shallow reservoir (low-pressure) and deep reservoir (high-pressure) in the Kakkonda geothermal field

1,000

Depth(m)

1338

Temperature log at Feb.14, 1996 (167 days after drilling) 2,000 Equilibrium temperature estimated from recovery trends Pre-tertiary system Kakkonda Granite 3,000 Temperature log at Jul. 21, 1995 (82.3 h after drilling)

Temperature Profile simplified from various data Inflection point dividing the hydrothermal convection zone and magmatic conduction zone

3,800 Chemical compound tablets with known melting point temperatures (one for 500°C was melted but one for 505°C was unmelted)

. Fig. 35.8 Temperature profile of the well WD-1a in the Kakkonda geothermal field, Japan [18, 20]

3.1 km, restricting the material constant A to be 100.85. Then, the strength curve on the plastic field is drawn as shown in > Fig. 35.9 [22]. The four points of stress ratio measurements of the differential strain curve analysis (DSCA) on the core samples [23] are well explained by the model of the strength profile drawn by the Byerlee’s law and the power law creep equation as shown in > Fig. 35.9. Particularly, closure of s1 value to s3 at the deepest DSCA stress ratio measurement indicates that the dramatic strength weakening occurred as being accommodated by the

35

Geothermal Energy

0

0

50

100

Stress (Mpa) 150

200

250

300

Four points of NEDO DSCA measurments Lost circulation zones (Schematic but after σ3 = σ v σ3 = σv observed depths) Max imu ms tren gth , λ= 0 (d ry) λ= Brittle-plastic λ= 0 . 2 0.3 transition 8( hy w σ3 = σv dro o l f λ sta = c i 0.4 t tic s λ ) a l = p 0.6 e t i r i o -d rtz a Due to the inflection Qu of the temperature profile

σ2 = σ v

atic

ost

2

Lith =σv (σ H

Depth (km)

1

3

)

λ=

8

0.

4

λ=

Crustal strength profile (shaded)

1.0

5

λ: pore pressure

. Fig. 35.9 Crustal strength – depth relation along the well WD-1a in the Kakkonda geothermal field, Japan [22]

plastic field as shown in > Fig. 35.9. Three points of DSCA stress ratio measurements in the brittle field are close to the dry line (l = 0). This is also reasonable because the sampling of cores could have been only performed from impermeable zones with no lost circulation. These observations strongly support that the well WD-1a actually penetrated the brittle-plastic transition [18, 20]. The brittle-plastic transition may primarily be expected in the temperature inflection point at the depth of 3,100 m and the temperature 380
C [18]. However, the graphical representation makes it clear that the brittle-plastic transition in a strict sense probably lies at a shallower depth, like 2,400 m, where the maximum strength is attained at 360
C (> Fig. 35.9). A zone of very high concentration of low-angle fractures is observed in the depth interval from 1,770 to 2,860 m (> Fig. 35.10) [24]. This fracture zone likely reflects the maximum strength zone of the bottom of the brittle layer because this zone may play a role of the dehydration front and dehydration-induced weakening front [24].

Distribution of Geothermal Resources in the World High-temperature hydrothermal resources (>150
C) are unevenly distributed in the world. > Figure 35.11 shows global topography, global bathymetry (topography of

1339

Contact of the granitic body

2,350.0m

2,085.0m 2,137.0m 2,240.0m

1,985.0m

1,900.0m

1,580.0m

1,291.7m 1,327.0m 1,345.0m

980.7m

0

4

Inferred from observation of cores

2

6

8

4,000

3,500

3,000

2,500

2,000

1,500

1,000

500

0

H2O (−)

H2O (+)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0 1

3

MgO

2

4

5

6

7

8

MgO component Abundance in weight %

Fe2O3/(Fe2O3+FeO)

9 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Fe2O3/ (Fe2O3+FeO) ratio

. Fig. 35.10 Chemistry of cutting samples from the contact metamorphic aureole of the Kakkonda Granite and high concentration of low-angle fractures [24]

3,800

3,500

3,000

2,500

2,000

1,500

1,000

500

273.3280.8m

42.0m

H2O (−) and H2O (+) components Abundance in weight %

35

Depth in meter

0

Depth Lost circu- Density of FMI fractures Mineral In m lation zones (Numbers/m) Isograd

b o u bl e (1 ,6 1 0 m ) c o rd i e r i te (2 ,0 2 0 m ) a n th o p hy l i d e (2 ,1 4 0 m ) c u m m i n g to n i te (2 ,3 2 0 m ) ctinopy roxe n e, g a r n e t (2 ,6 6 5 m ) adsandalus i te, p o ta s s i u m , fe l d s p a r, s p i n e l (2 ,8 6 0 m )

1340 Geothermal Energy

. Fig. 35.11 Global topography, global bathymetry, plate boundaries, active volcanoes, and representative geothermal power plants (Topographic data are taken from [1], drawing is made with GMT by [2], and active volcanoes are taken from [25])

Geothermal Energy

35 1341

1342

35

Geothermal Energy

ocean floors), plate boundaries, active volcanoes [25], and representative geothermal power plants. High-temperature hydrothermal resources that are hot enough for the steam flash–type power generation are associated with active volcanic zones so that most of geothermal power plants are developed in active volcanic zones. This is because sub-volcanic magma chambers or their sub-solidus equivalents (hot intrusive bodies) are serving for geothermal heat sources for the high-temperature hydrothermal reservoirs. Actually, young plutonic bodies are often penetrated by geothermal wells not only in the Kakkonda geothermal field, Japan, as described in the preceding section, but also in other geothermal fields such as The Geysers, in California, USA; Tongonan and Palinpinon, in the Philippines; and Mutnovsky, in Russia [26]. Active volcanic zones are associated with two types of plate boundaries: spreading and convergent. A typical spreading plate boundary is midocean ridges. In > Fig. 35.11, midocean ridges are not represented as volcanoes, but they are the largest volcanoes on the earth that are lineally continued. Their geothermal development has been difficult so far because of the high cost of submarine exploitations. As a result, most of geothermal power plants are built in the volcanic zones of the convergent plate boundaries. One exception is the Great Rift Valley in the eastern Africa, where spreading plate boundaries appear on shore. The other exception is the Salton Sea and Cerro Prieto geothermal fields in the western North America, where spreading plate boundaries or their transform faults appear on shore. The last exception is Iceland, which is situated on the mid-Atlantic ridge where the ridge appears above a sea level because of the strong volcanic activity in the hot spot. Most of geothermal power plants are developed in the volcanic zones of subduction zones. Particularly, the largest subduction zones are found in the circum Pacific regions. Although the first geothermal power generation was accomplished in Italy in 1904, the largest geothermal power country is currently the USA, the second is the Philippines, and the third is Indonesia. All of these are situated along the circum Pacific regions. Geothermal electricity plays a very important role in Central America, where 10% or higher ratios of electricity are supplied from geothermal power generation in many countries. It seems curious that very few geothermal power plants have been developed in South America, in spite of the huge geothermal potential in the Andes. The Copauhe geothermal power plant used to operate in Argentina, but it has been terminated. No geothermal power plant is currently operating in South America. In other words, South America has reserved a large potential for geothermal power development in the near future.

Global Geothermal Resource Potentials Assessment of global geothermal resource potentials is hard to accomplish because subsurface exploration data with uniform accuracy are seldom available on a global scale. However, a rough estimate is possible by analogical reasoning. Hydrothermal power resources, EGS power resources, and direct use resources are estimated here by analogical reasoning.

Geothermal Energy

35

Stefansson [27] estimated world geothermal assessment based on well-known data on active volcanoes [25]. Hydrothermal resources high enough in the temperature for the steam flash–type power generation are normally associated with active volcanoes, and therefore, his method is an excellent analogical reasoning by use of well-known data. Although the size of the active volcano varies from the 100-km-long Toba caldera in Indonesia to 0.6-km-long maars (explosion volcanic craters without remarkable tuff rings in its surroundings) such as Megata in Japan, these size differences might cancel one another by using statistical data. Here, modification is made from the original paper because some data have been updated. > Table 35.1 and > Fig. 35.12 show a relationship between the numbers of active volcanoes and assessed hydrothermal power resources in eight representative countries modified from the original paper [27]. A number of active volcanoes are taken from the catalog [25], where submarine volcanoes are excluded. Assessed hydrothermal power potentials are taken from each reference described in > Table 35.1. A regression equation is obtained between numbers of active volcanoes and estimated hydrothermal power resources in eight representative countries: E ¼ 221:7 n

(35.4)

where E = hydrothermal resource potential for geothermal power generation (MWe) v = a number of active volcanoes without submarine volcanoes The maximum exploitation depth of the > Eq. 35.4 is not strictly defined in the different assessment condition in each country, but it is roughly assumed to be a depth of 4 km. The > Eq. 35.4 is useful to estimate hydrothermal resource potentials when the

. Table 35.1 Number of active volcanoes and estimated geothermal potential for electrical generation in eight representative countries. The number of active volcanoes is taken from [25] where submarine volcanoes are excluded Country USA Indonesia Japan Philippines Mexico Iceland New Zealand Italy

Number of active volcanoes

Assessed hydrothermal power potentials (MW)

163 137 93 46

39,090 27,140 23,470 6,000

39 27 12 12

6,000 5,800 3,650 1,500

References William et al. [28] Darma et al. [29] Muraoka et al. [30] Wright [31] Mulas de Pozo et al. [32] Palmason et al. [33] Lawless [34] Buonasorte et al. [35]

1343

35

Geothermal Energy

45,000 USA

40,000 35,000 Assessed potential (MW)

1344

30,000

Indonesia

25,000 Japan 20,000

E = 221.7v R 2 = 0.9598

15,000 10,000 Philippines

Iceland 5,000 New Zealand 0 0

Mexico Itay 20

40

60

80

100

120

140

160

180

Number of active volcanoes

. Fig. 35.12 Correlation between the number of active volcanoes and estimated geothermal potential in eight representative countries slightly modified from [27]. The number of active volcanoes are taken from [25], where submarine volcanoes are excluded

subsurface exploration data are not fully available. If a number of global active volcanoes, 1,406 excluding submarine volcanoes, are input into this equation, about 312 GWe are obtained as a hydrothermal resource potential for geothermal power generation in the world. Only a few countries estimated the EGS resources. The EGS resources are, however, almost proportional to the width of the given area. Therefore, an estimate in the United States [19] can be used as teacher data, and it can be extrapolated to the world according to the area ratio. Tester et al. [19] estimated EGS resources to be at least 100 GWe in the United States for the exploitation to a depth of 10 km. The widths of the land area of the world and the United States are 148,890,000 km2 and 9,826,635 km2, respectively. Then, 1,500 GWe was obtained as a global EGS resource potential. Assessment of direct use resources is far more difficult to attain because the variety of uses: baths, swimming pools, snow melting, hot-water supply, space heating, greenhouses, and drying foods. Therefore, it needs some simplification. Stefansson [27] estimated hydrothermal resources lower than 130
C for direct use to be 4,400 GWth based on the resource frequency distribution like a power function. This seems an excellent estimate, because the number is almost 10% of the annual global terrestrial heat-flow energy. As described in the earlier section, an annual global terrestrial heat-flow energy Ehf = 1.3  1021 J/year, and 10% is 1.3  1020 J/year, which is

Geothermal Energy

35

equivalent to 4,120 GWth. Therefore, the estimate for direct use resources of 4,400 GWth seems reasonable.

Present State of Geothermal Development in the World The present state of geothermal development in the world is briefly described for geothermal power generation [36] and on direct use [10]. The installed capacity of geothermal power generation in the world is 10,715 MWe as of 2010, and the growth rate during the last 5 years was the second greatest, after the early 1980s, as shown in > Fig. 35.13. The produced electricity during the year 2010 was 67,246 GWh [36]. The capacity factor, a ratio of working time of the facility, of geothermal power plants is 0.72 throughout the world. This capacity factor is amazingly high compared with not only other renewable electricity sources, but also thermal or nuclear power sources. The five largest geothermal power-generation countries – the USA, the Philippines, Indonesia, Mexico, and Italy – account for about 75% of the world geothermal power capacity (> Table 35.2). The installed geothermal energy facilities for direct utilization at the end of 2009 was 50,583 MWth, and the thermal energy used was 438,071 TJ/year (121,696 GWh/year) as shown in > Fig. 35.14 [10]. Again, the growth rate during the last 5 years was rapid compared to the past. The capacity factor of direct use was 0.27 at the end of 2009, and

12,000 10,715 10,000 Installed capacity (MW)

8,933 7,972 8,000 6,833 5,834

6,000 4,764 4,000 2,110 2,000 200 0 1950

1,180 270

386 1960

520

720

1970

1980

1990

Calendar year

. Fig. 35.13 Growing installed geothermal power capacity in the world [36]

2000

2010

1345

1346

35

Geothermal Energy

. Table 35.2 Installed geothermal power capacity and electricity production in the world [36] Country ARGENTINA AUSTRALIA AUSTRIA CANADA CHILE CHINA COSTARICA EI SALVADOR ETHIOPIA FRANCE GERMANY GREECE

Installed in 2005 (MW) 0 0.2 1.1 0 0 28 163 151 7.3 15 0.2 0

Energy in 2005 Installed in (GWh) 2010 (MW) 0 0.5 3.2 0 0 96 1,145 967 0 102 1.5 0

0 1.1 1.4 0 0 24 166 204 7.3 16 6.6 0

Energy in 2010 (GWh) 0 0.5 3.8 0 0 150 1,131 1,422 10 95 50 0

GUATEMALA HONDURAS HUNGARY ICELAND

33 0 0 202

212 0 0 1,483

52 0 0 575

289 0 0 4,597

INDONESIA ITALY JAPAN KENYA MEXICO

797 791 535 129 953

6,085 5,340 3,467 1,088 6,282

1,197 843 536 167 958

9,600 5,520 3,064 1,430 7,047

NEVIS NEW ZEALAND NICARAGUA PAPUA NEW GUINEA

0 435 77 6

0 2,774 271 17

0 628 88 56

0 4,055 310 450

1,930 16 0 79

9,253 90 0 85

1,904 29 0 82

10,311 175 0 441

PHILIPPINES PORTUGAL ROMANIA RUSSIA SPAIN SLOVAKIA THAILAND THE NETHERLAND TURKEY USA TOTAL

0 0 0.3 0 20 2,564 8,933

0 0 1.8 0 105 16,840 55,709

0 0 0.3 0 82 3,093 10,715

0 0 2 0 490 16,603 67,246

Geothermal Energy

35

500,000 438,071

450,000 400,000

Utilization (TJ/yr)

350,000 300,000

272,372

250,000 200,000

190,699

150,000 112,441 100,000 50,000 0 1995

2000

2005

2010

Calendar year

. Fig. 35.14 Growing direct geothermal use in the world [10]

it was decreasing with passing time. This is because geothermal heat pumps are rapidly spreading among a variety of direct utilization methods, and the capacity factor of geothermal heat pumps is normally less than 0.2. Almost all countries are utilizing geothermal heat directly (> Table 35.3). Countries in colder regions tend to use more geothermal heat.

Geothermal Cascade Utilization Technology To date, geothermal resources tend to be used for a single utilization purpose, and the spent resources have been wasted into reinjection wells or rivers, in the case of lowtemperature direct use. However, a more efficient utilization is repeated consumption of energy such as a cascade from the high-temperature resources to the low-temperature resources as shown in > Fig. 35.15. This can be called geothermal cascade utilization. A typical example is seen in Iceland, where voluminous hot water spent in geothermal power plants is transported by pipelines, more than 25 km long, to a tank on the hill of Reykjavik City. Then, the hot water is distributed to each residence for space heating. This is a typical example of the geothermal cascade utilization. More efficient cascade utilization is possible with steam flash–type power generation, binary cycle power generation, space heating, and snow melting in descending order as shown in > Fig. 35.15. Cascade utilization makes geothermal resources several times more

1347

1348

35

Geothermal Energy

. Table 35.3 Direct geothermal utilization in the world [10] Country

Capacity (MWt)

Annual use (TJ/year)

Annual use (GWh/year)

Capacity factor

Albania Algeria Argentina Armenia

11.48 55.64 307.47 1.00

40.46 1,723.13 3,906.74 15.00

11.20 478.70 1,085.30 4.20

0.11 0.98 0.40 0.48

Australia Austria Belarus Belgium

33.33 662.85 3.42 117.90

235.10 3,727.70 33.79 546.97

65.30 1,035.60 9.40 151.90

0.22 0.18 0.31 0.15

21.70

255.36

70.90

0.37

360.10 98.30

6,622.40 1,370.12

1,839.70 380.60

0.58 0.44

2,464.90 0.80 36.60 20,931.80

0.25 0.85 0.46 0.27

Bosnia & Herzegovina Brazil Bulgaria Canada Caribbean Islands Chile China

1,126.00 0.10 9.11 8,898.00

8,873.00 2.78 131.82 75.348.30

Columbia Costa Rica Croatia Czech Republic

14.40 1.00 67.48 151.50

287.00 21.00 468.89 922.00

79.70 5.80 130.30 256.10

0.63 0.67 0.22 0.19

Denmark Ecuador Egypt El Salvador Estonia

200.00 5.16 1.00 2.00 63.00

2,500.00 102.40 15.00 40.00 356.00

694.50 28.40 4.20 11.10 98.90

0.40 0.63 0.48 0.63 0.18

Ethiopia Finland France Georgia

2.20 857.90 1,345.00 24.51

41.60 8,370.00 12,929.00 659.24

11.60 2,325.20 3,591.70 183.10

0.60 0.31 0.30 0.85

Germany Greece Guatemala Honduras

2,485.40 134.60 2.31 1.93

12,764.50 937.80 56.46 45.00

3,546.00 260.50 15.70 12.50

0.16 0.22 0.78 0.74

Hungary Iceland India Indonesia

654.60 1,826.00 265.00 2.30

9,767.00 24,361.00 2,545.00 42.60

2,713.30 6,767.50 707.00 11.80

0.47 0.42 0.30 0.59

Geothermal Energy

35

. Table 35.3 (Continued) Country

Capacity (MWt)

Annual use (TJ/year)

Annual use (GWh/year)

Capacity factor

Iran Ireland

41.61 152.88

1,064.18 764.02

295.60 212.20

0.81 0.16

Israel Italy Japan Jordan

82.40 867.00 2,099.53 153.30

2,193.00 9,941.00 25,697.94 1,540.00

609.20 2,761.60 7,138.90 427.80

0.84 0.36 0.39 0.32

Kenya Korea (South) Latvia Lithuania

16.00 229.30 1.63 48.10

126.62 1,954.65 31.81 411.52

35.20 543.00 8.80 114.30

0.25 0.27 0.62 0.27

Macedonia Mexico Mongolia Morocco

47.18 155.82 6.80 5.02

601.41 4,022.80 213.20 79.14

167.10 1,117.50 59.20 22.00

0.40 0.82 0.99 0.50

2.72 1,410.26 393.22 3,300.00

73.74 10,699.40 9,552.00 25,200.00

20.50 2,972.30 2,653.50 7,000.60

0.86 0.24 0.77 0.24

Papua New Guinea Peru Philippines Poland Portugal

0.10 2.40 3.30 281.05 28.10

1.00 49.00 39.58 1,501.10 386.40

0.30 13.60 11.00 417.00 107.30

0.32 0.65 0.38 0.17 0.44

Romania Russia Serbia Slovak Republic

153.24 308.20 100.80 132.20

1,265.43 6,143.50 1,410.00 3,067.20

351.50 1,706.70 391.70 852.10

0.26 0.63 0.44 0.74

Slovenia South Africa Spain Sweden

104.17 6.01 141.04 4,460.00

1,136.39 114.75 684.05 45,301.00

315.70 31.90 190.00 12,584.60

0.35 0.61 0.15 0.32

Switzerland Tajikistan Thailand Tunisia

1,060.90 2.93 2.54 43.80

7,714.60 55.40 79.10 364.00

2,143.10 15.40 22.00 101.10

0.23 0.60 0.99 0.26

Turkey Ukraine United Kingdom

2,084.00 10.90 186.62

36,885.90 118.80 849.74

10,246.90 33.00 236.10

0.56 0.35 0.14

Nepal Netherlands New Zealand Norway

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Geothermal Energy

. Table 35.3 (Continued) Country

Capacity (MWt)

Annual use (TJ/year)

Annual use (GWh/year)

Capacity factor

United States Venezuela

12,611.46 0.70

56,551.80 14.00

15,710.10 3.90

0.14 0.63

Vietnam Yemen Total

31.20 1.00 50,583.12

92.33 15.00 438,070.66

25.60 4.20 121,695.90

0.09 0.48 0.27

180°C Table 36.1, > Fig. 36.1).

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Hydropower

. Table 36.1 Profile of global hydropower development Theoretical Technical Economic Installed Hydropower Degree of development availability availability capacity output reserve (%) (GWh/yr) (MW) (GWh/yr) (GWh/yr) (GWh/yr) Africa Asia Oceania

2,590,234 19,701,583 633,384

1,303,246 7,654,565 195,987

848,434 4,487,377 88,644

21,486 329,737 13,470

94,124 1,107,622 40,259

11 25 45

Europe North America South America Total

2,900,767 7,574,535

1,120,541 1,763,478

752,348 1,014,910

178,814 167,042

530,999 664,244

71 65

5,696,000

2,615,299

1,536,197

137,908

607,577

40

39,096,600

14,653,115

8,727,911

848,456

3,044,825

35

Specific Hydropower Potential GWh/year/km2 0.000 - 0.012

0.034 - 0.062

0.106 - 0.169

0.248 - 0.376

0.671 - 1.044

0.013 - 0.033

0.063 - 0.105

0.170 - 0.247

0.377 - 0.670

1.045 - 2.485

. Fig. 36.1 Global hydro power density (GWh/yr/km2)

In 2007, there was an installed capacity of 848,400 MW and an output of 2,045,000 GWh/yr on the globe, taking up about 20% of power supply. The degree of hydropower development reached 35% if based on the output as percentage of the economic availability, with 11% in Africa, 25% in Asia, 45% in Oceania, 71% in Europe, 65% in North America, and 40% in South America, respectively (> Table 36.1).

Hydropower

36

The global total volume of water resources is about 55 trillion m3. Due to the uneven distribution in time and space, the total availability is about 9 trillion m3 only. According to the definition given by the International Commission on Large Dams, more than 50,000 large dams (higher than 15 m or 5–15 m, storage capacity larger than 3 million m3) have been built in the world up to date. These dams control about 3.5 trillion m3 water resources, about 38% of the total volume available on the globe, and play an important role in comprehensive water utilization and management. Many dams in the world serve the function of power generation. For instance, 44 out of the reservoirs with a storage capacity over 25 billion m3 on the globe serve the function of power generation, including 16 for the sole objective of power generation. These 44 reservoirs provide a total storage capacity of 2.5 trillion m3 (about 37% of the world total) and an annual output over 500 TWh/yr, taking up about 18% of the world hydropower generation. In 2007, out of the 370 dams higher than 60 m under construction in the world, 217 were designed for the primary or only function of power generation. According to the statistical data of 2008, there were 16 countries depending upon hydropower for over 90% energy supply, for example, Norway and Albania, 49 for over 50%, including Brazil, Canada, Switzerland, and Sweden; and 57 for over 40%, including most South American countries. The average degree of hydropower development in developed countries was higher than 60%, up to 90% in France and ever over 90% in Italy (> Table 36.2). The 50,000 large dams in operation are distributed geographically as follows: 59.7% in Asia, 21.1% in North America, 12.6% in Europe, 3.3% in Africa, 2.0% in South America, and 1.3% in Australia. . Table 36.2 Hydropower development by countries in 2008 Total Economic Hydropower Percentage in Hydropower installed Storage capacity capacity availability output economic installed (109 m3) Country (TWh/yr) (TWh/yr) availability (%) capacity (MW) (MW) China United States

1,753 376

565.5 270.0

22.9 71.8

172,600 78,200

792,730 687,000

692.4 1,350 650 568 793 213

Canada Brazil Russia India

536 763.5 852 442

350.0 331.7 170.0 121.7

65.3 43.4 20.0 27.5

72,660 83,752 47,000 37,000

114,950 88,620 224,240 112,060

Japan France Norway Italy Spain

114.3 72 205.1 54 37

92.5 64.6 121.8 51.3 23.3

80.9 89.7 59.4 95.0 63.0

22,000 25,200 29,040 17,460 18,450

268,280 111,200 27,890 98,626 62,300

20.4 7.5 62 13 45.5

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There were 5,443 dams higher than 30 m in China in 2009 and 4,685 in 2003, taking up 38% of the world total base on the data of 2003, the largest number of all countries. With regard to the number of built and ongoing dams higher than 30 m in 2003, the following countries were in the second to the seventh places, respectively: USA with 1,533; Japan with 1,075; Spain with 517; India with 504; Turkey with 376; and Italy with 322. By the function of reservoirs, statistics from the International Commission on Large Dams indicated that among 33,105 registered dams single-purpose dam accounts for 72% and the rest of 28% is for multipurpose. For single purpose dams, the distribution for each purpose lead to the following results: 48.6% for irrigation, 17.4% for hydropower, 12.7% for water supply, 10% for flood control, 5.3% for recreation, 0.6% for navigation and fish farming, and 5.45 for others. For multipurpose dams, the distribution for majority purpose lead to the following results: 24.6% for irrigation, 18.7% for hydropower, 16.3% for water supply, 18% for flood control, 12.2% for recreation, 6.4% for navigation and fish farming, and 3.8% for others. In order to have a better understanding of dam construction in the world, dams and reservoirs are tabulated below by number, height, storage capacity, and power output. With minor change over the recent years, the data are based on the statistical report published by the International Commission on Large Dams and the typical data produced by Chinese National Committee on Large Dams in 2005 (> Tables 36.3–36.6).

Overview of Hydropower and Dam Development by Continents Europe

In the early 1920s, most of the large dams in Europe were built in UK (220 in total). At the end of 2006, more than 5,280 large dams were registered in Europe, with the first numbers in Spain (1,188), France, and UK, over 500, respectively. The first objective of dams in Europe is power generation, which is followed by irrigation and water supply. In the European countries, the usage (and importance) of reservoirs varies considerably, particularly in the aspect of hydropower generation. This variation reflects the difference in topography, rainfall, and government policy. Many reservoirs designed for hydropower purposes are often located in mountainous areas and north European countries, obviously different from those for irrigation and water supply. The latter are relatively small in scale, generally in lowland countries and south European countries. About a quarter of the dams in Europe are designed for multipurpose operation. In several countries, hydropower contributes more than a half to the national power supply, for example, 97% in Albania, 70.1% in Iceland, 70% in Latvija, and even up to 99% in Norway. In 1960, dam construction and hydropower development reached the climax in many parts of Europe. However, the focus today is to maintain and repair existing dams as required by new acts and regulations. In 2006, the installed capacity of hydropower stations under construction in Europe was about 4,733.2 MW, which was distributed in 20 countries, including Germany, Greece, Iceland, Italy, Macedonia, Portugal, Slovenia, and Ukraine.

36

Hydropower

. Table 36.3 Countries with more large dams higher than 100 m Country

Number of dams > 100 m

Maximum height

Name of highest dam

China

130

305

Jinping-I Dam

Japan United States Spain Turkey

106 86 51 51

186 234 202 282

Kurobe No IV Dam Oroville Dam Almendra Dam Keban Dam

Iran India Italy Switzerland

47 30 28 25

315 260.5 262 285

Bakhtyari arch dam Tehri Dam Vaiont Dam Grande Dixence Dam

Brazil Mexico Romania Russia France

23 21 18 17 15

205 261 167.7 245 180

Irape Dam Chicoasen Dam Gura Apelor Dam Sayano-Shushenskaya Tignes Dam

Vietnam Canada Colombia Australia

14 14 14 13

170 244 250 180

A Luoi Dam Mica Dam Guavio Dam Dartmouth Dam

Austria Argentina

13 11

200 170

Kolnbrein Dam Piedra Del Aguila

. Table 36.4 First 10 built and on-going large dams No

Name of dam

1 2

Jinping-I Nurek

3 4 5 6

Dam height (m)

Purpose

Country

305 300

HC IH

China Tajikistan

Xiaowan Xiluodu Grande Dixence Keban

294.5 285.5 285 282

HCIN HCN H H

China China Switzerland Turkey

7 8 9 10

Kambarazin Hydropower Station-1 Inguri Vajont Chicoasen

275 271.5 262 261

H HI H H

Kyrgyzstan Georgia Italy Mexico

11 12

Manuel m. Torres Tehri

261 261

H IS

Mexico India

H-hydropower, I-irrigation, C-flood control, N-navigation, S-water supply

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. Table 36.5 First 10 built and ongoing reservoirs Storage capacity (108 m3) Objective Country

No Name of dam 1

Kariba

1,806

H

Zimbabwe/Zambia

2 3 4 5

Bratsk High Aswan Dam Akosombo Daniel Johnson (manic 5)

1,690 1,620 1,500 1,419

HNS IHC H H

Russia Egypt Ghana Canada

6 7 8 9

Guri Bennett w.a.c Krasnoyarsk Zeya

1,350 743 733 684

H H HN HNC

Venezuela Canada Russia Russia

10

LG Deux Principal cd-oo

H

Canada

617

H, power generation; I, irrigation; C, flood control; S, water supply; N, navigation

. Table 36.6 Top 10 built and ongoing hydropower stations No Name of dam

Time of Installed completion capacity (MW)

Annual power output (GWh)

Country

1 2 3 4

Three Gorges Itaipu Xiluodu Guri

2009 1991 2010 1986

22,500 12,600 12,600 10,000

84,000 90,000 57,120 52,000

China Brazil/Paraguay China Venezuela

5 6 7 8

Tucurui Sayano-Shushenskaya Xiangjiaba Krasnoyarsk

1984 1990 UC 1967

8,370 6,400 6,000 6,000

21,400 22,800 30,747 19,600

Brazil Russia China Russia

2001 1964

5,400 4,500

18,710 22,500

China Russia

9 Longtan (in Guangxi) 10 Bratsk UC, under construction

Asia

Asia has being reached the climax of hydropower development. Most of the under constructed large dams higher than 60 m are distributed in Asia, 276 in total. The International Commission on Large Dams listed a total number of 35,070 large dams in Asia in 2006. Most of the dams in Asia are built for the purpose of irrigation, and then power generation, flood control, and water supply. At present, the first objective of dams in Asia varies from one country to another, including irrigation in India and Turkey, flood control, irrigation, and power generation (including pumped storage stations) in China, flood control and pumped storage in Japan, and irrigation and power generation in Iran. There are nine Asian countries where hydropower takes over 50% of the national power

Hydropower

36

supply. As shown by statistical data of the International Commission on Large Dams, this percentage is 14% in China (based on the power output in 2007), 17.1% in India (2007), 18% in Russia, and 25.4% in Turkey. Generally, China, India, Turkey, Japan, and Iran are most vigorous in dam construction. The climax of dam construction in Asia appeared in the period of 1970–1980, with more than 200 dams built each year. In 2006, the installed capacity in progress was larger than 189,010 MW, mostly in China, and also in India, Iran, and Russia. India has a large population, but the water availability per capita is about 1,829 m3/yr only, less than 30% of the world average, representing water shortage. The number of dams in operation in India is 4,083, with a total installed capacity of 213 billion m3. The dams in India are 90% earth and rock-fill ones, including 2,600 higher than 15 m. The national installed capacity of hydropower is 37,000 MW. Tehri Dam, the highest rock-fill dam, 260.6 m, has been completed. Russia saddles the European and Asian continents, sharing long borders with China. There is a total annual mean precipitation of about 9.348 trillion m3 and runoff of 4.262 trillion m3, representing very rich water resources. At present, there are 101 dams in operation in the country, including 58 rockfill and 43 concrete ones, with a total storage capacity as large as 793 billion m3 and an installed capacity about 47,000 MW. There are 85 hydropower stations with an installed capacity over 10 MW. In addition, about 7,000 MW is under construction. The planned installed capacity is about 12,000 MW. Bureya Dam, a concrete gravity dam with a height of 140 m and a storage capacity of 3.5 billion m3, is the highest dam under construction. North America and Central America

According to statistical data of the International Commission on Large Dams, there were 8,252 large dams in North America and Central America in 2006, including some 6,510 in the USA. 4 countries out of 15 in the region, the hydropower generation is over 50% of national power supply. They are Canada, Costa Rica, Haiti, and Panama. The hydropower output of Canada is the largest in North America, the third place in the world, and that of the USA is in the fourth place. The sum of these two countries takes up more than onefifth of the world total. Flood control, power generation, irrigation, water supply, and recreation are the primary objectives of the large dams in the USA. After the Second World War, the number of dams built and put into operation boosted in this part. In the USA, the number of dams put out of operation exceeds the number of dams newly registered and constructed each year. The large dams under construction in Central America provide an installed capacity of about 3,047.1 MW (including Mexico). By the end of 2006, Mexico had built 668 large dams, with an annual output of 25,000 GWh. The installed capacity in progress is about 2,250 MW. South America

In 2006, there existed 799 large dams in South America, including almost half of them in Brazil (387 in total). The first objective is power generation and flood control. Now, there

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Hydropower

are many high dams under construction in South America, mostly in Brazil, Venezuela, and Ecuador, with a total installed capacity of 11,327 MW distributed in nine countries. Proposed projects will provide another installed capacity of 62,956 MW. Brazil is most active in hydropower development, which accounts for 76.6% of the national power output. Other countries keen on hydropower development include Paraguay (99.99%), Columbia (78%), Peru (65%), Venezuela (73.3%), French Guiana (60%), Chile (43.5%), and Ecuador (43.5%). In 2007, there was a total installed capacity of about 11,327 MW under construction in 13 South American countries. Africa

Africa is less capable in developing and regulating water resources. As suggested by the statistical data of the International Commission on Large Dams, there were 1,815 built large dams in Africa, including over 80% in South Africa (1,166), Zimbabwe (250), and Morocco (120). In 2006, more than 20 African countries were developing hydropower resources, but the number of dams higher than 60 m was not large, only 13. There was a total installed capacity of 7,489 MW in progress in 17 countries in 2007, including 3 countries with an installed capacity larger than 1,000 MW, namely, Ethiopia (1,277 MW), Guinea (1,291 MW), and Sudan (1,300 MW). In the arid and semiarid north and south parts of Africa, dams are built mainly for irrigation. In the middle and other humid parts, the first objective is power generation. The ‘‘Southern Africa Power Pool’’ has done something in investing in future power infrastructures here. In Africa, the percentage of hydropower in 22 countries takes up more than 50% of the national power supply, and even more than 90% in 5 countries including Zambia, Mozambique, and Namibia. Oceania

There are altogether 621 large dams here, mostly in Australia (541) and New Zealand (67). Dams are first for the objective of water supply, but also for power generation and irrigation as well. There are three countries where hydropower constitutes over 50% of the national power supply, namely, Fiji (50%), New Zealand (60%), and Papua New Guinea (65%). In Australia and New Zealand, the climax of dam construction was witnessed in 1980 (about 10 dams on the average each year). In 1990, the speed was slowed down. Now, there is only one 60 m high dam under construction in Australia, where the focus is shifted to small hydropower and water supply facilities.

Small Hydropower (SHP) Development Small Hydropower Under favorable circumstances, small hydropower (SHP) represents one of the cheapest methods of electricity generation. Of all the renewable energy sources small hydro (large as well) represents the highest density of resource. For a long time, small hydro has been

Hydropower

36

generally overshadowed and confused with large hydropower (LHP). The focus over the years in many developing countries (for instance, in some countries of Africa, Asia, and Latin America) has been large-scale hydropower schemes. SHP has attracted relatively little attention from entrepreneurs, equity investors, and project financiers in recent years in emerging economies with the exception of some of them. However, given the current global context, the cost competitiveness of the technology and the size of the remaining resource, investment analysts believe that small hydro has the potential to enjoy rapid expansion, particularly in emerging economies. Economically viable and proven smallscale hydropower technologies have been commercially developed and are available for generating both electrical and mechanical power for rural industrialization and development. In continents like Africa and Asia, small hydropower development is an adequate measure for electrification in rural areas. In industrialized countries (e.g., European Union), SHP development followed a very specific way [33]: Phase 1: decentralized energy demand by industry (up to 1940/1950) Phase 2: economic-driven decrease until 1970 Phase 3: energy crisis and boom until 1990 Phase 4: decrease driven by environmental concerns up to present Thousands of small hydroelectric plants were abandoned in Europe and North America during the period from the 1950s to the early 1980s. In 1990s, small hydropower plants virtually ceased to exist in the Former Soviet Union and Central and Eastern Europe. However, in the EU, there is a good hope that the last phase will change its trend due to a recently enacted legally binding targets for increasing renewable energy use by 20% by 2020. Actually, in some European countries (for instance, Balkan region/South Eastern Europe), there is ongoing boom of constructing new SHP plants. Similarly, small hydropower development is actually booming in the USA. Driven by federal incentives, the market continues to grow and SHP is now recognized as one of the most cost effective and environmentally friendly forms of renewable power. Similar trends can also be seen in other countries, in particular in Brazil, Canada, and China.

SHP Versus Large Hydropower (LHP) Major attributes of small (SHP) and large hydropower (LHP) are given in > Table 36.7. It is important to realize that SHP is not simply a reduced version of a large hydropower plant. Specific equipment is needed to meet the fundamental requirements of simplicity, high-energy output, environmental measures, and maximum reliability. A comparison of data from > Fig. 36.2 representing small and large hydropower utilization, shows that in all continents, with the exception of Europe, small hydro has big untapped resources that may be utilized in the future, with Europe having realized close to 50% of its potential.

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. Table 36.7 Major attributes of small (SHP) and large (LHP) hydropower Positive

Negative SHP LHP

SHP LHP

Emissions-free, with virtually no CO2, + NOx, SOx, hydrocarbons, or particulates

+


Frequently involves impoundment of large amounts of water with loss of habitat due to land inundation. Freshwater reservoirs might emit GHGs emissions.

Proven and reliable technology, indigenous resource, resistant to inflation

+

+

Altering river flows and natural flooding cycles, sedimentation/silting


/+ +

Renewable resource with high + conversion efficiency to electricity (90+%) Dispatchable with storage capability


+

Variable output – dependent on rainfall and snowfall

+

+

Impacts on river flows, water quality, aquatic ecology, including fish migration and oxygen depletion


/+ +

+

+/



/+ + Usable for base load, peaking, improves grid stability Attractive energy pay-back ratio, low + + operating and maintenance costs

Social impacts of displacing
indigenous people Health impacts in developing
countries

+

Long lifetime – 50+ years typical, up + to 100 years + Technology suitable for rural electrification notably in developing countries, output is consumed near the source + Promotes multipurpose uses (irrigation, navigation, flood defense, recreation)

High initial capital costs

+

+


/+ Long lead time in construction
of mega-sized projects

+

+

+

Structural dam failure risks

+


/+ +

Classification of Small Hydropower Plants A common classification of hydropower plants according to installed power capacity is shown in > Fig. 36.3. Hydropower plants are often subdivided into ‘‘large’’ hydro (LHP) that usually involve dams, and small hydro (SHP), involving mini, micro, and pico schemes that are normally run-of-river systems and have little or no water storage capacity. There is currently no agreement in the international community as to the definition of small hydropower. The upper limit is generally regarded to be 10 MW in capacity that

Hydropower

36

Hydropower potential used %

100 SHP

80

LHP

60

40

20

0 Africa

Asia

Oceania

Europe

North America

South America

Global

. Fig. 36.2 Proportion of the small and large hydropower currently used to the economically feasible potential in each region

10 kW Pico

500 kW Micro

1 MW Mini

10 MW Small

50 MW

Intermediate

100 MW

Medium

>100 MW Large

. Fig. 36.3 Common classification of various hydropower schemes according to installed power capacity

suggests still minimal negative impact on environment. However, small hydro in the USA can refer to projects between 1 and 30 MW, in Canada between 1 and 50 MW, while in China it is as high as 50 MW (> Table 36.8). Small hydro systems can either be connected to the grid and provide power to the grid or they can be used for independent and stand-alone applications in isolated remote areas. Micro, Mini and even small hydro plants may provide power only to an isolated community or a single home. Pico-Micro hydroschemes are generally stand-alone systems, that is, are not connected to the electricity grid. They are used for domestic electricity applications such as lighting, TV/radio, and battery-charging. It is becoming a mature technology which should now be considered as part of the menu of alternatives to grid extension, diesel generators, solar PV systems, and other energy systems presently being used in rural areas, especially developing countries. In comparison to these options, pico-hydro can be installed at a lower cost for the same energy output and in the markets where it has become established, subsidies have not been required.

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. Table 36.8 SHP definition and classification in selected countries Continent/ organization Africa Asia

Europe, ESHA (European Small Hydro Association), the European Commission and the UNIPEDE (International Union of Producers and Distributors of Electricity) North and Central America

South America

Australia and New Zealand

Major attributes of classification Guinea, Kenya, Nigeria, South Africa ( 36.13).

Developing Country is Facing Tough Work to be Forehead in Adapting Climate Change Due to the varying extent effect, climate change represents different impacts and consequences to countries in different stages of development. As Blair [4] pointed out in his report, the change in climate is the same whether the emissions originate in New York or Shanghai. And of course, the most vulnerable to the impact of climate change live in the poorest area of the world. Likewise, the poor or undeveloped countries that have not caused, are not causing, and will not cause significantly more greenhouse gas emissions . Table 36.13 Proposed hydropower development in the world Unit(MW) Africa Hydro capacity 7,489 under construction Planned hydro capacity

Asia

Oceania Europe

North South America America Total

130,479

160

5,940

24,236– 224,368– 416– 84,048 241,699 2,489

2,408

11,029– 18,435– 13,820 43,645

11,327

157,803

65,693– 75,556

344,176– 461,257

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Hydropower

N America 4% Europe 1%

S America 7%

Africa 5%

Australia 0%

Asia 83%

. Fig. 36.12 Distribution of hydropower installed capacity in 2007

S America 16%

Africa 18%

N America 10%

Europe 3% Australia 1%

Asia 52%

. Fig. 36.13 Distribution of proposed installed capacity

Hydropower

36

are responsible for the cost of climate change. They are most easily subject to the effect of climate change and their adaptability is the most vulnerable. Countries in different stages of development have different objectives and priorities of water storage facilities, and also different concerns. For less developed countries, the consequence of global climate change is often catastrophic to the extent that, due to the inadequate storage capacity, subsequent extreme weather events occur frequently and bring about worse disasters. The construction of water storage facilities is a crucial matter relating to their surviving and getting rid of poverty. Just as stated in the World Declaration on Hydropower Development (2008), a reliable electricity supply, taken for granted in many parts of the world, can be a lifesaving commodity in the less developed African nations. In general, both energy and water needs are critical in these nations, so the obvious multiple benefits of hydro schemes (particularly when storage reservoirs are included) are of special significance in Africa. The effects of extreme climatic conditions (large-scale floods and regular droughts) that Africa suffers from can be vastly mitigated by dam/reservoir schemes. Naturally, the supply of clean drinking water and irrigation water to enhance food security are major additional benefits of hydro schemes. Thus, the development of water and hydropower resources is of special significance for developing countries, especially the African countries, and one of the most urgent tasks to improve the livelihood.

To Accelerate Hydropower Development Needs New Concepts At the Session on Water Storage Facilities during the Fifth World Water Forum in March 2009, water security was defined as to maintain necessary hydrological conditions and water storage facilities for maintaining a healthy ecosystem in the climate change, everincreasing regional socioeconomic demand (including energy demand), and other conditions. In the country with a relatively high level of water security, the problem of water will not cause any major impacts on the poor. To maintain a healthy and robust water ecosystem is greatly significant for ensuring the water security of the poor and the vulnerable groups. Therefore, one needs to know ‘‘why to do this?’’ ‘‘how to do,’’ and ‘‘for whom (equality)’’ while constructing water infrastructures. The construction of new water storage facilities should follow the principle of sustainable development. However, the approval, investment, and implementation of new schemes should consider the protection of endangered species, provision of information for the public and sharing of benefits by all stakeholders, including downstream ecosystem users. This definition reflects the international community’s re-recognition of water security against the background of global climate change, and shows their concern about equality, poverty reduction, and other water-relating social issues in the present new situation. Hydropower development is a practice involving water security and energy security. In the past decade or so, however, hydropower development, especially the construction of subsequent large-scale water storage facilities was subject to incisive criticism from all walks of life, and the reply and response to such criticism was still pale. As the voice of

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striving for development and coping with climate change runs higher and higher in the world, the voice against dam construction is weakened to some extent. This change helps creating a good international opinion for the development of water and hydroenergy resources. Nevertheless, in the twenty-first century, the construction and operation of a dam and reservoir can no longer be considered as a purely scientific and technical matter. A wide range of other aspects are involved: economic, social, and environmental. While it is clear today that water and energy schemes can be built to be safe, economic, and in harmony with the environment, mitigating environmental pacts remains a high priority for the profession, and must continue to be so. Water storage infrastructure construction must be speeded up in a sustainable way, and joint actions should be taken to minimize the adverse impacts caused by the development, and base water development and management on new concepts, to make a greater progress in maintaining man harmonious with water and man harmonious with nature. In the light of this, the following four points are critical: First of all, the attitude to nature should shift away from simply exploiting natural resources and adopting restoration measures, but should aim to protect the natural environment at an early stage of planning; Second, decision making should not only be based on technical and economic feasibility, but also on social equity and environmental requirement. Third, project operation and management should not only involve traditional techniques to ensure safety, but should also play a role in protecting the ecosystem. Examples are ensuring minimum flows, and appropriate operation of reservoirs. Finally, benefit-sharing should be more inclusive, rather than just relating to a region or state. All stakeholders should be involved. One should remember that the members related to the project have the right to benefit from a project.

Joint Efforts are Expected in a Better and Sustainable Way for Hydropower and Dam Development The international community has made unremitting efforts and fruitful achievements in pushing forward the sustainable utilization of water and hydroenergy resources on the globe. For example, the ICOLD has issued the World Declaration on Hydropower (Africa) together with the AU, UPDEA, IHA, ICID, and WEC. This declaration is intended to call on all the stakeholders of dam and hydropower development to engage themselves into speeding up hydropower development in Africa while being faced with the tremendous potential and the golden opportunity in Africa. Being confronted with the great potential, the ICOLD is preparing for the World Hydropower Declaration to ally all forces of the international community to push forward the course of hydropower development in Asia. It was hardly imaginable that the supporters and opposers of dams could discuss the issue of global development peacefully. The common view regarding hydropower development on a big scale fully reflects that the demand of development is the ground of the

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main and common view today. Due to the complicated and global issue of climate change, the process of water and hydroenergy resources development and utilization involves numerous stakeholders. In the new century, no country or organization can meet the challenge by itself. Better communication and cooperation are needed to cope with global climate change by making great efforts to hydropower development.

Strategies of Hydropower Sector in Adapting Climate Change Water storage infrastructure has advantages on comprehensive utilization of water and energy. The practice in many countries especially in the developing world shows water and energy development plays an important role in the context of poverty mitigation and driving socioeconomic development. The experience all over world demonstrates that water and energy can be developed in a reliable, cheap, and environmental-friendly way [2]. However, hydropower can be an effective measure to anti-climate change on the one hand; it is also sensitive and vulnerable in front of the climate change on the other as hydropower is a sector which is highly subject to the natural condition such as landform, river runoff, etc. Therefore, analyzing possible impacts and set adapting strategies are urgently needed either for energy saving and GHGs emission reduction or its own development.

Possible Impacts on Hydropower Possible Impacts Scenarios of Climate Change on Hydropower Sector It is certain future climate changes will pose some challenges to the hydropower industry. Depending on rate and magnitude of climate change, future impacts on the hydropower industry could be mixed. In some regions, the industry will benefit, but in some others it is likely to be adversely impacted. In both cases, the hydropower industry has to adapt to the changed climatic conditions. Three potential climate change scenarios could emerge [31]: ● Increased frequency and magnitude of drought ● Increased frequency and magnitude of flood ● Both above In analyzing the impact of climate change on hydroelectric supply, Roy and Desrochers [36], first identified the most important activities that might be affected by climate change (> Fig. 36.14). Generally, three climate parameters, precipitation, temperature, and wind, are highly related to hydropower generation. Increases in temperature (and wind as well) result in higher evaporation, which reduce inflow and increase water losses from reservoirs.

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CLIMATE SCENARIO Precipitation /Wind WATER AVAILABILITY Water Management Generation planning

Temperature /Wind

EXTREME EVENTS

Security people

Load profile/volume

Security Installation

Generation Project planning

Transport Distribution

Installation design Design

Environmental Criteria Environmental Criteria

Energy supply

Hydraulic

Generation optimisation

Wind power design

ELECTRICITY DEMAND

Environmental Criteria

Financial criteria

Financial criteria

Financial criteria

. Fig. 36.14 Most important fields of activities in the hydropower sector that might be affected by climate change [36]

All three factors point to less (or, at least, less flexible) hydroelectric capacity at existing powerhouses. Reduced flows in rivers and higher temperatures reduce the capabilities of thermal electric generation; high temperatures also reduce transmission capabilities. The fields of activities can be arranged in three different groups (first-level concerns) according to the anticipated affects related to the modification of: ● The hydrological regime ! water availability ● The thermal regime ! electricity demand ● The occurrence of extreme events

Possible Impacts on Hydropower by Continents The consequences will include modifications in flow seasonality and consequently hydropower. The changes in temperatures and precipitations will thus have impacts on the runoff, which will increase by 10–40% from 2050 in the high latitudes, and decrease by 10–30% in the mid-latitudes [20]. Changes in the average climate may not have serious impacts on hydropower for short and medium term, but extreme weather events will eventually affect hydropower

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generation. In the past few decades, extreme weather events have caused significant impacts on hydropower production around the world, especially in the countries of South America.

Africa In 2007, the water level of Lake Volta, the largest man-made lake in West Africa, which normally supplies 60% of Ghana’s energy needs, was at an all times low (which is 71.65 m) 1.5 m below the critical minimum, as a result of low rainfall. The lack of water in the lake created a 300 MW power shortfall. Similar episodes were also reported in 1993 and 1994 [31].

Europe Possible changes in hydropower in Europe are mixed. By the 2070s, potential may decline by 6% overall or by 20–50% around the Mediterranean. However, increases of 15–20% are projected in Northern and Eastern Europe, while stable patterns are projected for Western and Central Europe [1]. According to the study performed by Lehner et al. [25], the results show that, following moderate climate and global change scenario assumptions, severe future alterations in discharge regimes have to be expected, leading to unstable regional trends in hydropower potentials with reductions of 25% and more for southern and south-eastern European countries. The results of the analysis of the consequences of probable climate changes for the Nordic (Scandinavia) electricity system demonstrate that climate change leads to a considerable increase in hydro inflow during the winter season as well as reduced demand for heating [32]. Almost all of the increase in inflow can be utilized by the hydro production system.

Australia and New Zealand Flows in New Zealand’s larger mountain-fed rivers are likely to increase benefiting hydroelectricity generation and irrigation supply [16]. From the early 2000s, Hydro Tasmania, operating on six major catchments on island (Australia) and having over 30 storages in these catchments has been pursuing greater insight into climate change and its potential impacts on its operations. These storages have a fill and empty cycle of approximately a decade and are used to support the hydro generation system during periods of drought and associated low inflows [6]. A review of the existing 80 years of hydrological records has shown a decline in yields especially over the past 30 years. There was a change in inflows around the 1950s with a drier period post 1950s (historical record 1924–2000). A further catalyst to starting to explore climate change was the recent decline in inflows to the Perth water supply system in Western Australia. The records showed a significant reduction (i.e., 38% of long-term average) in the mid-1970s and a further reduction (70% of long-term average) around the mid-1990s.

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Asia China’s climate has witnessed significant change over the past 50 years. These changes include increased average temperatures, rising sea levels, glacier retreat, reduced annual precipitation in north and northeast China, and a significant increase in southern and northwestern China. Extreme weather and climatic events are projected to become more frequent in the future, and water resource scarcity will continue across the country. The case study of the Chaobai river in the Hai river basin, used to supply water to Beijing, demonstrated that the inflow to the Miyum reservoir had been decreasing as a result of rainfall changes and human activities in recent years. The overall runoff in the basin from 2000 to 2005 has decreased by about 66%. Climate change projections using SRES A2 and B2 scenarios suggest that average annual temperature may increase by 2.4–2.8ºC, and precipitation may increase around 4–5% by 2050, increasing average annual inflow into the reservoir. While climate change projections indicate increased reservoir inflow in the long term, inflows may continue to decline in the medium term, according to SRES A2 scenario, necessitating adaption measures to assure adequate water supply for Beijing city [22]. Based on the analysis of three hydropower projects in India, Sri Lanka, and Vietnam the resulting impact on hydropower projects was indentified [19]. Waterstreams discharges tend to increase with rainfall and decrease with temperature. The rainy season would likely have higher water levels, but in the lean season water resources would become even more limited. The amount of energy generated would be affected to a certain extent, but the project viability may not change so much. Comparing the three cases, it is suggested that having larger installed capacity and some storage capacity might be useful to accommodate future hydrological series and seasonality. Tajikistan, which economically feasible hydropower potential amounts to 263 TWh/yr may experience significant impact on its power output as a result of changes in river basin runoff [8].

South America Over the next decades, Andean intertropical glaciers are very likely to disappear, affecting water availability and hydropower generation in South America. Runoff changes from precipitation variability will also affect hydropower generation in many Latin American countries [26]. Hydropower is the main electrical energy source for most countries in Latin America, and is vulnerable to large-scale and persistent rainfall anomalies due to El Nin˜o and La Nin˜a, for example, in Colombia, Venezuela, Peru, Chile, Brazil, Uruguay, and Argentina. On the other hand, increased energy demand, combined with drought, caused a virtual breakdown in hydroelectricity generation in most parts of Brazil in 2001, contributing to a GDP reduction of 1.5% or about US$10 billion. However, the results found are fundamentally dependent on the climate projections which, in turn, are still highly uncertain with respect to the future evolution of greenhouse gas emissions, greenhouse gas concentrations in the atmosphere, and global climate change (GCC) [34].

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North and Central America In the USA, hydropower yields in the Colorado River will likely decrease significantly. Diminished snowmelt runoff could lead to a decrease in the potential hydropower production, which now comprises about 15% of California’s in-state electricity production. If temperature rises to the medium warming range and precipitation decreases 10– 30%, hydropower output may be reduced up to 30%. It has to be noted, there is uncertainty in future precipitation projections. It is also possible that precipitation may increase and expand hydropower production potential [7]. In 2001, prolonged droughts caused the water levels in the Great Lakes to fall, resulting in significant reduction in hydropower generation at both the Niagara and Sault St. Marie power stations in Canada [12]. A similar low flow in 1965 caused a 20% decrease in generation [30, 31]. In the Columbia river basin, runoff required for hydropower generation in the summer will likely conflict with other environmental needs. Prognosis for the Pacific Northwest (PNW) hydropower supply under climate change has been worse than anticipated [27]. Differences between the predictions of individual climate models are found to contribute more to overall uncertainty than do divergent emissions pathways. Uncertainty in predictions of precipitation change appears to be more important with respect to impact on PNW hydropower than uncertainty in predictions of temperature change. The management adaptation potential of the Peribonka River water resource system (Quebec, Canada) is investigated in the context of the evolution of climate change. The main results indicate that annual mean hydropower would decrease by 1.8% for the period 2010–2039 and then increase by 9.3% and 18.3% during the periods 2040–2069 and 2070–2099, respectively. Overall, the reliability of a reservoir would decrease and the vulnerability increase as the climate changes [29]. Hydropower generation will be affected by changes in water availability, particularly in snowmelt-dominated basins, where impacts have already been reported. Hydropower production at facilities that are operated to meet multiple objectives (e.g., flood-risk reduction, irrigation, municipal and industrial water supply, navigation, in-stream flow augmentation, and water quality) may be especially vulnerable to changes [5].

Adapting Strategies In this context, adaption (> Fig. 36.15) of the hydropower industry to climate change may not be simple and straightforward. Many hydropower reservoirs and their operating criteria have been built based on the largest single observed or modeled event. But in the future, both magnitude and frequency of extreme events is likely to increase. So hydropower reservoirs may not be able to hold extra water or be able to generate electricity in the case of a rapid drop in water level caused by a drought triggered by the failure of rainfall. Retrofitting of spillways or redesigning

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High precipitation High temperature

Flooding High evaporation

Low precipitation High temperature

Draught High evaporation

ADAPTION • Re-design reservoirs to increase capacity • Retrofit spillways • Decrease sediment inflow through catchment management • Re-locate population from downstream areas ADAPTION • Forecast onset of droughts • Back-up reservoirs • Lower evaporation loss • Find alternative green energy supply

. Fig. 36.15 Possible future scenarios and adaption options [31]

reservoirs to increase capacity may be possible options. However, in many cases, retrofitting could be expensive and therefore not feasible. The economic and engineering life-cycles of many hydropower projects either recently built or under construction are within the time lines of climate change. Another major potential obstacle is mainstreaming climate change into policy planning. Hydropower planners often talk about the uncertainty of scenarios projected by the climate models. Many studies of climate change impacts use the output of one or several global climate models (GCM) to project future climate. GCM temperature and precipitation output and historical records are used as input to a hydrologic model to derive stream flow. For instance, if the river is a managed system with reservoirs, a water management or optimization model may be used to model reservoir operating rules. > Figure 36.16 is a schematic of this methodology. Those modeling climate agree with uncertainty of scenarios, but that does not mean the planners should not act until the level of uncertainty becomes smaller than at present. For future adaption, one solution could be to use a range of scenarios to capture the uncertainty. The hydropower sector usually relies on historical hydro-meteorological time series for operational strategies and future investment planning. Potential global warming affects global precipitation patterns and enhances melting of glaciers, which in turn affect seasonal runoff. Assuming future flows as stationary extension of measured runoff series is no longer a probable scenario in a warming climate. There is need for developing mechanisms for adjustment of historical time series based on historical and possible future climate trends. These adjustments need to take into account the time frame of possible scenarios or planning horizons. Different methods for sophisticated risk analysis accounting for climate change must be explored and extensively used [39].

Hydropower

Global Climate Models

Basin RainfallRunoff Model

Projected Temperature and Precipitation

36

Water Resources Management Models

Projected River Flows Performance Measures

. Fig. 36.16 Schematic for climate change impact studies for water resources [44]

New Emerging Hydropower Technologies The studies and the values of the World Energy Council, the International Hydropower Association, and the European Small Hydropower Association clearly show us that the usage of hydropower will certainly change within the next 20–50 years. Some countries will increase their amount of hydroelectricity produced, whereas in other countries less water will be available. Therefore, new hydropower technologies are being actively tested in a number of countries. There are many small dams in the world and the majority of them do not have a hydropower component. While this is not always an economic option, there is a significant market niche of this ‘‘sleeping’’ hydro potential in this area. Energy potential can be recovered by installing hydropower plants in irrigation, drinking water networks or even water treatment, navigation waterways infrastructure. For such schemes, electricity generation is not the first priority, but the second [10]. Electric power is also being developed from nontraditional water sources (also called ‘‘hydrokinetics’’), including river and ocean currents. The basic concept behind hydrokinetic power is not new. For centuries people have harnessed the power of river currents by installing water wheels of various sorts to turn shafts or belts. River current energy conversion systems are electromechanical energy converters that convert kinetic energy of river water into other usable forms of energy. Over the past few decades, a number of reports on technical and economic feasibility of this technology have emerged [23]. Installation of in-stream (kinetic) turbines directly in rivers, without a dam or other impoundment may provide an effective alternative mean for generating power. Such systems would potentially require little or no civil work, cause less environmental impact, and may possess significant economic value. However, the potentials of this

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technology as an effective source of alternative energy have not yet been explored to a great extent. Ocean or marine energy using offshore plants also can be also attributed to hydropower. There are five main technologies, such as tidal and current power plants, wave power plants, sea warmth power plants, and osmotic power plants, which could be used in future to produce electricity. The data on hydrokinetic potential worldwide are still very preliminary. Estimates in the USA have ranged from minimums of 23 GW to maximums of 400 GW [24]. An independent market assessment estimated the worldwide potential of ocean wave energy economic contribution in the electricity market to be in the order of 2,000 TWh/yr and is comparable to the amount of electricity currently produced worldwide by large-scale hydroelectric projects. According to Pike Research’s study, ‘‘Hydrokinetic and Ocean Energy’’ (2009), in the best scenario case, the ocean energy industry could yield global power generation capacity of up to 200 GW by 2025. In 2009, the USA had installed hydrokinetic generation capacity of less than 1 megawatt (MW), as compared to more than 77,000 MW of conventional hydroelectric generation capacity. Many hydrokinetic development projects are underway in the USA – as of 2009, the Federal Energy Regulatory Commission (FERC) has issued 146 preliminary applications to study development of 9,000 MW of proposed hydrokinetic generation capacity. Most of them are inland river projects and around half are designated to hold free flow power on the Missouri and Mississippi Rivers [35]. Any potential power will be located primarily along the coasts, where current wave and tidal prototypes are being employed, but future hydrokinetic technologies will also take advantage of the wave power in streams and rivers. This will benefit many of the inland states. First commercial projects of wave energy have been recently commissioned in Portugal, Scotland, and other countries.

Conclusion and Future Directions Climate change is regarded as the most severe challenge for the human being. The view on accelerating hydropower development and ensuring adequate water storage infrastructure to mitigate and adapt climate change has been widely accepted by international community. In view of water storage capacity or hydropower development, a developed country has well conducted a complete network whereas developing country is facing tough work to be forehead. Many countries stipulate ambitious plan to accelerate hydropower development in order to fulfil their voluntary target for reducing emissions. It can be expected that hydropower development will have a great leap forward in the future. However, in the new century, the construction and operation of a dam, reservoir, or a hydro plant can no longer be considered as a purely scientific and technical matter on the one hand and become more open and transparent on the other. The inquiry and criticism on large-scaled water infrastructure are kept receiving from various paths, whereas the response on it is inadequate. To eliminate the misunderstanding and get support for

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further development at global scope, cooperation among various stakeholders, government authorities, knowledge institutions, business companies, civil societies, and local communities is the key to the development and implementation of effective and sustainable water solutions.

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Section 5

Advanced Combustion

37 Reducing Greenhouse Gas Emissions with CO2 Capture and Geological Storage J. Marcelo Ketzer1 . Rodrigo S. Iglesias1,2 . Sandra Einloft1,3 1 CEPAC – Brazilian Carbon Storage Research Center, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil 2 FENG – Engineering Faculty, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil 3 FAQUI – Chemistry Faculty, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1407 CO2 Capture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1409 Post-combustion System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1410 Pre-combustion System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1410 Oxy-combustion System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1410 Chemical Looping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1412 Technological Options for CO2 Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1412 Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1413 Amines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1413 Physical Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1415 Solid Sorbents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1415 Zeolites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1415 Metal-Organic Frameworks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1415 Membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1415 Ionic Liquids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1416 CO2 Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1418 Technical Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1418 Description of the Geological Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1419 Injectivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1420

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_37, # Springer Science+Business Media, LLC 2012

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Reservoir Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1420 Oil and Gas Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1420 Saline Aquifers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1422 Coal Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1423 Trapping Mechanisms of CO2 in Geological Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1425 Structural and Stratigraphic Trapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1425 Hydrodynamic and Residual Trapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1425 Dissolution and Mineralization Trapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1425 Adsorption Trapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1426 Storage Capacity Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1426 Petroleum Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1428 Saline Aquifers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1428 Coal Beds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1429 Predicting the Fate of CO2 Stored in Reservoirs: Experimental and Numerical Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1429 Experimental Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1430 Numerical Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1431 Safety of Geological Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1433 Monitoring Stored CO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1435 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1435

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37

Abstract: CO2 capture and geological storage (CCS) is one of the most promising technologies to reduce greenhouse gas emissions and mitigate climate change in a fossil fuel–dependant world. If fully implemented, CCS may contribute to reduce 20% of global emissions from fossil fuels by 2050 and 55% by the end of this century. The complete CCS chain consists of capturing CO2 from large stationary sources such as coal-fired power plants and heavy industries, and transport and store it in appropriate geological reservoirs such as petroleum fields, saline aquifers, and coal seams, therefore returning carbon emitted from fossil fuels (as CO2) back to geological sinks. Recent studies have shown that geological reservoirs can safely store for many centuries the entire GHG global emissions. Here presented a comprehensive summary of the latest advances in CCS research and technologies that can be used to store significant quantities of CO2 for geological periods of time and, therefore, considerably contribute to GHG emission reduction.

Introduction CO2 capture and geological storage (CCGS, or simply CCS) is the integrated process where carbon dioxide is captured and separated at stationary sources, transported to an adequate storage site, and injected into the porous space of deep underground rock formations. Given the world’s current dependence on fossil fuels, which is expected to last for no less than a century, the storage of carbon dioxide in geological reservoirs is a recognized viable mitigation option, with potential to be applied in a worldwide scale and therefore having a measurable impact on the reduction of the escalating emissions of greenhouse gases. Since the increase in carbon dioxide concentration in the atmosphere is the outcome of continuous burning of fossil fuels extracted from the subsurface, the underlying motto of CO2 geological storage is to ‘‘put the carbon back to the ground’’ [1], hopefully reestablishing the equilibrium of this unbalanced carbon cycle. It is common ground that the stabilization of greenhouse gas emissions can only be achieved through a portfolio of solutions [2–4]. Several economic assessment models, such as the BLUE Map from the International Energy Agency [4], foresee that increasing contributions at different levels of renewable sources, nuclear power, improved energy efficiency and fuel switching at power generation and end-use level, and carbon capture and storage, will be capable of stabilizing emissions by the late half of the twenty-first century (> Fig. 37.1). CCS is expected to contribute with at least 20% of this reduction by 2050. Scenarios that exclude CCS would result in a cost increase to achieve emission stabilization in 2050 by at least 70% [4]. CO2 sources that are suitable for CCS projects must be large stationary facilities, usually venting more than 100,000 metric tons of CO2 per year [3]. These usually include power generation facilities (e.g., gas- or coal-fired power plants), natural gas processing plants, refineries, ethylene plants, hydrogen-producing plants from CH4 reform and coal gasification, cement and steel industries, among others. Depending on the type of source, costs, and technology maturity, CO2 can be captured and separated from other gases using post-combustion, pre-combustion, or oxy-combustion technological routes.

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70 Baseline emissions 62 Gt CCS industry and transformation 9%

60

CCS power generation 10%

CO2 emissions (Gt CO2/yr)

1408

Nuclear 6%

50

Renewables 21% 40

Power generation efficiency & fuel switching 7% End-use fuel switching 11%

30

End-use electricity efficiency 12%

20

End-use fuel efficiency 24% BLUE Map emissions 14 Gt

10

0 2005

WEO2007 450 ppm case

ETP2008 BLUE Map scenario 2050

. Fig. 37.1 CO2 emission reduction scenarios from the IEA for the twenty-first century. World Energy Outlook 2007 scenario: 450 ppm CO2 concentration limit by 2030. BLUE Map scenario: 14 Gt CO2 annual emissions by 2050. IEA Technology Roadmap © OECD/IEA, 2009 [5]

These systems will be further explained in detail in this chapter. Following separation, CO2 may be transported using pipelines and/or ships to a storage site, where it is compressed and injected in the subsurface through wells [6]. Transportation distances are an important factor to be evaluated in CCS projects due to the elevated cost of pipelines. Most countries that are willing to develop CCS projects have been carrying out surveys to map their large stationary sources of CO2, and the potential geological storage sites. This will provide an optimized source-sink match in order to reduce transportation of CO2 from the capture source to storage site. The most appropriate geological reservoirs for CO2 storage are sedimentary units such as oil and gas fields, saline (high salt-content fluid) aquifers, and coal deposits. These types of formations have large storage capacity in their porous space, and are evenly distributed worldwide [7]. Estimated capacities for oil and gas fields range between 675 and 900 billion metric tons (Gt) of CO2, for saline aquifers between 1,000 and 10,000 Gt CO2, and coal beds between 3 and 200 Gt [2]. These estimations are still highly uncertain, as they depend on selection criteria for validating a potential storage site (which may vary significantly for each assessment) and the methodology employed to calculate the effective pore volume available for storage [8, 9]. These methods and criteria will be further discussed in this chapter. Nevertheless, it is worth noting that even considering the lowest capacity estimations, storage volume of geological reservoirs is enough to contain 10 times the accumulated global emissions until 2050 (ca. 155 Gt CO2) [5].

Reducing Greenhouse Gas Emissions with CO2 Capture and Geological Storage

37

CCS in geological media is in its early stages of worldwide deployment. Currently, there are four large-scale demonstration and commercial projects in operation, although several more are under way [9]. The first one was started in 1996, in the Sleipner gas field in the North Sea, operated by Norway-based oil company StatoilHydro. In order to avoid a government-imposed tax for offshore greenhouse gas emissions, StatoilHydro started to strip CO2 from the natural gas extracted in this field, re-injecting it in the Utsira formation, a saline aquifer 800 m below the sea floor, and hundreds of meters above the Sleipner gas field. Approximately one million metric tons (Mt) of CO2 are injected in this formation each year. The project is still ongoing, and its success has been a benchmark for CCS development. In 2004, StatoilHydro and BP (British Petroleum) started a similar project in the InSalah gas field, in Algeria, re-injecting stripped CO2 from natural gas below the gas-water contact in the same formation, 1,800 m below the surface. Seventeen metric tons of CO2 are expected to be stored in this project. The Snøhvit gas field in the Barents Sea, also operated by StatoilHydro, started capturing CO2 in 2008, injecting 0.7 Mt each year. Lastly, the Weyburn-Midale is a transnational project (U.S./Canada) where CO2 is captured at the Great Plains Synfuels Plant and transported by pipeline over 320 km to Weyburn (province of Saskatchewan, Canada), where it is injected into the mature Weyburn-Midale oilfield for enhanced oil recovery (see following sections). In total, these projects presently store more than five million metric tons per year. Current global emissions of CO2 amount to ca. 26 billion metric tons per year, of which ca. 60% (13.5 Gt) come from large-scale stationary sources [3]. This means that approximately 2,700 times the current storage ratio will be necessary to deal with the present emissions. From these numbers, it would appear to be an overwhelming task, but the deployment of CCS projects, both in commercial or demonstration scale, have been steadily increasing in number in the past years, as well as the injection rates [10]. Approximately 100 large-scale projects (>1 Mt CO2/year) integrating capture and storage are now under development worldwide to be launched until 2020, and it is expected that by 2050, at least 3,000 commercial-scale CCS projects will be in operation worldwide [5]. The aim of this chapter is to present an overview of the main technologies and processes employed to capture and separate CO2 from stationary sources. Subsequently, storage options will be presented in detail, describing the main reservoirs and the methods employed to estimate their volumetric capacity. Safety issues and potential risks for human health and the environment derived from CO2 storage will also be addressed. The trapping mechanisms of CO2 in a reservoir, and the methods employed to investigate and monitor its interaction with the reservoir are described next. The last section will discuss the current knowledge gaps and requirements in CCS research that still need to be addressed in order to achieve the expected goals in CO2 emission reduction perspectives.

CO2 Capture CO2 capture from industrial processes is well known and in use in different applications. The separated CO2 is however vented to the atmosphere, as for example, in natural gas

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processing. The main purpose of CO2 capture applied to geological storage is to produce a concentrated CO2 stream (normally >90%) to transport and inject in an adequate site. To obtain CO2 for storage purposes, it is necessary to separate this gas from a mixture of gases and pressurize it to permit transport and storage, requiring energy. This process adds cost and reduces overall energy efficiency to no less than 25% percent, e.g., in a coalfired power plant, depending on the efficiency of the facility [11]. CO2 capture systems can be divided in four main technological routes, depending on the technology used and its applications (> Fig. 37.2). The following sections will describe each of these systems in more detail.

Post-combustion System In post-combustion, CO2 is removed from flue gas, separating CO2 from conventional diluted flue gas stream (N2, O2, H2O, NOx and SOx). The latter two are produced by combustion of fossil fuel or biomass, and their concentration also must be reduced to avoid solvent degradation [12–14]. In this process, air is used for combustion, resulting in flue gas at nearly atmospheric pressure with a low CO2 concentration (3–15% by volume) [15–17]. Different techniques can be used to capture CO2 from post-combustion flue gas, such as absorption by chemical sorbent, separation by membranes, adsorption in solids and cryogenic separation. Absorption technology, using ammonia-based solvents such as monoethanolamine (MEA) plays a dominant role in the present and probably will continue to do so in the near future [11, 12, 18].

Pre-combustion System In the pre-combustion system, CO2 is separated from H2, which is used as a fuel. Initially, coal, biomass, or natural gas are reacted with steam or oxygen in a gasification process to decompose the fuel in synthesis gas (syngas, mainly composed of CO+H2) which is reacted in a water-gas-shift reactor producing CO2 and more H2 [12, 19]. The shift conversion produces a stream with a high CO2 concentration (15–60% by volume), resulting in higher partial pressure of CO2 making it easier to separate, when compared to the post-combustion system. CO2 can be separated by a physical or a physical/chemical absorption process, which are the most utilized technologies. Membrane and solid sorbents can also be used, as well as cryogenic separation [12, 15].

Oxy-combustion System In oxy-combustion, the O2 is initially separated from air in an air separation unit, commonly through low-temperature cryogenic separation, and used in fuel combustion,

Air

Air separation

O2

Combustion

Gasifier/shift

O2

N2

P&H CO2 (>80% by volume)

Oxy-fuel combustion

CO2 capture

CO2 (3–15% by volume)

Pre-combustion

CO2 (15–60% by volume)

P&H

H2

CO2 capture

CO2

P&H

CO2 capture

. Fig. 37.2 Diagram illustrating CO2 capture routes in power generation using fossil fuels (P & H: power and heat)

Fuel

Air separation

Air

Combustion

Post-combustion

CO2

CO2

N2

CO2 compression

Reducing Greenhouse Gas Emissions with CO2 Capture and Geological Storage

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producing a flue gas with a high CO2 concentration (>80%). Reacting fuel with almost pure oxygen results in a high-temperature flue gas containing mainly CO2 and water that can be recycled to the burner to moderate the temperature [12, 15]. The main advantage of oxy-combustion is the significant increase of the CO2 partial pressure [19]. The CO2 can be easily separated from the flue gas, for example, by cryogenic methods.

Chemical Looping Chemical looping system can be considered as a variant of oxy-combustion system [11]. The chemical looping process supplies oxygen to fuel combustion/oxidation without direct contact with air, using a metal oxide as an oxygen carrier [20–22]. The flue gas contains only water and CO2. The water may be condensed and the CO2 compressed for transport and storage (> Fig. 37.3).

Technological Options for CO2 Separation In the whole carbon capture and storage-integrated process, the CO2 separation stage contributes with 70–80% of the costs [12, 23], so the possibility of reducing operating costs of CO2 capture is an important issue to make CCS viable. Another important aspect to investigate is the environmental impact of CCS implementation. A critical study of all available and in-development technologies is imperative to the carbon capture aiming the CO2 long-term storage. > Figure 37.4 presents a scheme of the technologies available for CO2 capture.

N2, O2

CO2, H2O

MexOy

Air reactor

MexOy-1

Air

. Fig. 37.3 A simplified scheme of the chemical looping process

Fuel reactor

Fuel

Reducing Greenhouse Gas Emissions with CO2 Capture and Geological Storage

Post-combustion (3–15% by volume)

CO2 capture technologies

Pre-combustion (15–60% by volume)

Oxy-fuel (>80% by volume)

37

Membranes

Polimeric

Solvents

Chemical solvents

Solid sorbents

Zeolites, activated carbon

Membranes

Polimeric

Solvents

Chemical and/ or physical

Solid sorbents

Zeolites, activated carbon, alumina

Membranes

Polimeric

Cryogenics

Distillation

Solid sorbents

Zeolites, activated carbon

. Fig. 37.4 Available technologies for CO2 capture

Solvents To capture CO2 from a stream, it is possible to use solvents that may interact with CO2 either by chemical or physical absorption. The choice of the solvent depends on the characteristics of the flue gas, like CO2 partial pressure and concentration. The chemical absorption is independent of the CO2 pressure due to the chemical character of the interaction solvent-CO2 and can be used even in low CO2 pressure and concentration. On the other hand, when compared to physics solvents, chemical solvents need thermal energy to release CO2, while physical solvents release CO2 by flash desorption. In postcombustion technologies, amines are the most used chemical solvent, and in precombustion technology, chemical or physical solvents can be used, or a mixture of both. Membranes and solid sorbents can be used in post-combustion, pre-combustion, and oxy-fuel routes, but a technological improvement is needed to transform these options in attractive alternatives from both technological and economical point of view.

Amines The use of amines aqueous solutions in CO2 separation is the most mature technology and has been used in the industry for decades [11, 15]. The absorption by amines in water is a well-known commercial technology of CO2 separation, for example, in natural gas, CO2 and H2S are removed via an amine-based scrubber, capturing the acid gases by a chemical reaction with amines and releasing the

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natural gas. The acid gases are then driven off by heating the amine solution, which is regenerated. This process is energy intensive [24–26]. > Figure 37.5 presents a typical cyclic process of the use of aqueous amines solutions in CO2 capture; in the first vessel occurs a chemical absorption and in the second vessel a heat-induced desorption followed by the solvent recuperation. In addition to energy penalty, it is known that N-methyldiethanolamine (MDEA) and diethanolamine (DEA) used for gas treatment and monoethanolamine (MEA) used for CO2 post-combustion separation decompose, causing environmental problems due to generated waste [3, 27, 28]. Despite being used for a long time, the search for a better understanding of the chemistry involved in amine-CO2 interactions is crucial to find an optimal formulation to lower the costs. In this sense, a study presented the results for CO2 absorption capacity for 76 different amines solutions, indicating that there are still possibilities to improve the CO2 absorption capacity of aqueous amine solutions. Seven amines were found to exhibit significant absorption capacity, most of them comparable to the industry standard monoethanolamine (MEA). Most of the selected amines, one primary, three secondary, and three tertiary, have a number of structural features in common like steric hindrance and hydroxyl functionality 2 or 3 carbons from nitrogen [29]. These results indicate that there are still possibilities to improve the CO2 absorption capacity of aqueous amine solutions. The main issues regarding new amines research and development are related to reduction of energy requirements, minimizing corrosion of scrubbers, allowing higher amines concentration, and improving regeneration procedures [16].

Other gases

Captured CO2

Desorber

Absorber

Flue gas from post-combustion Reboiller CO2 Other gases Solvent

Lean solvent

CO2 rich solvent

. Fig. 37.5 Process of CO2 capture using an aqueous amine solution

Reducing Greenhouse Gas Emissions with CO2 Capture and Geological Storage

37

Physical Solvents Physical solvents are so called for promoting a weaker bond between the solvent and carbon dioxide, when compared to chemical solvents. In this case, CO2 is absorbed without a chemical reaction, so this class of solvent is suitable for CO2 removal from flue gas with a higher CO2 partial pressure. Current state-of-the-art physical solvents are glycol-based solvents like Selexol and methanol-based Rectisol [12] as well as Propylene carbonate (Fluor process) [16].

Solid Sorbents Solid sorbents can be used to react with CO2 in a two-step process. Initially, a stable compound is produced, followed by releasing of CO2 in the subsequent step, with regeneration of the original compound. These materials can overcome the amines drawback, energy penalty, and solvent decomposition because of their lower energy requirements, cost advantage, and easiness of applicability over a relatively wide range of temperatures and pressures [30].

Zeolites Zeolitic materials comprise the largest group of the oxide molecular sieves and are used for many applications, as catalysis, gas separation and purification, and ion exchange. Zeolites X, Y, A, ZSM, chabazites have been widely studied to be used in the field of adsorbents [31]. Zeolites have high thermal, mechanical, and chemical stability characteristics that, allied with the porous size and stable crystal structure, make these materials good candidates to be used in CO2 adsorption processes [32, 33].

Metal-Organic Frameworks Metal-Organic frameworks (MOFs) represent a new class of porous hybrid materials formed by metal ions with well-defined coordination geometry and organic bridging ligands. These structures offer advantages for CO2 absorption: ordered structure, high storage capacity possible with low energy penalty for CO2 recovery, high thermal stability, adjustable chemical functionality, extra-high porosity, among others [16, 34].

Membranes Membranes are being used in many industrial separation and are currently dominated by polymeric membranes [11, 17] offering the advantage of cheap production on large scale

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when compared to metallic proton conducting or ceramic membranes [35]. Nevertheless, the membranes are low-cost options for processes that do not require a high-purity gas stream. Besides that, there are some other points related to the performance of membranes that limit their uses in carbon capture. For example, the low concentration of carbon dioxide in the flue gas indicates that a large volume of gases needs to be processed; the membranes are not resistant to temperature, demanding flue gas cooling prior the membrane separation; extra power is required to create a pressure difference across the membrane [11, 36]. Membranes are a promising technology in future for carbon capture, but research and development are necessary to make the costs and performance of this technology attractive.

Ionic Liquids Room temperature ionic liquids (RTIL) are liquid salts at room temperatures [37, 38]. The several possible combinations of cations and anions allow designing more efficient solvents for process and products [39]. Due to the excellent properties of RTIL-like negligible vapor pressure at room temperature, a stable liquid range of over 300 K, the great CO2 solubility and the density greater than water, there is a growing interest to use this kind of solvents in gas separation [38, 40]. As mentioned before, these compounds may combine good physical and chemical characteristics and the ability of selective dissolution of different organic and inorganic compounds by varying the composition of the ionic liquid being good candidates to be used in industrial applications [24]. The main problem with the RTIL is the costs. However, considering the small scale on which these solvents are produced, certainly the increased consumption would make the price lower. The capacity of reuse of these solvents must also be taken into account, as well as the energy save and the possibility of producing a specific and optimized ionic solvent for a particular reaction or application. > Table 37.1 presents some of the commonly used cations and anions in the RTIL synthesis. The anion exchange in RTIL makes possible to alter significantly the ionic liquid properties. The cation is responsible for the ionic compounds existence in the liquid state at room temperature, but it is the anion that controls properties such as solubility and stability [41]. The alkyl side chain in the cation may play a role in the CO2 solubility – increasing alkyl chain increases CO2 solubility – however, the effect is not as important as the substitution of the anion [40, 42]. To find new materials for the purpose of CO2 separation, it is important to study the solubility of CO2 in these solvents and understand the solvent-CO2 interaction. It was pointed out that CO2 presents high solubility in imidazolium-based ionic liquids even in low pressures [38, 43, 44]. Several works related the behavior of the solubility of different gases in 1-n-butyl-3-methyl imidazolium hexafluorophosphate [bmim]PF6 ionic liquids, showing that CO2 presents a superior solubility when compared to other gases like ethane,

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Reducing Greenhouse Gas Emissions with CO2 Capture and Geological Storage

. Table 37.1 Most commonly employed anions and cations in ionic liquid synthesis Some cations and anions for ionic liquid synthesis Cations

+ N

R

+ N R′

1,1-Dialkylpyrolidinium

R′ S+ R″ R

N+ S R

R′

R′

R

N,N-Dialkylpiperidinium

R

N+ N

1,2-Dialkylpyrazolium

N-Alkyl-thiazolium

R′ + N R″ R R′″

R

+ N

N

+ N R′

R

N,N-Alkyl-imidazolium

Tetraalkylammonium

Trialkylsulfonium

N-Alkylpyridinium

Anions F F F PF F F

F - F B F F

Hexafluorophosphate

Tetrafluoroborate

F

O

F F

O-

Trifluoroacetate

F

O O S N S

F

O O

F

F F F

bis-trifluoromethylsulfonylimide

propane, and oxygen, while carbon oxide, nitrogen, and hydrogen showed solubilities below the detection method [45]. The role of the anion was studied by comparing the solubility as a function of both pressure and temperature for a series of gases in 1-n-butyl3-methyl imidazolium tetrafluoroborate [bmim]BF4, 1-n-butyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide [bmim]Tf2N, and 1-n-butyl-3-methyl imidazolium hexafluorophosphate [bmim]PF6. The latter had the largest affinity for CO2 in all experimental conditions [40, 45]. Besides the imidazolium cation, metyl-tributylammonium, butyl-methyl pyrrolidinium, and tri-isobutyl-methyl phosphonium p-toluenesulfonate were tested using Tf2N as anion which, independent of the cation, had the largest affinity to CO2, suggesting that the nature of the anion has the strongest influence on the gas solubility [45]. A solubility study of SO2 and CO2 was carried out in 1-n-hexyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide [hmim]Tf2N, showing that SO2 presents a larger solubility in this ionic liquid when compared to CO2 [46]. Tang and coworkers reported that making the ionic liquids in the polymeric form significantly increases the ability of CO2 sorption when compared to ionic liquids. The poly (ionic liquid) synthesized from ammonium-based monomers have a CO2

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sorption capacity of 6.0–7.6 times higher than the RTIL [44, 47]. Quaternary ammonium polyethers manufactured by Evonik Degussa GmbH company, TEGO IL K5, TEGO IL P9, and TEGO IL P51P were screened as potential solvents for CO2 capture. The selection of these ionic liquids was based in the NETL and University of Pittsburg idea of an ‘‘ideal’’ physical solvent for CO2 capture [25]. Besides the characteristics like low vapor pressure, thermal stability, non-production of unwanted by-products, adequate viscosity, density and ability to dissolve CO2 at different temperatures and pressures, these solvents were evaluated according to Pearson’s ‘‘hard and soft acid-base principles’’ aiming to maximizing the CO2 solubility. CO2 is a Pearson ‘‘hard acid’’ having a strong affinity with Pearson ‘‘hard bases,’’ in this case the selected ionic liquids [25].

CO2 Storage Storing CO2 in the subsurface is not a trivial task. A large effort of multidisciplinary research is needed before actual large-scale injection of CO2 is started. Selection of a storage site is usually aided by a source-sink matching survey, which will limit the viable region for injection to those located close to large stationary CO2 sources. Geological criteria will then determine whether a given formation in the selected area is suitable for injection. These criteria are basically related to the reservoir storage capacity, the containment capability, and injectivity of CO2. Geological characterization methods, such as those used in the oil industry, will be required for this evaluation, often being an expensive and time-consuming step. Even if a suitable site is found, environmental and regulation issues must be assessed as well to ensure that the storage complex will operate within local safety standards and legislation. Furthermore, site operations must have a positive public acceptance, especially by local communities in the vicinity of the storage complex. This section will review some of the technical aspects related to the injection of CO2, and the characteristics of the geological media for storage and containment.

Technical Aspects CO2 is injected in a reservoir through an injection well, which is in many aspects similar to oil and gas production wells. However, wellbore materials have to be carefully selected. Cement and steel commonly employed for completion of production wells may experience corrosion by wet CO2 (an acid media that reacts strongly with cement, leaching components resulting in structural damage) [48]. Steel casings may also be corroded by this media. CO2 needs to be compressed in the surface to reach the reservoir. Ideally, it should be stored underground in a supercritical phase – a state where CO2 has gas-like viscosity (therefore with high mobility) and high density, which is advantageous for maximizing storage per pore volume. This state is reached when both temperature and pressure of CO2 are both above 31.1 C and 73.9 bar, respectively. Since there is an increase in pressure and

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100 0 20 11 0.5

Depth (km)

3.8 3.2

1

2.8

1.5 Assuming a geothermal gradient of 25°C/km from 15°C at the surface, and hydrostatic pressure.

2

2.7

2.7 2.5

0

200

400 Density of CO2

600

800

1000

(g/m3)

. Fig. 37.6 Variation of CO2 density with depth, assuming hydrostatic pressure and a geothermal gradient of 25 C/km from 15 C at the surface [3]

temperature with depth in the Earth’s Crust (geothermal and hydrostatic gradients, averaging ca. 30 C and 100 bar per kilometer, respectively), at approximately 800 m depth, CO2 is likely to be found in a supercritical state. One tonne of CO2 occupies 509 m3 at surface conditions, and the same amount occupies only 1.39 m3 at 1,000 m depth (temperature of 35 C and pressure of 102 bar) [49] (> Fig. 37.6).

Description of the Geological Media The geological media used to store CO2 are similar in many ways to a petroleum system. A storage system is composed of a reservoir and a caprock, and may or may not contain a trap [50]. A geological reservoir is a porous and permeable rock (commonly a sedimentary rock) that contains fluids such as water, oil and gas, CO2 or H2S, and can be used to safely store CO2. Porosity is the space within rock matrix (e.g., in between sand grains) and/or rock fractures that contain fluids, which will be partly occupied by CO2 during storage. A reservoir is preferentially a sedimentary rock (e.g., sandstone, limestone, coal) or less commonly a fractured metamorphic or igneous rock (e.g., basalts). Other less-known (in terms of operation and performance) target reservoirs include oil shales, gas hydrates within marine sediments, and engineered salt caverns [3]. These options are less investigated and will not be discussed here. CO2 stored in common geological conditions is typically found in a gas or supercritical phase, with density lower than water (ca. 600–800 kg/m3) and, therefore, it will tend to

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move upward in the reservoir and overburden sequence until it seeps on the surface [51]. To ensure that the CO2 will be retained since the first years after injection, it is necessary that the reservoir be sealed with an overlying impermeable caprock (permeability typically Fig. 37.7). The first two are already in their commercial phase and the latter, although proven in pilot scale, still needs to be demonstrated in larger scale [52].

Oil and Gas Fields Petroleum reservoirs are appealing targets for CO2 storage, for several reasons. First, the trapping efficiency is indicated for being able to hold hydrocarbons for millions of years. Also, these formations are often well studied by oil companies, with plenty of data available. Finally, the injection of CO2 has been already carried out in many oil fields (especially in the USA) for several years, to increase the pressure in the reservoir and improve the oil/gas recovery rates (a method known as enhanced oil recovery EOR) [53]. CO2 injection, often alternated with water, will result in a mixture with the residual oil

Storage in Depleted Oil & Gas Fields

Storage in Deep Saline Aquifers

. Fig. 37.7 Scheme of the possible reservoir options for CO2 storage

2 km

1 km

Enhanced Coalbed Methane Recovery (ECBM) Enhance Oil Recovery (EOR)

Storage in Deep Saline Aquifers

Oil and Gas Injected CO2 Stored CO2

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forming a single phase (depending on reservoir pressure and temperature, and oil properties), and/or displace formation water and petroleum to occupy pore space within the structural trap of the field. Mixing CO2 with oil within a reservoir typically reduces oil viscosity and enhances oil recovery up to 40% of residual oil left after conventional recovery [54]. Immiscible enhanced oil recovery with CO2, i.e., related to the physical displacement of oil with CO2, is also possible, but in this case, recovery factors are typically lower than miscible EOR [55, 56]. Enhanced oil recovery using CO2 is a proven technique that has been carried out by the oil industry since the 1970s to maximize oil exploration in mature fields, with currently approximately 80 projects being operated (all of them onshore), the majority located in the Permian Basin in west Texas, USA [53]. Overall, an additional 8–11% of the original oil in place can be produced from a petroleum field with CO2 EOR [53]. Unfortunately, the net emission reductions associated with an EOR project most likely will not be quite significant, as more fossil fuels are produced in the process. Furthermore, in many EOR projects currently running in the USA, CO2 is not captured from anthropogenic sources, but extracted from natural reservoirs in Colorado and New Mexico instead. To maximize CO2 storage in EOR projects, the CO2 produced together with oil must be separated and re-injected in the same or other reservoir. It is difficult to estimate how much CO2 will remain stored, as it depends on the field structure, the recovery rates, and injection methods. It is estimated that ca. 60% of the injected CO2 remains in the reservoir, and 10 Mt of CO2 have been currently stored by EOR projects worldwide [57]. It is estimated that up to 80% of oil reservoirs worldwide might be suitable for CO2 injection based upon oil recovery criteria alone [55, 56], with an overall capacity between 675 and 900 Gt CO2 [3].

Saline Aquifers Saline aquifers are formations that are geologically similar to oil and gas fields, save for the fact that its pores are filled mostly with highly saline water (brine). Salinity of these formation waters should be above levels that make them unsuitable for human consumption, which usually means concentrations higher than 10 g/L. Usually, only aquifers with salinity higher than seawater (35 g/L) are considered. As already mentioned, an ideal reservoir should be deeper than ca. 800 m, for a higher likelihood of CO2 being in a supercritical phase, with a high density and gas-like viscosity, therefore maximizing pore-volume filling and mobility within the reservoir [58]. Both porosity and permeability of the reservoir should be sufficiently high so as to ensure constant injection of CO2 for the time duration of the project (usually a few years, at least). Since the CO2 injected will displace the original fluid, a low permeability may cause clogging and reservoir overpressures that may result in hydraulic fractures of the reservoir. Physicochemical interactions between CO2 and reservoir rock and fluids should not

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37

deteriorate reservoir quality close to injection wells during injection phase (this topic will be described in greater detail further in the chapter). To be eligible for CO2 storage, a saline aquifer must present an overlying caprock with low permeability, being continuous and with minimum amounts of faults and fractures over the range of the estimated storage area. Moreover, this formation must resist the hydraulic overpressure imposed during the injection phase. The great advantage of saline aquifers over other storage reservoirs is their enormous theoretical capacity and worldwide availability and uniform distribution. On the other hand, there is much less information and data available for saline aquifers since the economic incentive for their study is nearly absent. Therefore, global storage capacity estimations for deep saline formations have been roughly estimated thus far, between 1,000 and 10,000 Gt CO2 [3].

Coal Fields Coal beds are able to trap CO2 by adsorption (see next section), and most of the world coal resources are unminable (usually because of depth), therefore being potential targets for CO2 storage. Like in oilfields, storage in coal beds may be economically valuable, when carried out in the methane recovery range (300–1,500 m) and in coals with moderate permeability (1–5 mD) [59]. In this case, injected CO2 will be adsorbed preferentially, displacing the naturally occurring methane from the coal matrix, which can be produced through wells – a technique known as enhanced coal-bed methane recovery (ECBM). A key issue for storage in coal is the identification of suitable coal beds. A detailed characterization of the coal is necessary to evaluate composition, rank, nonorganic material content, permeability, and adsorption capacity, providing the necessary information for site selection. In addition, technical limitations related to coal permeability, which is typically lower than in common conventional reservoirs, have to be considered. The injection of CO2 is known to cause coal swelling, which further decreases permeability and, consequently, injectivity [60]. Reactivity of coal with CO2 and/or formation water is another issue that requires investigation since the interactions of coal macerals (organic matter) with CO2 are largely unknown, and may lead to alterations that modify the coal matrix and its adsorption behavior toward CO2, methane, and other gases [61]. Due to these limitations, CO2 storage in coal beds is still in the early stages of development, compared to the other reservoir options, with a few ECBM demonstration projects currently deployed. Poland’s RECOPOL project is currently the most important demonstration of CO2 storage in coal beds to be concluded. ECBM tests and demonstrations have been carried out in the USA, in the San Juan Basin (Colorado), where many commercial coal-bed methane (CBM) operations are in place [59, 62]. A recent pilot project has been launched in southern Brazil (CARBOMETANO/Porto Batista project) to evaluate the potential for methane recovery and CO2 storage of the coal reserves in this country.

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Reservoir

CO2

Mineral grains

CO2

Formation fluids (brine/oil/gas)

. Fig. 37.8 Trapping mechanisms of stored CO2 in geological reservoirs

Caprock

Residual Saturation

Precipitated solid

Formation fluids with dissolved CO2

Mineral grains

Dissolution/Mineralization

CH4 (desorbed) CO2 (adsorbed)

Coal matrix Fluid (water)

Adsorption

37

Structural/Stratigraphic

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Trapping Mechanisms of CO2 in Geological Media There are at least six trapping mechanisms that can keep CO2 confined in a storage complex for long periods of time. These mechanisms, discussed in detail in this section and depicted in > Fig. 37.8, may vary with time within the reservoir over different timeframes and scales [3].

Structural and Stratigraphic Trapping CO2 may fill ‘‘closed’’ structural or stratigraphic traps in a similar fashion that oil and gas do in petroleum fields. In this case, CO2 will be accommodated within the reservoir below the caprock and, after equilibrium, it will be stored as an immiscible and immobile plume underneath the caprock. CO2 may occupy the entire pore volume of the reservoir within the trap from the top until its spill point, minus the volume of irreducible water (and oil and gas).

Hydrodynamic and Residual Trapping CO2 injected in an ‘‘open’’ reservoir, i.e., a reservoir with a caprock without a closure or trap, may form an immiscible plume that will migrate upward and up dip due to density differences between the CO2 and water (or oil) phases. Forces acting against the displacement of CO2 will retard plume movement and trap CO2 within the reservoir for a certain period of time. The displacement of this plume will leave a CO2 ‘‘tail’’ behind, in which storage occurs in pore space as residual gas at irreducible gas saturation (i.e., the minimum saturation of a fluid to be displaced in water media). These trapping mechanisms will commonly operate right after CO2 injection in saline aquifers.

Dissolution and Mineralization Trapping After injection, CO2 will start to dissolve in formation water and, depending on factors like pH, a different proportion of dissolved species will form: HCO3 , CO32 . Once dissolved, CO2 will be trapped within the reservoir aqueous phase as a dissolved species until geochemical conditions are changed (and proportion of dissolved species modified) or the fluids are displaced. Dissolved CO2 may change drastically geochemical conditions of the media, mostly by increasing acidification, which potentially can promote dissolution of minerals present in reservoir or caprock. Furthermore, the aqueous phase tends to be dried out in the vicinity of the CO2–water interface, as the supercritical CO2 absorbs water, leading to a more saturated saline fluid [63]. This may set off the precipitation of minerals in this region, such as halite. Dissolved CO2 species and cations originated from

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dissolution of minerals or present in water may interact to form carbonates such as calcite (CaCO3), magnesite (MgCO3), and siderite (FeCO3), among others. The type of carbonate formed will depend on pressure, temperature, pH, and geochemical conditions, notably the activity of the cations dissolved in water and kinetics of reactions. Once in a solid phase, CO2 will be stored within the reservoir until unlikely (in a period of ‘‘Reservoir Options’’ section above). After equilibrium, and depending on conditions, ca. 5% of the mass of CO2 stored in coal will remain as free gas in the cleat system (and retained below an impermeable caprock) and 95% as adsorbed CO2. CO2 will remain stored in coal if pressure and temperature conditions are unchanged. Changing pressure and temperature can only occur in a period smaller than 1,000 years by human intervention, through conventional mining, underground coal gasification or depressurization of the seam as in coal-bed methane production activities.

Storage Capacity Assessment Estimating CO2 storage capacity of a geological reservoir depends strongly on methodology. Global capacity estimations available are largely inaccurate and conflicting, as they tend to be based on sparse data and even erroneous assumptions [9]. A quick glance at some of these published even reveal some world estimates that are lower than regional values. Many studies extrapolate values from a local or regional site to basin or continental scales, but the enormous geological variations that occur in storage complexes even within the same sedimentary basin make it nearly impossible for this upscaling to be precise. Furthermore, capacity assessments were carried out using various approaches and methodologies. Recognizing these difficulties, the Carbon Sequestration Leadership Forum (CSLF), an international consortium for the development of CCS, launched in 2004 a Task Force to review and develop a standard methodology for storage capacity

Reducing Greenhouse Gas Emissions with CO2 Capture and Geological Storage

(a) Increased certainty of storage potential

37

Matched capacity Practical capacity

Increasing cost of storage

Effective capa

city

Theoretical ca

pacity

. Fig. 37.9 Capacity estimation resource pyramid [8]

estimation. A comprehensive review of this methodology was presented by Bachu and Bradshaw in 2007 [8, 9] and is briefly explained in this section. It was suggested that it should be important for this global effort of standardization to categorize the nature of capacity estimations in a resource pyramid (> Fig. 37.9) [8]. The first level, occupying the whole pyramid, is the theoretical capacity, and represents the physical limit of what the storage system can accept. It can be either interpreted as the whole pore space available or pore space minus displaceable original fluids (water, oil, etc.) Either way, it represents the maximum upper limit to a capacity estimate. When technical limits (geological and engineering) are applied to the assessment, an effective capacity upper limit is defined. Further restrictions due to legal and regulatory, infrastructure or economic barriers to storage result in a practical capacity subset. A final matched capacity estimation can be obtained by considering the previously mentioned source-sink matching assessment, taking into account injectivity and supply rates of CO2. As this organization is more conceptual, it is unlikely that a capacity estimation assessment will result in precise values for each different category. In effect, the ‘‘resolution’’ of the data will depend largely on the scale considered. Estimations focused on a given site or local scale will probably give a higher level of resolution, while at larger scales (regional, basin or country), this level of detail tends to decrease significantly. Assessments at basin- or country-scale are more likely to be conducted by governments, while estimations at site or local scale will probably be run by project operators. Increasing resolution will usually result in higher costs of data acquisition. Next, a brief description of capacity estimation methods (and their current gaps and difficulties) in the main reservoir options is presented [8, 9].

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Petroleum Fields Estimation of storage capacity in oil or gas fields is the most straightforward of all potential targets, as the oil industry gathers plenty of data from these reservoirs before and during exploration to establish the precise amount of petroleum reserves and resources. Furthermore, oil and gas fields are discrete volumes with fairly well-defined boundaries, which allows for a more precise assessment. On the other hand, petroleum production history and methods in a reservoir will influence directly the available storage space for CO2. Secondary or tertiary recovery techniques (injection of water or other substances for improved production) can reduce the available space. Also, if the reservoir is in hydrodynamic contact with underlying aquifers, water may flood the reservoir during oil/gas production, occupying the previously oil-filled space. Injection of CO2 can partially displace the water, although not all of the original oil-saturated volume will be available for storage due to residual saturation or viscous fingering effects. It is assumed that injection of CO2 in a petroleum field will be carried out until the original reservoir pressure is restored. However, this is not always possible, as the oil and gas exploration may damage the formation and/or caprock, limiting the maximum pressure. In other cases, injection can be performed beyond the original pressure as long as it does not compromise the safety of containment by the caprock, exceeding the rock-fracturing threshold or capillary entry pressure of this formation. Theoretical capacities for petroleum reservoirs can be calculated based on geometrical parameters (reservoir area and thickness), physical and hydrodynamic properties such as CO2 density and water saturation, and other data gathered from exploration activities, such as recovery factors, injected and produced water volumes. The effective storage capacity can then be obtained by applying a capacity coefficient (90%) carbon dioxide accumulations around the world that can be used as analogs for geologic storage of CO2 in both limestone and sandstone lithologies [78]. Many of these natural occurrences are exploited and primarily used for enhanced oil recovery (EOR) projects (see next section), particularly in the USA. Approximately 40 millions of metric tons of high-purity CO2 from natural sources were used in 1998 for EOR only in the USA, mainly in the Permian Basin of Texas and New Mexico. The McElmo Dome in southwestern Colorado is the best documented natural CO2 analog and the world’s largest supply of commercial carbon dioxide, with 1.6 Gt of original carbon dioxide in place. A large part of the 14.6 Mt of CO2 produced annually is transported to the Permian Basin by an 800 km long pipeline since 1984. There is no episode of CO2 leakage from the field to the surface detected by an alarm system installed on the surface since the beginning of its exploration in 1976 [79].

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Monitoring Stored CO2 The deployment of any CO2 storage project will most likely require, by regulating organisms, a constant monitoring and verification of the storage complex, usually operated during the injection phase and in the first years of decades following site abandonment (depending on specific regulations). Most monitoring techniques rely on proven technology which has already been in use for years in many applications, including oil and gas exploration, natural gas underground storage, and waste disposal. The choice for the appropriate monitoring methods and instruments will depend on the storage complex characteristics and regulatory requirements. Among the most important techniques for monitoring CO2 in the reservoir are geophysical methods such as seismic, electromagnetic, and gravity imaging, which allow to track the CO2 plume displacement in the host formation. Other important methods include geochemical monitoring, which relies on measuring changes in formation water (and/or gas) composition, collected in observation wells to evaluate changes caused by the injection of CO2, and atmospheric and surface monitoring, for detecting leakages and seepages of CO2 in the air and soil, in the surrounding areas of the storage complex [80]. Monitoring activities differ according to the stage in which a CCS project is found [81]. The first stage is the site selection and characterization, where the monitoring role is to gather enough data to establish accurate baseline conditions, to be compared with upcoming measurements. During the operational phase, usually taking place over a period of 30–50 years, monitoring is focused on ensuring operational safety and assessing injection well conditions, tracking migration of injected CO2, and updating storage performance predictions, usually comparing with data from simulations, laboratory experiments, and previous field tests. After operations are finished (when injection of CO2 is stopped), a closure phase ensues. In this stage, that may last years or decades (depending on the project or regulations), injection wells are plugged and abandoned, and must be monitored for a certain period of time. Most monitoring activities should also be continued during this period in order to demonstrate storage safety and performance. In a post-closure stage, the storage complex will most likely be handed to regulatory authorities, who would maintain data records. Further monitoring would no longer be needed, except in case of ongoing leakages or legal disputes, or in case additional data is required for future projects [81].

Future Directions CCS is a transition technology to an alternative energy future, possibly based on renewable sources. Optimism for its success is based on industrial experience – many of the technologies needed for implementation of CCS projects in commercial scale are already available and mature. But even proponents acknowledge that there are several issues that need to be dealt with before it can achieve widespread application with a significant impact in reducing emissions of greenhouse gases, especially when those regarding

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integration, cost-reduction, and scaling-up of known technologies in large-scale commercial projects. The IEA Technology Roadmap for CCS released in 2009 [5] envisions 100 commercial-scale projects for 2020, and a staggering 3,400 for 2050, in order to reach the expected CCS contribution for the stabilization of emissions. One of the major issues that need to be solved is the financing model. Governments are expected to contribute in these initial efforts, funding research and demonstration projects (and even funding pipeline networks since they could be shared by more than one project), but it is widely accepted that an economic driver has to be established to stimulate private initiatives in CCS operations. With the current model, commercial power plants and industrial facilities will not invest in CCS owing to the elevated costs and reduced efficiency and energy outputs. Injection of CO2 in deep saline aquifers, which are possibly the most suitable reservoirs for storage, has no economic return by itself, and requires some form of incentive to be deployed, as was the case in the Sleipner project, with Norway’s government taxes imposed over CO2 emissions offshore. The inclusion of CO2 geological storage in the United Nation’s Clean Development Mechanism is one solution that has been advocated strongly by many governments and stakeholders as a means to establish an economic driver for CCS projects. Recent efforts in this direction have been unsuccessful so far, as these mechanisms require a well-defined reckoning of stored CO2 quantities and emissions avoided for a given project. Storage in geological reservoirs still have uncertainties regarding safety regulations and long-term liabilities, and in the case of enhanced recovery of oil and methane, the net amount of emissions avoided. In the chain of a CCS integrated operation, the current bottleneck in the total cost is the capture and separation of CO2 from the stationary source, being responsible for no less than 70% of the global cost in a project. Capture technologies have long been used in the industry to remove CO2 from flue gas streams; however, there is still a strong need to develop and test new technologies (especially in the large scales required for CCS projects). In particular, the main challenges in capture technologies at the moment include: (1) diminishing costs of post-combustion capture, which are mainly related to energy penalty required for regeneration of solvents, and (2) developing novel, promising technologies such as oxycombustion via chemical looping and ionic liquids. From the storage viewpoint, the CCS challenges are related to scaling-up the rate of CO2 that must be injected per storage site. Even though CCS has been demonstrated in commercial scale (storage >1 Mt/year) by the projects mentioned earlier, future storage projects will have to increase this ratio several times. The peculiar characteristics of CO2 and its interaction with each part of the integrated CCS chain requires continuous research to improve existing technologies and materials, such as new CO2-resistant cements for injection wells, development of high-pressure compressors adapted for CO2, corrosion-resistant pipelines for transport, among others. Demonstrating safety of storage is also a key point in the development of this technology. This requires the improvement of existing and developing new monitoring techniques, which in turn can only be achieved through field testing in pilot and demonstration scale sites of injection. Successful demonstration of storage and monitoring techniques will further improve public perception of CCS as well. Geologic storage of

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CO2 is a relatively new concept to which most of the population is very unfamiliar overall. Communicating and introducing this technology to general public is a challenging task that has to carefully addressed in order to succeed. The recognition of CCS as an important technology for greenhouse gas emission reductions resulted in a prompt effort by several countries’ administrations in developing regulatory marks and legislations for this activity. However, the majority of nations (mostly non-OECD) still require regulations for this activity to be introduced in their legal system, and this presents a series of difficulties. First, the categorization of CO2 in a CCS project is a matter of discussion – it is usually unclear whether it should be treated as waste, commodity, etc. Legal responsibilities over environmental damage due to leakages need to be properly defined by regulators, for which a clear distinction of the storage complex boundaries is imperative. Liability for stored CO2 over the years is another issue that requires careful analysis since storage periods are likely to be much longer than the lifetime of a site operator. For all the potential that CCS in geological reservoirs has in becoming an important solution for the climate crisis, it was patently shown that many issues and gaps in this integrated technology are yet to be resolved to achieve this objective. And as with most of the challenges mankind has faced, this will probably hardly succeed if not through a global determination in solving it, mostly through the combined efforts of academia, industry, and government sectors.

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65. Ketzer JM, Iglesias R, Einloft S et al (2009) Waterrock-CO2 interactions in saline aquifers aimed for carbon dioxide storage: experimental and numerical modeling studies of the Rio Bonito formation (Permian), southern Brazil. Appl Geochem 24(5):760–767 66. Rosenbauer RJ, Koksalan T, Palandri JL (2005) Experimental investigation of CO2-brine-rock interactions at elevated temperature and pressure: implications for CO2 sequestration in deep-saline aquifers. Fuel Process Technol 86(14–15):1581–1597 67. Bateman K, Turner G, Pearce JM et al (2005) Large-scale column experiment: study of CO2, porewater, rock reactions and model test case. Oil Gas Sci Technol 60(1):161–175 68. Tsang C-F, Doughty C, Rutqvist J et al (2007) Modeling to understand and simulate physico-chemical processes of CO2 geological storage. In: Wilson EJ, Gerard D (eds) Carbon capture and sequestration: integrating technology, monitoring and regulation. Blackwell, New York 69. Steefel CI, DePaolo DJ, Lichtner PC (2005) Reactive transport modeling: an essential tool and a new research approach for the earth sciences. Earth Planet Sci Lett 240(3–4):539–558 70. Parkhurst DL, Appelo CAJ (1999) User’s guide to PHREEQC (version 2) – a computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations. U.S. Geological Survey Water Resources Investigations, Denver 71. Xu TF, Sonnenthal E, Spycher N et al (2006) TOUGHREACT – a simulation program for non-isothermal multiphase reactive geochemical transport in variably saturated geologic media: applications to geothermal injectivity and CO2 geological sequestration. Comput Geosci 32(2): 145–165

72. Palandri JL, Kharaka YK (2004) A compilation of rate parameters of water-mineral interaction for application to geochemical modeling. U.S. Geological Survey, Menlo Park 73. Wilson EJ, Gerard D (2007) Risk assessment and management for geologic sequestration of carbon dioxide. In: Wilson EJ, Gerard D (eds) Carbon capture and sequestration – integrating technology, monitoring and regulation. Blackwell, New York 74. Benson SM, Cole DR (2008) CO2 Sequestration in deep sedimentary formations. Elements 4(5): 325–331 75. Katz DL, Tek MR (1981) Overview of underground storage of natural Gas. J Petrol Technol 33:943–951 76. Nuclear Energy Agency (2008) Moving forward with geological disposal of radioactive waste. OECD, Paris 77. Baines SJ, Worden RH (2004) The long-term fate of CO2 in the subsurface: natural analogues for CO2 storage. In: Baines SJ, Worden RH (eds) Geological storage of carbon dioxide. Geological Society, London 78. Pearce JM (1996) Natural occurrences as analogues for the geological disposal of carbon. Fuel Energ Abstr 37(4):305 79. Stevens SH, Fox CE, Melzer LS (2000) McElmo Dome and St. Johns natural CO2 deposits: analogs for carbon sequestration. In: GHGT-5, Cairns 80. Arts R, Winthaegen P (2005) Monitoring options for CO2 storage. In: Benson SM (ed) Carbon dioxide capture for storage in deep geologic formations – results from the CO2 capture project. Elsevier, Amsterdam 81. Benson S (2007) Monitoring geological storage of carbon dioxide. In: Wilson EJ, Gerard D (eds) Carbon capture and sequestration – integrating technology, monitoring and regulation. Blackwell, New York

38 Chemical Absorption Mengxiang Fang . Dechen Zhu Institute for Thermal Power Engineering, Zhejiang University, Hangzhou, Zhejiang, China Principle of Chemical Absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1443 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1443 Mechanism of Chemical Absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1443 Typical Chemical Absorption System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1448 Amine-Based Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1448 Carbonate-Based Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1451 Ammonia-Based Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1452 Membrane Absorption Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1455 Enzyme-Based Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1456 Key Technologies of Chemical Absorption Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1457 Absorbent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1457 Properties of the Absorbent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1458 Absorbents for CO2 Capture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1460 Absorber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1480 Packed Tower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1480 Hollow Fiber Contactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1481 Super Gravity Rotating Bed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1482 Integration and Optimization of the Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1483 Recovery of CO2 Compression Heat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1483 Pressure Swing Regeneration Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1484 Regeneration Process Based on Facilitated Transport Membrane . . . . . . . . . . . 1486 Membrane Flash Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1487 Water-Splitting Electrodialysis Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1487 Environmental and Economic Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1488 Water Issue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1488 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1488 Water Balance Strategy for Power Plants with CO2 Capture . . . . . . . . . . . . . . . . . 1489 Environmental Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1491 Environmental Assessment of the Alkanolamines . . . . . . . . . . . . . . . . . . . . . . . . . . . 1491 Emission and Its Impact on the CO2 Capture Process . . . . . . . . . . . . . . . . . . . . . . . 1493

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_38, # Springer Science+Business Media, LLC 2012

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Management of Pollutant Releases and Their Impacts . . . . . . . . . . . . . . . . . . . . . . . 1497 Economical Factors of Chemical Absorption Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . 1498 Industry Application and Future Direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1500 Industry Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1500 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1500 Development of Chemical Absorption Technologies for CO2 Capture . . . . . . 1501 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1508 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1508 Future Directions of Chemical Absorption Technologies for CO2 Capture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1509

Chemical Absorption

38

Abstract: In order to explain the principle of chemical absorption, the equations of vapor–liquid equilibrium are first introduced and the effects on gas solubility caused by temperature and pressure are also covered. Amine-based systems, carbonate-based systems, aqueous ammonia, membranes, enzyme-based systems, and ionic liquids– based system are discussed as the typical and emerging state of the art for chemical absorption. Furthermore, design rule and method are given to help complete the design of typical chemical absorption systems. The key issues to hinder the application of chemical absorption are discussed, such as water-consumption-related issues, environmental effects, and economical factors. Finally, applications and future directions are discussed.

Principle of Chemical Absorption Introduction Chemical absorption is one of the most effective methods for CO2 separation and capture nowadays. Being of low equipment cost, high removal efficiency, stable operation conditions, and mature technology background, chemical absorption has already been widely applied to chemical engineering, food industry, and other fields. Chemical absorption is based on the solubility difference between CO2 and the other gas components in mixed gases. The difference between chemical absorption and physical absorption is whether CO2 reacts with the absorbent during the absorption process. Chemical absorption can be classified into nonrecycling processes and recycling processes. For the former processes, the rich CO2 solution cannot be regenerated. While for the latter processes, the absorbent can be recovered by the cycle of absorption and regeneration.

Mechanism of Chemical Absorption The CO2 volume fraction in flue gas from fossil-fuel-fired plants is generally between 3% and 15%. Since the gas emissions for the power plants are usually very huge, physical absorption methods seem to be too expensive for CO2 capture and storage of power plants currently. More studies are needed to support these methods. A number of demonstration power plants for CO2 capture have already or will be built in the recent years. Most of them choose amine-based chemical absorption, while the other plants choose ammonia or other solutions as the absorbents. In fact, more solutions can be applied as the absorbent for chemical absorption. The research and development of advanced absorbents will be still a big challenge in the future. Furthermore, the studies on absorber and regenerator and process optimization are also key factors to improve this technology. During the chemical absorption process, the CO2 solubility depends on the physical solubility in the absorbent, the chemical reaction equilibrium constant, the chemical equivalent ratio, and other factors. In addition, in cases where the chemical absorbent solution is a strong or weak electrolyte, dilute solution theory does not fit. Solubility of gases in the chemical absorbent is characterized by a uniform solubility increase with

1443

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Chemical Absorption

pressure. The higher the pressure, the lower the solubility enhancement is. In that case, the relationship between partial pressure and gas solubility is more complex than that of physical absorption. A vapor–liquid equilibrium under the following conditions is the simplest chemical absorption balance. It is assumed that 1. Only one chemical reaction happens in the system. 2. The activity coefficient does not relate to the composition of the components and it is considered to be 1 in the simplest case. 3. The physical solubility of gas xph is negligible relative to the chemical solubility of gas xch, that is to say, the total solubility can be written as follows: X ¼ Xph þ Xch  Xch

(38.1)

The chemical reaction equation can be written in the following form: nA þ mB ¼ kC þ 1D þ   

(38.2)

m k l B ¼ C þ D þ  n n n

(38.3)

Or Aþ

In the formula, A – dissolved gas B – chemical absorbent C, D – reaction products n, m, k, l – stoichiometric coefficients According to assumption (> 38.2), the equilibrium constant can be viewed as the function of the concentrations of the reaction components. If reactant A is consumed for x mol and the initial concentration of chemical absorbent B is B0, when the system reaches another equilibrium state, Kp ¼


nk


l

n l nx 
m xf Bo  mn x n

k nx

¼i

xh xf ðB o  jxÞj

(38.4)

In the formula, k

l

i ¼ ðk=nÞn ðl=nÞn    ; h ¼ ðk þ l þ   Þ=n j = m/n – the ratio of the stoichiometric reaction coefficients between dissolved gas and consumed absorbents. h is the total mole number or ions number of reaction products generated per mole gas. j is the mole number of consumed chemical absorbents per mole gas. If the first condition is correct, then the coefficients of i, h, j are all integers.

Chemical Absorption

38

> Equation 38.4 can be turned into the equation expressed in gas phase equilibrium form by equilibrium constant of physical solubility.

Xph ¼

PA PA ¼ Kph KH

(38.5)

PA is the partial pressure of gas A, Kph is physical equilibrium constant of gas A, KH is Henry equilibrium constant PA ¼ Kph

ix h KP ðBo  jxÞ

j

¼K

xh ðBo  jxÞj

(38.6)

Under these assumptions, K only relates with the temperature. What’s more, K reflects the state of gas–liquid phase physical equilibrium and chemical equilibrium. Kph ¼ A1 e

DH1 RT

and KP ¼ A2 e

DH 2 RT

(38.7)

DH1, DH2 – are the enthalpy change during the process of physical dissolution and chemical reactions, respectively. A1 and A2 are deviation coefficients. K ¼i

Kph DH ¼ ðA1  A2 Þe RT KP

(38.8)

DH – the total enthalpy change during the gas dissolution process with chemical reactions. Here, the utilization efficiency of chemical absorbent is defined as a = x/B0. T also reflects the state of chemical reactions. > Equation 38.6 can be written as: PA ¼ K

ðaBo Þh ðBo  jaBo Þ

j

¼ KBohj

ah ð1  jaÞj

(38.9)

Thus, no less than three constants were introduced into the vapor–liquid equilibrium equations. These constants can be measured by individual methods or obtained from a chemical solubility database. According to > Eqs. 38.6 and > 38.9, the chemical equivalents affect the curvature of the balance curve greatly, when K is equal to B0. Hence, the chemical absorbent of high h value, of which h is above 1, is hard to regenerate with a decrease of pressure. However, this absorbent is easy to regenerate with a decrease of pressure under the condition of purification or lower gas partial pressure. Derived from > Eq. 38.6, the increase of the initial absorbent concentration causes a drop of the gas partial pressure above the absorbent when the gas concentration in the solution stays constant. As > Eq. 38.9 shows, the effect of the absorbent concentration is different only judged by (hj) when a stays constant. If x!0, > Eq. 38.6 can be written in the following form: PA ¼

iKph xh  ¼ Kch x h KP B0j

(38.10)

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38 >

Chemical Absorption

Equation 38.9 can be written in the following form: hj

PA ¼ KB0 ah

(38.11)

According to > Eq. 38.11, during the process of chemical absorption, if x!0, the Henry law can be applied only when h equals 1. That is to say, one mole gas involved in the chemical reactions can produce only one mole product. In many cases, the experimental data can be described by > Eq. 38.6. The coefficients i, h, and j are all integers in the equation. For more complicated processes, such as two or more continuous and parallel reactions occurring during the process, the coefficients i, h, and j can be fractions, and they relate with xph. However, the meaning of the coefficients does not change at every case and it reflects the relative relationship between chemical equivalents. > Equation 38.6 can be used for calculation only when the relationship between Kph/KP and the components of the solution is considered. The reason is that for > Eqs. 38.4 and > 38.6, the concentration of the solution should be replaced by the activity of the solution. The equation for a real solution is
k=n l
l=n k n aC n aD KP;T ¼ (38.12) aph ðaB Þm=n KP, T – equilibrium thermodynamic constant. As ai ¼ gi Xi , hence k

PA ¼ k

Kg ¼

l

gn gn

l

h Kph i xch xhch gn gn Kph Kg   ¼   KP ðB0  jxÞj KP ðB 0  jxÞj gjB

(38.13)

– the coefficient related with chemical products and the activity of the j gB absorbent. By comparison of > Eqs. 38.6 and > 38.13, the two equations are consistent with each other when the change of the activity of solution components are mutually compensated, that is to say, g 6¼ 1 and Kg stays constant. Both the relationship between Kph and x and the relationship between Kph and B have additional effects on the gas dissolution for chemical absorption processes. Kph ¼ KH e ðaxþbBÞ

(38.14)

In this equation, a, b are constants x is solubility B is the concentration. Figure 38.1a shows the relationship between gas solubility and partial pressure above the surface. Curve 1 and curve 2 describe the chemical absorption process. Curve 3, curve 4, and curve 5 are descriptions of the physical absorption process. > Figure 38.1b shows the relationship between gas partial pressure above the solution surface and temperature. >

Chemical Absorption

2

P, 104 Pa 6

8

10 6

a

4

1 3

2

2 Ig P

Solubility α, m3/m3

50

4

38

25

1

3

0

a

4

250 500 Partial pressure, mmHg

5 750

b

The reciprocal of absolute temperature, 1/T

. Fig. 38.1 The equilibrium pressure and temperature curve in the gas–liquid system. The meanings of the curves in the figures are listed as follows: (1) When the temperature is 20 C, CO2 is injected into the MEA (monoethanolamine) solution of 2.5 mol/L (chemical absorption). (2) When the temperature is 60 C, CO2 is injected into the solution of 25% K2CO3+10% DEA (diethanolamine), (chemical absorption). (3) When the temperature is 25 C, C2H2 is injected into the N,N-dimethylformamide solution (physical absorption). (4) When the temperature is 25 C, C2H2 is injected into the propylene carbonate solution (physical absorption). (5) When the temperature is 25 C, C2H2 is injected into the water (physical absorption) [1]

When the reaction between the absorbent and the gas is completed, that is to say (ja!1), the gas solubility only depends on the physical absorption process. Hence, with the increase of operation pressure, the gas solubility increases at this time. Chemical absorption is different from physical absorption in that the solution heat during the chemical absorption process is rather huge; it even reaches 83.3125.8 kJ/mol. Hence, the gas solubility is affected strongly by the temperature. The lower the concentration of gas absorbed, the more the solution heat per gram of gas. The gas concentration above the surface of a regenerated absorbent solution is usually low and the partial pressure above the surface of the solution increases with the temperature. Compared to physical absorption, chemical absorption is fit for fine purification. The operation pressure has little effect on the absorption capacity of an absorbent. Chemical absorption is particularly good for the case that the absorption gas concentration is not high. Above all, the best method to regenerate an absorbent is to raise the operation temperature. The decrease of operation pressure is not a good choice. It is especially suitable for a strong absorbent, that is to say, DH and KP are large. With the decrease of DH and KP, the characteristics of a chemical absorbent are more like those of a physical absorbent, and the process setup needs to vary with that change.

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Chemical Absorption

Typical Chemical Absorption System Amine-Based Systems The idea of separating CO2 from flue gas streams started in the 1970s, not with concern about the greenhouse effect, but as a potentially economic source of CO2, mainly for enhanced oil recovery (EOR) operations. All the early plants capture CO2 with processes based on chemical absorption using amine-based solvents. Typical amine-based absorbents can be classified into three categories by the number of active hydrogen atoms adjacent to the nitrogen atom, primary amine with two hydrogen atoms, secondary amine with one hydrogen atom, and tertiary amine without hydrogen atom. Judged by the number of active nitrogen atoms, the amine-based absorbents can be classified into monoamine and multi-amines. The reaction mechanism between alkanolamines and CO2 can be expressed by the following description [2]: 1. Reaction mechanism between CO2 and primary amines or secondary amines When a primary amine and secondary alkanolamines are chosen to be the absorbents, the so-called zwitterions are formed at first due to the reaction between CO2 and amines. After that the zwitterions will react with alkanolamine and form carbamate. The detailed reactions are listed as follows: where R is an alkyl and R0 is H for primary amines and an alkyl for secondary amines [3]: RR0 NH þ CO2 Ð RR0 NHþ COO ðzwitterionÞ

(38.15) þ

RR0 NH þ RR0 NHþ COO Ð RR0 NCOO ðcarbamateÞ þ RR0 NH2

(38.16)

The total reaction is: þ

2RR0 NH þ CO2 Ð RR0 NCOO þ RR0 NH2

(38.17)

According to the total reaction, due to the restrictions of thermodynamics, the maximum CO2 absorption capacity is 0.5 mol CO2/mol absorbent. However, some amino acid root may be hydrolyzed into free amine. 

RR0 NCOO þ H2 O Ð RR0 NH þ HCO3

(38.18)

Hence, sometimes the maximum CO2 absorption capacity exceeds 0.5 mol CO2/ mole absorbent. The characteristics for CO2 absorption in amine solution are high reaction rate and low CO2 absorption capacity. 2. Reaction mechanism between CO2 and tertiary amines There is no excess hydrogen atom adjacent to the nitrogen atom for tertiary amines so that no zwitterions are produced in the following process. The reaction mechanism can be depicted by the following equations, where R, R0 , and R00 are alkyls [3]: RR0 R00 N þ H2 O þ CO2 Ð RR0 R00 NHþ þ HCO 3

(38.19)

38

Chemical Absorption

According to the above equation, there is no thermodynamic restriction for tertiary amines. The maximum CO2 absorption capacity is 1 mol CO2/mol absorbent. However, the absorption rate is rather low for tertiary amines. 3. Reaction mechanism between CO2 and sterically hindered amines The huge functional groups adjacent to the nitrogen atom can hinder the binding of CO2 and alkanolamine so as to reduce the stability of the amino acid root. Hence, the maximum absorption capacity for sterically hindered amines is the same as for tertiary amines. What’s more, the absorption rate is close to that of primary and secondary amines. Take AMP (aminomethylpropanol) as an example: The reaction mechanism of CO2 and AMP can be described by the following equation, where R is C(CH3)2CH2OH [4]:  CO2 þ RNH2 þ H2 O Ð RNHþ 3 þ HCO3

(38.20)

A continuous scrubbing system is used to separate CO2 from the flue gas stream. As illustrated in > Fig. 38.2, the flue gas is transported into the absorber after removing the dust and other air pollutants, especially SO2 and NOx. If necessary, the flue gas should also go through some cooling process and pressure enhancement process before it is sent to the absorber by the blower. Flue gas enters into the bottom of the packed column and contacts with the lean CO2 absorbent injected from the top of the absorber directly and in counterflow. CO2 in the flue gas reacts with the chemical absorbent and forms some weak salts so that CO2 is separated from the flue gas by the absorber. The rich CO2 solution is pumped to the regenerator, which is also called stripper. However, the rich CO2 solution needs to pass a lean/rich solution heat

MEA storage Exhaust gas MEA makeup

Condensed system CO2 product

Cooler Packed column

Lean solution pump Regenerator

Blower Dedusted and desulphurized gas

Lean/rich solution heat exchanger

Rich solution pump

. Fig. 38.2 Flow sheet for CO2 capture from flue gases using amine-based systems [5]

Reboiler

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Chemical Absorption

exchanger before it enters into the regenerator. The lean/rich solution heat exchanger aims to optimize the heat cycle of the whole process. It can heat the rich CO2 solution to a higher temperature that is closer to the stripping temperature. It can also decrease the lean CO2 solution to a temperature which is much closer to the absorption temperature. CO2 is regenerated in the stripper due to diverse reactions occurring at the higher temperature. The heat of the stripper is supplied by the reboiler. Then, the gas at the top of the stripper should be cooled to separate vapor from CO2. The solution regenerated at the bottom of the stripper is sent back to the absorber. Although amines have been used for many years, particularly in the removal of acid gases from natural gas, there is still enough space for process improvement. Amines are available in three forms (primary, secondary, and tertiary), each with its advantages and disadvantages as a CO2 solvent. In addition to options for the amine, additives can be used to improve system performance. Furthermore, design optimization is possible to decrease capital costs and reduce energy consumption. Past studies have shown that amine-based CO2 absorption systems are the most suitable ones for combustion-based power plants for the following reasons: ● These systems are effective for dilute CO2 streams, such as coal combustion flue gases, which typically contain only about 10–12% CO2 by volume. ● Amine-based CO2 capture systems are a proven technology that is commercially available and in use today. ● Amine-based systems are similar to other end-of-pipe environmental control systems used at power plants. These units are operated at ordinary temperature and pressure. ● A major effort is being made worldwide to improve this process in the light of its potential role in CO2 abatement. Thus, one can anticipate future technology advances. However, the amine systems used at low partial pressure conditions encountered with carbon dioxide in flue gases have inherent disadvantages: ● High heat of reaction which leads to the need for expensive cooling systems ● High regeneration energy needs which requires large quantities of low-pressure steam and correspondingly large stripper column reboilers ● The need for large volume absorbers with expensive packings to provide adequate mass transfer surface for the carbon dioxide absorption and reaction ● The need to circulate large quantities of amine solvents because of practical limitations of carbon dioxide loadings ● A high parasitic power loss caused by the need to overcome the pressure drops in the large absorbers These factors combined result in relatively high capital costs for the capture plant and high operating costs and consequential efficiency losses in host power plants where the capture plant is integrated. Furthermore, due to the viscosity of the amines, problems such as entraining, channeling, bubbling, and overflowing may happen. The amine-based systems also have problems with equipment corrosion.

Chemical Absorption

38

Improvements to amine-based systems for post-combustion CO2 capture are being pursued by a number of process developers. Some of them are Fluor, Mitsubishi Heavy Industries (MHI), and Cansolv Technologies. Fluor’s Econamine FG Plus™ is a proprietary acid gas removal system that has demonstrated larger than 95% availability with natural gas fired power plants, specifically on a 350 t/day CO2 capture plant in Bellingham, MA. It is currently the state-of-the-art commercial technology baseline. MHI has developed a new absorption process, referred to as KS series absorbents. An innovative factor in this development is the utilization of a new amine-type solvent for the capture of CO2 from flue gas [6]. Cansolv Technologies, Inc. proposes to reduce costs by incorporating CO2 capture in a single column with processes for capturing pollutants, such as SO2, NOx, and Hg. DC1031 tertiary amine solvent has demonstrated fast mass transfer and good chemical stability with high capacity – a net of 0.5 mol of CO2/mol of amine per cycle compared to 0.25 mol/mol for monoethanolamine (MEA) [7]. R&D pathways to improved amine-based systems include modifying tower packing to reduce pressure drop and increase contacting area, increasing heat integration to reduce energy requirements, using additives to reduce corrosion and allow higher amine concentrations, and improving regeneration procedures.

Carbonate-Based Systems Carbonate systems are based on the ability of a soluble carbonate to react with CO2 to form bicarbonate, which can be heated to release CO2 and revert to a carbonate. A major advantage of carbonates over amine-based systems is the significantly lower energy required for regeneration. The University of Texas at Austin has been developing a K2CO3-based system in which the solvent is promoted with catalytic amounts of piperazine (PZ). The K2CO3/PZ system (5 M K; 2.5 M PZ) has an absorption rate 10–30% faster than a 30% solution of MEA and favorable equilibrium characteristics. A benefit is that oxygen is less soluble in K+/PZ solvents; however, piperazine is more expensive than MEA, so the economic impact of oxidative degradation will be about the same [11]. Analysis has indicated that the energy requirement is approximately 5% lower with a higher loading capacity of 40% versus about 30% for MEA. System integration studies indicate that improvements in structured packing can provide an additional 5% energy savings and multi-pressure stripping can reduce energy use by 5–15% [8]. The reaction mechanism between CO2 and K2CO3/PZ can be expressed as follows: PZ þ CO2 þ OH

! PZCOO þ H2 O

(38.21)

PZ þ CO2 þ H2 O

! PZCOO þ H3 Oþ

(38.22)

PZ þ CO2 þ PZ PZ þ CO2 þ CO3

2

! PZCOO þ PZHþ 

! PZCOO þ HCO3

(38.23) 

(38.24)

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Chemical Absorption

PZ þ CO2 þ PZCOO

! PZCOO þ Hþ PZCOO

PZCOO þ CO2 þ H2 O PZCOO þ CO2 þ PZ PZCOO þ CO2 þ CO3 2 PZCOO þ CO2 þ PZCOO

! PZðCOO Þ2 þ H3 Oþ ! PZðCOO Þ2 þ PZHþ

(38.25) (38.26) (38.27)

! PZðCOO Þ2 þ HCO3 

(38.28)

! PZðCOO Þ2 þ Hþ PZCOO

(38.29)

CO2 þ OH PZ þ CO2 þ H2 O PZCOO þ CO2 þ H2 O

! HCO3  þ

! PZH þ HCO3

(38.30) 

! Hþ PZCOO þ HCO3 

(38.31) (38.32)

The K+/PZ solvent was introduced by Cullinane as an alternative to the widely used MEA. MEA has a high capacity and a fast rate of CO2 absorption. According to Cullinane, the K+/PZ solvent has a higher CO2 capacity than MEA because PZ is a secondary amine and potassium carbonate increases the absorption capacity. Furthermore, the rate of absorption was increased due to the presence of secondary amine groups in PZ, the high pKa, and the large quantity of carbonate/bicarbonate. He reported a CO2 absorption rate 1.5 to 3 times faster than with 30 wt% MEA. The flow sheet of carbonate-based systems is similar to that of an amine-based system. Although the K+/PZ system has several advantages over amine-based systems, the technology is still not mature. Lots of experimental data on this idea is still lacking. The pros and cons of this system still need to be tested.

Ammonia-Based Systems Ammonia-based wet scrubbing is similar in operation to amine systems. Ammonia and its derivatives react with CO2 via various mechanisms, one of which is the reaction of ammonium carbonate (AC), CO2, and water to form ammonium bicarbonate (ABC). The gas–liquid chemical reactions can be expressed by the following reaction equation: NH3 ðlÞ þ CO2 ðgÞ þ H2 OðlÞ

! NH4 HCO3 ðsÞ

(38.33)

However, the actual steps of the chemical reaction are complex and must pass through several intermediate reaction steps: 2NH3 ðgÞ þ CO2 ðgÞ

! NH2 COONH4 ðsÞ

(38.34)

The formed NH2COONH4 is further hydrolyzed: NH2 COONH4 ðsÞ þ H2 OðlÞ

! NH4 HCO3 ðsÞ þ NH3 ðgÞ

(38.35)

Then, the NH3 reacts with H2O to form NH4OH: NH3 ðgÞ þ H2 OðlÞ

! NH4 OHðlÞ

(38.36)

38

Chemical Absorption

The hydrolyzed product NH4HCO3 of reaction reacts with NH4OH to form (NH4)2CO3: NH4 HCO3 ðsÞ þ NH4 OHðlÞ

! ðNH4Þ2 CO3 ðsÞ þ H2 OðlÞ

(38.37)

The (NH4)2CO3 then absorbs CO2 to form ammonium bicarbonate: ðNH4 Þ2 CO3 ðsÞ þ H2 OðlÞ þ CO2 ðgÞ

! 2NH4 HCO3 ðgÞ

(38.38)

All the reaction equations are reversible. This reaction has a significantly lower heat of reaction than amine-based systems, resulting in energy savings, provided the absorption/ desorption cycle can be limited to this mechanism. Ammonia-based absorption has a number of other advantages over amine-based systems, such as the potential for high CO2 capacity, lack of degradation during absorption/regeneration, tolerance to oxygen in the flue gas, low cost, and potential for regeneration at high pressure. There is also the possibility of reaction with SOx and NOx – critical pollutants found in flue gas – to form fertilizer (ammonium sulfate and ammonium nitrate) as a salable by-product. > Figure 38.3 gives the typical flow sheet for CO2 capture from flue gases using aqueous ammonia systems [9]. A few concerns are related to ammonia’s higher volatility compared to that of MEA. One is that the flue gas must be cooled to the 288300 K (USE KELVIN) range to enhance the CO2 absorptivity of the ammonia compounds and to minimize ammonia vapor emissions during the absorption step. Additionally, there is concern over ammonia losses during regeneration, which occurs at elevated temperatures. R&D process improvements

Flue gas 38,000 t/day

Steam 3,900 MM Btu/h Air 43,700 t/day Coal (III. No. 6) 4,200 t/day 11,666 Btu/Ib 2.5 wt% Sulfur

PC boiler

Particulate filter

Base Plant: H Supercritical steam cycle H Case 7C of reference [3] with steam rate adjusted for AA

Ammonia regenerator

82 MW parasitic load

Ammonia scrubber

Net power to grid 400 MW

Ammonia contactor

Steam to ammonia stripper

Mercury 0.45 t/day

Steam

Aqueous NH3 (Aq. 7wt. %j) 1,300 t/day)

ECOTM reactor Activated carbon

125 ⬚F 14 Psig

CO2 8,780 t/day 1,500 Psig

Crystallizer

Granulator

Ammonium nitrate Ammonium sulfate 443 t/day

Dryer

. Fig. 38.3 Flow sheet for CO2 capture from flue gases using aqueous ammonia systems (NETL 2007)

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Chemical Absorption

include process optimization to increase CO2 loading and the use of various engineering techniques to eliminate ammonia vapor losses from the system during operation [9–11]. Another ammonia-based system, under development by Alstom, is the chilled ammonia process (CAP), which was first tested in a 5-MW pilot test in 2007 at We Energies Pleasant Prairie Power Plant. It was also tested in mid-2008 on AEP’s 1,300-MW Mountaineer Plant in New Haven, WV, as a 30-MW (thermal) product validation with up to 100,000 t of CO2 being captured per year. This process uses the same AC/ABC absorption chemistry as the aqueous system described above, but differs in that no fertilizer is produced and a slurry of aqueous AC and ABC and solid ABC is circulated to capture CO2 [12]. The process operates at near-freezing temperatures (273–283 K), and the flue gas is cooled prior to absorption using chilled water and a series of direct contact coolers. > Figure 38.4 gives the schematic of the chilled ammonia process. Technical hurdles associated with the technology include cooling the flue gas and absorber to maintain operating temperatures below 283 K required to reduce ammonia slip, achieve high CO2 capacities, and for AC/ABC cycling, mitigating the ammonia slip during absorption and regeneration, achieving 90% removal efficiencies in a single stage, and avoiding fouling of heat transfer and other equipment by ABC deposition as a result of absorber operation with a saturated solution. Both the aqueous and chilled ammonia processes have the potential for improved energy efficiency over amine-based systems, if the hurdles can be overcome.

Gas Water Rich solution Lean solution CO2 From FGD

Steam

REF

Clean combustion gas

Stripper

G6

Pressurized CO2 G7 Water wash G5 Cooling Cooling

DCC2

REF REF G2

G3

G4 Steam

Booster fan

G1

CO2 Absorber

CO2 regenerator

DCC1

Bleed

REF

Cooling and cleaning

Refrigeration System

CO2 absorption

CO2 regeneration

. Fig. 38.4 Schematic of the chilled ammonia process (PT/PE Sector – Communications – November 2006,Chilled Ammonia Process for CO2 Capture – content owner: Sean Black)

Chemical Absorption

38

Membrane Absorption Systems There are a variety of options for using membrane contactor to recover CO2 from flue gas. In one concept, flue gas would be passed through a bundle of membrane tubes, while an amine solution flowed through the shell side of the bundle. CO2 would pass through the membrane and be absorbed in the amine, while impurities would be blocked from the amine, thus decreasing the loss of amine as a result of stable salt formation. Also, it should be possible to achieve a higher loading differential between rich amine and lean amine. After leaving the membrane bundle, the amine would be regenerated before being recycled. > Figure 38.5a shows the principle of membrane absorption for the CO2 capture process. > Figure 38.5b gives the true structure of a hollow fiber membrane, and > Fig. 38.6 gives the experimental schematic of membrane absorption. Obviously, it looks similar to the amine-based system.

Liquid–gas interface Solvent inlet

CO2

membrane

a Flue gas inlet

b . Fig. 38.5 (a) The principle of membrane absorption. (b) Typical structure of a hollow fiber membrane

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Chemical Absorption

CO2 MFC Lean gas Stripper GC

Absorbent (40⬚C)

Membrane contactor

Heat exchanger

80⬚C

CO2 absorbed absorbent CO2 rich gas (25⬚C) Reboiler (105⬚C) CO2 stripped absorbent

Cooler

. Fig. 38.6 Experimental schematic of CO2 capture from flue gas by membrane absorption. MFC mass flow controller, GC gas chromatograph [14]

R&D pathways to an improved system include increasing membrane selectivity and permeability, preventing membrane wetting and particle block, and decreasing cost [13].

Enzyme-Based Systems Biologically based capture systems are another potential avenue for improvements in CO2 capture technology. These systems are based upon naturally occurring reactions of CO2 in living organisms. One of these possibilities is the use of enzymes. An enzyme-based system, which achieves CO2 capture and release by mimicking the mechanism of the mammalian respiratory system, is under development by Carbozyme (see > Fig. 38.7). The process, utilizing carbonic anhydrase (CA) in a hollow fiber contained liquid membrane, has demonstrated at laboratory scale the potential for 90% CO2 capture followed by regeneration at ambient conditions. This is a significant technical improvement over the MEA temperature swing absorption process. The CA process has been shown to have a very low heat of absorption that reduces the energy penalty typically associated with absorption processes. The rate of CO2 dissolution in water is limited by the rate of aqueous CO2 hydration, and the CO2-carrying capacity is limited by the buffering capacity. Adding the enzyme CA to the solution speeds up the rate of carbonic acid formation; CA has the ability to catalyze

Chemical Absorption

38

The cabozyme permeation process Flue gas in N2 O2 CO2

Sweep gas out CO2 rich CLM CA

CA

HCO3

CA = carbonic anhydrase

O2 N2 CA CO2 lean

CA

Membrane

Flue gas out

Sweep gas in

. Fig. 38.7 Schematic of the carbozyme permeation process [17]

the hydration of 600,000 molecules of carbon dioxide per molecule of CA per second compared to a theoretical maximum rate of 1,400,000 [15]. This fast turnover rate minimizes the amount of enzyme required. Coupled with a low makeup rate, due to a potential CA life of 6 months based on laboratory testing, this biomimetic membrane approach has the potential for a step change improvement in performance and cost for large-scale CO2 capture in the power sector. Although the reported laboratory and economic results may be optimistic, the ‘‘Carbozyme biomimetic process can afford a 17-fold increase in membrane area or a 17 times lower permeance value and still be competitive in cost with MEA technology’’ [16]. The idea behind this process is to use immobilized enzyme at the gas/liquid interface to increase the mass transfer and separation of CO2 from flue gas. Technical challenges exist before this technology can be pilottested in the field. These limitations include membrane boundary layers, pore wetting, surface fouling [18], loss of enzyme activity, long-term operation, and scale-up.

Key Technologies of Chemical Absorption Systems Absorbent The absorbent is one of the most important factors to affect the process of chemical absorption. The type of absorbent and the rational weight concentration/mixing weight ratio are the main characteristic parameters of chemical absorption technologies. An absorbent of high absorption rate and absorption capacity can help to minimize the equipment size and decrease the loss of absorbent, while an absorbent of lower

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Chemical Absorption

regeneration energy consumption can basically decrease the total energy consumption of the whole process. The optimal choice of absorbent can make the chemical absorption technology more challenging than the other methods. What is more, the capital cost of absorbent, the physical properties of absorbent, and whether degradation reactions can occur with the other component in the flue gas are also important factors to be considered.

Properties of the Absorbent The chemical absorbent for CO2 capture should meet some basic requirements. > Table 38.1 lists the physical properties, molecular formula, and market price of several typical amines. Absorption Capacity

The CO2 solubility in the absorbent, the temperature effect, and pressure effect on the solubility are the most important properties for an absorbent. The main index for the process such as circulation rate of absorbent, heat consumption and electricity consumption for regeneration process, operation conditions for regeneration, and the equipment size all depends on the solubility. The Selectivity of Absorbent

This parameter refers to the ratio between the CO2 solubility a2 and the solubility a1 of the other gas component which is closest to CO2. C¼

a2 Kph;1 ¼ a1 Kph;2

(38.39)

Among the equation, C – selectivity coefficient Kph,i – solubility coefficient of less dissolved component i During the whole absorption process, the consumption of less dissolved gas, the possibility of complete separation of the mixed gases, the characteristics of the process, and many coefficients are related to the selectivity of the absorbent. Saturated Vapor Pressure

In order to avoid the consumption of absorbent, the vapor pressure under the absorption temperature should be low and the boiling point of the absorbent should be high enough. The requirement for the saturated vapor pressure depends on the pressure of the absorption process and the weight concentrations of the absorbent solution. In some cases, an easily volatile absorbent may be employed. However, it only seems to be sensible during the process that absorption temperature is decreased and operation pressure is increased. Especially detailed process requirements need to be taken into account.

1.036

In the molecular formulae,

j

CH3

R ¼ CH2 CH2 OH

R0 ¼ CH2 CHOH

a

Estimated price ($/kg)

1.058

1.08

1,013 (20 C) 534.9

100

96.4

380 (30 C) 669.8

1.33

1.33

24.1 (20 C) 825.6

21.2

28.0

10.5

Vapor pressure (Pa) 48.0 (20 C) 100 Solubility in the water (wt%, 20 C)

Viscosity (cps) Evaporation heat (kJ/kg) 1.013  105 Pa

360

269

171

R2-N 149.19 1.1258

R2-NH 105.14 1.0919

R-NH2 61.09 1.0179

Molecular formulaa Molecular weight Density (g/cm3) (20 C) Boiling point ( C) (1.013  105 Pa) Freezing point ( C)

Item

42

2.138

101 (20 C) 518.6

100

0.97

198 (45 C) 429.1

87

1.33

21.0 1.33

249

R2-NH 133.19 0.9890

247

R2-NCH2 119.17 1.0418

1.499

26 (24 C) 509.5

100

1.33

95

221

ROC2H4-NH 105.14 1.0550

Diethylene Monoethanolamine Diethanolamine Triethanolamine Methyldiethanolamine Diisopropanolamine glycolamine (MEA) (DEA) (TEA) (MDEA) (DIPA) (DGA)

. Table 38.1 The physical properties of commonly used alkanolamines [47]

Chemical Absorption

38 1459

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Chemical Absorption

Boiling Point

To some extent, once the requirement for the saturated vapor pressure is met, the optimal boiling point for the absorbent should be generally above 423 K. In many cases, the boiling point of the absorbent is not expected to be high, that is to say, a low saturated vapor pressure is the ideal condition. It is necessary to carry out distillation when the byproducts accumulate in the circulated solution. If the boiling point of the solution is too high, the distillation temperature has to be raised rather high to meet the requirements of energy consumption. Otherwise, the distillation should be carried out under high vacuum conditions. Factually, the boiling point of the absorbent is usually between 443 K and 473 K. The saturated vapor pressure is usually up to 13.33 Pa at 303 K. Freezing Point

The freezing point is also an important factor. Both the choice of the operation temperature and the storage condition depends on the freezing point. The mixed solution of absorbent, which usually refers to mixed solution composed of the absorbent and water, should not to be frozen easily. Density

The density of the absorbent seldom affects the application of the absorbent. However, the density of the absorbent is better to be low when the other properties are the same. Viscosity

The viscosity of the absorbent affects the heat transfer rate and mass transfer rate. Hence, it affects the size of the according equipment. It also has effects on the electricity consumption for solution transfer. Above all, the viscosity of the absorbent is better to be small when the other properties are the same. Thermochemical Stability

The residence time of the absorbent in the system should be long. It usually needs to be completely changed every 6–18 months. Therefore, the thermochemical stability should be guaranteed. Even the degradation such as oxidizing which occurs very slowly should be considered during the choice of absorbent. Another requirement for the absorbent is that the corrosion rate should be low and the market price should be not too high.

Absorbents for CO2 Capture Industry Used Absorbent

Until now, alkanolamines solution, alkali solution, and hot caustic potash solution have been widely used in many industries to separate CO2 by chemical absorption methods, such as in the food industry, fertilizer industry, and so on. > Table 38.2 lists the physical properties of the commonly used alkanolamines.

269

28.0 1.33

96.4

380 (30 C)

669.8

1.058

171

10.5 48.0

100

24.1 (20 C)

825.6

1.036

In the molecular formulae,

j

CH3

R ¼ CH2 CH2 OH

R0 ¼ CH2 CHOH

a

105.14 1.0919

61.09 1.0179

Molecular weight Density (g/cm3) (20 C) Boiling point ( C) (1.013  105 Pa) Freezing point ( C) Vapor pressure (Pa) (20 C) Solubility in the water (wt%, 20 C) Viscosity (cps)

Evaporation heat (kJ/kg) 1.013  105 Pa Estimated price ($/kg)

R2-NH

Molecular formulaa R-NH2

Item

1.08

534.9

1,013 (20 C)

100

21.2 1.33

360

149.19 1.1258

R2-N

2.138

518.6

101 (20 C)

0.97

429.1

198 (45 C)

87

42 1.33

21.0 1.33 100

249

133.19 0.9890

R2-NH

247

119.17 1.0418

R2-NCH2

1.499

509.5

26 (24 C)

100

95 1.33

221

105.14 1.0550

ROC2H4-NH

Diethylene Monoethanolamine Diethanolamine Triethanolamine Methyldiethanolamine Diisopropanolamine glycolamine (DGA) (MEA) (DEA) (TEA) (MDEA) (DIPA)

. Table 38.2 The physical properties of commonly used alkanolamines [20]

Chemical Absorption

38 1461

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38

Chemical Absorption

Maddox proposed a method to choose the absorbent [19]. The CO2 partial pressure and the CO2 volume ratio before/after the chemical absorption process are considered to be the key factors. When the CO2 partial pressure is no more than 103.4 kPa, the alkanolamine solutions are the best choices. In chemical absorption processes, the CO2 partial pressure can be lower than 34.5 Pa. When the CO2 partial pressure is 103.4–689.5 kPa, both the alkanolamine solutions and hot potassium carbonate solutions can decrease the CO2 partial pressure to be lower than 6.9 kPa. When the CO2 partial pressure is above 689.5 kPa, even the physical absorbent can decrease the CO2 partial pressure to be 6.9–20.7 Pa. According to Maddox’s method on the selection of absorbent, alkanolamine solutions are the best choices for coal-fired power plants. The reason is that the coal-fired flue gas is usually of low CO2 partial pressure, high volume, and high removal efficiency requirement of CO2. Aqueous solutions of alkanolamines are the most commonly used chemical absorbents for the removal of acidic gases (CO2 and H2S) from natural, refinery, and synthesis gas streams. Among them, aqueous monoethanolamine (MEA) as a primary amine has been used extensively for this purpose, especially for removal of CO2. It has several advantages over other commercial alkanolamines, such as high reactivity, low solvent cost, low molecular weight and, thus, high absorbing capacity on a mass basis and reasonable thermal stability and thermal degradation rate. Generally speaking, MEA solution is currently the most widely used absorbent in fossil power plants. To have a better understanding of the role played by MEA in the CO2 capture process, the simple analysis on MEA is given according to the index raised above. > Table 38.3 shows the evaluation for the conventional solvents MEA and MDEA [20].

. Table 38.3 Comparison of MEA and MDEA in the CO2 capture process Monoethanolamine (MEA)

Methyldiethanolamine (MDEA)

+ Fast reaction + Low molecular weight ! high solution capacity on a weight basis  Low net (cyclic) capacity  High heat of reaction with CO2 (due to carbamate formation)  High corrosion  Irreversible reaction products with carbonyl sulfide (COS) and carbon disulfide (CS2)

 Slow reaction  High molecular weight

 High vapor pressure + Yellow chemical (good biodegradability) + Low cost (+)

+ High net (cyclic) capacity + Low heat of reaction with CO2 + Low corrosion + Low degradation + Low vapor pressure  Red chemical (low biodegradability)  High cost

38

Chemical Absorption

Absorption and Regeneration Characteristics of CO2 in MEA Solutions A large number of

studies have already been carried out in this field. Here is a brief introduction of absorption/regeneration characteristic data for MEA solutions. The absorption rate and maximum net cycle capacity of several amines are given in > Fig. 38.8. Regeneration heat needs for the system are usually hard to measure. Especially hard to define is the true value for each option. Generally speaking, the heat required to regenerate

5.0M MEA 2.6M MDEA 2.9M AEEA 2.0M PT 2.5M BEA 3.3M EMEA 4.0M MMEA 2.5M PZ

40

30

20

10

0 0.00

0.20

a

0.40 0.60 0.80 α, CO2 loading [mol CO2 /mol amine] 0.30

2.5 MEA

MEEA

ΔQmax 0.25

Qmax[mol CO2/L]

2.0

0.20 1.5 0.15 1.0 0.10 0.5

0.0 0.00

b

1.00

Δ Qmax[mol CO2/L]

r CO2 , absorption rate × 105 [mol/L/s]

50

0.05

0.10

0.20 0.30 0.40 0.50 αlean[mol CO2/mol amine]

0.00 0.60

. Fig. 38.8 (a) Absorption rate of CO2 in amine-based solvent at 313 K. (b) Comparison of maximum net cycle capacity in 5 M MEA and 2.9 M AEEA [21]

1463

1464

38

Chemical Absorption

the solution in the desorber column of the CO2 capture process (reboiler heat duty) can be described as the sum of three terms: qreb ¼ qsens þ qvap;H2O þ qabs;CO2

(38.40)

Where qsens is the sensible heat to raise the solvent from the temperature downstream the rich-lean heat exchanger (RLHX) to the reboiler temperature, qvap,H2O is the heat of evaporation required to produce that part of the stripping steam in the reboiler which does not condense on its way up in the column and which is ultimately being condensed in the overhead condenser, and qabs,CO2 is the overall heat required to desorb the CO2 from the solution. The third term (qabs,CO2) corresponds to the heat of absorption of the solvent with the CO2. The same amount of heat that is being released in the exothermic reactions in the absorber column must be provided in the desorber column to reverse the absorption process and to drive out the CO2. The heat of absorption consists of three terms (Kim et al. 2009): 1. Nonideal mixing 2. Dissolution of gas into the liquid 3. Chemical reaction Heat must therefore be provided in the reboiler to break up the CO2/solvent complex formed during the absorption process (heat of reaction) and to desorb the dissolved molecular CO2 from the solution (heat of dissolution). > Figure 38.9a shows the comparison of stripping heat needs for different absorbents, and > Fig. 38.9b gives the distribution of energy associated in reboiler heat duty for different absorbents. Generally speaking, when the actual CO2 loading is around 0.2 mol CO2/mol MEA for the absorption/desorption process, the regeneration heat consumption is around 3.9–4.5 MJth/ kgCO2, which equals to 1.6 MJe/kgCO2 [23, 24]. The heat of evaporation occupies the main energy consumption. Hence, it is meaningful to reduce the evaporation heat consumption for the MEA scrubbing process. Degradation of MEA The degradation of MEA in the flue gas is rather complicated. It

may be caused by the following reasons: Thermal degradation, oxidation degradation, and the formation of heat-stable salts are three main reasons. The detailed mechanisms are discussed here. ● ● ● ● ● ● ●

Thermal degradation CO2-induced degradation Degradation caused by COS and CS2 Degradation caused by CO Formation of heat-stable salts and reaction of amines with strong acids Oxidation Sulfur and polysulfide degradation

Chemical Absorption

38

650 MEA MEA/MDEA (b = 0.2) MDEA/PZ (b = 0.4) MDEA

600 550 qStr (kJ/molCO2)

500 450 400 350 280 260 240 220 200 4

8

a

Energy distribution (%)

125

12

24 16 20 CMEA or CMDEA (%)

(a) MEA-MDEA blend

28

32

Sensible heat Heat of vaporization Heat of reaction

100

75

50

25

0 MEA

b

MEA-MDEA (1:1) MEA-MDEA (1:2) Absorption solvent

. Fig. 38.9 (a) Stripping energy needs in solutions of different weight concentration. (b) Distribution of energy associated in reboiler heat duty for different absorbents [22]

Thermal Degradation Polderman describes the mechanism for thermal degradation of MEA by carbamate polymerization. In the absorber, MEA associates with CO2 to form MEA carbamate as illustrated below. NH2 HO MEA

+

CO2

NH HO

CO2–

ð38:41Þ

MEA Carbamate

This reaction is normally reversed in the stripper, but in some cases the MEA carbamate will cyclize to form 2-oxazolidone, which is also a reversible reaction, as shown below:

1465

1466

38

Chemical Absorption

O NH HO

CO2–

NH

O

MEA Carbamate

+

ð38:42Þ

H2O

2-Oxazolidone

Yazvikova found that MEA carbamate can also react with a free MEA molecule and irreversibly dehydrolize to form N,N0 -di(2-hydroxyethyl)urea. O NH + CO2–

HO

MEA Carbamate

NH2

HO MEA

HO

OH NH

NH

+ H2O

N, N'-di(2-hydroxyethyl)urea

ð38:43Þ The former product, 2-oxazolidone, can then react with another molecule of MEA to form 1-(2-hydroxyethyl)-2-imidazolidone, which is sometimes referred to as HEIA. O

O NH

O

+

HO

NH2

HN

N

OH

+ H2O

ð38:44Þ

2-Oxazolidone 1-(2-hydroxyethyl)-2-imidazolidone (HEIA)

HEIA can then be hydrolyzed to form N-(2-hydroxyethyl)-ethylenediamine or HEEDA. O NH HN

N

OH

+ H2 O

HO

NH2 + CO2

ð38:45Þ

N-(2-hydroxyethyl)-ethylenediamine (HEEDA)

These four species (2-oxazolidone, dihydroxyethylurea, HEIA, and HEEDA) plus further polymerization products are believed to be the main products of thermal degradation. The rate of formation of these products is a function of temperature (faster kinetics), CO2 loading (more carbamate present), and MEA concentration. Oxidation Degradation The use of amines for CO2 capture from flue gases involves one distinct difference and challenge from traditional amine acid gas capture: the presence of dioxygen (O2) and its role in the oxidative degradation of the amine. It is important to realize that degradation conditions will vary within the gas-treating plant. Different mechanisms may be involved in different parts of the plant. For instance, the highest O2 concentration and the lowest temperature will occur within the absorber while the highest temperature and lowest O2 content will be found in the reboiler.

Chemical Absorption

38

Oxidation of most stable organic compounds is sluggish at room temperature and occurs readily only at high temperature. Obviously, the amines in flue gas capture applications experience a higher temperature, but still low relative to pyrolysis conditions. This low kinetic reactivity of dioxygen can be explained by considering spin conservation requirements. The ground state for O2 is a triplet (a biradical). Most stable organic compounds and the dioxygen reduction products, H2O and H2O2, are singlet molecules. The direct reaction of a triplet molecule with a singlet to give singlet products is a spin-forbidden process. This means that the reaction between dioxygen and a substrate should occur at a very low rate, which is determined by the time required for spin inversion to occur. This is generally a slow process except at elevated temperatures. In reported studies of amine autoxidation, combinations of high O2 partial pressures, higher than ambient process temperatures, and long reaction times (often several weeks) had to be employed to see substantial degrees of reaction. Metal ion spiking resulted in much faster reactions. The metal ions may directly react with amines, but in the presence of dioxygen, they may act as catalysts to activate the dioxygen. Metal complexes, due to their abilities to act as radicals with varied spin multiplicities can provide spin-allowed pathways for reaction. Thus, the reaction of dioxygen and amines is spin-allowed if the number of electrons on a ternary complex (metal ion + amine + O2) remains constant throughout the reaction. ● Dioxygen complex intermediates as oxidants. Amine complexes of Fe(II), Cu(I) and other metal ions have been shown or proposed to form dioxygen complexes, both stable and short-lived [5, 14]. Oxidation of amines via dehydrogenation of the C–N bond has been demonstrated via Co(II) dioxygen complexes, though the reaction was limited to amines with aromatic groups that could form conjugated imine products. Aliphatic amines such as tetraethylenepentamine did not oxidize in these cobalt systems and the amine ligand/Co(II) system was well known to form stable dioxygen complexes [25]. Other metal complex dehydrogenations of coordinated amines which may proceed via short-lived O2 complex intermediates include autoxidation of ethylenediamine (dehydrogenation of both C–N bonds) with Ru(II) [26, 27] and Os(II) [28], macrocyclic amines with Fe(II) [29], and peptides with Co (II) [30]. Whether or not dioxygen complexes are involved, dehydrogenation reactions (imine formation and subsequent imine products) of amines should be considered when in the presence of transition metal ions and dioxygen. ● Free radical pathways for autoxidation. In studies of the iron chelate hydrodesulfurization degradation, it was noticed that long (several days) exposure to air sparging at room temperature did not cause degradation. This was consistent with the predicted slow amino acid hydrolysis and oxidation by Fe(III). It was only after introducing the reducing agent H2S that ligand degradation was detected. Iron chelates, synthesized with Fe(II) and converted to Fe(III) with air, also exhibited degradation. This chemistry can be explained in terms of dioxygen reduction products such as superoxide, peroxide and hydroxyl radical.

1467

1468

38

Chemical Absorption

OH– Lean amine

O–

–

HO2

•

–H –H

Rich amine O2

+e–

O•2– +H+

+e– + 2H+

+

pKa – 11.7

H2O2

+e– – OH–

+

–H

+

pKa – 138

pKa – 11.8

HO•

+e– + H+

H2O

pKa – 4.7

HO2•

. Fig. 38.10 Primary dioxygen reduction species at amine process conditions [31]

It should be remembered that these reduction intermediates are weak acids and may exist in two protonation states in amine solutions. As shown by the pKa values in > Fig. 38.10, superoxide should exist in the anionic form, peroxide in both mono and diprotonated forms, and the hydroxyl radical can also exist as the oxide radical anion. For example, with pKa values of 11.7 and 11.8 (values at 298 K), both oxide radical anions and hydroxyl may exist in an unloaded (lean) amine solution, while high CO2 loadings will lower the pH enough so that hydroxyl will predominate. The rate constant for reaction of the glycine anion has been reported to be ten times higher for hydroxyl than for the oxide radical ion. For the amino acid chelants, it was noted that the most reactive species was the hydroxyl radical (HO·). Compilations of reaction rates show that compounds such as EDTA, NTA, HEDTA, and glycine have reaction rate constants of 109–1010 L/mol/s. Products that were seen to build up in solution had lower reactivities toward hydroxyl. For instance, the rate constant for oxalate (which can build up to problem levels in the process) was only 7.7  105. It was also shown that additives which had high hydroxyl radical rate constants (such as thiosulfate and sulfite) could act as hydroxyl radical scavengers. Because the rate constants were close to diffusion limitations and because of the high substrate concentrations, these additives could only act as competitive scavengers and not totally eliminate the degradation. Data on reactivity of amines with dioxygen reduction intermediates are harder to find, but some of the results shown in > Table 38.4 support the highest reactivity for hydroxyl. It should be mentioned that alternatives to the hydroxyl radical have been proposed to account for some subtle differences between Fe (II)/H2O2/O2 reactions and reactions of hydroxyl produced via pulse radiolysis. For purposes of this discussion, it is easiest to consider the chemistry in terms of the hydroxyl radical. Once the reaction has been initiated by formation of the carbon-based radicals, subsequent reaction with dioxygen should be extremely rapid, as shown by representative rate constants presented in > Table 38.5. > Figure 38.11 shows the reaction proposed for the dioxygenation of a MEA radical.

Chemical Absorption

38

. Table 38.4 Rate constants for dioxygen reduction intermediates at 298 K [31] Reaction

Rate (L/mol/s)

Dioxygen: RH + O2 ! products

Slow

n-propylpyrrolidine + O2 Superoxide: RH + O2  ! R · + HO2  (HOCH2)3CNH2 + O2  Glycine + O2 

1.1  103

Glycine + HO2  Peroxide: RH + HO2  ! R· + HO· + H2O Hydroxyl: RH + HO· ! R· + H2O Ethylenediamine + HO

Fig. 38.13. As shown in > Fig. 38.14, the feed

1471

1472

38

Chemical Absorption

MDEA contained HSS

NaOH

DI water Na2SO4

C

A

III A–

II

Na2SO4

C

A

I

A– OH–

OH–

MDEAH+

Na+

Na2SO4 Impurity ions Aqueous MDEA solution

Na2SO4 NaOH

. Fig. 38.13 Principles of HSS removal from aqueous solution of MDEA using a three-compartment ED [32]

solutions of NaOH and MDEA were added to compartments I and II, respectively. Two electrodes are positioned, one on either side parallel to the membranes. Applying a voltage to the electrodes generates an electric field. It is well known that the anion-exchange membrane permits the passage of anions only while the cation-exchange membrane permits the passage of cations only. Therefore, OH in compartment I migrates through the anion-exchange membranes and then reacts with binding amine (MDEAH+ A), as shown in > Eq. 38.47. OH þ MDEAHþ A ! A þ MDEA þ H2 O 





(38.47)

SCN , HCOO , H3CCOO, where A symbolizes impurity anions such as Cl , and H3CH2CCOO. Once impurity anions such as Cl, SO42, SCN, HCOO, H3CCOO, and H3CH2CCOO were replaced by OH in compartment II, they would pass through Anion-exchange membrane (AEMs) and reach compartment III under the action of DC electric field. The [MDEAH]+ ions were kept and purified in compartment II. The same more matrixes could be settled in an electrodialysis apparatus according to the above-mentioned arrangement principle. SO42,



Chemical Absorption

38

1,000,000

100,000

PCO2* (Pa)

10,000 100⬚C 1,000

100

Hiliard 3.5 m MEA Hiliard 7.0 m MEA Hiliard 11.0 m MEA Dugas 7.0 m MEA Dugas 9.0 m MEA Dugas 11.0 m MEA Dugas 13.0 m MEA Jou 7.0 m MEA

80⬚C 60⬚C

10 40⬚C 1 0.05

0.15

a

0.25

0.35

0.45

0.55

CO2 loading (mol/molalk)

MEA partial pressure (PA)

30

7 m MEA_60⬚C 20

11 m MEA_40⬚C 10

7 m MEA_40⬚C 0 0.0

b

0.1

0.2 0.3 0.4 Loading (mol CO2 /equivalent of amine)

0.5

0.6

. Fig. 38.14 (a) MEA–CO2–H2O system: CO2 solubility comparison between FTIR technique and other methods. (b) MEA partial pressure in 7 and 11 m MEA systems for 313 K and 333 K [33] Corrosion and Polarization Behavior of MEA All amine-treating plants have experienced

corrosion problems [20]. Corrosion occurs in the forms of general, galvanic, crevice, pitting, intergranular, selective leaching, erosion, and stress corrosion cracking. The plant areas susceptible to corrosion are the bottom of absorbers, regenerators, reboiler bundles, pumps, and valves where the acid gas loading and temperatures are high [34].

1473

1474

38

Chemical Absorption

According to a survey conducted for refinery plants [35], the process equipment that is frequently out of service due to severe corrosion problems are reboiler, rich amine exchanger, regenerator, condenser, absorber, and amine cooler. Although a number of factors contribute to severe corrosion, the major causes reported are poor plant design and operation, such as high flow velocity in pipelines, high operating temperature in reboiler and insufficient steam for solvent regeneration, and the presence of process contaminants. Corrosion problems essentially lead to substantial expenditure in addition to the process costs. According to CC Technologies & NACE International [36], in 1998, the plant expenditure due to corrosion in the USA was estimated at $276 billion while that for petroleum refining alone was $3.7 billion. Of this total, the maintenance-related expenses were estimated at $1.8 billion, the vessel turnaround expenses were at $1.4 billion, and the fouling-related costs were approximately $0.5 billion annually. This reflects a significant impact of corrosion problems in plant operations. The corrosion mechanism at the interface between the carbon steel surface and the CO2-loaded MEA aqueous solution was examined using the obtained results and previous work published in the literature. Let us consider chemical reactions taking place in the bulk solution due to CO2 absorption (reactions > 38.48–38.52), possible electrochemical reactions due to corrosion (reactions > 38.53–38.56), and possible chemical reactions due to formation of corrosion products (reactions > 38.57 and > 38.58) [37]. Dissociation of water: 2H2 O

! H3 Oþ þ OH

(38.48)

Hydrolysis of CO2: 2H2 O þ CO2

! H3 Oþ þ HCO3 

(38.49)

! H3 Oþ þ CO3 2

(38.50)

! RNH2 þ H3 Oþ

(38.51)

Dissociation of bicarbonate ion: H2 O þ HCO3  Dissociation of protonated amine: RNH3 þ þ H2 O Carbamate reversion: RNHCOO þ H2 O

! RNH2 þ HCO3 

(38.52)

Iron dissolution: Fe

! Fe2þ þ 2e

(38.53)

Reduction of hydronium ion: 2H3 Oþ þ 2e

! 2H2 O þ H2 ðgÞ

(38.54)

Chemical Absorption

38

Reduction of bicarbonate ion: 2HCO3  þ 2e

! 2CO3 2 þ H2 ðgÞ

(38.55)

Reduction of undissociated water: 2H2 O þ 2e

! 2OH þ H2 ðgÞ

(38.56)

Formation of ferrous hydroxide: Fe2þ þ 2OH

! FeðOHÞ2

(38.57)

! FeCO3

(38.58)

Formation of ferrous carbonate: Fe2þ þ CO3 2

Essentially, corrosion occurs due to electrochemical reactions comprising anodic and cathodic reactions. The anodic reaction is iron dissolution (reaction > 38.53) while the cathodic reactions are reductions of oxidizers available in the solution. In the absence of O2, some possible oxidizers in this system are H3O+, undissociated H2O, and HCO3. According to Veawab and Aroonwilas [37], undissociated H2O and HCO3 are major oxidizers whereas H3O+ plays a minor role. As such, possible primary corrosion reactions are reactions (> 38.53), (> 38.55), and (> 38.56). Previous studies show that factors listed below affect the corrosion and polarization behavior of MEA solution to different extent. > Table 38.6 summarizes some of them: pH, conductivity, electrochemical parameters, and corrosion rate for uninhibited MEA–H2O– CO2 system. ● Increasing the O2 partial pressure accelerates corrosion due to the increasing oxidizer concentration in the solution. Dissolved O2 is required for the corrosion control that raises the system potential to passivation where a passive film of hematite (ɤFe2O3) is established on the metal surface. ● A greater solution velocity causes a higher corrosion rate due to the enhancement of the transport rates of corroding agents between metal surface and bulk solution. ● Raising the solution temperature enhances the corrosion rate. This is the result of the increases in rates of iron dissolution and oxidizer reduction during the corrosion process. ● An increase in CO2 loading in solution causes corrosion rate to increase. This is due to the increase in concentrations of corroding agents (HCO3 and H+), which causes rates of oxidizer reduction to increase. ● An increase in amine concentration makes a solution more corrosive due to the increase in HCO3 available in the solution, which induces a greater rate of iron dissolution. ● The precorroded carbon steel corrodes faster than the nonprecorroded steel due to the faster rates of both iron dissolution and oxidizer reduction reactions.

1475

pH

s (mS/ ba (mV/ cm2) decade)

Ecorr (mV Ag/AgCl) icorr (mA)

583.00 6.00

9.25 22.48 110.25 127.81 815.13 3.66E + 02 0.11 2.69 1.77 8.65 5.83 1.05E + 01

2,000 rpm, a = 0.20, 80 C

40 C, a = 0.20

80 C, a = 0.20

10.50 19.69 – 0.57 1.00

9.14 22.99 76.00 0.02 0.46 10.00

10.13 kPa O2, 5.0 kmol/m3 MEA

634.00 10.00

122.35 826.86 3.15E + 02 1.71 8.59 3.90E + 01

9.23 21.81 97.67 0.13 1.85 8.96

1,000 rpm, a = 0.20, 80 C

175.00

356.00

2.12E + 01

134.50 833.00 1.99E + 02 8.50 7.00 3.41E + 00

–

673.00 4.00

573.00 36.00

686.00

113.11 775.00 1.75E + 02 1.045 4.00 2.41E + 01

2.82E + 01

7.95 43.68 88.00 0.07 2.17 4.80

846.00

80 C, a = 0.55

101.71

10.19 20.29 92.88 0.00 0.02 0.00

40 C, a = 0.20

662.00 1.50

Epp (mV Ag/AgCl)

9.06 23.18 72.92 0.02 0.33 0.78

106.93 853.00 8.02E + 01 1.11 3.50 7.63E + 00

bc (mV/ decade)

80 C, a = 0.20

0.00 kPa O2, 5.0 kmol/m3 MEA

Experimental condition

–

8.94E + 00 7.25E  01

1.42E + 01 5.25E  01

1.4E + 01 1.79E + 00

2.52E + 01 1.82E  00

1.42

9.44E + 00 3.25E  01

icrit (mA)

580.00

1.40E + 01

408.00

2.60E + 01 448.00 0.00E + 00 4.00

7.25E + 02 708.00 2.5E + 01 31.00

4.72E + 02 604.00 4E + 00 19.00

2.55E + 02 635.00 1.5E + 01 26.00

15.00

0.08

0.43 0.03

1.43 0.07

1.21 0.15

0.67 0.09

0.11

0.31 0.03

Eb (mV Corrosion rate Ag/AgCl) (mm/year)

8.45E + 01 522.00 4.5E + 00 4.50

ipass (mA)

38

. Table 38.6 Summary of pH, conductivity, electrochemical parameters, and corrosion rate for an uninhibited MEA–H2O–CO2 system [38]

1476 Chemical Absorption

8.17 46.24 76.00 0.11 1.38

9.13 23.36 76.85 0.03 0.58 3.15

2.74E + 02

1.87E 02

1.41E + 02

116.64

152.16

9.14 23.31 99.34 0.07 0.31

9.10 24.04 84.63 0.12 0.36

14 days

28 days

790.00

789.00

780.00

8.31E + 02

4.74E + 02

2.07E + 02

642.00

653.00

648.00

653.00 1.00

501.00

507.00

507.00

1.31E + 04

7.59E + 03

8.05E + 03

1.59E + 02 4.5E + 00

2.04E + 04

2.60E + 04

2.52E + 01

699.00

699.00

705.00

2.83E + 03

1.04E + 03

1.96E + 02

546.00

523.00

528.00

2.56E + 01 481.00 0.26E + 00 23.00

7.10E + 01

7.80E + 01

1.41E + 01

1.94

1.83

0.80

0.37 0.01

1.06

0.72

0.55

s, conductivity; ba, anodic Tafel slope; bc, cathodic Tafel slope; Ecorr, corrosion potential; icorr, corrosion current density; Epp, primary passivation potential icrit, critical current density; ipass, passivation current density; Eb, breakdown potential; a, CO2 loading (mol/mol)

135.8

9.15 23.03 63.49 0.06 0.03

7 days

10.13 kPa O2, 5.0 kmol/m3 MEA, 80 C, a = 0.20

80 C, a = 0.20

795.00

795.00

788.00

136.00 839.00 1.59E + 02 5.00 1.00 4.5E + 01

150.42

8.32 21.89 117.00 0.00 0.52

9 kmol/m3 MEA, a = 0.55

5.07 kPa O2, 5.0 kmol/m3 MEA

120.90

8.52 32.62 105.90 0.04 3.16

113.00

7 kmol/m3 MEA, a = 0.55

10.13 kPa O2, a = 0.55, 80 C

80 C, a = 0.55

Chemical Absorption

38 1477

1478

38

Chemical Absorption

Volatility of MEA Amine volatility is a key screening criterion for amines to be used in CO2 capture. Excessive volatility may result in significant economic losses and environmental impact. It also dictates the capital cost of the water wash. There are several publications on the VLE (vapor–liquid model) of the binary MEA– H2O system, but only few data on directly measured MEA volatility, more specifically the vapor phase mole fraction of MEA. Lenard et al. [55] measured the gas phase composition of MEA in binary aqueous solution (343 and 363 K) using gas chromatography. These data were represented using a three-parameter Redlich–Kister expansion. Cai et al. [39] measured isobaric VLE at 101.3 and 66 kPa (373–443 K) using the standard curve of refraction index versus mole fraction of the binary mixture at 20 C. The liquid phase activity coefficients were calculated with the UNIFAC group contribution model as published by Larsen et al. [40]. These data are in the high-temperature range. At temperatures relevant to absorption-stripping, McLees [41] directly measured the volatility of MEA in a binary system (3.5, 7.0, 23.8 mMEA) as well as in blends having piperazine (PZ) as a promoter. PZ volatility was also measured for 0.9, 1.8, 2.5, and 3.6 m PZ. The data was obtained by hot gas Fourier transform infrared spectroscopy (FTIR). Efforts were also made to model the experimental data in terms of binary interaction parameters by utilizing the NRTL model within AspenPlus®. There have also been other thermodynamic measurements of MEA–H2O. Touhara et al. [42] measured the total pressure of this system at 298 and 308 K. Nath and Bender [43] measured total pressure for pure substances as well as binary and ternary mixtures of alcohols, alkanolamines, and water from 60 C to 95 C in a vapor-recycle equilibrium cell. Specifically, the MEA–H2O system was studied at 60 C, 78 C, and 91.7 C. Activity coefficients for each system were calculated using the Wilson and UNIQUAC equations and were seen to have negative deviations from an ideal solution (> Table 38.7).

New Type Absorbent

Although MEA is considered to be the most reliable absorbent for CO2 capture in power plants nowadays, there still exist a lot of inherent problems. The disadvantages of MEA

. Table 38.7 Amine volatilities and enthalpies for various systems at nominal lean loadings [33] Solution

Loadings (mol CO2/mol solvent)

Volatility (ppm)

DH;excess apparent (kJ/mol)

DHvap (kJ/mol)

7 m MDEA/2 m 0.1 PZ 8 m PZ 0.29

6/2

27/87

102/135

8

37

85

12 m EDA 7 m MEA 5 m AMP

9 31 112

40 33 10

108 55 75

0.44 0.45 0.25

Chemical Absorption

38

include high enthalpy of reaction with CO2, leading to higher regeneration energy consumption, the formation of a stable carbamate and also the formation of degradation products with COS or oxygen bearing gases, inability to remove mercaptans, vaporization losses because of high vapor pressure and more corrosiveness than many other alkanolamines and, thus, the need for corrosion inhibitors when used in higher concentration. In addition, the market price of MEA is relatively high. Based on the analysis above, nowadays the laboratory research generally sets MEA as a base absorbent. 1. Aqueous ammonia In 1997, Bai proposed to replace traditional amine solutions by aqueous ammonia solutions to capture CO2 from coal-fired flue gas. The related experiments show that the maximum CO2 removal efficiency can reach 99% and the absorption capacity is up to 1.20 kg CO2/kg NH3. Under the same experimental conditions, the maximum CO2 removal efficiency is 94% and the absorption capacity is 0.40 kg CO2/kg MEA. That is to say, the absorption capacity of aqueous ammonia is three times that of MEA. Furthermore, the aqueous ammonia has other advantages over MEA, such as fewer erosion and degradation problems. Especially, the market price of aqueous ammonia is much lower than that of MEA. However, there are also inherent problems for aqueous ammonia. The vitality of ammonia is really a problem issue. In addition, the regeneration of ammonia can easily cause the loss of ammonia. Aqueous ammonia also brings secondary pollution problems. Hence, how to control the slip of ammonia and regeneration conditions becomes a key factor for the research of aqueous ammonia. In order to reduce the emission of ammonia slip, some research organizations try to control the operation temperature for the absorption process to be 273–283 K. However, this method can increase the energy consumption because of the large volume, high-temperature flue gas. 2. Ionic liquids Ionic liquids are a new type of absorbent made of molten salts. They are pure liquid substances around room temperature. Ionic liquids are entirely made of positivecharge ions and negative-charge ions. The compositions of the ions for ionic liquids are made of organic cations and inorganic or organic anions. It is estimated that, although the number of ionic liquids can reach 1018, the number of commonly used ionic liquids is only around 100. Common cations are imidazolium, pyridinium, ammonium, phosphonium, and sulfonium, while the anions are Cl, Br、, NO3、, TFO, DCA, BF4, PF6, Tf2N, and so on. Ionic liquids attract the attention of researchers worldwide in the field of CO2 capture and storage, because the ionic liquids show low corrosion, easy separation, and high recycling efficiency. Former studies show that the CO2 absorption mechanism of functional ionic liquids is similar to that of alkanolamine solutions and ionic liquids are of higher CO2 loading and lower regeneration energy consumption than MEA. But there is still a long way to go to overcome some difficulties in ionic liquids research. The disadvantages of ionic liquids mainly include high viscosity, decomposition, and toxicity in the presence of water and high capital cost.

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Chemical Absorption

3. Mixed amines A single absorbent to satisfy all the requirements for a CO2 separation process seems hard to find. Some researchers try to combine the advantages of several amines [92]. The new types of mixed amines are expected to have high CO2 absorption capacity, high CO2 loading, and low regeneration energy consumption. Generally speaking, monoethanolamine and diethanolamine have the advantage of high absorption rate, while triethanolamine has the advantage of low energy consumption. Based on the analysis above, mixed amines have become a new research direction nowadays. Although sterically hindered amines seem to be rather expensive, they have also become a research object because of high absorption capacity and absorption rate. For example, the mixed absorbents developed by MHI which are called KS-1/KS-2 and KS-3 employ sterically hindered amines as a component of the absorbent. The KS serial absorbent has already been verified to be better than the standard, single MEA solution. The energy consumption is reported to be reduced by 40% compared to that of a MEA process. Zhejiang University developed MEA/MDEA and MDEA/PZ mixed amine absorbents, and the test result shows that they can decrease energy consumption by over 5–10%. In addition, some researchers try to develop other chemical absorbents. For example, China’s Zhejiang University and Korea’s KAIST tried to put amine into aqueous ammonia to develop a new absorbent. > Table 38.8 lists the common absorbents tested in the laboratory.

Absorber Packed Tower A packed tower is a common choice in the traditional chemical absorption process to remove CO2. The technology of the packed tower is mature, and it has already developed a huge market although there are still some problems. Low speed in mixing and mass transfer would lead to the big size of equipment and huge investment. The direct contact of gas and liquid would lead to such problems as entraining, channeling, bubbling, and overflowing. Hence, strengthening the mass transfer in reaction equipment and solving the operation problems in the contact of gas and liquid are the key points to reduce the tower size as well as the investment. Recent studies show that the development of new packing and the improvement of inner attachment structure inside of the packed columns would strengthen mass transfer so as to reduce the size of equipment. The new packing can lower the system resistance and strengthen the mass transfer capacity. As a result, the performance of the equipment will be improved. > Figure 38.15 shows the typical structure of a packed tower and some new packing.

Chemical Absorption

38

. Table 38.8 Common absorbents for CO2 capture in the laboratory research Absorbent type

Abbreviation

Primary amine

MEA DGA

Molecular formula

Literature

Monoethanolamine Diethylene glycolamine N-Propanolamine N-Propanolamine N-Butanolamine N-Butanolamine Ethylamine Ethylamine

NH2(CH2)2OH NH2(CH2)2O(CH2)2OH

[44] [45]

NH2(CH2)3OH NH2(CH2)4OH NH2CH2CH3

DEA

Diethanolamine

NH (CH2CH2OH)2

DIPA BAE MAE EEA MDEA TEA DEEA

(CH3)2CHNHCH(CH3)2 CH3(CH2)3NH(CH2)2OH NH(CH3)CH2CH2OH CH3CH2NH(CH2)2OH CH3N(CH2CH2OH)2 N(CH2CH2OH)3 (CH3CH2)2N(CH2)2OH

Ethylenediamine DETA

Diisopropanolamine 2-(butylamino)-Ethanol 2-Methylaminoethanol – Methyldiethanolamine Triethanolamine N,N-diethyl ethanolamine Ethylenediamine Diethylenetriamine

[44] [44] Singh et al. (2009) Tan et al. (2005) [46] [47] [47] [48] [49] [50] [48]

NH2CH2CH2NH2 H2N(CH2)2NH(CH2)2NH2

AEEA TETA

– Triethylenetetramine

NH2(CH2)2NH(CH2)2OH H2N((CH2)2NH)2(CH2)2NH2

Cyclamine Sterically hindered amine

PZ AMP KS

Piperazine – KS

NH(CH2)2NH(CH2)2 NH2C(CH3)2CH2OH Unknown

Amino acid salt

PG PT SG HPC

Glycine potassium Sulfur potassium Amino acetate Hot potassium carbonate

NH2CH2COOK NH2(CH2)2SO3K NH2CH2COONa K2CO3

Secondary amine

Tertiary amine

Polyamine

Carbonate

Name

[44] Xiang et al. (2003) [51] Xiang et al. (2003) [52] [53] Wang et al. (2002) [54] [54] [55] [56]

Hollow Fiber Contactor Many researchers hope to find a new CO2 absorption equipment to reduce the equipment size. A hollow fiber contactor is one type of new absorption equipment widely studied now [58]. In a hydrophobic hollow fiber contactor, gas and the absorbent solution flow in different sides of the hollow fiber. Gas and liquid contact indirectly, and absorbent entraining, channeling, bubbling, and overflowing can be avoided. At the same time, a hollow fiber’s large surface area (1,000–3,000 m2/m3) can reduce the volume of the

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Chemical Absorption

Return flow from condenser

Structured packing Bearing shelf liquid collector discharge hole Feed packing liquid distributor filter plate

b Curved gluten flat ring packing

Bearing board Slip gas inlet Tower bottom

Recycle pipe to reboiler Skirt seat Base ring

a

product from the bottom of tower

Packed tower

c Flexible plum flat ring packing

. Fig. 38.15 Packed tower and some packing [57]

equipment effectively. Studies show that using hollow fiber contactor can reduce the size of an absorption and regeneration tower by 63% compared with a packed tower. For the fiber contactor, keeping the effectiveness of the fiber and high equality of mass transfer during the operational process is a main point in research and development (> Fig. 38.16).

Super Gravity Rotating Bed To solve the size problem of the common packed tower, Ramshaw [59] put forward the concept of a super gravity rotating bed. High-speed rotation of the central axis can cause

Chemical Absorption

Vacuum and/or strip gas

38

Strip gas

Distribution Hollow fiber Collection Cartridge tube Housing membrane Baffle tube

Aqueous stream

Aqueous stream

. Fig. 38.16 Illustration of typical hollow fiber contactor [60]

centrifugal super gravity, which can strengthen the transfer, mixing, and reaction process. Studies show that the mass transfer rate of such a super gravity rotating bed is 10–1,000 times that of common packed tower. Therefore, the volume of the reactor can be greatly reduced. Some researchers have studied the CO2 removal process of rotating beds and obtained the effect on CO2 absorption characteristics of related operation and design parameters. Chen Minggong [62] proposes the rotating disc super gravity bed which has some improvements to traditional rotating packing beds, as shown in > Fig. 38.17. Recently, studies of super gravity rotating beds are mainly carried out in the chemical industry. The knowledge of inside flow fluid structure with high gas flow, mass transfer strengthening of flue gas decarbonization, and the adaptability of real gases are lacking.

Integration and Optimization of the Process Integration and optimization of the process mainly refers to the effort that most researchers paid to the regeneration process. As the traditional heat regeneration process is usually of high energy penalty, many researchers focus on to decrease the regeneration energy consumption.

Recovery of CO2 Compression Heat Fisher tried to improve the heat regeneration process to recover the compression heat in the new process, which is shown in > Fig. 38.18. Compared with the conventional heat

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Chemical Absorption

3 c

1

2

b

4

2

5 3 7

7

a 4

4

8

5

6 d

a

b

. Fig. 38.17 Two kinds of rotating bed for CO2 capture. (a) Structure of a wire packing rotating bed (1-packing; 2-rotor; 3-shaft; 4-seal; 5-liquid distributor; 6-shell; a-liquid inlet; b-gas outlet; c-gas inlet; d-liquid outlet). (b) Structure of a disc packing rotating bed (1-Shaft; 2-concentric ring wave disk packing; 3-gas inlet; 4-gas outlet; 5-separator of gas and liquid; 6-spray tube; 7-Filler; 8-liquid outlet with seal) [61]

regeneration process, the CO2 cooling process at the top of the stripper has already been canceled. The gas is directly sent to the multistage compression equipment. At the first stage compression, the gas is compressed to 8.61 MPa and the heat of the compression is transferred to the reboiler. The cooler gas is then sent to the gas–liquid separator. After H2O is separated, CO2 is further compressed to 13.9 MPa in order to meet the requirements for transportation and storage. It is obtained from former modeling research that the improvement can cut the regeneration energy consumption by 18–39% and CO2 avoided capital costs can be decreased by 4.6–9.8%.

Pressure Swing Regeneration Process Different from the traditional regeneration process at constant pressure, the new regeneration process proposed by Jassim and Rochelle [64] operates at varying pressure. > Figure 38.19 shows the schematic of a pressure swing regeneration process. In the new process, the pressure inside the stripper has been changed by two-stage compression equipment. A pressure gradient (4/2.8/2 bar) forms due to the reason mentioned above.

Chemical Absorption

38

1485

13.9 Mpa (2015 psia) CO2 to sequestration CO2 pump Compression Rich amine from heat exchanger

Knockout

Condensate MEA stripper Steam

8.61 Mpa (1,250 psia)

Amine reboiler

Lean amine to pump and heat exchanger

. Fig. 38.18 Integration of compression heat (multistage condensation) [63]

High pressure CO2

ΔT = 10⬚C 4 atm Rich Lean

Multistage compressor 2.8 atm

Steam

2 atm

Stripper

. Fig. 38.19 Pressure swing regeneration process [64]

Reboiler

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38

Chemical Absorption

Jassim and Rochelle [64] also suggest combining the recycling of compression heat and pressure swing regeneration. As the simulation results show, compared to the conventional heat regeneration process, the new combination process can reduce the heat loading of the reboiler by 0.15–0.41 GJ/tCO2, and the total system energy consumption decreases by 0.03–0.12 GJ/tCO2.

Regeneration Process Based on Facilitated Transport Membrane Due to the advantage of facilitated transport membrane (FTM), Teramoto [47, 65, 66] tried to make some improvement for traditional supported liquid membrane (SLM) and they proposed the regeneration process based on FTM, which is shown in > Fig. 38.20. The CO2 absorption process and the regeneration process can be combined in the single FTM contactor. At the bottom of the contactor, the membrane pores are dumped. Gas and absorbent contact at the shell side of the contactor and CO2 is captured into the absorbent. At the top of the contactor, the CO2-rich solution is regenerated. The experimental results show that, under the optimal operation condition, the minimum energy consumption can be lower than 0.211 kWh/kg CO2, which is much lower than 1.26 kWh/kg CO2 for the traditional process. It is also lower than the energy consumption of 0.78 kWh/kg CO2 [67] of KS absorbents developed by MHI.

Reject gas

Enriched CO2 >90% (WET)

Permeation of carrier solution Vacuum pump Stripping of gas

Hollow fiber membrance

Seawater pump

Seawater

Feed gas CO2/NO2 Liquid reservoir

Circulation of carrier solution

Blower

Pump

. Fig. 38.20 Regeneration process based on facilitated transport membrane [65]

Chemical Absorption

Treated gas

38

Absorber Membrane flash module 40⬚C CW 30⬚C

CO2 Porous membrane

Vacuum pump

Pre-heat- CO2 exchanger Feed gas

40~70⬚C Liquid circulation pump

Heat source

Utilizing low HW temperature energy 80⬚C

. Fig. 38.21 Schematic of the membrane flash process [24]

Membrane Flash Process Some researchers [24, 68] proposed a new regeneration process based on membranes, which is called membrane flash process (MFP). > Figure 38.21 shows the schematic of MFP. MFP applies a capillary facilitated transport membrane to regenerate CO2. It also achieves the regeneration by decreasing the pressure during the regeneration process. The CO2-rich solution can reach high regeneration efficiency at 343 K. It is obtained from the simulation results that the energy consumption of the new process is only about 30% of the original process. Hence, it is a rather good way to reduce the regeneration energy consumption. But how to prevent membrane wetting is a big challenge.

Water-Splitting Electrodialysis Process Kang and other researchers [69] proposed to replace the traditional heat regeneration process by water-splitting electrodialysis (WSED), which is shown in > Fig. 38.22. In the new process, a bipolar membrane is used in the WSED regeneration process. The bipolar membrane consists of a series of anion and cation exchange regions. When there is current, all the carbonate or bicarbonate will be removed from the fixed-charge region, thus recycling the CO2. At the same time, H2 and OH are produced in this region. The H2 and OH produced under strong power in this region move to the nearby area along the reverse direction. In this region, OH is used for the regeneration process. Experimental results show that using KOH absorbent, the absorption temperature is 323 K and the WSED process temperature is 45 C. In the long run, the average CO2 absorption efficiency can reach 95.45%.

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Chemical Absorption

CO2 rich absorbent

Mix. gas

Hollow fiber membrane

+

–

Membrane contactor

WSED

CO2 omit gas

CO2 lean absorbent

Absorption

Pure CO2

Desorption

. Fig. 38.22 Schematic of the water-splitting electrodialysis process. WSED water-splitting electrodialysis [69]

Environmental and Economic Issues Water Issue Introduction Carbon capture technologies could increase the water demand on thermoelectric power plants. It is important to estimate and explore the possible effects CO2 mitigation will have on water demands. Current carbon capture technologies under development for coalbased power generation require large amounts of water. This analysis assumes that aggressive carbon mitigation policies will be put in place in the near future that would require all new and existing PC (pulverized coal) plants with scrubbers and IGCC (integrated gasification and carbon capture) plants to utilize carbon capture technologies by 2030. The water requirements, at full load, for PC and IGCC plants with and without carbon capture derived from the detailed performance study and used in this analysis are shown in > Fig. 38.23. All additional cooling systems required for the retrofits and all new PC and IGCC capture ready plants are assumed to be recirculating systems based on current regulations and concerns with once-through systems. It is astonishing that water needs may hinder the application of CCS (carbon capture and storage) technologies. As an Australian report states, coal-fired power plants incorporating carbon capture and storage could be one-quarter to one-third more water intensive. However, the addition of CO2 capture and compression even increases water consumption by 50–90%, which is indicated in the latest NETL (National Energy Technology Library) report. Whichever the value is in absolute numbers, it seems to be rather

Chemical Absorption

1,600

Withdrawal Consumption

1,400 Water (gal/MWh)

38

1,200 1,000 800 600 400 200 0 Subcritical PC

Subcritical PCw CO2 Capture

Supercritical Supercritical PCw CO2 PC Capture

IGCC

IGCC CO2 Capture

. Fig. 38.23 Relative water usage for new PC and IGCC plants. 1 gal= 1 L [70]

unacceptable as the basic water requirement for coal-fired plants is huge. Especially, it is unacceptable for places which are short of water, such as the Western USA and Western China.

Water Balance Strategy for Power Plants with CO2 Capture When considering a mode of operation which requires no makeup water, a subset of interrelated factors affecting the water balance should be assessed, such as: ● Flue gas temperature, absorber inlet and outlet: Due to the increased degradation of the amine by an increase in temperature, it is recommended to precool the flue gas to a temperature below at least 80 C. ● Temperature profile within the absorption section of the absorber: As the CO2 is absorbed into the solvent, the temperature of the down-flowing solvent will increase due to the exothermic absorption reaction and, thus, some water will inevitably be vaporized. Toward the top part of the column, the colder solvent will recover parts of the water vapor via condensation, and the temperature at the top section will determine the extent of this recovery. The resulting temperature profile along the column shows a pronounced bulge, the size and position of which depend on various factors including solvent flow rate and gas inlet CO2 content [71]. For the optimal design case described later, the peak temperature occurs at the top of the column. The driving force of mass transfer decreases with an increasing temperature in contrast to the reaction rate which increases. Consequently, the temperature bulge results in less favorable driving forces, although the kinetics becomes faster. If the former dominates,

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Chemical Absorption

it may be of interest to provide methods that increase the thermodynamic driving forces by reducing the temperature bulge, which can be done by removing heat either within the absorber by intercooling, or prior to the absorber, by means of precooling. ● Absorber inlet lean amine temperature specification: The solvent temperature at the top of the absorption section will influence the absorber outlet gas temperature, thereby determining the amount of condensed water in the absorber section, though this effect is reasonably small. ● Washing sections in the top of the absorber and desorber: The main purpose of the washing section is to reduce the loss and emission of amine into the atmosphere. Thus, the process water fed to the top of the washing section must be almost free of amine. In addition, the temperature of the cleaned flue gas before being released into the atmosphere (and thus its water content) is largely dependent on the temperature of the large recycling of water around the lower water wash section. These factors imply the establishment of a fine balance in order to keep the net water build-up or loss to a minimum, that is, close to zero on average. On this basis, a control strategy including the following steps was proposed (> Fig. 38.24): 1. Precooling the flue gas prior to the absorption column ● By reducing the temperature of the flue gas slightly below its dew point, some excess water will be produced in the direct contact precooler (DCC). This water is filtered and routed to a buffer tank (stream 5 in > Fig. 38.24), which serves as the makeup water source for the water wash section of the upper part of the absorber, while also securing a proper water balancing during the transient conditions of the

6 25 C Cleaned flue gas

Buffer tank

Compressor 8

25 C

Dense CO2

9 CW 7

CW

Absorber

5 HRSG

CW Fan 2

1

Flue gas cooler

3

Desorber Reboiler

4

Steam

CW Rich solution

Filter

Lean solution

. Fig. 38.24 The absorption system with a water-balancing strategy (indicated with bold streams) [72]

Chemical Absorption

38

plant. The amount of excess water produced will be a trade-off between the cost of the cooling water requirement due to an increase in the size of the fresh cooling water recycling (stream 4 of > Fig. 38.24) and possibly of the precooler, and the possibility of a lower desorber reboiler duty and live steam demand, which is discussed later. 2. Water recycling ● As the content of the amine in the water separated from the compression section and retrieved from the desorber condenser is almost negligible, these water sources (stream 6 of > Fig. 38.24) can be utilized in the water wash section in the upper part of the absorber. Therefore, a bleed stream from the desorber reflux stream can be recycled to the absorber water wash section. The rest can be used in the desorber water wash section, in conjunction with a locally cooled water recycling circuit. 3. Gas cooling upon leaving the absorption column A temperature adjustment in the water wash section is required in order for the cleaned flue gas to leave the column at a desired humidity level, which corresponds to the amount of inlet water. Possible solutions could be: ● Temperature measurement at the top of the absorber and adjustment of the cooling duty in the lower water wash section (stream 7 of > Fig. 38.24) to approach the dew point (i.e., the dew point of the flue gas accounted for the CO2 removal). This is accomplished by controlling the temperature of the cooler outlet in the lower water wash circulation. The advantage of doing it in this manner is that the temperature is easily measured and the accuracy becomes higher than with other online measurements. The drawback of this solution is that the inlet gas dew point varies as the flue gas concentration changes. ● Online measurement of moisture in both the flue gas from the HRSG (heat recovery steam generator) unit and in the cleaned flue gas effluent. An adjustment is then made by controlling the temperature in the water of the cooler outlet of the lower water wash circulation. One drawback of doing it this way may be obtaining incomplete measurements of the moisture if the samples are not properly heated since accurate online moisture measurements are generally difficult to achieve.

Environmental Effect Environmental Assessment of the Alkanolamines Amine-based processes have been used commercially for removal of acid gas impurities from process gas streams, and they are currently the most popular way to remove CO2 in industry. For natural gas sweetening operations, typically alkanolamines like monoethanolamine (MEA), diethanolamine (DEA), and N-methyldiethanolamine (MDEA), as well as mixtures of alkanolamines are used. Capture by absorption relies on large-scale use of chemicals, and emissions of the solvent may occur through the cleaned exhaust gas as

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Chemical Absorption

degraded solvent and as accidental spills. It is thus important that the chemicals used have low or no environmental effect. > Figures 38.25 and > 38.26 show chemical test and ecotoxicity testing results of different absorbents based on EC-50.

Alanine 1-Amino-2-propanol 2-Amino-2-ethyl-13-propanediol 2-Amino-2-methyl-13-propanediol 2-Amino-2-methylpropanol(AMP) 3-(2-Aminoetyl)aminopropylamine 3-Amino-1-cyclohexylaminopropan 3-Amino-1-methylaminopropane 3-Aminopropanol 4-Amino-1-butanol Diethanolamine(DEA) Diethylaminoethanol Diethylenetriamine Diglycolamine(DGA) Diisopropanolamine Dimethylamin Dimethylaminopropylamin Dimethylpropanolamin Ethanolamine(MEA) 2-Ethylaminoethanol Ethylenediamine Glycine 2-Methylaminoethanol Morpholine N-(2-hydroxyethyl)-ethylenediamine NN'-bis(2-hydroxyethyl)ethylenediamine NN'-dimethylethanolamine Neopentandiamine N-methyldiethanolamine(MDEA) N-tertbutylethanolamine Piperazine 1-(2-Hydroxyethyl)-Piperazine Piperidine 1.3-Propanediamine Pyrrolidine Sarcosine Spermidine Spermine Tetrahydrothiophenedioxide Tetra-N-methyl-propanediyldiamine Triethanolamine Triethylamine 0

20

40

60

80

100

BOD (% of ThOD)

. Fig. 38.25 The biodegradability of all the chemicals tested, results shown as percent degraded with regard to the theoretical oxygen demand (ThOD). The red line shows the lowest acceptable value for a chemical to be released in the marine environment, while the green line is the lower limit for a chemical to be released independent of the ecotoxicity [73]

Chemical Absorption

38

Alanine 1-Amino-2-propanol 2-Amino-2-ethyl-13-propanediol 2-Amino-2-methyl-13-propanediol 2-Amino-2-methylpropanol(AMP) 3-(2-Aminoetyl)aminopropylamine 3-Amino-1-cyclohexylaminopropan 3-Amino-1-methylaminopropane 3-Aminopropanol 4-Amino-1-butanol Diethanolamine(DEA) Diethylaminoethanol Diethylenetriamine Diglycolamine(DGA) Diisopropanolamine Dimethylamin Dimethylaminopropylamin Dimethylpropanolamin Ethanolamine(MEA) 2-Ethylaminoethanol Ethylenediamine Glycine 2-Methylaminoethanol Morpholine N-(2-hydroxyethyl)-ethylenediamine NN'-bis(2-hydroxyethyl)ethylenediamine NN'-dimethylethanolamine Neopentandiamine N-methyldiethanolamine(MDEA) N-tertbutylethanolamine Piperazine 1-(2-Hydroxyethyl)-Piperazine Piperidine 1.3-Propanediamine Pyrrolidine Sarcosine Spermidine Spermine Tetrahydrothiophenedioxide Tetra-N-methyl-propanediyldiamine Triethylamine 100

101

102 EC-50 (mg/L)

103

104

. Fig. 38.26 Results of the ecotoxicity testing, shown as concentration where compounds inhibited algal growth by 50% (EC-50). The blue line shows the lowest acceptable value (10 mg/L) for a chemical to be released in the marine environment [73]

Emission and Its Impact on the CO2 Capture Process Pollutant emissions potentially harming human health and the environment essentially stem from two sources in CO2 capture processes: point of discharge and fugitive emissions. The emissions from the point of discharge are intentional, predictable, and quantifiable based on plant operating conditions. Such emissions are the treated gas released from the absorber top and the waste of process solution released from solution reclamation or

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Chemical Absorption

other purification units. Fugitive emissions are unintentional releases from process equipment and piping during plant operation. Details of these emissions are given below. Point Discharge of Treated Gas

A CO2 capture unit releases the treated gas from the absorber top to the atmosphere on a continuous basis. The treated gas is basically composed of the flue gas with a reduced CO2 content and vapors of process solution. The flue gas entering the CO2 capture unit contains a great number of substances. Most of these substances, by themselves, have significant impacts on human health and the environment, and they are currently controlled under the environmental laws and regulations. Most gaseous components, including CO, HCl, HF, NOx , and SOx , are toxic. From MSDS (material safety data sheets), the organic compounds resulting in detrimental carcinogenic damage include benzo(a) anthracene, benzo(a)pyrene, benzo(b)fluoranthene, benzo(k)fluoranthene, chrysene, naphthalene, acetaldehyde,benzene, benzyl chloride, bis(2-ethylhexyl)phthalate, chlorobenzene,chloroform, 2,4-dinitrotoluene, dimethyl sulfate, ethyl benzene, ethyl chloride, ethylene dichloride, ethylene dibromide, formaldehyde, isophorone, methyl bromide, methyl chloride, methyl hydrazine, methyl tert-butyl ether, methylene chloride, tetrachloroethylene, styrene, and vinyl acetate. In addition, trace metals, such as arsenic, beryllium, cadmium, chromium, cobalt, lead, and nickel, are toxic and also carcinogenic. Despite their adverse impacts, flue gas substances are not considered to be contributors to any environmental impacts caused by the CO2 capture unit integrated into a power plant. This is because these flue gas substances are intrinsically and originally produced from the coal combustion regardless of the installation of a CO2 capture unit. Vapors of process solution are, however, considered to be the actual emissions resulting from the CO2 capture unit. The emission of process solution vapors greatly depends on the operating conditions of the absorber top and the thermodynamic properties (that is vapor pressure) of the chemicals contained in the process solution. As an example, the vapor pressure of MEA is a function of absorber temperature (at the top) and chemical concentration (i.e., it increases with increasing MEA concentration and temperature). Any substance with high vapor pressure tends to vaporize and leave the top of the absorber very easily with the treated gas. A water wash and/or a well-designed mist eliminator are commonly installed at the top section of the absorber to reduce such entrainment and volatility loss. According to the vapor pressures, for each chemical, besides water vapor, vapors of certain absorption solvents and degradation products can be released from the absorber top, but the release of corrosion inhibitors is considered negligible due to the extremely low partial pressure of the compounds. The primary amine MEA tends to cause greater solvent volatility loss than other alkanolamines but still less than methanol. On average, the entrainment can lead to the emission of up to 8.5 mg amine/Nm3 of treated gas (Veldman 1989), and the total solvent loss is about up to 1.6 kg solvent/t CO2 for gas-fired flue gas [74]. The entrained vapors of absorption solvents should cause low toxicity to human health and the environment due to their diluted concentrations in the atmosphere.

Chemical Absorption

38

The level of exposure depends on many factors, including environmental, geographic, and atmospheric conditions, which can affect the distribution and dispersion of pollutants from the source of discharge into the air. The US laws regulate MEA by OSHA (Occupational Safety Health Administration) and DEA by NESHAP (National Emission Standards for Hazardous Air Pollutants), while the Canadian laws control DEA as ‘‘need to be declared’’ in NRPI. The other solvents are not enforced by any laws yet. The degradation products, including formic acid, 1-propanamine, 2-butanamine, acetone, ammonia, butanone, and ethoxyethene, also have a tendency to vaporize and entrain with the treated gas, since their vapor pressures are higher than the vapor pressure of water at 20 C. It was found that 2-butanamine, ammonia, and ethylamine are fairly toxic and can affect human health through skin burns and irritation. From its MSDS, 2-butanamine is also reported to be very harmful to aquatic organisms. However, 2-butanamine, ammonia, and ethoxyethene are currently not regulated under any laws, while the rest are enforced by US laws. Formic acid and butanone are controlled under Canadian laws. According to general practice for gas treating processes, a side stream of process solution must be purified to remove suspended solids, degradation products, and other process contaminants so that the concentration of active absorption solvents can be maintained. The solution purification is carried out through continuous adsorption, using mechanical and activated carbon filtration, and periodic thermal reclaiming. The filtration removes solid contaminants and large molecules of degradation products. As such, it results in routine disposal of wastes in the form of filter sludge/filter waste products, filter bag, cartridge, suspended solids, and used activated carbon. The thermal reclaiming is in operation to remove heat-stable salts, nonvolatile organics, and suspended solids via a side stream of 0.5–2% of the process solution [20]. The reclaiming operation will be performed when the content of heat-stable salt anions in the process reaches 1.2 wt% of the solution (CCR Technologies Inc.) or when the degradation product exceeds 10 wt% of active alkanolamine solvents [20]. This generates a reclaimer waste comprising mostly heat-stable salts and solid precipitates and also small amounts of absorption solvents, corrosion inhibitor, and other additives. As an example, approximately 0.003 m3 of reclaimer waste/t of CO2 captured was produced in a commercial FG Econamine process [74]. Examples of reclaimer waste samples and their concentrations obtained from the IMC Chemical Facility in Troca, CA in 1998 are summarized in Table 6 (Strazisar et al. 2003; [75]). Among the chemicals present in the reclaimer wastes, heavy-metal corrosion inhibitors make the process waste toxic to humans and the environment. According to the US Environmental Protection Agency (EPA), corrosion inhibitors containing vanadium, antimony, and cyanide compounds are considered hazardous substances, and they are priority/toxic pollutants under the CAA (Clean Air Act) and also considered hazardous wastes under RCRA (Resource Conservation and Recovery Act). In Canada, uses of toxic substances, including several inorganic heavy metals, are controlled under CEPA (Canadian Environmental Protection Act). Many countries and regions around the world are introducing a series of controlling regulations to provide guidelines on the use and discharge of these toxic substances, especially inorganic salts and salts of heavy

1495

1496

38

Chemical Absorption

metals. In Europe, for example, the European Union (EU) has charged the Paris Commission (PARCOM) with providing a framework for legislation [76, 77]. Other highlighted regulations include the Emergency Planning and Community Right to Know Act of 1986, regulations adopted by the US Occupational Safety and Health Administration (OSHA) in 1993, and adoption of the Chemical Hazard Assessment and Risk Management (CHARM) model in the UK and other European countries (Singh and Bockris 1996). Because of the adopted regulations, the use of toxic corrosion inhibitors makes disposal of the industrial waste difficult and costly ([20], Singh and Bockris 1996). Restriction on the use of other heavy-metal inhibitors can be anticipated in the near future. Arsenic is a good example of the corrosion inhibitors; it was used effectively in gastreating plants but is now banned from industrial applications due to its high toxicity and impacts on the environment. Some degradation products, especially heat-stable salts and cations, are being regulated under laws and regulations. Their impacts are mostly irritation and burns. However, there are no regulations to control the emissions of such degradation products with high toxicity as 1H-imidozole, 2-butanamine, and 2-methylpropanenitrile. The process wastes are generally disposed of by incineration and landfilling. Incineration involves the supply of energy and the phase change of wastes either from solid to liquid or gas or from liquid to gas. As a result, burning the process wastes produces ashes of both degradation products and additives together with vapors of amine solvents. Some of these products are harmful to humans and the environment, as described previously. To reduce the release of trace metals, a posttreatment of incineration (i.e., wet scrubber) should be used. In contrast to incineration, placing the process wastes in landfills does not result in a phase change of wastes, thus minimizing the emission of vapors of any toxic substances. Nevertheless, the process wastes should be neutralized prior to disposal in landfills. Fugitive Emissions

Fugitive emissions also contribute to environmental impacts in addition to the above point-source emissions. During plant operation, the process fluids can be unintentionally released from the CO2 capture unit mainly through leaks, which are usually a consequence of deterioration of process equipment and pipes, corrosion, impact damage, and vibration. Such emissions are unpredictable, random, intermittent, and can occur everywhere on the site, such as at pumps, valves, flanges, connectors, pressure relief devices, sampling connections, open-ended lines, instruments, vents, drains, and meters. According to the European Sealing Association (ESA) (2005), for any commercial plant, valves, especially control valves, contribute to the greatest extent to leakage losses (50–60%), followed by relief valves (15%), tanks (10%), pumps (10%), and flanges (5%). Apart from leakage losses, working and breathing losses also account for some fugitive emissions. Working loss occurs when the storage tanks of absorption solution are being filled. The quantity of solution vapor released from the tanks depends on temperature, vapor pressure of the solution, and pumping rate. Breathing losses are caused by thermal expansion of the solution vapor in the tanks as a result of temperature increase during daytime. Regardless of their sources, fugitive emissions release certain amounts of process

Chemical Absorption

38

fluids and materials, including untreated flue gas, treated gas, absorption solvents, corrosion inhibitors, degradation products, and chemical additives, whose impacts to humans and the environment were previously discussed. The importance of fugitive emission has been recognized in environmental laws and regulations. Accidental Release

Accidental release is a large release, spill, or discharge of process fluids as a result of accidents and emergency operations. The quantities of such releases are much larger than those of the fugitive emissions. According to the American Petroleum Institute (API) (2001), accidental release can be caused by failures of process equipment due to physical erosion, wear and tear, corrosion, malfunctions of process controls and instrumentation that lead to overpressure, overheating, and liquid overflow, as well as improper operations that lead to foaming, pluggings, or blockage of process equipment and piping.

Management of Pollutant Releases and Their Impacts Although the impacts of a CO2 capture unit integrated to the power plant is not severe, an Environmental Management System (EMS) should be practiced to control pollution, minimize waste production, ensure progress toward an environmental goal, and provide safety plans for normal plant operation and accidents. The EMS requires a commitment from top management to establish a corporate environmental management policy and educate employees on the policy [78]. Proper operation, monitoring, and maintenance of process equipment, piping, and instrument and control systems play a key role in reducing emissions of hazardous substances from process points of discharge, fugitive sources, and accidental events. Pipeline and tube bundles in the heating elements should be regularly monitored, due to deterioration by corrosion. Trays or packings in both absorber and regenerator should be kept clean from sludge deposit. The amounts of heat-stable salts or any particulates in the process solution must be kept low to avoid foaming problems, which are a primary cause of entrainment at the absorber top. Repair, replacement, and modification of the existing equipment must be done promptly when the damage is identified. Several publications provide guidelines for amine plant operations. Bacon and Demas [79] recommended tests on lean- and rich-amine solution loadings, total heat-stable salts, anion and cation assay, soluble iron content of solutions, degradation products, and foaming tendency [79]. Pauley (1991) suggested that the amine solution should be sampled and tested regularly for organic acids, heat-stable salts, amine concentration, soluble metal content, iron sulfide content, liquid hydrocarbon content, and water content (Pauley 1991). Nielsen et al. (1995) provided a set of maximum concentrations of heat-stable salts that should be kept to prevent severe corrosion (e.g., 250 ppm for oxalate; 500 ppm for formate, glycolate, malonate, sulfite, and sulfate; 1,000 ppm for succinate; and 10,000 ppm for thiosulfate) (Nielsen and Lewis 1995). The recommendations for leakage reduction from these process components are summarized in > Table 38.9.

1497

1498

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Chemical Absorption

. Table 38.9 Equipment modifications for control of equipment leak (European Sealing Association (ESA), 2005) [80] Equipment

Modification

Valves

Sealless design Avoid using valves with rising stem (gate valves and globe valves) Install the rupture discs before the safety valve to damp small pressure fluctuation Sealless design Closed-vent system Dual mechanical seal with barrier fluid maintained at a higher pressure than the pumped fluid Weld together Correct selection and installation of the gasket and regular maintenance Minimize the number of flanged connection

Pump seals

Flanges and connectors Pressure relief devices

Closed-vent system Rupture disk assembly Open-ended lines Blind, cap, plug, or second valve

Standard plans for the worst and the most likely emergency scenarios should also be developed to effectively and immediately mitigate accidental release. Such plans must at least provide proper procedures for handling the release and cleanup of hazardous pollutants and must be distributed to and well understood by both plant employees and local authorities, such as local police, fire fighters, and hospitals.

Economical Factors of Chemical Absorption Systems Economic considerations of chemical absorption systems are another key factor to affect the application of the capture technology. All the commercial technology seems hard to satisfy the requirement of power plants due to the problem of high cost. > Figure 38.27a–c, respectively, show different CO2 capture technology on COE (cost of electricity), thermal efficiency, and CO2 capture cost (NETL report 2008). It is easily derived from the above charts that these technologies are still rather expensive to be applied. More research needs to be performed to cut the energy consumption and capital cost so as to meet the economical requirements. Above all, although chemical absorption is considered to be the most mature technology nowadays for CO2 capturing, there is still a long way to go to put it into practice in large-scale power plants. Chemical solvent scrubbing processes are expected to improve between now and 2020. Improvements will be made by a combination of design optimization in a competitive market and technology developments, such as new solvents.

Chemical Absorption

38

Increase in COE (%) 160 140 120

133

139

Case 6

Case 7

100 100

80 60

66

64

59

40 37

20 0

a

Case 1

Case 2

Case 3

Case 4

Case 5

CO2 capture technology effect on COE (Cost of electricity). Efficiency (%LHV) 45 40 35

41.6 34

30

33.8 30

29

25

31.1

28.5

29.5

20 15 10 5 0

Base

b

Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 Case 7 CO2 capture technology effect on thermal efficiency S/t CO2 avoided

90 80

84

70 60 50 40 30 20

42

47

42 24

25

10 0

c

Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 CO2 capture technology effect on CO2 capture costs

. Fig. 38.27 CO2 capture technology economy. Base – refers to the standard pulverized coal power plant; Case 1 – refers to conventional MEA scrubbing technology; Case 2 – refers to aqueous ammonia scrubbing technology; Case 3 – refers to oxyfuel combustion technology; Case 4 – refers to IGCC technology; Case 5 – refers to membrane separation technology; Case 6 – refers to pressure swing adsorption technology; Case 7 – refers to temperature swing adsorption technology

1499

1500

38

Chemical Absorption

Combustion power generation processes are also expected to improve and these improvements will contribute to an overall improvement in the economics of power plants with post-combustion CO2 capture.

Industry Application and Future Direction Industry Application Introduction To assess the potential of CCS as an option for reducing global CO2 emissions, the current global geographical relationship between large stationary CO2 emission sources and their proximity to potential storage sites has been examined. Globally, emissions of CO2 from fossil-fuel use in the year 2000 total about 23.5 Gt CO2/year. Of this, close to 60% was attributed to large (>0.1 Mt CO2/year) stationary emission sources. > Table 38.10 lists the profile by process or industrial activity of worldwide large stationary CO2 sources with emissions of more than 0.1 Mt CO2/year. The most promising near-term strategy for mitigating CO2 emissions from these facilities is the post-combustion capture of CO2 using chemical absorption with subsequent geologic sequestration. While MEA absorption of CO2 from coal-derived flue gases on the scale proposed above is technologically feasible, MEA absorption is an energyintensive process and especially requires large quantities of low-pressure steam. It is the magnitude of the cost of providing this supplemental energy that is currently inhibiting the deployment of CO2 capture with MEA absorption as means of combating global

. Table 38.10 Profile by process or industrial activity of worldwide large stationary CO2 sources with emissions of more than 0.1 Mt CO2/year [81] Process

Number of sources

Emissions(MtCO2/year)

Fossil fuels Power

4,942 (62.66%)

10,539 (78.38%)

Cement production Refineries Iron and steel industry Petrochemical industry

1,175 638 269 470

932 798 646 379

Oil and gas processing Other sources Biomass Bioethanol and bioenergy Total

N/A 90

50 33

303 7,887

91 13,466

Chemical Absorption

38

warming. Hence, all governments are rather cautious to make a plan of CO2 mitigation. > Table 38.11 lists some CCS projects for power plants, which are related to chemical absorption.

Development of Chemical Absorption Technologies for CO2 Capture Although a large number of chemical absorption methods have been proposed for CO2 capture already, the most technically matured technologies are limited. Amine scrubbing, ammonia process, and membrane technologies seem to be the most feasible technologies in the near-term. The following analysis is given based on these technologies. However, it is rather meaningful to have a further study on the new methods such as ionic liquids and the other related chemical absorption methods. Amine Scrubbing

Improvements to amine-based systems for post-combustion CO2 capture are being pursued vigorously by a number of process developers. Fluor Econamine FG plus™ is a proprietary acid gas removal system that has demonstrated greater than 95% availability with natural gas fired power plants. It is currently the state-of-the-art commercial technology baseline, and as such is used to compare other CO2 capture technologies. MHI has developed a new absorption process, referred to as KS-1™. An innovative factor in this development is the utilization of a sterically hindered amine solvent for the capture of CO2 from flue gas [124]. Cansolv Technologies, Inc. also proposes to reduce costs by incorporating CO2 capture in a single column with processes for capturing pollutants such as SO2, NOx, and Hg. DC103R™ tertiary amine solvent has demonstrated fast mass transfer and good chemical stability with high capacity net of 0.5 mol of CO2/mol of amine per cycle compared to 0.25 mol/mol for monoethanolamine (MEA) [125]. Ammonia Process

An ammonia-based system, under development by Alstom is the chilled ammonia process (CAP). This process uses the same AC/ABC absorption chemistry as the aqueous system described above, but differs in that no fertilizer is produced and a slurry of aqueous AC and ABC and solid ABC is circulated to capture CO2. The process operates at near freezing temperatures (32–50F USE KELVIN), and the flue gas is cooled prior to absorption using chilled water and a series of direct contact coolers. Technical barriers associated with the technology include cooling the flue gas and absorber to maintain operating temperatures below 50_F USE KELVIN (required to reduce ammonia slip, achieve high CO2 capacities, and for AC/ABC cycling), mitigating the ammonia slip during absorption and regeneration, achieving 90% removal efficiencies in a single stage, and avoiding fouling of heat transfer and other equipment by ABC deposition as result of absorber operation with a saturated solution. This process and aqueous ammonia scrubbing technology has the potential for improved energy efficiency over amine-based systems, if the barriers can be overcome.

1501

Clean coal project E.ON UK, Ruhrgas by supercritical coal

Operator/ partners

Chemical absorption technology. Two facilities CO2 flooding for EOR

Post-combustion. Chilled ammonia. EOR

The International Test Centre for CO2 Capture (ITC)

Alstom and AEP

USA & Canada A $5.2 and a $3.3 million demonstration plants

–

Alstom, AEP

Unknown

N/A

1,500 t/year (nominal)

2 t/h (18,000 Underground t/year nominal) reservoir

Phase 1: 2008 Phase 2: 2011

Ongoing research

Power plant by 2008 Capture Demo ready by 2012

Feasibility study completed 2007. Plant online 2011/ 2012. CCS not determined

Under study

Phase 1 30 MWth, Phase 1: 100 kt phase 2 200 MW coal Phase 2: 1.5 Mt

Coal-fired plant and gas powered plants. Absorption by MEA and mixedamine (MEAMDEA) solvents

660 MW pulverized coal plant Absorption

For CCS: 1.7 million t/year

Study ongoing. Plant start-up 2013

Under study

–

2  800 MW coal

Time schedule

2 million t/year Considered later Planned operation stage from 2012 CCS considered later

Amount of CO2 Transport and handled storage

2  800 MWe supercritical coal power plants

Gas source and capture process

250 million GBP for 500 MW supercritical coal power plant power plant 100 million GBP for CCS

1 billion GBP

1 billion GBP (power plants)

Cost/funding €

University of Regina. Many public and industrial partners

Enel (Italy), Inst. Of Geology and Vulcanology

Clean coal project Scottish & Supercritical coal Southern Power, Mitsui, CCS later stage Siemens, UK Coal

Italy: Brindisi Capture and CO2 capture storage project – Zero Emission Project

Ferrybridge Project

Tilbury Project Clean coal project RWE Power Supercritical coal

Kingsnorth Supercritical Plant Project

Main focus

38

UK and Italy

Project name

. Table 38.11 Some CCS projects for power plants related to chemical absorption

1502 Chemical Absorption

Beijing CO2 capture/ thermal power recovery plant CO2 capture demo

China

Xi’an Thermal Power Research Institute

unknown

Coal fired plant and gas powered plants. Absorption by MEA

Natural gas/heavy oil boiler

3,000 t/year (nominal)

Commercial CO2 Operation since 16th July 2008

Commercial CO2 Operation since Oct. 2005

Unknown

100,000 t/ year (nominal)

MHI, KEPCO

Operation since April 1991

Operation since July 2006

Operation since Oct. 1999

MHI, Japanese Unknown chemical company

CO2 capture/ recovery

Japan CO2 capture project

N/A

CO2 recycled in process

CO2 for Operation since 1994 commercial sale

3,600 t/year (nominal)

60,000 t/year (nominal)

Flue gas from natural 60,000 t/year gas/oil boiler (nominal)

Flue gas from coal power plant

Flue gas of steam reformer/ammonia plant

Start-up 2011

Start-up 2010

Unknown

Sumitomo Chemical plants, MHI, Fluor

CO2 capture/ recovery

Sumitomo CO2 capture

144 km Active oil field

N/A

Unknown

Unknown

4.6 Mt/year (phase1) 7.4 Mt/year (phase2)

Natural gas from LNG 3 million t/year 120 km Sub-sea plant saline aquifer

Combined cycle natural gas

Flue gas from natural 700 t/year gas power plant (nominal)

R&D of solvents

Nanko Pilot Plant

MHI, JPOWER RITE

CO2 capture

Matsushima CO2 capture

Japan

CO2 capture/ recovery

Malaysia CO2 capture project

MHI Petronas Fertilizer

MHI, JGC Petronas

Capture and storage

Bintulu CCS project (Malaysia)

Unknown

MHI, Marubeni Unknown Vietsovpetro

Capture and storage

White Tiger CCS project (Vietnam)

Vietnam and Malaysia

Chemical Absorption

38 1503

CO2 capture/ recovery

Shanghai Shidongkou Power Plant

International Power (low emissions technology demo fund)

Fairway Power Total 445 million. 75 million from Several LETDF partners

Post-combustion capture, storage

Fairview Power Project

Total $369 million. 50 million from LETDF and 30 million from Victoria Govt

unknown

Cost/funding €

Post-combustion capture and sequestration

China Huaneng Group and Shanghai Electric Company

Operator/ partners

Hazelwood 2030 Project

Australia

Main focus

Project name

Time schedule

CO2 utilized for ash water treatment and sequestrated as CaCO3 Return to coal seams

Initial: 30% of current CO2 emission. Target: 80% of emission 100,000 t/year

Post-combustion capture of 200 MW brown coal power plant Post-combustion capture; coal seam methane 100 MW station

Commencing April 2007. Lifespan 10 years

Start-up early 2007. Completed end of 2009. CO2 capture operational early 2008

Commercial CO2 Operating since May, 2010

Amount of CO2 Transport and handled storage

2 *660 MW USC units _ (Ultra super critical boiler)

Gas source and capture process

38

. Table 38.11 (Continued)

1504 Chemical Absorption

Chemical Absorption

38

Membrane Technology

Chemical modification of polymeric membranes is one of the most promising approaches for greatly enhancing separation performance. Therefore, further development of existing modification methods or invention of new modification techniques for existing gasseparation materials may accelerate the commercialization of polymeric membranes for the hydrogen economy. However, long-term stability and performance of the polymeric membranes at elevated temperature are necessary to maintain the robustness of the membrane-based systems. Biological capture systems are another potential avenue for improvements in CO2 capture technology. These systems are based upon naturally occurring reactions of CO2 in living organisms. Carbozyme, Inc. has developed a biomimetric technology that promises significant cost and performance advantages over amine-scrubbing systems for the capture of CO2 from combustion flue gases. The Carbozyme technology has three key features: (1) a rapid catalyst, CA (carbonic anhydrase); (2) a high-efficiency mass transfer hollow fiber design; and (3) low energy requirement that does not use high value steam. The process, utilizing carbonic anhydrase in a hollow fiber contained liquid membrane, has demonstrated at laboratory scale the potential for 90% CO2 capture followed by regeneration at ambient conditions. This is a significant technical improvement over the MEA temperature swing absorption process. The CA process has been shown to have a very low heat of absorption that reduces the energy penalty typically associated with absorption processes. Carbozyme’s biomimetric process can afford a 17-fold increase in membrane area. Phase Transitional Absorption Method

The main obstacle to taking conventional MEA scrubbing technology into worldwide use for bulk CO2 removal is the energy required for absorbent regeneration in the desorber. However, several scholars propose to employ new phase transitional absorption method to decrease energy consumption greatly. Liang Hu (US Patent 7541011) [82] put forward a phase transitional absorption method in 2006. In this phase transitional absorption, the liquid absorbent was composed of two or three or more compounds. In the components of absorbent, some of the components called activated agent that reacted with absorbed gas to form a new compound. The activated agent is made of one or more members selected from the group consisting of alkaline salts, ammonium, ammonia, alkanolamines, amines, amides, and combinations thereof. Some of the components called solvent that play the role of improving the physical and chemical properties of the absorbent. The solvent is made of one or more members selected from the group consisting of water, alkanes, unsaturated hydrocarbons, alcohols, ethers, aldehydes, ketones, esters, carbohydrate, and combinations thereof. During absorption, the activated agent reacted with absorbed gas to form new compounds. The new compounds were not soluble in solvent and separated out from absorbent to form new liquid phase with rich absorbed gas. An example for explanation is as follows. Compound A was an activated agent in liquid. Compound B was a solvent. Compound A dissolved in solvent B. A and B formed solution for CO2 absorption. During absorption, compound A reacted with CO2 to form

1505

1506

38

Chemical Absorption

A∗CO2. A∗CO2 was not soluble in solvent B. A∗CO2 formed new phase. After separation of phase A∗CO2 with solvent B, solvent B was cycled back. A∗CO2 was forward to regeneration. After regeneration, the compound A was cycled back and mixed again with solvent B for CO2 absorption. The method is carried out in an absorber, where a liquid absorbent, a gas mixture containing CO2 were introduced from an inlet. During absorption, the second liquid phase was separated out from the absorbent. CO2 was accumulated in one of liquid phases. After absorption, two liquid phases were separated. One of the liquids with CO2 was forward to desorber. After regeneration, the liquid was cycled back to absorber. The liquid phase with lean CO2 was back to absorber directly to complete the cycle. The studies show that, the absorption rate by using this method of phase transitional absorption (80% solvent B and 20% activated agent A) was three times than DEA (20% by volume) aqueous solution, while the CO2 loading capacity by phase transitional absorption is four to six times higher than that by standard 20% MEA solution. In this invention, the absorbent was consisted of 80% solvent B and 20% activated agent A. After absorption, A∗CO2 phase was separated. Only 20% of the absorbent (A∗CO2) was forward to regeneration. This is a saving in regeneration energy. The studies show that, A∗CO2 started decomposition at about 353 K. The decomposition amount of A∗CO2 is the function of temperature. The total percentage of the carbon dioxide in solution was evolved up to the temperature. Professor David W. Agar also has the similar idea in the phase transitional absorption field. His team mainly focuses on the thermomorphic biphasic solvent system (Patent WO/2008/015217) and extractive regeneration (> Fig. 38.28) [83]. The utilization of new amine solvents for CO2 absorption, which undergo thermally induced phase separation (thermomorphic phase separation) was investigated. This type of amines, designated lipophilic amine, has limited aqueous solubility. Upon mixing with water, it forms biphasic conjugate solution of amine-rich organic phase and water-rich aqueous phase. Depending on the composition of the solvent, it allows absorption starting from

Treated gas

CO2

T 1 < T2

Temperature T1 single phase

Temperature T1 single phase org. aq. Flue gas

Temperature T2 dual phase

. Fig. 38.28 Process for thermomorphic biphasic solvent system [61]

Chemical Absorption

38

Cost reduction benefit

heterogeneous aqueous solution with high absorption rate and capacity surpassing those of conventional alkanolamines. The amine-rich organic phase disappears during absorption as the result of dissolution of ionic reaction products between CO2 and amine into aqueous phase. Thus, the loaded solvent is literally homogeneous liquid. During regeneration at elevated temperature, the loaded solution undergoes thermally induced liquid–liquid phase separation. The regenerated amine forms a layer of organic phase at the top of the loaded solution, which acts as a solvent to extract the subsequent regenerated amine and drives the equilibrium toward desorption side. Therefore, the lipophilic amine solvents regeneration is enhanced by auto-extractive effect. With these characteristics, not only high loading approaching 1:1 (CO2:amine) at 1 atm partial pressure of CO2 could be achieved but also regeneration at moderate temperature 80 C could be carried out. To improve the regeneration of lipophilic amine, a new method by extractive regeneration was investigated. The idea is to destabilize the equilibrium of the loaded lipophilic amine solution by means of extraction using inert foreign solvent. The regeneration of lipophilic amine can be carried out even at low temperature (40 C) and the foreign solvent can be separated from the extracted amine by flashing or simple distillation at low temperature. Aspen simulations done on the separation indicates the feasibility of the lipophilic amine – foreign solvent separation. In brief, the lipophilic amine solvents provide a new degree of freedom for effective CO2 absorption with low temperature and cost regeneration. The exceptional characteristic of the solvent is the high net capacity and low regeneration temperature, which leads to a very significant cost reduction. Regeneration using waste heat can be expected.

• Chemical looping

es

on

ti va no

nc va ad

In

Advanced physical solvents

Amine solvents

OTM boiler Ionic liquids

Biological processes

MOFs

• Pbi

membranes Solid sorbeats

Enzymatic membranes CAR process

• Membrane systems

ITT/s

Advanced amine solvents

Physical solvents

Key:

Cryogenic oxygen

Post combustion Pre- combustion Oxy combustion

Time to commercialization

. Fig. 38.29 Innovative CO2 capture technologies – cost reduction benefits versus time to commercialization [17]

1507

1508

38

Chemical Absorption

Future Directions Introduction Post-combustion capture involves the removal of CO2 from the flue gas produced by combustion. Existing power plants use air, which is almost four-fifths nitrogen, for combustion and generate a flue gas that is at atmospheric pressure and typically has a CO2 concentration of less than 15%. Thus, the thermodynamic driving force for CO2 capture from flue gas is low (CO2 partial pressure is typically less than 15 kPa creating a technical challenge for the development of cost effective advanced capture processes. In spite of this difficulty, post-combustion carbon capture has the greatest near-term potential for reducing GHG emissions, because it can be retrofitted to existing units that

. Table 38.12 Pros and cons of current CO2 separation technologies CO2 capture technology

Pros

Cons

Amine scrubbing

Applicable to CO2 partial pressures

Process consumes considerable energy

Ammonia process

Recovery rates of up to 95% and Solvent degradation and equipment product purity >99 vol.% can be corrosion occur in the presence of O2 achieved Concentrations of SOx and NOx in the gas stream combine with the amine to form irregenerable, heat-stable salts Rectisol™ refrigeration costs can be high Lower heat of regeneration than Ammonium bicarbonate decomposes at MEA 140_F (USE KELVIN), so temperature in the absorber must be lower than 140_F (USE KELVIN) Higher net CO2 transfer capacity than MEA Stripping steam not required Offers multi-pollutant control

Membrane technology

Ammonia is more volatile than MEA and often provides an ammonia slip into the exit gas Ammonia is consumed through the irreversible formation of ammonium sulfates and nitrates as well as removal of HCl and HF

No regeneration energy is required Simple modular system

Membranes can be plugged by impurities in the gas stream Preventing membrane wetting is a major challenge

No waste streams

Technology has not been proven industrially

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38

generate two-thirds of the CO2 emissions in the power sector. > Figure 38.29 indicates that as innovative CO2 capture and separation technologies advance significant cost reduction benefits can potentially be realized once they are commercialized. Obviously, as a method of post-combustion capture chemical absorption is the most likely technology in the upcoming years. > Table 38.12 shows the pros and cons of current CO2 separation technologies.

Future Directions of Chemical Absorption Technologies for CO2 Capture To predict the future directions of chemical absorption technologies is a hard task. Every technology occupies its own advantages and disadvantages. The predictable truth is that the improvement of the chemical absorption technologies is the future work. Whatever the novel technology turns out, the technology should occupy the basic elements such as absorbent, absorber and cyclic process. Hence, the future direction must have great improvement on the related problems. Some potential directions for the existing technologies are analyzed in > Table 38.13.

. Table 38.13 Future directions of chemical absorption technologies for CO2 capture Technology for CO2 capture

Future direction

Amine scrubbing

● Absorbent studies 1. Set an evaluation criterion for the selection of amines 2. Mixed amines 3. Ionic liquid 4. New solvents ● Absorber studies 1. New packings 2. High efficiency reactors ● Process integration and optimization 1. Heat integration

Ammonia process

Membrane technologies

2. Water balance Optimization of regeneration process Slippery control of ammonia Selection of additives for ammonia solution Plugging mechanism of membrane and control measures Wetting mechanism of membrane and control measures Selection and pretreatment of membrane Optimization of process

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39 Oxy-fuel Firing Technology for Power Generation Edward John (Ben) Anthony CanmetENERGY, Natural Resources Canada, Ottawa, ON, Canada Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1516 Oxy-fuel Pulverized Fuel Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1517 Emissions: SOx, NOx, and Other Micro-pollutants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1520 NOx Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1520 SOx Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1521 Major Pilot Plant Developments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1523 Other Issues for Oxy-fuel Firing in Pulverized Fuel Combustion Systems . . . . . . . . . 1524 Biomass Firing in Oxy-fuel Combustion Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1524 Oxy-fuel CFBC Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1525 CO Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1527 NOx Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1527 SO2 Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1528 Other Issues for Oxy-fuel Firing in CFBC Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1533 Flue Gas Issues and Conditioning for Oxy-fuel Technology . . . . . . . . . . . . . . . . . . . . . . . . 1535 Larger-scale Tests and Future Industrial Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1536 Oxy-fuel CFBC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1536 Oxy-fuel Retrofit Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1538 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1538

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_39, # Springer Science+Business Media, LLC 2012

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Abstract: In order to generate pure streams of CO2 suitable for sequestration/storage, various routes are possible, involving either pre-combustion strategies such as the use of gasification technology combined with shift reactors to produce H2, or alternatively postcombustion strategies such as CO2 scrubbing with, for example, amine-based carriers. One of the more direct approaches is to carry out the combustion in pure or nearly pure oxygen–oxy-fuel combustion–to produce primarily CO2 and H2O in the combustion gases, resulting in almost complete CO2 capture. Until recently, the primary avenue for deploying this technology was with conventional pulverized fuel-fired boilers, and there is already one large demonstration plant operating in Europe with more being planned in the future. However, more recently oxy-fired fluidized bed combustion (FBC) has also become increasingly important as a potential technology, offering as it does fuel flexibility and the possibility of firing local or indigenous fuels, including biomass in a CO2-neutral manner. Both oxy-fuel combustion technologies have been examined here, considering factors such as their economics, and potential for improvement, as well as challenges to the technology, including the need to generate CO2 streams of suitable purity for pipeline transport to available sequestration sites. Finally, the emission issues for both classes of the technology are discussed.

Introduction The idea that anthropogenic CO2 could cause significant global warming was first presented over 114 years ago by Savante Arrhenius [1]; by 1907, the use of fossil fuels as a potent cause of CO2 emissions had also been clearly spelled out: ‘‘The enormous combustion of coal by industrial establishments suffices to increase the percentage of carbon dioxide in the air to an appreciable amount.’’ [2], albeit that Arrhenius saw global warming as a potential benefit. Unfortunately, it has taken a further 60 or more years for the potential for damage due to these phenomena to be universally recognized [3, 4]. Against this background, world populations have been burgeoning, and the use of fossil fuels to meet mankind’s energy needs has increased and shows no signs of stopping in the near future. To further complicate the picture many countries have aging thermal power plants, most of which will have to be replaced in the next couple of decades. At this point the major hope for continuing to use fossil fuels for widespread power generation in an environmentally benign manner lies in the technology known as carbon capture and sequestration (CCS), as renewable and nuclear technologies would not be able to quickly fill the gap if fossil fuels were simply abandoned. In practice, this means that the norm may well be to build thermal power plants to incorporate back-end technologies for CO2 capture following a carbon-capture-ready philosophy [5]. Thus, if ‘‘new’’ technologies are to be introduced on a wide scale, they had best either be already commercialized, such as gasification, or in a near-market-ready state. Fortunately, for oxyfuel combustion technology, in which the fuel is converted in a stream of nearly pure oxygen (90–95% plus) using pulverized fuel (PF) or pulverized coal (PC), research is now well underway with various larger pilot-scale demonstrations either completed or under

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39

Flue gas recycle

Air separation unit

Air

Oxygen

Nitrogen

Flue gas clean-up

CO2 Separation unit

Particulates and condensed water

Nitrogen and oxygen

Boiler

Coal

Recovered CO2 stream

. Fig. 39.1 Schematic of generic oxy-fired boiler configuration

construction, as will be seen later in this chapter. The oxy-fuel technology, in its currently typical configuration, is presented in a schematic in > Fig. 39.1. As an alternative there is also the possibility of retrofitting existing boilers, and here too oxy-fuel technology can potentially meet this challenge in an economically attractive fashion when compared with other CO2-neutral options [6]. Finally, it should also be added that there are side benefits of oxy-fuel combustion, the most obvious being that thermal NOx levels are expected to be significantly reduced, since N2 in air is largely absent from the oxidant. This chapter focuses on oxy-fuel PF and circulating fluidized bed (CFB), and it will not discuss oxy-fuel technology in which water is used instead of CO2 to moderate flame temperatures, as any such technology is much further from commercialization than oxyfuel technology with flue gas recycle (FGR), and/or may pose excessive technical challenges at the present time [7]. Nor will this chapter consider hybrid systems combining, for instance, amine scrubbing and oxy-fuel, although they have been proposed [8], for the same reason, namely, that such concepts are probably significantly further removed from commercialization than ‘‘conventional’’ oxy-fuel technology.

Oxy-fuel Pulverized Fuel Technology Oxy-fuel work in PF systems traces its origins to pioneering research carried out by Argonne National Laboratories in the 1980s [9]. Subsequently, in the 1990s, significant oxy-fuel research and development (R&D) work was initiated elsewhere, with a number of small pilot plant programs, including CanmetENERGY (Canada), Air Liquide (USA), and the International Flame Research Foundation (IFRF) R&D program in Ijmuiden (The Netherlands) looking initially at natural gas firing [10]. In addition to the early small-scale pilot plant work there were various economic evaluations of the technology versus backend scrubbing, primarily for natural gas-fired systems and there are now at least three major reviews in the open literature available to describe such developments [10–12].

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The economic studies often suggested that oxy-firing was not a preferred technology or, if so, only slightly better, with efficiencies in the mid-40% range and costs somewhat higher than back-end capture of CO2 for natural gas, and there has been vigorous debate about the results of such evaluations. The paper of Kvamsdal et al. [13] is typical of such studies, looking at nine potential concepts and ranking oxy-firing of natural gas as only of moderate performance, while noting the significant energy losses associated with the cryogenic separation of air (6.6% in that study with a further loss of 2.4% for compression, when expressed in percent of the net plant efficiency, based on the fuel’s lower heating value). More recent studies also confirm efficiency losses of 8–10% (on the same basis) for both natural gas- and coal-fired systems [14]. Studies, which tend to focus more on coal, seem to show a fairly similar picture in terms of overall economics, that is, that oxy-fuel PC looks comparable to PC technology with back-end CO2 capture. Thus, Bouillon et al. [15] came to the conclusion that the penalties for both post-combustion and oxy-fuel combustion–integrated processes were around 44 €/t CO2. In a later study, Hadjipaschalis et al. [16] carried out an analysis for a 500 MW steam plant, with assumed efficiency of 33.5%, a generation capacity factor of 85%, and 90% CO2 capture rate. The results of their study indicate that the oxy-fuel combustion plant represents a competitive technology, which currently seems to be the most economical–having the lowest electricity costs and lower CO2 avoidance costs. Similarly, a major Canadian study done for the Canadian Clean Power Coalition (CCPC) in 2007 [17] came to the following conclusions: ● The oxy-fuel combustion technology was found to have technical and environmental benefits comparable to post-combustion capture and it was the most economic option in one of the cases studied, which was based on a green-field site in Alberta utilizing low-S coal, where flue gas desulfurization (FGD) was not required for oxy-fuel but was for post-combustion capture. The assumption in this case was that most SO2 emissions would be captured in the CO2 compression phase. In the two other sites studied (Saskatchewan and Nova Scotia), the amine-based post-combustion options were found to be more economic, but the difference was marginal. ● It was also found that parasitic energy losses directly related to CO2 capture were the largest single cost item, closely followed in most cases by capital charges. These costs were similar for both oxy-fuel and amine-based capture if FGDs were present in both cases. The capital and operating costs of the air separation unit (ASU) represent a major problem for oxy-fuel economics and improvements in this area will have major benefits. ● Operating and maintenance (O&M) costs were found to make up a relatively minor portion of the total charges. ● The CCPC study also found that oxy-fuel combustion was expected to capture slightly more CO2 than post-combustion technology, which tended to help its cost-per-tonnecaptured figures. ● Retrofits based on oxy-fuel were found to be significantly more expensive compared to back-end retrofits that left the existing boiler plant intact.

Oxy-fuel Firing Technology for Power Generation

39

Finally, Farley [6] also quotes costs which suggest that post-combustion capture and oxy-fuel technologies are comparable, but in apparent contrast to the 2007 CCPC [17] study, suggesting that a significant advantage lies in the fact that oxy-fuel technology can be retrofitted to existing plants [6]. From the above citations, it is clear that the oxy-fuel combustion concept is comparable with post-combustion capture in terms of cost, and it represents a mid-term solution with considerable potential for commercialization, as opposed to many of the schemes evaluated where scale-up presented significant uncertainties. It is also clear that very significant economic gains can be made if oxygen could be produced more cheaply. Buhre et al. [10] summarized some key conclusions about oxy-firing as follows: ● Typically 31% oxygen, rather than 21% for air-fired boilers, must be used to achieve a similar adiabatic flame temperature, and to achieve this level requires recycle of about 60% of the flue gas. ● The much higher CO2 and H2O proportions in the flue gases result in increased emissivity, so a retrofitted boiler will have similar radiative heat transfer to an air-fired boiler for an O2 proportion of 30%. ● Gas flows will be reduced to about 80% of those in the air case. ● Emissions of minor species such as SO2 and NO will be higher in the recycled gases, unless they are removed in the recycle process. Such conclusions are useful, but are dependent on case-specific factors such as how much air leakage there is into the boiler (1% or less is desired), and details concerning auxiliary systems. The choice of whether flue gas recycle should be wet or dry is also important. Zheng et al. [7] suggest that, as an approximate guideline, coals with less than 1% sulfur content are suitable for wet flue gas recycle, while coals with higher sulfur levels are not, because of concerns over corrosion associated with high SOx levels. Zhou and Moyeda [18] suggest that typical wet flue gas recycle should be in the range of 70–75%. Wet flue gas recycle lowers the adiabatic flame temperature of the gas, while dry recycle allows higher flame temperatures but reduces the overall gas velocity. > Table 39.1 gives an expected comparison for air-fired and oxy-fuel combustion with wet flue gas recycle taken from Zhou and Moyeda [18]. These authors also note that the efficiency of such a plant is less than that of a conventional plant without carbon capture, but greater than that of an air-fired plant

. Table 39.1 Comparison of burner gas compositions (wt%) (From Zhou and Moyeda [18]) Composition

Conventional air-fired

Oxy-fuel with wet FGR

O2 CO2 H2O

3.2 14.7 5.85

3.1 69 27.5

NOx (ppm)

154

82

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Oxy-fuel Firing Technology for Power Generation

fitted with an amine system, and this is a conclusion on which there is considerable debate, as noted above. Finally, a last comment to be made on such plants is that since the oxygen used has to be produced cryogenically, and hence is expensive, excess oxygen levels should ideally be kept as low as possible.

Emissions: SOx, NOx, and Other Micro-pollutants As PC firing is the ranking coal combustion technology, dating back to at least the 1940s when early attempts were made to use pulverized coal in fire tube boilers, it is not surprising that an enormous amount is known about the emissions from such systems [19]. The obvious differences between air- and oxy-firing (with FGR) using pulverized coal are the high levels of CO2 (of the order of five times or more) and water (of the order of two to three times more), and the somewhat smaller flue gas volumes that will tend to concentrate the emissions of micro-pollutants in the flue gas stream. Other differences would include the effect of somewhat higher oxygen levels in the burner of around 30%, which together with the lower flue gas levels, allows a similar exit oxygen content to the air-fired case (> Table 39.1), and possible effects on fuel devolatilization and char combustion due to the differences in the gaseous environment. Also, absolute emissions might well vary if the flame length and its temperature and/or the gas concentrations change, and it has been shown, for instance, that at high flue gas recycle ratios, flame temperatures may fall by as much as 100
C or more [20]. This affects the combustion process itself, and reduces flame stability, although such effects are lower for high volatile coals, in line with the results of earlier work [10]. Much of the early work was done in thermogravimetric analyzers (TGAs) and other laboratory-scale devices, with low heating rates, which are atypical of pulverized fuel firing. However, there is now more information from systems with realistic heating rates. Thus, for instance, wire mesh tests done with two coals in an oxy-fuel environment (30% O2/70% CO2) showed evidence of a small rise in ignition temperature of around 20
C for the coals used in this study [21]. Experiments were done in an entrained flow reactor (0.08 m diameter, and 2 m length) with a bituminous coal, but failed to find any evidence of char-CO2 gasification reactions [22]. In addition, unlike earlier studies this one found no significant change in volatile production between air- and oxy-firing, but char burned faster in air than in oxy-fuel conditions, suggesting that the CO2 is important in reducing the burning rate when external mass transfer dominates the combustion process, which is also in agreement with other earlier work [23].

NOx Production The production of nitric oxides can occur in combustion systems by means of three mechanisms:

Oxy-fuel Firing Technology for Power Generation

39

● Prompt NOx – where hydrocarbon radicals in the flame front react with the nitrogen in the combustion gases ● Thermal NOx – where oxygen reacts at temperatures above about 1,000
C to form NOx (the so-called Zeldovich mechanism) ● Fuel nitrogen reactions Prompt NOx is more important in gaseous hydrocarbon flames, while thermal NOx would reasonably be expected to be substantially reduced by a factor of about 20 due to the effective removal of nitrogen from the oxidant, but fuel nitrogen mechanisms can still be expected to be important and give rise to significant NOx production. In a recent study using a quartz flow reactor, high CO2 levels were shown to compete for H atoms (the main source of chain branching and hence radical production) and thus reduce the rate of oxidation of HCN [24]. Similar arguments concerning the change of OH/H radical concentrations in methane oxy-fuel flames have also been advanced from measurements and modeling done by Mendiara and Glaborg [25]. Since HCN is an important intermediate for the production of NO, this implies that the elevated CO2 levels in oxy-fuel combustion should also decrease NO formation from fuel nitrogen. These results are interesting in that they are in contradiction to an earlier study which stated that the influence of CO2 on NOx was negligible [26]. However, both measurements [27, 28] and modeling [29] have shown reduced NOx levels, even without flue gas recycle, which itself also causes a reduction in NOx production. Another difference between the air and oxy-fuel cases is that the CO levels can be higher for oxy-fuel systems, depending on flame temperature and the degree of recycle. However, in measurements of CO profiles when burning lignitic fuels in a small oxy-fuel combustor, Hja¨rstam et al. [28] showed that this did not necessarily reflect in emissions of either CO or NO leaving the boiler.

SOx Production Sulfur in fossil fuel combustion is released as SO2 and SO3, and except in the case of, for example, ashes with very high Ca contents (e.g., the French Gardanne lignite, which has an extremely high natural Ca/S molar ratio in its ash), more than 90% of the S in the fuel will typically be found as SO2 in the flue gas [30]. Flue gas recycle will tend to concentrate micro-pollutants and > Fig. 39.2, in a CanmetENERGY small-scale pilot plant study at high temperatures appropriate to suspension firing, shows SO2 levels for oxy-fuel with recycled flue gas versus the air-firing case. SO2 is the dominant sulfur form, as even at lower temperatures oxidation of SO2 to SO3 tends to be very slow and dependent on the presence of catalytic reactions. However, higher SO2 levels mean that fly ash components will tend to react more readily if they can sulfate [31]. In early studies, both Hu et al. [32], who carried out experiments in a small flow reactor burning coal (1.1% sulfur), and Croiset and Thambimuthu [33], operating the CanmetENERGY oxy-fuel combustor with an eastern US bituminous coal (1% sulfur), reported a decrease in sulfur release for oxy-fuel combustion, ranging from 75% without

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Oxy-fuel Firing Technology for Power Generation

1,400 1,200 SO2 (ppmv) for Lignite

1522

1,000 800 600 400 200 0 0.00

SO2, Air

1.00

SO2, O2/RFG

4.00 2.00 3.00 Distance from Burner Tip (m)

5.00

6.00

. Fig. 39.2 SO2 emissions from CanmetENERGY oxy-fired pilot plant (oxy-fuel case at 35% O2)

flue gas recycle to 65% with recycle. Hu et al. [32] suggested that the reduced SO2 levels they experienced were due to ash reactions, the possible formation of other sulfur compounds (COS and/or H2S), or retention of sulfur in the char. The reaction of ash with sulfur in pulverized coal-fired systems is well established, especially for lignites and western US coals [30], although the ash content of the coal used in their experiments was only 2%. The possibility that some of the sulfur is retained in the char is also reasonable for a small flow reactor, but suggestions of other sulfur compounds do not seem likely if oxidizing conditions prevail. Croiset and Thambimuthu [33] ruled out capture in the ash and significant losses of SO2 in condensate from the flue gas recycle for their experiments and instead postulated the production of elevated SO3 levels. Subsequent experiments have not, however, suggested such dramatic reductions in SO2 releases, at least where Ca levels in the ash are not high, but elevated levels of SO3 are indeed found. Thus, Tan et al. [27] found that SO3 concentrations could be up to three or four times higher for oxy-fuel with wet flue gas recycling than for the corresponding airfired situation, with levels consistently around 5%, whereas normal levels would vary in the range of 1–5%, depending on the sulfur content of the fuel, air/fuel mixing patterns, and excess air in the furnace. This picture for SO3 levels has also been confirmed in later experiments. Thus, Maier et al. [34] found an elevated level of SO3, and indicated that the average SO3 concentrations for their experiments were in the range of 36–121 ppm, for an average SO2 concentration of 1,791 ppm, and flue gas moisture of 28.9 vol%. > Table 39.2 gives average SO2 and SO3 levels for their experiments (note that SO2 levels are also elevated, as expected). However, it is clear that an increase in SO3 up to about 5% may occur, which is sufficient to cause the acid dew point to be raised, leading to a real potential for enhanced corrosion, if flue gases go below that temperature. Based on their data, Maier et al. [34] predict an increase in the acid dew point of around 30
C for oxy-fuel conditions, from 138
C for air to 169
C for oxy-fuel. Ahn et al. [35] have also noted that SO3 levels are likely

Oxy-fuel Firing Technology for Power Generation

39

. Table 39.2 Average measured SO2/SO3 concentrations in ppm (From Maier et al. [34]) Firing mode Air Oxy-fuel

SO2 (ppm)

SO3 (ppm) 733

8

1,758

85

to be elevated, based on their experiments with a small pilot-scale combustor at the University of Utah, and that on average the SO3 levels under oxy-fuel-fired conditions are about four times higher than in the air-fired situation. Both of these studies are in agreement with the work of Fleig et al. [36], who explored the SO3 levels to be produced for the oxy-fuel combustion of lignite for wet recycling and indicated that they should be about four times higher than in the air-fired case, with a resulting rise in the acid dew point of 20–30
C. As a result of these higher SO2 and SO3 levels, there are concerns about corrosion and deposition on boiler walls and surfaces; however, research is still in its early days. Nonetheless, the large boiler companies have initiated research programs to generate information on these potential problems and it can be expected that significant results will be produced in the next several years [37, 38]. It should also be added that on the positive front, air pollution control (APC) devices may be reduced in size, leading to some cost reductions and this is especially true for FGD if wet flue gas recycle is used. Concerning the use of FGD equipment, while there were questions initially on the effect of high CO2 concentrations on limestone effectiveness in FGD, Vattenfall’s experience showed that SO2 removal rate and limestone usage are the same for air and oxy-fuel cases [39]. For a very detailed analysis of the issues relating to sulfation in oxy-fired PF systems, the interested reader is referred to a very recent review article by Stranger and Wall [40].

Major Pilot Plant Developments There are now a large number of major pilot plant and pre-commercial demonstration projects worldwide, and these include: ● Germany – 30 MWth demonstration unit [39, 41, 42]. ● USA – Jupiter Oxygen Corporation, 15 MWth burner test facility, National Energy Technology Laboratory (NETL) [43, 44]; Demonstration of a 30 MWth oxy-fired unit (the Clean Environmental Development Facility in Alliance, Ohio), Babcock & Wilcox Power Generation Group, Inc. (B&W PGG) and Air Liquide [45, 46]. ● United Kingdom – 40 MWth Doosan Babcock Demonstration unit [47]. ● France – 30 MWth Lacq Project, Total, in partnership with Air Liquide [48]. ● Australia – Callide Oxy-fuel Project (30 MW unit) and various other projects [49]. Another possibility also exists, that of retrofitting older conventional power plants to operate in an oxy-fuel mode [50]. Moreover there is considerable research underway to

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Oxy-fuel Firing Technology for Power Generation

develop cheaper methods of oxygen production, such as membrane technologies, which have the potential to make oxy-fuel technologies even more attractive, either by themselves (especially for smaller-scale applications) [51], or possibly by first carrying out a first-stage air separation, prior to the cryogenic separation, thus reducing the size of the unit and the energy used in making oxygen at 90%+ purity [52]. However, for now at least it is also clear that the classic approach of cryogenic air separation can, in principle, meet the needs of a new generation of oxy-fuel power plants [53] and the use of this technology is generally assumed in this chapter.

Other Issues for Oxy-fuel Firing in Pulverized Fuel Combustion Systems Biomass Firing in Oxy-fuel Combustion Systems The idea of using biomass in pulverized coal blends is well established, and there are efforts in most countries to supplement the coal fuel supply with biomass (a carbonneutral fuel), as an approach to the reduction of carbon emissions. In Canada, for instance, trials have been undertaken with up to 100% biomass firing in the 227 MWe Atikokan Generating Station in Ontario [54]. Unfortunately, there are a number of issues, the first, and probably most important, being that there is usually insufficient biomass in a given area to supply a commercial-scale power plant. Secondly, the properties of biomass differ from coal, and so torrefaction or pelletization, before the fuel is then pulverized, is effectively essential if such fuels are to be used directly, and modifications of the fuel feed system are necessary. On this point, it is instructive that the Atikokan unit had a dust explosion in its coal feeding system during preparations for further biomass trials [54]. One ingenious suggestion is that biomass, which typically has high moisture, might be co-fired with coal, thus providing an alternative method to flue gas recycle; however, as noted above the problem with such an approach would be the need to obtain sufficient biomass for such a concept to be applied [55]. Another issue for biomass is fouling, and depending on the nature of the coal ash (i.e., does it contain sufficient Ca in the form of CaO that it can carbonate), it is evident that the fouling and deposit behavior of an ash might be different in an oxy-fuel environment compared to that in an air-fired one. Fryda et al. [56] carried out some experiments in a drop tube using biomass blends and a Russian and South African coal. They report some small changes in K, Na, and Ca in the deposits depending on operating conditions and speculate that the ‘‘lower char temperature’’ in oxy-fuel combustion may be producing such effects. At the present time, it appears that general conclusions are probably premature, but it seems likely the greatest barrier to using biomass in oxy-fuel combustion is probably simply insufficient supply, although other issues such as the inhomogeneity of biomass, potentially high alkali metal content for some types of biomass, and the cost of good quality biomass, especially if the biomass must be pelletized before pulverization, are also potential concerns.

Oxy-fuel Firing Technology for Power Generation

39

Oxy-fuel CFBC Combustion Oxy-fuel combustion has been thoroughly studied for pulverized coal combustion, but to date there has been relatively little attention paid to oxy-fuel circulating fluidized bed combustion (CFBC), although the concept was examined over 30 years ago for bubbling FBC [57]. More recently the boiler companies, Alstom and Foster Wheeler, have explored the oxy-fuel CFBC concept using pilot-scale tests [58, 59]. Alstom’s work included tests in a unit of up to 3 MWth in size, but did not involve recycle of flue gas [60]. Foster Wheeler’s work [58] also involved pilot-scale testing, using a small (30–100 kW) CFBC owned and operated by VTT (Technical Research Centre of Finland) and this work along with CanmetENERGY’s work with its own 100 kW CFBC appears to be the first in which units were operated with oxy-fuel combustion using flue gas recycle. Foster Wheeler is currently developing its Flexi-burn™ technology, which would allow a CFBC boiler to operate either in air- or oxy-firing conditions [61]. The advantages of the CFBC technology are already well known in terms of its ability to burn a wide range of fuels, both individually and co-fired, to achieve relatively low NOx emissions, because temperatures are too low for significant thermal NOx production, and to accomplish SO2 removal by limestone [62]. Another advantage of CFBC technology, in the context of oxy-fuel firing, is the fact that hot solids are kept in the primary reaction loop by means of a hot cyclone. This solid circulation potentially provides an effective means, in conjunction with the recycle of flue gas, to control combustion and effectively extract heat during the combustion process, thus allowing either a significant reduction of the amount of recycled flue gas or alternatively, permitting the use of a much higher oxygen concentration in the combustor. These factors allow the economics of oxy-fired CFBC to be significantly improved over PC or stoker firing by reducing the size of the CFBC boiler island by as much as 50% [60]. In considering the scale-up of CFBC units above 300 MWe, both Foster Wheeler and Alstom are now offering much larger units and Foster Wheeler has in operation a 460 MWe supercritical CFBC boiler [59, 63]. Advantages more difficult to quantify for the technology relate to: the possibility of cofiring biomass, so that in conjunction with CCS, the overall combustion process may potentially result in a net reduction of anthropogenic CO2; and the potential for this technology to be used with more marginal fuels, as premium fossil fuel supplies wane. The co-firing option offers a potentially interesting advantage of CFBC technology, since it is well established that CFBC can burn biomass and fossil fuels at any given ratio ranging from 0% to 100%, thus offering the possibility of using local and seasonally available biomass fuels in a CO2 ‘‘negative’’ manner. The ultimate availability of premium coal for a period of hundreds of years has also recently been called into doubt with suggestions that coal production may peak well before the end of this century. Thus, Mohr and Evans [64], for example, have developed a model which suggests that coal production will peak in 2034 on a mass basis and 2026 on an energy basis. A good general discussion of these ideas can also be found in Wikipedia [65]. In the event of such solid fuel shortages, fluidized bed combustion is ideally suited to

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Oxy-fuel Firing Technology for Power Generation

exploit the many marginal coals and hydrocarbon-based waste streams available worldwide. Currently R&D on oxy-fired CFBC technology is being undertaken in numerous countries, including Canada, Finland, Poland, China, and the USA among others. However, to date most test work has been done at small scale (in the Fig. 39.3) was first described in 2006, for the tests carried out by Hughes et al. [66]. However, that initial work was marred by the fact that the unit still had significant air leaks and, as a consequence, high CO2 levels were not produced in the off-gases, which is a typical problem for this type of unit. Completely successful results from the unit were first presented in 2007 [67]. CanmetENERGY’s mini-CFBC consists of a 0.1 m inside diameter stainless steel riser (> Fig. 39.3) covered with 100 mm of insulation. Independent feed augers can supply multiple fuel types and a sorbent, with solid fuel feed rates of up to 15 kg/h. Oxygen, CO2, and recycled flue gas flow rates are controlled by a combination of mass flow controllers and rotameters. Bed temperature is in the range of 750–950
C, which is the typical range for fluidized bed combustion. Superficial gas velocity can be varied up to 8 m/s, although the unit is more normally operated at around 4 m/s. Fuels and limestones primarily tested to date are given in > Tables 39.3 and > 39.4, respectively. Jia et al. [67, 68] have reported that it was easy to change from air-fired to oxy-fired mode, at least with the pilot-scale units and > Fig. 39.4 shows a typical result. Another important, albeit anticipated, result was that CaCO3 was stable at typical bed temperatures (850
C), as is indicated in > Fig. 39.5, which means that sulfation can be expected to proceed via direct reaction (see > section on ‘‘SO2 Emissions’’).

Oxy-fuel Firing Technology for Power Generation

39

Gas analysis Baghouse Stack

Cooler Solid feed hoppers Condensate Knock-out

Drain

Secondary gas Electric heaters

Recycle blower

Primary gas

. Fig. 39.3 CanmetENERGY’s 5.5 m high, 100 mm diameter minibed oxy-fired CFBC

CO Emissions In the initial work done by Hughes et al. [66], CO was elevated with levels of up to 0.75% and it was speculated that this might be due to elevated CO2 levels, based on equilibrium considerations. However, more careful work later with much higher CO2 levels failed to establish such behavior, and instead showed that CO levels were extremely sensitive to cyclone temperature (see > Fig. 39.6) [67], which is also in good agreement with work by Kno¨big et al. [69].

NOx Emissions A series of oxy-fuel combustion trials [67, 68] indicated that fuel nitrogen conversions were always lower or comparable with those in air firing, as indicated by > Table 39.5.

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Oxy-fuel Firing Technology for Power Generation

. Table 39.3 Analysis of fuels Eastern bituminous coal (EB) Proximate analysis (wt%) (dry) Moisture (wt%) (as analyzed) Ash Volatile matter Fixed carbon Ultimate analysis (wt%) (dry) Carbon Hydrogen Nitrogen Sulphur Ash Oxygen (by difference) Heating value (MJ/kg)

Kentucky coal

Highvale coal

Petroleum coke

1.08

2.01

10.39

0.66

8.86

11.31

19.17

1.00

35.78 55.56

37.35 51.34

33.76 47.076

11.46 86.97

77.81

74.05

59.78

86.91

5.05 1.49 0.95 8.86

5.06 1.62 1.56 11.31

3.49 0.79 0.22 19.17

3.22 1.83 5.88 1.00

6.04 32.51

6.40 30.93

16.58 23.27

1.16 34.71

Two tests done with petroleum coke at a nominal 950
C showed, if anything, a very similar level of fuel nitrogen conversion of 3.3% and 3.7% with Havelock and Katowice limestone, respectively, despite the fact that this temperature meant that the limestone must have calcined and, therefore, might be expected to influence fuel nitrogen conversion via catalytic processes, as suggested early on by Lyngfelt and Leckner [70].

SO2 Emissions Sulfur capture is an important issue, because one of the main reasons for using this technology under air-firing conditions is the ability to capture SO2 in situ with limestone addition. An important difference between oxy-fuel combustion and air firing is that, at least until a temperature of around 900
C (depending on the partial pressure of CO2), sulfation can be expected to occur with CaCO3 (i.e., the limestone will not calcine) (> Reaction 39.1), instead of the indirect mechanism, which is the normal route for atmospheric pressure FBC systems (> Reactions 39.2 and > 39.3). CaCO3 þ SO2 þ 1=2O2 ¼ CaSO4 þ CO2

(39.1)

CaCO3 ¼ CaO þ CO2

(39.2)

CaO þ SO2 þ 1=2O2 ¼ CaSO4

(39.3)

39

Oxy-fuel Firing Technology for Power Generation

. Table 39.4 Analysis of limestones Havelock

Katowice

Cadomin

53.99

54.32

54.59

MgO SiO2 Al2O3 Fe2O3

0.59 1.23 Figure 39.9 provides an example of the CO2 emissions over a 2½-day trial under oxy-fuel conditions, indicating that it is possible

Oxy-fuel Firing Technology for Power Generation

39

to maintain excellent control on CO2 levels and combustion conditions; these tests are briefly described in a recent paper by Kuivalainen et al. [100]. To date performance has been excellent, which is a very positive sign for the further development of the technology. Foster Wheeler is also the first company to commercialize supercritical CFBC technology (Lagisza Power Plant, Poland) and with this as the basis, it is now working with the power company ENDESA on the development of a 500 MWe supercritical Flexi-burn™ CFBC (> Fig. 39.10 provides a general schematic of the technology). The predicted CO2 capture for the Flexi-burn CFBC technology is 90% of emissions and it is

Validation test, September 28-October 2, 2009 100 90 80 CO2, %

70 60 50 40 30 20 10 0 0

0.5

1

1.5

2 2.5 Time, day

3

3.5

4

4.5

. Fig. 39.9 Tests on oxy-fired combustion using CanmetENERGY’s 0.8 MWth CFBC

N2, (Ar) 95-97% O2, (Ar, N2) Mix

Fuels

Flexi-burn CFB boiler

Air separation

Flue gas recycle

Flue gas cleaning

CO2/H2O

G

Ventgas

Condensation compression purification H2O

Steam turbine

Air

CO2 Transport storage

. Fig. 39.10 Schematic of a Flexi-burn CFB power plant (With permission of the Foster Wheeler North America Corporation)

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Oxy-fuel Firing Technology for Power Generation

anticipated that it could be available by 2020 [61]. Ultimately, Foster Wheeler believes that it could offer such technology at the 600–800 MWe size with 600
C steam temperature. Following the extensive tests at CanmetENERGY in Canada, demonstration tests are scheduled to start in 2010 at the 30 MWth CIUDEN pilot CFB facility, which will provide a full experimental CCS platform for the demonstration and validation of the flexible air/ oxy-fuel CFB combustion. Finally, it must be noted that Alstom has also announced its intention of carrying out a 100 MWe oxy-fuel CFB demonstration, although at the time of writing no further information appears to be available in the open literature [101]. At this point in time it appears that oxy-fired CFBC technology is making major strides to enter the commercial arena, and there seems little doubt that before the end of the decade it will also be available as a commercial and competitive CCS technology along with oxy-fuel PF technology.

Oxy-fuel Retrofit Plans The US DOE’s FutureGen program, which for the first 7 years of its existence had the objective of constructing, operating, and demonstrating a gasification plant with hydrogen production and carbon capture and sequestration, was recently and somewhat surprisingly refocused as an oxy-fuel retrofit, and is now referred to as FutureGen 2 [102]. At present, the plan is to retrofit the existing pulverized coal-fired Ameren 200 MWe Unit 4 in Meredosia, Illinois, with oxy-fuel technology, but if this does not proceed the project will look for a new site [103]. If a retrofit is chosen, this will require a new boiler, ASU, and CO2 purification and gas compression unit. About 90% CO2 is to be captured and transported by a new pipeline to a storage site yet to be determined. US DOE has committed US $1 billion to the project partners (State of Illinois, Ameren, Babcock & Wilcox, American Air Liquide, and the FutureGen Alliance). Construction is set to begin in 2012.

Conclusions Oxy-fuel PF represents an advanced technology suitable for power generation with high levels of CO2 capture (90% plus). At this point in time there has been more than 20 years of research done in this area and the first large-scale demonstration units (30 MWth) are already operating. There appear to be no major barriers to implementation other than the capital costs, and it seems likely that full-scale demonstration units will be operating by the end of the next decade (and in the case of retrofit installations, much earlier than that). By contrast oxy-fuel FBC technology is far less developed and the first few pilot-scale units with flue gas recycle are only now being operated. Nonetheless, again there seem to be no major barriers to the technology, and Foster Wheeler, for example, is predicting that there will be full-scale demonstrations operating by 2020.

Oxy-fuel Firing Technology for Power Generation

39

Acknowledgments The author gratefully acknowledges the assistance and advice of Dr. David Granatstein (granatstein technical services/CanmetENERGY) and Drs. Yewen Tan and Murlidhar Gupta (CanmetENERGY), for a number of valuable discussions during the preparation of this chapter, as well as suggestions for various amendments and improvements, and he would also like to thank Professor Filip Johnsson of Chalmers University, Sweden for valuable suggestions about potential problems for oxy-fuel CFBC.

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40 Integrated Gasification Combined Cycle (IGCC) Lawrence J. Shadle . Ronald W. Breault U.S. Department of Energy, National Energy Technology Laboratory, Morgantown, WV, USA Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1546 History of Gasification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1546 Basics: Chemistry and Physics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1552 Devolatilization and Coal Dependence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1553 Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1556 Gasification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1557 Gasification Versus Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1560 Integrated Gasification Combined Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1562 Gasification Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1563 Fixed/Moving Bed Gasifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1567 Examples of Fixed Bed Gasifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1571 Fluidized Bed Gasifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1574 Examples of Fluidized Bed Gasifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1576 Entrained Flow Gasifier Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1578 Examples of Entrained Bed Gasifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1580 Transport Gasifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1584 KBR Transport Gasifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1586 Carbon Capture Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1587 Conventional Acid Gas Control Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1587 Physical Sorbent Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1589 Chemical Sorbents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1593 Future Directions in Research and Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1597 Recent Gasification Systems Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1597 Gasification R&D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1598 Gas Cleanup and CO2 Capture Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1600

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_40, # Springer Science+Business Media, LLC 2012

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Abstract: The chemistry and technology of gasification is presented within the global context of enabling the cleanup of fossil and biomass fuels for energy production. The historical development of gasification is compared and contrasted to combustion processes. While gasification has historically been applied to the production of highvalued chemical products, the focus here is to offset commodity power production using fossil fuel technologies less amenable to carbon capture. For this reason, integrated gasification and combined cycle processes are discussed with respect to electrical power production. The 12 major gasifiers being marketed today are described, some of which are fully deployed while others are in various stages of development. The hydrodynamics and kinetics of each are reviewed along with salient differences in performance, such as gas composition, when using a variety of fuels under different conditions. Critical operational features are discussed including oxidizing media, air or oxygen blown; the system pressure; fuel feedstock; and downstream cleanup. Thermal integration is discussed with respect to its impact on the gasifier performance and gas cleanup is also considered with respect to the removal of potential pollutants and the shifting to environmentally benign transportation and process fuels.

Introduction History of Gasification The concept of progress has changed dramatically over the past century. The development of new industry was considered progress regardless of the impact on the environment. From the first time man could see images of the fragile planet earth, he has become increasingly aware that one must learn how to not only tap the earth’s natural riches, but also how to preserve and serve as guardians of her most common resources – air and water. Coal was one of the critical natural resources leading to the industrialization that allows man the luxury of planning the planet’s future. As the world emerged into the Industrial Age, coal provided more than just the fuel for heat and industry. Coal gas also played a key role in the innovative development of tools, materials, and lighting. In 1609, Jean Baptist van Helmont first heated and observed the release of gas from coal. He wrote how the coal ‘‘did belch forth a wild spirit or breath. . . not susceptible of being confined in vessels, nor capable of being reduced to a visible body.’’ Helmont surely wondered about this spirit and called it ‘‘gas’’ as derived from the Dutch word ‘‘Geest’’ for ghost [1]. The first coal gasifier was used by Fontana in 1780 when he directed a flow of water (steam) over red-hot, or incandescent, coal that was partially burned in air. The process can be described using two reactions. Heat was provided by burning coal with air and then the air was replaced with steam to gasify the hot char and produce synthesis gas, a combustible mixture of carbon monoxide and hydrogen. Fontana called the resulting coal gas ‘‘blue water gas,’’ because it produced a pale blue flame when burned in air [2]. Coal gasification supplied lighting and heating for industrializing America and Europe beginning in the early 1800s. The first public street lighting with coal-derived gas was in

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Pall Mall, London on January 28, 1807. This was where coal-derived fuel gas became commonly known as ‘‘town gas.’’ Town gas was a gaseous product from coal, containing nearly 50% hydrogen, with the remainder made up of methane and carbon dioxide, and 3–6% carbon monoxide. Not long after that, Baltimore, Maryland began the first commercial gas lighting of residences, businesses, and streets in 1816. A typical town gas plant for the era is shown in > Fig. 40.1 and contrasted to today’s vision of a FutureGen power plant. Both images represent progress to different generations. Gasification was the leading energy source in many industries in need of process fuel gas since the early 1800s. The light bulb was not discovered by Thomas Edison until late in the nineteenth century, 1879. The first electric power plant was not built until nearly two decades after the American Civil War in 1882. However, as early as 1792 Murdock, a Scotch engineer used Fontana’s process to produce a fuel gas and light his house. James Watt, the inventor of the steam engine employed Murdock to light one of his foundries with this newly discovered coal gas [3]. By 1875, every medium and large-sized

. Fig. 40.1 Artist’s view of Baltimore’s Bayard Street Station (top) from ‘‘Progressive Magazine’’ of 1889 picturing the plant prior to 1850 and a FutureGen power plant (bottom) depicting a modern, green-field, zero-emission integrated gasification combined cycle (IGCC) plant

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city in America and Europe developed coal gasworks and distribution networks. Gasworks were a large number of batch gasifiers set up in series so that a continuous stream of fuel could be supplied to residential and industrial users. The ‘‘blue water gas’’ produced from cyclic gas generators of the type used by Fontana were not directly usable for street or household lighting. While the heating value was high enough to sustain combustion, the blue flame was not bright enough. Early developers learned that the coal gas needed to add ‘‘illuminates,’’ that is, C2+ hydrocarbons, to provide a bright luminous yellow flame. However, too many or the wrong types of higher hydrocarbons would produce condensable species like tars and naphthalene and the gas would eventually foul and plug the pipelines. Noxious and poisonous gases, such as hydrogen sulfide, hydrogen cyanide, and ammonia, were also produced. It was soon found that the undesirable components could be separated and cleaned from the coal gas. Cooling with a direct water spray and filtering of the gases were usually effective in removing the condensables and noxious impurities. By the mid-1800s, there were two main types of coal gasifiers, cyclic gas generators similar to those first used by Fontana and gas producers. The cyclic gas generators produced a high-quality fuel gas. This high heat value is accomplished by collecting only the products during the steam blast and venting the products of combustion during the air blast. The carbureted gasifier produced ‘‘town gas,’’ which was particularly well suited for lighting. The original cyclic gas generators were ideal industrial fuels used in kilns, boilers, brick ovens, and curing materials particularly where particulate impurities were to be avoided. These batch units were typically loaded by hand, and more importantly, the glowing hot ash or coke also had to be removed by hand – often with nothing more than a shovel. In addition to the obvious benefits to gas workers of the time, many economic advantages were possible by making this cyclic process continuous. Gas manufacturers learned that they could improve both the rate and efficiency of gas making by introducing steam and air together into the coal. In this way, the steam was available to gasify the carbon at the same time that heat was being produced from coal combustion. The result was the ability to substantially increase the overall conversion of coal to gas. This led to the development of the fully continuous gasifier of today with respect to both coal and air/steam. Thus, the modern gas producers were developed. The development of gas producers did not, however, displace the cyclic gas generators. By 1936, the Federal Trade commission reported that there were 3,800 machine-fed and still about 1,000 hand-fed gas producers in the USA [4]. By firing air and steam simultaneously, the product gas in these producers now contained the unreactive, or inert, nitrogen that is present in the air stream fed to the gasifier. Air is, in fact, 79% N2 and only 21% O2 by volume. This added nitrogen is merely a diluent and plays no role in the combustion or gasification reactions. To make matters worse, this diluent must be heated both during the gasification process and later as the fuel is burned. As a result, the producer gas is only about one half of the heating value compared to ‘‘town gas.’’ There are several process ramifications when using this low-quality gas fuel. Economic transportation of producer gas is limited to a short distance. Upon combustion the flame

Integrated Gasification Combined Cycle (IGCC)

40

is longer, cooler, and more luminous. Still many industrial applications could take advantage of the peculiar flame properties of this low heating value fuel. For instance, the relatively low temperatures and long flame are useful to avoid hot spots and nonuniformities in glass making. In contrast to traditional coal combustion, coal gasification processes can be thought to include: pyrolyzers, cokers, cyclic gas generators, and gas producers. All of these processes are heated with sub-stoichiometric air, that is, insufficient oxygen to completely convert the coal to the final products of combustion. The products of all of these processes are a solid fuel, condensable hydrocarbons and tars, and flammable gases. Both the quality and quantity of these products depends upon how the coal is heated, the gas atmosphere used during the process, and the temperature. The product distribution generated from these coal technologies is presented in > Table 40.1. As is still true today, the coal gas in those early gasifiers was produced in several different types of reactors depending on the desired products and end use. Gasification technology development has had its ups and downs. It is worthwhile to note some of the highpoints. Gasification was the foundation for modern chemical industry. In 1920, Fischer and Tropsch developed a catalyst to convert the hydrogen and carbon monoxide from coal gasifier gas to hydrocarbon liquids. By the mid-1930s nearly

. Table 40.1 Operating conditions and product distribution for various coal conversion processes using bituminous (bit.), subbituminous (subbit.), and brown coal [1, 5] Gas producers Product composition

Blue water Town gas gas

Fixed bed

Fluid bed

Entrained gasifier

Oxidant

Steam

Steam

Air, steam

Oxygen, steam

Air, steam

Fuel

Bit. coal

Exit temp. (
F) Gases (wt%)

–

Bit. coal –

Bit. coal 287

H2 CO CH4 Illuminatesa

50.5 38.5 1 –

40.5 34 10.2 8

14.5 25 3.1 –

52.7 N2 CO2 4.7 Char (wt%) Gas HVb (kJ/m3) 11,178 a

0.5 2.9

52.7 4.7 19.5 20,493 6,222

Oxygen, steam

None

Brown coal Subbit. coal 900 2,000

Bit. coal

Bit. coal

2,000

1,800

36 44.4 1.6 0

12.9 23.5 0.02 0

35.8 50.7 0.1 0

46.5 6.3 32.1 0.31

0.8 15.7 20 9,948

60.3 3.1 11.8 4,359

0.2 13.1 11.4 10,432

0.95 0.9 75 21,760

Noncondensable gases consisting of hydrocarbons with carbon chains between C2 and C4 Gas HV is the heating value of the gas

b

Coke oven

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Integrated Gasification Combined Cycle (IGCC)

two million liters of gasoline and oil per year were produced in German gasification plants. Individual reactors in the early Fischer–Tropsch plants yielded only about 5,000 L of gasoline per day. Literally 100 such gasifiers were used in these first plants. During the Second World War, this coal-derived oil was one source of synthetic fuel for the German war machine. Gasification technology has been a mainstay in the refining industry for the production of synthesis from coal, heavy residual oils, and petroleum coke since the 1950s. After World War II, South Africa required their own independent sources of oil and gas, when international economic sanctions cut off their access to world petroleum supplies in protest to their social policies of apartheid. While South Africa had no domestic oil and gas supplies, it had ample coal reserves. Gasification technology was chosen to supply the needed liquid transportation fuels and the South African Coal, Oil, and Gas Company (SASOL) employed the Fischer–Tropsch process. The SASOL coal gasification plant has been operated since 1955 producing liquid fuels from coal. The individual reactors in these plants are 100 times larger than the plants used in Germany during the Second World War. SASOL operations were increased tenfold by their expansions in 1977 and 1982. Today, SASOL has the largest gasification capacity in the world. By 1982, SASOL had a capacity of nearly 2.5 million gallons of oil and gasoline per day using Lurgi Fixed Bed Gasifiers. The SASOL plants remain the largest collection of coal gasifiers in the world today (> Table 40.2). Gasification has been used extensively in the last 50–60 years to convert coal and heavy oil into hydrogen – for the production of ammonia/urea fertilizer. The chemical industry and the refinery industry applied gasification in the 1960s and 1980s, respectively, for feedstock preparation. In 1984, the USA responded to pressure from Oil Producing Exporting Countries to control oil prices by developing the Synthetic Natural Gas (SNG) plant in North Dakota known as the Great Plains Gasification Plant. Like SASOL this large-scale demonstration selected fixed bed technologies developed by Lurgi and Synthane. Coal gasifiers were also built in the late 1970s using entrained (Texaco and Dow) and fluidized bed gasifiers (U-GAS®) primarily in oil refineries and chemical plants. In 1977, the USA passed Clean Air Act Amendments, which identified the concept of benchmarking technologies with respect to the best available control technology (BACT). This drove an interest in integrated gasification combined cycle (IGCC). Several utilityscale IGCC power trains were built in the 1990s as demonstration plants using entrained gasifiers including the Tampa Electric’s TECO plant using two Texaco (now GE Energy) gasifiers and the Wabash plants using 2 E-Gas (now ConocoPhillips) gasifiers. Coal-based plants using today’s gasification technology are efficient and clean. Gasification has been demonstrated to be superior to conventional utility power systems in response to tightening environmental regulations and as a result of the development of the highly efficient gas turbines or the combined power cycles, and the relative ease and level of maturity of the associated gas cleanup technology. However, the technology still lacks the experience base in the power sector and so has had difficulty to raise the large capital investments required. Technologies have been developed for gasifiers to shift the product

Integrated Gasification Combined Cycle (IGCC)

40

. Table 40.2 Thirty largest gasification plants worldwide [6] Plant owner

Country

Gasifier

Sasol Chemical Ind. South Africa Lurgi (Pty.) Ltd./Sasol Ltd. Sasol Chemical Ind. South Africa Lurgi (Pty.) Ltd./Sasol Ltd. Dakota Gasification Co. United Lurgi States SARLUX srl Italy Texaco Shell MDS (Malaysia) Malaysia Sdn. Bhd. Mitteldeutsche Erdoo¨l- Germany Raffinerie GmbH ISAB Energy Italy

MWth Year out

Fuel

Product

1977 5,090

Bit. coal

FT liquids

1982 5,090

Bit. coal

FT liquids

Shell

1984 1,900.3 Ligruite and ref. resid. 2001 1,216.7 Visbreaker residue 1993 1,032.4 Natural gas

Shell

1985 984.3

Texaco

2000 981.8

Visbreaker residue ROSE asphalt Bit. coal

SNG and CO2 Electricity, H2 and steam Middistillates H2, methanol and elec. Electricity, H2 and steam FT liquids

Sasol Chemical Ind. (Pty.) Ltd./Sasol Ltd. Global Energy, Inc.

South Africa Lurgi

1955 970.6

Germany

Lurgi

1964 848.3

Municipal waste

Nippon Petroleum Refining Co. Millenium (Quantum)

Japan

Texaco

2003 792.9

Vac.residue

United States Germany

Texaco

1979 656.2

Natural gas

Shell

1978 642.5

Heavy vis. residue

Shell Nederland Netherlands Shell Raffinaderij BV Sokolovska Uhelna, A.S. Czech Lurgi Republic

1977 637.3 1996 636.4

Visbreaker residue Liguite

H2 and electricity Electricity and steam

Global Energy, Inc.

Electricity

Hydro Agri Brunsbuu¨ttel

Electricity and methanol Eletricity Methanol and CO Ammonia

E-Gas

1995 590.6

Petcoke

VEBA Chemie AG

United States Germany

Shell

1973 587.8

Elcogas SA

Spain

PRENFLO 1997 587.8

Vac. residue Ammonia and methanol Coal and Electricity petcoke

Motiva Enterprises LLC United States api Energia S.p.A. Italy

Texaco

2001 519.5

Texaco

2001 496.2

Fluid petcoke Visbreaker residue

Electricity and steam Electricity and steam

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Integrated Gasification Combined Cycle (IGCC)

. Table 40.2 (Continued) Plant owner

Country

Gasifier

MWth Year out

Fuel

Product

Chemopetrol a.s.

Czech Republic

Shell

1971 492.1

Vac.residue

Demkolec BV Ultrafertil S.A.

Netherlands Shell Brazil Shell

1994 465.9 1979 451.1

Tampa Electric Co.

United States China

Texaco

1996 451.1

Bit. coal Asphalt residue Coal

Methanol and ammonia Electricity Ammonia

GTI

1994 410.1

Bit. coal

India

Texaco

1982 405.3

Esso Singapore Pty. Ltd. Singapore

Texaco

2001 363.6

ExxonMobil

Shanghai Pacific Chemical Corp. Gujarat National Fertilizer Co.

BASF AG China National Petrochem. Corp./ Sinopee Quimigal Adubos

United States Germany

Texaco

2000 347.2

Texaco

1974 341.8

China

Texaco

1988 341.8

Portugal

Shell

1984 328.1

Electricity

Fuel gas and town gas Ref. residue Ammonia and methanol Residual oil Electricity, H2 and steam Deasphalter Syngas pitch Vac. resid. Methanol and fuel oil Visbreaker Gases residue Vac.residue

Ammonia

stream from carbon dioxide to clean-burning hydrogen gas. When coupled with the wellproven acid gas removal technology, carbon dioxide can be removed and concentrated for market applications or to be sequestered. Gasification is posed to be a leading technology capable of addressing the challenges to global climate change.

Basics: Chemistry and Physics Gasification has been around for more than 200 years, so why the interest in it now? There are many reasons, but the two most significant are the continuing high price of natural gas and highway transportation fuels. Granted that these prices are moderated occasionally. However, the price of gasoline has fluctuated widely over the past decade. The second significant reason is the need for energy independence. In other words, the use of domestic energy sources such as coal not only for electricity production but also for synthetic natural gas (SNG) and liquids for transportation is a must. Gasification is a technology for converting coal to a gaseous product often called synthesis gas or fuel gas depending on the application. The product gas can literally be

Integrated Gasification Combined Cycle (IGCC)

40

converted to almost anything, other than electrons, and can potentially be competitive even there [7]. Gasification is often considered the baseline technology and foundation for developing many advanced carbon-based fuels. For example, gasification is the key conversion step for converting coal to H2, synthetic natural gas (SNG), liquid fuels, and the capture of CO2 for sequestration. Gasification has excellent environmental performance such that some states’ Public Utility Commissions have identified Integrated Gasification Combined Cycle (IGCC) plants for power generation as the best available control technology (BACT). In addition, the uncertainty of carbon management requirements and the potential suitability of IGCC for CO2 controls make it an ideal choice for power. So, what is gasification? Strictly speaking, gasification is the reaction of carbon with steam to produce carbon monoxide and hydrogen. Because this reaction is highly endothermic and because coal and biomass are not simply carbon, gasification technology is more complex than that. As compared to combustion, gasification is a the conversion of organic matter to carbon monoxide and hydrogen by reaction of substoichiometric mixtures of the solids fuel and oxygen usually in the presence of excess water or steam. It is useful to consider the conversion processes involved in solid fuel gasification individually. Coal undergoes a series of chemical and physical changes, as shown in > Fig. 40.2. As the coal is heated, most of the moisture is driven out when the particle temperature is about 105
C. Drying is a rapid process and is essentially complete when the temperature exceeds the boiling temperature of water.

Devolatilization and Coal Dependence A large percentage of coal weight is lost during devolatilization, or pyrolysis. Pyrolysis occurs rapidly as the coal heats up above 300
C and continues up to temperatures required for gasification. If the heating rate is slow, pyrolysis can reach completion at temperatures as

H2O

Coal

Drying 100 °C

CO, CO2, H2, H2O, CH4, tar

Devolatilization 500–900 °C

O2 Char

Combustion 1,000–1,300 °C

CO, CO2, H2 O Ash

Char

CO2, H2, H2O

Gasification 900–1,200 °C

CO, CO2, H2, H2O Ash

. Fig. 40.2 Simplified schematic of reaction pathways contributing to coal conversion in a gasifier

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Integrated Gasification Combined Cycle (IGCC)

low as 450
C, but for rapid heating processes pyrolysis continues as the coal heats up to 700–1,000
C required for gasification. Given and others [8, 9] describe the organic matter in coal as a macromolecular network with varying contents of lower molecular structures and components which are mobile but entrapped within that solid structure. During pyrolysis, mobile components evolve. Labile bonds are broken producing lower molecular weight fragments. Fragments and low molecular weight components vaporize and escape from the coal particle forming light gases and tar. The more reactive or higher molecular weight fragments with low vapor pressure can remain in the coal under typical devolatilization conditions and reattach to the coal’s macromolecular network. This can be thought of as the precursor to char. The devolatilization gas that does not condense at room temperature and pressure are called light or fixed gases, and consists mainly of CO, CO2, CH4, H2, and H2O. The portion of the volatile matter that condenses at room temperature and pressure is called tar. Tar is a mixture of hydrocarbons with an average molecular weight ranging from 200 to 500 amu [19]. The yield and chemical nature of tar depends upon the coal rank; in general, higher rank coal produces lower amounts of tar. The solid product left over from devolatilization is char. Devolatilization alters the coal porosity from 2–20%, typical of coal, to over 80% in the char. The surface area increases from 10–20 m2/g (coal) to 200–400 m2/g as measured by with nitrogen gas in a BET (Brunauer Emmet Teller) apparatus [10]. This increased surface area increases the rate of subsequent combustion and gasification reactions. The volatile yield, its composition, and the residual char reactivity depend upon the coal petrology, degree of geologic maturation, and process conditions [11–13]. Coal rank is the relative measure of the extent of maturation for an organic sediment due to exposing the deposited organic detritus to elevated pressures and temperatures during the geologic eras required for its burial, subsidence, and compaction [14]. Organic materials increase in level of maturity from: BIOMASS < PEAT < LIGNITE < SUBBITUMINOUS < BITUMINOUS < ANTHRACITE:

Maturation processes are characterized by first the loss of water and oxygen functionality, followed by increase in polymeric molecular size, and finally the condensation of aromatic structures. Classification for low-rank coals, subbituminous coals and lignites, is based upon the inherent moisture content and their calorific value [15]. Low-rank coal volatiles contain a large proportion of the fixed gases and the tars produced are low molecular weight. Their tars are typically limited to one and two-ring aromatic structures, but contain a wide variety of heteroatomic functionality. Chars produced from heating low-rank coals are open and exhibit a greater degree of disorder and more heteroatomic functionality (H, O, N, and S) than their higher rank counterparts. As a result, these chars have high gasification reactivities [16–18]. It is the potential for the reactive oxygen functional groups such as the carboxyl groups to chelate exchangeable cations that can atomically disperse catalytic species such as Ca, K, and Na to dramatically enhance gasification rates [18]. Coals that are higher in rank than subbituminous have lower oxygen contents, but still substantial volatile matter. Reactive oxygen functionality such as esters, carbonyl and

Integrated Gasification Combined Cycle (IGCC)

40

carboxyl groups are gone in the bituminous rank coals, but phenols, furans (cyclic oxygen), and ethers linkages persist [11]. The volatile matter consists of less fixed gases, but more higher molecular weight aromatic hydrocarbons with less heteroatomic functionality than the lighter counterparts formed from lower rank coals. Bituminous coals are differentiated by their volatile matter content and are classified as high-, medium-, or lowvolatile bituminous coals. These high molecular weight tar compounds, when combined with the residual macromolecular network during heating, form what is known as metaplast [19]. The quantity, volatility, and solubility characteristics of tars in bituminous coals are favorable to dissolve or melt the coal’s macromolecular network, which makes up the bulk of organic matter in this rank coal. During metaplast formation, the particle traps evolving gases and swells to an extent, which depends on its composition and the heating conditions. When rapidly heated in drop tube reactor, bituminous coals produce char cenospheres often greater than three times the size of the feed coal [20]. The residual chars formed after devolatilizing bituminous coal are more highly ordered carbons consisting largely of condensed polynuclear aromatic structures. Thus, in spite of their lower density and extremely high porosities, bituminous coal chars are inherently less reactive than their lower rank counterparts. Low-volatile bituminous coals can be distinguished from anthracite by the relative hydrogen to carbon content, which decreases as the rank increases due to the condensation of aromatic rings into highly condensed and unreactive polynuclear aromatic structures. Tar yields from these high-rank coals are quite small and fixed gases evolved consist mainly of CO, H2, and CH4. Process conditions also influence devolatilization and the products, volatiles and char. Key parameters include heating rate, final temperature, and pressure. At slow-heating rates (less than 1 K/s), the volatile yield is relatively low. It is under these conditions that the total volatile yield will be equal to the volatile matter content determined from the ASTM (American Society for Testing and Materials) Proximate Analysis, which is an analysis done at a slow-heating rate. Under rapid-heating rate (500–105
C/s), the volatile yield is 20–40% more than that at slow-heating rates [4]. At any given temperature, only a certain fraction of the volatiles is released. Significant devolatilization begins when the coal temperature is about 500
C. As the temperature is increased, more volatiles are released. The maximum volatile yield occurs when the temperature is above 900
C, the temperature at which ASTM Proximate Analysis is conducted. Higher gasifier temperature also reduces the amount of tar in the gasifier products because of increased cracking rate of tar into lighter gases. The amount of tar also decreases with increasing pressure and decreasing heating rates. The predominant source of CH4 in the gasifier product gas is from the devolatilization process, and its production is favored by low temperature and high pressure. Therefore, the amount of methane in the product of moving bed gasifiers, which operate at a low temperature, is higher than that in typical fluidized bed and entrained bed gasifiers [21]. As such it is apparent that predicting the early stages of gasification, devolatilization, for coal is quite complex. While the rate is rapid and can be simulated as being coincident

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Integrated Gasification Combined Cycle (IGCC)

with coal heating, the yields, stoichiometry, physical characteristics, and resulting reactivity of the products are dependent upon many factors. One common, simple, and expediant approach is to scale the devolatilization yield with temperature based upon the ultimate yield determined in the ASTM Proximate Analysis [22]. This provides a relative distribution of volatile matter in the gas phase that is dependent on the coal feedstock, which can then be modeled to react further to produce fixed gases, depending on the thermal environment in the gasifier. The more rigorous two-stage pyrolysis model is often employed to explain the effects of heating rate and pressure on tar yields [23]. In this model, primary tars are produced initially within the coal particle followed by their subsequent cracking and release via a second reaction. Thus, if the heat rate is fast enough to raise the particle temperature sufficiently for tar vaporization, the high molecular weight primary tars are released into the gas phase before they can reattach to the char. However, at lower heat rates or higher pressures, these low-volatile primary products stay longer within the particle and crack there to form lighter volatile products which can escape as well as fixed carbon which reattaches to the char. Anthony and Howard [24] have demonstrated that thermal decomposition of the complex coal macromolecular structure can be modeled by a series of parallel reaction pathways in which the reaction progresses along the most favorable route which can be simulated using distributed activation energies. The activation energies increase as the extent of conversion increases. Another more rigorous approach is to characterize the evolution rates of these individual gas species themselves dependent on precursor species as identified by more detailed characterization of the cross-linked nature of coal. Such approaches have included the use of infrared [25] and NMR spectroscopic analysis [26]. These methods have been further refined through the development of volatile percolation models such as FLASHCHAIN [27] and CPD (Coal Percolation and Devolatilization) [19, 26] to account for the variations in thermal and mass transfer during volatile release due to variations in process pressure, heating rates, and particle sizes. NETL’s C3M efforts are designed to incorporate all of these models in a platform that can be used with various computational fluid dynamic codes.

Combustion Char in an oxygen atmosphere undergoes combustion. In gasifiers, partial combustion occurs in an oxygen-deficient or reducing atmosphere. Gasifiers use 20–30% of the oxygen theoretically required for complete combustion to carbon dioxide and water. Carbon monoxide and hydrogen are the principal products, and only a fraction of the carbon in the coal is oxidized completely to carbon dioxide. The combustion reaction is written in a general form as follows: ð1 þ lÞC þ O2 ! 2l CO þ ð1  lÞCO2

0 DH298K ¼ 172:5l  393:5 kJ=mol

where l varies from 0 (pure CO2 product) to 1 (pure CO product). The value of l depends upon the gasification conditions and is usually close to 1. This is quite important since the ratio of CO/CO2 determines how much of the carbon in the char is converted to gas.

Integrated Gasification Combined Cycle (IGCC)

40

Computational models for coal oxidation under these conditions are quite common, but vary in the manner they treat the value of l. Arthur conducted tests on various carbons often cited to model the temperature dependence for this stoichiometric coefficient [28]. As the temperature of reaction increases, carbon monoxide is favored. Wen [4, 30] incorporated this concept by including a particle-size dependence such that larger particles with greater thermal mass have a greater tendency to reach higher temperatures, higher values for l, and yield greater proportions of CO. Monazam and others [29] have employed Arthur’s temperature dependence directly into plug flow and stirred tank models. The carbon–oxygen reaction is quite fast and highly exothermic. Under typical gasifier conditions, the carbon–oxygen reaction rate is controlled by the rate of the diffusion of oxygen to the particle surface. For a particle size of 50 mm, the diffusion rate is the ratelimiting step for temperatures above 750 K. For smaller particles, the diffusion of O2 into the particle becomes dominant only at a higher temperature (e.g., 1,600 K for 20 mm particles). The heat released by the partial combustion provides the bulk of the energy necessary to drive the endothermic gasification reactions.

Gasification As a result of these rapid oxidation kinetics, all oxygen is rapidly consumed in a combustion zone, near the injection of oxidant. Further conversion of char occurs through the much slower, reversible gasification reactions with CO2, H2O, and H2. C þ CO2 $ 2CO

0 DH298 K ¼ 172:5 kJ=mol

C þ H2 O $ CO þ H2 C þ 2H2 $ CH4

0 DH298 K ¼ 131:3 kJ=mol

0 DH298 K ¼ 74:8 kJ=mol

The rate of gasification reaction depends upon the char properties and the gasification conditions. Typical orders of magnitude of the relative reaction rates for various oxidants are provided in > Table 40.3. In general, gasification rates increase with temperature according to Arrhenius expression. The kinetic parameters reported by Wen et al. [4, 30] are commonly used to model the kinetics of coal gasification. This is used by Syamlal et al. [31] in MFIX [32] and by . Table 40.3 Relative gasification rates at 10 kPa and 800
C Reaction

Relative rate

C + O2 C + H2O C + CO2

105 3 1

C + H2

103

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Integrated Gasification Combined Cycle (IGCC)

Slezak et al. [33]. During combustion and gasification, the particle mass and temperature are governed by the following reactions developed from the mass and energy balances for a reacting coal particle: dmp ¼ Rate dt dTp dmp mp Cp ¼ hAp ðT1  Tp Þ þ hreac þ eAp sðyR 4  Tp 4 Þ dt dt where mp is the reacting particle mass, Cp its heat capacity, Tp its temperature, Ap its area, h the gas–solid heat transfer coefficient, T1 the bulk process gas temperature, hreac the heat of reaction, e the voidage, s the view factor, and yR the refractory wall temperature. The refractory wall is a corrosion and heat-resistant brick often used to line the gasifier walls. The term on the left of the latter equation represents the change in the sensible heat in the particle during the coal conversion. At any instant in time, this is equal to the heat transferred between the gas and the particle (first term on the right), plus the heat gained or lost due to the heat of reaction (second term on right), plus the radiant heat transfer. The combustion reaction is normally modeled as a shrinking core model graphically depicted in > Fig. 40.3 where the coal particle is depicted initially, after the reaction front has progressed in time so that a coal ash layer has built up and when the reaction has progressed to near completion. In coal, this is complicated by potential coal swelling initially. The initial gas–char reactions involve fast surface combustion of oxygen. These reaction occur at the surface because the processes are limited by the relatively slow diffusion of oxygen into the porous coal char at these temperatures. This is the shrinking particle and constant density stage of the process. After the oxygen is depleted, the gasification of char becomes relatively slow as compared to diffusion, and so gasification reactions are kinetically limited. This second stage of heterogeneous gas char reactions take place uniformly throughout the particle volume and result in decreasing particle density and constant diameter. The reaction rate (per unit area) employed for combustion and gasification is obtained from comparing the relative reaction rates associated with gas–solid film diffusion, chemical reaction, and diffusion through the reacted char layer:

Gas film Ash Ash Solid reactant

Time

Shrinking unreacted core

. Fig. 40.3 Shrinking core model for the combustion of coal

Time

Integrated Gasification Combined Cycle (IGCC)

Rate ¼

1 kdiff

þ

1 kr Y 2

1 1 þ kdash

1 Y

40


ðPi  Pi  Þ 1

where kdiff is the gas film diffusion constant, kr is the Arrhenius rate constant, kdash is the ash film diffusion constant, Y is the char conversion factor defined as the ratio of the unreacted core radius to the initial radius of the particle, Pi is the partial pressure of reactant i, and Pi∗ is the back reaction equilibrium pressure of reactant i [30]. Variations in the relative rates are normally accounted for by adjusting the frequency factor or pre-exponential term. Differences in char reactivity as a result of degree of disorder of the carbon structure are also treated by adjusting this pre-exponential factor [29]. Differences in the degree of disorder in the char are due to differences in heat treatment history, number of imperfections due mainly to heteroatoms (i.e., organic O, S, and N), degree of condensation in the aromatic structure (due to level of maturity in the sediment). In addition, it is important to note that elevated pressures increases the partial pressure of the oxidant and thus increases the gasification rate relative to the absolute increase in overall pressure [29]. Another important chemical reaction in a gasifier is the water–gas shift reaction: CO þ H2 O $ CO2 þ H2

0 DH298 K ¼ 41:2 kJ=mol

The relatively low heat of this reaction contributes to the low activation energy and quick approach to equilibrium. As a result, the gasifier product distribution can often be estimated from the conversion and the equilibrium constant for this reaction. However, this equilibrium constant is dependent on temperature and the equilibrium will be frozen at the process or downstream temperature depending on the effective quench rates in the various processes. Thus, the equilibrium temperature for a different process configurations must be experimentally established. Detailed computational modeling has the potential to incorporate all of these complex reaction pathways to provide insight into how to predict changes in this effective equilibrium temperature and thus how modifications will alter gasifier product distributions. Mineral matter in the coal catalyzes gas phase reactions. Other gas phase reactions are the combustion of CO, H2, and CH4 and tar cracking. One intermediate product from these gas phase reactions in a gasifier is the formation and further conversion of soot. This can play a pivotal role in determining the performance, reliability, and efficiency of the downstream cleanup process units as well as determining the overall process performance. Gasification turns any carbon-containing material into synthesis gas, as depicted in > Fig. 40.4. Carbon reacts with water, in the form of steam, and oxygen at relatively high pressure, typically greater that 3,000 kN/m2, and at temperatures typically reaching 1,500 K to produce raw synthesis gas or syngas. Syngas is a mixture composed primarily of carbon monoxide and hydrogen and some minor by-products. The by-products are removed to produce a clean syngas that can be used as a fuel to generate electricity and steam. Syngas is the basic chemical building block for a large number of uses in the petrochemical and refining industries. Syngas production is the first step in the efficient manufacture of the clean burning hydrogen fuel. Gasification adds value to low- or negative-value feedstocks by converting them to marketable fuels and products.

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Integrated Gasification Combined Cycle (IGCC)

Oxygen

Coal

Extreme Conditions: 3,000 kN/m2 atm. or more 1,400 K Corrosive slag and H2S gas

Products (syngas) CO (carbon monoxide) H2 (hydrogen) [CO/H2 ratio can be adjusted]

By-products H2S (hydrogen sulfide) CO2 (carbon dioxide) Slag (minerals from coal)

Gas clean-up Before product use

Water

. Fig. 40.4 Gasification process basics

There are a number of previous reviews and extended writings on gasification available to get a deeper understanding of the process and various gasification technologies. These include the book by Higmans [34], the Gasification Technologies Council web site http:// www.gasification.org/, the DOE Gasification website http://www.netl.doe.gov/technolo gies/coalpower/gasification/index.html, and numerous conferences including Gasification Technologies Annual Conference, the Clearwater Conference, and the Pittsburgh Coal Conference.

Gasification Versus Combustion Gasification and combustion can essentially be considered as two ends of a continuum for reactions of coal and oxygen, where water can be added as a reactant to increase the H2 content of the products. > Table 40.4 is a list of the most significant reactions and the enthalpy change associated with each of these reactions with respect to weight of carbon or carbon monoxide. Looking at the first two reactions in the table, it is seen that coal denoted here with a C for carbon is reacted with one oxygen atom denoted here as 1/2 O2 to get carbon monoxide and with two oxygen atoms (2) to get carbon dioxide. In reality, this second reaction is not a one-step process as the solid phase carbon reacts with one oxygen atom to produce carbon monoxide, which then reacts with the second oxygen atom to form carbon dioxide. All of the reactions in the table are exothermic except the two reactions identified as gasification with steam and gasification with carbon dioxide. These two endothermic reactions are the reactions that are most often referred to as gasification, where the solids carbon is turned into a reactive gas through a reaction with

Integrated Gasification Combined Cycle (IGCC)

40

a ‘‘nonreactive’’ gas (H2O or CO2). In addition to these two reactions being endothermic, they also require high temperatures to proceed. In > Table 40.5, combustion and gasification are compared and contrasted. Combustion is referred to as full oxidation and gasification as partial oxidation. Combustion occurs in an oxidizing (excess oxygen) environment and gasification occurs in a reducing (oxygen depleted) environment. For power production, gasification using a gas turbine is more efficient, has lower emissions, and competitive capital costs compared to

. Table 40.4 Gasification and combustion chemistry Reaction process

Chemical formula

Change in enthalpy

Gasification with oxygen Combustion with oxygen Gasification with carbon dioxide

C + ½ O2 ! CO C + O2 ! CO2 C + CO2 ! 2 CO

9,123 kJ/kg C 32,822 kJ/kg C 14,577 kJ/kg C

Gasification with steam Gasification with hydrogen Water gas shift Methanation

C + H2O ! CO + H2 C + 2 H2 ! CH4 CO + H2O ! CO2 + H2 CO + 3 H2 ! CH4 + H2O

11,048 kJ/kg C 6,215 kJ/kg C 1,512 kJ/kg CO 7,399 kJ/kg CO

. Table 40.5 Contrasts between combustion and gasification [7] Combustion

Gasification

Chemical process

Full oxidation

Partial oxidation

Chemical environment Primary product ‘‘Downstream’’ products Current application Efficiency

Excess oxygen (air)-oxidizing

Oxygen-starved – reducing

Heat (e.g., steam) Electric power Dominates coal-fired power generation worldwide 35–37% (HHVa)

Syngas (CO and H2) Electric power, pure H2, liquid fuels, chemicals Mostly chemicals and fuels, power generation demonstrated 39–42% HHVa

NSPSb $1,000–1,150/kW High experience, low risk

1/10 NSPSb Competitive Reliability needs improved

Emissions Capital cost Maturity/risk

a HHV is the high heating value or gross calorific value as determined by bringing all the products of combustion back to the original precombustion temperature, and condensing any vapor produced b NSPS is the New Source Performance Standards

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Integrated Gasification Combined Cycle (IGCC)

combustion. With respect to the competitiveness of the cost, it is the cost of electricity that is nearly the same for both technologies, the higher capital cost of gasification is offset by the improved efficiency. Combustion is the dominant power-producing technology in the world and as such is lower risk with demonstrated reliability.

Integrated Gasification Combined Cycle IGCC plants, as shown in > Fig. 40.5, convert carbonaceous fuels/materials into electricity and could be considered first generation plants – those not requiring CO2 separation or sequestration. In these plants, the carbon-containing material is fed to the gasifier along with oxygen and steam to produce the raw syngas. The raw syngas is cleaned of particulate matter and sulfur. The clean syngas is fed to the combustion turbine with the products going to a heat recovery steam generator and steam turbine. IGCC systems with carbon capture [1] are similar to IGCC systems without carbon capture as can be seen by comparing > Figs. 40.5 and > 40.6. In > Fig. 40.6, the IGCC system is shown with precombustion capture of the carbon for sequestration. The primary difference between the two processes is that the clean syngas passes through a shift reactor and an absorption tower to remove the carbon in the form of carbon dioxide. The shift

Gas cleanup

Particulate removal

Gasifier

Particulates Sulfur by-product

Gaseous constituents

Solid by-product Combustor

Air separator Air Coal, petroleum coke, biomass, waste, etc.

Oxygen

Compressed air

Solids Air

Gas turbine Electric power Generator

Air Heat recovery steam generator Steam Solid by-product

Steam

Stack Generator

Steam turbine

. Fig. 40.5 IGCC system without carbon capture [7]

Electric power

Integrated Gasification Combined Cycle (IGCC)

Particulate removal

Gasifier

40

Gas cleanup

Particulates Sulfur by-product

Gaseous constituents

Particulate removal

Solid by-product Air separator

Gas cleanup

Combustor

Shift reactor

Gas separator Carbon dioxide to sequestration

Gasifier Particulates

Gaseous constituents

Sulfur by-product

Fly ash by-product Air separator

Combustor

. Fig. 40.6 Changes in the downstream IGCC process flow schematic with carbon capture [7]

reactor converts the CO in the syngas by reacting it with water over a catalyst to form H2 and CO2 with the latter going to sequestration. A conceptual poly-generation IGCC plant (one that generates multiple products) is depicted in > Fig. 40.7. In this concept, the clean syngas is shifted to change the CO/H2 ratio. A partial shift adjusts the ratio to be comparable to the end hydrocarbon product being synthesized. If clean carbon dioxide free power is being made as the product, the gas stream will undergo a full shift to produce hydrogen to fire in the turbine.

Gasification Processes Gasifiers fall into four primary configurations: moving bed, fluidized bed, entrained flow, and transport, as shown in > Fig. 40.8. Each of these is defined based upon how the reactor brings about contact with the coal and the reactive gas. The gas and solids temperature profiles differ dramatically as they traverse through these different gasifier types. In a typical moving bed gasifier designed for coal, the solids are loaded into the top of the gasifier and move slowly down in a packed moving bed as the coal below is consumed and converted to gas. The oxidant gas is introduced in the bottom of the gasifier through a grate and passes up through the residual coal ash. In a dry bottom gasifier, this flow of air or oxygen and steam through the insulating ash layer serves to cool the grate while preheating the oxidizing gas. The gas then meets the coal char in the oxidizing zone resulting in a high-temperature combustion zone near the bottom of the gasifier. In a slagging gasifier, the temperature in this combustion zone are permitted to

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Integrated Gasification Combined Cycle (IGCC)

Gas cleanup

Gas cleanup

Synthesis gas conversion

Shift reactor

Fuels and chemicals

Sulfur by-product

Sulfur by-product

Carbon dioxide sequestration Hydrogen

Combustor Air mpressed air

Gas separation

rator

Combustor

Air Compressed air

Gas turbine

Fuel cells

Electric power

Gas turbine

Electric power

Electric power

Generator

Generator Air

Heat recovery steam generator

Heat recovery steam generator Stack

Generator bine

Stack

m

Electric power

eam turbine

Generator

Electric power

. Fig. 40.7 Changes in the downstream IGCC process flow schematic for a poly-generation plant [7]

exceed the ash melting temperatures and the molten minerals flow through slag taps designed to remove the slag while maintaining countercurrent gas flow up into the gasifier. This is the region where the interstitial gas velocity attains a maximum. Channeling in the gasifier can result if the velocities entrain fines and begin to erode the downcoming particles depending on the size distribution of the feed coal and char. Coal throughput is limited by the gas velocity within combustion zone which if exceeded will lead to channeling, excessive tar production and fines carryover into downstream gas cleanup components. Immediately above the combustion zone, the oxidant is depleted but the temperature is high enough to gasify carbon primarily with steam. The strongly endothermic gasification reactions result in rapid cooling of the product gas stream. As a result, the peak temperature of the gasifier is confined to a relatively narrow region of the moving bed. The heat of reaction are distributed among the rising product gases and the settling coal char and ash. After gasification reactions slow due to dropping gas temperatures, the product gas still holds sufficient sensible heat to pyrolyze, dry, and preheat the coal before it exits the reactor at a relatively low temperature. The sensible heat is the heat absorbed or evolved by a substance solely due to a change in temperature. The greatest part of time in the moving bed gasifier is spent in this drying, heat-up, and pyrolysis region of the gasifier

Ash

Gas

Gasifier top

Gasifier bottom

Gasifier top

0

0

Coal

Gasifier bottom

Gas

. Fig. 40.8 Four basic coal gasifier types [7]

Steam, oxygen, or air

Coal

Ash

Fluidized bed

Steam, oxygen, or air

Coal

Moving bed

500

Gas

1,000 1,500 2,000 2,500 Temperature — °F

Ash

Gas

1,000 1,500 2,000 2,500 Temperature — °F

Steam, oxygen, or air

500

Steam, oxygen, or air

Coal

Recycle drive gas

Product gas, ash

Coal

Gas

0

Coal

Steam, oxygen, or air Gasifier 0 bottom

Gasifier top

Gasifier bottom

w

Gasifier top

Coal, sorbent or inert

Transport

Slag

Steam, oxygen, or air

Entrained Flow

1000

Coal, Char

1500

Slag

2000

2500

Recycle, Gas

2,500

Gas 1,000 1,500 2,000 Temperature — °F

500

500

Steam, oxygen, or air

Integrated Gasification Combined Cycle (IGCC)

40 1565

1566

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Integrated Gasification Combined Cycle (IGCC)

as is apparent by the long thermal heat-up portrayed in > Fig. 40.8. The volatile matter released during devolatilization undergoes a vaporization and condensation depending on the volatility of the tars, which results in some secondary cracking but ultimately may result in the production of significant quantities of tars in the product stream. For biomass and very high volatile matter coals, an alternative co-current configuration is often preferred to reduce the quantity of complex tar products. In this configuration, the oxidizing gases are primarily introduced along with the fuel at the top of the gasifier and product gas withdrawn at the bottom along with the solid waste. The result is twofold: the tars must traverse through the combustion zone and are cracked and partially combusted, and the product gas temperature is relatively high similar to the fluidized bed gasifiers. In a fluidized bed gasifier, the oxidant gas is introduced at the bottom with sufficient flow and velocity to support the weight of the entire inventory of coal, char, and ash or sorbents. The coal may be introduced at the top or deeper into the fluidized bed to reduce the amount and vapor pressure of tars. Both are heated rapidly to gasification temperatures near 1,000
C and mixed thoroughly, approaching the performance of a stirred tank reactor. The inventory is sufficient to obtain 10–30 min solid residence times. Pyrolysis, combustion, and gasification reactions take place throughout the reactor. The solids may be taken off either through an overflow stream or an underflow removal system depending on process concept goals. The product gas is removed off of the top at process temperature and must be cooled and any entrained fines removed. Due to the mixing, large solids surface area, and relatively low fluid bed temperatures, the product gases are richer in hydrocarbons from the cracking of tars and relatively high CO/CO2 ratio. The solids are withdrawn at temperatures below mineral melting temperatures, dry, either from the top of the reactor to be sent to a combustor for complete conversion, or from the bottom as a mineral-enriched solid waste, as shown in > Fig. 40.8. An entrained gasifier may be upflow or downflow, but it is dilute co-current flow with both coal and oxidant gas moving in the same direction rapidly approaching 1,500
C (> Fig. 40.8). The coal spends less than 10 s residence time, and all minerals are melted and removed from the gasifier as molten slag. In that time, the coal particle must be dried, heated, pyrolyzed, and then combusted and gasified in essentially a plug flow reactor. The product gas exits the gasifier at these high reaction temperatures and must be quenched, either directly or indirectly, in order to be further cleaned by removing particulate and then sulfur and other acid gases. The transport gasifier is a blend of the fluidized bed and entrained bed gasifiers with the oxidant entering the gasifier at the very bottom with recycle solids and unreacted coal char. The concept is to deplete all the oxygen prior to adding the coal in a section above the combustion zone. The coal is rapidly dried, heated, and pyrolyzed and gasified with steam. The product gas exits the gasifier after 3–10 s, but the tars are cracked over the hot mineral surface area in the recycled solids. The char and inert minerals in the transport gasifier experience internal mixing spending 10–50 s residence time. These solids are captured using two stages of disengagers and/or cyclones, excess solids are extracted and cooled, but the bulk of the solids are recycled back into the transport reactor to maintain process temperature, avoid agglomeration, and assist cracking of low-volatile hydrocarbons.

Integrated Gasification Combined Cycle (IGCC)

40

A comparison of the four basic gasifier types is presented in > Table 40.6. The moving/ fixed bed gasifier category refers to the Lurgi Mark IV (dry bottom) and the British Gas Lurgi (slagging) with both having dry coal feed systems. Both of these are countercurrent flow systems that operate principally as plug flow reactors. Entrained flow gasifiers are also plug flow reactors with very little back-mixing. There are three principle-entrained flow gasifiers produced by ConocoPhillips, General Electric and Shell. The Shell unit is a dry-feed gasifier whereas the ConocoPhillips and the General Electric are slurry-fed gasifiers. The moving bed gasifiers utilize coarsely crushed coal and require the long residence times as a result, while the entrained flow reactor uses finely crushed coal and the residence time are correspondingly short. On the other hand, the fluidized bed and the transport gasifiers are dry fed and non-slagging gasifiers. These are well-mixed reactors operating with lower peak temperatures then the plug flow reactors. These gasifiers have coal residence intermediate between the moving bed and the entrained gasifier, and thus utilize particles sizes that are also intermediate between them. Each of these four gasifier types have process options which make it possible to gasify any coal types. The moving bed is the most efficient and thus requires the least oxidant, while the entrained gasifier has the greatest coal throughput (feed rate per cross-sectional area). The transport gasifier was developed in order to maximize coal throughput while utilizing lower quality feedstocks which are unattractive in entrained gasifiers. The issues associated with each gasifier type is also listed in > Table 40.6.

Fixed/Moving Bed Gasifiers A sketch of the Fixed/Moving Bed Gasifiers is shown in > Fig. 40.9. Lurgi produces the non-slagging unit of this type while British Gas designed the slagging version of this . Table 40.6 Comparison of salient features for each of the four different gasifier types Entrained flow

Moving bed

Fluidized bed

Ash Condition Coal Feed

Dry

Slagging

Dry

Agglomerate Slagging

Dry

2 in.

2 in.

¼ in.

¼ in.

100 Mesh

1/16 in.

Fines

Limited Better than dry ash Low High

Good

Better

Unlimited

Better

Low

Any

Any for dry feed

Any

Moderate Moderate

High

Moderate

Moderate Moderate Carbon conversion

Low Raw gas cooling

Moderate Control carbon inventory and carryover

Coal Rank

Oxidant Low Low Req. Steam Req. High Low Issues Fines and hydrocarbon liquids

Transport flow

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Integrated Gasification Combined Cycle (IGCC)

Pressurization Product gas Drying Devolatilization

Gasification Combustion Steam and O2

Depressurization

. Fig. 40.9 Typical configuration for dry and slagging moving bed

technology, often referred to as the British Gas Lurgi (BGL). These units are both countercurrent flow and are characterized by very high combustion zone temperatures and low gas and solid exit temperatures. The high combustion temperatures provide the thermal energy required to drive the highly endothermic gasification reactions located immediately above. The reactor configuration effectively recuperates the sensible energy in the gas by exchanging the heat with the incoming coal in the devolatilization and coal drying zones giving these gasifiers the highest cold gas efficiency of any of the gasifier types. As a result, however, the product gas contains hydrocarbons, tar, and water released in the devolatilization and drying zones of the gasifier. Hydrodynamically, the reactors resemble flow through a porous medium, as shown in > Fig. 40.10. Although in this gasifier, both the continuous phase (gas) and the solids phase flow. These two components flow in a countercurrent fashion. That is, the solids move down while gas moves up. These types of reactors can be problematic due to nonuniform flow, which may be a result of particles agglomerating and over packing with fines. All of these issues lead to poor interphase mixing, unreacted carbon, hot spots, and lower conversion. Kinetically, the moving bed is a low-temperature reactor operating in the kinetic controlled shrinking core reaction mode pictured in the sketch shown in > Fig. 40.11. The burnout time or conversion time for a particle fed to the top of the gasifier is t¼

2rB R kC O2

where t is the time for complete conversion, rB is the coal particle density, 2 is 1/stoichiometric coefficient for O2, R is the particle radius, k is the combined kinetic and mass transfer rate constant, and C is the concentration of O2 [35].

Integrated Gasification Combined Cycle (IGCC)

40

. Fig. 40.10 Moving bed gas solids flow patterns

Time

. Fig. 40.11 Particle time history in moving bed

> Table 40.8 presents typical product gas compositions for air-blown operation of the Lurgi dry bottom configuration are presented for subbituminous and bituminous coals. Lower rank coals produce more CO2 and hydrocarbons because of their lower heating value and higher volatile content. More process energy is required to provide sensible and latent heat for the lower quality fuel, thereby driving the combustion reaction further to completion. Lower rank coals have inherently greater oxygen content and release more carbon dioxide directly from pyrolysis. In addition, the lower rank coal char is more reactive and thus reacts faster and so maintains a lower process temperature producing a greater relative proportion of CO2/CO. Typical product compositions are provided in both > Tables 40.7 and > 40.8. A study of the relative impact of different process parameters for a moving bed gasifier was reported by Monazam and Shadle [29]. A plug flow model was developed including mass and energy balances for the major gas and solids product streams during devolatilization, gasification, and combustion of coal. Then, a sensitivity study was conducted on each of the operating and design parameters for the gasifier when operated under a given

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Integrated Gasification Combined Cycle (IGCC)

. Table 40.7 Typical product compositions for oxygen-blown moving bed gasifiers [36–38] Oxygen blown Slagging moving bed

Dry bottom moving bed Coal type Brown/lignite Pressure up to 92 atm Gas composition (dry)

Subbituminous Bit 25 24–100

Anth 

Bit 21–32

CO CO2 H2 N2

17.4–19.7 30.4–32.2 37.2–37.2 0.5–0.5

15.1 30.4 41.1 1.2

15.2–19.5 28.9–32.4 38.3–42.3 0.5–1.6

22.1 30.8 40.7 0.4

55–61.2 2.4–3.5 28.1–31.5 3.3–3.3

CH4 H2S

11.8–12.1 0.1

11.7 0.5

8.6–10.1 0.8–1.1

5.6 

5–8.3 1.3–1.3

. Table 40.8 Typical product compositions for air-blown moving bed gasifiers [36, 39] Air blown Dry bottom moving bed Coal type Pressure (atm) Gas composition (vol% dry)

Subbituminous 5.3–20

Bituminous 1

CO CO2 H2 N2 CH4

8–17.4 13.1–17.1 14.4–23.3 38.5–53.7 2.5–5.1

22.7–27.8 5.9–6.3 16.2–16.6 48–50.5 1.7–3.6

H2S

0–0.2

0

coal feed rate. The base conditions are presented in > Table 40.9. The average responses and normalized response factors are summarized for each independent parameter in > Table 40.10. As expected from review of kinetic equations above, increased process pressures and gas velocities (air/coal) were the two most significant factors influencing (increasing) the rate of conversion or burning rate. Increased particle size resulted in slower conversion. Steam/air ratio was the most critical parameter impacting the

Integrated Gasification Combined Cycle (IGCC)

40

. Table 40.9 Base conditions used for the sensitivity study [29] P dp

Pressure (kPa) Particle size (cm)

2,850 0.5

S/A To Tog Vg D

Steam/air ratio Initial temperature (K) Inlet gas temperature (K) Gas superficial velocity (cm/s) Bed diameter (cm)

0.2 920 590 3 30

L

Bed depth (cm)

66

temperature and gas composition over the range tested. Only variations in the efficiency factor had significant impact on the gas product quality.

Examples of Fixed Bed Gasifiers British Gas Lurgi (BGL)

The British Gas Lurgi gasifier shown in > Fig. 40.12 is a ‘‘slagging’’ version of Lurgi gasifier. The BGL gasifier was developed by British Gas during the period from 1958 to 1965 at the Gas Council Midlands Research Station where it operated the gasifier at 380 kg/h [40]. It is a dry-feed, oxygen-blown, refractory-lined gasifier. It is good for wide range of coals including opportunity fuel blends with RDF (refuse-derived fuel), tires, and wood waste. It is a modular design by Allied Syngas which will build, own, and operate in North America. A 19,000 kg/h demonstration plant operated from 1986 to 1990. And the first commercial plant at Schwarze Pumpe operated from 2000–2005. Multipurpose (MPG) Gasifier

Lurgi developed the MPG technology shown in > Fig. 40.13 based on its fixed bed gasification process. It is an oxygen-blown, down-fired, refractory-lined gasifier good for wide range of feedstocks including petroleum coke (petcoke) and coal slurries as well as waste. It operates in a quench configuration for coal/petcoke feedstocks. Lurgi demonstrated a ‘‘Reference plant’’ at Schwarze Pumpe, which has been in operation since 1968. Lurgi Mark IV Gasifier

The Lurgi Mark IV gasifier is an extension of the original proven moving bed Lurgi gasifier. As shown in > Fig. 40.14, it has a dry-feed system with lock hoppers to provide the pressure seal. It is an oxygen-blown, dry bottom gasifier. There is extensive experience worldwide with low-rank coals. There are eight plants operating worldwide including one in North Dakota producing 18,600 MWth Syngas in 14 gasifiers. The plant has two trains of seven gasifiers each. It was originally designed to have one unit as a spare in each train. Operating all seven gasifiers has improved the plant’s economic performance.

1571

533–645 589 0.09 .153 0.041 0.23 0.065 0.17 0.03 0.004

1.5–4.6 3 0.06 0

0.105 0.46 0.86 1

0.007 0.133

Base 25.7 7.3

14.8 4.4 31.1 30.5

1,352 1,106

Range Dep.Var. CO (vol%) CO2 (vol%)

H2 (vol%) H2O (vol%) Burning rate (kg/h) Comb. Length (cm)

Ts,Max.(K) Tg,Out (K)

Inlet T0g (K)

Vg (cm/s)

Independent parameters

0.21 0.114

0.59 2.96 0 0.18

0.1–0.4 0.2 0.77 1.48

Stm./Air

.069 0.04

0.067 0.28 0.25 1.5

0.35–0.8 0.48 0.083 0

Dp (cm)

0.004 0.014

0.027 0.114 0.05 0.2

0.4–0.6 0.5 0.027 0.04

«

0 0.132

0.135 0.57 0 0

33–132 66 0.11 0.044

L (cm)

0.21 0.2

0.18 0.07 0 0.190

0.5–100 1 0.13 0.13

h

0.064 0.092

0.078 0.26 0.89 0.91

1,400–4,300 2,860 0 0

P (kPa)

40

. Table 40.10 The relative importance (dimensionless) of each of the operating parameters on performance variables in the gasifier general linear model [29]

1572 Integrated Gasification Combined Cycle (IGCC)

Integrated Gasification Combined Cycle (IGCC)

(ASC/SVZ type) Feed

Feed lock Gas offtake Stirrer (for caking coals only) Wash cooler Crude gas Steam, oxygen and tar

Slag quench Slag lock Slag

. Fig. 40.12 British Gas Lurgi gasifier [7]

Residues coal/oil tars slurries Oxidant (O2, air) Steam

Burner

Water quench

Gas-offtake Soot slurry

Slag

. Fig. 40.13 Lurgi multi purpose gasifier [7]

40

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Integrated Gasification Combined Cycle (IGCC)

Feed

Feed lock

Gas offtake

Wash cooler Crude gas

Ash grate (rotating) Ash lock

Steam/oxygen

Ash

. Fig. 40.14 Lurgi mark IV gasifier [7]

Fluidized Bed Gasifiers Figure 40.15 represents a typical configuration of a fluidized bed gasifier. Operating in the fluidized bed mode, these reactors are very well mixed. All processes take place simultaneously throughout the bed. Lime, limestone, or dolomite can be added for in-bed sulfur removal. The requirement to capture sulfur can limit the maximum temperature in these gasifiers to about 1,832
F or less which, also keeps the ash from slagging. Gasification kinetics determines bed volume, and the fluidization velocity determines cross-sectional area such that the bed height is fixed. Tar is cracked in the freeboard. The Gas Technology Institute’s (GTI’s) U-GAS® process and Winkler gasifier are examples of fluidized bed gasifiers. Hydrodynamically, fluidized beds are more complicated than fixed bed reactors where bubbles of excess gas induce and promote mixing, as shown in > Fig. 40.16. The better mixing of gas and solids leads to better interphase transport and better conversion of the coal. In addition, the mechanical movement of the solids against each other essentially scrubs the ash from particles. Fluidized bed gasifier have been conceived with indirect heating due to the high heat trasfer rates with heat exchange surfaces; however, the most successful process have been directly heated. The reactors performance approaches that of a continuous stirred process. Kinetically, because of the scrubbing of the reacted layer, the burnout or conversion follows a shrinking particle as pictured in > Fig. 40.17. The conversion time can be calculated from the equation 2r R t¼ B kC O2

>

Integrated Gasification Combined Cycle (IGCC)

40

Partial quench Freeboard

Product gas

Pressurized coal feed Steam and O2

Fluidized bed

Ash depressurization

. Fig. 40.15 Fluidized bed gasifier concept

. Fig. 40.16 Bubbling fluidized bed hydrodynamics shoing bubbles rising through the denser emulsions phase and splashing particles and clusters into the freeboard

where t is the time for complete conversion, rB is the coal particle density, 2 is 1/stoichiometric coefficient for O2, R is the particle radius, k is the combined kinetic and mass transfer rate constant, and CO2 is the concentration of O2 [35]. These units have moderate cold gas efficiencies and they accept a broad range of coals. Typical gas compositions are presented in > Table 40.11 for oxygen-blown gasification in

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Integrated Gasification Combined Cycle (IGCC)

Ash

Ash

Ash

Ash

Time

. Fig. 40.17 Particle time history in fluidized bed depicting the conversion of different size coal particles across the entire timescale due to mixing

. Table 40.11 Gas composition for oxygen-blown fluidized-bed gasifiers [36–39] Coal type

Lig

Bit

Pressure (atm) Gas composition (dry) CO CO2

1–30

30

31–53 6.7–19.5

52 5.3

H2 N2 CH4 H2S

32.8–40 0.3–1.7 0.3–3.1 0.44

37.3 0.3 3.5

a fluidized bed when using lignite and bituminous coal. > Table 40.12 presents air-blown gas composition data for the same coal types.

Examples of Fluidized Bed Gasifiers U-GAS®

The U-GAS® process is a fluidized bed gasifier incorporating a dry-feed system, as shown in > Fig. 40.18. It can operate on all coals and coal/biomass blends. It is highly efficient in either the air- or oxygen-blown configuration producing a non-slagging/bottom ash. There is presently a 30-year-license agreement with Synthesis Energy Systems (SES) in place. There is 20+ years of experience including plants in Shanghai, Finland, and Hawaii. Two plants are presently in operation producing 520 MWth Syngas. High-Temperature Winkler Gasifier

The High-Temperature Winkler Gasifier, shown in > Fig. 40.19, is a fluidized bed gasifier utilizing a dry feed and operating either in the oxygen or air-blown modes. It produces a dry bottom ash. It was developed to utilize lignite coal but is capable of efficiently

Integrated Gasification Combined Cycle (IGCC)

40

. Table 40.12 Gas composition for air-blown fluidized-bed gasifiers [37–39] Coal type

Lig

Bit

Pressure (atm)

1

5–30

Gas composition (dry) CO CO2 H2

22.5 7.7 12.6

12.54–30.7 6.4–4.47 14.4–28.56

55.7 0.8

47–54.3 0.2–3.59

N2 CH4 H2S

Coal

Syngas Cyclones Gasifier

Air /O2 / Steam

Fluidized bed

Air /O2 / Steam Bottom ash removal

. Fig. 40.18 U-GAS® process [7]

gasifying a broad range of feedstocks. The R&D is complete and has been marketed for waste materials as the Uhde PreCon® process. A demonstration plant shut down in 1997. It under went 20 years of testing for 67,000 operating hours gasifying 1.6 million metric tons dry lignite to produce 800,000 metric tons methanol.

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Integrated Gasification Combined Cycle (IGCC)

. Fig. 40.19 High-temperature Winkler gasifier [7]

Entrained Flow Gasifier Performance There are seven entrained flow gasifiers in the market place at this time. These are the ConocoPhillip’s E-Gas, GE (formerly Texaco), Shell Gasification Process (SGP), Prenflo™, Mitsubishi Heavy Industries (MHI), Siemens Fuel Gasification Technology, and Lurgi’s Multi-Purpose Gasifier (MPG) gasifiers. A general sketch of these units is depicted in > Fig. 40.20. In these gasifiers, widely dispersed very fine particles are radiantly heated to high temperature for slagging and rapid gasification. Some of the issues are: obtaining uniform feed, slurry drying, and separation of gas production from the heat recovery. The volume is determined from conversion time for average particle. These units have a relatively low cold gas efficiency and high O2 demand. Hydrodynamically, entrained flow gasifiers are quite simple with respect to the conversion of the coal particle and the reacting gas. They operate in a co-current manner with the solids and gas moving either in up flow or down flow, as shown in > Fig. 40.21, and are characterized as plug flow processes. The solids concentrations are less than 2% or 3% by volume and spend less than 10 s in the reactor. Nonuniform flow can occur, which can lead to poor bulk mixing, unreacted carbon, and hot spots. The conversion of a coal particle in an entrained flow gasifier is shown in > Fig. 40.22. The kinetic model to predict the burnout or total conversion of a coal particle in an entrained flow gasifier is t¼

2rB R 3kg C O2

Integrated Gasification Combined Cycle (IGCC)

40

Gasification products

Gaseous constituents

Oxygen or air

Coal and, petroleum coke.

Slag by-product

. Fig. 40.20 Typical entrained flow gasifier [7]

. Fig. 40.21 Hydrodynamics for entrained flow gasifiers

where t is the time for complete conversion rB is the coal particle density, 2 is 1/stoichiometric coefficient for O2, kg is the mass transfer rate constant, and C is the concentration of O2 [35]. These gasifiers can burn a fairly wide range of fuels when operated with a dry feed but are more limited when firing the fuel fed as a slurry since a large amount of energy is required to vaporize the water in the slurry. Typical gas compositions for these gasifiers are presented in > Table 40.13.

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Integrated Gasification Combined Cycle (IGCC)

Time

. Fig. 40.22 Bulk diffusion controlled conversion in entrained flow gasifiers

. Table 40.13 Typical gas composition for entrained flow gasifiers [38, 39] Oxygen blown Gasifier

Dry-entrained

Coal type

Brown/lignite

Slurry-entrained Sub-bit

Bit

Bit

Pressure (atm) 30 Gas composition (dry)

30

25–30

42

CO CO2 H2 N2

62.01 6.88 30.42 0.34

64.48 1.33 33.37 0.51

61.53–64.97 0.81–1.63 30.61–32.08 0.51–4.80

49.46 12.30 35.95 0.97

CH4 H2S

0 0.23

0 0.31

0 1.33–1.42

0.36 1.33

Examples of Entrained Bed Gasifiers GE Energy

The GE Energy gasifier shown in > Fig. 40.23 was initially developed by Texaco which became the Chevron–Texaco gasifier upon the merger of those two companies which eventually sold the technology to GE. The technology is a coal-water slurry fed, oxygenblown, entrained-flow, refractory-lined slagging gasifier. Two versions of the gasifier have been offered: gasifier with radiant cooler and a full quench gasifier with the latter taking precedence currently. The gasifier is good for bituminous coal, pet coke (petroleum derived coke), or blends of pet coke/low-rank coals. Commercially, GE Energy provides gasification technology in an EPC (engineer procure construct) alliance with Bechtel for guarantees on total IGCC plant. Presently, there are 64 plants operating, producing more than 15,000 MWth Syngas. There are six plants in the planning phases. ConocoPhillips E-Gas

The ConocoPhillips E-gas Gasifier shown in > Fig. 40.24 was originally developed by DOW Chemicals and demonstrated at the Louisiana Gasification Technology Inc. (LGTI) from 1987 through 1995. It is a two-stage gasifier with 80% of feed to first stage (lower). The gasifier is coal-water slurry fed, oxygen-blown, refractory-lined gasifier with

Integrated Gasification Combined Cycle (IGCC)

Oxygen from air separation plant

40

Coal slurry

Feed water

Radient syngas cooler Syngas High pressure steam “Black water” recycled Slag to recovery

. Fig. 40.23 GE energy gasifier [7]

continuous slag removal system, and dry particulate removal. The E-Gas process is good for a wide range of coals, from pet coke to PRB to bituminous and blends. Commercially, ConocoPhillips provides gasification technology and process guarantee. Project-specific EPC and combined cycle supplier alliances provide balance of plant components and guarantees. There is one 590 MWth Syngas plant operating and six plants in planning. Shell

The Shell gasifier, SGP, has its roots dating back to 1956 leading to their first demonstration facility in1974 [41]. In the Shell gasification process, coal is crushed and dried and then fed into the Shell gasifier as a dry feed. The gasifier, as shown in > Fig. 40.25, is an oxygen-blown, water-wall gasifier eliminating refractory durability issues. It is good for wide variety of feedstocks, from pet coke to low-rank coals and has been run on biomass as well. Commercially, Shell provides the gasification technology and has alliances with both Black and Veatch and Uhde to provide the EPC. There are 26 plants operating producing 8,500 MWth Syngas. There are 24 plants in planning. Siemens

The Siemens gasifier was initially developed in 1975 for low-rank coals and waste by Deutsches Brennstoffinstitut in Frieberg, Germany, and was first demonstrated at

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Integrated Gasification Combined Cycle (IGCC)

E-GasTM entrained-flow gasifier

Fuel gas

Second stage First stage

Coal slurry

Char

Oxygen (from air separation plant)

Slag/water slurry Slag by-product

. Fig. 40.24 ConocoPhillips E-Gas [7]

. Fig. 40.25 Shell gasifier [7]

Slag quench water

Integrated Gasification Combined Cycle (IGCC)

Fuel

40

Gas to pilot burner Oxygen

Burner Pressur. water outlet

Cooling screen

Pressur. water inlet Quench water Cooling jacket Gas outlet

Water overflow

Granulated slag

. Fig. 40.26 Siemans gasifier [7]

Schwarze Pumpe in 1984 at a thermal rating of 200 MW [34]. The technology was marketed under the name GPS by the Noell Group and later under the name Future Energy until purchased by Siemens in 2006. The gasifier, as shown in > Fig. 40.26, is a dry-feed, oxygenblown, top-fired reactor with a water wall screen in the gasifier. It is good for a wide variety of feedstocks, from bituminous to low-rank coals. Siemens provides the gasification island and power block. They recently were awarded $39 million contract for two gasifiers 500 MW each for China’s Shenhua DME (dimethyl ether) Project. Presently, there is one plant operating producing 787 MWth Syngas and they have one plant in planning. MHI Gasifier

The Mitsubishi Heavy Industries (MHI) gasifier is based upon the Combustion Engineering air-blown slagging gasifier and codeveloped between Combustion Engineering (and its subsequent owners) and MHI. As shown in > Fig. 40.27, it has a dry-feed system, suitable for low-rank coals having high moisture contents. It is an air-blown two-stage

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Integrated Gasification Combined Cycle (IGCC)

Coal gas + char

Char Reductor Coal

Coal Air

Combustor

Air

Molten slag

. Fig. 40.27 MHI gasifer [7]

entrained bed slagging gasifier utilizing membrane water-wall construction. There is one demonstration plant in operation producing 250 MWe and located in Nakoso, Japan. It started operations in September of 2007. PRENFLO™ Gasifier/Boiler (PSG)

The PRENFLO™ Gasifier/Boiler is a pressurized entrained flow gasifier with steam generation being marketed by Uhde. As shown in > Fig. 40.28, it is an oxygen-blown, dry-feed, membrane wall gasifier that is able to gasify a wide variety of solid fuels including hard coal, lignite, anthracite, refinery residues, etc. A demonstration plant in Fu¨rstenhausen, Germany gasified 48 TPD. The technology is used in the world’s largest solid-feedstock-based IGCC plant in Puertollano, Spain.

Transport Gasifier Kellogg, Brown and Root (KBR) has developed the transport gasifier at the Department of Energy’s (DOE’s) Power Systems Development Facility at Southern Company Services Wilsonville, Alabama plant. The transport gasifier (> Fig. 40.29) is based upon the hydrodynamic flow field that exists in KBR’s catalytic cracking technology. It has excellent gas–solids contact and very low mass transfer resistance between gas and solids. It has a highly turbulent atmosphere that allows for high coal throughput and high heat release rates at a low temperature that avoids problems with slag handling and liner erosion. Hydrodynamically, transport reactors are circulating fluidized beds which have more complicated hydrodynamics than fixed bed reactors or bubbling fluidized beds. In this type

Integrated Gasification Combined Cycle (IGCC)

40

Gas reversal chamber

Quench pipe

HP evaporator II HP evaporator I

Raw gas

Quench gas recycle 235°C

HP boiler

Transfer lines

HP vessel

Coal dust N2 O2/H2O

Immersion shaft Slag

. Fig. 40.28 PRENFLO™ [7]

of reactor, both excess gas and excess solids are fed to the reactor where the high gas velocity carries the solids upward. The excess solids tend to form clusters, which act like large particles and fall back into the lower riser where they break up and start to rise again. The results of an Eulerian–Eulerian simulation of the process is presented in > Fig. 40.30 where the deep blue is a gas void and the yellow and red areas are clusters moving down while the dispersed solids are moving up. These reactors have better mixing of gas and solids leads to better interphase transport and better conversion of the coal. In addition, the mechanical movement of the solids against each other essentially scrubs the ash from particles. Kinetically, because of the scrubbing of the reacted layer, the burnout or conversion follows a shrinking particle, as pictured in > Fig. 40.31. The conversion time can be calculated from the equation: t¼

2rB R kC O2

where t is the time for complete conversion, rB is the coal particle density, 2 is 1/stoichiometric coefficient for O2, R is the particle radius, k is the combined kinetic and

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Integrated Gasification Combined Cycle (IGCC)

Disengager

To primary gas cooler Cyclone

Riser

Mixing zone Coal Sorbent Air Steam Startup burner (Propane)

Loopseal

J-leg

Standpipe

Air / O2 steam

. Fig. 40.29 KBR transport gasifier. The Loopseal and the J-leg are nonmechanical valves designed to transfer solids but provide resistance to gas flows

mass transfer rate constant, and CO2 is the concentration of O2 [35]. These units have moderate cold gas efficiencies and they accept a broad range of coals. Typical gas compositions for three different coals from the experimental facility are presented in > Table 40.14.

KBR Transport Gasifier The KBR transport gasifier shown in > Fig. 40.32 operates in either oxygen or air-blown configurations. It operates air blown for power generation and oxygen blown for liquid fuels and chemicals. It has a high reliability design based on years of designing and building FCC (fluidized catalytic cracking) units for the petroleum industry. It is a nonslagging gasifier with no burners and utilizes a coarse, dry, low-rank coal feed. Presently, there is a 560 MWe IGCC with a 2  1 combined cycle being designed for the Mississippi Power Company in Kemper County, MS in design.

Integrated Gasification Combined Cycle (IGCC)

40

. Fig. 40.30 A 2-dimensional view of clustering in the riser of a circulating fluidized bed hydrodynamics depicting the solid fraction where red pixels represent solids fraction of 0.6 and navy blue is a solids fraction of 0

Ash

Ash

Ash

Ash

Time

. Fig. 40.31 Particle time history in circulating fluidized bed riser depicting particle size reduction and ash sloughing off as conversion proceeds

Carbon Capture Technologies Conventional Acid Gas Control Technologies Acid gas control technologies remove the sulfur and/CO2 from the syngas. There are a number of commercial technologies that can be classified as physical sorbents, chemical sorbents, and single species processes. Physical sorbent processes are known by their commercial names: Rectisol, Selexol™, Purisol™, and Morphysorb™. Chemical sorbents are represented by MDEA (methyldiethanolamine) and other amines. There are two

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Integrated Gasification Combined Cycle (IGCC)

. Table 40.14 Typical gas analysis from the transport gasifier pilot plant [42] Coal type Mode

Subbituminous

Lignite

Air

Oxygen

Air

Oxygen

Air

Oxygen

Pressure (atm)

30

30

30

30

30

30

39.1 19.9 36.2

18.8 11.7 14.8

37.9 21.8 37.4

13.3 13.4 15.7

25.5 28.6 41.9

0.1 4.8

53.2 1.6

0.1 2.9

55.6 2

0.1 3.9

Gas composition (dry) CO 23.7 CO2 7.6 H2 11.8 N2 CH4

54.3 2.6

Bituminous

Primary Cyclone Disengager

Hot-gas filter Vessel and Ash hopper

Bed Material Charge Hopper Dip leg Standpipe Coal feed Hopper

Steam Superheater

Quench Systems

Air Preheaters L-valve Steam Manifold EERC MS18902. CDR

. Fig. 40.32 Schematic of KBR transport gasifier

commercial single species processes: Crystasulf ™ for sulfur control and FluorSolvent™ for CO2 control. A general schematic of an IGCC power plant with a desulfurization– decarbonization process is shown in > Fig. 40.33 [43]. This particular configuration is the preferred configuration when using one of the physical sorbents like Selexol™ as shown

Integrated Gasification Combined Cycle (IGCC)

40 Sulfur

Cryogenic ASU

Oxygen coal

Gasifier *GE/Texaco *CoP/E-Gas *Shell

Syngas cooler/quench

Sulfur recovery

Steam

Steam

Cl, PM removal

Water gas shift

Syngas cooler

2-stage selexol Fuel Gas Reheat/ Humid.

CO2 CO2 Comp.

N2 Dilution 2

3,100 kN/m 3 4,470 kJ/m

Combined cycle power island

CO2 15,200 kN/m2 90km Pipeline

CO2 storage

Gross Power (MW) 2 Comb. Turbines: 464 1 Stm. Turbine: 200-300

. Fig. 40.33 Pre-combustion current technology IGCC power plant with CO2 scrubbing (Adapted from [43])

and a sour shift. The advanced warm desulfurization technologies being developed by DOE are more efficient, use a sweet shift process, and then finally remove the CO2. There are many configurations that can be assembled to achieve a site-specific optimum design. The plant configuration in > Fig. 40.33 utilizes an oxygen stream of 95% purity produced from a cryogenic air separation unit (ASU). No air extraction from the syngas combustion turbine. It produces 1,800 psig, 537 K superheated steam with a single 535 K reheat. The CO2 is captured at high pressure from a relatively low syngas volume and produces CO2 at high pressure, which is then boosted to 15,200 kN/m2 for sequestration.

Physical Sorbent Processes The physical sorbent processes are known by their commercial names: Rectisol®, Selexol™, Purisol™, and Morphysorb®. These systems operate at low temperature with Rectisol® operating at 40
C. As one would expect, there is a large heat penalty paid for using these processes, but the level of purity achievable warrants and pays for that expense – particularly when producing high value chemicals. Rectisol®

The Rectisol® is a physical acid gas removal process using an organic solvent (methanol) at subzero temperatures, nominally 40
C. It can purify synthesis gas down to very low total sulfur and CO2 levels. The main advantages of the process are the rather low utility consumption figures for regeneration as compared to the chemical sorbents, the use of a cheap and easily available solvent, and the flexibility in process configurations. With regard to performance, the Recitsol® process is capable of achieving total sulfur (H2S + COS) in the 0.1–1 ppm range, CO2 levels in the 10–50 ppm range, and limit the

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Integrated Gasification Combined Cycle (IGCC)

H2S

Feedgas

H2S Stripper

Methanol

Absorber

CO2 Stripper

Flash Tanks

Tailgas CO2

Stripping gas

Syngas

. Fig. 40.34 Basic flow diagram/process scheme for Rectisol® (Adapted from [44])

H2S in CO2 by-product to levels on the order of 5 ppm. Further detail can be found in review articles [44–48]. The simple process flow diagram is displayed in > Fig. 40.34. The syngas is mixed with methanol and enters the absorber column where H2S, COS, and CO2 are absorbed. The pure or cleaned syngas leaves the top of the column where it passes through a heat exchanger to cool the incoming syngas and methanol mixture. The CO2 and sulfur compounds are removed in separate fractions as the solvent flows through a two-stage stripper. A pure CO2 product is recovered from the top of the first stripper after passing through a heat exchanger to help cool the incoming syngas and methanol mixture. An H2S/COS-enriched Claus gas fraction is recovered from the top of the second stripper and passes through a heat exchanger to help cool the incoming syngas and methanol mixture. CO2 capture with Rectisol® scrubbing is based on low temperature (refrigerated methanol  40
F or
C), which is capable of deep total sulfur removal as well as CO2 removal. It is the most expensive AGR process giving the deepest cleaning. It is predominantly used in chemical synthesis gas applications where total sulfur requirements are less than 0.1 ppmv. It has been proposed for use in IGCC for CO2 removal but no published cost studies presently exist. Selexol™

The Selexol™ process uses a physical solvent to remove acid gas from streams of synthetic or natural gas. The process may be regenerated either thermally, by flashing, or by stripping gas. The Selexol™ process is ideally suited for the selective removal of H2S and other sulfur compounds, or for the bulk removal of CO2. The Selexol™ process uses Union Carbide’s Selexol™ solvent, a physical solvent made of a dimethyl ether of

Integrated Gasification Combined Cycle (IGCC)

40

CO2 absorber

CO2 rich

H2S absorber

20 atm Flash

CO2 rich selexol

11 atm Flash 3.4 atm Flash 27 atm

Reabsorber H2S/CO2 rich

H2S concentrator

Purge

To claus Acid gas stripper

Steam

. Fig. 40.35 Selexol™ process flow chart (Adapted from [49])

polyethylene glycol (DPG or DEPG or DMPEG). The Selexol™ solvent is chemically inert and is not subject to degradation. The Selexol™ process also removes COS, mercaptans, ammonia, HCN, and metal carbonyls. This process allows for construction of mostly carbon steel due to its nonaqueous nature and inert chemical characteristics [46, 47, 49–51]. The Selexol™ process can be tailored for either bulk or trace acid gas removal. Because of the staged separation of acid gases (> Fig. 40.35), Selexol™ is primarily used in the following applications and markets: 1. Selective removal of H2S and COS in integrated gasification combined cycle (IGCC), with high CO2 rejection to product gas (85% +) and high sulfur (25–80%) feed to the Claus unit 2. Selective removal of H2S/COS plus bulk removal of CO2 in gasification for high-purity H2 generation for refinery or fertilizer use 3. Treatment of natural gas to achieve either LNG or pipeline specification with dewpoint reduction The Selexol™ process was introduced over 30 years ago. It has been and continues to be the dominant acid gas removal system selection in gasification project awards within the past several years. A process flow diagram for a Sexol process for a gasification plant to remove CO2 is shown in > Fig. 40.36. It has two absorber tower stages. The first stage is for removing

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Integrated Gasification Combined Cycle (IGCC)

Treated gas

CO2 absorber

Acid gas CO2

Accumulator

Stripper Filter

Sulfur absorber Feed gas

Water Reflux pump

Concentrator

Water Reboiler

Exchanger

. Fig. 40.36 Selexol™ scrubbing for CO2 capture (Adapted from [51])

H2S and the second is for removing the CO2. The H2S is separated from the solvent in an acid gas stripper column while the CO2 is removed from the solvent in a series of Flash drums. Selexol™ has a number of beneficial properties. It is a physical liquid sorbent, capable of having high loadings at high CO2 partial pressure levels. It is highly selective for H2S and CO2 such that there is no need for a separate sulfur capture system. A big advantage of Selexol™ and other physical sorbents is that there is no heat of reaction (DHrxn) with only a small heat of solution. The Selexol™ sorbent is chemically and thermally stable and has a low vapor pressure – keeping losses to a minimum. There is 30+ years of commercial operating experience on 55 plants worldwide. Selexol™ does have a couple of disadvantages. Namely, it requires gas cooling to about 35
C (100
F) and it requires considerable heat for CO2 regeneration by flashing. Purisol™

The Purisol™ process is a second acid gas removal process developed by LURGI. It uses normal methyl pyrrrolidone or NMP as the solvent. Its operating conditions and overall process configuration are similar to that of Selexol™, however, it is not as widely used. Additional information can be found elsewhere [45, 46]. Morphysorb®

Morphysorb® is a proprietary solvent CO2 removal process developed by GTI and owned by both GTI and Uhde. It uses N-formyl morpholine/N-acetyl morpholine mixtures

Integrated Gasification Combined Cycle (IGCC)

N-formyl-morphoine (NFM)

N-acetyl-morphoine (NAM)

O

O

H2C H2C N HC=O

CH2

H2C

CH2

H2C

40

CH2

CH2 N H3C-C=O

. Fig. 40.37 Morphysorb® chemicals

(See > Fig. 40.37). It can be used for both bulk or trace removal of acid gas components in subquality natural gas upgrading to either pipeline or LNG specification, selective removal of H2S from natural/synthesis gas for generation of acid gas stream suitable for Claus plant feed, and selective removal of H2S, CO2, COS, CS2, mercaptans, and other components from coal/oil gasification syngas at IGCC facilities [52, 53]. Morphysorb® offers a number of benefits relative to chemical and some other physical sorbents. It has higher solvent loading, which leads to either lower circulation or higher throughput. It has lower co-absorption of hydrocarbons, which translates into fewer losses or in other words, less recycle gas flow for recovery of these hydrocarbons. It has lower CO and H2 absorption. It assists in the hydrolysis of COS. It is low in corrosivity, and thereby low environmental hazard as well as low capital and operating costs. There is one natural gas commercial application owned by Spectra Energy Transmission, which was started in late 2002. It processes 450 MMscfd after a plant expansion of 50%. The solubility of the mophysorb® sorbent is presented in > Fig. 40.38.

Chemical Sorbents There are a number of chemical sorbents that have been used for acid gas control. All of these fall into the chemical category called amines. Primary, secondary, and tertiary amines have all been used (> Fig. 40.39). Primary amines are monosubstituted ammonia like monoethanolamine (MEA). Secondary amines are bi-substituted ammonia like diethanolamine (DEA). Tertiary amines are tri-substituted ammonia like methyldiethanolamine (MDEA). The process flow diagram for a typical amine-based process is shown in > Fig. 40.40. The absorption of acid gases (H2S, SO2, CO2) in amine solution is conducted with a twocolumn operation. The acid gas is absorbed in the first column. The second column is used to regenerate the amine. The process relies on countercurrent flow to achieve optimum mixing. A lean solution (low acid gas) enters the top of the absorber and flows to the bottom while acid gas enters the bottom of the absorber tower and bubbles

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Integrated Gasification Combined Cycle (IGCC)

40 °C 40 10 °C Pressure (atm)

1594

30

20 DMPEG Morphysort

10

0 0

0.20 0.25 0.1 0.15 Capacity (m3/L solvent @ STP)

0.05

0.3

0.35

. Fig. 40.38 Morphysorb® CO2 solubility [52]

Primary amines

HO

H

H

C

C

Secondary amines

HO

H

CH2

Tertiary amines

CH2

HO N

N

H H H Monoethanolamine (MEA)

HO

CH2

H

CH2

CH2 N

CH2

HO

Diethanolamine (MEA)

CH2

CH3

CH2

Methyldiethanolamine (MDEA) H H

HO

H

H

C

C

H

H

O

H

H

C

C

H

H

Diglycolamine (DCA)

H N H

H H H H H H

CC C

OH

NH

HO

CH2 CH2

HO

CH2 CH2

C CC

N OH

H H Diisopropanolamine (DIPA)

. Fig. 40.39 Commonly used amine-based chemical sorbents

CH2 CH2

Triethanolamine (TEA)

OH

Integrated Gasification Combined Cycle (IGCC)

40

Sweet gas Acid gas

Trim cooler

Absorber

Stripper Sour gas

Flash tank

. Fig. 40.40 Process flow diagram of a typical amine treating process used in industrial plants

to the top. The rich amine (high acid gas) liquid enters the stripper where the acid gases are released and the ‘‘clean’’ amine is returned to the absorber. The acid gases exit from the top of the stripper. The MEA/DEA/MDEA is regenerated in the stripper column. It is beneficial to be sure the amine concentration is at proper level in order to optimize the H2S, SO2, CO2 removal. The final amine concentration can be controlled by the adding amine makeup. Additional information can be found on line [48]. Single Species Processes CrystaSulf ®: Sulfur Control

The CrystaSulf® process for direct treatment of sour gas can be used for recovering sulfur from gas streams that contain as little as 0.2–25 LPD of sulfur, which have historically been problematic. In this size range, the operating costs of throwaway H2S scavenging chemicals are too high, and traditional amine/Claus approaches are unwieldy and capital intensive. Aqueous-iron redox systems showed promise in this range, but often proved unacceptable because of their operating problems. Therefore, the new breakthrough sulfur recovery technology, CrystaSulf®, which can remove sulfur economically without the operating problems of aqueous-iron systems for plants of this size. Using a gentle SO2 oxidant, CrystaSulf® converts inlet H2S to elemental sulfur. Elemental sulfur is soluble in the CrystaSulf® solution; thus, there is no danger of sulfur plugging high-pressure equipment that plagues aqueous-iron systems. Meeting pipeline H2S specifications is easy, and CO2 has been shown to have no effect on the CrystaSulf® process [54]. The process has a number of advantages, particularly for these medium-scale systems. It has lower capital cost, lower overall treatment cost, and much lower maintenance and clean-out costs. It can directly treat high-pressure streams with a solids-free solution which is easy to pump and requires a very low circulation rate. The nonaqueous solvent has high solubility for elemental sulfur and therefore has no sulfur particles in circulating liquor and needs no sulfur settling additives or surfactants. It avoids problems of foaming

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and plugging associated with aqueous-iron redox system. It produces large sulfur particles in a crystallizer that separate and purifies easily, yielding a much higher sulfur purity product than possible with aqueous-iron redox systems. A process flow diagram for the process is shown in > Fig. 40.41. The Fluor Solvent process has significant advantages over an amine-treating process in an offshore environment when treating large gas volumes where the CO2 partial pressure is high. The Fluor solvent process configuration is much simpler. It requires no heat for solvent regeneration. It requires no makeup water. It produces a dry product gas. The solvent is minimally corrosive, resistant to foaming, and biodegradable. The chemical structure is shown in > Fig. 40.42. Fluor Solvent: CO2 Control

Sweet gas Lean solution Absorber

Vent

Sour gas

SO2 absorber

Vent Heat Flash tank

SO2 enriched

Crystallizer

Cool

Filter Air Sulfur

. Fig. 40.41 Process flow diagram for Crystasulf ® process

CH3

CH

CH2

O

O C O

. Fig. 40.42 FLUOR solvent chemical structure

Burner

Integrated Gasification Combined Cycle (IGCC)

40 CO2

Recycle compressor Absorber

Flash drums

Treated gas

Feed gas

Water Condensate

Turbines Circulation pump

. Fig. 40.43 FLUOR solvent process schematic (Adapted from [55])

> Figure 40.43 shows the configuration of the Fluor solvent process for low-tomedium CO2 content applications [55]. The process consists of an absorber and two flash drums. A pressurized flash drum with low-, medium-, and high-pressure zones and a vacuum flash drum with zones at atmospheric pressure and at vacuum.

Future Directions in Research and Development Recent Gasification Systems Studies The use of advanced gasification power systems were identified as the most favorable coal alternative for reducing carbon dioxide emissions [56]. The cost of capturing 90% of the carbon dioxide from a coal gasifier was compared with coal combustion in both conventional and new ultra supercritical steam systems, and natural gas fired power systems. The capital, operating, and maintenance costs were evaluated for a green field 640 MWe power plant based upon reasonable process design alternatives for each. Without carbon capture both IGCC and pulverized coal combustion (PC) can achieve 39% efficiency based upon the high heating value (HHV) for bituminous coals and meet or exceed 2010 environmental requirements. Available commercial capture technology can remove 90% of CO2, but at significant increase in cost of electricity (COE). The total IGCC plant cost was found to be 20% higher than pulverized coal (PC), but with carbon capture and

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Integrated Gasification Combined Cycle (IGCC)

sequestration the total for PC exceeded that of IGCC With carbon capture and sequestration, IGCC was the lowest coal-based option (in 2007 dollars) [56]: ● Natural gas combined cycle: 96 mills/kWh ● IGCC: 105 mills/kWh (average) ● PC: 116 mills/kWh (average) where 1 mill is equal to 0.001 USD. Gasifiers have lower product gas volume in the fuel gas stream as compared to the flue gas from coal and natural gas combustors. The carbon footprint for various coal gasification scenarios has been considered using a life cycle analysis [57]. Life cycle analysis considers the energy and costs required from cradle to grave including mining, mine reclamation, transportation, mineral preparation, processing, waste disposal, sequestration, and monitoring of the wastes. Coal biomass mixtures were considered in various power systems and compared against a baseline natural gas power system. Gasification with biomass coal co-firing was found to be able to match natural gas performance. It was found that a combination of gasification and biomass co-firing when used with shift cleanup and sequestration, could dramatically reduce the carbon footprint relative to natural gas.

Gasification R&D The U.S. Department of Energy is involved in a wide range of research, development, and demonstration (RD&D) activities to improve the fuel and product versatility, process efficiency, and system. The challenge is to achieve widespread market penetration in the most large-scale markets including power generation, chemical processing, and gas and liquid synthesis. The program goals are to improve gasifier efficiency and process control; improve process train reliability, reducing downtime and expenses from redundant process components; and improve the flexibility of gasification processes to handle a wider variety of grades and types of feedstocks. Research is being funded on the capture and sequestration of carbon dioxide (CO2). The DOE’s Office of Fossil Energy conducts the Gasification Technologies Research and Development (R&D) Program. The focus of the Advanced Power Systems Program is on electricity production and its intent is to foster public–private partnerships and provide technology to utilize the extensive U.S. fossil fuel resource. Having collaborated with industry over the decades of the 1980s and 1990s to bring coal gasification to commercial-scale demonstration plants, the emphasis is now shifting to refining and expanding gasification potential to bring the technology to its potential as a near-zero emission clean coal technology. The Gasification Technologies R&D Program consists of four distinct areas: (1) adapt gasification technologies to a range of coal feedstock varieties, more tightly control gasifier performance and gas production, and improve overall efficiency; (2) cleanup of produced gases to meet increasingly stringent environmental standards; (3) better separate product gases and oxygen from air to improve economics, efficiency, and facilitate gas cleanup; and (4) identify economic and infrastructure issues with various gasification applications [58].

40

Integrated Gasification Combined Cycle (IGCC)

Advanced Gasification Fuel Feed System • All ranks of coal • Solid or slurry • Injector reliability

Coal

Air Separation O2

• Membrane durability • Process integration • No nitrogen in product

Gas Separation Capture, Storage

Syngas Separation (and Warer-Gas- Shift)

Feed Water

CO2 Gasifier • Single train reliability • Refractory materials durability • Alternate High designs Pressure

Clean Syngas CO/H2

CO, H2

Fuels, Chemicals, Power

Shift Reactor, Converter • Membrane durability • Low flux • Contaminant sensitivity • Heat removal

Gas Cleaning

Steam

Raw Syngas

Instrumentation & Control • Durability • Accuracy • On-line temperature measurement Slag Residue Overall Systems:

Process By-Products Heat Exchangers, Scrubbers, Filters • Mild temperatures • Multi-contaminant control • Near-zero emissions • Process Integration & Intensification

• Reduce capital, operating & maintenance costs • Maintain or increase reliability • Increase integrated process efficiency

. Fig. 40.44 Gasification research and development areas and major technology issues

The key issues identified in the U.S. DOE’s programs are listed in each of these research areas in > Fig. 40.44. Gasifiers need to be able to operate efficiently on lower grade fuel feedstocks including low rank, high mineral contents, and biomass. In order to be efficient in using these resources, utilities must be able to introduce these lower quality fuels into gasifiers without using quantities of water in excess to what is required for rapid gasification. Otherwise, the large latent heat of water vaporization will increase the inefficiencies due to unrecoverable heat losses. The reliability of the solid fuel feed system has historically been the single most frequent cause for unplanned shutdown in coal-fired systems. Lack of reactor availability due to downstream fouling, refractory failures, and

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Integrated Gasification Combined Cycle (IGCC)

loss of the solids fuel feed systems are being addressed by research on fly-ash formation, refractory durability, alternative gasifier concepts, as well as improved diagnostics, instrumentation, and control systems.

Gas Cleanup and CO2 Capture Research Gas cleaning systems research funded by the U.S. DOE includes improving heat exchangers, scrubbers, and filter technologies. For example, researchers at the Power System Development Facility have demonstrated improvements in particulate filtration reliability, filter element durability, and developed fail safe devices to insure removal of particulate matter to protect downstream turbines and cleanup systems [59, 60]. One research goal is to intensify and better integrate cleaning processes by taking steps where possible to develop multicomponent cleanup systems thereby reducing the number of process units. Alternative gasifiers such as the transport reactor employ milder temperatures, which reduce the severity of the environment with which the process materials must survive. These milder temperatures allow the use of more robust cleanup technologies. Research is being supported on gas separations in order to remove, capture, and sequester CO2. Commercial cryogenic air separation units have the greatest share of the oxygen production from air separation; however, the energy-intensive nature of this process has targeted this process operation as having a high potential for improvement. In addition to developments in cryogenics, leading alternatives include pressure swing absorption and membranes. Gas separations are also critical to gas cleanup and to tailor the product distribution. In a zero-emission gasifier power plant, the product syngas is shifted to CO2 and H2 and the CO2 must be separated from the mixture. Shift reactors utilize the water gas shift reaction (see above) and catalytically convert the product distribution in the direction desired. Shift reactors employed in gasifier facilities such as the Great Plains Gasification facility in North Dakota are required to alter the H2/CO ratio from 1.5:1 produced in the gasifier to 3:1 to optimize production of synthetic natural gas (CH4, methane). The process demands (selectivity and yields) are different to produce H2 as a clean burning fuel. Research is also needed to improve the separation systems at the elevated temperatures and pressures consistent with water gas shift catalysts operations. Contamination of membranes and other separation systems are potential poisons potentially damaging sorbents and catalysts. A recent review of some novel methods for CO2 separations includes electrochemical pumps, membranes, and chemical looping [61]. Chemical looping is a process in which the oxidant in a combustor or gasifier is supplied from a metal oxide rather than using oxygen from air. The metal oxide is thereby reduced by reaction with the hydrocarbon fuel. After the oxidizing the fuel, the reduced metal oxide is transferred to an air reactor where it is reoxidized. The metal oxide can then be cycled back into the fuel reactor to complete the loop. The result is a flue gas from the fuel reactor without nitrogen and concentrated in carbon dioxide. The air reactor produces a vitiated air stream (i.e., air partially depleted in oxygen). A variety of metals have

Integrated Gasification Combined Cycle (IGCC)

40

been proposed including nickel, calcium, iron, and copper. Economic analyses have indicated very promising results [62]. Increasing regulatory limits on the release of CO2 could give gasification a competitive advantage in future markets. Gasification has a distinct economic advantage over competing technologies in capturing and sequestering CO2 from process streams. Acid gas cleanup systems presented above have been traditionally used to remove trace pollutants such as sulfur, but the scale required to remove one of the principal gases, that is, CO2, from utility-scale gas streams elevates the need to significantly increase the efficiency and reduce the cost of the process. The U.S. Department of Energy’s research goals keep the cost of removing 90% of the carbon from the product gas stream to less than 30% increase over the cost without carbon capture. What was considered acceptable energy costs when removing trace pollutants becomes onerous when scrubbing out 15% of the gas stream. CO2 sorbent or solvents operate by absorbing carbon dioxide at low temperature, transferring the sorbent to a regenerator and releasing the carbon dioxide by increasing the temperature. This is known as a temperature swing absorption and regeneration process. Amines form an ionic bond with acid gases such as carbon dioxide. Traditional scrubbing is conducted in aqueous or methanol solutions, however, these liquid processes lose significant quantities latent heat of vaporization of these liquids. Methods to improve heat integration, increase heat exchange, and reduce latent and sensible heat losses are under investigation. Low-volatile ionic liquids (mostly amines) and solid-supported amines are being developed to optimize these processes. After surveying the performance in terms of capacity and absorption rates of over 100 solidsupported sorbents, several very promising sorbents were identified for use in flue gas. The sorbent capacity target of over 2 moles of CO2 per kg of sorbent [63] was achieved using a polyamine bonded to a mesoporous silica developed at NETL [64]. This sorbent is currently being evaluated in a circulating fluidized bed process at a 1 kW scale on a utility slip stream.

Acknowledgments The authors would like to express their gratitude to the U.S. Department of Energy in making resources and the time available to prepare this manuscript. In addition we would also like to extend appreciation to Peter Smith, Ranjani Siriwardane, Esmail Monazam, Tom O’Brien, and Mehrdad Shahnam for their contributions.

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41 Conversion of Syngas to Fuels Steven S. C. Chuang FirstEnergy Advanced Energy Research Center, Department of Chemical and Biomolecular Engineering, The University of Akron, Akron, OH, USA Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1606 Reaction Pathway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1608 The Nature of Active Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1612 Circumventing Fischer–Tropsch Chain Growth Kinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . 1613 Ethanol Synthesis Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1615 Hydrocarbon Synthesis Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1617 Reactor Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1618 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1619

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_41, # Springer Science+Business Media, LLC 2012

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Abstract: This chapter examines the reaction pathways and the selectivity of the catalysts for the conversion of syngas to liquid hydrocarbons and ethanol fuels. Rh is by far the most active catalyst for ethanol synthesis. Co- and Fe-based catalysts exhibit excellent activity for hydrocarbon fuel synthesis from high H2/CO and low H2/CO ratio syngas, respectively. Regardless of the differences in the catalyst selectivity, all of these CO-hydrogenation catalysts produce methane as one of the major products. So far, no approaches are effective in suppressing CH4 formation. Development of a costeffective liquid-fuel process from syngas with a low net fuel cycle CO2 emission requires consideration of (1) the overall system, including the source of raw materials and byproducts and (2) analysis of carbon footprint of each step from raw materials to the desired products and undesired by-products.

Introduction Synthesis gas (syngas), a mixture of CO and H2, has long been recognized as an important building block for manufacturing a wide range of chemicals and liquid fuels [1, 2]. > Figure 41.1 illustrates the pathways from raw materials (i.e., coal, natural gas, and biomass) to syngas and syngas to liquid fuels. Syngas can undergo the water–gas shift reaction to produce high purity H2 and the reversed water–gas shift reaction to produce high purity CO. Individual CO and H2 are important precursor for a number of reaction processes such as ammonia synthesis, carbonylation, and hydrogenation. The driving force for the development of syngas to liquid fuel and chemicals has been mainly from the cost of crude oil and natural gas. Growing concerns on the effect of CO2 on climate changes and the potential for stringent regulations on CO2 emission demand consideration of the carbon footprint (i.e., a measure of the total quantity of all greenhouse gases emitted by a specific entity or process over a period of 1 year) of producing, distributing, and using liquid fuels. Liquid hydrocarbon fuel is the dominant form of the transportation fuel of which combustion produces more than 19 lb of CO2 per gal of the fuels [3]. It is very unlikely that a cost-effective approach could be developed for capture of CO2 produced from the use of transportation liquid fuels. The use of coal- and natural gas-derived transportation fuels will lead to a net fuel cycle CO2 emission. In contrast, the use of biomass, which is produced from the photosynthesis reaction of CO2 with H2O, has been expected to lower the net fuel cycle CO2 emission, given similar level of carbon footprint of producing the liquid fuels [4]. The key differences in raw materials (i.e., coal, natural gas, and biomass) and their usage include the hydrogen to carbon ratio, contaminants, and cost. These different characteristics have a significant impact on the net fuel cycle CO2 emission. Biomass is generally considered as an environmentally benign fuel; biomass has also been misconstrued as a fuel with zero net fuel cycle CO2 emission. However, biomass suffers from low energy density and the diversity of its sources. The latter introduces the complexity of preprocessing steps which require the sophisticated control of gasification and syngas clean up processes. The extent of lowering carbon footprint of using

Conversion of Syngas to Fuels

41 Fuel

Natural gas/coal Syngas production

Fischer-Tropsch synthesis

Biomass

Separation

Cracking

Separation Chemical

. Fig. 41.1 Syngas production and conversion pathways

biomass-derived fuel can only be determined from careful analysis of the energy usage in collection, preprocessing, syngas generation, and clean up. A recent study has shown that coupling use of coal and biomass as a feedstock with (1) electricity and liquid-fuel production and (2) CO2 capture and storage could be a promising approach for the production of liquid fuels with a low net fuel cycle CO2 emission [4]. The primary use of syngas has been in methanol synthesis and Fischer–Tropsch (FT) synthesis. Methanol can serve as a fuel or a precursor for the synthesis of many industrial chemicals. Hydrocarbons and oxygenates from the FTsynthesis can serve as an excellent clean fuel – an alternative to petroleum-based fuel because it is free of sulfur and nitrogen compounds commonly present in the petroleum-based fuels. This chapter will focus on direct synthesis of hydrocarbons and oxygenates from synthesis gas on heterogeneous catalysts. Direct synthesis of hydrocarbons and oxygenates from syngas has been a subject of extensive studies due to its importance in the production of liquid transportation fuels. The syngas reaction process (i.e., CO hydrogenation) was first reported on nickel catalysts, producing methane at 1 atm (0.1 MPa) and 200–300
C (473–573 K) [2]. Increasing reaction pressure and replacing Ni with Co leads to the formation of liquid hydrocarbons. Further increasing reaction pressure and temperature to 150 atm and 450
C on alkalized Fe catalysts leads to the formation of oxygenates. Extensive studies have shown that Group VIII metals and some of their sulfides are active catalysts for CO hydrogenation [5–10]. FT synthesis, methanol synthesis, and ethanol synthesis involve the use of the same reactants, CO and H2. Each of these syntheses is a subclass of CO hydrogenation reactions. The development of the synthesis process such as CO hydrogenation reaction generally involves a sequence: thermodynamics, catalyst preparation, mechanistic study on a molecular scale, kinetics studies on a micro-reactor, scale-up of the reactor on a macroscale, and system integration, shown in > Fig. 41.2. An effective catalyst development strategy must take both physical and chemical characteristics of the catalytic process into account, considering the active sites, reaction pathways, catalyst shape, pore structure, and the reactor type. The thermodynamics of the synthesis reaction can be easily calculated and have widely been reported [11]. The reactions for producing hydrocarbons and oxygenates are highly thermodynamically favorable, except for methanol. DG, the change in Gibbs free energy for the formation of Cn product (i.e., the species containing n number of carbon atoms), decreases as the product carbon number increases. Most scientific literature on this synthesis reaction can be classified into three areas: (1) mechanistic studies for elucidation of catalytic reaction mechanisms, i.e., reaction pathways and the nature of active sites [12], (2) catalyst preparation, characterization, reaction kinetics studies [13],

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Conversion of Syngas to Fuels

Fluidized bed reactor ~1 m System integration Autoclave TT Reactor design 20 cm 10–15 mm

Heat and mass transfer

2–4 mm

10 μm

Characterization

Spectroscopy Mechanistic study

Oxide support

10−10 Å

10−6 µm

10−3 mm

10−2 cm

1 m

Log Scale [m]

. Fig. 41.2 The relationship among different levels of catalytic process research and development

and (3) reactor modeling [14]. The catalytic reaction steps have been shown to occur in sec scale [15]; the reactor process in min scale, depending on the reactant residence time. This chapter will elaborate on our current understanding of the reaction mechanism, discuss the approach for preparation of durable catalysts, and touch on the reactor modeling and scaling up issues.

Reaction Pathway The reaction pathway and selectivity for hydrocarbon and oxygenate formation from the CO hydrogenation are governed by reaction conditions and catalyst compositions. A summary of these catalysts and a description of their typical selectivities are given in > Table 41.1. The reason for the formation of a wide range of C1 to Cn products (i.e., C1: methane, methanol; C2 ethylene, ethane, ethanol, and acetaldehyde; C3: propylene, propane, propanol, propionaldehyde, and acetone, Cn: species containing n number of carbon atoms) can be traced to the polymerization and network characteristics of the reaction which consists of a large set of parallel and series reaction pathways, shown in > Fig. 41.3.

Conversion of Syngas to Fuels

41

. Table 41.1 Typical product selectivity of various CO hydrogenation catalysts Key catalyst component

Selectivity

I. Group VIII metals Fe, Co

Linear and branched hydrocarbons: alkanes/alkenes; and oxygenates: 1-alcohols, aldehydes, esters, ketones [16–18] Methane, hydrocarbons, and polyethylene at high pressures [19]

Ru Ni and Pt Rh

Methane, low carbon-number hydrocarbons C2 oxygenates, including ethanol, acetaldehyde, and acetic acid [20, 21] Methanol [22]

Pd II. Mixed oxides Zn oxide Cr oxide Th oxide

[23] Promotes methanol and ethanol formation on Rh Methanol and branched alcohols (C4) Hydrocarbons: branched alkanes; and oxygenates: methanol (CH3)2O, branched alcohols Cu/Zn Oxide Methanol Alkali – Cu/Zn oxide Methanol and higher alcohols [24] CuCoCr0.8 K0.09Ox (an IFP catalyst) Branched higher alcohols

III. Coprecipitated Ni-based catalysts Na-Ni Alkali-Mn-Na

[25]

IV. Mo-based catalysts Mo Alkali-Mo sulfide Alkali-K-Co-Mo

[27] Hydrocarbons C1–C5 linear, primary alcohols C1–C4 alcohols [28]

Methane Methane, acetaldehyde [26]

Depending on the types of metals and metal oxides, listed in > Table 41.1, as well as their surface state and structure, these catalysts are able to catalyze each rate of the steps in the reaction network to a certain extent. CO dissociation :  CO !  C þ  O (41.1) ∗

CO: adsorbed CO; ∗C: surface carbon;  O: adsorbed oxygen Hydrogenation :  C þ x  H !  CHx  ∗



(41.2)



CO þ x H ! CHx O

∗

(41.3)

∗

x = 2 or 3. CH2: adsorbed methylene; CH3: adsorbed methyl; H: adsorbed hydrogen. Chain growth :  CHx þ  CH3 !  C2 Hxþ3 





CHx O þ CH3 ! C2 Hxþ3 O

(41.4) (41.5)

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Conversion of Syngas to Fuels

C2H4 (g) CH4 (g) H2O (g) CO2 (g) ∗CO

2∗H

∗H ∗H

∗CHX

∗CH2

C3H6 (g)

∗H

−H

∗C2HX

C3H8 (g) ∗H

–H ∗CH2

∗C3HX

∗CH2

etc.

∗O + ∗C −H2O

−H2O −CO

CO (g)

C2H6 (g)

−H2O

∗CO

−CO

∗CO

CHx chain

∗CO

∗CO dissociation step

∗H

∗CHXO

∗CH2

∗H CH3OH (g)

∗C2HXO

∗CH2

∗H

growth step ∗CH2 ∗C3HXO etc. ∗H

C2

C3

Oxygenates

Oxygenates

. Fig. 41.3 The CO hydrogenation

∗

C2Hx+3: adsorbed ethylene or ethyl; ∗C2Hx+3O: adsorbed C2 oxygenated species. CO insertion :  CHx þ  CO !  C2 Hx O

(41.6)

Dehydration :  C2 Hx O !  C2 Hx2þ H2 O

(41.7)

The first set of steps in the overall CO hydrogenation reaction network is adsorption of reactants, H2 and CO. All of the CO hydrogenation catalysts must possess the ability to chemisorb hydrogen dissociatively, H2 + 2∗ ! 2 H∗ (2∗: two empty sites) and chemisorb CO in either a dissociative or non-dissociative form. Group VIII metals have shown such a capability of adsorbing H2 and CO. A surface science study shows the ability of metals to dissociate CO is related to their position in the periodic table (> Table 41.2) [29]. This relationship is a result of the difference in the Fermi energy, Ef, reflecting in the ability of the metal in electron back donation to the 2p∗ vacant orbital of CO, as illustrated in > Fig. 41.4 [29]. This back donation would weaken the CO bond and stabilize the M–C bond. Metals such as Fe on the left-hand side of the ambient temperature line possess Ef above the level of the 2p∗ orbital, tend to dissociate adsorbed CO. In contrast, metal on the right-hand side of 200–300
C (473–573 K) line such as Pd, Pt, and Cu exhibit activity for chemisorbing CO non-dissociatively. Metals between these two lines would possess moderate CO dissociation ability and produce both adsorbed CO and adsorbed carbon on their surface. Although the practical catalysts containing supports

Conversion of Syngas to Fuels

41

. Table 41.2 Adsorption of CO metal surface Dissociative Cr Mn Fe Mo Tc Ru W Re Os

Co Rh Ir

Ambient temperature line (

Ni Pd Pt

Non-dissociative Cu Ag Au

)

200–300°C (437–537 K) line ( )

2π O

2π∗ C

5σ

Occupied metal atomic orbital

. Fig. 41.4 Interaction of CO with metal surfaces

and additives are significantly more complex than the simple metal surface, the relationship in > Table 41.2 holds for a number of SiO2-supported catalysts. The CO dissociation activity decreases in the order: Ni/SiO2 > Ru/SiO2 > Rh/SiO2 > Pd/SiO2. The ranking of CO dissociation activity is consistent with the prediction by the above theoretical mode of electron back donation from the metal surface to the 2p∗ empty orbital of adsorbed CO and the Fermi level of metals. The most direct impact of the CO dissociation activity is on the selectivity of the reaction. High CO dissociation activity favors the formation of adsorbed carbon which can further hydrogenate to form CHx, leading to the formation of hydrocarbons such as CH4. In contrast, poor CO dissociation activity allows adsorbed CO to be hydrogenated to methanol. Metals such as Rh in the forms of either single crystal or supported catalysts with moderate CO dissociation activity exhibited good selectivity toward C2 oxygenates [30]. This observation is consistent with the proposed C2 oxygenate formation mechanism that C2 oxygenates are produced from both dissociatively and non-dissociatively adsorbed CO [31].

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The Nature of Active Sites The active sites responsible for CO dissociation have been shown to be the reduced metal ensemble sites which consist of a number of surface atoms. Chain growth step involves more than two CHxO or CHx species and would be expected to occur on the ensemble sites. In contrast, CO insertion has been demonstrated to occur on a single Rh site. Results of Rh single-crystal studies indicated that oxidized Rh sites catalyze for CO insertion [32, 33]; the observation that sulfided Rh catalyzes the formation of propionaldehyde from ethylene hydroformylation further confirms that the Rh+ site is an active site for catalyzing CO insertion [34]. Rh0 and Rh+ sites chemisorb CO in various forms which yield specific infrared bands as shown in > Fig. 41.5. Due to the low tendency for electron back donation from Rh2+ and Rh3+, these sites chemisorb CO, giving high wave-number IR bands in the 2,120–2,145 cm1 range [35]. The structure of chemisorbed CO and its wave number are closely related to the nature of the sites it resides on. From the position of the IR band of adsorbed CO, information about the site that it is adsorbed onto can be inferred. For example, observation of vibrational bands corresponding to bridged CO on Rh implies that surface sites are in a reduced state as well as that the sites exist as an ensemble (i.e., not isolated). Similarly, from the position of linear CO, the oxidation state of the metal site can be deduced as well (i.e., Rh0, Rh+, Rh2+, etc.). It is interesting to note that adsorbed CO on Rh-based catalysts exhibits infrared bands with excellent resolution and intensity. In contrast, infrared spectra of adsorbed CO on Fe- and Co-based catalysts have been vague and seldom reported in the literature. This may be due to the difficulty in keeping Fe and Co in the reduced state during in situ infrared study of CO adsorption.

Gem Dicarbonyl 2090–2100 cm−1 2010–2030 cm−1

Linear CO 2030–2070 cm−1 2090–2100 cm−1 O Bridged CO 1800–1870 cm−1

C

C

C

O

O

O

C

Tilted CO

2−

Mo Mo

O Mn+

Mn+ O2−

Mo

Mo

Mo

Mo

M

Mo Mo

Mo

O2− Mn+ Mn+ O2−

Oxide support

. Fig. 41.5 Adsorbed CO on supported Rh catalysts

o

O

Mn+

C

C

1+ O2− Mn+ O2− M

O

Mo

Mn+ O2−

Conversion of Syngas to Fuels

41

The formation of high carbon-number products involves C–C bond formation steps which have been shown to occur via CHx chain growth steps specifically on Rh/SiO2 catalysts, a illustrated in > Fig. 41.3. This reaction pathway consists of a subset of the overall CO hydrogenation reaction network, where (1) higher hydrocarbon intermediates, CnHx species, are produced from chain growth, (2) high hydrocarbon products, CnH2n and CnH2n+2, are produced from hydrogenation of CnHx, and (3) higher oxygenates are produced from the insertion of adsorbed CO into CnHx species. Chain growth resembles radical propagation, while hydrogenation and CO insertion correspond to chain termination steps of the polymerization kinetics and mechanism. Both methylene (∗CH2) and methyl (∗CH3) species have been proposed to serve as precursors for the chain growth [13–15]. Due to a lack of experimental techniques for in situ studies of such adsorbed intermediate species, the exact structure of chain growth precursor (i.e., x for CHx) remains to be determined. Owing to the polymerization characteristics of the reaction, carbon-number (Cn) distribution in hydrocarbon and oxygenated products generally follows the Anderson– Schulz–Flory (ASF) distribution in which the concentration of Cn product is inherently greater than that of Cn+1 product [36]. Variations in reaction conditions and catalyst composition allow adjustment of the chain growth probability parameter, a (a = k1/ (k1 + k2 + k3): chain growth probability; k1: the rate constant for chain growth; k2: the rate constant for hydrogenation; k3: the rate constant for CO insertion). High temperature (i.e., temperatures above 300
C) and 1 atm pressure shift the product distributions toward CH4 and lower hydrocarbon products; intermediate temperature (230–275
C) and pressure (10–50 atm) shift the products toward higher oxygenates. Ni, Ru, Fe, and Co-based catalysts exhibit excellent activity for the synthesis of higher hydrocarbons. Ru is the most active catalyst which produced primarily long chain hydrocarbons via the CHx chain growth pathway. The reaction pathways on Fe- and Co-based catalysts have been studied extensively by probe molecules and isotope tracing techniques. Results of 14 C-tracing studies suggest that the chain growth proceeds primarily via oxygenated intermediates, CnHxO on Fe-based catalysts and partially on Co-based catalysts [38]. In this pathway, oxygen dissociates from the CnHxO intermediate in the chain termination. Mixed oxide catalysts catalyze methanol as a major product and higher alcohols (i.e., ethanol, propanol, and various isomers of C4 alcohols) as minor products through the CHxO chain growth pathway, shown in > Fig. 41.3. Mo-based catalysts also follow the same CHxO pathway to produce higher yields of higher alcohols than the mixed oxide catalysts, but require operating at very high pressure (>200 atm).

Circumventing Fischer–Tropsch Chain Growth Kinetics The most significant challenge in the investigation and development of FT synthesis chemistry is the selective synthesis of C2+ hydrocarbons or oxygenates without producing methane. Voluminous work has been done on circumventing this selectivity limitation of ASF.

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Various approaches, including (1) unsteady-state operation, (2) use of shape-selective supports, (3) interception of intermediate products, and (4) addition of olefins to the reactant stream have been studied. While unsteady-state operation can skew the product distribution to a certain extent, it inherently produces methane and significantly increases the difficulty in reactor operation and control. The use of shape-selective supports such as zeolites was expected to limit the chain growth through either geometric or diffusional constraints. However, the shape-selective effects have been shown to be temporary or the results of errors in data analysis. At present, no definite evidence to support the lasting shape-selective modification of the ASF has been reported. The approach of intercepting reaction intermediates utilized either multifunctional catalysts or multistep processes for catalyzing the secondary reaction processes such as isomerization and hydrocracking. FT/zeolite catalysts use metals such as Co, Fe, or Ru to catalyze the formation of FT products and the acidic function of zeolites to isomerize and crack FT products. Two-step processes with two different reactors are used if conditions for the cracking, isomerization, or other processes are significantly different from those of the FT synthesis. Addition of an olefin to the CO/H2 feed stream has been shown to increase the higher hydrocarbon yields through chain incorporation. This approach is not economically viable due to the cost of the added olefin and the high tendency of olefin hydrogenation. All of these attempts have failed to produce steady-state product distributions that deviate significantly from the ASF kinetics. Methane and methanol (C1 products) have always been produced with higher yields than C2 or higher carbon-number products. An alternative to higher hydrocarbon synthesis is the selective synthesis of C2 oxygenates from syngas. C2 oxygenates may be produced with high selectivity since they share the common precursor, CHx, with methane. Theoretically, both C2 oxygenates and methane should be considered as C1 products in the ASF kinetics. In fact, a high C2 oxygenate selectivity (up to 75% carbon efficiency) has been achieved on promoted Rh catalysts at 573 K and 10 MPa [31]. This selectivity is significantly higher than the maximum selectivity of 25% for C2 products predicted by ASF distribution, further supporting the theoretical basis of considering C2 oxygenates as a C1 product in ASF. Nevertheless, high hydrogenation activity of Rh leads to methane formation. Improved control of the chain termination and chain growth steps are needed to circumvent ASF distribution of the FT synthesis. A number of studies have shown that different types of adsorbed hydrogen are responsible for the chain termination (i.e., hydrogenation of alkyl species) and chain growth steps [23–28]. Results from these studies suggest the possibility of controlling ASF distribution by manipulating the hydrogen reactivity. Examination of the FT mechanism in > Fig. 41.3 shows that the suppression of termination requires inhibition of both hydrogenation and CO insertion. If the site for hydrogenation of surface carbon to form CHx is the same as that for hydrogenation of CHx to form methane, inhibition of hydrogenation could suppress the CHx formation, decreasing the FT synthesis rate. A great deal of work has shown that alkali promoters enhance higher hydrocarbon formation and decrease methane/paraffin formation,

Conversion of Syngas to Fuels

41

indicating that the site for CHx formation is not the same as that for hydrogenation of CHx [23–27]. NMR studies show that the suppression of methane/paraffin formation is a result of limited migration of adsorbed hydrogen brought about by potassium promoters [31]. Although complete suppression of methane formation may never be achieved, it remains to be determined what extent of methane suppression can be achieved through limiting migration of adsorbed hydrogen. The challenge is to suppress methane formation and enhance CO insertion for further improving C2 oxygenate selectivity.

Ethanol Synthesis Catalysts Ethanol is one of the oxygenated products (i.e., alcohols, aldehydes, and acids) synthesized from CO hydrogenation (i.e., the reaction of CO with H2). The catalytic synthesis of C2+ oxygenates (ethanol, propanol, and higher alcohol; acetaldehyde, propionaldehyde, and higher aldehydes; acetic acid, propanoic acid, and higher acids) has been a subject of intensive interest because of their high value added and versatile applications [1, 36]. The early developments of C2+ oxygenates synthesis from CO hydrogenation took place in Germany. In 1913, BASF discovered that cobalt and osmium catalysts produced a mixture of oxygenates, including alcohols, aldehydes, ketones, and acids at pressures above 20 MPa and temperatures up to 673 K [37]. Since that time, a significant amount of work has been done to determine the activity, selectivity, and durability (i.e., deactivation characteristics) of catalysts for the higher oxygenate and Fischer–Tropsch (FT) synthesis [6, 38–40]. Most studies on the effect of additives on C2+ oxygenate synthesis have been focused on Rh/SiO2 [41, 42], which give a moderate selectivity toward acetaldehyde and ethanol as compared to Rh/La2O3 and Rh/TiO2. Additives such as Mn [43], Na [16], Sc, Ti, and La enhanced CO dissociation; Ag, Cl, Zr, Zn, S [7], Ti, La [44], and V promoted CO insertion [12, 45]; alkali species promoted CO dissociation and suppressed hydrogenation. With the knowledge of the specific additive effect and extensive catalyst screening studies, Rh-Mn-Fe-Li (1:1:0.1:0.1 in the atomic ratio)/SiO2 catalyst with a 4.5 wt% Rh loading emerged as one of the most active and selective catalyst for C2 oxygenate synthesis, exhibiting ethanol selectivity up to 44% and a total C2 oxygenate selectivity of 56% with about 0.178 mol/Kg-h in the ethanol production rate at CO/H2 = 0.5, 50 atm, 270
C, SV (space velocity) = 12,000 h1 in the Japanese C1 chemistry program in the 1980s [42]. Note that SV is defined as the ratio of the reactor volume to the inlet volumetric flow rate at room temperature. Researchers in China have rediscovered the high activity and selectivity of the Rh–Mn–Fe–Li (1:1:0.075:0.05 in the weight ratio) with a 1 wt% Rh loading showing 27% in ethanol and 56% in C2 oxygenate selectivity and 9.1 mol/kg-h in the C2 oxygenate production rate at CO/H2 = 0.5, 30 atm, 320
C, SV (space velocity) = 12,000 h1 [46]. The best C2 oxygenate selectivity obtained in our laboratory with a Rh-Ag (1:1 in the atomic radio)/SiO2 with a 3 wt% Rh loading was 59% with a 0.25 mol/kg-h in C2 oxygenate production rate at CO/H2 = 1, 20 atm, 240
C, SV (space velocity) = 11,000 h1 [21]. This Rh–Ag catalyst showed negligible activity toward

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ethanol. These results are summarized in > Table 41.3 for comparison. While it is difficult to compare the results of these studies due to the use of different conditions, the rate data at various temperatures can be further adjusted with the activation energy of 23 kcal/molK, the average value found from literature [47], to the rate at 280
C. The production rates at 280
C show that the C2 oxygenate rate on these promoted catalysts are in the range of 0.23–2.2 mol/kg-h which are close to the rates of higher hydrocarbon formation in the Fischer–Tropsch synthesis [16]. The results of the rate comparison suggest that the size of pilot or commercial scale ethanol synthesis reactors should be in the same range of the Fischer–Tropsch synthesis reactors. Although the results of the study by Yin et al. are significantly higher than those of others, further verification is needed [46]. Studies on the effect of reaction conditions show increasing temperature and pressure increased the rate of C2 oxygenate formation and further increasing temperature above 320
C can shift the reaction selectivity toward methane and cause a rapid catalyst deactivation. This is the reason why the long-term pilot scale study is conducted at 280
C in the Japanese C1 chemistry program [42]. Use of a 200 cm3 (about 400 g) of Rh–Mn–Li/SiO2 and 200 cm3 of Cu–Zn/SiO2 catalyst mixture in a pilot scale unit showed that the mixed catalysts produced 0.14 mol/kg-h in the ethanol production rate with 70% ethanol selectivity at CO/H2 = 0.5, 40 atm, 280
C, SV (space velocity) = 16,000 h1 decayed less than 15% of its activity in a period of 1 year. The results of this study are the only pilot scale data available in the literature. Examination of the catalyst preparation procedures and their characterization results showed that the activity, selectivity, and durability of the Rh-based catalysts for ethanol synthesis can be further improved with adjusting the following catalyst characteristics: Control of Rh particle size. The average Rh particle size of 3.5 nm has been shown to give the highest selectivity for C2 oxygenate synthesis [42]. The single reduced Rh site chemisorbing linear CO has been demonstrated to be active for CO insertion [48]; Rh ensemble sites (i.e., a group of surface Rh atoms) are active for CO dissociation. 3.5 nm Rh particle appears to contain the appropriate ratio of the sites for CO dissociation and CO insertion to give the highest C2 oxygenate selectivity. Fine-tuning promoter composition. On the basis of the mechanistic information and results of previous studies, the optimum catalysts for ethanol synthesis will be a multicomponent catalyst which consists of 3.5 nm Rh particle size and appropriate amount of each promoter to enhance CO dissociation and CO insertion and to balance hydrogenation of C and CHx. The role of each promoter based on our and other studies discussed above is summarized below: Ag: Suppress CO dissociation and promote CO insertion. Mn: Enhance CO dissociation and CO insertion. Li: Suppress hydrogenation. Fe: Promote CO insertion. Cu: Promote hydrogenation of acetaldehyde and acetic acid to ethanol without promoting hydrogenation of CHx species [42]. Cu-based catalysts, which lack CO dissociation activities, are not able to accommodate CHx species and catalyze hydrogenation of

Conversion of Syngas to Fuels

41

CHx to the undesired methane (i.e., CH4). Cu-based catalysts will be especially useful to promote ethanol formation from Rh–Ag catalysts which showed high C2 oxygenate selectivity, but low ethanol selectivity. Although the specific role of each promoter has been identified, it remains unclear about the optimum composition of the promoters for enhanced ethanol synthesis.

Hydrocarbon Synthesis Catalysts The above ethanol synthesis catalysts serve as an excellent example to illustrate the importance of identifying the role of each component in a multicomponent catalyst. In fact, almost all of practical heterogeneous catalysts consist of multicomponents. The FT’s Fe- and Co-based catalysts consist of more than four components [49]. The traditional FT Fe catalysts are either in the formed fused iron oxides or coprecipitated catalysts. The fused Fe catalysts prepared at 1,500
C contains K2O as chemical promoter and MgO or Al2O3 as the structural promoters. These structural promoters can atomically disperse in the Fe oxide phase and serve as the spacers between metal crystallite after reduction of Fe oxides. The coprecipitated catalyst is prepared by coprecipitation of Fe and Cu nitrate solution with Na2CO3. The concentration of catalyst precursors, the precipitation temperature, and the pH govern the final catalyst form, i.e., the types of oxides, the surface area, and the porosity. Prior to the reaction, the fused catalyst has to be activated by hydrogen reduction; the coprecipitated catalysts are activated by syngas. Removal of reduced product, H2O, from reduction is necessary to avoid sintering of reduced metals and accelerate the activation process. It is interesting to note that the commonly used impregnation method is not used because a large fraction of the chemical promoters could end up adsorbing on or reacting with the support. In contrast to Fe-based catalysts, cobalt-based catalysts are prepared by impregnation on high surface area supports with a low cobalt loading, i.e., 20 wt% or less. Co-based catalysts may contain Cu or noble metals to facilitate the reduction of cobalt oxide particles, oxidic promoters such as lanthanide, thorium, cerium, titania, and zirconium oxides to stabilize the Co dispersion on the support, and Mn to suppress hydrogenation and to enhance chain growth. Both Fe-based and Co-based catalysts show increase in the selectivity toward high hydrocarbon at low temperature and H2/CO ratios. Selection of either Fe- and Co-based catalysts requires further consideration of issues of cost, deactivation, the CO/H2 ratio of syngas gas, and the overall net fuel cycle CO2 emission. Co-based catalyst is less sensitive to H2O deactivation. The cost of Co-based catalyst is significantly higher than that of Fe-based catalysts. In addition to the cost and H2O sensitivity issues, Co catalysts produced H2O, does not have the water–gas shift activity; Fe catalysts produced CO2 with a high water shift activity. Thus, Fe catalysts are used for the low H2/CO ratio syngas from coal; Co catalysts are considered for the high H2/CO ratio syngas from natural gas.

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. Table 41.3 Comparison of Rh-based catalyst activities and selectivities

Catalyst

C2 oxygenate/ Experimental ethanol selectivity (%) conditions

Rh–Mn–Fe–Li Pressure: 50 atm 1:1:0.1:0.1 Temperature: 543 K 4.5 wt% Rh SV : 12,000 h1 CO/H2 = 0.5 Rh-Mn-Fe-Li Pressure: 30 atm 1:1:0.075:0.05 Temperature: 593 K Rh–Ag Pressure: 20 atm 1:1 Temperature: 513 K SV : 11,000 h1 CO/H2 = 1

C2 oxygenate C2 oxygenate production rate at 280
C production rate (mol/kg-h) (mol/kg-h) Reference

56/44

0.23

0.23

[42]

56/27

9.1

2.2

[46]

59/-

0.25

1.25

[21]

Reactor Issues CO hydrogenation is a highly exothermic reaction releasing 140–150 kJ/mol of the heat per CH2 added onto the Cn products or 165–180 kJ/mol CO converted. Rise in reactor temperature will lead to catalyst deactivation and the enhanced formation of undesired methane. Commercial FT reactors include multitubular fixed bed, slurry bubble column bed, fixed fluidized bed, and entrained fluidized bed. These reactors are designed for maximum heat removal to avoid catalyst deactivation. The fixed bed reactor possesses the advantage of simplicity and low cost as well as the disadvantage of difficulty in controlling the reaction temperature. Slurry bubble reactors contain high heat capacity inert media which facilitates the removal of the reaction heat; however, it may cause complications due to attrition of the catalyst particles. Ethanol synthesis from syngas is also a highly exothermic process. So far, ethanol synthesis has only been reported to be carried out in the fixed bed reactor.

Conversion of Syngas to Fuels

41

Future Directions Almost every element in the periodic table has been tested as promoter for both hydrocarbon and ethanol syntheses. The effects of concentration of promoters generally follow a trend: increasing the promotion effect in the low concentration range and decreasing the promotion effect in the high concentration range. Without gaining an in-depth understanding of the promoter–metal, metal–support, and promoter–support interaction, as well as the effect of these interactions on the nature of active sites for the rate-determining step, further variation in the concentration of promoters and the addition of different sequences and combinations of promoters are unlikely to generate the breakthrough results in catalyst selectivity and durability. The emphasis on the basic research should be placed on in situ studies since the nature of the catalyst surface is strongly influenced by the reaction environment where both reactants and products are present. The ratedetermining step can be identified by careful design and use of transient techniques. The use of transient techniques coupling with isotope tracer has been shown to be highly effective in determining the rate-determining step [50]. In addition to determining the effects of the promoters on the catalyst activity, selectivity, and durability, the focus should be placed on the promoter effects on the rate-determining step. Catalyst development deals with catalyst activity, selectivity, and deactivation resistance. The deactivation usually resulted from sintering and sulfur-poisoning. Sintering of metal crystallite may be addressed by addition of the nanoscale spacer to serve as the barrier for the migration of small reduced metal crystallite. Sulfur compounds bind strongly on the reduced metal sites. Instead of modifying metal surface site to impart the sulfur resistance, it may be more effective if a cost-effective approach can be developed to remove sulfur compounds and sulfur content of the syngas to the ppb level. The global emphasis on development of the low carbon dioxide emission technologies shifted the focus from the use of coal-based syngas to biomass-based syngas. The challenge in the biomass routes will lie at the cost of biomass gasification and purification of its syngas. The issues such as the cost of shipping and pretreating are common for all of biomass-related conversion processes. Syngas conversion to fuel processes have to be examined by considering the overall system, including the life cycle of each species in the process and the energy efficiency of each processing step.

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35.

36.

37.

38.

39.

40.

41.

selectivity, and surface composition. J Catal 66(2):257–266 Konishi Y, Ichikawa M, Sachtler WMH (1987) Hydrogenation and hydroformylation with supported rhodium catalysts: effect of adsorbed sulfur. J Phys Chem 91(24):6286–6291 McKee ML, Worley SD (1988) A theoretical study of rhodium/carbonyl species. J Phys Chem 92(13):3699–3700 Biloen P, Sachtler WMH (1981) Mechanism of hydrocarbon synthesis over Fischer-Tropsch catalysts. Adv Catal 30:165–216 Schindeler HD (1989) Coal liquefaction – a research and development needs assessment, vol II. US Department of Energy, McLean Davis BH (2001) Fischer-Tropsch synthesis: current mechanism and futuristic needs. Fuel Process Technol 71(1–3):157–166 Klier K, et al.(1988) Mechanism of methanol and higher oxygenate synthesis. Studies in Surface Science and Catalysis. Methane Conversion, Proceedings of a Symposium on the Production of Fuels and Chemicals from Natural Gas 36:109–125 Vannice MA (1975) Catalytic synthesis of hydrocarbons from hydrogen-carbon monoxide mixtures over the group VIII metals. I. Specific activities and product distributions of supported metals. J Catal 37(3):449–461 Nonneman LEY et al (1990) Role of impurities in the enhancement of C2-oxygenates activity: supported rhodium catalysts. Appl Catal 62(2): L23–L28

41

42. Yoneda Y (1989) Progress in C1 chemistry in Japan. Kodansha/Elsevier, Tokyo 43. Boffa A et al (1994) Promotion of CO and CO2 hydrogenation over Rh by metal oxides: the influence of oxide Lewis acidity and reducibility. J Catal 149(1):149–158 44. Underwood RP, Bell AT (1988) Lanthanapromoted rhodium/silica. II. Studies of carbon monoxide hydrogenation. J Catal 111(2):325–335 45. Ichikawa M et al (1985) Selective hydroformylation of ethylene on rhodium-zinc-silica. An apparent example of site isolation of rhodium and Lewis acid-promoted carbonyl insertion. J Am Chem Soc 107(24):7216–7218 46. Yin H et al (2003) Influence of iron promoter on catalytic properties of Rh–Mn–Li/SiO2 for CO hydrogenation. Appl Catal A 243(1):155–164 47. Chuang SC, Goodwin JG Jr, Wender I (1985) The effect of alkali promotion on carbon monoxide hydrogenation over rhodium/titania. J Catal 95(2):435–446 48. Chuang SSC, Pien SI (1992) Infrared study of the carbon monoxide insertion reaction on reduced, oxidized, and sulfided rhodium/silica catalysts. J Catal 135(2):618–634 49. Davis BH, Occelli ML (eds) (2009) Advances in Fischer-Tropsch synthesis, catalysts, and catalysis. Chemical Industries, CRC Press, Boca Raton, 2009, Vol 128, 403 pp 50. Chuang SSC, Guzmanm F (2009) Mechanistic Investigation of Heterogeneous Catalysis by Transient Infrared Methods. Topic in Catal 52: 1448–1458

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42 Chemical Looping Combustion Edward John (Ben) Anthony CanmetENERGY, Natural Resources Canada, Ottawa, Ontario, Canada Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1624 Chemical Looping Combustion Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1625 Choices of Oxide Carriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1626 Preparation of Chemical Looping Particles and Related Issues . . . . . . . . . . . . . . . . . . . . 1628 CaS/CaSO4 System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1631 Cu System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1633 Fe System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1634 Ni System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1635 Pilot Plant Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1636 Use of Natural Gas in Chemical Looping Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1637 Solid Fuels in Chemical Looping Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1639 Effects of Sulfur . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1643 Hydrogen Production and Reforming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1644 Applications Relating to Hydrogen Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1644 Reforming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1646 Pressurized Chemical Looping Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1647 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1648 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1648 Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_42, # Springer Science+Business Media, LLC 2012

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Abstract: Chemical looping combustion (CLC) and looping cycles in general represent an important new class of technologies, which can be deployed for direct combustion as well as be used in gasification applications. In this type of system, a solid carrier is used to bring oxygen to the fuel gas, so that it can be subsequently released as a pure CO2 stream suitable for use, or, more likely, for sequestration. The solid is then regenerated in a reactor using air, so that the technology effectively achieves oxygen separation from air without the use of a cryogenic process or membrane technology. In a sense, cycles using liquids, such as amine scrubbing, could also be regarded as a type of looping cycle, the key being that the carrier must be regenerated and reutilized for as long as possible. However, this chapter will restrict itself to considering the uses of solid carriers only and, more specifically, those in which oxygen is transported and not CO2 as is the case for calcium looping. Particular focuses of this chapter will be on the use of this technology for H2 production and gasification applications, as well as its use with solid fuels. Another issue that will be discussed is high-pressure cycles, which are ultimately necessary if such systems are to be integrated into high-efficiency electrical energy cycles.

Introduction Chemical looping combustion (CLC) was first suggested by Lewis, Gilliland, and Reed in a paper published in Industrial and Engineering Chemistry [1]. In this paper, they carried out an experimental investigation of the use of CuO to oxidize methane to CO and H2 using a small fluidized bed reactor at a temperature of 925
C to avoid both the use of oxygen and high net heat requirements normally required in the reforming process. Subsequently, these workers proposed the use of this approach for the production of pure CO2 from a hydrocarbon gas [2]. Later, the idea of using a metal oxide to combust a gaseous hydrocarbon was again proposed as a method of achieving ‘‘controlled combustion’’ by Richter and Knoche [3], who explored the Ni system, and proposed the Cd system based on a theoretical analysis (although, since Cd has a low melting point of around 321
C, this would seem to preclude its use, even if its noted toxicity did not). Although the work of Richter and Knoche clearly references the earlier work of Lewis and his colleagues in 1949, the contribution of Lewis and his colleagues in proposing the basic ideas of CLC seems to have been largely ignored in subsequent developments. In subsequent work Richter emphasized the potential benefits of employing such a cycle in combination with a solid oxide fuel cell, and stressed the potential benefits of producing three separate fluid streams, namely, CO2, H2O, and N2 (when air is used to oxidize the carrier) [4]. In a thermodynamic study done by Jerndal et al. [5], 27 possible systems were examined, based on the potential of an oxide to achieve complete or near-complete conversion of CH4, H2, and CO. Factors like stability in air and melting temperatures were also examined and metal oxides based on Ni, Cu, Fe, Mn, Co, W, and sulfates of Ba and Sr were shown to offer possible chemical looping systems, although for some reason the sulfate of Ca was not considered. However, it is to the Ni-, Cu-, and Fe-based systems that most of this chapter will be devoted.

Chemical Looping Combustion

42

Early experimental work was done extensively in either thermogravimetric analyzers (TGAs) or subsequently in fixed bed reactors in Japan by various workers including, most notably, Ishida and his coworkers [6, 7], using primarily Ni-based carriers, all of which demonstrated that the reaction was fast enough to be employed in practice, and that soot formation or carbon deposition on the particles did not appear to be a major problem if the oxidation reaction was carried out at a high enough temperature [8]. This work uses the term chemical looping combustion, and also clearly identifies the benefits of such an approach in terms of producing a pure stream of CO2 for sequestration after water has been removed. Subsequent research has been heavily directed to pilot plant studies, using fluidized beds, and has been carried out most notably in places like Chalmers University, Sweden, with a major focus on developing practical systems [9]. These developments will be discussed in considerable detail below since it is the practical application of these technologies and their demonstration at the industrial scale in the next several decades that is key to their contribution to a carbonconstrained world.

Chemical Looping Combustion Concept Until quite recently, when efforts have been made to use these cycles with solid fuels, nearly all of the proposed cycles involved reaction of a gaseous hydrocarbon with a metal oxide that is taken from a higher to a lower state of oxidation, following the global reaction scheme: ð2n þ mÞMy Ox þ Cn H2m ¼ ð2n þ mÞMy Ox1 þ mH2 O þ nCO2

(42.1)

Alternatively, if a reforming step is being considered, the amount of oxidant is reduced to allow for the production of CO and H2, as in the original concept of Lewis et al. [1]: nMy Ox þ Cn H2m ¼ nMy Ox1 þ mH2 þ nCO

(42.2)

In the case of combustion (Rx. 1), after the water produced from hydrocarbon oxidation is removed, the flue gas stream contains an effectively pure stream of CO2 suitable for sequestration. The metal oxide is regenerated in a separate reactor by reaction with air (Rx. 3), and the regenerated solid can be transferred back for further reaction with the fuel gas (> Fig. 42.1): My Ox1 þ Air ¼ My Ox

(42.3)

Typically, the oxidation reaction is strongly exothermic and the reduction step is not (an exception is the CuO/Cu cycle in which both oxidizing and reducing cycles are exothermic [10]), so that overall, the system yields the heating value of the fuel. Such a cycle represents an elegant way of oxidizing a fuel gas by effectively achieving air separation, without using cryogenic or membrane technology, and, in addition, avoiding or minimizing the formation of fuel-NOx. In practice, these cycles typically operate at temperatures in the range of 800–1,200
C, which normally ensures that the reactions

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Chemical Looping Combustion

CO2, H2O

O2-depleted air

My Ox−1

Fuel reactor

Air reactor My Ox

Fuel

Air

. Fig. 42.1 Typical metal oxide looping cycle

occur at a sufficient rate to be compatible with a fluidized bed system, and to ensure that agglomeration and sintering are minimized. In principle, they can be run either at atmospheric or high pressure, although the vast bulk of the research done to date has been at atmospheric pressure. It should also be noted that Rx. 1 and 2 are idealized since many oxides permit multiple oxidation states, and complete conversion of the oxide need not necessarily occur in either Rx. 1–3 to ensure effective use of the chemical looping reagent [11].

Choices of Oxide Carriers Any given oxide system will have a carrying capacity, which can be defined as: Rx ¼ ðmox  mred Þ=mox

(42.4)

where mox is the mass of the fully oxidized sample and mred is the mass of the reduced sample. The values of mox for the common systems (Fe2O3/Fe3O4, Ni/NiO, Cu/CuO) are 0.03, 0.22, and 0.24, respectively, and the oxidation reactions are of the type shown below: 3Fe2 O3 þ CO=H2 ¼ 2Fe3 O4 þ CO2 =H2 O

(42.5)

CuO þ CO=H2 ¼ Cu þ CO2 =H2 O

(42.6)

NiO þ CO=H2 ¼ Ni þ CO2 =H2 O

(42.7)

Chemical Looping Combustion

42

Other systems of course exist, such as the Mn3O4/MnO and CoO/Co systems: Mn3 O4 þ CO=H2 ¼ 3MnO þ CO2 =H2 O

(42.8)

CoO þ CO=H2 ¼ Co þ CO2 =H2 O

(42.9)

which have received limited investigation [12]. There is one notable nonmetallic system, the CaSO4/CaS system, that has the highest carrying capacity of all, at 0.47, and this system will be discussed later. It should also be mentioned that there has been some success in preparing oxygen carriers with mixed oxide systems, which together show better overall performance. For example, the addition of small amounts of Ni was shown to improve the performance of various oxygen carriers and it is suggested that this arises because Ni0 can catalyze methane conversion by methane pyrolysis and steam reforming [13]. In practice, it is more usual and useful to consider the carrying capacity of the particles themselves, since they contain an inert substrate to support the active component and the oxygen-carrying capacity figures will be lower and depend on the formulation of the particle itself. Also, in some instances, the carrier itself will form a compound with the support material that is itself inert, an example of this being Al2O3 with Ni, which forms a Ni spinel (NiAl2O4) that is not itself active as an oxygen carrier and consumes some of the Ni otherwise available for reaction [14]. Thus, for instance, Abad et al. [15] give figures for three oxygen carriers based on Fe, Ni, and Cu, showing that their actual carrying capacities are 0.013, 0.084, and 0.02, respectively. While the carrying capacity of the material and the particles made from it will be of major significance, there are obviously a number of other factors that must be considered. Kinetics is clearly one, and based on an evaluation of 600 different oxygen carriers (i.e., predominantly the Ni, Cu, and Fe systems with different inert substrates), Johansson concluded that Ni and Cu were the most reactive [16]. Another potential concern is the melting point of the active material since sintering will be significantly enhanced if the carrier must be operated near its melting point for kinetic reasons. Here, the material with the lowest melting point of those commonly considered for chemical looping cycles is Cu, which has a melting point of 1,083
C, and since operation of chemical looping systems is normally in the range of 700–1,000
C, this has been somewhat of a concern for the copper system; however, extensive experimentation has shown that Cu-based chemical looping systems can be operated satisfactorily with Cu at a temperature range of up to 950
C [16]. Another issue is thermodynamic limitations for the oxidation cycle; thus, the Ni/NiO cycle cannot convert a hydrocarbon completely to CO2 and H2O, having a conversion of 98.8%, for instance, at 1,000
C, with higher conversions at lower temperatures. In the case of CoO/Co, the thermodynamics are even less favorable with a conversion of 93% at 1,000
C [16]. Finally, there are the issues of toxicity and availability. Ni is a known carcinogen, and Co would be considered as toxic in other than trace amounts, at which levels it is a micronutrient. Copper also has minor toxicity issues. However, the factors that are more likely to limit the use of such materials are their availability, cost, and reactivity. In this situation, there will always be a tendency to prefer iron-based systems if their

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reactivity can be increased sufficiently for practical applications, since iron-based materials are always likely to be more available, less costly, and less toxic than any other metal/ metal oxide system. Unfortunately, the iron-based systems have a rather low carrying capacity and are the least reactive of the common systems being considered, that is, Ni, Cu, and Fe systems. Nonetheless, as will be seen below, because of their relatively low costs and essential lack of toxic or environmental concerns, iron-based systems continue to receive considerable attention.

Preparation of Chemical Looping Particles and Related Issues In a detailed analysis of the cost limits for looping cycle materials, Abanades et al. [17] noted that: "

A makeup flow of sorbent is required to compensate for the natural decay of activity and/or sorbent losses during many sorption/desorption cycles. It must be emphasized that this decay is to some extent always unavoidable because of [a] wide range of chemical and physical interactions of the sorbent inside the reactor and transport lines and the sorbent losses associated with gases leaving the system.

In consequence, in the analysis of Abanades et al. [17], they stressed that in order for costs to be kept to a reasonable limit, it is necessary to reduce the amount of makeup of expensive sorbents by increasing the number of reaction cycles to a figure approaching tens of thousands. Unfortunately, unlike, say, Ca looping for CO2 capture or the CaS/CaSO4 looping cycles, where one can envisage using natural limestones or natural anhydrite materials, respectively, nearly all of the earlier efforts at making chemical looping reagents envisage using relatively expensive materials that have to be prepared in the form of synthetic particles, an exception being the use of natural ilmenite (FeTiO3) [18]. This issue was apparent with the pioneering work of Lewis et al. [1], who noted that CuO itself did not work well due to a rapid growth in particle sizes, and instead used Cu on supports including silica gel, alumina gel, and kaolin, with the carriers ground to the required size and the metal deposited on it. In the work of Lewis et al. [1], a copper nitrate solution was mixed with the carrier and the copper deposited on the particles by thermal decomposition in an oven. Variants of this approach include the so-called dissolution method adopted by Japanese workers, a typical recipe for which is as follows: "

Ni(NO3)2·6H2O and Al(NO3)3·9H2O were dissolved into a mixture of distilled water and 2-propanol, and the solution dried at 100
C for 3 h, at 150
C for 5 h and finally at 500
C for 3 h. Subsequently, the agglomerates were crushed in a ball mill, and water slurry introduced into a spray dryer. The resulting particles were then baked in an oven for 10 h, during which baking a NiAl2O4 support is produced on which the active Ni component is maintained [19].

An alternative approach also used in some of the earlier Japanese work was to grind the oxide together with the carrier after wetting (for periods of up to 2 days), and then sinter

Chemical Looping Combustion

42

the particles for 10–12 h, after which they were sieved and held in a desiccator [20]. More recently, freeze-dry granulation has been explored at Chalmers University in Sweden (e.g., [16, 21]), and an example of the procedure employed is found in > Table 42.1. Yet another approach, the so-called sol-gel method, is also being developed and involves the formation of a colloidal suspension (sol) and gelation of the sol to form a wet gel, which after drying forms a ‘‘dry gel’’ state (xerogel), which is then processed to make sorbent particles [22]. However, the procedure of producing the carrier outlined by these workers is of considerable complexity to that outlined in > Table 42.1. Numerous other efforts are underway, such as for instance efforts to develop a cheap wet impregnation method [14]. Very recently, Jerndal et al. [23] have reported considerable success in producing suitable particles by means of spray drying, which is a technology that could be used to scale up the production to make the large amount of carrier particles needed by an industrial unit at a reasonable cost. This must be regarded as a very positive, if early, result, although spray drying produced a high degree of cenospheric particles. What is clear from the above is that, while making reactive materials is important for any practical applications, their longevity, especially if they are used in fluidized bed systems, which transport materials from one vessel to another (oxidizer, regenerator), will be critical, and there will be major pressure to reduce the cost of such carriers for largescale applications such as will be required if CLC is to be employed in thermal power generation. To date, such tests as have been done in pilot-scale equipment, supplemented with crush tests to measure the individual strength of particles under ambient conditions, have suggested that the best particles produced are strong enough to survive extremely well in the small-scale units that have been studied [24–26]. Thus, De Diego et al. [25]

. Table 42.1 Synthesis of a CLC particle ● The oxygen carrier particle was prepared by freeze-granulation and was composed of 40-wt% active material of CuO and 60% ZrO2 ● A water-based slurry was prepared by mixing CuO (Panreac No. 141269) and ZrO2 (SigmaAldrich No. 24.403-1) ● This mixture was ball-milled for 24 h – A small amount of dispergent was also added to this mixture in order to improve slurry characteristics ● After milling, an organic binder was added to the slurry to keep the particles intact during later stages in the production process, that is, freeze-drying and sintering ● Spherical particles were produced by freeze-granulation, that is, the slurry is pumped to a spray nozzle where passing atomizing air produces drops, which are sprayed into liquid nitrogen where they freeze instantaneously ● The frozen water in the resulting particles is then removed by sublimation in a freeze-drier operating at a pressure that corresponds to the vapor pressure over ice at 10
C ● After drying, the particles were sintered at 950
C for 6 h using a heating rate of 5
C/min

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Chemical Looping Combustion

suggest that a loss of 0.01% per cycle is reasonable based on their experimental work, implying a lifetime of particles of 10,000 cycles (5,000 h in their tests), which they suggest is equivalent to a particle cost of less than 1 €/t of CO2 captured. Similarly, in a later paper, De Diego et al. [26] suggested a loss of 0.04 wt%/h, with a particle lifetime of approximately 2,400 h, or replacement of the bed inventory 3.4 times per year. Very similar conclusions were reached by Lyngfelt et al. [24] for the Grace Reactor (> Fig. 42.2) where these workers suggested that particle lifetimes of 40,000 h were possible. The same workers studying the NiO/NiAl2O4 particles in a 1,016-h test using their 10-kW reactor, reported that the largest decrease of fines occurred in the first 100 h, and estimated that a particle lifetime of 33,000 h could be achieved with these particles [27]. Nonetheless, as large demonstrations and early efforts at commercialization are being developed, the production of large quantities of such materials by less complicated and, hence, less expensive methods will continue to be a priority as will verifying the fact that such materials can withstand full-scale operation with minimal carrier loss, especially if they are used directly with solid fuels.

Flue gas

Air reactor CO2-H2O

Fuel reactor

Fuel

Air

. Fig. 42.2 Schematic of Grace 10-kW chemical looping reactor

Chemical Looping Combustion

42

CaS/CaSO4 System As noted above, the CaSO4/CaS system has the highest carrying capacity of all, at 0.47, and is also unique in that it employs a nonmetallic system. Coupled to the very high carrying capacity, it has another obvious advantage in that anhydrite (CaSO4) and gypsum are available in large quantities in the natural environment and can, therefore, be obtained at relatively low cost. CaS itself might be more problematic in that it can react with water to release H2S, but otherwise this system seems at first sight particularly promising. Unfortunately, there are some obvious problems, first that the system can lose SO2 via direct oxidation of CaS: CaS þ 3=2O2 ¼ CaO þ SO2

(42.10)

as well as the well-known reaction: CaS þ 3CaSO4 ¼ 4CaO þ 4SO2

(42.11)

which occurs in the temperature region above 900
C [28], where one might expect to operate a chemical looping system, which means that unless conditions are carefully controlled the active system will lose sulfur in the form of SO2. Secondly, one can reasonably expect such natural materials to sinter and to lose activity rapidly as is the case, for example, with natural limestone in Ca looping cycles, where CaO is used to remove CO2 from hot flue gases [29]. In addition, one would expect the attrition from such systems to be relatively high when compared with other chemical looping carriers unless synthetic materials are prepared, in which case the system loses some of its obvious advantages. The loss of SO2 was demonstrated in studies done by Southeast University in China, who used a natural anhydrite (94.4% pure), with an oxygen capacity of around 0.444, which they tested in a fixed bed reactor (24-mm dia.) [30]. They found that conversion of natural gas was low unless temperatures were in the range of 950
C, but that high temperatures were associated with a loss of SO2 from the reactor of up to 6% in the flue gases. These workers also noted that there was a small loss of SO2 even at 850
C. In addition, there was some agglomeration of particles at higher temperatures. These workers also explored the performance of this system for simulated syngases, again using the same natural anhydrite, but this time in a small fluidized bed reactor (25-mm dia.), and found that the mass conversion rate for this system was considerably less than the metal oxide systems. They also noted that CaO became the main component after the 20th oxidation cycle, due to the loss of SO2 [31, 32]. In a study by Shen et al. [33], Rx. 11 was identified as the main cause of sulfur loss from the system, and these workers recommend recapturing the SO2 by feeding a small amount of limestone into the system. They further recommend that the air reactor should be between 1,050
C and 1,150
C, while the fuel reactor should be operated between 900
C and 950
C. These problems with this system might well suggest that it would not be the first to be explored despite its obvious advantages. However, it is clear that a more detailed examination of other sources of the natural oxidizers could be explored, or that one could

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consider making synthetic carriers such as, for instance, sulfating dolomite, in the hope that the magnesium component might reduce sintering, and/or adding a guard bed to capture any SO2 escaping the system, perhaps in the form of CaS or CaSO4 so that the material could be recycled back to the reactor. Wang and Anthony [34] also proposed such a system (> Fig. 42.3) in which syngases from a material like petroleum coke are oxidized by CaSO4, which is then regenerated in a separate reactor that can be used to generate heat and power, and supported their ideas with an ASPEN™ simulation. In this system, any loss of SO2 will occur together with the oxidized syngas stream, and must be separated from the CO2 stream or sequestered with it. They also proposed the possible use of dolomites if reactivity issues were significant, and made similar points to that of Song et al. [32] who discussed the use of this cycle with solid fuel. They stated that these materials are intrinsically cheap and so, having a fairly high makeup rate, may be acceptable for this system, whereas it would most certainly not be for a more expensive carrier. In the work by Song et al. [32], they suggest that complete separation of carrier and ash might not be problematic, because for a really cheap natural sorbent, even if there are ash–sorbent interactions, sintering issues, or losses of SO2 leading to high losses of sorbent/carrier, it may still be possible to operate economically with such a cycle, although this clearly would not be ideal. Yet another suggestion for dealing with the problem of loss of SO2 comes from the work of Tian and Guo [35], whose research noted that the amount of SO2 released was also dependent on the partial pressure of CO, and suggested that in a pressurized system the release rate of SO2 could be minimized if the partial pressure of CO was high enough, even at 1,000
C.

O2 depleted air

CO2

Fuel

Gasifier 900°C 2C + 2CO2 = 4CO

CO/CO2

Reduction reactor 900°C

CaS

4CO + CaSO4 = 4CO2 + CaS

Oxidation reactor 1,000°C

CaSO4

CaS + 2O2 = CaSO4 Air

Ash Fresh CaSO4

Heat

. Fig. 42.3 Schematic of chemical looping process for combustion of solid fuels using the CaSO4/CaS system (From Wang and Anthony [34])

Chemical Looping Combustion

42

This brings us to the final reason for considering this system, and that is that it was proposed by Alstom Ltd., as part of a $4-million US Department of Energy Program from the National Energy Technology Laboratory (NETL) Existing Plants Program, aimed at demonstrating the conversion of solid fuels in a specially designed 3-MWth pilot plant [36]. The system considered by Alstom has a number of looping cycles working together: a CaSO4-CaS cycle, a CaCO3-CaO cycle for CO2 removal, and a thermal loop involving bauxite. This system is evidently of considerable complexity as has been critically noted by Wang and Anthony [34], but apparently has very attractive potential costs for avoided CO2 ($11–13/ton of CO2) [37]. The pilot plant is expected to be running sometime in 2010–2011, and interested readers can follow developments for this system via the US DOE website [38].

Cu System The copper system was the first chemical looping system to be explored with the groundbreaking work of Lewis et al. [1] and it was also used to provide an example of a chemical looping process in the paper by Richter and Knoche [3]. Copper is attractive because it can be used to make extremely reactive oxygen carriers, and is in addition a reasonably inexpensive material with relatively low toxicity. In addition, it has one interesting feature, namely, that both the oxidation and reduction are exothermic; this property can feed into a number of schemes, the most obvious of which is a fuel reactor that does not need to be supplied with heat, as is the case for other systems. However, its tendency to agglomerate with the potential to cause defluidization in fluidized bed systems is still an important consideration [39]. This is also the view presented in two reviews carried out on chemical looping in 2006 and 2008; based on the available literature, both stress the tendency of copper carriers to agglomerate and the need to avoid higher temperatures. In the first review, Tan et al. [40] suggest that Cu-based carriers are restricted to relatively low temperatures because of a tendency to agglomerate above 800
C, while in a review published 2 years later, Hossain and de Lasa [41] explicitly state that ‘‘Cu also has a relatively low melting point (1085
C) and as a consequence cannot be used above 900
C.’’ An early exception to these views can be found in the work of De Diego et al. [25] who note that, under proper conditions, it is possible to produce Cu-based carriers with high reactivity and low attrition rates, which also do not agglomerate in a fluidized bed, thus negating the main reason to avoid such carriers. In this paper, they also note that they have carried out tests for 20 cycles at 950
C in a fluidized bed reactor without evidence of problems. Moreover, it can be argued, however, that the more recent literature suggests a somewhat more positive picture, although temperatures above 900
C are generally still avoided. Thus, a number of workers have reported good success with CuO supported on Al with trials of up to 200 h in a 10-kW reactor, showing very little signs of agglomeration, albeit that the temperatures were around 800
C [26, 42], and these workers note that theirs is the first demonstration of good performance exhibited by a Cu-based material

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operating at high temperature in a continuous chemical looping process. Equally, Chuang et al. [10] have argued that co-precipitated CuO-Al2O3 carriers perform better than wetimpregnated carriers and show no sign of copper redistribution in the carrier or agglomeration in the temperature range of 800–900
C, while Tian et al. [43] report excellent performance of nano-structured Cu-BHA (barium hexaluminate) carriers over the temperature range of 700–900
C. Finally, Mattisson et al. [21] have argued that, based on the work of Ada´nez and his coworkers [25, 42, 44, 45], it should be possible to manufacture Cu-based oxygen carriers that do not agglomerate at higher temperatures. This is important for the work Mattisson et al. [21] are discussing, because they are interested in using copper oxide systems for a process they call chemical looping with oxygen uncoupling, in which the metal oxide releases gaseous oxygen. This phenomenon is potentially valuable in gasification schemes for solids, which are otherwise rate-limited by the reaction rate of H2O or CO with the solid, and this will be discussed in more detail later in this chapter. It is interesting to note in the experiments described by Mattisson et al. [21] that the copper carrier (CuO/ZrO2) is regenerated at temperatures of 905
C and 955
C. Finally, it is worth remarking that Cao et al. [46] suggested that the Cu/CuO system was particularly suited for the conversion of solid fuels due to its exceptional reactivity, based on thermogravimetric and differential scanning calorimetry experiments [46]. The subject of solid fuels conversion will be discussed later on.

Fe System As noted earlier, this is the least reactive of the common systems (i.e., Ni, Cu, and Fe); however, it is the most environmentally benign, and potentially it is also the cheapest. There has as a result been considerable interest in this system, and work has been done both on synthetic and natural hematite carriers (Fe2O3) [47] and natural ilmenite (FeTiO3) [18, 48, 49]. Early work in a fixed bed reactor using hematite showed that the particles developed cracks and the authors suggested that a binder would probably be desirable to manufacture a synthetic carrier [47], and later work was almost exclusively focused on systems using a carrier; thus, for instance, in his list of studies (Table 1–5 of his work), Johansson [16] lists 7 studies with Fe2O3, and 38 for Fe2O3 with various carrier materials. In a study of an Al2O3-supported carrier with 40% Fe2O3, Abad et al. [50] carried out tests for 40-h duration at temperatures ranging from 800
C to 950
C in a 300-W fluidized bed reactor. They noted that there was no sign of agglomeration under conditions examined, but that the conversions of CH4 were relatively low with combustion efficiencies reaching 94%, as compared to 99% with syngas, which reflects the general realization that iron-based oxygen carriers can be expected to be less reactive. Experiments done in a fixed bed reactor at 900
C with an iron-based carrier supported on titania prepared by a wet impregnation method, showed that the Fe reacted with the TiO2 to form ilmenite. Although the amount of active carrier was reduced, reasonable performance with CH4 was achieved, but the reactivity of the Fe-based carrier was less than would have been expected for Cu- or Ni-based carriers [51, 52]. An interesting method of dealing with

Chemical Looping Combustion

42

the reactivity problems associated with the iron system is to add Ni at a low level, and Ryde´n et al. [53, 54] report that by adding 10% NiO/MgAl2O4 they were able to produce a material with similar behavior to a pure NiO/MgAl2O4 carrier. In later work, they report that addition of the equivalent of 5 wt% of a NiO material changed the combustion efficiency in a small fluidized bed operated at 900
C from 76% to 90% for the conversion of CH4 [55]. Pro¨ll and his colleagues [18] have carried out experiments with ilmenite in a 120-kW dual fluidized bed system and reported what they describe as reasonable fuel conversions (between 60% and 90%) at 950
C for syngas (mixtures of CO and H2), but much more limited performance with CH4, around 30–40%. They also found that low load was associated with poorer conversion and the addition of natural olivine, at a level of 18% of the bed material, helped to achieve a moderate increase in CH4 conversion. These results are fairly similar to those obtained earlier by Leion et al. [48], who carried out tests in a small fluidized bed reactor (22-mm dia.) at a nominal 950
C, in which they looked at either pure methane or syngas (50% CO and 50% H2) conversion; again they report good conversion of syngas but much poorer conversion of CH4. It is also interesting that, unlike Cao et al. [46], Rubel et al. [56] who carried out experiments on a beneficiated high-carbon coal gasification char, using a thermal analyzer–differential scanning calorimeter–mass spectrometer system, recommended Fe-based carriers as the best for solid fuels conversion. In particular, they noted that their experiments showed that Fe2O3 and an iron-based catalyst remained more durable through multiple oxidation/reduction cycles. Finally, it is interesting to note that some research has recently been done on syngas production from mixed cerium–iron systems with natural gas [57, 58]. Both the cerium and iron are considered to contribute to oxidation in the fuel reactor, and in the work of He et al., the Cu and Mn oxide systems were also explored. Ce/Fe molar ratios of greater than 1 were found to perform best by He et al. [57], and similar results were obtained by Li et al. [58]. Perhaps the only negative comment that can be made is that any benefits of price in terms of using the iron system must be compromised for such systems, even allowing for the fact that cerium is the most abundant of the rare earth elements.

Ni System The vast majority of chemical looping research work has concentrated on using Ni-based carriers and, thus, as an example of the 105 studies recorded by Johansson [16] (Table 1–5 of his work), 67 of them employed Ni-based carriers. It also appears to be extensively addressed in the early work of Ishida’s group in Japan [6, 7, 19, 59]. Despite the concerns with the cost of Ni and potential toxicity problems as discussed earlier, and the fact that the reaction does not go to completion with CH4 (conversions of 99% at 1,000
C) [5], its excellent performance and stability on suitable inert matrices, such as Al2O3 and YSZ (yttria-stabilized zirconia) in particular at temperatures up to 1,000
C, have meant that it is the preferred candidate for research work at least. Numerous other inert matrices have

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been explored such as titania-supported nickel oxide [52, 60]; bentonite [61], with MgO as an additive to Al2O3 and NiAl2O4 to prevent agglomeration under reducing conditions [62] and NiAl2O4 acting as the inert matrix in NiO/NiAl2O4 particles [63, 64]; SiO2; and sepiolite (Mg4Si6O15(OH)2·6H2O) [65], and all of these have been reported as successful, although it appears that Al2O3 and YSZ are probably the most successful and commonly used and there appear to be some problems with SiO2 as an inert matrix [65, 66]. NiAl2O4 is an interesting carrier in that it can also, in principle, react with CH4, but in the presence of NiO in the particle it is assumed to be inert [63, 64]. Work has also been done on the use of Ni with a lanthanum-modified g-Al2O3 inert substrate [67]. These workers noted that the lanthanum addition improved the reducibility of the oxygen carrier and speculated that the lanthanum inhibits nickel aluminate formation. Very recently, an interesting suggestion has been made to reduce the cost of a Ni-based carrier, and that is to combine it with ilmenite, and based on a limited set of experiments done in a 120-kWth dual fluidized bed reactor, it has been suggested that the performance of a properly designed NiO-based carrier will be close to that of the NiO-based carrier with up to 90% ilmenite [68]. However, an overall conclusion that can be drawn from the literature is that at least to date the Ni/NiO oxide system is preferred for most research work; whether that translates into the commercial scale of course waits to be demonstrated.

Pilot Plant Research In a review article published in 2006, Johansson et al. [69] list 11 studies carried out in 10-W, 40-W, 300-W, and 1-kW reactors using the NiO, Fe2O3, Co3O4, Mn3O4, and CuO systems with different stabilizers and test durations ranging from 3 to 60 h. Nearly all of the research was done with natural gas, although one study was done with CH4 and another with a synthetic gas mixture. Since that date, there has been considerable focus on achieving longer trials in larger reactors, albeit that reactor sizes at university laboratories at least are generally limited for practical reasons. More importantly, it is now commonplace to carry out trials for several hundred hours and the Grace Project [24] carried out at Chalmers University, in Sweden, and tests done by Ada´nez et al. [70] on a 500-Wth chemical looping system using an impregnated Ni-based oxygen carrier, this time built and operated at the Instituto de Carboquı´mica, in Spain, are two examples of this type of facility and longer-duration testing. Equally impressive, the operation of a 10-kWth unit using the copper system (CuO-Al2O3 carrier) has been demonstrated with no evidence of significant agglomeration [26, 42] and tests of 1,016-h duration have been achieved with a Ni-based system, carried out again at Chalmers University, Sweden, in their 10-kW unit [27]. From the point of view of duration, these tests give as much reasonable assurance as one could ask that it is possible to operate these systems indefinitely. Finally, it should be remarked that implicit in this discussion is the idea that dual fluidized bed reactors are likely to be used for commercial-scale operation, and this is, for example, the assessment of Hossain and de Lasa [41] in their review of the literature.

Chemical Looping Combustion

42

However, it is worth noting that some workers are considering the possibility of building industrial-scale fixed bed systems [71]. Arguments they make against dual fluidized bed systems include concerns that the gas-particle separation cyclones required between the two reactors are likely to be very expensive for commercial-scale systems and will also be associated with damage to the oxygen carrier particles, and that attrition of fines will be a problem for gas turbines, something which has been an issue for pressurized fluidized bed systems, for instance [72].

Use of Natural Gas in Chemical Looping Systems A fairly obvious caveat that can be raised about nearly all CLC R&D until 2008 or 2009 is that it depends on the use of natural gas and/or syngas and, moreover, it is somewhat limited in temperature to around 1,000
C due to the sintering of the solid carriers. This point was made strongly by Tan et al. [40], who noted that at the time of writing, the technology was only suitable for use with gaseous fuels. They also expressed concerns about the carryover of char if the technology was used with gasification. However, they did note that it appeared to offer significant flexibility for use with industrial boilers, gas turbines, and even fuel cells. This limitation is obviously considerable for thermal power systems because natural gas by itself is an ideal fuel, offering extremely high efficiencies and the cheapest power generation. What the technology clearly offers is very effective CO2 removal, and it is interesting to explore what other advantages it might have with natural gas. The group of Professor Bolland, at the Norwegian University of Technology and Science, has carried out significant work performing simulations of CLC plants. In 2004, it carried out a simulation of a CLC power station, using the NiO system, with a circulating fluidized bed for the oxidation or regeneration and a fluidized bed (bubbling) for the fuel reactor. The simulation demonstrated that the oxidation reactor exhaust temperature and the oxidation reactor air inlet temperature were very significant, but making various assumptions, the work indicated an optimum efficiency of 55.9%. In an examination of the effect of part load on plant efficiency, for a natural gas–fired power cycle using CLC, Naqvi et al. [73] noted a drop of 2.6% in efficiency when reducing the load down to 60% for a CLC concept, but stated that this system performed better than a conventional combined cycle system. The same group subsequently looked at nine concepts for natural gas firing, including six oxy-fuel and two precombustion capture [74], and concluded that chemical looping technology showed among the best results, with a plant efficiency of 55.1%, exceeded only by an advanced zero-emissions power plant and a solid oxide fuel cell integrated with a gas turbine. > Figure 42.4 shows the scheme considered by these workers. However, they noted that CLC and other advanced concepts might not be realized at the scale of the analysis. Wolf et al. [75] made a comparison of the nickel- and iron-based systems for power generation with natural gas with CO2 capture, and concluded that overall efficiencies of almost 53% were achievable for a natural gas combined cycle incorporating a chemical

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Chemical Looping Combustion Chemical looping combustion (CLC) MeO

CO2 to compression

OX Condenser

CO2/steam turbine

Red

NG

O2 depleted Air

HRSG

Me

Condenser 0.04 bar

H2O Air Generator Steam turbine

. Fig. 42.4 Natural gas–fired chemical looping scheme (Taken with permission of Professor Bolland, Norwegian University of Science and Technology, from the paper by Kvamsdal et al. [74]). NG natural gas, HRSG heat recovery steam generator

looping system, provided that the temperature of the air reactor could be kept at 1,200
C. Here, they considered two interconnected pressurized fluidized beds. However, they did note that this efficiency strongly depended on the exit temperature of the air reactor being only 1,000
C, and the system did not look any better than conventional technology with backend CO2 removal. Consonni et al. [76] carried out an analysis of a chemical looping cycle for a utilityscale application using natural gas, and came to the conclusion that employing chemical looping combustion should not pose a significant problem when using commercially available gas turbine technology, an important consideration because, as they note, unless CLC becomes the technology of choice for power generation, it is unlikely that manufacturers will ever offer a gas turbine specifically designed to operate at the optimum conditions for an integrated chemical looping combined cycle system. In their simulations, unfired configurations with maximum process temperatures were able to reach net efficiencies of 43–48%, while fired configurations, where the temperature is raised from 850
C to 1,200
C by supplementary firing, could achieve 52% net efficiency. A possible limitation is that a preliminary economic analysis indicated that the cost of CO2 avoided by integrated chemical looping combined cycle plants with a maximum CLC temperature of 850
C is about 50 €/t for both fired and unfired concepts. The authors of this study note that this compares unfavorably with the cost of alternative technologies; however, considerable caution should be exercised about such conclusions given that no practical carbon capture and sequestration technology currently exists at the utility scale. Finally, it is of interest that Damen et al. [77] made a detailed study of various schemes for electricity and hydrogen production with CO2 capture, and suggested that chemical looping combustion was promising and that net electric efficiencies might reach between 50% and 55% for CO2 capture of 85–100% for CLC systems.

Chemical Looping Combustion

42

Solid Fuels in Chemical Looping Combustion The use of solid fuels is evidently an extremely desirable goal. Unfortunately, syngas must first be made, albeit that it is likely to be very reactive as has been demonstrated in fluidized bed experiments [78], while natural gas represents a premium fuel, with the lowest greenhouse gas potential of any fossil fuel even if burned in a conventional cycle. Unfortunately, the direct use of such fuels evidently poses significant problems. If fluidized beds are to be used, there is the issue of making sure that a significant amount of char carbon does not enter the air reactor, reducing the benefit of the inherent separation, although this is perhaps not as much of a problem as has been occasionally suggested, since even amine scrubbing is likely to be operated with only 80–85% CO2 removal for large-scale units [79]. In addition, choices will have to be made in terms of the amount of steam and/or CO2 to be used for fluidization in the fuel reactor. Another problem of course is the potential of ash interaction with the oxygen carrier, which, as has been seen here, is likely to be expensive unless an iron-based natural ore can be used; in short, it will very strongly and adversely affect the economics of a chemical looping system if the makeup of an expensive carrier becomes excessive [17]. However, by far the biggest problem is that direct solid–solid reactions are not favored in this system. After the solid fuel (presumed to be coal but could be petroleum coke) has devolatilized, CO2 and H2O in the system must first gasify the resulting char by Rx. 12 and 13, and this process is inherently slow in fluidized bed environments, at least for most coals (a possible exception is lignite), which is why coal gasification is normally done at high temperatures and pressures with fine particles in entrained flow systems [80]. C þ H2 O ¼ CO þ H2

(42.12)

C þ CO2 ¼ 2CO

(42.13)

It should be noted that Siriwardane et al. [81] have proposed that, if there is sufficient contact between the fuel carbon and the carrier, genuine solid–solid reactions are possible, and they call this mechanism ‘‘fuel-induced oxygen release.’’ Furthermore, they have demonstrated this by work with pure carbon and CuO. Specifically, they suggest that reaction of CuO in the bulk of the particle may proceed by carbon–CuO contacts produced by surface melting of metallic copper at temperatures as low as 500–600
C, and they note that the Tamman temperature for copper (i.e., half the absolute melting point of the substance, which is the temperature at which bulk diffusion becomes rapid in a solid) is particularly low (406
C). Nonetheless, it seems most unlikely that this process by itself could achieve or explain the good conversions in a fluidized bed of char carbon by copper oxide recently reported by Dennis and Scott [82]. They used relatively large particles (+600 mm, 1190 mm) of porous alumina, impregnated with copper, so that the direct contact between the copper and the char was relatively limited. They proposed [82] that the conversion of the char by the chemical looping agent, when the bed was fluidized by nitrogen, was in fact mediated by gaseous CO2 (produced by the reaction itself), reacting with the char to produce an

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Chemical Looping Combustion

intermediate of CO, which was then rapidly converted to CO2 via reaction with the oxygen carrier. Unfortunately, their model was not able to fully account for the conversion seen. Subsequent work using an iron-based oxygen carrier [83] was able to account for the conversion of the char in a bed fluidized by nitrogen, without the need to invoke a solid– solid reaction. In this case, a model that only incorporated the Boudouard reaction and the combustion of the CO intermediate by the oxygen carrier was sufficient to quantitatively account for the observed conversions. The model was found to be very sensitive to the kinetics of conversion of the char by CO2, which may explain, in part, the difficulties encountered by Dennis and Scott [82]. It is difficult to rule out some contribution from a direct solid–solid reaction between the oxygen carrier and the char, and the controlling mechanism may depend on temperature, the metal oxide, and the degree of contact between the char and the oxygen carrier. This problem was previously of interest for the reduction of iron oxides, and the idea that the reaction may proceed by gaseous intermediates and the Boudouard reaction under some conditions (e.g., higher temperatures, more reactive chars) and direct reduction under others (e.g., vacuum, lower temperatures) is not new (see, e.g., Srinivasan and Lahiri [84]). The experiments of Dennis and Scott [82] and Brown et al. [83] were carried out at temperatures high enough for the Boudouard reaction to be significant, with reactive chars, while those by Siriwardane et al. [81] used finer particles and observed some reaction at temperatures at which the Boudouard reaction can be neglected. This mechanism does, however, appear to offer an explanation for the finite rate of reaction reported by Dennis and Scott [82] in the following words: ‘‘However, the observation of finite rates of conversion in a bed of active carrier, fluidized by nitrogen is a curiosity, which we have not been able to explain satisfactorily.’’ Despite the potential problems, the idea of using solid fuels in a chemical looping cycle was explored over a decade ago, and the work of Lyon and Cole [85] provides an extremely interesting example of this early attention. These workers called the concept unmixed combustion and looked at the possibility of using the Cu/CuO, FeO/Fe2O3, and Ni/NiO systems with the oxygen carriers supported on g-Al2O3 for a number of applications including a dual fluidized bed combustion scheme working at elevated pressure. To support this work, they also carried out a limited series of tests in batch mode with coal and Fe2O3 in a small fluidized bed, as well as a number of other experiments with methane, and concluded that the chemical looping approach had considerable promise for a range of applications including solid fuel conversion. In 2007, Chalmers University started a series of experiments on petroleum coke [49, 86, 87]. Petroleum coke, unlike most coals, normally has extremely high carbon contents (80% plus), low ash (1% or less), high sulfur (5–8%), low volatiles (5–10%), and elevated V (a potential agglomerating agent in fluidized beds) in the ash. Furthermore, it is a relatively unreactive fuel for fluidized bed applications, and primarily its high energy value and low price are the driving force for its use [88]. Hence, success with this fuel would be a very positive result for the application of chemical looping technology for solids under standard fluidized bed conditions. The first reported set of experiments was conducted in a small quartz fluidized bed, using 20 g of oxygen carrier

Chemical Looping Combustion

42

(60% Fe2O3/40% MgAl2O4) at a nominal temperature of 950
C, and the carrier was subjected to 100 cycles (100 h). This work showed that conversions were sensitive to the amount of steam in the fluidizing gas and rose with the addition of SO2, which, as noted by Lyon and Cole [85], can effectively oxidize char carbon. In a second series of tests, this time using a 10-kWth chemical looping combustor, an 11-h operation was logged, at a nominal temperature of 950
C, using ilmenite as the oxygen carrier [87], and the resulting carbon conversions were in the range of 60–75%. While these are low figures, the authors commented that improved reactor design would enhance performance, and it must be remarked that the oxygen carrier is known to be one of the less reactive carriers. More recently, the same group has looked at petroleum coke combustion, this time using a CuO carrier for a temperature range of 850–950
C in a batch fluidized bed [21]. Here, the carrier actually releases oxygen in a process that can be described in the following manner: Mex Oy ¼ Mex Oy2 þ O2

(42.14)

and this process, which the authors call chemical looping with oxygen uncoupling (CLOU), allows much faster rates of reaction, rather than depending on the gasification reactions (12) and (13). In the case of Cu, the overall global reaction is: 4CuO þ C ¼ 2Cu2 O þ CO2

(42.15)

and the use of this reaction with solid fuels is also discussed much earlier in the patent of Lewis and Gilliland [2]. In work with a South African coal, again using their 10-kWth fluidized bed facility and ilmenite as the oxygen carrier, Berguerand and Lyngfelt [89] report solid fuel conversions in the range of 50–80% and they stress the problems associated with loss of carbon fines from their cyclone and suggest various ways in which performance could be improved. These workers have also carried out a more extensive series of trials on petroleum coke and five different coals (South African, Chinese, Indonesian, Taiwanese, and French) using a quartz fluidized bed reactor and two oxygen carriers, a synthetic iron-based carrier (Fe2O3/MgAl2O4) and ilmenite [48] at a temperature of 950
C. This work again confirmed the importance of steam levels for high conversions, and found that the two carriers performed similarly. These workers have also recently developed a model for residence time analysis of the CLC of solid fuels, which can give the mass-based reaction rate for chars from the batch tests [90]. The NiO oxide system with NiAl2O4 inert (77%) has also been examined at Southeast University in China for a bituminous coal from Inner Mongolia using a small, electrically heated fluidized bed and 1 g (nominal) coal samples [91]. These workers noted that the gasification rate was slow compared with syngas, and they suggested that 100% steam as a gasification agent would improve the performance; they found that the best performance was achieved at the highest temperature they explored, 900
C. A small amount of Ni-containing material was found in the cooler designed to remove water vapor, and they suggested that in a commercial system, a nitric acid treatment of these ‘‘ashes’’ might be

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Chemical Looping Combustion

used to recover the Ni. In a more recent paper, the same group explored the use of a dual fluidized bed system consisting of a spouted fluidized bed fuel reactor and a fast fluidized bed as the air reactor [92] using the same bituminous coal as in previous studies. Again they used the NiO system with a very similar amount of NiAl2O4 inert (67.3%). As with previous studies, carbon conversions were somewhat limited, and in these experiments it reached only 92.8%, even at a temperature of 970
C in the fuel reactor. These workers at Southeast University have also studied the use of CaSO4 as an oxidizing agent for coal in a small, electrically heated fluidized bed [93]. This work showed that increasing the steam/CO2 ratio improved the gasification of coal and overall performance, but again they had problems with loss of SO2 from the system. Another problem was that sintering of the natural anhydrite became worse at 950
C, effectively negating the benefits of operating at higher temperatures. Chemical looping has also been considered for use with lignite and lignitic char [82, 83, 94, 95], which, because of their low rank, provide the most reactive coals with the highest volatile content and, thus, might be a particularly good choice of solid fuel for chemical looping. In their first study on lignite (Hambach from Germany) and its char, they explored the possibility of a process in which the coal is fed batchwise for a limited period into the reactor, its feed is then stopped until the char content in the bed is sufficiently small, and then air is reintroduced into the system to regenerate the solid oxide carrier [94]. Their first experiments were done with a small bubbling bed quartz reactor, using Fe2O3 as the oxygen carrier at a nominal temperature of 900
C, fluidized with N2 and CO2 mixtures or steam or air, and while they note that the process was not optimized in their experiments, the initial results were sufficiently encouraging to suggest that this approach offered a potentially interesting process. These workers subsequently carried out more detailed work with the same system operating at temperatures of 800–900
C with fluidizing gases consisting of mixtures of nitrogen, air, CO, and CO2 as desired [83]. They note that combustion of char also occurred when the bed was fluidized only with nitrogen, and they suggest that this is most unlikely to be due to a solid–solid reaction, but rather by small amounts of residual oxygen forming CO and CO2. In their most recent paper, these workers have also looked at the copper system, and again found a reaction when the bed is fluidized with N2, which they also suggest cannot be due to a solid–solid reaction. These experiments were done at 900
C for up to 20 cycles and showed no significant deterioration in the performance of the CuO carrier. Given the challenges of solid fuel conversion, Xiang et al. [96] suggest that ‘‘direct reaction between the coal and oxygen carrier in the CLC is not expected to be feasible because the reaction rate is likely to be too slow.’’ They also note that coal ash interactions with carriers may reduce the reactivity of the carrier, and raise the issue of carbon bypassing to the air reactor, all of which they suggest will cause the advantages of easy CO2 separation to be lost. Instead, they suggest that coal slurry should be fed through the air reactor, and the resulting syngases used to reduce the carrier in the fuel reactor. In this way, this concept was supported by an ASPEN™ simulation, and the authors suggest this is a particularly promising route, although they do note that there are some issues with ‘‘pipe gasification.’’

Chemical Looping Combustion

42

Xiao et al. [97, 98] have examined the performance of a Chinese bituminous coal in a small fixed bed reactor at pressures up to 0.6 MPa, with an iron ore–based oxygen carrier using a laboratory-scale fixed bed reactor. In this work, the cycle responsible for providing oxygen was assumed to be Fe2O3/Fe3O4. The primary focus of these studies was to determine what effect pressure had on performance rather than reactor design or scale-up, and therefore, issues such as the amount of carrier required per MWfuel were not examined in these studies. In the initial study by Xiao et al. [97], these workers looked at three to five reaction cycles and found that increasing the pressure up to about 0.5 MPa enhanced the reduction of the oxygen carrier, but that slightly lower conversions were obtained at 0.6 MPa, which was the highest pressure examined in this work. In a subsequent study, experiments were carried out for up to 20 cycles [98]. Interesting results from this study included: no evidence of agglomeration or the formation of large grains, a high stable average CO2 production (96%), and no evidence of deterioration of the oxygen carrier.

Effects of Sulfur Fairly recently the potential effects of sulfur have started to receive attention [65, 99–101]. Sulfur may be reasonably expected in natural gas prior to cleaning, in various industrial gases, and, of course, in coal syngas. Concerns expressed for the effects of sulfur include possible poisoning of the oxygen carrier, release of sulfur compounds in the gases from the air and fuel reactor, and, in the case of Ni, the possibility of melting and agglomeration phenomena due to the low melting point of Ni3S2 (melting point 791
C). In a study of a Ni-based carrier with alumina inert support, Ada´nez et al. [99] looked at the behavior of methane, ethane, and propane, as well as performing experiments with H2S addition in their 500-Wth unit. Without H2S they obtained excellent performance with high hydrocarbon conversion and no evidence of carbon formation, which was a concern especially for the higher hydrocarbons (these tests showed no signs of agglomeration or carbon formation, with or without the addition of H2S), but there was deterioration in the performance of the oxygen carrier when H2S was added to the system and sulfur compounds were found in emissions from both the air and fuel reactors. What is an extremely positive result from this work is that the oxygen carrier fully recovered its activity after the carrier was oxidized in the air reactor, suggesting that sulfur compounds do not do damage to the long-term performance of such carriers. However, it is the conclusion of these workers that high concentrations of sulfur should best be avoided in a chemical looping system operating with a Ni carrier. Ksepko et al. [65] have also recently done tests on the NiO system using a range of inert supports including sepiolite (a complex magnesium silicate), SiO2, ZrO2, and TiO2, with simulated coal-derived synthesis gas in a thermogravimetric analyzer, including tests in which 4,042 ppm of H2S was added. This work also supported the work of Ada´nez et al. [99] in showing the formation of nickel sulfide compounds, and again they showed that sulfur in these compounds was released in the oxidation stage. Another such study has been performed by Shen et al. [101] using a Ni-based oxygen carrier prepared by

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a co-precipitation method, with Al2O3 as a support using both a thermogravimetric analyzer and a small 1-kWth reactor consisting of a spouted fluidized bed as the fuel reactor and a fast fluidized bed operating as the air reactor. This work takes a very detailed look at possible reaction mechanisms with sulfur and also produces similar findings to the two other studies reported here on the Ni system. Finally, the group of Ada´nez has now looked at the Cu system with g-Al2O3 as the inert support with their 500-Wth reactor, for reaction with CH4 with H2S addition [100]. Here, the fuel reactor was operated at 800
C and 900
C, and the compound of concern is Cu2S, although with a melting point of 1,130
C, it seems unlikely that it would perform worse than Cu (1,085
C), other than by the formation of eutectic mixtures. Overall, their results were extremely positive with no evidence of impairment of combustion efficiency, even with H2S levels at 1,300 vppm, or agglomeration; the majority of the sulfur compounds were found in the emissions from the fuel reactor with very little being released from the air reactor, except at low equivalence ratios (Ø) of less than 1.5, where there was evidence of Cu2S formation. (Here Ø is defined as the oxygen requirement of the fuel, divided by the potential oxygen release from the carrier, with a value of 1 being equivalent to the complete conversion of the fuel to CO2 and H2O.) One interesting result was that, in experiments done to explore a possible regeneration of the carrier, where the H2S feeding to the air reactor was suspended and the fuel feed was decreased to achieve an equivalence ratio of 1.9, there was a sudden release of SO2 (3,300 ppm) and the gas composition returned to values corresponding to normal combustion for this system. These workers attribute this to a solid–solid reaction: Cu2 S þ 2CuO ¼ 4Cu þ SO2

(42.16)

and these results can reasonably be interpreted to be in agreement with the work of Siriwardane et al. [81], who suggest that the copper system is capable of significant solid– solid reaction at standard chemical looping conditions.

Hydrogen Production and Reforming Applications Relating to Hydrogen Production The production of H2 is important for many reasons, some of them being longer term, such as introducing the H2 economy, possibly with the use of fuel cells, and encompassing the transportation industry [102], rather than just stationary power sources or industrial processes, as are the bulk of examples considered in this chapter. However, H2 itself is an important chemical, produced in very large amounts (of the order of 65 million t/a [103]) and is of profound interest to some national economies, such as in the case of Canada for oil sands upgrading, where current needs are around 1 million t/a, but have been predicted to rise to 7.7 million t/a by 2030 [104]. Thus, cheap methods of producing H2 are desired, especially if this can be produced in a CO2-neutral manner, since about 48% of H2 is produced from natural gas while another 48% comes from oil or coal, with electrolysis supplying the rest [103].

Chemical Looping Combustion

42

The idea of using H2 to fuel CLC was considered early on by Jin and Ishida [105], but reasonably most of the research and development has been concentrated on various schemes for H2 production [66, 106–108]. Thus, Zafar et al. [66] looked at the possibility of integrated hydrogen and power production for the CuO, Mn2O3, NiO, and Fe2O3 systems with SiO2 as a support. For their experimental work, they used a small quartz fluidized bed reactor and they looked at performance for the fuel-rich situation. The concept they proposed was that methane is first converted into CO2 and H2, and then shifted in a separate reactor; in particular, they were interested in the potential performance of the oxygen carriers, which they ranked in the order of decreasing reactivity as NiO/SiO2 > CuO/SiO2 > Mn2O3/SiO2 > Fe2O3/SiO2. An interesting study has been performed by Chiesa et al. [106], which envisages the use of three reactors using the iron system, and natural gas. Here, in the fuel reactor, hematite (Fe2O3) is reduced primarily to Wustite (Fe(1  y)O where 0.05 < y < 0.17 [11]) by oxidizing the natural gas; in the steam reactor, most of the reduced FeO reacts with steam to form magnetite (Fe3O4), and finally, in the third reactor, the Fe3O4 is reoxidized to Fe2O3. Among the interesting points about such a scheme is that, unlike most chemical looping schemes, it involves the metal in more than two oxidation states, and the result of the simulation performed suggested that it was economically preferable simply to produce H2, rather than H2 and electricity. This study suggested that the economics of such a scheme were comparable with those of other approaches, but that the environmental benefits in terms of 100% CO2 capture were better, given that the best alternative would at most achieve no more than 80% CO2 capture. A fairly similar scheme, again with an iron-based carrier, has also been explored using coal as the fuel source, by Xiang et al. [108] for the simultaneous production of hydrogen and electricity, again with three reactors, using an ASPEN™ plus simulation. For the system considered by the authors, they note that the costs of such a system are high but the environmental benefits are significant. One limitation they see in a scheme producing both H2 and electricity is that it is not possible to greatly vary the ratio of hydrogen production to electricity because this is dependent on the circulation rates for the oxygen carrier and hence the heat balance for the three reactors. The iron system with H2 production from coal syngas, using an ASPEN™ simulation based on bench-scale results, is also explored by Fan et al. [109], again with a very positive evaluation. This scheme has also been explored experimentally, but this time using mixtures of CO, CO2, and N2 as the fuel source, in a small packed bed reactor (dia. 103 mm), by workers at the University of Cambridge [11] whose work supported the general feasibility of such a scheme for producing very pure H2. In 2009, these same workers carried out simulations of the same scheme, looking at steam pressures of 0.1 and 1 MPa, and showed that it was possible to achieve the necessary heat integration [110]. Finally, this scheme has also been explored experimentally using a lignitic coal and its chars [111] and a small fluidized bed reactor using batches of hematite or Fe2O3, and demonstrated successful reduction of the hematite with potassium carbonate–promoted chars, production of H2 via the reaction of water with the FeO, Fe produced by reaction with char, and final oxidation of the resulting magnetite (Fe3O4) to hematite (Fe2O3) by reaction with air.

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Reforming The chemical looping process can be utilized for reforming by using the oxygen carrier to supply heat to drive reactions such as: CH4 þ CO2 ¼ 2CO þ 2H2

(42.17)

CH4 þ H2 O ¼ CO þ 3H2

(42.18)

or the more familiar

Alternatively, chemical looping can be used simply to make a syngas containing CO and H2 directly (as in Rx. 2; i.e., an autothermal scheme), which was the subject of the first published paper on chemical looping using the copper system [1]. A detailed review of R&D in Europe within the framework of the CACHET project was produced by Ryde´n et al. [53]. This evaluation, which looks at results from thermogravimetric analyzers, and various batch and continuous fluidized bed facilities (up to a scale of 140 kWth), including a semicontinuous pressurized facility (with reforming pressures up to 1 MPa), has suggested that autothermal reforming is feasible with the standard metal oxide systems (NiO, Fe2O3, Mn3O4, and CuO) with syngas compositions close to those expected on thermodynamic grounds, and that carbon formation can be avoided provided that the fuel is diluted with around 30% by volume of steam. The work reported in this study suggests that adding Ni to Fe- and Mn-based carriers is a promising approach to improve the performance of these systems, with Ni also acting as a catalyst to promote the formation of CO and H2 from CH4. The work at elevated pressure was also successful, with no adverse pressure effects or evidence of carbon formation over the range of conditions examined. With respect to carbon formation, Ryde´n et al. [112] make the interesting point that any carbon formation in the fuel reactor is not necessarily problematic since it can be converted to CO2 in the air reactor and this could be seen as another benefit of the chemical looping process. Recently, De Diego et al. [113] have carried out reforming trials of up to 40-h duration using a Ni-based carrier and a 900-Wth continuous atmospheric chemical looping reforming pilot plant with a temperature in the air reactor of 950
C and in the fuel reactor ranging from 800
C to 900
C. They report excellent CH4 conversions of greater than 98%. The product gases are strongly dependent on the oxygen carrier circulation rate and these workers recommend a NiO-reacted/CH4 molar ratio of around 1.25. In this work, no deterioration of the carrier, agglomeration, or defluidization issues were detected and the attrition rate was negligible. In recent tests done in a 140-kW reactor using two different NiO-based carriers (with NiAl2O4 and MgAl2O4 as inerts), excellent performance has been reported [114]. No carbon formation occurred for global air/fuel ratios larger than 0.4, even though the steam/carbon ratio was less than 0.4, and no CO2 emissions were detected from the air reactor. An unusual choice, the CaSO4 system has also been analyzed for propane reforming (as an analog for liquefied propane gas, LPG) by Kale et al. [115]. They suggested that, at a recommended temperature of about 700
C, significant carbon or methane formation

Chemical Looping Combustion

42

should be avoided, and they also noted that sulfur release is unlikely below about 780
C. Unfortunately, there is no experimental work to support this analysis, and issues with the kinetic rate for reaction and sintering of a natural form of CaSO4 could reasonably be expected to be problematic, in line with the work done so far for use of this system in combustion. This work also suggests that, by using the CO2 and H2O for reforming with more propane, the ‘‘risks’’ of carbon sequestration are eliminated; however, any benefits of CO2 reduction depend entirely on the subsequent fate of the syngas.

Pressurized Chemical Looping Systems The use of pressure is of interest for a number of reasons. For thermal power, the dominant reason is the possibility of high-efficiency cycles via combined cycle operation and, in addition, depending on the pressure of operation, less or no energy would be needed to compress the CO2 to levels necessary for pipeline transportation for final sequestration. This approach has had its most notable commercial successes with gasification and integrated gasification combined cycle operation [80]. However, pressurized fluidized bed technology, although it has been developed to the 350-MWe demonstration size, has not had the same success, and the largest such unit will shortly be closed down because of poor availability and other problems [116]. In general, problems with access to the equipment due to the existence of the pressure vessel (which translate into availability problems) and, above all, the need to operate with expensive ruggedized turbines, have meant this technology could reasonably be considered moribund at this point. However, given the very low attrition rates observed, as discussed earlier in this chapter, from hot beds of oxygen carriers, it is to be hoped that, for gaseous fuels at least, pressurized applications might have less problems. Normally, in pressurized gasification and combustion applications, it is the oxidant (either air or oxygen) that is compressed; in the case of pressurized chemical looping cycles, the fuel gas must be pressurized, and this will mean that the amounts of solid oxide carrier to be circulated to the fuel reactor must be significantly increased. A very early examination of the effect of pressure on the Ni system, using a thermogravimetric analyzer [105] for H2 conversion, showed that increased pressure (up to 909 kPa) reduced the temperature for the commencement of both reduction and oxidation (by about 50
C), and that the oxidation rate was nearly independent of pressure. In a subsequent study, looking at NiO/NiAl2O4 and CoO-NiO/YSZ particles in a TGA, with simulated coal gas, the same workers found evidence of methanation and carbon deposition, but the carbon deposition could be resolved by increasing the H2O/ CO ratio from 0.5 to 1 at elevated pressure (up to 909 kPa) [117]. They also reported that the overall reaction rate increased with increasing pressure. However, a later study using a pressurized thermogravimetric analyzer (PTGA), carried out with pressures up to 3 MPa using H2/N2 and CO/CO2/N2 mixtures, showed that increasing total pressure reduces the reaction rate of the oxygen carriers examined, and it was speculated that increasing pressure might affect the internal structure of the

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oxygen carrier [118]. In analyzing this study to map the range of operation conditions for Cu-, Fe-, and Ni-based carriers [15], the same group notes that there will be a need for higher solid inventories than expected due to the increase in gas concentrations at higher pressure, and suggests that even at 1 MPa the iron system might present problems because of the upper limit for transport capacity of solids in the riser. Siriwardane et al. [61] looked at the behavior of a nickel oxide (60% by wt) oxygen carrier supported on bentonite, using a high-pressure flow reactor operating at 101– 690 kPa, and showed a rather more complicated picture for this system, with improved reaction at the highest pressure. However, the same workers also examined a copper oxide carrier using bentonite with a tapered-element oscillating microbalance, at pressures up to 690 kPa, and concluded that reaction pressure has a negative effect on reaction rates [44], in agreement with work by Garcia-Labiano et al. [118].

Future Directions What is now missing in the development of CLC are the first commercial- or nearcommercial-scale demonstrations of the technology, similar to those being developed, for instance, by the US DOE for the CaSO4 system [38]. In a related effort, Tobias Pro˝ll of the Technical University of Vienna has informed the author that they have developed a process flow sheet and design criteria for a 10-MWth demonstration plant firing natural gas. For this work, the overall efficiency estimated is only 36%, but it is suggested that this is reasonable considering the size of the plant. It is the practical application of these technologies and their demonstration at the industrial scale in the next several decades that are key to their contribution to a carbon-constrained world. Although this chapter is devoted to considering primarily fossil fuels, or syngas derived from them, and focuses in particular on CH4, syngas, and coal, there are of course numerous other possible applications for chemical looping processes. Examples include the synthesis of methanol from methane with a reduced carbon footprint [119], a novel methanol power system using chemical looping with low-temperature reduction of methanol [120], and a number of schemes involving chemical looping including coalto-liquids, as explored by Professor Fan’s group at Ohio State University [109]. No attempt to consider these in detail is made here; they are noted simply to indicate the vast range of possibilities associated with the future of this technology.

Conclusions Chemical looping is a relatively new technology, which had its beginnings some 60 years ago. However, it only began to receive major attention in the last 25 years or so. Major strides have been made taking the technology from work primarily involving fixed beds and thermogravimetric analyzers to numerous small pilot-scale fluidized bed reactors, with trials achieving upward of 1,000 h. In addition, numerous possible systems have been

Chemical Looping Combustion

42

explored, although the bulk of research has focused on Ni-, Cu-, and Fe-based carriers together with a vast number of possible inert substrates. Straight combustion of natural gas and, more recently, solid fuels has been explored including various schemes for the production of hydrogen. There has also been significant development in the area of reforming using this technology. What is currently lacking are larger-scale demonstration units and the development of such facilities is urgently needed if the technology is to progress. However, for now, this technology can be seen as one of the most interesting and promising, available for use in a future carbon-constrained world.

Acknowledgments The author gratefully acknowledges the assistance and advice of Dr. David Granatstein (Granatstein Technical Services/CanmetENERGY) and Dr. Stuart Scott (Lecturer in Sustainable Energy, Department of Engineering, University of Cambridge) for a number of valuable discussions during the preparation of this chapter as well as for suggesting various amendments and improvements.

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Chemical Looping Combustion 84. Srinivasan NS, Lahiri AK (1975) On the mechanism of iron oxide reduction by carbon. Metall Trans B 6(2):269–274 85. Lyon RK, Cole JA (2000) Unmixed combustion: an alternative to fire. Combust Flame 121: 249–261 86. Leion H, Mattisson T, Lyngfelt A (2007) The use of petroleum coke as fuel in chemical-looping combustion. Fuel 86:1947–1958 87. Berguerand N, Lyngfelt A (2008) The use of petroleum coke as fuel in a 10 kWth chemicallooping combustor. Int J Greenhouse Gas Control 2:169–179 88. Anthony EJ (1995) Fluidized bed combustion of alternative solid fuels: status, successes and problems of the technology. Prog Energy Combust Sci 21:239–268 89. Berguerand N, Lyngfelt A (2008) Design and operation of a 10 kWth chemical-looping combustor for solid fuels – testing with South African coal. Fuel 87:2713–2726 90. Markstro¨m P, Berguerand N, Lyngfelt A (2010) The application of a multistage-bed model for residence-time analysis in chemical-looping combustion of solid fuel. Chem Eng Sci 65(18):5055–5066 91. Gao Z, Shen L, Xian J et al (2008) Use of coal as fuel for chemical-looping combustion with Nibased oxygen carrier. Ind Eng Chem Res 47:9279–9287 92. Shen L, Wu J, Xiao J (2009) Experiments on chemical looping combustion of coal with a NiO based oxygen carrier. Combust Flame 156:721–728 93. Zheng M, Shen L, Xiao J (2010) Reduction of CaSO4 oxygen carrier with coal in chemicallooping combustion: effects of temperature and gasification intermediate. Int J Greenhouse Gas Control 4(5):716–728 94. Scott SA, Dennis JS, Hayhurst AN, Brown T (2006) In-situ gasification of a solid fuel and CO2 separation using chemical looping. AIChE J 52:3325–3328 95. Dennis JS, Scott SA, Hayhurst AN (2006) In situ gasification of coal using steam with chemical looping: a technique for isolating CO2 from burning a solid fuel. J Energy Inst 79:187–190 96. Xiang W, Wang S, Di T (2006) Investigation of gasification chemical looping combustion

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combined cycle performance. Energy Fuels 22:961–966 Xiao R, Song Q, Song M et al (2010) Pressurized chemical-looping combustion of coal with an iron ore-based oxygen carrier. Combust Flame 157:1140–1153 Xiao R, Song S, Zhang S et al (2010) Pressurized chemical-looping combustion of Chinese bituminous coal: cyclic performance and characterization of iron-ore based oxygen carrier. Energy Fuels 24:1449–1463 Ada´nez J, Garcı´a-Labiano F, Gaya´n P et al (2009) Effects of gas impurities on the behavior of Ni-based oxygen carriers on chemical-looping combustion. GHGT-9. Energy Procedia 1:11–18 Foero CR, Gaya´n P, Garcı´a-Labiano F et al (2010) Effect of gas composition in chemicallooping combustion with copper based oxygen carriers: fate of sulphur. Int J Greenhouse Gas Control 4(5):762–770 Shen L, Gao Z, Wu J, Xiao J (2010) Sulfur behavior in chemical looping combustion with NiO/Al2O3 oxygen carrier. Combust Flame 157:853–863 McGlashan NR (2010) The thermodynamics of chemical looping combustion applied to the hydrogen economy. Int J Hydrogen Energy 35:6465–6474 Harrison DP (2009) Private communication. University of Louisiana, Lafayette, September 2009 Larsen R, Wang M, Santini D et al (2004) Might Canadian oil sands promote hydrogen production technology for transportation. Argonne National Laboratory Presentation, Chicago, IL, 20 Apr 2004 Jin H, Ishida M (2001) Reactivity study on a novel hydrogen fueled chemical-looping combustion. Int J Hydrogen Energy 26:889–894 Chiesa P, Lozza G, Malandrino A et al (2008) Three-reactors chemical looping process for hydrogen. Int J Hydrogen Energy 33:2233–2245 Go KS, Son SR, Kim SD et al (2009) Hydrogen production from two-step steam methane reforming in a fluidized bed reactor. Int J Hydrogen Energy 34:1301–1309 Xiang W, Chen S, Xue Z, Sun X (2010) Investigation of coal gasification hydrogen and electricity co-production with three-reactors chemical

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Section 6

Advanced Technologies

43 Low-Temperature Fuel Cell Technology for Green Energy Scott A. Gold Department of Chemical and Materials Engineering, University of Dayton, Dayton, OH, USA Introduction to Fuel Cell Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1659 Chapter Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1660 A Brief History of Fuel Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1661 Fundamentals of Fuel Cell Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1662 Performance Metrics for Comparing Fuel Cells and Other Energy Systems . . . . . 1662 Description of Basic Operation of a Fuel Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1663 Thermodynamics and Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1665 Fuel Cell Thermodynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1665 Thermodynamic Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1666 Electrochemical Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1668 Fuel Utilization Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1668 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1668 Kinetic Processes in Fuel Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1669 Reaction Kinetics and Activation Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1669 Charge Transport and Ohmic Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1672 Mass Transfer and Concentration Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1674 Fuel Crossover Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1676 Summary of Electrode Polarization Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1677 Low-Temperature Fuel Cell Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1678 PEM Fuel Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1678 Hydrogen PEM Fuel Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1678 Direct Alcohol Fuel Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1679 Direct Formic Acid Fuel Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1679 Alkaline Fuel Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1680 Enzymatic and Other Biofuel Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1681

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_43, # Springer Science+Business Media, LLC 2012

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Fuel Cell Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1681 Membrane Electrode Assembly, Flow Field, and Fuel Cell Stack . . . . . . . . . . . . . . . . 1682 Fuel Processing, Storage, and Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1683 Thermal Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1686 Power Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1687 Technical Challenges and Current Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1687 Hydrogen Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1688 Catalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1689 Electrolyte Membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1692 Bipolar Plate Materials and Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1695 How Green Is My Fuel Cell? Or Life Cycle Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1695 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1696 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1698

Low-Temperature Fuel Cell Technology for Green Energy

43

Abstract: Fuel cells convert chemical energy to electrical energy via an electrochemical reaction. They are more efficient than traditional heat engine–based power systems and can have zero or near-zero emissions during operation. A leading alternative green energy technology, fuel cells are finding applications in many areas, including transportation, portable power, and stationary power generation. These divergent uses have driven development of several different types of fuel cell technologies. A brief overview of these will be provided in this chapter; however, the focus will be on low-temperature proton exchange membrane (PEM) technologies predominant in portable power and automotive applications. Fuel cell operating principles will be reviewed, focusing on thermodynamics, efficiency, reaction kinetics, and transport phenomena in order to develop a framework for evaluating different fuel cells and comparing them with other power systems. Theoretically, much improvement in fuel cell performance is possible, and is needed along with means of lowering economic costs in order for fuel cells to see more widespread use. Some of the major technical challenges in these regards are outlined along with approaches being investigated to meet these challenges. Life cycle assessment and its application to fuel cells will be discussed to evaluate environmental impacts associated with manufacturing, operation, and disposal.

Introduction to Fuel Cell Technology Fuel cells are one of the leading alternative energy technologies for a variety of applications, including automobiles, portable electronics, and many others. These electrochemical power generators convert chemical energy to electrical energy, in a manner similar to that of batteries. Fuel is oxidized at the anode to produce electrons and mobile ions. The mobile ions pass through an electrolyte to reach the cathode while the electrons pass through a circuit, providing electrical current power some external load before returning to the cathode. At the cathode, the mobile ions are reduced, completing the reaction. This basic description applies to the most common fuel cells for which protons or other positive ions are the mobile ions, including the most common low-temperature fuel cell, the hydrogen proton exchange membrane (PEM) fuel cell, in which hydrogen fuel is oxidized to form protons (the mobile ions), and electrons. The electrons pass through an external circuit while the protons pass through the PEM. Oxygen (the oxidant) combines with the protons and electrons at the cathode to form water, completing the overall reaction. This process continues producing electricity so long as fuel and oxidant are supplied to the cell, whereas in a battery, the fuel and oxidant are contained in the electrode materials themselves. There are many different varieties of fuel cells in addition to the hydrogen PEM fuel cell discussed above. These may be classified based on the type of materials used for the electrolyte, the type of fuel utilized, or typical operation temperature. Some of the most common varieties of fuel cell are described in > Table 43.1. This chapter will be concerned with the most common types of low-temperature fuel cells which primarily utilize proton exchange membranes, or PEMS: hydrogen PEM fuel cells, direct methanol fuel cells

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Low-Temperature Fuel Cell Technology for Green Energy

. Table 43.1 Summary of types of fuel cells Fuel cell type

Fuel

Mobile ion Electrolyte

Operating temperature Main applications

Alkaline (AFC)

Pure H2

OH


KOH

50–200 C

Proton exchange membrane (PEMFC) Direct methanol (DMFC), formic acid (DFAFC) and other liquid fuels Phosphoric acid (PAFC)

Pure H2 H+ (tolerates CO2)

Solid polymer (e.g., Nafion) Solid polymer (e.g., Nafion)

30–100 C

H+ Methanol, formic acid, other alcohols

20–90 C

H+ Pure H2 (tolerates CO2, 1% CO)

Phosphoric 220 C acid

Molten carbonate (MCFC)

H2, CH4, other CO32
hydrocarbons (tolerates CO2)

Lithium and potassium carbonate

Solid oxide (SOFC)

H2, CH4, other O2
hydrocarbons (tolerates CO2)

Solid oxide (e.g., yttria stabilized zirconia)

Enzymatic biofuel cells

Sugars or alcohols

H+

Solid polymer (e.g., Nafion) or biological fluid

Space program (historical) Vehicles and mobile power

Portable electronics

200 kW CHP systems

650 C

Medium to largescale stationary combined heat and power (MW capacity) 500–1,000 C All size stationary combined heat and power systems (2 kW to multi-MW capacity) 20–40 C

Bio-implants and energy scavenging (research)

(DMFCs), direct formic acid cells (DFAFCs), and other direct liquid fuel cells. Hightemperature technologies such as solid oxide and molten carbonate fuel cells will be covered in more detail in the next chapter as they have very different technical challenges and are being developed primarily for larger scale power generation.

Chapter Overview The goals of this chapter will be to provide context for the evaluation of fuel cell technology as a green energy alternative. A short history of the development of this

Low-Temperature Fuel Cell Technology for Green Energy

43

technology will be provided, followed by a discussion of means of comparing fuel cells with other energy technologies. Technical background on the thermodynamic, reaction, and mass transfer processes occurring in a fuel cell are then provided along with a brief overview of each of the major low-temperature fuel cell technologies. A fuel cell is only one part of a total power system. Fuel storage and delivery, thermal management, and power management subsystems are among the many components of a total fuel cell power system. Key characteristics and design criteria for each of these will be reviewed. Fuel cell technology, while holding much promise, is only beginning to find its way into commercial applications. Some of the major technical challenges that are providing roadblocks to more widespread use of fuel cells will be highlighted along with a brief discussion of current research aimed at solving these problems. If only efficiency and emissions are considered, fuel cells are a truly ‘‘green’’ technology. Emissions are primarily water vapor and carbon dioxide, and in well-designed systems, a very high fraction of the usable energy in the fuel is converted to electricity. However, a more rigorous analysis that considers everything from mining of raw materials to final disposal is needed to compare the environmental impact of different energy technologies. Life cycle assessment of fuel cell technology will be reviewed as a means of evaluating how truly ‘‘green’’ fuel cell, or any technology, truly is. This chapter will conclude with some speculation on what the future might hold for fuel cell technology.

A Brief History of Fuel Cells Sir William Grove is credited with demonstrating the first fuel cell in 1839, ironically at about the same time the first internal combustion engines were developed. For much of the next century, fuel cells essentially remained a curiosity studied by academics and hobbyists. Beginning in the 1930s, F.T. Bacon made great advances in alkaline hydrogen fuel cells [1]. Bacon’s designs were adopted and further developed by Pratt and Whitney and later United Technologies and utilized for power generation in American space program [1]. Throughout the Apollo space program, alkaline fuel cells were used to provide on-board power for electrical systems. The high energy density (energy per unit weight or volume) of fuel cells made them ideal for this use where minimizing payload weight is crucial. This concern has also been one of the primary drivers of ongoing research and development of fuel cells for portable commercial electronics (e.g., laptop computers, cell phones, etc.). Since 2000, several electronics manufacturers, including Samsung, NEC, Casio, and LG have introduced fuel cell power systems for portable electronic devices, though these have yet to reach any large markets [2, 3]. In the 1990s, environmental and regulatory concerns as well as issues relating to the cost and supply of oil led automotive companies begin to develop hydrogen fuel cell technology for electric vehicles in earnest. This work has begun to bear fruit as many different types of hydrogen vehicles have been introduced around the world by auto manufacturers. Iceland in particular has embraced the move toward a hydrogen economy [4]. Daimler-Benz began developing hydrogen-powered busses in the early 1980s, which are now being

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utilized in Australia [5] and many cities in Europe through the Europe-wide Clean Urban Transport (CUTE) [6]. Honda has developed its FCX Concept vehicle utilizing a 100-kW hydrogen fuel cell, which began road testing in Japan in 2002 and was available for lease in 2007 in California [7]. Similarly, Both Ford and General Motors have been developing vehicles with hybrid fuel cell power system some of which have been evaluated on North American roads [8]. These are only a few examples of the many fuel cell vehicles under development and/or evaluation in recent years. If the progress of recent years is any indication, fuel cell technology has a very exciting future.

Fundamentals of Fuel Cell Operation Performance Metrics for Comparing Fuel Cells and Other Energy Systems The most obvious measures of fuel cell performance metrics include current, voltage, and power output as well as the lifetime of the cell before refueling is required. These are of somewhat limited value in comparing different fuel cells or fuel cells to other power sources however, as they are dependent on size. In comparing different fuel cells to one another, current and power should be compared on a per unit area basis. Voltage is not impacted by the area of the electrodes, but can be increased by connecting cells in series as is done in batteries. As the lifetime of a fuel reservoir is primarily dependent on the size of that reservoir, a better measure for comparing fuel cells is the fuel utilization efficiency, or the fraction of fuel fed to the system that is converted to power. The most common measures used to compare fuel cells to other energy systems are energy density and power density. These can both be measured gravimetrically (i.e., energy or power per unit mass) or volumetrically (i.e., energy or power per unit volume). Graphically, plots of energy density versus power density called Ragone plots are often utilized to compare energy sources, such as the one shown in > Fig. 43.1. One of the more attractive features of fuel cells is that they provide a relatively high energy density. A driving factor in the development of new electronic devices is reducing size and weight. Currently, batteries comprise a large fraction of the weight of laptop and tablet computers, mobile phones, and other devices, motivating efforts to develop fuel cells for such systems. Weight reduction is also important in automotive applications, though less critical than for portable electronics. Various efficiency measurements are also utilized in comparing fuel cells to other energy systems. In general, these are based on thermodynamics; however, because of fundamental differences in the mechanisms of operation, such measures often create more confusion than clarity. These measures will be discussed in greater detail later in this chapter.

Low-Temperature Fuel Cell Technology for Green Energy

43

1000 Fossil Fuel Combustion

Fuel Cells

Energy density (Wh/kg)

100

Li Ion Batteries

Lead Acid Batteried

10

Supercapacitors 1

Conventional Capacitors

0.1

0.01 10

100

1000

10000

Power density (W/kg)

. Fig. 43.1 A Ragone plot illustrating approximate energy and power densities of various energy technologies

Description of Basic Operation of a Fuel Cell The hydrogen proton exchange membrane fuel cell (H2 PEM FC) provides a chemically simple example to illustrate the fundamental principles for all types of fuel cells. In this type of cell, the hydrogen fuel is oxidized at the anode to form protons and electrons. H2 ! 2Hþ þ 2e


(43.1)

An electrolyte acts to physically separate the two half cell reactions and force the electrons to pass through a circuit where they can do electrical work before returning to the cathode while the mobile hydrogen ions pass through the electrolyte (see > Fig. 43.2). The protons and electrons ultimately combine to reduce oxygen at the cathode and form water as a waste product. 1 O2 þ 2Hþ þ 2e
! H2 O 2

(43.2)

Thus, the overall reaction for a hydrogen fuel cell is H2 þ O2 ! H2 O

(43.3)

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Low-Temperature Fuel Cell Technology for Green Energy

Current e−

H2

e−

Load

e−

e−

e−

e−

Anode 2H + + 2e−

Cathode 2H + + 2e− + ½O2

H 2O

H+ H2O

H2 H+

H+

O2

Cathode Catalyst

Anode catalyst

1664

Electrolyte membrane

. Fig. 43.2 Illustration of the basic operation of a hydrogen proton exchange membrane fuel cell

The various types of fuel cells outlined in > Table 43.1 operate in the same general manner in that fuel is oxidized at the anode and electrons are forced through a circuit while mobile ions move through an electrolyte to combine at the cathode in a reduction reaction. They differ in the specific fuels, mobile ions, and typical operating conditions. As will become evident, each type of fuel cells has its own strengths and weaknesses, which determine the applications for which they are suitable. In this section, the some of the fundamental science and engineering principles of fuel cell operation will be reviewed, beginning with a discussion of thermodynamics in fuel cells. From thermodynamics, the maximum performance in terms of electrical potential that can be generated by a given fuel cell can be determined. This ‘‘ideal’’ limit also provides a means of evaluating the potential of a given fuel cell technology as well as providing important, but sometimes confusing, means of evaluating fuel cell efficiency. While thermodynamics provides theoretical limits on performance, practical limits are imposed by kinetic and transport processes. Reaction kinetics, particularly for oxygen reduction, significantly limit fuel cell performance driving significant research to develop improved catalysts. An overview of these topics is provided in the following sections. For a more detailed discussion, the reader is referred to any of a number of fuel cell and electrochemistry texts [9–14].

Low-Temperature Fuel Cell Technology for Green Energy

43

Thermodynamics and Efficiency Fuel Cell Thermodynamics For an isothermal, isobaric system, the maximum amount of work that can be done by the system is equal to the Gibbs free energy change for that system. In the case of a fuel cell, electrical work (Welec) is of interest and the Gibbs free energy change occurs as a result of the overall fuel cell reaction, thus we can mathematically state: 0 Welec ¼
DGrxn

(43.4)

0 where DGrxn is the standard state change in the Gibbs free energy of the reaction. The change in Gibbs free energy is related to the change in enthalpy of the reaction (Hrxn) by > Eq. 43.5,

DG ¼ DH
T DS

(43.5)

where DS is the enthalpy of the reaction at absolute temperature T. The value TDS represents thermal energy unavailable for being converted to electrical work and places a fundamental limit on the efficiency of a given fuel cell. Electrical work is accomplished by moving charge carried by electrons through an electrical potential gradient DE, thus electrical work can be expressed as the product of the total charge (Q = nF) and the field strength, Welec ¼ DEQ ¼ nFDE

(43.6)

where n is the number of moles of electrons produced in the fuel cell reaction and F is Faradays constant. Combining > Eqs. 43.4 and > 43.6, we get DE0, the maximum standard state reversible voltage for the overall reaction in a fuel cell: DE 0 ¼


0 DGrxn nF

(43.7)

Cell potential can be related to reactant and product concentrations at a given temperature by considering a general reaction of A and B to form products C and D: aA þ bB ! wC þ dD

(43.8)

The Gibbs free energy for such a reaction is familiar from basic thermodynamics as: DG ¼

0 DGrxn RT

ln

aCw aDd aAa aBb

! (43.9)

where aA, aB, aC, and aD are the activities of species A, B, C, and D, respectively and R is the gas constant. The activities of course are dependent upon the physical state of the reactants or products. For an ideal gas, the activity of species i can be expressed: ai ¼

Pi P0

(43.10)

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Low-Temperature Fuel Cell Technology for Green Energy

where Pi is the partial pressure of species i and P0 is the standard pressure (usually 1 atm). For an ideal solution, the activity of species i is expressed ai ¼

½i  ½i 0

(43.11)

where [i] and [i]0 are the concentration and standard state concentrations of species i. If the reactants and products for the generic reaction (> Eq. 43.8) are presumed to be in an ideal solution, then > Eq. 43.9 can be rewritten as ! w d ½ C  ½ D  0 DG ¼ DGrxn RT ln (43.12) ½Aa ½Bb Substituting > Eq. 43.7 into > 43.12 yields the familiar Nernst equation, !   RT ½Cw ½Dd 0 DE ¼ DE þ ln nF ½Aa ½Bb

(43.13)

relating the cell potential or emf, DE, to the standard state potential and reactant concentrations at a given temperature. As this equation illustrates, the cell potential increases with the concentration of the reactants. The overall reaction in a fuel cell is of course the sum of two half cell reactions, which often are studied separately. The total cell potential is expressed as a difference between the thermodynamic electrochemical potentials of the half cell reactions at the cathode and anode, respectively, DE ¼ Ecathode
Eanode

(43.14)

Thermodynamic Efficiency As noted previously, the entropy of the overall fuel cell reaction places a fundamental limit on fuel cell efficiency. Thermodynamic efficiency is of course an important concept in evaluating fuel cells, or any other system that converts energy to work. The standard definition of thermal efficiency, e, for any system is e¼

Wout Qin

(43.15)

where Wout is the work done by the system and Qin is the energy supplied to the system. For transportation applications where internal combustions engines are standard, it is useful to compare fuel cell efficiency to that of such heat engines. For a heat engine, the maximum efficiency is that of a reversible Carnot cycle. Applying the first law of thermodynamics to a completely reversible system requires that all thermal energy supplied to the system (Qin) is either converted to work (Wout) or rejected to the surroundings (Qout), so that > Eq. 43.7 above can be expressed as: eCarnot ¼

Qin
Qout Qin

(43.16)

Low-Temperature Fuel Cell Technology for Green Energy

43

where eCarnot is the Carnot efficiency. This can also be expressed in the more familiar manner in terms of the low and high reservoir temperatures of the system, eCarnot ¼ 1


Tlow Thi

(43.17)

Thi and Tlow are the absolute temperatures of the respective thermal reservoirs in the heat engine. Tlow is typically limited to the ambient temperature. As > Eq. 43.17 illustrates, 100% efficiency is approached as the temperature difference between the two reservoirs in a heat engine becomes very large. An internal combustion engine, however, is not a completely reversible Carnot engine. The combustion process introduces significant irreversibility to the system and serves to limit the achievable efficiency. Practical values for thermodynamic efficiency of heat engines are around 40% [15]. It is frequently noted that an advantage of fuel cells is that not being heat engines, they are not Carnot limited [9–11]. Fuel cells are often operated nearly isothermally and directly convert chemical energy to electrical work. Not surprisingly, > Eqs. 43.16 and > 43.17 are not valid or even meaningful for fuel cells. This does not mean that fuel cells are not thermodynamically limited as > Eq. 43.15 above still determines the maximum thermodynamic efficiency possible. Neither should it be misunderstood that the theoretical limit of efficiency is higher for fuel cells than heat engines. As shown in > Eq. 43.7, the maximum amount of energy available to do work in a fuel cell is given by the Gibbs free energy of the overall fuel cell reaction, providing a limiting value for Wout in > Eq. 43.15 when determining the maximum theoretical thermodynamic efficiency of a fuel cell. It is common to assume that fuel cells are operating isothermally and in thermal equilibrium with the surroundings. Care should be taken before the latter of these assumptions is made, especially if the fuel cell operates at a temperature significantly above ambient [16]. The higher heating value of the fuel, or the enthalpy of combustion to a vapor phase product, DHHHV, as shown in > Eq. 43.18 is most commonly used for Qin: efc ¼

DGrxn DHHHV

(43.18)

This is justified by the fact that fuel combustion is used to provide energy to a heat engine, thus providing a convenient means of comparison. Nonetheless, this choice presents some challenges that can lead to significant confusion. > Equation 43.18 can also give efficiencies of greater than 100% for some systems in which there is a positive entropy change on reaction. Lutz et al. proposed a modified solution to deal with this, noting that energy for a positive entropy change must be taken from the surroundings [17]: 
DHR if DSR  0 Qin ¼ (43.19)
DHR þ T DSR if DSR > 0 where DHR and DSR are the enthalpy and entropy of reaction, respectively. In direct comparisons of the thermodynamic efficiencies of heat engines and fuel cells conservation of exergy or availability, not energy, should be considered [16]. For both an

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Low-Temperature Fuel Cell Technology for Green Energy

ideal fuel cell and a Carnot engine, exergy is completely conserved. However, when full systems are taken into account, the situation changes. An ideal heat engine is supplied with heat, not chemical fuel. Combustion irreversibility significantly limits the maximum efficiency of heat engine system, though not of the heat engine itself [16]. Likewise, fuel processing and heat rejection by the fuel cell system should also be considered. A fair comparison would also use the same chemical fuel as a feed to both systems, though in practice such a situation may not be realistic.

Electrochemical Efficiency Another measure of efficiency in fuel cells is the electrochemical efficiency, defined as the ratio of the actual cell voltage to the ideal cell voltage. eelectrochem ¼

DE DE 0

(43.20)

The ideal potential was described previously in > Eq. 43.6. The actual cell potential is inevitably reduced from the ideal value, due primarily to various cell polarization losses, which will be discussed in more detail later in this chapter. The primary value of this efficiency measure is in comparing fuel cells to one another. It is sometimes referred to as the voltage or activation efficiency as it is closely related to limitations imposed by reaction kinetics, as will be discussed subsequently in this chapter.

Fuel Utilization Efficiency Fuel utilization, mentioned previously, provides yet another type of efficiency measure for fuel cells. In practice, some fraction of the fuel supplied to a fuel cell remains unreacted. The fuel utilization efficiency can be thus defined as the ratio of the mass of fuel reacted in the cell to the mass fed to the cell. efuel ¼

mreacted fuel mfed fuel

(43.21)

By combining this measure with the electrochemical efficiency expressed in > Eq. 43.20, yet another efficiency value can be defined, the total electrochemical efficiency: etotal ¼ efuel

DE DE 0

(43.22)

Summary Thermodynamics are fundamental to understanding fuel cell operation. As shown above, the maximum achievable efficiency in a fuel cell is limited in that not all reaction enthalpy

Low-Temperature Fuel Cell Technology for Green Energy

43

can be converted to work. Of course, this is true of any other type of system as well as some fraction of energy is inevitably lost to entropy. Several different measures of efficiency can be defined from thermodynamic considerations. Reported efficiency values are not always explicitly defined in the fuel cell literature, with further challenges introduced in comparing efficiency from different types of systems, requiring care on the part of anyone working with such values.

Kinetic Processes in Fuel Cells Other limitations on fuel cell performance occur due to activation, ohmic, and mass transfer effects [9–11]. The effect of these losses on a typical current–voltage curve for a fuel cell is shown in > Fig. 43.3. Each of these will be described in more detail in this section.

Reaction Kinetics and Activation Polarization Irreversible kinetic effect in the half cell reactions of a fuel cell lead to activation losses in the observed voltage output. In terms of the current–voltage characteristic, activation losses are most evident under low current conditions. Often, the ideal open circuit voltage is not observed due to these effects. The activation or voltage efficiency, described in > Eq. 43.20, provides a measure of this loss term. A deeper look at the relationship

E0

Thermodynamic voltage limit Activation loss regime

Oh V

mic

loss

reg

ime

j

Limiting current

Mass transfer loss regime

jL

. Fig. 43.3 Typical current–voltage characteristic curve illustrating major sources of voltage loss

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Low-Temperature Fuel Cell Technology for Green Energy

between reaction kinetics and the current voltage characteristics of a fuel cell can provide some helpful insight into the source and means of preventing activation losses. > Equations 43.1 and > 43.2 describe the reactions occurring at the anode and cathode of a hydrogen PEM fuel cell. More generally, an oxidation reaction where the reductant (Red) loses electrons occurs at the anode of a fuel cell, Red ! Ox þ ne


(43.23)

while a reduction where the reactant, the oxidant (Ox), gains electrons occurs at the cathode. Ox þ ne
! Red

(43.24)

The overall reaction for a generic fuel cell can thus be expressed as Ox þ ne
, Red

(43.25)

The activation barriers to these reactions determine the overall reaction rate, hence the rate at which electrons are generated and consumed at each electrode and how much current is supplied by the fuel cell. For simplicity, consider a single-step elementary reaction at each electrode. The rate of the half cell reactions, R, can be expressed as RRed ¼ kRed ½Oxo ROx ¼ kOx ½Redo

(43.26)

yielding a net reaction rate of R ¼ RRed
ROx ¼ kRed ½Oxo
kOx ½Redo

(43.27)

where kRed and kOx are the reduction and oxidation rate constants while the [Red] and [Ox] are the surface concentrations of the reduced and oxidized species, respectively. The current density, j, at each electrode is related to reaction rate (R) by Faraday’s constant for an n electron reaction: j ¼ RnF

(43.28)

so that the net current generated by the fuel cell is j ¼ jRed
jOx ¼ nðFkRed ½Oxo
FkOx ½Redo Þ

(43.29)

The activation barriers for the anodic and cathodic reactions at the equilibrium potential z z can be defined as DG0a and DG0c , respectively. In the presence of an electric field, E, the anodic activation energy for the oxidation reaction is decreased and the cathodic activation energy for reduction increased by some fraction a of the applied field, as shown in > Eqs. 43.30 and > 43.31.   z DGaz ¼ DG0a
nð1
aÞFD E
E 0

(43.30)

  z DGcz ¼ DG0c þ naFD E
E 0

(43.31)

Low-Temperature Fuel Cell Technology for Green Energy

43

Rate constants can be expressed as a function of the Gibbs free energy of the reactions in an Arrhenius-type equation from transition state theory as   z! z!
DGc
DG0c
aF ðE
E 0 Þ kRed ¼ ARed exp (43.32) ¼ ARed exp exp RT RT RT for the reduction reaction at the cathode and   z! z!
DGa
DG0a ð1
aÞF ðE
E 0 Þ kOx ¼ AOx exp ¼ AOx exp exp RT RT RT

(43.33)

for the oxidation reaction at the anode. At equilibrium, E = E0 and the rate of the forward (reduction) and reverse (oxidation) reactions are equivalent and the net current is zero. While the net current is zero, both half cell reactions continue to occur and current does flow; however, the anodic and cathodic currents are equal and in opposite directions. This current is referred to as the exchange current density, j0, defined in > Eq. 43.34: 0 0 ½Oxo ¼ nFkOx ½Redo ¼ j0 nFkRed

(43.34)

Here the standard rate constants are defined from > Eqs. 43.35 and > 43.36 for the case when E = E0: z!
DG 0c 0 kRed ¼ ARed exp (43.35) RT and 0 kOx

z!
DG0a ¼ AOx exp RT

(43.36)

Exchange current is an indicator of catalyst activity; the more active the catalyst, the greater the exchange current. Substituting the rate constants from > Eqs. 43.35 and > 43.56 into > Eq. 43.34 gives: z! z! DG0a DG0c j0 ¼ nFAOx exp (43.37) ½Oxo ¼ nFARed exp ½Redo RT RT The Butler–Volmer equation describing the current density generated from a fuel cell is found by combining > Eq. 43.29 with > Eqs. 43.32, > 43.33, and > 43.37:     
aF ðE
E 0 Þ ð1
aÞF ðE
E 0 Þ j ¼ j0 exp
exp (43.38) RT RT The Butler–Volmer equation is considered one of the most important in electrochemistry, and is presented with a variety of different forms with a more complete derivation in most electrochemistry and fuel cell texts [9–13]. The derivation presented here is only

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rigorously valid for a single-step reaction, though modifications can be made to account for more complex reaction mechanisms. Nonetheless, it still provides a good approximation of fuel cell kinetics and is instructive in describing key variables impacting reaction kinetics. The Tafel equation (> 43.39) describes an important limiting case of the Butler– Volmer equation for high overpotential, relating activation polarization, act, directly to the rate of an electrochemical reaction.     RT j 0 act ¼ E
E ¼ ln (43.39) anF j0 From the Butler–Volmer and Tafel equations, it is apparent that as more current is drawn from a fuel cell, a greater voltage loss is required. It also points the way toward how kinetic activity can be increased, namely, by increasing reactant concentration, z reducing the activation barrier to the reaction (DG0a ), and/or increasing operating temperature (T). Side reactions and catalyst poisoning are also important, acting to reduce the overall reaction rate in a fuel cell. Methanol and formic acid oxidations have more complex mechanisms than hydrogen oxidation, and the intermediates formed can impact reaction kinetics, in particular carbon monoxide, CO. Carbon monoxide poisoning is also an issue in hydrogen PEM fuel cells when the hydrogen comes from reformed hydrocarbons such as methane. These issues will be discussed further in > section on ‘‘Fundamentals of Fuel Cell Operation.’’

Charge Transport and Ohmic Losses Ohmic losses are the result of resistance to charge transport in the system and include interconnect or electronic resistance (Rinterconnect or Relectronic) within the external circuit, contact resistances (Rcontact) between different layers of the fuel cell associated with the transfer of electrons from the electrodes to the circuit or of ions from the electrocatalyst to the electrolyte (Ranode and Rcathode) and resistance to ionic motion in the electrolyte (Relectrolyte), illustrated in > Fig. 43.4. The total ohmic resistance in the cell is described by > Eq. 43.40. Rohmic ¼ Rinterconnect þ Ranode þ Rcathode þ Relectrolyte ¼ Relectronic þ Rcontact þ Relectrolyte

(43.40)

The different terms used here reflect the variation in the nomenclature found in the literature. Using Ohm’s law, ohmic overpotential losses, ohmic, can be easily described: ohmic ¼ jRohmic

(43.41)

Generally, electronic transfer is rapid and contact resistance negligible, and thus have a minimal impact on fuel cell performance. The main source of ohmic loss is from the rate of ionic transport in the electrolyte. The slope of the linear region of the current–voltage plot in > Fig. 43.3 at intermediate voltages is due largely to ohmic losses. In the presence of

Low-Temperature Fuel Cell Technology for Green Energy

Rcathode

Ranode

Relectrolyte

Rinterconnect

Anode

43

Electrolyte

Rinterconnect

Cathode

. Fig. 43.4 Ohmic losses in a typical fuel cell result from resistances to current flow connected in series, including interconnect resistance (Rinterconnect) due to the conductivity of the bipolar plate, electrode resistances (Rcathode and Ranode) in the catalyst, and gas diffusion layers of the anode and cathode respectively, and electrolyte resistance (Relectrolyte) due to the ionic conductivity of the electrolyte material

only an ohmic loss term, current density is directly proportional to the electric field driving the motion of the charge carrier, with the proportionality constant, s, being the conductivity. j¼s

dV dx

(43.42)

For an electrolyte of thickness L, the conductivity of interest is ionic: j ¼ sionic

V L

(43.43)

Writing this expression in terms of the area of the electrolyte, we get the familiar expression for Ohm’s law, where resistance is sA/L. i¼

Asionic V V ¼ L Rionic

(43.44)

Equations 43.42–43.44 make evident that it is desirable to maximize the ionic conductivity of the electrolyte as well as to minimize its thickness in order to minimize ohmic losses. The most widely used electrolytes in hydrogen and other low-temperature fuel cells are solid sulfonated fluoropolymers, most notably Dupont’s Nafion®, the general structure of which is illustrated in > Fig. 43.5. Similar sulfonated fluoropolymer membranes are marketed by 3M and Dow, among others. The fluoropolymer backbone of these materials provided a mechanically strong, chemically resistant structure while the sulfonic acid groups lend both hydrophilicity and surface acidity that facilitate proton conduction.

>

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Low-Temperature Fuel Cell Technology for Green Energy

CF2 CF2

CF2 x

CF

O

y O

CF2 CF

z

O

CF2 S

CF2

OH CF3

O

. Fig. 43.5 Chemical structure of Nafion®

The performance of these membranes is a strong function of water content, with water acting as a vehicle to carry protons through the membrane [18]. The phenomenon of water molecules being carried through the membrane by protons is referred to as electroosmotic drag. The production of water at the cathode in conjunction with electroosmotic drag creates a concentration gradient that leads to back diffusion of water. Total water transport is thus the sum of fluxes due to electroosmotic drag from anode to cathode and diffusion from cathode to anode [9]. The critical nature of water in proton transport limits the operating conditions of PEM-based fuel cells using Nafion®. At temperatures above 80 C and/or under conditions of low relative humidity, Nafion® can become dehydrated resulting in a loss of proton conductivity. At temperatures about 120 C, the polymer itself starts to degrade. As a consequence, practical operating temperatures are limited to below 80 C and humidification of hydrogen and air streams is often necessary.

Mass Transfer and Concentration Polarization In order for chemical reactions to occur at the respective electrodes, fuel and oxidant must reach the catalyst via mass transfer. Similarly, reaction products must be removed from the catalyst’s surface. Under high current conditions, the fuel cell is limited by the rate of transport of fuel to the anode surface. Two regions are of interest in a fuel cell with regard to mass transport, the porous electrode surface where molecular diffusion is important and the flow field of the bipolar plate where bulk convective flow dominates. The oxidation and reduction reactions occur at the catalyst surfaces on each respective side of the membrane electrode assembly. A concentration gradient develops as fuel and oxidant are consumed at the anode and cathode, respectively. The catalyst itself is on a support of microscale particles with nanoscale porosity, thus diffusion is occurring both within the pores of the support as well as in the larger void spaces between catalyst particles. The rate of diffusive mass transfer of reactants in the catalyst layer provides a fundamental limit to fuel cell performance. Diffusive flux, Jdiff, can be described by Fick’s

Low-Temperature Fuel Cell Technology for Green Energy

43

first law of diffusion, which for the case of steady state, one-dimensional diffusion in the x-direction in a planar catalyst layer becomes Jdiff ¼
D

dc c 
cR0 ¼
Deff R dx d

(43.45)

where the diffusivity (D) and the concentration derivative in the x-direction (dc/dx) are expressed in terms of the surface and bulk concentrations of reactant (cR and cR0 , respectively), the effective diffusivity of the reactant in the catalyst layer (Deff ), and the diffusion length taken as the thickness of the catalyst layer (d). The catalyst layer is typically porous in order to maximize reactive surface area and on the order of 100–300 mm thick [9]. Effective diffusion coefficients in this layer are generally on the order of 10
2 cm2 s
1 [9]. At steady state, the flux of reactants is equal to the rate of consumption of the reactant, which in turn determines the rate of current generation. The diffusion-limited current density can be related the reactant flux using Faradays constant, j ¼ nFJdiff Combining expressed:

>

Eqs. 43.45 and

>

(43.46)

43.46, the current density due to diffusion can be

j ¼
nFDeff

cR
cR0 d

(43.47)

A limiting current density, jL, of the fuel cell would occur when the surface concentration reaches zero. jL ¼ nFDeff

cR0 d

(43.48)

The higher jL is, the greater the operating range of the fuel cell. It is thus desirable to design catalyst layers and structures so as to minimize the diffusion length or layer thickness and to maximize the effective diffusivity. Combining the Nernst equation (> Eq. 43.13) that describes the effect of concentration on voltage with the results described above from Fick’s Law yields an expression for the concentration polarization loss in a fuel cell, conc,     RT j conc ¼ ln 1
(43.49) nF jL where jL is the limiting current, as described by > Eq. 43.48 where all of the reactant is consumed at the catalytic active site on the electrode surface. The bulk concentration of reactants is determined by flow field design. Maximizing this value will also serve to maximize the limiting current as described by > Eq. 43.48. With the exception of very small systems, most fuel cells are flow systems with multiple cells connected in series to supply sufficient voltage. In addition to collecting current from the fuel cells, flow field structures or bipolar plates serve to supply reactants to the cell through a series of channels machined into the plate. The channels maybe arranged in any of a variety of complex patterns, some of the most common of which are illustrated in

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Low-Temperature Fuel Cell Technology for Green Energy

Fig. 43.6 including serpentine, parallel, and interdigitated designs. Critical dimensions of these channels are typically on the order of mm or cm. To date, no particular design enjoys consensus support as optimal. In addition to mass transfer, pressure drop and fuel utilization must also be considered in design of flow fields, as well as material and manufacturing cost. High flow rates favorable to mass transfer can result in incomplete fuel utilization and also result in a greater pressure drop, requiring more energy to move fuel and oxidant through the system. Analysis of flow field design using computational fluid dynamics continues to be an active area of fuel cell research [19].

>

Fuel Crossover Polarization Ideally, a fuel cell electrolyte is impermeable to both fuel and oxidant. In practice however, fuel crossover also presents challenges with Nafion, especially in direct methanol fuel cells [20–22]. Though not negligible, crossover is less of a concern in hydrogen [23] and direct formic acid fuel cells [24]. The most obvious impact of crossover is in the reduction of fuel utilization efficiency. To quantify the effect of crossover, an internal current density, jn, is defined

. Fig. 43.6 Some common, simple flow field patterns, including (a) serpentine, (b) parallel, and (c) interdigitated channel designs

Low-Temperature Fuel Cell Technology for Green Energy

jn ¼ nfuel ðnFAÞ

43 (43.50)

where nfuel is the fuel crossover rate (mol s
1 cm
2), n is the total number of the electrons participating in the reaction, F is Faraday’s constant, and A is the area of the electrolyte membrane. Including this term in the expressions for activation, ohmic, and concentration polarization losses (> Eqs. 43.39, > 43.41, and > 43.49) illustrates the impact of crossover on each of these loss terms.  act ¼ E
E 0 ¼

   RT j þ jn ln anF j0

ohmic ¼ ðj þ jn ÞRohmic     RT j þ jn conc ¼ ln 1
nF jL

(43.51) (43.52) (43.53)

Activation overpotential can be further impacted by crossover if the fuel is oxidized at the cathode or acts as a poison to the cathode catalyst.

Summary of Electrode Polarization Effects The major contributions to voltage loss in an operating fuel cell have been described in the preceding sections. These include activation, ohmic, concentration, and crossover polarization effects. The polarization losses at the anode and cathode are the result of activation and concentration polarization losses at each respective electrode, anode ¼ act;a þ conc;a

(43.54)

cathode ¼ act;c þ conc;c

(43.55)

and

where activation and concentration polarization terms are described by either Eqs. 43.39 and > 43.49 or Eqs. > 43.51 and > 43.53, depending on the relative importance of crossover. These overpotentials change the anode and cathode potentials from their theoretical values, as shown in > Eqs. 43.56 and > 43.57:

>

0 þ janode j Eanode ¼ Eanode

(43.56)

0 Ecathode ¼ Ecathode
jcathode j

(43.57)

and

The overall cell potential is then the difference between the cathode and anode potentials described above less ohmic polarization, DEcell ¼ Ecathode
Eanode
ohmic

(43.58)

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where ohmic polarization is given by > Eq. 43.40 or > 43.52 depending on the importance of fuel crossover. Substituting > Eqs. 43.56 and > 43.57 into > Eq. 43.58 yields:  0   0 
jcathode j
Eanode þ janode j
ohmic (43.59) DEcell ¼ Ecathode Rearranging terms and substituting the theoretical standard state open cell potential from > Eqs. 43.7 and > 43.14: DEcell ¼ DE 0
jcathode j
janode j
ohmic

(43.60)

> Equation 43.60 clearly illustrates how each of the polarization terms served to reduce the operating potential of a fuel cell from its theoretical maximum. Using basic concepts of thermodynamics, reaction kinetics, electrochemistry, and transport phenomena, we can see how relatively simple fundamental mathematical models of fuel cell performance can be developed, facilitating analysis of working cells, providing means of comparing research results, and enabling model-based control algorithms.

Low-Temperature Fuel Cell Technologies One way of classifying fuel cell technologies is by the typical operating temperatures. As previously noted, this chapter will deal with low-temperature technologies. Hightemperature fuel cells, including molten carbonate and solid oxide fuel cells, will be discussed in subsequent chapters. Proton exchange membrane or PEM fuel cells form the most widely studied category of fuel cells. These include hydrogen PEM fuel cells, direct alcohol cells such as the direct methanol fuel cell (DMFC), and direct formic acid fuel cells (DFAFCs). Alkaline and biological fuel cells will also be discussed briefly here, though these technologies are not currently of great importance for power generation.

PEM Fuel Cells A key characteristic of these fuel cells is the proton exchange membrane, or PEM. The PEM is also sometimes referred to as a polymer electrolyte membrane as the most widely used materials are sulfonated perfluoropolymers such as Nafion®. This solid electrolyte serves as an electronic insulator, proton conductor, and the heart of the membrane electrode assembly, most notably for hydrogen PEM fuel cells but also for DMFCs and DFAFCs.

Hydrogen PEM Fuel Cells In a hydrogen PEM fuel cell, hydrogen fuel is oxidized at the anode while oxygen is reduced at the cathode in the reactions shown in > Eqs. 43.1–43.3. The mobile ion produced is the proton, H+, with platinum on a carbon support serving as the catalyst

Low-Temperature Fuel Cell Technology for Green Energy

43

at both the anode and cathode. The theoretical open circuit voltage at 25 C, assuming liquid water as the product is 1.23 V [9–11]. Hydrogen PEM fuel cells are without doubt the most widely studied and used today. This technology supplies power on NASA spacecraft, and is the primary fuel cell technology being developed by the automobile industry. The low-temperature operation of hydrogen PEM fuel cells makes them suitable for portable applications as well.

Direct Alcohol Fuel Cells Direct alcohol fuel cells utilize a proton exchange membrane in a manner similar to hydrogen PEM fuel cells. Methanol is the most common fuel for such cells [25]; however, significant research into ethanol has also been pursued. In these cells, protons are extracted directly from the alcohol, usually in a liquid state, at the anode. These are primarily being developed for portable power applications due to their high energy density and relative ease of fuel storage [9–11]. By far, the most widely studied in this class of fuel cells is the direct methanol fuel cell, or DMFC. As the name implies, methanol is oxidized at the anode of a direct methanol fuel cell via the reaction shown below. CH3 OH þ H2 O ! 6Hþ þ 6e
þ CO2

(43.61)

Oxygen is reduced at the cathode, similarly to a hydrogen cell: 3 O2 þ 6Hþ þ 6e
! 3H2 O 2

(43.62)

The overall reaction for a DMFC is then: 3 CH3 OH þ O2 ! 2H2 O þ CO2 2

(43.63)

The theoretical open circuit voltage of a DMFC is 1.18 V at 25 C, though in practice, 0.6– 0.8 V is more common due to kinetic limitations for both oxidation and reduction reactions. The slow oxidation kinetics are compounded by catalyst poisoning from carbon monoxide formed as an intermediate product in the oxidation mechanism [25, 26]. The other major limitation in DMFC performance is fuel crossover through the PEM [20–22]. This problem limits practical methanol concentrations to 1–2 M in working DMFCs. Despite these problems, DMFCs are one of the leading technologies being pursued for portable power generation.

Direct Formic Acid Fuel Cells In recent years, direct formic acid fuel cells (DFAFCs) have emerged as a rival technology to DMFCs for portable power applications [9, 27]. As the name implies, formic acid is oxidized at the anode:

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Low-Temperature Fuel Cell Technology for Green Energy

HCOOH ! CO2 þ 2Hþ þ 2e


(43.64)

As with hydrogen PEM fuel cells and DMFCs, oxygen is reduced at the cathode: 1 O2 þ 2Hþ þ 2e
! H2 O 2

(43.65)

The overall reaction in a DFAFC is thus: 1 HCOOH þ O2 ! H2 O þ CO2 2

(43.66)

This cell gives a theoretical open cell voltage of 1.48 V, much higher than that for either DMFCs or hydrogen PEM fuel cells [27]. The leading catalysts for formic acid oxidation are palladium rather than platinum based, offering a potential cost advantage over DMFCs [28, 29]. The major drawback for formic acid is that its energy density is significantly lower than that of methanol [27]. However, since formic acid crossover through Nafion® is much lower than that of methanol, this problem can be compensated for by the use of higher fuel concentrations [24, 27]. Progress with these fuel cells has been very rapid and they show much promise for the future.

Alkaline Fuel Cells Hydrogen is utilized as the fuel in alkaline fuel cells; however, instead of protons, hydroxyl ions serve as the mobile ions in an alkaline electrolyte, most commonly potassium hydroxide. The anode and cathode reactions are given in > Eqs. 43.67 and > 43.68, respectively. H2 þ 2OH
! 2H2 O þ 2e


(43.67)

1 O2 þ 2e
þ 2H2 O ! 2OH
2

(43.68)

Alkaline fuel cells hold a special place in fuel cell history as they were the first power systems demonstrated to be of practical use for power generation [10, 30]. Francis Bacon is credited for pioneering development of these fuel cells in the 1940s and 1950s, and this technology was the one chosen by NASA to provide electrical power onboard its first spacecraft [10, 30]. Alkaline fuel cells have several advantages over other fuel cell technologies, one of which is that the oxygen reduction reaction at the cathode occurs at a lower activation overvoltage than in acidic PEM fuel cells allowing the cells to operate higher voltages (up to 0.875 V) and consequently higher efficiency [9, 10]. Non-precious metal catalysts can also be utilized making these fuel cells very low in cost [9, 10]. In spite of these advantages, NASA and much of the fuel cell world began turning away from alkaline fuel cells in favor of PEM-based technology in the 1970s and 1980s, and today they receive far less research and development attention. The chief disadvantage of

Low-Temperature Fuel Cell Technology for Green Energy

43

alkaline fuel cells is their sensitivity to CO2, which reacts with the alkaline electrolyte to form carbonates, reduce the availability of hydroxyl ions as well oxygen solubility in the electrolyte [9, 10]. The electrolyte must thus be sealed from the air to maintain a long cell life and very pure hydrogen must be utilized. Hydrogen reformed from hydrocarbon sources inevitably contains some degree of CO2, which would have to be removed prior to use in an alkaline fuel cell. While this technology does have its challenges, they do not appear to be more substantially formidable than those associated with other technologies, as others have noted [31, 32]. However, the limited research attention currently directed toward alkaline fuel cells makes it unlikely that they will surpass PEM fuel cell technology in importance or value in the near future.

Enzymatic and Other Biofuel Cells Biological fuel cells utilize enzymes (either alone or with a microorganism) to catalyze the electrochemical reactions in a fuel cell [33–36]. As such, their operation is limited to conditions where the organisms can survive and/or the enzymes can remain stable and not denature, typically nearly neutral pH and from around 20–40 C. Typical fuels include sugars and simple alcohols. A key advantage of these is their inherent selectivity as enzymes typically only catalyze very specific substrates. This selectivity, however, comes at a price as it is the result of a complex protein matrix surrounding the active center of a given enzyme where the reaction occurs. While conferring great selectivity on the enzyme, this matrix also serves in effect as an electrical insulator, reducing the transduction efficiency of electrons produced at the active center to an electrode where it can be collected. Poor transduction efficiency also plagues microbial fuel cells. Probably the greatest challenge associated with enzymatic fuel cells is the poor stability of the enzymes themselves. Currently, practical lifetimes of enzymatic fuel cells are limited to days or weeks as the enzymes denature in a working cell. Biofuel cells are not currently nor are they expected to be of major importance for power generation; however, they do have potential for some niche applications such as energy scavenging, biosensors, and in vivo power generation [33–36].

Fuel Cell Systems The fuel cell or fuel cell stack in and of itself is only part of a full power system. Specific requirements vary widely depending on the type of fuel cell and the application; however, several other systems and components are often necessary. These might include fuel delivery and fuel processing systems, thermal management systems, and power management systems [9]. These systems add cost to the total system and utilize a fraction of the energy produced. Accounting for these is important not just in cost and performance calculations, but also in evaluating the environmental impact of a fuel cell.

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Membrane Electrode Assembly, Flow Field, and Fuel Cell Stack At the heart of a fuel cell is the membrane electrode assembly or MEA. This consists of up to five layers including the proton exchange membrane at the center, anode and cathode electrocatalyst layers on either side of the membrane and gas diffusion layers, illustrated in > Fig. 43.7. The proton exchange membrane is most commonly Nafion®, a perfluorocarbon polymer manufactured by DuPont. Gas diffusion layers are most commonly made from carbon paper or carbon fabric. The catalyst, most commonly platinum based, may or may not be supported on a high surface area (>75 m2 g
1) conductive carbon support. Whether supported or pure metal, the catalyst is used to make an ink with an appropriate solvent. Typically, a small amount of Nafion® is added to the catalyst ink. The ink may be applied to the proton exchange membrane or the gas diffusion layer via screen printing, spraying, inkjet, or some similar technique [37]. The layers are then bonded together, typically by hot pressing [37]. The MEA is in turn sandwiched between flow field plates which, often referred to as bipolar plates, also serve as current collectors. These are typically machined from graphite and contain flow channels to supply fuel and oxidant to the anode and cathode, respectively. As noted previously, a single fuel cell can supply a maximum, open cell voltage of around 1 V, depending on the specific type of fuel cell being used. Practical operating voltages are usually around 0.6–0.7 V, where power output is maximized. Most applications, however, require anywhere from a few volts to several hundred volts. For this reason, Graphite flow fields Gas diffusion layers Proton exchange membrane

Anode catalyst layer

Cathode catalyst layer

. Fig. 43.7 Layers of a typical membrane electrode assembly and flow field

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43

fuel cells are commonly connected in series in vertical stack where a flow field plate serves as the anode for one cell and cathode for a neighboring cell, hence the name bipolar plate. Using a fuel cell stack in this manner allows the voltage requirements of any given application to be met.

Fuel Processing, Storage, and Delivery One of the more challenging aspects of fuel cell design is providing fuel to the cell. The approach to solving this problem depends in large part on the type of fuel cell being employed and the needs of the target application. The approach to this design challenge has a major impact on the energy density of the overall fuel cell system. Trends in hydrogen storage research will be discussed in the subsequent section on > ‘‘Hydrogen Storage.’’ Probably the simplest solution to the problem of fuel storage and delivery is that of liquid-powered fuel cells where the fuel is directly electrooxidized, such as in direct methanol and direct formic acid fuel cells. These types of fuel cells are of interest primarily for small-scale, portable power systems. While such fuels have high energy densities, kinetic and transport limitations limit fuel cell performance, imposed in part by the fuel delivery systems. For small-scale fuel cells, a passive fuel delivery system may be employed, placing the fuel reservoir in direct contact with the anode or using gravity, surface tension, evaporation, or a similar mechanism to supply fuel to the cell or stack. Such an approach helps to minimize the weight of the total system allowing a high system energy density to be achieved; however, it also can lead to mass transfer limitations. The use of a passive fuel delivery system is typically only sufficient for the smallest of fuel cells. There are several fuel storage options for hydrogen PEM fuel cells. The most notable of these are direct hydrogen storage in the form of a compressed gas or cryogenic liquid, storage in the form of chemical hydrides, and the use of a hydrogen carrier such as methane or ammonia. Each of these involves very different balance of plant requirements, as will be discussed below. Current hydrogen vehicles utilize compressed hydrogen gas tanks for fuel storage. This approach is arguably the simplest and most straightforward. Tank pressures of up to 700 bar can currently be achieved. The safety of a high-pressure, explosive gas presents a significant concern in such systems. To safely maintain such high pressures requires the use of a heavy storage tank, as well as protective measures for lines, valves, regulators, etc. This weight dramatically reduces the overall energy density of the system, which has driven research efforts toward an alternative hydrogen storage methodology. Additionally, a significant amount of energy must be expended to pressurize the hydrogen. For fuel delivery, the pressure of the tank can in most cases provide a sufficient driving force to move hydrogen through the fuel cell stack. Liquid hydrogen presents similar, though magnified challenges as even more energy is required to cool and liquefy the hydrogen and the cost and weight of a vacuum insulted the storage tank are large.

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One alternative approach to hydrogen storage and delivery that has attracted much attention is the use of solid state, metal or chemical hydrides or hydrogen adsorbents. Generally, these materials release hydrogen as they are heated, thus thermal management is critical for a fuel delivery system using these materials. The hydrogen supplied in this manner can be extremely clean, lacking the performance degrading impurities such as CO that are found in hydrogen obtained from hydrocarbons. There are still many challenges associated with solid-state hydrogen storage materials, including the need to further increase hydrogen capacity and to reduce the energy required for recharging the materials with hydrogen after use. To date, the use of these materials is still confined primarily to the research laboratory. The use of hydrogen carriers provides another alternative for hydrogen storage and delivery in fuel cell systems. Common hydrogen carriers in fuel cell systems include organic hydrocarbons such as methane, methanol, formic acid, and even gasoline as well as inorganic compounds such as sodium borohydride and ammonia. These are attractive for many applications in that they provide greater gravimetric and volumetric energy densities than hydrogen itself. They are also typically easier to store and transport, and often a supply chain infrastructure already exists for them. It should be noted that hydrogen gas is not naturally occurring and is most commonly derived from methane, natural gas, or some other source industrially. Hydrogen carriers are generally not able to be used directly by a fuel cell. Instead, they must be reformed, or chemically processed to yield hydrogen. The need for fuel reforming or a fuel processing subsystem generally limits this hydrogen storage and delivery methodology to stationary power-generation applications. Fuel reforming systems have an added advantage in that they can often be configured to run with multiple hydrogen carriers providing fuel flexibility. Reforming of hydrogen carriers may occur internally within the fuel cell stack or more likely external to the fuel cell in a separate reforming subsystem. In either case, the carrier is chemically converted to hydrogen and by-products via a chemical reaction before it can be utilized by the fuel cell to provide power. Design goals for a fuel processing system include minimizing energy required by the system as well as the amount of impurities and pollutants produced (particularly CO and other catalyst poisons), and maximizing the hydrogen yield from the system. A common figure of merit for comparing different fuel sources is the carrier system effectiveness, defined as the ratio of the percentage of energy in the carrier converted to electricity to the percentage of energy in pure hydrogen converted to electricity in the same fuel cell. Care should be taken in using this or any other measure comparing fuel cell performance as often such calculations are reported based upon the fuel only, neglecting the energy used in the fuel processing step or other system components. When using a hydrogen carrier, the required fuel processing subsystem is often extremely complex, which is why such systems are primarily of interest only for larger, stationary power systems. The major components of such a system include a fuel reformer or similar reactor to convert the carrier to hydrogen and by-products, a water gas shift reactor to increase the hydrogen to carbon monoxide ratio, and a hydrogen cleanup unit

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to remove carbon monoxide and any other impurities that may poison fuel cell catalysts or must otherwise be removed. There are three common reforming reaction types for hydrocarbons: steam reforming, partial oxidation, and autothermal reforming. Operating temperatures for these reactions range from 600 to 1,000 C depending on the fuel and type of process. Steam reforming involves the endothermic reaction of the hydrocarbon with steam, as the name implies,   1 Cx Hy þ xH2 OðgÞ , xCO þ y þ x H2 ! CO; CO2 ; H2 ; H2 O (43.69) 2 The endothermic reaction makes thermal management challenging in steam reforming reactors. This approach provides the highest hydrogen yield, but also the least fuel flexibility. A generic partial oxidation reaction of a hydrocarbon is shown in > Eq. 43.70. 1 1 Cx Hy þ xO2 , xCO þ yH2 2 2

(43.70)

Unlike steam reforming, this reaction is exothermic, simplifying thermal management and allowing for faster reactor start-up, though at a higher operating temperature. Partial oxidation provides a greater degree of fuel flexibility than steam reforming. Unfortunately, this approach to reforming provides the lowest hydrogen yield as well as the highest degree of pollutant emissions. Autothermal reforming combines aspects of both steam reforming and partial oxidation, as shown in the generic reaction for the process:     1 1 Cx Hy þ zH2 OðgÞ þ x
O2 , xCO þ z þ y H2 ! CO; CO2 ; H2 ; H2 O 2 2 (43.71) As both exothermic and endothermic reactions are combined in a single process, thermal management is somewhat simplified eliminating the need for heat exchangers and allowing a physically smaller system to be constructed. However, a more complex control system design is necessitated. Hydrogen yield from autothermal reforming is greater than with partial oxidation, though not as high as with steam reforming. An alternative to reforming hydrocarbon fuels is production of hydrogen from solid carbonaceous material (e.g., coal) via gasification or from biomass through anaerobic digestion. A generic gasification reaction is shown in > Eq. 43.72. C þ aO2 þ bH2 O , cCO2 þ dCO þ eH2 þ other species

(43.72)

The full mechanism involves several elementary steps and varies depending on the carbon source. As with reforming, reaction temperatures are high, ranging from 700 to 1,400 C Common polluting by-products include sulfur and nitrogen oxides. Anaerobic digestion is attractive from an environmental standpoint in that it utilizes renewable biomass such as sewage, livestock waste (i.e., manure), plant matter, or food processing waste as

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the hydrogen carrier. Through a series of chemical reactions facilitated by bacteria, the biomass is converted to methane, CO2, and subsequently to hydrogen. By-products include CO and CO2 as well as hydrogen sulfide. The hydrogen gas produced in the reforming, gasification, or anaerobic digestion stage cannot be fed directly to a fuel cell as it also contains by-products, notably carbon monoxide, which can poison fuel cell catalysts. Most hydrogen PEM fuel cell catalysts can withstand CO concentration levels no greater than about 100 ppm. Two processes are typically employed to clean up this hydrogen gas stream before it is sent to the fuel cell, a water gas shift reactor followed by a chemical separation/cleanup process. The reversible water gas shift reaction, CO þ H2 O , CO2 þ H2

(43.73)

describes an equilibrium between water vapor and carbon monoxide with hydrogen and carbon dioxide. The goal in utilizing such a reaction is to maximize the hydrogen to carbon monoxide ratio in the product stream. Typically, CO content can be reduced to 0.2–1.0 mol% in this way. The final cleanup of the hydrogen stream can be accomplished using any of several methods or a combination of methods. Chemically, selective methanation or selective oxidation of CO can be utilized. Unfortunately, both of these reactions also consume some amount of hydrogen. Physical separation processes, including adsorption and membrane processes, can also be employed. Adsorbents such as high surface area carbon, silica, and zeolites can provide a great deal of selectivity and also consume very little power in an operating separation system. Palladium–silver alloy membranes can also be used as hydrogen diffuses through membrane at a faster rate than other species.

Thermal Management Not all energy from the fuel cell reactions is converted to electricity; some is lost as heat. A thermal management system serves to dissipate this heat in order to control the operating temperature of the fuel cell. The degree of thermal management required varies depending on the size and type of fuel cell system. For small portable systems, passive thermal management relying on natural convection is often sufficient as the amount of heat produced is small. However, for larger systems producing on the order of 100 W or more, significant heat can be produced overheating the cell and/or creating significant thermal gradients. In such cases, active cooling is necessary. A common approach is to utilized forced convection with a fan, blower, or pump pushing air or cooling fluid through additional cooling channels within the bipolar plates. Liquid coolants with their high heat capacity are commonly used in automotive fuel cells. Liquid coolants create additional challenges in system design as their larger pressure drop requires greater energy to pump them through the system, and unlike ambient air, they are necessarily in limited supply on-board the system and must be recycled. A key figure of merit for an active thermal management system design is its effectiveness ratio, defined as the ratio of

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the heat removal rate to the electrical power consumption rate. The goal of system design is thus to minimize power is consumed by fans, blowers, or pumps moving the cooling media through the system while maximizing the rate of heat dissipation. Typical values of effectiveness ratios for well-designed systems range from 20 to 40 [9]. For systems that include a high-temperature fuel reformer and/or an afterburner to combust unused hydrogen leaving the fuel cell, employment of a heat recovery mechanism is necessary to maximize the overall efficiency of the system. Using one or more heat exchangers, heat emitted from the fuel cell or an afterburner that combusts unused hydrogen leaving the fuel cell can be used to supply energy to a fuel reforming subsystem.

Power Management Power management is critical for any fuel cell–based power system and typically includes electrical circuitry for four tasks: (1) power regulation, (2) power inversion, (3) monitoring and control, and (4) power supply management [9, 10]. The power supplied by a fuel cell is not stable as the voltage varies with current load, environmental conditions (temperature, humidity, etc.), and other factors. Typically, DC/DC converters are utilized to convert fuel cell voltage output to a stable, specified value, forming the main component of a power regulation system. The DC power produced by the cell, however, must be converted to AC for many applications, such as supplying power to AC motors used in electric vehicles and other AC electric devices that traditionally might be powered from the electric grid. Power inversion serves to convert DC power to AC power. The total fuel cell system is essentially an electrochemical processing plant. Process monitoring tools such thermocouples, pressure gauges, provide inputs to feedback control loops. The process controls serve to adjust variables such as fuel feed flow rate and coolant flow rate in response to perturbations in the system to maintain steady performance of the system as a whole. Finally, power supply management is necessary to deal with rapid changes in load requirements. For example, a typical car would require 25 kW of power on average, but as much as 120 kW at peak (e.g., during rapid acceleration). Fuel cells have a relatively slow response to rapid changes in power demands, on the order of seconds to hundreds of seconds, as pumps, compressors, and other components must respond in order for the power output to begin to change. Batteries and supercapacitors are the main components of the power supply management systems, acting as energy buffers to reduce response time to the order of milliseconds.

Technical Challenges and Current Research Many technical challenges remain to be overcome if fuel cells are to be competitive both in terms of performance and economics with currently dominant technologies. The biggest of these are hydrogen storage, catalysis, electrolyte membrane, and bipolar

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plate materials. An overview of these issues will be provided here. References cited should provide a good starting point for the reader interested in a more in-depth study of these topics.

Hydrogen Storage For automotive and other mobile applications, storage of hydrogen is one of the greatest technical challenges for fuel cell technology. High-pressure and cryogenic hydrogen storage, while conceptually simple, have an assortment of problems. An ideal hydrogen storage technology would have both high gravimetric and volumetric hydrogen density, be stable at temperature up to 50 C, enable rapid delivery of hydrogen to the fuel cell, and be capable of being regenerated. The US Department of Energy has set targets in this regard as part of a National Hydrogen Energy Roadmap, some of which are summarized in > Table 43.2 [38]. It should be noted that these targets are for hydrogen storage systems, not hydrogen storage materials. A number of materials are capable of meeting energy density goals, if only the material is accounted for. Hydrocarbons materials meet DOE targets, but reforming of these fuels to produce hydrogen also yields CO2 and catalyst poisoning CO in addition to H2. The reforming process is also energy intensive. As previously noted, this approach is generally seen as promising only for stationary power generation. Solid-state hydrogen storage materials are currently a major research focus in fuel cell technology [38–40]. In general, solid-state hydrogen storage solutions can be grouped into two categories: hydrogen physisorption systems and chemical hydrides. The majority absorbents investigated for hydrogen physisorption are either various forms of carbon (e.g., graphene and carbon nanotubes) [41–43] or metal organic frameworks [42, 44], though these are certainly not the only materials under investigation. The advantages of physisorption systems are their low cost, simple design, and ability to adsorb hydrogen at low pressures [40]. However, to date no absorbent material has been able to meet the DOE hydrogen density goals, much less system the hydrogen density goals for a full

. Table 43.2 Summary of DOE hydrogen storage goals 2010 Gravimetric system energy density (net useful energy /maximum system mass) Volumetric system energy density (net useful energy /maximum system volume) Storage system cost

1.5 kW∙h kg

2015
1

6 wt% H2 1.5 kW∙h L
1 0.045 kg H2 L
1 4 $/kW∙h net

3 kW∙h kg
1 9 wt% H2 2.7 kW∙h L
1 0.081 kg H2 L
1 2 $/kW∙h net

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43

system. Further, they typical desorb hydrogen at near or slightly above room temperature, making them unattractive for many practical applications [40]. Nonetheless, this approach continues to be widely investigated and some new adsorbents, in particular metal organic frameworks, show promise. Among the most promising solid hydrogen storage materials are metal and complex chemical hydrides. Metal hydrides of interest involve the lightest metals, such as Li, Be, Na, Mg, B, and Al, in order to meet hydrogen density goals [40, 45, 46]. Some examples include LiAlH4, LiBH4, LiNH2, NaAlH4, NaBH4, and MgH2 among many, many others [40, 45, 46]. Some of these advanced hydride materials can meet hydrogen density goals, but present a host of other system challenges. Many of these hydrides are unstable to the point of explosion in the presence of air and/or water, requiring that they be sealed in a working system. Typically, hydrides are heated to release hydrogen, often in a highly exothermic reaction, leading to sintering of material; also there is typically a volume change on hydrogen discharge [47]. Heavier metals may be added to the system in small quantities as a catalyst to enhance dehydrogenation kinetics. Ball milling and other processes to create small particles, even nanostructured materials, are also commonly utilized as a means of enhancing reaction kinetics in metal hydrides [48]. Rehydrogenation is accomplished by placing the used material in a pressurized hydrogen atmosphere, typically requiring an excessive amount of energy [45, 46]. Among the most promising hydrogen storage materials are the chemical hydrides ammonia borane (NH3BH3) and related compounds [49, 50]. Ammonia borane (AB) is a stable power in air and readily soluble in a number of common solvents. Hydrogen is released in a three-stage process, shown below, with a 6.5 wt% hydrogen yield in the first stage, 13.1 wt% in the second, and 19.6 wt% in the third. A rehydrogenation process has not been perfected, but progress has been made on this front and the reactions involved are all thermodynamically favorable [51]. As with the metal hydrides, improving reaction kinetics is a challenge as is the volume change on reaction. Enhanced kinetics have been observed with a number of metal catalysts as well as with ammonia borane incorporated into mesoporous matrices. A slightly acidic environment has been observed to considerably enhance dehydrogenation of AB.

Catalysis Anode and cathode reactions in low-temperature fuel cells require catalysts to achieve reaction rates sufficient for fuel cells to be practical. Leading catalysts for fuel cells are based on expensive, precious metals such as platinum, palladium, and ruthenium. Sufficient progress has been made to reduce metal loading has been reduced to the point that catalysts are often no longer the largest cost contributor to fuel cell systems. However, should fuel cell technology become more widespread, this may change as increasing demand for catalyst metals would be expected to drive up prices. The largest fraction of the environmental impact of fuel cell technology remains in the mining, processing, and transport of the catalyst material.

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From a performance standpoint, the greatest activation losses occur at the cathode of hydrogen fuel cells in the oxygen reduction reaction. Not surprisingly, this is the focus of significant research and development efforts [52]. The complex mechanism of oxygen reduction provides insight into some of the challenges. The desired pathway for the reaction is the direct oxygen reduction shown in > Eq. 43.74. 1 O2 þ 2Hþ þ 2e
! H2 O 2

(43.74)

However, the formation of hydrogen peroxide, O2 þ 2Hþ þ 2e
! H2 O2

(43.75)

and various platinum oxides Pt þ H2 O ! PtO þ 2Hþ þ 2e


(43.76) 

occurring at standard potentials of 0.68 and 0.88 V versus NHE at 25 C, respectively, contribute to a reduction in the open circuit voltage in the cell. The most active catalysts for oxygen reduction are platinum alloys, containing predominantly platinum (75 wt%, metals basis) [37]. The stability of the alloy in contact with the acidic membrane surface is a key factor that must be considered, as the base metal in the alloy can dissolve into the membrane [37]. Alloys that showed both high activity and stability included PtCr, PtZr, and PtTi [37]. Hydrogen peroxide produced at the cathode can also impact catalyst stability, especially for non-platinum catalysts [53]. The considerable cost of platinum has also spurred research into cheaper catalyst materials [52] though to date none has been found with sufficient activity and stability to supplant the platinum alloys. Iron- and cobalt-based catalysts have shown some promise, particularly in porphyrins and in the presence of pyrrole and pyridine structures [54, 55]. Metal-free carbon catalysts doped with nitrogen or nitrogen and boron have drawn considerable attention of late [56, 57]. Nitrogen appears to have some beneficial effect in each of these types of catalyst, though the mechanism is still a subject of investigation [56]. Though the activity of these alternative catalysts is still not as good as that of platinum, the lower cost could justify their use in some applications. A number of metals will catalyze the hydrogen oxidation reaction, though platinum is the most active. Activation losses at the anode of hydrogen fuel cells are generally quite small. The primary focus of research on hydrogen oxidation catalysis is related to poison resistance. Hydrogen is most commonly derived from natural gas reforming, which inevitably results in the formation of not only hydrogen, but also CO and CO2. CO in particular is a notorious catalyst poison [58]. The most widely studied CO resistant catalysts are Pt–Ru alloys, though others have been examined [59]. Unlike with hydrogen oxidation, significant activation losses are associated with both the methanol and formic acid oxidation reactions in DMFCs and DFAFCs, respectively. Methanol oxidation catalysis research has been recently reviewed by several authors [25, 59]. As with hydrogen oxidation, improving resistance to carbon monoxide poisoning is one of the major challenges in improving methanol oxidation catalysts, though it is

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more critical as CO is formed through the electrooxidation reaction mechanism itself rather than appearing as an impurity in the fuel. The electrooxidation of methanol occurs predominantly through an indirect pathway that is initiated by the adsorption of methanol (CH3OHad) onto the catalyst, a step that requires three to four adjacent metal atom sites arranged triangularly on the catalyst surface [60]. CH2 OH ! CH2 OHad

(43.77)

This is followed by dehydrogenation of the adsorbed methanol on the surface of the catalyst, forming carbon monoxide (COad) as a strongly adsorbed reaction intermediate [9, 61–63]. CH2 OHad ! COad þ 4Hþ þ 4e


(43.78)

Subsequently, an activated hydroxyl, OHad, or similar activated hydrous intermediate is required for complete oxidation of the adsorbed carbon monoxide [9, 60–62]. The formation of this OHad species, H2 Oad ! OHad þ Hþ þ e


(43.79)

is the rate-determining step for the overall methanol electrooxidation reaction. In the presence of the activated OHad complex, COad is oxidized to carbon dioxide (CO2), the final reaction product. COad þ OHad ! Hþ þ e
þ CO2

(43.80)

Summing > Eqs. 43.78–43.80 gives the overall electroxidation reaction for methanol, shown previously in > Eq. 43.61, which produces six protons and electrons per methanol molecule reacted. Platinum has the highest reactivity of any pure metal catalyst and is the predominant catalyst used for this reaction [9, 62]. Unfortunately, the rate determining step for methanol electrooxidation, the dissociation of water to form an adsorbed active hydroxyl described in > Eq. 43.79, occurs at well above desired operation fuel cell anode voltages, requiring an overpotential greater than 0.6 V versus a reversible hydrogen electrode (RHE), well above the thermodynamic methanol electrooxidation potential of 0.03 V [9, 60]. Minimizing the overpotential required for active hydroxyl formation is key to improving anode electrocatalyst performance in DMFCs. The same challenge applies to improving CO tolerance in hydrogen oxidation catalysts. Bimetallic PtRu catalysts are the most widely used for enhancing CO tolerance for both hydrogen and methanol electrooxidation [9, 59, 63, 64]. The overpotential required for the oxidation of water on Ru surfaces is significantly lower than on platinum at 0.3 V versus RHE. While improving performance overall, ruthenium creates some additional problems with regard to its stability in a fuel cell environment [65] and high cost. The instability of multimetallic electrodes in general is of concern due to metal dissolution in the acidic fuel cell environment and at excursion potentials typically experienced during start/stop cycling. Dissolved ruthenium from the anode has been shown to diffuse

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through the membrane and adsorb onto the cathode catalyst surface, negatively impacting the oxygen reduction reaction. Elimination of these problems and further improvement of the water electrooxidation overpotential limitation continues to drive research into alternative catalysts. A wide range of bimetallic and trimetallic combining platinum with an oxophilic cocatalyst have been explored [63, 64]. In most cases, the mode of enhancement is via an electrocatalytic bifunctional mechanism, although some are thought to additionally experience to a lesser degree a ligand effect, reducing the strength of the Pt surface bond to the COad reaction intermediate. Both enhancement mechanisms have been found in PtRu catalysts. An interesting alternative to purely metallic catalysts, several groups have examined metal oxides as cocatalysts with platinum. These are believed to increase the availability of activated hydroxyl species for the bifunctional pathway through oxygen vacancies in the metal oxide structure [66, 67]. Formic acid oxidation catalysis has also drawn much attention in recent years, and the resulting reduction in activation losses have dramatically increased interest in direct formic acid fuel cells as an alternative to direct methanol cells [27]. The best catalysts to date have been found to be Pd and PdV-based materials [27–29]. Resistance to CO poisoning is also a challenge with formic acid electrooxidation, though much less so than in methanol electrooxidation. Formic acid electrooxidation may proceed through one of three pathways: (1) through a formate intermediate HCOOH ! HCOOad þ Hþ þ e
! CO2 þ Hþ þ e
;

(43.81)

(2) a direct pathway, shown above as > Eq. 43.64, and (3) an indirect pathway through an adsorbed CO intermediate as seen in methanol electrooxidation, HCOOH ! COad þ H2 O

(43.82)

where adsorbed CO is subsequently oxidized as illustrated in > Eqs. 43.79–43.80 [60]. Poisoning due to impurities in formic acid, namely, acetic acid and methyl formate has been shown to be a problem [27].

Electrolyte Membranes The drawbacks of Nafion® and related ionomers have led to numerous efforts to develop new proton conducting membrane materials. The greatest technical challenges associated with Nafion® and other related sulfonated fluoropolymers are poor performance at elevated temperatures and low humidity levels. The need for water as part of the proton conduction mechanism results in a practical limit of 80 C for the operating temperature in Nafion® based fuel cells and leads to the requirement that hydrogen and oxygen streams in hydrogen PEMS be humidified. Excessive methanol crossover is also a problem when using Nafion® in DMFCs. These shortcomings have led to innumerable efforts to develop alternative membrane materials. The characteristics of an ideal fuel cell membrane are outlined in > Table 43.3. The relative importance of each of these is highly dependent on the application. For example, cost is of somewhat less importance for fuel cells targeting

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. Table 43.3 Summary of the ideal characteristics of an ideal proton exchange membrane. The relative importance of these is highly dependent upon the specific application Ideal proton exchange membrane characteristics High proton conductivity Low electronic conductivity Thermal stability Water retention in dry environments Low permeability to fuel Low electroosmotic drag coefficient Good mechanical properties Chemical stability Low cost

portable power applications as the cost per watt hour of current battery technologies remains quite high. Conversely, cost requirements are of great concern in automotive applications. One of the chief motivations for using fuel cells for portable power is to take advantage of their high theoretical energy density; therefore it is desirable to utilize the highest fuel concentrations possible in these typically liquid fed cells. The importance of resistance to fuel crossover is magnified by this desire to operate at high fuel concentrations while the use of aqueous liquid fuels makes water retention concerns of much less significance. Despite much effort, sulfonated perfluoropolymer materials remain dominant for all PEM-type fuel cells today. Still, it is reasonable to expect that different classes of materials may eventually emerge from this ongoing research. Several reviews of these efforts have been published recently [68–72]. New membrane materials that have been reported in the literature can be very broadly classified into four main groups: new ionomers, solubilized acids in a polymer matrix, composites of ionomers and insoluble solids, and inorganic solid acids and their composites. A significant number of ionomers have been investigated, the majority being sulfonated aromatic polymers and sulfonated fluorocarbons and perfluorocarbons with similar chemical functionality to Nafion®. Notable examples of the former include sulfonated polyetheretherketone (SPEEK) and sulfonated polyetherketone (SPEK). These have the advantage of low cost but tend to be less chemically and mechanically stable than sulfonated perfluorocarbons and do not provide significant advantages in proton conductivity [69, 71]. Another approach has been to incorporate soluble acid species, most commonly a mineral acid such as phosphoric or sulfuric acid or a low molecular weight amphoter such as imidazole or pyrazole [68, 70, 71]. Examples of this approach include polybenzimidazole (PBI)/phosphoric acid membranes. The main problem with this approach is the tendency of the acid or amphoter to diffuse or leach out of the membrane [68, 70, 71]. One of the most widely pursued approaches has been the development of composites of ionomers (most commonly Nafion® or SPEEK) and insoluble solid materials.

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This approach has shown promise, yielding moderate improvement in proton conductivity and water retention in comparison with ionomers alone [68, 70, 73, 74]. The solids incorporated in these composites are typically chosen for their hydrophilicity and/or surface acidity and are most commonly incorporated as nanoparticles. Materials that have been incorporated into composites with Nafion® and/or SPEEK include alumina, silica, titania, zirconium phosphate, zirconia, and many others [68, 70, 74, 75]. It has been speculated that proton conduction in ionomers with added ceramic nanoparticles is enhanced by proton transport along the surfaces of the nanoparticles [68, 70, 74, 75]. The majority of the observed improvement is most likely due to increased water retention in these membranes [68, 75]. The perfluorocarbon backbone of Nafion® and related materials adds a degree of hydrophobicity contributing to their poor ability to retain water [76, 77]. The addition of ceramic nanoparticles has been observed to enhance water retention in those membranes [70, 74, 75] allowing the membranes to be effective at higher temperatures and lower relative humidity than ambient conditions. Porous materials have been the subject of several recent studies, being used primarily as structural components in a PEM. One of the most notable examples of this approach is the Gore® membrane in which the pores of a porous Teflon® membrane are filled with Nafion® [71]. Several other studies have utilized porous silicon, filling the pores with Nafion® and other ionomeric materials with some success. In a similar vein, porous alumina has been filled with solid acid materials for use as a PEM [78, 79]. Recent work has demonstrated that porous ceramics themselves may be viable as potential PEM materials. While metal oxides, clays, and other ceramics exhibit bulk proton conductivities several orders of magnitude lower than that of Nafion®, a fact which has led many to dismiss such materials from consideration as potential PEM materials, surface proton conductivities of these materials have been observed to approach or exceed that of Nafion® at the same temperatures [80]. A major advantage of ceramic materials is that they can readily be fabricated into very thin films, thus the total proton conduction rate can be very rapid even if the conductivity of the material is low. This can be of particular value in microscale fuel cells being investigated for providing onboard power for computer chips, sensors, and similar small devices [81]. Recent work examining high surface area, nanoporous metal oxide membranes has sought to take advantage of this rapid surface conduction, demonstrating membrane proton conductivities within less than an order of magnitude of Nafion® at comparable temperatures [80, 82, 83]. Thin, nanoporous metal oxide membranes have most commonly been formed by casting via a sol-gel process followed by a heat treatment to sinter the nanoparticles. Proton transport in such membranes at low temperatures is believed to be dominated by a surface mechanism. Anderson et al. when studying xerogel membranes of SiO2, TiO2, and Al2O3 noted that the proton conductivity of all three materials increased with temperature, but no correlation was found with water content of the ambient air [80]. The surface hydrophilicity of these materials combined with very large surface tensions in nanoscale pores should strongly enhance water retention and likely contribute to the observation of no correlation between proton conductivity and ambient humidity [80]. A strong correlation of proton conductivity with surface acidity was however seen [80].

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Bipolar Plate Materials and Manufacturing Bipolar plates or flow fields are one of the largest contributors to the cost of fuel cell systems, contributing as much as a third of the total cost in some systems [84–86]. Ideal materials for bipolar plate should be thermally and electrically conductive; chemically compatible with other fuel cell materials, reactants, and products; low in weight and volume; and mechanically strong enough to maintain high gas pressures when sealed [9]. The great challenge is finding materials that simultaneously meet performance requirements and can be easily and cheaply manufactured. Graphite is most commonly used; however its brittleness, porosity, and high cost of machining have led to research efforts to develop numerous alternatives. The brittleness and porosity of the material require relatively thick plates to be uses, increasing the weight of the system. The difficulty and expense of machining graphite, however, presents the greatest problem with using graphite for bipolar plates. Various metals have been suggested as alternative bipolar plate materials, including stainless steel, titanium, and aluminum [87]. Machining costs remain a problem with metals; however, corrosion in a fuel cell environment provides the greatest barrier viability as the oxides of most metals are insulators. A number of different promising coatings to increase corrosion resistance of metal bipolar plates have been and continue to be studied [87]. Carbon/carbon materials have shown excellent performance properties as bipolar plates. These are manufactured by preforming a plate from a carbon fiber or graphite composite with phenolic resin. After the plate is formed, chemical vapor impregnation (CVI) is used to deposit carbon in the pores of the material providing a hermetic seal. The CVI process provides the main drawback of carbon/carbon materials as it utilizes methane as the carbon source and requires temperatures of 1,400–1,500 C as well as long processing times [88]. Warping of the material is also a common problem associated with the CVI process [88]. Polymer composites represent the most widely studied and promising alternative bipolar plate materials [89–92]. Their chief advantage lies in the low-cost, rapid manufacturing techniques that can be employed, such as injection molding for thermoplastic composites and compression molding for thermoset composites [86]. Typical composites contain between 60 and 80 wt% graphite to supply sufficient electrical conductivity [86]. To enhance mechanical strength, small amounts of carbon or glass fiber are often added. Nonetheless, poor mechanical properties are the primary disadvantage of polymer composite bipolar plates [86].

How Green Is My Fuel Cell? Or Life Cycle Analysis Fuel cells offer many potential advantages, many of which have been highlighted here already, including very high thermodynamic efficiencies without directly using fossil fuels. While these are indicators of an environmentally friendly alternative energy technology, they can be deceiving. Life cycle assessment provides a means of systematically analyzing

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the environmental impact of energy systems or any device over the lifetime of that device, from raw materials to final disposal [93]. This process goes by several different names, including life cycle analysis, cradle-to-grave analysis, and ecobalance. Procedures for this process are codified as part of the ISO 14000 environmental management standards [94]. Life cycle analysis for fuel cells would involve both direct economic costs associated with the manufacturing and use of the fuel cell as well as environmental costs to society. While the process is useful and necessary, it is also complicated by a host uncertainties associated with estimating each of these items and even determining what items to include. Some of these challenges have been reviewed recently by Reap et al. [95, 96]. Because fuel cells, as well as other energy technologies, are constantly evolving, it is important that life cycle assessment be a continual process, which will inevitably require some degree of forecasting until the technology matures [97]. Any change in the materials used or the manufacturing processes will impact the overall environmental impact. Several life cycle assessment studies relating to fuel cells, especially for automotive applications, have been published in recent years which illustrate some of the challenges involved. As one might expect, the longer the lifetime of the fuel cell or any technology, the less important the impact of the manufacturing process is. The manufacturing process for fuel cells is thus less important in long lifetime cells used for stationary power generation than it is in cells used for transportation with shorter lifetimes [97]. Fuel cells offer definite environmental advantages in operation when compared to combustion engines. The impact of the manufacturing process, however, reduces this advantage significantly. A life cycle assessment of fuel cell manufacturing process by Pehnt compared impact of manufacturing to fuel cell use, accounting for production of graphite for the flow field, platinum mining and refining, and membrane production [98]. The biggest environmental impacts were found to be from platinum metals production for catalyst, thus recycling of these is important in minimizing environmental impact [98]. If only economic factors are considered, fuel cells cannot yet compete with gasoline or hybrid gasoline/electric vehicles [99]. However, Ogden et al. [100] evaluating several different automotive engine and fuel technologies (hydrogen, internal combustion/ hybrid, Diesel, Fisher–Tropsch liquids, etc.) concluded that hydrogen fuel cell vehicles offered the lowest ‘‘societal life cyle cost,’’ which included vehicle first cost (assuming large-scale mass production), fuel costs (assuming a fully developed fuel infrastructure), externality costs for oil supply security, and damage costs for emissions of air pollutants and greenhouse gases calculated over the full fuel cycle. The assumptions employed here are a topic of some debate and an illustration of the challenges involved in life cycle analysis. It is likely solid-state hydrogen would be supplied in the form of a replicable fuel cartridge or something similar.

Future Directions The major technical challenges have been reviewed on the preceding pages, including hydrogen storage, catalysis, electrolyte membrane materials, and bipolar plate materials

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and manufacturing, among others. Progress in solving these technical challenges will certainly play a large role in determining the role of fuel cells in meeting future energy needs. In addition to progress on meeting technical challenges, the future of fuel cell technology and energy technology in general, depends strongly on complex economic, political, and social factors. In order to achieve widespread use, fuel cells must be at a minimum cost competitive, though ideally offering a cost advantage, in comparison with the current dominant technology in a given market. Historically, interest in fuel cells and other alternative energy technologies has corresponded strongly with the price of oil and gasoline. Some have expressed concerns lithium prices may go up considerably as the use of advanced batteries becomes more widespread. Beyond market considerations, energy prices are heavily impacted by government policies and geopolitical considerations. The world’s largest oil reserves are also located in some of most politically volatile regions. Other energy technologies, including green technologies, are subject to such forces as well. Lithium used in advanced batteries is currently plentiful, but many of the world’s largest reserves of this material are also found in volatile regions of the world. Fuel taxes, environmental regulations, and in the USA, CAFE (corporate average fuel economy) standards are among the many governmental policies that impact the prices paid by consumers for energy. Research and development progress is also impacted by government funding priorities. For example, NASA’s use of fuel cells in spacecraft beginning in the 1960s provided a major impetus to research and development efforts [1]. Some governments have also invested in green public transportation, including the use of hydrogen fuel-cell powered busses in Australia, Iceland, and the European Union [4–6]. In 2009, the Obama administration moved to eliminate Department of Energy funding for hydrogen fuel cell research, though this was ultimately restored by Congress. Subsidies and rebates in various forms are also a way in which green energy technologies of one type or another have been advanced by governments. Economically, it is reasonable to expect small-scale fuel cells for portable power applications to be the first to achieve widespread market penetration, likely in the very near future. Fuel cells can already produce power at costs per W/h close to those of current advanced battery technologies which dominate such markets. The importance of weight, volume, and lifetime in this market also provides a potential advantage to fuel cells with their high energy densities and the lack of a need for lengthy recharging cycles. Advances made for fuel cells in this market should help improve competitiveness of fuel cells in other markets, such as the automotive industry. Though several major automotive companies area actively developing fuel cell vehicles, it will likely be some time before fuel cell vehicles become common on roadways, barring significant changes in economic conditions. Fuel cells and other electric vehicle technologies offer benefits in terms of lower emissions and fossil fuel usage, but are not currently cost competitive. Fuel cell vehicles currently in public use benefit from significant government subsidies. The key to fuel cell vehicles becoming a major force in the marketplace will be reducing their cost relative to internal combustion engines and competing electric vehicle technologies. Key technical challenges that impact the cost of fuel cells are discussed in > section on ‘‘Technical Challenges and Current Research’’ on the preceding

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pages. An additional challenge is posed by the need to develop infrastructure to support such vehicles. Currently, only a handful of hydrogen fueling stations exist in the USA, concentrated in California. Long term, it is likely that hydrogen will be stored in a solid state form, as discussed in > section on ‘‘Hydrogen Storage.’’ The nature of the infrastructure necessary to support vehicles using solid hydrogen storage materials is unclear.

Conclusion Fuel cells technologies are among of the most promising green energy technologies for a number of applications. Their high energy density makes them a very attractive alternative to batteries for portable power applications. Unlike batteries, they need not be recharged, merely refueled. These characteristics along with having little or no emissions during operation and their high efficiency make fuel cell promising for transportation and stationary power generation. That fuel cells are efficient and have minimal emissions should not be taken to mean they have no environmental impact. Fundamental thermodynamic considerations place a limit on the possible performance of a fuel cell, as they do with any energy technology. Kinetic and transport-related issues place practical limits on fuel cell performance. From life cycle analysis, however, it is found that the primary environmental impact of fuel cells occur during manufacturing. Fuel cell systems range from the very simple passive microscale and miniature power applications to complex stationary power systems. Subsystems making up the balance of plant, including fuel processing and delivery, thermal management, and power management reduce the overall energy density of the system and add to the environmental impact of the overall system, requiring careful design. There are currently only a few niche applications where fuel cells are widely used, though this can be expected to change in the near future. Many companies are actively developing fuel cells for an array of applications. The first to market will likely be for portable electronics. Automotive fuel cells are seeing use in public transportation and in some prototype vehicles, though it will likely be longer before roadways are filled with such vehicles. Improvement in the technology and its cost competitiveness is still needed in a number of areas for fuel cells to reach their full potential. Nonetheless, a number of indicators point to a hydrogen-based economy sometime in the future.

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44 Solid Oxide Fuel Cells Nigel M. Sammes1 . Kevin Galloway1 . Mustafa F. Serincan2 . Toshio Suzuki3 . Toshiaki Yamaguchi3 . Masanobu Awano3 . Whitney Colella4 1 Department of Metallurgical and Materials Engineering, Colorado School of Mines, Golden, CO, USA 2 Department of Mechanical Engineering, University of Connecticut, Storrs, CT, USA 3 National Institute of Advanced Industrial Science and Technology (AIST), Nagoya, Japan 4 Sandia National Laboratories, Albuquerque, NM, USA Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1704 General Principles of a Fuel Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1704 General Principles of an SOFC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1706 Materials and Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1709 Electrolyte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1709 Cathode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1709 Anode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1710 Stacking and Types of SOFC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1711 Power Output and System Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1714 New Concepts for SOFCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1715 Intermediate Temperature SOFCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1716 Concept, Manufacture, and Results of the Microtubular SOFC . . . . . . . . . . . . . . . . . 1717 Modeling of SOFC Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1720 Leakage Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1720 Parametric Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1722 Transient SOFC Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1723 Thermal-Fluid Model Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1724 Results from Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1725 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1727

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_44, # Springer Science+Business Media, LLC 2012

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Abstract: This chapter describes the concept, electrochemical reactions, and fabrication of a solid oxide fuel cell (SOFC). The chapter initially describes how SOFC systems differ from other electrical devices and how they differ from other types of fuel cells; for example, they are all solid state (ceramics), run at high temperature and have the potential for directly running off hydrocarbon fuels. The chapter then studies the basic principles of the fuel cell, and describes each of the components in more detail (the anode, cathode, and electrolyte). The discussion then moves on to how single SOFC’s can be stacked in a number of ways, to form systems, and what the advantages and disadvantages of each is. Finally, the chapter discusses one such SOFC system in more detail, that of the microtubular SOFC. Here the chapter examines how these microtubes are made, what they are made from, and how they have the potential for running at low temperature for small applications such as auxiliary power units (APU), for example. The paper then concludes with some micro and macro-modeling on the microtubular SOFC, describing issues such as mass and thermal transport, the effect of altering a number of parameters, and how the modeling results compare to real data. The chapter concludes with some future directions on solid oxide fuel cells.

Introduction Recent awareness of environmental protection and fast growth of the world’s energy consumption has led the public, policy makers, entrepreneurs, technology developers, and scientists to search for alternative means to carry out and convert energy. Fuel cells are promising devices, potentially emerging as the substitutes for traditional energy converters, such as the internal combustion engine. Their improved environmentally friendly nature, and high efficiency, can potentially allow fuel cells to be employed from small portable applications, such as laptops and cell phones, to large scale stationary applications for central heating facilities and electricity generation.

General Principles of a Fuel Cell A fuel cell is an electrochemical energy conversion device that uses chemical energy to produce electricity. Similar to a battery, the electrodes are separated by an electrolyte in a fuel cell and electricity is generated due to the electrochemical reaction going on inside the cell. However, reactants are stored inside the battery thus, the performance of the battery decreases when the charge inside the battery drops until it eventually goes dead and needs to be recharged. On the other hand, reactants flow into the fuel cell continuously and electricity is generated as long as the supply continues. A general cross-sectional view of a fuel cell is depicted in > Fig. 44.1. Fuel enters the negative electrode (anode) and oxidant enters the positive electrode (cathode) in a gaseous state. Porous electrodes that allow the reactant gases to pass through are separated by an electrolyte. The chemical reactions occur at the electrode–electrolyte

Solid Oxide Fuel Cells

2e–

44

Load

Fuel in

Oxidant in

1/2

H2 Positive ion or Negaitive ion

O2

H2O

H2O

Depleted fuel and product gases out

Depleted oxidant and product gases out Anode

Cathode Electrolyte (Ion conductor)

. Fig. 44.1 Schematic of a generalized fuel cell

interface often with the help of catalysts especially for the oxidation reaction. Fuel entering the anode is separated into electrons and ions, which are protons when the fuel is hydrogen. The ions pass through the electrolyte to the cathode side, while the electrons go through an external circuit connecting the anode and cathode providing electricity. At the cathode, ions combine with the oxidant and the electrons. To get a reasonable voltage and current output, cells are combined in parallel and series to form a fuel cell stack. The types of fuel cells are defined by the electrolyte material. Though each type of fuel cell has different properties, they share some characteristics. The energy conversion process from the chemical reaction is common for all of them. Although other fuels such as methanol are used in fuel cells, hydrogen is used as the typical fuel. Finally each type of fuel cell stack generates direct current (DC) electricity. The characteristics of fuel cells make them favorable over conventional energy converters in many applications. These characteristics, which vary for the different types of fuel cells, determine the applications for which they can be employed. Efficiency: Direct conversion of the chemical energy to electrical energy is not limited by the Carnot cycle efficiency; hence, fuel cell efficiencies are greater than heat engines. Depending on the fuel cell type, stack efficiency of up to 50–60% is possible. If the surplus heat is utilized, an overall system efficiency of up to 80–90% is realizable.

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Power density: Higher power is maintained from a fuel cell that has the same size as that of most of the conventional energy conversion devices, such as internal combustion engines, partly owing to higher efficiency. Low emissions: When pure hydrogen is used as the fuel, the fuel cell maintains a zero emission characteristic. However, in case of utilizing hydrogen from carbon-rich fossil fuels, oxides of nitrogen, sulfur and carbon are released; yet the emissions values are far below those of conventional energy converters. Even when the hydrogen from natural gas is used as energy source, the higher conversion efficiency allows for the production of less CO2. Reliability and availability: Since the moving parts of a fuel cell system is in the auxiliary components and the fuel cell systems are relatively simple, the maintenance requirements are reduced, and the life of the fuel cells is generally longer than conventional systems, although there are a number of exceptions, depending on the material-set utilized. Due to the low maintenance requirements, therefore, system availability is higher. It is reported that a PC25 (by UTC Power) fleet consisting of more than 200 units have demonstrated 90% availability during four million operating hours. Also power is available 99.9999% of the operating time. Thermal output and cogeneration capability: Depending on the type of the fuel cell, product heat can be utilized by means of domestic hot water applications or space heating. Also, in case of higher thermal output, fuel cells can be used with other devices such as turbines to enhance the system efficiency. Despite these positive characteristics, there are also a number of negative features of the fuel cells, such as high costs, insufficient infrastructure, and immaturity of the technology.

General Principles of an SOFC The solid oxide fuel cell system will now be discussed in more detail. The SOFC consists of a ceramic electrolyte, usually yttria stabilized zirconia (YSZ), with an air electrode (cathode) and a fuel electrode (anode) on either side, as described in > Fig. 44.2. A solid oxide fuel cell (SOFC) is an all solid-state electrochemical device producing both electricity and waste heat directly from the electrochemical conversion of a fuel with an oxidant. Because it produces electricity by electrochemical means, there is no necessity to have any moving parts, and thus the SOFC overcomes the Carnot limitation inherent in all heat engines. Hence, the SOFC has high-energy efficiency, which can be further increased by using waste by-product heat in applications such as cogeneration (greater than 50% electrical efficiency is possible, with efficiencies approaching 75% with cogeneration). The SOFC also has a number of advantages over conventional systems including its modularity whereby single units can be stacked, its flexibility, and its ability to use a number of different fuels. It has a number of disadvantages including cost (far greater than conventional systems/kW at the moment), raw-material availability (possibly a problem in the long term), and it has no real history, unlike the turbine engine. It should however be noted that the fuel cell was invented by Sir William Grove over

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44

SOFC fuel cell Electrical current e–

Fuel in

Air in e–

e– e– O= H2 Excess fuel and water

O2

O=

Unused gases out

H2O

Anode

Electrolyte

Cathode

. Fig. 44.2 Diagrammatic representation of the elements of the SOFC

150 years ago, but was never commercialized possibly due to the invention of the turbine and its use and development in the turbine-driven aeroplane. Now, as has already been stated, the SOFC system consists of a ceramic electrolyte, usually yttria stabilized zirconia, with an air electrode (cathode) and a fuel electrode (anode) on either side. The electrolyte must be of a high percentage theoretical density so that the two fuels are physically separated and have no opportunity of mixing. The cell (anode/electrolyte/cathode) is operated at a high temperature primarily to allow the ionic conductivity of the electrolyte to be high enough to produce a reasonable current density, although other factors such as reaction kinetics must also be considered. Fuel (currently H2, although other hydrocarbon fuels are being studied) is fed to the anode, where it undergoes an oxidation reaction and releases electrons to an external circuit. Oxidant (either air or pure oxygen) is fed to the cathode where it is reduced and accepts electrons from the external circuit. The flow of electrons around the external circuit produces DC electricity. The oxygen is transported as oxygen ions across the electrolyte via the vacancy mechanism. > Figure 44.2 summarizes the SOFC operation. As explained above, the electrolyte is usually based on yttria stabilized zirconia, which is an oxygen ion conductor. Other oxygen-ion conductors have been studied, including for example, doped-CeO2 systems, perovskite-based systems, and doped-Bi2O3. Most of these other oxides, although they are superior oxygen ion conductors, are prone to reduction at low oxygen partial pressures (as found at the anode), and thus show n-type electronic conductivity, which reduces the efficiency of the overall system. Doped-LaGaO3 is a new material that does show promise as an SOFC electrolyte, because it does not appear to be reduced at the anode. Much work is still necessary, as preliminary studies appear to show it to be mechanically weak.

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Now it is important to study the reactions occurring in the SOFC cell. At the cathode (described in more detail below), reduction of oxygen occurs, via equation: O2 þ 4e0 ¼ 2O2 The main function of the cathode is to provide reaction sites for the reduction reaction to take place. At the anode, however, an oxidation reaction takes place, whereby the oxide ion is oxidized, releasing an electron. 2O2 ¼ O2 þ 4e0 Thus, the SOFC can be regarded as an oxygen concentration cell, and the electromotive force (EMF) is, therefore, dependent upon the oxygen partial pressure at the anode and the cathode. The oxygen partial pressure at the anode is based not upon oxygen being present, but upon the oxidation of the fuel. In this example we will consider H2. The oxidation of H2 is given by: 1

H2 þ O2 ¼ H2 O 2

The oxygen partial pressure at the anode is, therefore, given by: 

PO2

PH2 O ¼ PH2 Kox

2

where Kox is the equilibrium constant for the oxidations reaction described above. Substitution yields, where E 0 is the reversible voltage at the standard state, given by: E ¼ E0 þ

RT RT PH2 ln PO2 þ ln 4F 2F PH2 O

Under standard state conditions, E equals the reversible standard voltage at the standard state, E 0, and thus we can say that the following equation is applicable: E0 ¼

RT ln Kox 2F

Now, E0 ¼ 

DG 0 4F

where DG 0 is the Gibbs free energy of the reaction given in equation (at 1,250 K this is 178.2 kJ/mol). This value will differ for different combustion reactions, such as CO, CH4, and CH3OH. Now, this reaction occurs at the anode, which, like the cathode, must perform under quite specific conditions. The reversible EMF produced by the reaction is approximately 1 V (0.924 V at 1,250 K, and 0.997 V at 1,000 K). This EMF is of little practical benefit, and thus single cells are connected in electrical series in what is known as a stack. The height of

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44

the stack (or number of cells) varies depending on the design, and the power output required. Many designs have been examined; however, the two most common ones today are the tubular and planar designs, described below.

Materials and Reactions Electrolyte The electrolyte must be fully dense so that the fuel and air are physically separated, and have no opportunity of mixing. The cell (anode/electrolyte/cathode) is operated at a high temperature primarily to allow the ionic conductivity of the electrolyte to be high enough to produce a reasonable current density, although other factors such as reaction kinetics must also be considered. Fuel (such as H2, or other hydrocarbons) is fed to the anode, where it undergoes an oxidation reaction and releases electrons to an external circuit. Oxidant (either air or pure oxygen) is fed to the cathode where it is reduced and accepts electrons from the external circuit. The flow of electrons around the external circuit produces DC electricity. The oxygen is transported as oxygen ions across the electrolyte via a vacancy mechanism. The electrolyte is usually based on yttria stabilized zirconia, which is an oxygen ion conductor. Other oxygen-ion conductors have been studied including, for example, doped-CeO2 systems, perovskite-based systems, and doped-Bi2O3. Most of these other oxides, although they are superior oxygen ion conductors, are prone to reduction at low oxygen partial pressures (as found at the anode), and thus show n-type electronic conductivity, which reduces the efficiency of the overall system, although this may not be such a problem for doped-ceria. Doped-LaGaO3 is also a material that does show promise as a SOFC electrolyte, because it does not appear to be reduced at the anode.

Cathode The cathode must be a good electronic conductor with a high surface area, and catalytically active toward this reaction. The cathode must also have the following requirements: stability at high temperature and under the oxidizing gas present; compatibility with the other cell components; similarity of thermal expansion coefficient to that of the other components (otherwise it is prone to peeling off the electrolyte); retention of its porosity (and thus number of reaction sites) during the life-time of the cell; and retention of its catalytic activity during the lifetime of the cell. Because of the high temperature and oxidizing environment, most metals cannot be used. Only noble metals will withstand the environments found at the cathode, but these materials are too expensive for a commercial system. Many oxide materials have a high electronic conductivity, but they are either incompatible with the electrolyte or have a thermal expansion coefficient very different to those of the other cell components. Doped-LaMnO3 meets almost all the

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requirements of the cathode, and is the most commonly used material. Traditionally, Sr-doped (on the A-site of the perovskite) is used, due to its good electronic conductivity. Sr enhances the electronic conductivity by increasing the Mn4+ content by substitution of La3+ by Sr2+, as described in the equation below, and increases with increasing Sr content. At Sr contents greater than 20–30 mol%, metallic conduction is observed. LaMnO3 þ xSr2þ ! La3þ 1x Sr2þ x Mn3þ 1x Mn4þ x O3 The electronic conductivity occurs via the small polaron conduction mechanism. Ca doping has a similar effect to that of Sr doping, causing a significant increase in the electronic conductivity, with increasing Ca content.

Anode The anode must provide the reaction sites for the electrochemical oxidation of the fuel gas to occur. Hence, the anode must be stable under the very reducing conditions of the fuel atmosphere, have sufficient electronic conductivity, have excellent catalytic activity for the reaction (and remain catalytically active during the lifetime of the cell), be chemically compatible with the other cell components, have a high surface area to allow a large reaction zone to occur (the anode must also remain with a high surface area, and not degrade with time), have a similar thermal expansion coefficient to that of the other cell components, and be relatively low cost and easily fabricated. Because of the reducing environments metals can be used, although the high temperatures limit these to Co, Ni and noble metals. Electronically conducting ceramic materials can also be used (provided they do not reduce under the anode atmosphere). Currently, Ni is the anode of choice, primarily due to its good catalytic activity for hydrogen oxidation, its low cost, and its good stability. YSZ powder is added to the Ni metal in the form of a metal/ceramic composite for two reasons. Firstly, the YSZ inhibits the Ni coarsening during the operation, and secondly, the YSZ acts to lower the thermal expansion coefficient of the metal composite (which is much higher than the electrolyte) closer to that of the other cell components. The optimum amount of YSZ depends upon the percolation theory. Too much YSZ, and the sample does not electronically conduct (due to a minimal/no electron pathways), too little YSZ, and the composite has too high a thermal expansion coefficient. The effect of Ni content on the electronic conductivity is shown in > Fig. 44.3. It is obvious that the percolation threshold is at approximately 30 vol% Ni. Most anodes have approximately 40–50 mol% Ni in the composite, which appears to produce a relatively stable system. However, all anodes are found to degrade with time, due to either slight oxidation of the Ni to NiO, or due to sintering of the Ni particles. Alternative anode systems are being studied, particularly in respect to internal reformation of hydrocarbons, rather than having to use H2 as a fuel. Ni, although an extremely good catalyst for the oxidation of H2, is also very good at cracking natural gas into C. The C is then liable to form whiskers which lift the anode from the electrolyte surface, thus greatly reducing its activity. Other catalytic electrode materials being studied do not cause

Solid Oxide Fuel Cells

44

104 Lower surface area YSZ 103

Conductivity, Ω−1 cm−1

102

Higher surface area YSZ

101

100

10−1

10−2

0

10

20

30 40 vol % nickel

50

60

. Fig. 44.3 The conductivity of Ni/YSZ as a function of Ni content, at 1,000 C (After Dees et al. [1])

methane (and other hydrocarbons to crack) and thus may allow for a direct internal reformation reaction to take place. These include, for example, doped-CeO2-based systems, and perovskites. Currently, however, there are still many problems to be solved when investigating alternative electrode materials and the technology of today either externally reforms the hydrocarbon, or uses a high steam to carbon ratio in the feed stream. Both of these are not totally acceptable, as large efficiency losses are observed. Typically, the EMF produced by the reactions described above are of little practical benefit, and thus single cells are connected in electrical series in what is known as a stack. The height of the stack (or number of cells) varies depending on the design, and the power output required.

Stacking and Types of SOFC Many designs have been examined; however, the two most common ones today are the tubular and planar designs, shown in > Fig. 44.4. The planar design consists of electrolyte components configured as thin (approximately 50 mm) planar plates, or laid down on

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Solid Oxide Fuel Cells

a cathode, and more typically, an anode support. On either side of these plates are the anode and cathode materials. Between each cell is what is known as an interconnect. The interconnect has two main purposes; it serves as a bipolar gas separator, contacting the anode and cathode of adjoining cells, and sometimes has ribs on both sides to form gas channels. The properties of the interconnect are quite tight, as it must be electronically conducting, stable in both reducing and oxidizing environments and at high temperatures; relatively cheap (as it is usually the thickest component); dense (for the same reasons as the electrolyte, so that the fuel and air gases do not mix); easy to fabricate; compatible with the other cell components; and possess a similar thermal expansion coefficient to those of the other cell components. The interconnect is usually based on the perovskite LaCrO3. To increase the electronic conductivity, A (such as Ca or Sr) and/or B-site (such as Co or Fe) are added, which have the same effect as that of the Mn3+ in the cathode, to increase the amount of Cr4+ ions. Once the stack has been fabricated, the system is sealed using a ceramic or glass ceramic seal with a similar thermal expansion coefficient as the cell, and gas manifolds are placed around it, similar to those shown in > Fig. 44.5. Interconnect Cathode Air Electrolyte

a

Interconnect Anode Fuel

Anode Electrolyte Cathode

Air

Fuel

b

. Fig. 44.4 The SOFC stack designs (a) tubular, (b) planar (After Kordesch and Simader [2])

Fuel out

Oxidant out

Fuel in

Oxidant in

. Fig. 44.5 Gas manifolding in the planar SOFC design (After Minh and Takahashi [3])

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44

The tubular design, on the other hand, uses a very different concept. Here, an electrolyte tube (either anode or cathode supported, or unsupported) has electrodes on the inside and outside. The Siemens design (which uses traditional SOFC materials) has an electrolyte that is typically electro-vapor deposited (EVD) onto a porous cathode support tube (although other methods have been examined). On the outside of the electrolyte/cathode tube is placed the anode, using a dip-coating technique. The interconnect (Mg-doped LaCrO3) is then added using EVD processing, and the tubular cells (which are closed at the bottom) are bundled together, using Ni-felt to connect the anode of one cell to the adjacent anode for parallel connection, and to the Ni-plating on the interconnect for series connection as shown in (> Fig. 44.6). As the tubes are themselves already sealed, there is no requirement for a sealant, as required in the planar design. The gas manifolding is relatively straightforward with oxidant (air) being fed down the center of the tubes via an oxidant plenum. The fuel is fed from a fuel plenum at the bottom and up along the outside of the tubes, where the oxidation reaction takes place. The spent fuel flows through a porous ceramic barrier, enters the combustion chamber, and combines with the spent oxidant. This heat is then used to preheat the oxidant entering the cell. The exhaust gases exit the generator at approximately 900 C. The gas-manifolding concept is described in > Fig. 44.7. Power is obtained from the cell, or stack, by applying a load between the anode and cathode, and hence drawing current. The power output (P) is thus the product of the current drawn and the EMF across the cell, after the losses have occurred, namely,

Interconnection strip

Nickel felt contact

Air electrode Air Fuel electrode

Electrolyte

Positive current collector

Negative current collector

Fuel

. Fig. 44.6 Electrical connection in the tubular SOFC design (After Kordesch and Simader [2])

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Oxidant Oxidant Exhaust Conbustion/ oxidant preheat zone

Excess oxidant Unreacted fuel

Individual cell

Fuel Fuel

. Fig. 44.7 Gas manifolding in the tubular design (After Singhal [4])

P = I (E  RTI), where E is the thermodynamic EMF across the cell, and RTI are the losses (RT is the total resistance of the cell, and I the current).

Power Output and System Efficiency SOFC efficiency consists of a number of elements. ● Thermodynamic efficiency. This is given by the assumption that the Gibb’s free energy of the cell reaction may be totally converted to electrical energy, etherm ¼

DG DH

● EMF efficiency. This is shown by the fact that the cell voltage, in an operating cell, is always less than the reversible voltage. As the current is drawn from the fuel cell, the cell voltage falls due to a number of losses, as described in > Fig. 44.8. The EMF efficiency is given by the ratio of the operating cell voltage under load to the equilibrium cell voltage. This difference is due to a number of polarizations (or overpotentials), as described in the equation below, which shows that the total polarization losses () is the sum of a number of losses:  ¼ a þ d þ r þ ohm

Solid Oxide Fuel Cells

44

Reversible cell voltage

Cell voltage

Voltage losses due to activation overpotential

Voltage losses due to ohmic drop Voltage losses due to diffusion overpotential

Cell current

. Fig. 44.8 Typical voltage losses in a running SOFC cell

where the subscripts denote a = charge transfer polarization, d = diffusion polarization, r = reaction resistance, ohm = ohmic losses. Power is obtained from the cell, or stack, by applying a load between the anode and cathode, and hence drawing current. The power output (P) is thus the product of the current drawn and the EMF across the cell, after the losses have occurred; P = I (E  RTI), where E is the thermodynamic EMF across the cell, and RTI are the losses (RT is the total resistance of the cell, and I the current).

New Concepts for SOFCs Yttria-stabilized zirconia (YSZ) is the most common type of electrolyte material used in SOFC designs. However, due to its poor conductivity at lower temperatures, SOFCs using YSZ electrolytes operate at relatively higher temperatures, that is, above 750 C, to generate practical output power. This requires use of high quality alloy metal interconnects in order to prevent corrosion and increases the cost of these systems. On the other hand with the use of ceria-based rare earth oxides as electrolyte materials, which have high conductivities at lower temperatures, SOFCs running at intermediate temperatures (IT-SOFCs) possess desirable assets. Minimizing ionic interdiffusion between the electrode/electrolyte interfaces, mitigation of sintering problems seen at high temperature operation, use of inexpensive materials, and lower operating costs are the main advantages. Albeit providing these advantages, the common problem with ceria-based electrolytes is that they can be reduced under fuel cell operating conditions and become electronically conductive. As a result the cell is short circuited and the performance decreases.

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Solid Oxide Fuel Cells

SOFC electrodes are designed to provide a good conductive medium for both ions and the electrons. Hence, they are typically compounds of metal and ceramic materials to serve as mixed ionic and electronic conductors (MIEC). Both anode and cathode are porous structures to supply reactants and remove by-products. However, the design of the porous structure should be carried out meticulously. An open network of pores must be maintained throughout the structure to utilize all the electrode volume. Also the porosity must be high enough to prevent mass transfer limitations; however, higher porosities may lead to structural instabilities. Thus, the supporting electrode is always less porous than the other. One of the most important features of the electrode design is to maintain high catalytic activity. This is achieved by longer triple phase boundaries (TPBs) where gas phase in the pores, ionic conductor, and electronic conductor regions in the electrodes have a common interface. TPBs are where the anode and cathode reactions take place. To have a high quality TPB distribution, the electrodes must possess an open network of pores as well as the electrode materials must be sintered well to provide good bonding between the metallic and the ceramic components. Another important parameter for the SOFC design is the thermal expansion characteristics of the components. Using the electrolyte material in the anode and the cathode alleviates the mismatch between different layers. A common dilemma related to the cathode design is the trade-off between electronic conductivity, ionic conductivity, and the thermal expansion coefficient. The cathode design must be carried out taking into consideration all these three parameters simultaneously to optimize the cell performance while considering the structural stability. Keeping all this in mind, SOFCs are still far from commercial viability, mainly due to problems such as: cost targets, operating life, system optimization, and eventual integration with traditional devices in hybrid systems, aiming at maximizing the overall electrical efficiency.

Intermediate Temperature SOFCs Solid Oxide Fuel Cell applications have long been limited by the necessity to operate at high temperatures, causing prolonged start-up times and materials constraints, among other cost increasing constraints. Considerably, decreasing the operating temperature of SOFCs seems an absolute necessity for efficient power production, specifically in mobile applications where start-up time and materials cost is of increasing importance. Reducing the operating temperature of SOFCs below 650 C can extend the lifetime of the SOFC stack, lower cost by allowing the use of metal materials, and can decrease the degradation of SOFC and stack materials. Tubular SOFC designs have been shown to be stable for repeated cycling under rapid changes in electrical load and in cell operating temperatures. However, tubular SOFC capital costs are very high. This is mainly due to their low power density and to the materials to be used for safe operation at the high temperatures typical of SOFC stacks. In this respect, microtubular SOFCs aim at solving both the problems affecting the typical tubular SOFC. In fact, their lower diameter and operating temperature promise to: (1) reduce capital costs,

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(2) increase power density, (3) increase thermal shock resistance, and (4) reduce start-up and shutdown times. Microtubular SOFCs have also been shown to be able to endure the thermal stresses associated with rapid heating up to operating temperatures. In contrast to planar SOFC designs, when the diameter of tubular SOFC is decreased, it is possible to design SOFC stacks for high volumetric power densities. However, the literature dealing with thermal, electrical, and electrochemical performance of microtubular SOFCs is scarce at best, since this is an emerging technology with respect to the tubular one. Here one such microtubular SOFC technology will be discussed, that of the anode supported microtubular SOFCs with a cermet anode of NiO and GDC (Gadolinum Doped Ceria), a GDC electrolyte and a cathode in LSCF (La0.6Sr0.4Co0.2Fe0.8O3y). These cells were tested at operating temperatures ranging from 450 C to 550 C. Such experimental analysis was carried out varying cell temperature and fuel flow, in order to assess the effects of these two parameters on the electrochemical performance of the cell. To this scope, a parametric study is also presented.

Concept, Manufacture, and Results of the Microtubular SOFC The microtubular SOFCs were fabricated using traditional extrusion and coating techniques. The anode slurry was prepared and consisted of NO powder, GDC powder, and cellulose as the binder. The anode components were mixed with water using an industrial mixer for 1–2 h and left to age overnight. Placing a vacuum over the anode mixture allowed for excess air to be removed. Anode tubes were extruded from the anode mixture using a ram extruder and a custom-made die. The anode tubes were allowed to dry, were cut to the desired length, then dip-coated in GDC electrolyte slurry, and allowed to dry. The GDC electrolyte slurry is composed of the same GDC powder described above, and organic ingredients such as binder (poly vinyl butyral), dispersant (fish oil), and solvents (toluene and ethanol). The desired electrolyte thickness was achieved through multiple electrolyte coatings and subsequently the tubes were sintered at 1,450 C for 6 h in air. Next, the electrolyte-coated anode tubes were dip-coated in cathode slurry consisting of the LSCF and GDC powder, and organic ingredients similar with those of the electrolyte slurry. The cathode dip-coated tubes were dried in air and sintered at 1,000 C for 1 h in air to complete the fuel cell fabrication. An Environmental Scanning Electron Microscope (ESEM) was used to check the electrode and electrolyte microstructure. In order to carry out the experimental activities, measuring the fuel cell electrochemical performances, a specific support was also manufactured. Such a support is capable of sustaining the fuel cell when it is mounted in the furnace; it also allows the gas distribution on the anode and cathode sides and assures the electrical connection with the electrical load and potentiostat. Each tube was connected to two alumina tubes allowing the inner anode gas distribution, sustaining the cell in the furnace. The entire system was placed on an alumina half tube support in order to yield stronger structure (> Fig. 44.9). > Figure 44.10 shows how each microtube was mounted for testing within a vertically mounted microtube furnace (Carbolite), and also

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Alumina tube Micro-tubular SOFC

Anode current collector wires

Cathode current collector wires

Half tube support

. Fig. 44.9 Showing how the micro-SOFCs were supported for testing

Anode Electrolyte Cathode

0.0 mm

1.0 mm

2.0 mm 0.0 mm

0.25 mm 0.0 μm

50.0 μm

. Fig. 44.10 Showing how the micro-SOFCs were mounted for testing

shows a cross-sectional ESEM image of the fabricated microtubular SOFC, with porous electrodes and a dense electrolyte. Cells were tested vertically as shown in order to ensure evenly distributed flow of fuel gas across the anode surface (horizontally oriented cells are subject to uneven fuel gas distribution due to gravity). Each tube was equipped with four 0.5 mm silver sensor wires attached for collecting current for anode and cathode sides. The anode electrical connection was realized using two long silver wires fixed using nickel paste. A silver wire was wrapped around the tubular fuel cell (on the cathode), as a reel, and fixed with silver paste for the cathode electrical connection. The silver paste and nickel paste were brush painted on the cathode and anode surfaces to reduce the contact resistance between the silver sensor wires and the electrode surfaces. The pastes are porous enough at operating temperatures

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that fuel and oxygen are able to pass through them to arrive at their respective electrodes. Ceramabond 552 (Aremco) was used as a sealant between anode, alumina tubes, and alumina half tube support. The four current collecting wires from the cell were connected to an impedance analyzer and the electrical load at operating temperature ranges between 450 C and 550 C. Individual cells were run using humidified hydrogen gases (2–3% of H2O) as fuel to the anode side, while the cathode side (outside surface of tube) was exposed to atmospheric conditions. The microtubular SOFC was brought up to 450 C at 3 C/min from room temperature under atmospheric conditions with air exposed to both anode and cathode sides. After arriving at the operating temperature of 450 C, the cell was exposed to 15 sccm-humidified H2 (3% H2O by volume). The cell immediately began to reduce and produce a voltage as shown in > Fig. 44.11. The cell voltage rose to 0.94 V after only 1 min and the cell continued to produce a voltage of 0.94 V thereafter. In order to understand whether the cell had fully reduced in this time, impedance measurements were taken in increments after the cell had started up. The start-up impedance information is shown in > Fig. 44.12. The information gathered through the impedance analysis shows that the entire cell impedance decreases the longer the cell has been run. The ohmic impedance of the cell remains relatively constant at around 1 O; however, the electrode polarization resistances decrease with time until around 50 min where no further change in electrode polarization resistance is observed as a function of time. The electrode polarization resistance decreased by as much as 0.5 O in 10 min after the cell had started up. After start-up behavior analysis, the cell was held at 450 C and IV characterization of the cell was performed for varying flow rates of humidified H2 (3% H2O by volume) through the cell. > Figure 44.11a–c outlines the performance of the cell for varying fuel utilizations at 450 C and concentration polarization losses are apparent in the IV curves shown. The fuel utilization was calculated from equation Uf = i/(nFv), where the current drawn from the cell (i), the number of electrons transferred in the reaction between H2

Voltage (V)

Start up behavior at 450°C 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0

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Air

. Fig. 44.11 Microtubular SOFC Start-up behavior

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Impedance after start up at 450⬚C 0.6 0.5 0.4 0.3 0.2 0.1 6E–16 –0.1 0

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5 min after start 15 min after start 35 min after start 55 min after start 65 min after start 75 min after start 5

. Fig. 44.12 Impedance spectra during the first 75 min of running

and ½ O2 (n = 2), the flow rate of fuel (v), and the inlet temperature of the fuel were used to calculate the fuel utilization (Uf ) of the cell for the varying flow rates of fuel through the cell. The temperature of the inlet fuel stream is important because the density of H2 entering the fuel cell is dependent on this parameter. As can be seen in > Fig. 44.13a–c since at higher temperatures more current can be drawn from the cell, more hydrogen is necessary to drive the higher currents and fuel utilization values change for a specific flow rate. Thus, balancing fuel utilization with performance loss is an important issue when designing an efficient system since the performance of the cell is closely related to the fuel utilization.

Modeling of SOFC Systems In modeling studies of solid oxide fuel cells, the common approach is to either model the cell isolated from its surrounding, or to include some aspects of the surrounding environment by truncating the domain where the variables associated with the transport phenomena have not yet settled down to their ‘‘free stream’’ values. When large gradients (of these variables) are present, these approaches may lead to misrepresentation of the physics. For example, large differences in temperature or species concentration between the SOFC and its surroundings result in larger length scales for heat and mass transfer. Therefore, if a single cell is to be modeled with some portion of the physical domain, boundary conditions should be selected at the boundaries where truncation takes place; otherwise, a broader domain should be selected to cover spatial variations. However, selecting a larger domain requires further computational effort due to the mismatch between the aspect ratios of different parts of the computational domain.

Leakage Currents There are a considerable number of studies to characterize the electron transfer process in the electrolyte. In early attempts, implicit relations of fuel cell electrochemical parameters

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Fuel utilizations for varied flow rates at 450⬚C 1

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Fuel utilization: varied flow rates 550⬚C

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. Fig. 44.13 (a–c) Fuel utilization and power density of the cells running at (a) 450 C, (b) 500 C, and (c) 550 C

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were suggested as solutions to the electron transport equation in the electrolyte. Riess developed an explicit solution relating oxygen partial pressures and cell voltage to the electron flux across the electrolyte. His approach has been widely accepted in modeling studies. With some modifications to his derivation, some other forms of solutions also exist in the literature. Previously, Godickemeier developed a model to study the GDC electrolyte with the perspective of optimizing the cell design. Leah et al. developed a model to show that the use of MIEC electrolytes under certain conditions do not cause critical efficiency drops. Baron et al. further reported a reasonable fit of their model results to the experimental data when leakage currents were included.

Parametric Analysis Although there are substantial works in modeling of SOFCs, few modeling studies have focused on the parametric analysis. Parametric analysis is an important method to understand the fuel cell behavior and compare the performance of the system affected by various factors. These factors can be related to either the cell geometry and material properties or operational conditions. Changes in the geometry of the cell come along with uncertainties in the parameters related to reaction kinetics as the latter cannot be predicted without additional experiments. If the fuel cell performance is desired to be compared for two different cathode thicknesses, parameters related to reaction kinetics have to be updated for the new geometry as the distribution of the three-phase boundaries will change along with the percolation of the phases in the new geometry. Many of the modeling studies found in the literature carrying out parametric analyses of SOFCs focus on the geometrical aspects of the system. However, these studies neglect the abovementioned uncertainties arising with the change of the electrode geometry and are incapable of providing a precise tool to assess the effects of the geometrical parameters. Therefore, the effects of geometry on the fuel cell performance are not considered in this study. There are also studies focusing on the operational parameters such as utilization, flow rate, temperature, and pressure. Ni et al. developed a model to conduct parametric analysis to address the effects of operating conditions on the overpotentials. Their work constitutes a 1D model employing electrochemical relations and mass balances, and does not include energy and momentum balances. Jiang et al. built a thermal and electrochemical model of a tubular SOFC to study the effects of operating conditions such as pressure, temperature, and flow rate. Their model is a lumped model and does not consider spatial distribution of the variables. Lisbona et al. analyzed an SOFC stack with the balance of plant to develop relations between cell performance and the operational parameters such as utilization, air flow rate, and inlet gas temperature. The developed model consists of only electrochemical relations, and the transport phenomena inside the stack are not considered. Colpan et al. developed a model employing thermodynamic calculations to identify the effects of utilization on cell output power and efficiency. Bove et al. carried out a utilization analysis for a tubular SOFC. Their model employs energy balance and electrochemical relations along with the simple algebraic relations for gas compositions.

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Although these models constitute significant contributions to the field, they either do not incorporate the sophisticated transport phenomena in the fuel cell rigorously or they underestimate the effects of spatial distributions of the transport variables.

Transient SOFC Modeling While there are a number of significant modeling efforts, both in steady state and in transient, transient SOFC models typically are not as elaborate as steady-state models. Some of the transient models are lumped models neglecting all the spatial variations. They are mainly developed for control or to simulate the fuel cell as part of the larger system. Transient models incorporating transport phenomena vary from 1D to 3D models. 3D models are developed generally for planar SOFC, whereas exploiting the axial symmetry of the tubes, 2D models are preferred and most of the time sufficient to represent an SOFC with a tubular design. Achenbach presented one of the first transient studies on SOFCs. He developed a 3D transient model to investigate the voltage responses of a planar SOFC to certain load changes. Ioara et al. developed a 1D model for a planar direct internal reforming SOFC in which they concluded that neglecting the variation of the gas stream properties may lead to incorrect dynamic response predictions. Jia et al. provide detailed analysis of the effects of operating parameters on the steady state and transient performance of a tubular SOFC. Employing a 1D model, they represented the conservation laws with a control volume approach. In a recent study by Barzi et al. dynamic responses of a tubular SOFC are predicted during the start-up. Their 2D model incorporates mass, momentum, and species balances accompanied with a circuit representation of charge balances. Bhattacharyya et al. compared the dynamic behavior of the cell with the experiments in their 2D model of a tubular SOFC. Along with investigating dynamic response of the cell to the changes in voltage, they also predicted the response of the cell to the changes in hydrogen flow rate. Ota et al. compared transient characteristics of a standard tubular cell with a microtubular cell with a modeling framework presented therein. Their modeling framework is based on simplifications instead of taking into account full coupling of the sophisticated transport phenomena. They reported that timescales of a standard tubular cell to a specific voltage response is six times larger than that of a microtubular cell. Another modeling study on microtubular SOFCs is presented by Nehter. In this study, he compared a common microtubular cell with a cascaded one. Although localized temperature and species concentrations are provided in his 2D axial symmetric model, momentum balance and multicomponent species transfer are not included. Mass balance is carried out in a simple way via algebraic equations describing the electrochemical and shift reactions. Although there are many simplifications in the models of Ota et al. and Nehter, their studies are significant since, to the knowledge of the authors, they are the only modeling efforts emphasizing dynamics of microtubular SOFCs. Since the characteristics of a microtubular SOFC are very different than a standard tubular cell, there is still need for a rigorous model to study the dynamics of such a cell.

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Thermal-Fluid Model Description The work performed by Serincan et al. employed two separate models to have a more accurate representation of the actual fuel cell test system: (1) a furnace model and (2) a fuel cell model. With the predictions from the former, boundary conditions were determined for the fuel cell model. > Figure 44.14 represents the geometrical domains for the furnace model and the fuel cell model. The model exploited the axial symmetry of the tubular geometry therefore reducing the modeling domain into a 2D axisymmetric domain, assuming the anode and the cathode current collectors were uniformly distributed on the electrode surfaces. > Figure 44.14 (not drawn to scale) also shows the cross section of the axisymmetric geometry. The actual model geometry can be visualized by revolving this cross section around the symmetry axis, that is, centerline of the anode tube. Mass, species, and momentum conservation equations were solved in the gas channels and the porous electrodes, and energy conservation were applied for the entire domain. Ionic charge balance was applied in the anode, the electrolyte, and the cathode, whereas the electronic charge balance was applied in the anode and cathode.

Room atmosphere 1, 2, 3, 4

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Equations 1. Continuity 2. Momentum 3. Species 4. Heat 5. Electronic charge 6. Ionic charge ∗ Momentum equation in porous media

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FC model bound Alumina tube 4

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∗

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Furnace model boundaries

Fuel cell model boundaries

Air channel 1, 2, 3, 4 z

e

r

r

a

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b

. Fig. 44.14 (a) Furnace model domain, (b) Fuel cell model domain. Numbers represent the equations solved in each section of the domain

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The microtubular cells considered in this study were fabricated and characterized as described above. The anode-supported cells employed a GDC electrolyte coated on a NiOGDC anode, and (LSCF)-GDC cathode. It is well known that GDC electrolytes are prone to internal current leakages. GDC can reduce, and become electronically conductive, especially at elevated temperatures. A fraction of the electrons generated at the anode can then be transferred to the cathode through the electrolyte. As a result the cell is shortcircuited and a drop in the open circuit potential is experienced. The effect of current leakages becomes less significant at higher current densities, because they are inversely proportional to the ionic current density. In this work, the electronic current leakages were modeled as boundary conditions to the electronic charge equation at the electrolyte interfaces of anode and cathode, while describing the boundary conditions. The furnace model was used to explicate the transport phenomena in the furnace and the surrounding room atmosphere, and estimated the transport properties at the boundaries of the fuel cell model domain. Computational domain for furnace model was chosen by trying different dimensions until the gradients disappeared, and/or not to have a significant effect on the distribution inside the furnace.

Results from Modeling The furnace model consisted of the furnace, fuel cell as a whole, alumina tubes shown in (> Fig. 44.9), air channel and the surrounding room atmosphere. In the air channel and the room atmosphere species, momentum and heat equations were solved. In the fuel cell, these equations were modified accordingly to account for porous media transport. In the furnace walls and alumina tube only heat equation was solved. The difference between the furnace temperature and the room temperature invokes natural convection, which transmits the air to the fuel cell. To implement natural convection in the model, a nonisothermal flow equation was used. Another approach could have been to apply a Bousinesq approximation to the Navier-Stokes equation, which would be based on linearization of density with respect to the changes in temperature and concentration. Further, Maxwell Stefan equations coupled with heat and momentum equations were used to model the species balance. On the other hand, the fuel cell model included truncated air and fuel channels, alumina tubes, anode, electrolyte and cathode as is seen in > Fig. 44.14. In the air and fuel channels, species, momentum, and heat equations were solved. In the anode and cathode, in addition to these equations that were modified for porous media, ionic and electronic charge equations were also solved. In the electrolyte ionic charge equation was solved along with heat equation. In the alumina tubes only heat equations were solved. Maxwell–Stefan equations were used to model the multicomponent species balance instead of Fick’s Law, which is applicable only for binary mixtures. To model momentum transfer, non-isothermal flow equations were solved, with the non-isothermal continuity equation, to take into account the density changes with temperature and species concentration. In the porous electrodes momentum equations were modified in the form of

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non-isothermal Brinkmann equations. Darcy’s Law for momentum transfer in porous media was not chosen as it does not include stress tensors in its formulation. Heat equations were formulated in order to include enthalpy transfer. Heat transfer due to radiation was modeled as boundary conditions. Electronic and ionic charge balances were implemented in the form of Ohm’s Law throughout the anode, electrolyte, and the cathode domains. The results of the furnace model described above showed that oxygen concentration at the boundaries strongly depend upon the fuel cell operation conditions, and the importance of assigning the right boundary condition. The model results were also compared with experimental data, and related polarization curves show good agreement for a set of different operating temperatures. Having a good match with the same set of fitting parameters for three different polarization curves suggest the model captures the temperature dependence of the fuel cell electrochemistry well. Temperature distribution in the cell was evaluated and the average radial temperature gradient was calculated as 2.25 C/mm, whereas the axial average gradient was found to be 18 C/mm. It was predicted that the temperature may rise by up to 120 C for an SOFC operating at 0.2 V. This temperature rise is attributed to the ohmic heating due to the losses during fuel cell operation. It was further shown that it was a good assumption for a microtubular SOFC to lump all the losses at the anode due to the very small thickness of the tube. Leakage currents were found to be the reason for an OCV drop of 0.18 V at 550 C and their effects diminish gradually until they vanish around cell voltages of 0.6 V. It was also shown that at higher operating temperatures the internal current leaks associated with the electron transfer through the electrolyte were more significant. It was predicted that if the output current demand is 0.53 A/cm2, the fuel cell has to generate an ionic current density of 0.65 A/cm2 at 550 C, as under this condition the leakage currents sum up to 0.12 A/cm2. The dependency of current density on transport properties was also studied and the effects of temperature and species concentration were shown on the current density profiles. Moreover exchange current density as a measure of reaction rate was considered and it was suggested from model results that anode thickness can be reduced to promote reactant diffusion to the active catalyst sites. Effects of temperature, fuel flow rate, fuel composition, anode pressure, and cathode pressure on the SOFC performance were investigated. It was shown that increase in temperature results in better cell performance due to increase in catalytic activity, ionic conductivity and decrease in mass transport losses. It was found that with higher flow rates, the performance of the cell increases; however the efficiency decreases due to the lower utilization. In conjunction with this it was advised that the fuel flow rate should be chosen according to the desired operating range such as at mid-range current densities lower flow rate as suggested because of the efficiency of the cell, and in the higher current density range, higher flow rate should be chosen (i.e., a stoichiometric flow control) because of the output power implications. It was also shown that the utilization of the fuel was not zero when the cell does not generate current because the reacted fuel is not enough to overcome the internal current leakages. When fuel composition was considered, higher hydrogen content was favorable for power output, efficiency, and thermal management.

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Increases in anode side and cathode side pressures have two distinct effects on cell performance: increase in pressure reduces reactant diffusivity but increases catalytic activity. However, the latter overwhelms the adverse effects of decreased mass transport and cell performance is always observed to improve with larger back pressure. When the effects of pressure on the anode and cathode sides are compared, it was seen that it was more sensitive to changes in the air pressure mainly due to the slow reaction kinetics of the cathode. Response of the cell to a change in voltage was also investigated. An overshoot was observed in the current density response as a result of the combined effect of fast electrochemical reaction and slower dynamics of the mass transfer. It was predicted that timescales of a microtubular SOFC is in the order of 20 s governed by the dynamics of heat transfer.

Future Directions Solid Oxide Fuel Cells (SOFC) have tremendous potential for a number of applications from small mW to W scale, all the way up to MW scale systems. However, research around the world is concentrating in the development of suitable materials and fabrication processes to bring down the price of the SOFC to make it a commercially viable product. Programs are underway internationally to look at novel SOFC geometries utilizing cheaper materials that work at lower temperatures. The demonstration of a lowtemperature SOFC running directly off methane or natural gas, signals an important new opportunity for making simple, cost-effective power plants. Changes in cell composition and design have resulted in improved power densities, with higher power densities contributing to lower weight, size, and cost of the final fuel cell systems. This is the future direction that has to be optimized to allow these systems to become a reality.

References 1. 2. 3.

Dees DW, Claar TD, Easler TE, Fee DC, M’razek FC (1987) J Electrochem Soc 134:2141 Kordesch K, Simader G (1996) Fuel cells and their applications. VCH, Weinheim Minh NQ, Takahashi T (1995) Science and technology of ceramic fuel cells. Elsevier, Amsterdam

4.

Singhal SC (1991) In: Grosz F, Zegers P, Singhal SC, Yamamoto O (eds) Proceedings of the 2nd international SOFC symposium, Athens. Commission of the European Communities, Luxembourg, p 25

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45 Molten Carbonate Fuel Cells Takao Watanabe Energy Engineering Research Laboratory, Central Research Institute of Electric Power Industry (CRIEPI), Yokosuka, Kanagawa, Japan Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1731 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1731 High Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1731 Various Fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1732 Internal Reforming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1732 CO2 Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1732 Easier Manufacturing of Large Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1732 Principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1732 Cell Stack Configuration and Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1733 Matrix and Electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1733 Metallic Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1735 Cell Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1735 External and Internal Reforming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1736 External Reforming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1736 Internal Reforming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1736 Basic Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1737 Current–Voltage (I–V) Characteristic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1737 Life Characteristic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1737 Performance Improvements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1738 Voltage Enhancement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1738 Voltage-Determining Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1738 Reducing Voltage Loss Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1739 Pressurized Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1739 Life Extension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1740 Electrolyte Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1740 Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_45, # Springer Science+Business Media, LLC 2012

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Matrix Pore Coarsening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1741 Nickel Short-Circuiting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1741 System Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1743 Basic Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1743 Natural Gas–Fueled External Reforming System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1744 Natural Gas–Fueled Internal Reforming System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1745 Integrated Coal Gasification MCFC Combined Cycle (IGMCFC) . . . . . . . . . . . . . . 1746 Development Status of MCFC in the World . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1746 Dawn of the Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1746 USA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1747 Europe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1748 Asia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1748 Development Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1749 Cell Stack Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1749 System Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1750 Economy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1750 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1751 Expansion of Market Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1751 Development of Power Generating Systems with Novel Function . . . . . . . . . . . . . . . 1752

Molten Carbonate Fuel Cells

45

Abstract: Molten carbonate fuel cell (MCFC) is a high-temperature fuel cell. Because of high-temperature operation, various fuel gases can be widely used and internal reforming of hydrocarbon fuel is also possible, resulting in improving fuel utilization and providing higher power generation efficiency. Many MCFC plants are being installed as the stationary cogeneration power supply using various fuels in various countries in the world, and among them, the world’s largest fuel cell power plant has 2.8 MW electric capacity. The power generation efficiency of the systems including smaller 300 kW units reaches 47% (LHV, net, same as above unless otherwise noted). In addition, the hybrid systems which contain both MCFC and gas turbine have been demonstrated, and a new carbon dioxide (CO2) recovering hybrid system concept with extremely high value of 77% efficiency is proposed. The advantage of MCFC is not only the use of city gas but also the use of digestion gas from the sewage disposal plant. In the future, it is expected to develop a large-scale centralized electric power generating plant using the coal gasification gas. The MCFC is one of the key technologies to reduce CO2 emission for the future.

Introduction The MCFC is a high-temperature fuel cell operated at approximately 600–650
C. Along with the features of general fuel cells that are high power generation efficiency, capacity flexibility, and excellent environmental property, it has a lot of additional attractive features such as the variety of an applicable fuel, improvement of the power generation efficiency by a combination with the gas turbine, and/or by the internal reforming. The MW class plants are already introduced, and its commercialization is just around the corner. This chapter outlines the features of MCFC, the principle, the basic performance, the configurations of cell/stack/system, and current development situations and issues. The future directions are also given.

Features The MCFC uses carbonate which is in a molten state for an electrolyte, and the electrochemical reactions take place through carbonate ion. Besides the features of the general fuel cells such as high efficiency, capacity flexibility, and the superior environmental sustainability, the MCFC has additional features as follows.

High Efficiency Because the operating temperature is around 600–650
C, it can form the power generation systems combined with the gas turbine and the steam turbine by using the high-quality exhaust heat from the MCFC. It can attain much higher power generation efficiency.

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Molten Carbonate Fuel Cells

Various Fuels Due to high operating temperature, electrode reactions take place in fast speed, and thus expensive platinum (Pt) catalyst is unnecessary, resulting in avoiding carbon monoxide (CO) poisoning. Therefore, the application of the CO-containing gasification gases such as coal, biomass, and waste is also possible.

Internal Reforming When methane-based fuel is in use, internal reforming can be applied using steam and heat generated inside the fuel cell. The internal reforming can be expected to improve the generation efficiency by increasing fuel utilization and lowering energy consumption for cooling the MCFC to maintain the operating temperature. The internal reforming can also simplify the system configuration by eliminating the external reformer.

CO2 Concentration Because the electrochemical reactions take place through carbonate ion, CO2 is necessary for the cathode reaction. On the other hand, same amount of CO2 is generated at the anode. Therefore, the CO2 generated at the anode is generally circulated to the cathode side. It is called the CO2 recycling. Because the generation of CO2 at the anode increases the concentration of CO2 at the anode exhaust, low concentration of the CO2 at the cathode inlet can be increased at anode exhaust. For example, if low CO2-containing flue gas from thermal power station is supplied to the MCFC cathode, we can obtain high CO2-containing gas which can separate CO2 easier.

Easier Manufacturing of Large Cells The MCFC generally adopts a planar multilayered structure, using metal separators and sheets of active components manufactured by tape casting method. Therefore, it is rather easy to make it big and to be adopted large capacity power plants from the production viewpoint.

Principle Figure 45.1 shows the principle of the MCFC operation [1]. The electrolyte is a liquid that melts under the operating temperature. Hydrogen (H2) supplied to the anode reacts with carbonate ion (CO32) in the electrolyte. The electron is discharged from the anode and steam (H2O) and CO2 are generated at the same time. Reacting with the electron, >

Molten Carbonate Fuel Cells

45

(Fuel gas chamber) Fuel gas H2, CO

H2

(Anode) (Electrolyte) (Cathode)

H2O

CO2 e–

Fuel exhaust H2O, CO2

e–

2-

CO3

e–

Air+CO2 O2, N2, CO2

Electricity

e–

O2 CO 2

Oxidant exhaust

(Oxidant gas chamber)

N2

Operation temperature: 600⬚C to 650⬚C

. Fig. 45.1 Principle of the MCFC

oxygen (O2) and CO2 supplied to the cathode generate CO32. These reactions are expressed as follows. Anode : H2 þ CO3 2 ¼ H2 O þ CO2 þ 2e

(45.1)

Cathode : CO2 þ 1=2O2 þ 2e ¼ CO3 2

(45.2)

Total : H2 þ 1=2O2 ¼ H2 O

(45.3)

The electron is discharged from the anode and taken into the cathode through an external circuit in a series of reaction. Power generation by the fuel cell is achieved by flowing the electron. Because the operating temperature is high and nickel (Ni) is used for both electrodes, Ni acts as a catalyst and CO in the fuel gas (if there is any) supplies H2 by the shift reaction (CO + H2O = H2 + CO2) relating to the reaction of (> 45.1). The operating temperature of MCFC is high enough for the proceeding of the shift reaction. Therefore, it becomes possible to use the gasification gas of coal, biomass, and waste, which contain certain percentage of CO. In addition, a big characteristic of the MCFC is to have to contain CO2 in the supplied oxidant gas, because the ion in the electrolyte that contributes to the reaction is CO32.

Cell Stack Configuration and Materials The actual cell consists of the matrix sheet, the electrode (anode and cathode) sheets, and the metallic components that provide reactant gas passageway and current collection, as shown in > Fig. 45.2. Then, the size of the cell is described.

Matrix and Electrodes The matrix has a porous ceramic structure consisting of LiAlO2. It is usually impregnated with the electrolyte liquid maintained by capillary force under the operating temperature. Mixed carbonate of Li2CO3 and K2CO3 or of Li2CO3 and Na2CO3 is used as the

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Molten Carbonate Fuel Cells

Fuel gas inlet Corrugate plate Anode Electrolyte matrix Cathode Current collector Cell frame Oxidant gas inlet

. Fig. 45.2 Configuration of MCFC cell

electrolyte. A g type has been used for LiAlO2 mainly, but the a type is examined recently from a point of the stability for carbonate. Moreover, the coarse particle or fiber of alumina (Al2O3) is mixed to keep the mechanical strength. Both anode and cathode provide reaction places for the reactions (> 45.1) and (> 45.2), and are placed on the surface of the thin electrolyte film (matrix). Therefore, the electrodes are required to have high electric conductivity, optimal pore size, and porosity for providing sufficient active area (reaction places), adequate wettability for maintaining electrolyte stable, stable porosity structure, etc. Because mean pore sizes of the electrodes are larger than that of the matrix by single digit, capillary force in the matrix is stronger than that in the electrodes. Then, pores within the matrix are firstly filled up and then excess electrolyte is impregnated in the pores within the electrodes. Matrix is usually filled up 100% with electrolyte and the pores of the electrodes are filled by 20–40% of the void volume. 1. Anode: The anode is required to have high corrosion resistance for melted carbonate under the fuel gas atmosphere. It also should be stable under steam and CO2 generated at the anode. Therefore, the porous sheet sintered from fine nickel (Ni) particle is used. Chrome (Cr) and aluminum (Al2O3), etc., are usually added for the improvement of creep resistivity at high temperature. 2. Cathode: The cathode is operated under a severe condition of oxidative atmosphere, and thus the metallic oxide is used. Typically, the porous media made of oxidized nickel particle is used. Nickel oxide (NiO) does not have sufficient electric conductivity; however, the electric conductivity is given by lithium in molten carbonate being doped in the cathode. 3. Manufacturing of the sheets: The electrodes and the matrix are made by the tape casting method and the formed sheets are cut for required sizes. The tape casting method is a useful process for simple, easy, quantitative, and cost-effective production. In the process, the slurry to the mixture of the fine particle of the raw material with the

Molten Carbonate Fuel Cells

45

solvent is thinly spread by a doctor blade on a substrate sheet and dried. The spread sheet is about 0.5 mm in thickness and about 1 m in width. The electrodes and matrix are called active components and they are cut to have rectangular shape like PAFC.

Metallic Components 1. Gas flow channels: Gas flow channels for fuel and air (it is accurately called ‘‘oxidant gas’’ because it contains CO2) are formed using the metallic end plates which sandwich active components. The outer periphery of the end plates touches the electrolyte matrix directly, and the wet seal covered with the liquid film of the impregnated electrolyte is formed and prevents gas leakage to the outside. Stainless steels such as SUS316L and SUS310S are machined or pressed for the end plate. The nickel clad steel is used as a center plate of the separator, which is exposed to both reducing and oxidizing condition on each side in consideration of corrosion resistance with the carbonate. 2. Current collector: Moreover, the current collector is placed within the gas flow channel for better electric contact between the electrode and the end plate. Perforated metal plates with same materials to the end plates are generally used. 3. Separator: Because the voltage of a single cell is about 0.7–0.8 V, it is necessary to obtain a high voltage of several 100 V or more to operate the power conditioner efficiently. Therefore, it is required to pile up the single cells through the metallic separator plates. This is called a stack. The separator has gas flow channels on both side instead of the end plate for single cell and it connects single cells in series electrically. The number of cells in the stack is usually 100–300. 4. Gas flow directions and manifolds: There are three ways for fuel and oxidant flow directions at a cell. These are cross-flow, parallel-flow, and co-flow. It is chosen in consideration of the operating temperature and the current distribution in the cell. There are also three ways for distributing reactant gases to each cell within a stack, which are external-manifold, internal-manifold, and hybrid-manifold. External-manifold is adopted in the PAFC stack. However, internal-manifold which has a penetration hole through the cell is sometimes selected for MCFC stack. It is also chosen in consideration of reactant gas flow directions within the cell. External-manifold is selected in the case of cross-flow like PAFC. However, internal-manifold could be adopted in the case of paralleland co-flow. There are both merits and demerits from the viewpoint of the manufacturing process, electrolyte migration in the stack, effective electrode surface area of the cell, etc.

Cell Size The thickness of the single cell is several mm with the two electrodes and electrolyte matrix (active components). The size of stacked cell is slightly bigger than general PAFC, and the length is about 1 m on a side of the rectangular shape. The separator is produced using a metal part with about the same size. > Table 45.1 shows a general specification of each material that composes the cell [1].

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Molten Carbonate Fuel Cells

. Table 45.1 Specification of MCFC components Mean pore Diameter (MPD), porosity, etc.

Component

Material

Thickness

Anode

Ni–Al–Cr

0.7–1.0 mm

Cathode

Lithiated Ni

0.3–0.8 mm

Electrolyte support

g-LiAlO2, a-LiAlO2

0.5–1.0 mm

Electrolyte

Li2CO3–K2CO3 Li2CO3–Na2CO3

–

Porosity: ca.60% Specific surface: 15–20 m2/g –

Separator

SUS310S, SUS316L, Ni SUS316L-Ni clad

–

–

MPD: 4–6 mm Porosity: ca.60% MPD: 8–10 mm Porosity: ca.80

External and Internal Reforming Either an external reforming or an internal reforming method is adopted for the supplying H2 to the system as a reactant at the anode. Reforming reaction is expressed as follows: CH4 þ H2 O ¼ 3H2 þ CO

(45.4)

The external reforming is a method that the reformer is installed separately from the stack, same as the PAFC system, and H2 is generated from natural gas outside the stack. In the internal reforming method, the reforming catalyst is loaded within the fuel flow channel of the cell and H2 is generated in parallel with power generation. The MCFC can adopt the internal reforming method because of its high-temperature operation.

External Reforming In the external reforming, natural gas and steam mixture are supplied to the separated reformer and H2 rich gas is produced through a catalyst loaded tube heated from outside. Reforming rate (methane conversion rate) is limited by the reforming condition and the number of Balance of Plants (BOPs, equipments configuring the fuel cell system other than the fuel cell stack) is increased. The advantage of this method is that it can avoid undesirable effect of electrolyte on the catalyst (please see below) because the reformer is separated and located upstream of the stack.

Internal Reforming The internal reforming enables a system compact, stack cooling load small, and to improve methane conversion rate and efficiency, because endothermic reforming reaction

Molten Carbonate Fuel Cells

45

proceeds further by using both steam and heat, which are generated within the cell during consuming H2 at the same time. On the other hand, the reforming catalyst is exposed to the electrolyte, which might cause damaging catalyst. Indirect internal reforming method is usually adopted to avoid this problem [2]. The exclusive reforming plates are sandwiched every several cells in the stack and pre-reformed gas from the reforming plate is supplied to the cells.

Basic Performance Current–Voltage (I–V) Characteristic Basic performance of the fuel cell can be represented by the current–voltage characteristics which affects largely on the efficiency and cost of the plant. The current–voltage characteristic of the MCFC is expressed by straight line as shown in > Fig. 45.3. Because of hightemperature operation, voltage loss with electrode reaction is small. The cell voltage is generally over 1 V in no load and it becomes 0.7–0.8 V with load of 150 mA/cm2 current density. The operating cell voltage of MCFC is higher than other types of fuel cells in the current density range of 100–250 mA/cm2. It is one of the appropriate MCFC operating conditions at this current density range.

Life Characteristic To discuss the stability of the cell, voltage decay characteristic (life characteristic) is important. It affects on the efficiency change and eventually on the cost of electricity. Typical voltage decay pattern of the MCFC is shown in > Fig. 45.4. In general, the cell voltage decays gradually and linearly until certain time, and then drops rapidly after.

E

Cell Voltage

By Nernst Loss hNE By internal resistance R ir X J (= hir) By anode reaction R a X J (= ha) By cathode reaction R c X J (= hc)

: Voltage drops

V = E-

V

hNE - (Rir + Ra + Rc) x J Current

. Fig. 45.3 Current–voltage performance

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Gradual decay period (by electrolyte loss) cell voltage

1738

Rapid decay period (by Ni short circuiting)

40,000 hours with 10% loss 0.25%/1000 h decay rate operation time

. Fig. 45.4 Voltage decay pattern

The rapid drop is caused by ‘‘nickel short-circuiting’’ as described later. The voltage drop means not only the decrease of plant efficiency but also the change in relevant BOP’s operating conditions. Because it is generally considered that the acceptable change of the operating conditions is about 10%, practical MCFC life should be the time when cell voltage decreased to the ca. 90% level from the initial voltage during the linear decay range, or the time when the rapid voltage drop started. The reason of the voltage decay will be described in next section. For keeping high efficiency and reducing cost of electricity, it is important to control the voltage decay rate as small as possible and to delay the starting point of rapid voltage drop after the target lifetime. The current goal of life is generally considered about 30,000–50,000 h as same as other types of fuel cells.

Performance Improvements Voltage Enhancement Voltage-Determining Factors There are several voltage-determining factors as shown in > Fig. 45.5 [3, 4]. The voltage loss caused by internal resistance is relatively small, and the loss caused by electrochemical reaction at both anode and cathode are large. The electrolyte of the MCFC is the mixture of Li2CO3 and K2CO3 (Li/K) or the mixture of Li2CO3 and Na2CO3 (Li/Na). The reaction voltage loss is large using either electrolyte, and the reaction voltage loss at the cathode is larger than the one at the anode. Nernst loss means the decrease of theoretical voltage caused by the gas composition change by electrode reactions and it is mainly caused by the anode reaction. The composition of fuel gas changes larger than that of oxidant because H2O and CO2 are produced at the anode with higher fuel utilization (about 80% in natural gas fueled system) which means the concentration of H2 is drastically reduced. Oxidant utilization is usually set at lower level (about 30–50%), meaning higher flow rate, for stack cooling. This is the reason why the fuel-side Nernst loss is larger than the oxidant side.

Molten Carbonate Fuel Cells

45

1150 1100

Pressure : 0.1MPa, Temp : 650⬚C Utilization : Uf/Uox=60/40%

Nernst Loss

Voltage (mV)

1050 1000 950

(102)

(106)

(58) 31/28

(38) 27/11

(8)

(12)

900 850

Anode Overvoltage (RaxJ ) Cathode Overvoltage (RcxJ ) O2–/CO2 Internal Resistance (RirxJ ) Output Voltage

(34) (44) 849

871

800 Li/K

Li/Na

. Fig. 45.5 Voltage-determining factors

Reducing Voltage Loss Factors The MCFC is expected to replace the conventional centralized thermal power plants in the future. Such large-scale power plants are operated with very high efficiency; therefore, the MCFC power plant is required to be operated with much higher efficiency. If the fuel cell system generates electricity only by the fuel cell, the system efficiency is almost proportional to the cell voltage. Therefore, the fuel cell voltage should be maintained as high as possible and it is important to reduce the voltage loss factors as can be seen from > Fig. 45.5. It is effective to reduce the voltage loss, first of the cathode reaction, and then of the anode reaction and the internal resistance. For the reaction loss reduction at the electrodes, it is important to realize adequate electrolyte distribution, designed by optimizing the microstructure and wettability of the electrodes. For the internal resistance reduction, higher ionic conducting electrolyte or thinner matrix is applied.

Pressurized Operation Pressurized operation is another way to increase the cell voltage. Higher operation pressure increases theoretical voltage (Nernst potential) and reactant gas solubility which means the decrease of reaction voltage loss, and it can eventually provide higher plant efficiency. It corresponds to push up the voltage–current characteristic indicated in > Figs. 45.3 and > 45.6 shows the pressurized characteristic of the MCFC up to 5 MPa range [5]. Regardless of electrolyte composition, the cell voltage increases in proportion to a logarithm of the pressure. However, above about 3 MPa, the cell voltage is suppressed or decreases in some cases. This is caused by the methanation reaction in which methane is

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1000

950 Li/Na Cell Voltage (mV)

1740

900 Li/K 850

800

750 0.1

Current Density:150mA/cm2 Temperature : 923K Fuel : H2/CO2/H2O=32/8/60 Oxidant : Air/CO2=70/30 1.0

10

Operation Pressure (MPa)

. Fig. 45.6 Pressurized performance

produced from carbon and hydrogen elements in fuel gas, resulting in lowering hydrogen composition and decreasing theoretical voltage. The methanation reaction is described as follows. 3H2 þ CO ¼ CH4 þ H2 O

(45.5)

The reasonable operation pressure range might be up to about 3 MPa based on these data, and it is possible to use gas turbine for the existing combined cycle power plant, which pressure range is less than about 2 MPa.

Life Extension The factors decreasing cell voltage during operation and determining MCFC life are electrolyte loss such as matrix pore coarsening and nickel short-circuiting, as described in > Fig. 45.7.

Electrolyte Loss Pores within the matrix are filled up with electrolytes. Excess electrolytes which cannot enter into the matrix are distributed to the anode and the cathode. The distribution ratio is determined by the balance of capillary forces between the anode and the cathode. High cell voltage is attained by adequate electrolyte distribution with proper amount within the electrodes. From its viewpoint, pore distributions determining capillary force and total

Molten Carbonate Fuel Cells

45

Matrix coarsening

Vaporization (Anode) (Matrix)

Creepage

(Cathode) (Current collector) Corrosion

Ni short-circuiting

Electrolyte loss

. Fig. 45.7 Life-limiting issues

electrolyte amount are important design factors which affect strongly on cell performance. Meanwhile, it is well known that the amount of electrolyte decreases with time by some reasons. Electrolyte loss changes the distribution to inadequate one and it leads voltage drop. Most of the loss is caused by the corrosion reaction with metallic components of the cell, and the corrosion products with high electric resistance increases internal resistance. The electrolyte loss is also caused by vaporization and creepage. Usually, corrosionresistant treatment is applied on the surface of the metallic components. In addition, electrolyte loss is controlled by reducing the number or the total surface area of the metallic components. Current technology is considered to be able to control the loss that meets the present target life.

Matrix Pore Coarsening Matrix pore coarsening is caused by dissolution and deposition of LiAlO2 that is ceramic material constituting the matrix during longtime operation. The pore coarsening decreases electrolyte holding force and electrolyte moves out to the electrodes or leaks outside. The electrolyte distribution changes within the electrode and finally voltage decays. One of solutions is the change of the phase of LiAlO2 from g to a.

Nickel Short-Circuiting ‘‘The nickel short-circuiting’’ is a phenomenon that forms the internal short circuits between the anode and the cathode by metal nickel particles in the matrix. > Figure 45.8 shows that NiO as cathode material dissolves as Ni2+ ion into the electrolyte by reacting

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Molten Carbonate Fuel Cells

H2O

H2

CO2 (Anode)

Ni 2−

2+

CO3

Ni

Ni Ni Ni Ni Ni Ni Ni Ni

(Cathode)

NiO CO2

. Fig. 45.8 Nickel short-circuiting phenomenon

with CO2 in the oxidant gas, and metallic nickel particles are precipitated when Ni2+ ions react with dissolved H2 from fuel gas. Those reactions are expressed as follows: Ni2þ þ H2 þ CO3 2 ¼ Ni þ H2 O þ CO2 NiO þ CO2 ¼ Ni

2þ

þ CO3

2

(45.6) (45.7)

The nickel short-circuiting time can be expressed by the next equation [6, 7]. ts ¼ APco2 a Lb

(45.8)

where A is a coefficient, PCO2 is a CO2 partial pressure at cathode, L is an electrolyte thickness, and a ffi1, and b ffi 2. As can be seen, this phenomenon occurs in a shorter time under higher CO2 partial pressure in oxidant gas, and the occurrence time of the short-circuiting can be delayed by using thicker matrix. However, thick matrix increases internal resistance and decreases cell voltage. There are several trade-offs for cell stack design. The setting of the electrolyte thickness is an example of a typical trade-off to influence the cell voltage, and it is one of the essential design points from the nickel short-circuiting viewpoint. In order to avoid the nickel shirt-circuiting, the changes of electrolyte composition, matrix material, and operation condition with lower CO2 partial pressure are attempted. Recently, it is proposed as one of the solutions to use Li/Na electrolyte instead of conventional Li/K electrolyte. As for the Li/Na electrolyte, the solubility of the nickel is about a half compared with Li/K system as shown in > Table 45.2, and it would be possible to delay the nickel short-circuiting behind. Moreover, this electrolyte can decrease internal resistance because the electric conductivity of the ion is higher as shown in > Fig. 45.5, and can improve the voltage of the cell. It is concurrently tried to decrease nickel solubility by a small amount of additive to the electrolyte or to control the precipitation of nickel particles by the improvement of the matrix structure.

Molten Carbonate Fuel Cells

45

. Table 45.2 Comparison of Li/Na and Li/K electrolyte Li/KCO3

Li/NaCO3

Composition

mol%

62:38

53:47

Melting point Basicity NiO solubility Surface tensiona

ºC pO2 mole frac.(106) N/m

488 6.9 41.9 0.22

495.8 6.62 22 0.24

Densitya Viscositya Vapor pressurea Ionic conductivitya

g/m3 Ns/m2 g/m3 1/(Wcm)

1.93 8.3  103 3.2  1010 1.4–1.6

1.97 8.1  103 3.5  1010 2.1–2.3

O2 solubility

Mol/(cm3atm)

3.3  107b

1.8  107

a

650 ºC Li/K = 50/50

b

System Configurations Basic Configuration The MCFC power generation system is composed of the fuel processing system, the air supply system, the MCFC, and the inverter, etc., so that fuel and air can be supplied to the stack in appropriate temperature conditions, same as the case of PAFC system. Because the MCFC can utilize various kinds of fuels, the fuel processing system is different from the kind of fuel. It will contain a steam reformer for natural gas, and a gasifier and a gas clean-up unit for coal, biomass, or wastes. In addition, the shift converter which was applied to reduce CO in fuel gas in the case of PEFC and PAFC is unnecessary. Because the operation temperature of the MCFC is about 600–650
C, the exhaust heat can be used for temperature control at the inlet gas of the stack and for reforming reaction at the reformer. In addition, it is possible to configure a hybrid power generation system including a gas expander and a steam turbine at MCFC downstream as a bottoming cycle. The details of the natural gas or coal-fueled MCFC power generation systems are described below. The natural gas–fueled pressurized external reforming system or ambient pressure internal reforming system has already realized about 47% efficiency. As for the future large-scale plants, simulation results show that the natural gas–fueled pressurized external reforming system with 1,000 MW capacity would be about 65%, the pressurized internal reforming system with 700 MW capacity would be about 69%, and the integrated coal gasification system (IGMCFC) with 600 MW capacity would be about 57% efficiency [8].

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Molten Carbonate Fuel Cells

Natural Gas–Fueled External Reforming System Configuration of the natural gas–fueled pressurized external reforming MCFC power generation system is shown in > Fig. 45.9 [9]. In this system, natural gas mixed with steam is supplied to the reformer, converted to H2 and CO, and used at MCFC. CO should be a certain lower level for low-temperature fuel cells. However, the MCFC has no catalyst which has poisoning problem like low-temperature fuel cells. Moreover, CO can be shifted to H2 by fast shift reaction under high-temperature condition. Even in the case that H2 is consumed for power generation, CO can shift to H2 very fast. Therefore, CO can be considered as an effective fuel in the MCFC. However, high-temperature condition also allows Boudouard reaction, which forms solid carbon from gaseous CO around fuel supply line. The Boudouard reaction is expressed as follows: 2COðgasÞ ¼ CðsolidÞ þ CO2 ðgasÞ

(45.9)

Thus, it is required that the fuel gas should be in a certain condition to avoid this reaction, and humidifying the fuel gas is one of the countermeasures. MCFC exhaust gas from the anode contains combustible components and they can be used as a heat source of an external reforming in the natural gas system. Actually, certain quantity of non-reacted fuel is necessary, and the quantity of H2 and CO that can be utilized for anode reaction (fuel utilization) is decided from the calorific value required for reforming reaction. Oxygen as one of the reaction species at the cathode is supplied from air compressor connected to the expander turbine at the same pressure to the fuel gas. Reaction specie, CO2, is recycled from the anode exhaust, which contains the produced CO2 at the anode. The amount of the produced CO2 is same to the required amount for the cathode reaction. The fuel exhaust from the MCFC contains not only CO2 but also un-reacted flammable species, such as H2, CO, and CH4. It is supplied to the burner of the reformer to supply

H2O, CO2 Natural Gas

CO,H2 Reformer

O2, N2

MCFC O2, CO2, N2

C

T

G

HRSG Air

. Fig. 45.9 Natural gas–fueled external reforming MCFC system

CO2, N2

Water

Molten Carbonate Fuel Cells

45

heat for reforming. The burner has another role to complete oxidizing the flammable species before supplying CO2 mixed gas to the cathode. The combustion gas from the reformer combustor is mixed to the air from a compressor, and it is supplied to the cathode. Heat is generated within the MCFC by the internal resistance or electrode reactions same as the PAFC. Therefore, it is necessary to control the MCFC temperature and to keep it at constant value. Because any liquid coolant such as water cannot be applied for cooling of high-temperature fuel cells, large quantity of the oxidant gas (cathode gas including O2 and CO2) is circulated through the cathode channel for cooling the MCFC. The inlet temperature of the circulated oxidant gas should be set around 600
C and the outlet temperature should be around 650
C for adequate temperature operation. Therefore, the cathode gas recycling is adopted. The oxidant gas supplied to the cathode is a mixture of the combustion gas from the reformer, a part of cathode exhaust gas and fresh air from outside. The generated heat in the stack is removed by the oxidant whose inlet and outlet temperatures are adjusted by controlling the flow rate of recycling gas and the fresh air from outside. Finally, high-temperature pressurized exhaust gas from the cathode is led to the turbine expander and this recovers power for air compressor. In addition, the surplus power can generate electricity using a power generator connected to the expander, and this also contributes to enhance the entire system efficiency. The necessity H2O (steam) for reforming reaction is supplied from the recovered water from the anode exhaust gas by condensing before supplying to the reformer.

Natural Gas–Fueled Internal Reforming System As mentioned above, the internal reforming can be applied to the MCFC because of hightemperature operation [9]. The internal reforming can produce reaction specie H2 from CH4 within a stack. Therefore, the system can eliminate an external reformer. Conventional external reforming reaction has a limitation of the CH4 conversion ratio by the equilibrium composition with given fuel composition, temperature, and pressure. In contrast, the internal reforming does not reach the equilibrium as long as electricity is generated; that is, H2 is consumed at the anode. The reforming reaction proceeds further and eventually CH4 conversion is approaching approximately to 100%. This means that almost no residual CH4 exists at the anode. As a result, the concentration of H2 and the system efficiency increase. In addition, the heat generated from the stack can be used for reforming reaction and the flow rate of the oxidant can be reduced so that the parasitic power for cathode recycling blower can be reduced. The operation temperature of the MCFC is 600–650
C, which is slightly lower than the typical reforming temperature around 700–800
C. Therefore, reforming catalyst must be placed inside the stack. On the other hand, there could be a problem regarding the catalyst performance decay caused by the electrolyte vapor, and therefore, pre-reforming plates are usually installed upstream and sandwiched between every several cells to avoid the problem. The internal reforming system is usually operated at ambient pressure condition for enhancing CH4 conversion rate in the stack, and air blower can be utilized instead of using the expander turbine.

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Molten Carbonate Fuel Cells

Integrated Coal Gasification MCFC Combined Cycle (IGMCFC) Figure 45.10 shows the configuration of coal-fired power plant [10]. The hightemperature fuel cells, as described above, can use a fuel containing CO. The gasified coal gas containing mainly CO can be supplied directly to the MCFC after being purified. The coal gas contains trace impurities which adversely affect the performance, and therefore gas purification equipment is required. The stack has no upper limit of fuel utilization because there is no need to use anode exhaust as a heat source for reforming like natural gas fueled system. Thus, the fuel utilization can be maximized to improve the efficiency as far as uniform fuel distribution to each cell is attained. Fuel exhaust from the stack contains CO2 and it is recycled to supply to the cathode same as the natural gas fueled system. Additional combustor is necessary instead of reformer burner to burn any flammable species contained in the anode exhaust with CO2. The cathode exhaust gas is then fed to the heat recovery steam generator (HRSG) after recovering mechanical power and generating additional electricity at the expander turbine generator. The generated steam is supplied to the steam turbine with other generated steam at the stack or gasifier for producing additional electricity.

>

Development Status of MCFC in the World Dawn of the Development It is said that the development of MCFC started from the experiment by Baur of Germany using melted carbonate as electrolyte in 1921 at about 1,000
C. The concept of the matrix where the electrolyte was impregnated was introduced in 1946 by Davtyan of the Soviet

Clean-up

Coal

CHO

Gasifier

Water H2O, CO2

G T CO, H2

MCFC

Cat. burner Air

Air/oxygen facility

1746

O2, CO2, N2 Steam turbine

C

G

G

T O2, N2 HRSG

Air

. Fig. 45.10 Configuration of integrated gasification MCFC combined cycle

CO2, N2

Water

Molten Carbonate Fuel Cells

45

Union, and the porous nickel electrode was adopted in 1958 by Netherlands Broers and others. The research was actively advanced for the combination of the electrolyte and the electrodes in the Netherlands and the USA. Meanwhile, the MgO matrix, and the Fe, Ni, Co, Ag, Zn electrode has been attempted and the current prototype was completed in around 1970 [11]. Above fundamental research results have been expanded in the USA since the late 1970s. The US ERDA (US Energy Research and Development Administration) started the national program in 1976 and the US DOE (Department of Energy) has taken over the program in 1978. Other countries such as Netherlands, Japan, Italy, etc. have started their developments since around 1980 as if responding to the activities in the USA.

USA The US DOE has promoted the development of MCFC in the USA. In the early 1970s, the final goal was set as a centralized power plants using coal. However, development focus has moved to the MW class small- or middle-sized distributed generators as a cogeneration plant since 1990s. The IGT (Institute of Gas Technology, presently GTI, Gas Technology Institute), UTC (United Technologies Co.), GE (General Electric Co.), etc. have developed and established basic technologies under the DOE’s program. Afterword the venture companies such as the ERC (Energy Research Co., presently FuelCell Energy) and the MCP (MC Power Co.) have taken over the developments and the governmental program for market introduction was continued focusing on the product development and performance improvement until 2003. Thereafter, getting a financial support from the government or the states, the systems as distributed generators are being introduced into the states which have great concern with the environmental issues in particular. The main player of the development and the introduction is FCE Co. (FuelCell Energy) now [2]. FCE has a longtime development history in MCFC of the ambient pressure internal reforming type that is called DFC in the company. A 2 MW internal reforming system was demonstrated in 1997. FCE currently produces a lot of 300 kW commercial cogeneration systems (sub MW system) with a Hot Module structure (horizontal stack) jointly developed with Germany MTU Onsite Energy Co. FCE now produces three different capacity models including two kinds of the MW system. Sub-MW system (DFC300, 47% net efficiency) has been installed about 70 units in total so far, mainly in the USA, Japan, and South Korea. MW class systems adopting FCE’s own configuration are 1.4 and 2.8 MW system (DFC1500, DFC3000, respectively, both 47% net efficiency) [12]. These MW class plants are initially built by the combination of the subMW units. But now for lowering the cost, the module consisting of four vertical stacks in a container (one module in DFC1500, two modules in DFC3000) becomes a mainstream [13]. According to the company’s report, the capacity of the base stack was initially about 250 kW (AC) around the year 2000, and it is increased to 300 kW in the year 2006. Now it is expected to be 350 kW shortly. The life of the stack was improved from 3 to 5 years, recently [14]. The plant’s specifications of FCE are shown in > Table 45.3 [2].

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Molten Carbonate Fuel Cells

. Table 45.3 Specification of the MCFC plants (FCE) Type

DFC300

DFC1500

DFC3000

Net output (kW)

300

1,400

2,800

2,338 (3,935)

4,677 (7,870)

Net efficiency (%, LHV) 47  2 Exhaust heat Temp. (ºC) 121 (49) utilization Heat output 506 (852) (MJ/h) Size (m) (L  W  H [chimney]) Total weight (t) Noise (dB(A), @3m)

8.5  6.1  4.6

17.0  12.2  9.2

23.8  12.5  6.4

35 72 (65)

104

163

Exhaust (mg/MWh)

NOx: 4,500, SOx: 45, PM10: 0.009

(): option

Europe The MCFC has been developed as the distributed cogeneration in Europe. In Germany, MTU Onsite Energy is developing the Hot Module design from the viewpoint of low cost BPOs [15, 16]. The 250 kW stack made by FCE in the USA is introduced to the MTU’s ambient pressure internal reforming 250 kW system. The Hot Module structure has a horizontal stack inside a cylindrical cathode gas-filled container. Cathode gas is circulated within the container for controlling stack temperature. The system has features such as less piping and compact. MTU Onsite Energy supplied the company’s own 250 kW system (HM300) within Europe, and is developing the larger HM400 system in recent years. Both systems can utilize biogas, digestive gas, methanol, as well as natural gas. In addition to these, the company’s 320 kW stack was supplied to Wa¨rtsila¨ Marine Inc. for the ship use demonstration project in Finland. Italy developed 100 kW class stack (pressurized: 0.35 MPa, external reforming, external manifold, cross-flow type, and 0.75 m2  150 cells) and Compact Unit (CU) plants with Spain in the MOLCARE program in 1999. The Compact Unit contains the hightemperature modules including the stack and the reformer in the same pressure vessel. Based on the results, Ansaldo Fuel Cells Co. (AFCo) has been leading the development of the 500 kW modules with the Twin Stack concept [17]. In this Twin Stack concept, two stacks are integrated with catalytic combustor and reformer at the bottom of each stack [18]. More than ten demonstrations were planned not only in Italy but also in Spain and Turkey, and about half were demonstrated. AFCo has developed a 200 kW stack until now.

Asia In Japan, the development for energy conservation has been promoted as a national project in the earlier phase in the world in late 1970s. In this project, the target was set

Molten Carbonate Fuel Cells

45

especially for electric power company use, aiming immediate application as natural gas–fueled plant as well as considering the future coal-fueled plant. The 1,000 kW pressurized external reforming system was operated in 1999. Fuel was LNG and operation pressure was 0.5 MPa. The efficiency target of 45% (HHV, gross) was attained [19]. Another 200 kW pressurized internal reforming system was demonstrated in parallel. These results were reflected in two 300 kW systems using fermentation digestion gas of the garbage and gasified wood biomass gas as part of the power supplies which constituted a microgrid at the world exposition at Aichi in EXPO 2005. The generation efficiency achieved 51% (gross) at the maximum. Meanwhile, the longtime continuous operation over 66,000 h by a single cell was demonstrated. Its decay rate was less than 10% per 40,000 h and met the present target. Also CO2 concentration from the flue gas from the conventional coal-fired thermal plant was demonstrated by supplying the flue gas to the cathode side of 50 kW MCFC stack [20]. KEPRI (Korea Electric Power Research Institute) plays a key role to develop the pressurized external reforming system in Korea [21]. Based on the fundamental researches in KIST (Korea Institute of Science and Technology), POSCO and RIST (Research Institute of Industrial Science & Technology) participate in the program. The 125 kW system developed with own technology was demonstrated in 2009. The internal reforming system is under development in parallel and its demonstration is planned in 2010. Apart from these, POSCO Power has been promoting the introduction of MCFC plants [22]. Introducing the technology from FCE in the USA, the company built a new factory for BOPs with 50 MW annual productions in Korea in 2008. Mounted stacks have been supplied from FCE so far; however, POSCO Power has a plan to build another factory for stack assembling with cell components being supplied from FCE.

Development Issues Cell Stack Issues Not only applicable to the MCFC, it is necessary for a newly developed technology to achieve higher performance, longer life, and lower cost for accelerating the commercialization of MCFC. In MCFC, it is necessary to exceed above items of the existing power generation technology. The basic cell and stack technology has been almost established to achieve the immediate objective except the cost. Among the remaining issues needed to be solved, a life extension issue is one of the most important ones. The nickel short-circuiting is the most important problem for the pressurized system aiming higher efficiency. Handling the impurities included in coal gasification gas should also be considered in the future. In addition, the stack design technology enabling lightening the weight of the stack, producing larger cells, and achieving uniform gas distribution for tall stack should be improved continuously.

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Molten Carbonate Fuel Cells

The nickel short-circuiting is caused by the dissolution reaction of cathode NiO into the electrolyte, which needs to be avoided. The comprehensive measures are required from the viewpoint of the cathode material, the electrolyte composition, and the operation condition, etc. The effects of impurities in the fuel gas is not the urgent issue right now, but it must be resolved when gasified fuels, such as biomass, waste, and eventually coal, will be used on the way to promoting the expansion of application fields. These gasified fuels contain the sulfur compound, the halogenated compound, and the nitrogenous substance, etc. These affect largely on the cell performance even though the concentration is ppm order. The effects are being clarified through every kind of actual cell test, and gas cleanup system that reduces impurity content to the acceptable level is under development. The maximum number of stacked cell is currently about 300, and it is expected to increase the number for efficient integration of the stack from the viewpoint of the entire plant. Thus, it is important to develop stacking technology and to select an appropriate number of stacked cells, because number of the cells in the stack is restricted by the gas distribution for each cell through the manifold. Reducing the weight of the stack will become more important issue from the viewpoint of the economy or transportation in the future. Additionally, the improvement of the output power density is also important.

System Issues It is thought that the development of the constitution apparatus was almost completed for the natural gas–fueled system. The plant operation method such as start/stop, load change, and emergency shutdown is considered to be almost established, because many natural gas units are shipped to the market from the US and German manufacturers and much experience is being accumulated. The establishment of the operating method for the hybrid system and the pressurizing system combined with the gas turbine for higher efficiency will become important in the future. For the future system using biomass, waste, or coal, it is required to develop the technologies on gasification, gas cleanup, effective heat exchange, system configuration including topping/bottoming cycle, operation of pressurized system including carbon deposition avoidance, etc.

Economy About the economy, stack cost reduction is the most important at present. It could be attained by, for example, reducing the number of parts, reducing the amount of the material use, lightening weight, and increasing power density. A great decrease in the stack cost by mass production is necessary. The cost reduction of the BOP equipments is also important. It is said that the BOP cost occupies large part especially in sub-MW small capacity system.

Molten Carbonate Fuel Cells

45

FCE is developing multi-MW systems for this reason. In addition, not only fixed cost reduction but also variable cost reduction is important. Improving the system efficiency and accumulating operation experience, it is expected that the operation and maintenance cost will be greatly reduced in the future. Fuel cell has shorter lifetime compared to the general power generation plants, so that the stack is expected to be replaced in the period corresponding to its lifetime. Replacing cost affects largely in the cost of electricity. Recently the tentative target of stack life is set around 30,000–50,000 h and it becomes achievable by technology developments except pressurized operation. However, there could be another increment of the cost to realize the target life. It is important to introduce the stepped performance targets based on the market introduction progress. In the initial market penetration phase, the plant price might be rather expensive but initial market would be established. The stack production can be expected to increase dramatically and large cost reduction can be attained. Once an initial market is formed, the introduction of a small system increases, reliability is confirmed, and the awareness level rises. It enters the cycle of the virtuous circle. Then it could be expected to lead to the application of a larger power plant.

Future Directions Expansion of Market Introduction The market introduction of the MCFC is pushed forward as a cogeneration system of the small or medium size mainly applying the internal reforming system developed in the USA or Germany now. However, it concentrates in the country and the state where the promotion plan of the subsidies and grant is well prepared. Therefore, the MCFC market can be understood to be never independent economically at present. As a future direction, fundamental developments such as high efficiency, long life, lower cost, etc. should be continued. Accumulating experience of more market introduction, it is required to reach the level of real competition to existing conventional technologies. As mentioned above, the development of the following directions should be pushed forward. ● Addition of load following and various operability function to the above-mentioned small power supply for load management ● Diversification of fuel that allows using waste and biomass, etc., for the communitybased small power supply ● Enhancement of the efficiency higher than the existing large-scale thermal power plants, intending centralized natural gas–fueled MCFC plant ● Demonstration of high-efficiency integrated coal gasification MCFC combined cycle (IGMCFC)

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Molten Carbonate Fuel Cells

Development of Power Generating Systems with Novel Function In addition to the expansion of the above-mentioned market introduction, the power generating system that has a new function to make the best use of a MCFC’s inherent features have been proposed.Some of those systems have been demonstrated. It is possible to expand the application field much more by achieving those. 1. DFC/T (an internal reforming hybrid system) FCE proposed a high efficient natural gas fueled hybrid system that operates the internal reforming MCFC at ambient pressure and locates the gas turbine upstream. > Figure 45.11 shows its configuration. The power generation efficiency of about 71% is calculated in 20 MW class [23]. In parallel to this, the company has applied DFC300 stack and micro gas turbine to the system. Maximum output of 320 kW, 58% power generation net efficiency was achieved and approximately 8,000 h of operation was demonstrated [24]. Based on current DFC3000, 3.4 MW scale has been engaged in system design [25], the first unit is planned to introduce a project underway in Connecticut. 2. DFC-ERG (a pipeline energy collection system) The DFC-ERG (Energy Recovery Generation) system is a highly effective hybrid system that applies the gas expander to the decompression process of the natural gas supplied by the gas pipeline in place of a conventional valve. It combines MCFC in addition, and uses the rejection heat of MCFC for the preheating for preventing the gas temperature being decreased at the decompression process [26]. FCE demonstrated the concept in the first 2.2 MW pilot plant set up in Toronto in 2009, and achieved average power generation efficiency 62.5% and availability factor (uptime rate) 93% during 1 year operation. In the latter half 6 months, the peak power generation efficiency was 70% and availability was 96% [2].

Steam (to S/T) Fuel

Fuel Processing

HR

MCFC

SG

Steam (to S/T)

Exhaust

Air

G . Fig. 45.11 Internal reforming hybrid system

TC

C

Molten Carbonate Fuel Cells

45

Stiochiometric CH4/O2 supply

Combination of MCFC and high temperature GT

Pre-reformer 1CH4

Anode IR-MCFC Cathode

5CO2+5H2O

T Burner

HRSG LPT

4CO2+2O2 Noble gas supply

2O2 4CO2

CO2 recovery

1CO2

condenser Minimum exhaust CW loss

2H2O

3H2O

. Fig. 45.12 Ultrahigh efficiency system with CO2 recovery

3. DFC-H2 (a trigeneration system) DFC-H2 system is also being developed by FCE [27]. Hydrogen aiming to be used for fuel cell vehicle can be generated as well as electricity and heat at the same time. This technology is to be built into hydrogen stations in California. The plan is underway to generate 300 kW of power and about 150 kg/day or more hydrogen, based on biogas generated in sewage treatment process. 4. CO2 recovery system CRIEPI (Central Research Institute of Electric Power Industry) proposes the CO2 recovery type hybrid system using oxygen in place of air, and showed the extremely high efficiency of 77% in 300 MW class [28]. > Figure 45.12 shows its flow diagram. Only natural gas and oxygen are supplied with stoichiometric ratio to the system, and the final products are only H2O (steam) and CO2. CO2 is easily recovered after condensing steam. In addition, O2 and CO2 with composition of 1:2 (noble gas) maximize the cathode potential and achieve the high cell voltage. Moreover, no mixture of N2 by not using air enables realizing minimum effluent gas flow and minimum exhaust heat quantity. It can also contribute to high efficiency.

References 1. U.S. Department of Energy (2004) Fuel Cell Handbook, 7th edn. U.S. Department of Energy, West Virginia

2. http://www.fuelcellenergy.com/ 3. Morita H, Mugikura Y, Izaki Y, Watanabe T, Abe T (1998) Model of cathode reaction resistance in

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5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

Molten Carbonate Fuel Cells

molten carbonate fuel cells. J Electrochem Soc 145:A1511–1517 Morita H, Komoda M, Mugikura Y, Izaki Y, Watanabe T, Masuda Y, Matsuyama T (2002) Performance analysis of molten carbonate fuel cell using Li/Na electrolyte. J Power Sources 112:509–518 Yoshikawa M, Mugikura Y, Watanabe T, Ohta T, Suzuki A (1999) The behavior of MCFCs using Li/K and Li/Na carbonates as the electrolyte at high pressure. J Electrochem Soc 146:2834–2840 Mugikura Y, Abe T, Yoshioka S, Urushibata H (1995) NiO dissolution in molten carbonate fuel cells: effect on performance and life. J Electrochem Soc 142:2971–2977 Yoshikawa M, Mugikura Y, Watanabe T, Kahara T, Mizukami T (2001) NiO cathode dissolution and Ni precipitation in Li/Na molten carbonate fuel cells. J Electrochem Soc 148:A1230–A1238 Watanabe T (2001) Development of molten carbonate fuel cells in Japan – application of Li/Na electrolyte. Fuel Cells 1:1–7 Krumpelt M, Ackerman J, Herceg J, Zwick S, Slack C, Lwin Y (1982) Gas systems. Fuel Cell Semin Abstr 127–133 Bonds T, Dawes M, Schnacke A, Spradlin L (1981) Fuel cell plant integrated systems evaluation. Electric Power Research Institute Final Report, EM-1670 Mamantov G, Braunstein J (eds) (1981) Advances in molten salts chemistry, vol 4. Plenum, New York, p 391 Leo T, Brdar D, Bentley C, Ludemann B, Farooque M, Oei P, Rauseo T (2007) Stationary DFC® power plants status. Fuel Cell Semin Abstr 50–53 Farooque M, Leo A, Pawlaczyk R, Rauseo A, Venkataraman R (2009) Direct fuel cell stack design evolution. Fuel Cell Semin Abst DEM331:140–143 Farooque M, Venkataraman R, Rauseo T, Carlson G, Berntsen G (2007) Direct fuel cell (DFC®)

15. 16. 17. 18.

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26. 27.

28.

improvements based on field experience. Fuel Cell Semin Abstr 44–47 http://www.mtu-online.com/?L=1 Rolf S (2006) Operation Experience with MTU’s Hot Module. Fuel Cell Semin Abstr 186 http://www.ansaldofuelcells.com/en/index.htm Marcenaro B (2008) Development and industrialisation of MCFC systems at ansaldo fuel cells. Fuel Cell Semin Abstr RDP33-1:145–149 Nakayama T (2000) Current status of the fuel cell R&D program at Nedo. Fuel Cell Semin Abstr 9–13 Toyota M, Dairaku M (2009) Development of CO2 capture system with MCFC. Fuel Cell Semin Abstr HRD33a-2:95–99 Kim S, Choi Y, Kuk S, Jun J, Lim H (2008) Status and recent progress of MCFC stack development in Korea. Fuel Cell Semin Abstr RDP33-3:154–157 http://poscofuelcell.com/english/ Ghezel-Ayagh H, Sanderson R, Leo A (1999) ultra high efficiency hybrid direct fuel cell/turbine power plant. Carbonate fuel cell technology V, PV99-20. The Electrochemical Society 297–305 Ghezel-Ayagh H, Walzak J, Junker S, Patel D, Michelson F, Adriani A (2007) DFC/T® power plant: from sub-megawatt demonstration to multi-megawatt design. Fuel Cell Semin Abstr 54–57 Ghezel-Ayagh H, Walzak J, Patel D, Jolly S, Lukas M, Michelson F, Adriani A (2008) Ultra high efficiency direct fuelcell systems for premium power generation. Fuel Cell Semin Abstr RDP33-2:150–153 http://www.fuelcellenergy.com/dfc-erg.php Patell P, Lipp L, Jahnke F, Holcomb F, Heydorn E (2009) Co-production of renewable hydrogen and electricity: technology development and demonstration. Fuel Cell Semin Abstr COM43-1:373–376 Koda E et al (2006) MCFC-GT Hybrid System Aiming At 70% Thermal Efficiency. ASME Turbo Expo 2006

46 Photocatalytic Water Splitting and Carbon Dioxide Reduction Jacob D. Graham . Nathan I. Hammer Department of Chemistry and Biochemistry, University of Mississippi, Oxford, MS, USA Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1756 Photocatalytic Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1759 Photocatalytic Water Splitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1762 Photocatalytic CO2 Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1772 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1774

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_46, # Springer Science+Business Media, LLC 2012

1756

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Photocatalytic Water Splitting and Carbon Dioxide Reduction

Abstract: Photocatalytic water splitting, which involves the simultaneous reduction and oxidation of water producing hydrogen and oxygen gas, provides a means of harnessing the sun’s power to generate an energy source in a clean and renewable fashion. Photocatalytic reduction of carbon dioxide to form hydrocarbons such as methane not only promises reduced emission of an important greenhouse but also a new source of fuel. Concerns over the effects of global climate change and the eventual demise of fossil fuels makes the search for clean alternative energy sources a top priority. This chapter details the progress in these two increasingly important areas: hydrogen production by photocatalytic water splitting and photocatalytic carbon dioxide reduction.

Introduction It is an understatement to say that the consumption of energy is a critical requirement for modern human civilization. The rapid industrialization and technological progress that permeates every facet of life would not be possible without the cheap and abundant energy sources enjoyed by mankind today. Annual worldwide energy consumption reached 497 exajoules in 2006, and with current conditions, energy demands are expected to grow 44% by the year 2030 [1]. Currently, fossil fuels provide the vast majority of this energy as they are easily obtainable, abundant, and energetically dense. In order to keep up with this pace, society’s reliance on fossil fuels will grow dramatically in the coming years if alternative sources of energy are not developed. It is now well accepted in society that human dependence on fossil fuels presents a number of problems. Competition for fossil fuel–based sources of energy will have destabilizing geopolitical effects as the supply of these valuable resources declines. However, the most publicized consequences of the continued use of fossil fuels come in the form of environmental pollution. Sulfur dioxide, nitrogen oxides, cadmium, and mercury are all released as a result of burning fossil fuels, with coal being the largest contributor. Under the right conditions, these pollutants produce easily visible results in the form of acid rain and smog, while other combustion products, such as carbon dioxide, may not appear to have an immediately visible effect. Although CO2 can generally be considered harmless (at least physiologically to plants and animals – including humans), the quantities released annually into the atmosphere (about 6 billion tons) could possibly result in climate-altering effects. Concerns over ‘‘global warming,’’ and more recently, ‘‘global climate change’’ have captivated the attention of world governments and are currently transforming society in areas ranging from concern over automobile emissions to managing carbon footprints [2–10]. Certain atmospheric gases such as CO2 are thought to trap long wavelength, thermal radiation in the Earth’s atmosphere through the ‘‘Greenhouse Effect’’ and CO2 itself is considered a greenhouse gas. Other important greenhouse gases include water, methane (CH4), nitrous oxide (N2O), and ozone (O3). The historical development of the Greenhouse Effect is rather quite interesting and dates back to the nineteenth century and scientists including Svante Arrhenius [11]. The basic mechanism behind the Greenhouse

Photocatalytic Water Splitting and Carbon Dioxide Reduction

46

. Fig. 46.1 Various wavelengths of solar radiation are absorbed by the Earth’s surface and transformed into heat, which is eventually re-radiated back into space. Greenhouse gases, such as CO2, absorb some of this infrared radiation and re-emit it in all directions, including back toward the Earth’s surface

Effect is depicted in > Fig. 46.1. Radiation from the sun is absorbed by the Earth and is converted to heat. This heat is radiated back into space but some wavelengths of radiation corresponding to the vibrational normal modes of greenhouse gases are absorbed by these gases. This energy is then reemitted in all directions, including back toward the Earth, rather than into space. The overall effect is a ‘‘trapping’’ of heat energy in the atmosphere. Ice core samples possess trapped gaseous bubbles that reveal atmospheric CO2 concentrations dating back as far as 800,000 years [3, 4]. They have shown a correlation between higher CO2 concentration and higher average global temperatures. However, this correlation is delayed from the effect of the oceans and other buffer systems [2]. With current conditions, an eventual average global temperature increase of several degrees Celsius is possible. Along with sea level rise, acidification of the oceans, and glacial melt, the rise in average temperature could destabilize much of the Earth’s current ecology with altered fauna migration and flowering times. These circumstances also would likely diminish food supplies as environmental conditions change. Although the dangers of global climate change have been in public thought for decades, solutions remain elusive for technical and economic reasons [12]. The possible solutions to global warming are numerous and varied, but most can be divided into two avenues of approach: removing sources of CO2 or capturing released CO2. An example of a geoengineering form of the latter would be injecting CO2 underground. Groundwater is the major sink for CO2 injected underground, and the possibility of long-term containment is difficult to predict [13]. While removing CO2 from the atmosphere would help in reversing the trend of global warming, replacing current fossil fuel–dependant energy

1757

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Photocatalytic Water Splitting and Carbon Dioxide Reduction

sources with non-CO2-emitting energy sources is a more long-term solution. Of all the 6 billion tons of CO2 released annually, 80% is due to the burning of fossil fuels. Nuclear, geothermal, wind, hydroelectric, and solar methods of energy production emit no CO2 and are much cleaner sources of energy than fossil fuels. A geothermal, wind, or hydroelectric energy supply is renewable and clean but has limited implementation in specific areas. Nuclear energy is a very real alternative to fossil fuels but is not renewable and fissile materials will eventually be depleted. Solar derived energy has the most potential as a permanent replacement for fossil fuels and as a means by which to transform one form of energy into another and photovoltaics have emerged as perhaps the most promising avenue for that capture and conversion. Although the development of solar energy as an alternative energy source seems like the perfect solution to society’s energy needs, long-term storage and realistic energy density are obstacles. Many have touted hydrogen gas as an attractive alternative to fossil fuels as an energy carrier [14–17]. Hydrogen’s reaction with oxygen yields only water and heat and this heat can easily be used as a source in automobiles or generators [15]. Hydrogen storage in tanks involves high pressure or cryogenic storage [18, 19]. Other methods involve hydrogen adsorption onto certain specialized surfaces with metal hydrides having the highest hydrogen storage density [19]. Currently, most hydrogen production is dominated by steam reformation of natural gas [15]. An efficient, cheap, and renewable method of hydrogen production would allow hydrogen gas to become the primary energy carrier in automobiles and in stationary applications. Coupling the storage and transportation potential of hydrogen gas with solar energy–based production would allow for the creation of an inexpensive and highly useful source of energy. It is often noted in reviews and by advocates of solar energy that the sun provides many thousands of times the annual energy consumption of the Earth, and harnessing only a fraction of this energy would be adequate. Shown in > Fig. 46.2 is a solar emission spectrum obtained on the campus of the University of Mississippi. This emission mimics a blackbody curve and it is readily apparent that most of the light from the Earth’s yellow sun that reaches the Earth’s surface is in the visible region of the electromagnetic spectrum. The number of photons reaching the Earth’s surface drops dramatically as ultraviolet (UV) wavelengths are approached. Dips in the spectrum correspond to absorption by different atmospheric gases such as water vapor. Various methods exist for harvesting solar energy, but the use of photocatalysts provides perhaps the most viable option with their reversible oxidation-reduction capabilities. Photocatalytic water splitting, which involves the simultaneous reduction and oxidation of water producing H2 and O2, provides a means of harnessing the sun’s power to generate an energy source in a clean and renewable fashion. Besides the production of an alternative to fossil fuels, photocatalytic processes can turn the tide against global climate change in a more direct way. Photocatalytic materials can reduce carbon dioxide to form hydrocarbons such as methane and ethanol, essentially taking exhaust and turning it back into fuel. This chapter details the progress in these two increasingly important areas: hydrogen production by photocatalytic water splitting and photocatalytic carbon dioxide reduction.

Photocatalytic Water Splitting and Carbon Dioxide Reduction

46

Energy (eV) 2.0

2.5

1.75

Relative Intensity

3.0

400

500

600

700

Wavelength (nm)

. Fig. 46.2 Solar emission spectrum obtained at the University of Mississippi

Photocatalytic Processes A photocatalytic process relies on a semiconductor’s adsorption of light to create stored energy and the use of that energy to do some form of useful work – in this case, serving as a catalyst for the production of a desired reaction product. In semiconductors, groups of closely spaced electronic energy levels form bands, namely, the conduction and valence bands, as shown schematically below in > Fig. 46.3. When incident light has energy that is greater than that of the band gap of the semiconductor material, electrons in the valence band of the material are excited to the conduction band. At the same time, holes are created in the valence band. Photocatalytic reactions then occur on the surface of the seminconductor, where these newly generated electrons and holes are located. Many important considerations go into the engineering of a useful photocatalyst. A few of these include matching the band gap to the radiation wavelength (or frequency/energy) to be employed, the suppression of the recombination of electron–hole pairs, and appropriate sensitization by other materials. The conduction band is higher in energy and less populated with electrons than the valence band and the energy separation of these two bands is commonly referred to as the band gap. This band gap limits the minimum energy (or wavelength) of incident photons able to be absorbed. Photons that are absorbed promote electrons (e
) across the band gap from the filled valence band into the empty conduction band creating a hole (h+) in the valence band. Thermal relaxation of the electron–hole pair to the band edge can occur or recombination of the electron–hole pair can result, although this takes longer to occur (on a picosecond timescale). While the electron–hole pair exists, the photocatalyst can

1759

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Photocatalytic Water Splitting and Carbon Dioxide Reduction

A− Reduction A

-

e- e eConduction Band Photons Band Gap

Valence Band h+ h+ h+

B Oxidation B+

. Fig. 46.3 In a semiconductor, electrons (e
) are promoted from the valence band to the conduction band when photons of light are absorbed. Electron holes (h+) are created with the excitation of electrons. The creation of this electron–hole pair allows for the reduction and oxidation of other species

perform useful reduction and oxidation reactions by accepting electrons into its valence band or donating the promoted electrons in its conduction band. When an electron moves to the surface of the photocatalyst and has the correct potential, anion radicals (A
in + > Fig. 46.3) are produced, while cation radicals (B in > Fig. 46.3) are produced from electron holes at the surface. As mentioned above, there are a number of design considerations to keep in mind in order to create a useful photocatalytic material. Suppression of the recombination of electron–hole pairs in a photocatalyst is essential to improving its efficiency [20–24]. Trapping of a promoted electron, hole, or both impedes the detrimental recombination process. An example of electron–hole trapping would be using a sacrificial reagent to donate electrons to a photocatalyst after excitation. Electrons donated into the valence band provide a longer lifetime for the excited electron in the conduction band. Oxygen and several inorganic oxidizing species have been shown to serve as good recombination inhibitors [22]. Sensitization of semiconductors by dye molecules is another important design element employed to both increase the excitation rate and extend the excitation wavelength window [22, 25]. Photoelectrons are provided by a photosensitive dye that is in contact with the semiconductor material and charge separation occurs at the surfaces between the dye, semiconductor, and an electrolyte. The semiconductor serves primarily as the charge carrier, rather than the source of electrons and holes. Physically adsorbing the molecules to be reduced or oxidized (A and B, respectively, in > Fig. 46.3) by the photocatalyst is another important design element that is essential to successful catalytic activity [22, 26]. This is because of the fact that the recombination of

46

Photocatalytic Water Splitting and Carbon Dioxide Reduction

photogenerated electrons and holes is very fast. There is no time for diffusion of the charge acceptor to the site of oxidation or reduction. Electron transfer is kinetically competitive only when the donor or acceptor molecule is adsorbed before the reaction of interest is to take place [22]. Doping of other atoms and molecules into semiconductor photocatalysts to modify the electronic structure is also an important area of research in recent years that will be discussed in the later sections of this chapter [22, 27–45]. The number of photocatalysts developed for water splitting and carbon dioxide reduction increases more each year and many of these materials are cataloged below in the following two sections of this chapter. Important considerations already mentioned above in creating an effective photocatalyst include suppressing electron–hole recombination and achieving effective charge separation. Another important consideration is the selection of the best semiconductor for the desired photocatalytic reaction. The choice of semiconductor material and the other species that are incorporated into it such as sensitizers and dopants are critical in achieving the optimal overlap of band gap with the wavelengths of light. Shown in > Fig. 46.4 are the band structures of a few representative semiconductor photocatalysts relative to the Normal Hydrogen Electrode (NHE) at pH = 0 [45]. In the NHE, hydrogen’s standard electrode potential is defined as zero (2Hþ þ 2e
! H2 ; E ¼ 0:0 V) and the potential of all other electrode reactions are defined as relative to hydrogen. To effectively use the abundant visible solar radiation shown in > Fig. 46.2, the band gap (the height of the bar in > Fig. 46.4) needs to be less than about 3 eV. This energy corresponds to photons of about 400 nm, right at the visible edge of the solar emission spectrum. However, to be effective in water splitting or carbon

−2.0

CdSe

H+/H2 WO3 Fe2O3 2.3eV

MoS2 1.75eV

1.1eV

3.0eV

Si 2.25eV

1.7eV

3.0eV

3.2eV

3.4eV

GaP

2.8eV

2.0

5.0eV

V vs. NHE (pH0)

1.0

TiO2

2.4eV

CdS

KTaO3 SrTiO3 0

SiC

ZnS

ZrO2

3.6eV

−1.0

O2/H2O

3.0

4.0

. Fig. 46.4 Band structures of common semiconductor photocatalysts relative to NHE. Note that in this representation, the valence band is at the bottom and the conduction band is on the top. (Reproduced with permission from [45])

1761

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Photocatalytic Water Splitting and Carbon Dioxide Reduction

dioxide reduction, the location of the top and bottom of the band gap is also very important. Photocatalytic materials have promising and practical uses in many areas as wide ranging as organic synthesis [22, 45] and the degradation of hazardous waste [46, 47]. Here, the interest is in the application of semiconductor photocatalysts to the splitting water to create a new source of hydrogen gas and the reduction of carbon dioxide to useful forms. In the following two sections, the application of photocatalytic semiconductor materials for these purposes is discussed and many examples of recently developed materials are listed.

Photocatalytic Water Splitting Water splitting is the simultaneous reduction and oxidation of water to produce H2 and O2. In the early 1970s, the Honda–Fujishima effect was reported, in which water splitting was achieved with a TiO2 electrode under ultraviolet (UV) irradiation [48, 49]. In their configuration, which is illustrated in > Fig. 46.5, a platinum electrode and a TiO2 electrode are connected through an external load and immersed in water. When irradiated with UV light, current flows from the platinum electrode to the TiO2 electrode. Oxidation proceeds at the TiO2 electrode, while reduction proceeds at the platinum electrode. These processes are given by: 1 2hþ þ H2 O ! O2 þ 2Hþ 2 Reduction : 2e
þ 2Hþ ! H2

Oxidation :

Pt

(46.1) (46.2)

TiO2

h+ e− e− H2 e− e−

h+

H+ + O2

e−

h+ H+

H2O

e−

UV

h+

Honda-Fujishima effect

. Fig. 46.5 Cartoon schematic of the photocatalytic water splitting setup employed by Honda and Fujishima [48, 49]

Photocatalytic Water Splitting and Carbon Dioxide Reduction

46

where h+ are electron holes. The overall chemical equation for this process is thus: 1 H2 O ! O2 þ H2 2

(46.3)

Not all semiconductor materials are appropriate for the photocatalytic splitting of water. As mentioned above, it is important to choose a semiconductor material that exhibits a band gap appropriate for the desired photochemical reaction. In the case of water, the top level of the valence band must be more positive than the oxidationreduction potential of > Eq. 46.1 – the oxidation of water to form oxygen gas and two protons. This reaction occurs at 1.23 V relative to NHE. The lower level of the conduction band must be more negative than the oxidation-reduction potential of > Eq. 46.2, the reduction of the hydrogen cation, to create the desired product hydrogen gas. This, as all freshman chemistry students can attest to is 0 V relative to NHE. Honda and Fujishima’s choice in their original paper was TiO2. As evident from > Fig. 46.4, the band gap for TiO2 is approximately 3.2 eV (different sources report 3–3.5 eV, depending if the TiO2 is in the rutile or anatase form), requiring photons with wavelengths less than about 400 nm. This energy requirement is right on the edge of usable visible light and therefore either violet or ultraviolet photons are required to mobilize electron–hole pairs in TiO2. This is unfortunate since most photons hitting the Earth are longer in wavelength as illustrated from > Fig. 46.2. For this reason, there have been many attempts to improve on the efficiency of the photocatalytic water splitting process. Since Honda and Fujishima’s initial discovery, a number of architectures for achieving efficient photocatalytic water splitting using both ultraviolet and visible light have been developed. However, the overall quantum efficiencies of these architectures have been less than stellar (less than 10% for catalyzing > Eq. 46.3) [43] and wide-scale utilization has still not been achieved. For solar-based water splitting to be practical, several goals must be met. One is that the photocatalyst must efficiently adsorb solar radiation. TiO2, for example, requires UV light, while most of the sun’s photons have energy in the visible region of the electromagnetic spectrum (or longer wavelengths) as shown in > Fig. 46.2. The band gap of the photocatalyst must also be tuned so that both the reduction and oxidation processes necessary for water splitting are energetically possible. This requirement is indicated in > Fig. 46.4 with dotted lines intersecting the various photocatalyst materials for these two processes. Another consideration is that these reduction and oxidation reactions be spatially separated to prevent recombination of the freshly produced H2 and O2. This last requirement needs clever engineering of the photocatalytic material and is one reason for the large number of publications in this area each year. Excellent reviews summarize the extensive literature that has been amassed over the past few decades on the subject of photocatalytic water splitting. These reviews detail the various photocatalytic materials employed and the clever architectures that have been engineered to improve the efficiency of this process. > Table 46.1 catalogs a number of the reports described in detail in these literature reviews [43, 45, 50, 51]. The band gap of the photocatalyst material and the light source employed to mimic solar radiation in most cases are listed. Also included in > Table 46.1 are the H2 and O2 activities reported from

1763

1764

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Photocatalytic Water Splitting and Carbon Dioxide Reduction

. Table 46.1 Materials for photocatalytic water splitting Photocatalyst

Band gap (eV) Cocatalyst

(AEP)6In10S18,

Light source

H2 activity (mmol/h)

300 W Xe

20 per 0.25 g

O2 activity (mmol/h)

(AgBi)0.5MoO4

3

Pt

0

10.7

(AgBi)0.5WO4

3.5

Pt

0.1

5.8

AgLi1/3Sn2/3O2

2.7

Pt for H2

53

AgLi1/3Ti2/3O2

2.7

Pt for H2

24

AgNbO3

2.86

Pt for H2

AgTaO3

3.4

NiOx

400–450 W Hg

8.2

37

21

10

22

11

Ag3VO4

2

Pt for H2

300 W Xe

B/Ti Oxide

3.2

Pt

400–450 W Hg

NiO, Pt

Hg/Xe

BaBi4Ti4O15

3.1

Pt

BaCeO3

3.2

RuO2

BaTaO2N

2

Pt for H2

BaTa2O6

4.1

NiO

400–450 W Hg

629

303

RuO2

200 W Hg–Xe

33

16

NiOx

400–450 W Hg

2,366

1139

NiO

400–450 W Hg

2,080

910

Pt for H2

300 W Xe 41.8 per g

20.5 per g

Ba2In2O5

BaTi4O9 Ba5Nb2O15

3.85

Ba5Ta4O15 BiVO4

2.4

400–450 W Hg

400 W Hg

Bi2MNbO7 (M = Al, Ga, In), M2BiNbO7 (M = Ga, In)

400 W Hg 2.7

Bi2Mo2O9

3.1

Bi2Mo3O12

2.88

8.2

3.7

59

26

15

Bi2LaTaO7

Bi2MoO6

17

421

Pt for H2

55 1.8

Pt for H2

Bi2S3

8 500 W Xe

0.011 mL/h/ 0.001 g

Bi2WO6

2.8

Pt for H2

450 W Hg

1.6 per g

3

Bi2W2O9

3

Pt

450 W Hg

18

281

33

31

0.6

3

Bi2YTaO7

400 W Hg

Bi3TiNbO9

3.1

Bi4Ti3O12

3.1

BiCu2VO6

2.1

Pt for H2

BiZn2VO6

2.4

Pt for H2

Ca0.25La0.75TiO2.25N0.75

2

Pt for H2,IrO2 for O3

CaIn2O4

Pt

450 W Hg

2.3 6 5.5

230

RuO2

400 W Xe or 200 W Hg/Xe

21

10

200 W Hg/Xe

1.5

0.2

1.5

46

CaSb2O6

3.6

RuO2

CaNbO2N

1.9

Pt for H2

Photocatalytic Water Splitting and Carbon Dioxide Reduction

46

. Table 46.1 (Continued) Photocatalyst

Band gap (eV) Cocatalyst

Light source

H2 activity (mmol/h)

O2 activity (mmol/h)

CaTa2O6

4

400–450 W Hg

72

32

400–450 W Hg

30

CaTiO3:Rh

NiOx Pt for H2

CaTO3

3.5

NiOx

CaTaO2N

2.5

Pt for H2

Ca2Nb2O7

4.3

NiOx

101

400 W Hg

1.7 mmol/h/ 0.5 g

0.8 mmol/ h/0.5 g

Pt

300 W Xe

4.21 per 0.5 g

0.38 per 0.5 g

200 W Hg/Xe

3

1 83

Ca2Sb2O7

3.9

RuO2

Ca2Ta2O7

4.4

NiO

400–450 W Hg

170

CdS

Pt

150 W Hg

1–10 per 5 mg

CdS

Pt/RuO2

450 W Xe

2.8 mL/44 h/ 2.75 mg

CdS

Variable

Variable

CdS–ZnS

17

15 400–450 W Hg

Ca2Nb4O11 Ca2NiWO6

8.5

2.35

300 W Hg

CeO2

1.4 mL/44 h/2.75 mg

250

500 W Xe

2.5 per 0.8 g

CeO2:Sr

RuO2

400–450 W Hg

110

55

CeTaO4

NiO

400 W Hg

Not significant

Not significant

400 W Hg

Trace

CoTa2O6 Cr:PbMoO4

2.26

Cr/Ta:SrTiO3

Pt for H2

300 W Xe

Pt

300 W Xe

0.21

400 W Hg

Trace

CrTaO4

120 per 0.5 g 0.11

Cs2La2Ti3O10

3.4–3.5

NiOx

400–450 W Hg

700

340

Cs2Nb4O11

3.7

NiOx

400–450 W Hg

1,700

800

Cs2Ti2O5

4.4

None

500

Cs2Ti5O11

3.75

None

90

Cs2Ti6O13

3.7

None

38

CsLa2Ti2NbO10

3.4–3.5

NiOx

400–450 W Hg

115

400 W Xe

0.3

CuIn5S8

400 W Xe

1.8

Cu2O

300 W Xe at >460 nm

1.7 per 0.5 g

400 W Hg

Trace

450 W Hg

800

400

30

30

CuInS2

Ca2Nb3O10/K+

Pt

FeTaO4 (Ga0.88Zn0.12)(N0.88O0.12)

2.6

Rh2
xCrxO3

Ga1.14In0.86O3

3.7

Pt

50

0.9 per 0.5 g

550

1765

1766

46

Photocatalytic Water Splitting and Carbon Dioxide Reduction

. Table 46.1 (Continued) H2 activity (mmol/h)

O2 activity (mmol/h)

46

23

Photocatalyst

Band gap (eV) Cocatalyst

Ga2O3

4.6

NiO

Ga2O3:Zn

4.6

Ni

4,100

2,200

GaN

3.4

Rh2
xCrxO3

450 W Hg

19

9.5

GaN:Mg

3.4

Light source

RuO2

450 W Hg

730

290

GaN:ZnO

RuO2

450 W Hg and 300 W Xe

1 mmol/h/ 0.3 g

0.29 mmol/h/ 0.3 g

GaN:ZnO

Cr/Rh oxide

450 W Hg and 300 W Xe 400

198

1,400

700

Gd2Ti2O7

3.5

Gd3TaO7 Ge3N4

3.6

NiOx

400–450 W Hg

NiO

400 W Hg

RuO2

450 W Hg

H+–Cs2Ti2O5

None

852

H+–CsCa2Nb3O10

Pt

8,300

10

H+CsLaNb2O7

Pt

2,200

3

H+–KCa2NaNb4O13

Pt

18,000

39

H+–KCa2Nb3O10

Pt

19,000

8

H –KLaNb2O7

Pt

3,800

46

H+–KSr2Nb3O10

Pt

4300

30

H+–RbCa2Nb3O10

Pt

17,000

16

H+–RbLaNb2O7

Pt

2,600

2 110

+

H1.8Sr0.81Bi0.19Ta2O7

3.88

None

400–450 W Hg

250

Pt

500 W Hg–Xe

0.4

4

NiOx

400–450 W Hg

940

H2Ti4O9

100 W Hg

560

H4Nb6O17

100 W Hg

220

H2K2Nb6O17 H2La2/3Ta2O7

459

HCa2Nb3O10

Pt

HCa2Nb3O10

Pt

750 W Hg

78 per 0.1 g

None

Pt for H2

300 W Xe

1.1

1.3

In2O3/Cr:In2O3

NiO, Pt

Hg/Xe

InP

Pt

250 W Hg

2–5 per 30 mg

K0.5La0.25Bi0.25Ca0.75 Pb0.75Nb3O10

Pt

450 W Xe

Trace amounts

NiOx

400–450 W Hg

170

KCa2Nb3O10

Pt

450 W Hg

100 per g

None

KCa2Nb3O10

RuOx

450 W Hg

96 per 0.3 g

47 per 0.3 g

NiOx

400–450 W Hg

230

116

Pt

500 W Hg/Xe

Fig. 46.4. > Equations 46.4– 46.12 detail the important reactions that lead to the various observed organic products in this and later studies: 1 Initial Oxidation : 2hþ þ H2 O ! O2 þ 2Hþ (46.4) 2 Initial Reduction :

e
þ Hþ ! H


Initial Reduction : e þ CO2 ! Subsequent Reactions : 

CO
2

þ  CO
2 þ 8 H þ h ! CH4 þ 2H2 O

(46.5) (46.6) (46.7)

þ  CO
2 þ 6 H þ h ! CH3 OH þ H2 O

(46.8)

þ  CO
2 þ 2 H þ h ! CO þ H2 O

(46.9)



þ  CO
2 þ 2 H þ h ! HCOOH

(46.10)

þ  CO
2 þ 4 H þ h ! HCHO þ H2 O

(46.11)

þ  CO
2 þ 12 H þ 2h ! C2 H5 OH þ 3H2 O

(46.12)

  





Shown in > Fig. 46.6 is a photograph of a setup employed at the University of Mississippi for the photocatalytic reduction of carbon dioxide. A 450 W Xe arc lamp is employed as a substitute for solar radiation. The light is directed using a high reflection focusing mirror into a flask containing the reaction solution. This solution contains the photocatalyst (such as TiO2), gaseous CO2, water, and other reductants. After irradiation for an extended period of time (6–10 h) the resulting hydrocarbon products can be determined using quantitative and qualitative analytical methods. Compared to water splitting, photocatalytic carbon dioxide reduction is much less developed in the literature. Since Inoue’s first report, a number of new photocatalytic materials have been developed in attempts to improve upon both the conversion efficiency of carbon dioxide to hydrocarbons and the variety of hydrocarbon products possible. > Table 46.2 lists a number of these studies [42, 53]. As in the case of photocatalytic water splitting, TiO2-based materials dominate the carbon dioxide reduction literature. This includes pure TiO2 with varying choice of reductants or TiO2 doped with other species such as copper (Cu) that aid in red-shifting the absorption profile more into the visible region of the electromagnetic spectrum. The reasons for the dominance of TiO2 in both water splitting and carbon dioxide reduction include TiO2’s good photoactivity, inertness, resistance to corrosion, and low cost [53].

1773

1774

46

Photocatalytic Water Splitting and Carbon Dioxide Reduction

Xe Lamp

Photocatalytic Solution

Mirror

Lamp Power Supply

Sonicator

. Fig. 46.6 Photograph of a setup employed at the University of Mississippi for the photocatalytic reduction of carbon dioxide

Newer materials based on materials such as WO3 offer alternatives to TiO2, but to date, titanium dioxide remains the most successful and widely employed material. For carbon dioxide reduction, using water as a reductant is a cheap and effective option that would be ideal for widespread adoption of this technology. However, the solubility of carbon dioxide in water is low, and the reduction of CO2 in water has to compete with the formation of hydrogen gas (H2) and hydrogen peroxide (H2O2). For these reasons, other reductants and mixtures of various reductants in different conditions have been investigated. In particular, the use of basic solution offers advantages over pure water with hydroxide ions acting as hole scavengers and extending the recombination time of the electron–hole pairs [53, 75].

Future Directions Photocatalytic water splitting and photocatalytic carbon dioxide reduction each offer the promise of cheap and plentiful sources of energy for society’s future. In addition, the transformation of carbon dioxide from a harmful waste product to usable energy source is a win/win proposition. However, the development of efficient photocatalytic materials that make either of these processes viable on large scales has not been realized. With such a clear and potentially substantial payoff, many synthetic chemists have been attracted to this problem. In this very active field, advances are constant as the search for an ideal photocatalyst continues.

Photocatalytic Water Splitting and Carbon Dioxide Reduction

46

. Table 46.2 Materials for photocatalytic carbon dioxide reduction Photocatalyst

Band gap (eV) Reductants

TiO2

3.2

0.96 kW Xe HCOOH Methanol, ethanol, 2propanol, and nitric, hydrochloric, and phosphoric acids

[54]

TiO2

3.0–3.5

Water

75 W Hg

CH4, CH3OH, CO

[55]

TiO2

3.2

Water

75 W Hg

CH4, CH3OH, CO

[56]

TiO2

3.0

Water in NaOH solution

4.5 kW Xe

HCOOH, CH3OH, CH3CH2OH, CH4, C2H6, C2H4

[57]

TiO2

3.0

2-propanol

4.2 kW Xe

CH4, HCOOH [24]

TiO2

3.2

Water

Hg

CH4

TiO2

3.2

Water

Hg

CH4, H2, CO [59]

TiO2

3.2

Water

Hg

CH4, CHOOH, CH3CH2OH

TiO2 in liquid CO2

3.0

Water

990 W Xe

HCOOH

[61]

Cu–TiO2

3.2

Water

450 W Xe

CH4, C2H4

[62]

Cu–TiO2

3.2

Water

Hg

CH3OH

[63]

TiO2/Cu–TiO2

3.3

NaOH solution

Hg

CH3OH

[64]

TiO2/zeolite

3.2

Water

75 W Hg

CH4

[65]

TiO2/zeolite, TiO2/ molecular sieves

3.2

Water vapor

Hg

CH3OH

[66]

TiO2 nanocrystals in SiO2 3.9

2-propanol

500 W Hg

CO, HCOO
[67]

TiO2–SiO2

3.6

Acetyl acetone

Solar 6.35 mW/cm2

CH4

[68]

TiO2–SiO2 with Cu and Fe 3.6

Acetyl acetone

Solar 2.05 mW/cm2

CH4, C2H4

[68]

TiO2 nanocrystals in SiO2 3.9

Lithium nitrate in 2-propanol

500 W Hg

CO, HCOO
, [69] NH3, (NH2)2CO

Ru-TiO2/SiO2

Water

1,000 W Hg HCOOH, [70] CH2O, H2, CH4, CH3OH

3.2

Light source

Products

References

[58] [60]

1775

1776

46

Photocatalytic Water Splitting and Carbon Dioxide Reduction

. Table 46.2 (Continued) Photocatalyst

Band gap (eV) Reductants

Light source

Products

References

Rh/TiO2

3.2

Hydrogen

Hg

CO, CH4

[71]

Sol–gel-prepared Cu/ TiO2

3.2

NaOH solution

Hg

CH3OH

[72]

TiO2/Pd/Al2O3,TiO2/Pd/ SiO2 CuO/ZnOand Li2O/ TiO2 supported over MgO, Al2O3

Water

Hg

(CH3)2CO, CH4, C2H6, HCHO, HCOOH, CH3OH, C2H5OH

[73]

Pd/RuO2/TiO2,Pd/TiO2

Aqueous Na2SO3 and NaOH

450 W Xe

HCOO


[74]

Cu/TiO2, sol–gel prepared Cu/P-25

NaOH solution

Hg

CH3OH, O2

[75]

Pt/K2Ti6O13 with Fe-based catalyst

Water

300 W Xe and 150 W Hg

H2, CH4, HCHO, HCOOH, CH3OH, C2H5OH

[76]

Ti containing mesoporous silica thin film

4.0–5.0

Water vapor

100 W Hg

CH4, CH3OH [77, 78]

Ti-MCM-41 and Ti-MCM-48

4.0–5.0

Water vapor

Hg

CH4, CH3OH [79]

Ti-b zeolite

4.75–6.0

Water vapor

100 W Hg

CH4, CH3OH [80]

Ti silicalite molecular sieve

4.0–5.0

Methanol

266-nm Nd: HCO2H, CO, [81] HCO2CH3 YAG laser

ZrO2

5.0

Hydrogen

500 W Hg

ZrO2

5.0

Hydrogen

500 W Hg

CO

[83]

ZrO2

5.0

Methane

500 W Hg

CO

[84]

MgO

8.7

Hydrogen

500 W Hg

CO

[85]

CdS surface modified by 2.4 DMF

Triethylamine

300 W halogen tungsten

Not reported

[86]

CdS surface modified by 2.4 thiol

Propanol

500 W Hg

HCOO
, CO, [87] H2, (CH3)2CO

[fac-Re(bpy)(CO)3(4-Xpy)]+

TEOA/DMF

500 W Hg

CO, H2

[88]

[fac-Re(bpy)-(CO)3Cl]

Et3N/DMF

500 W Hg

CO, H2

[89]

[fac-Re(bpy)-(CO)3P (OiPr)3]+

TEOA/DMF

500 W Hg

CO, H2

[90]

CO

[82]

Photocatalytic Water Splitting and Carbon Dioxide Reduction

46

. Table 46.2 (Continued) Photocatalyst

Band gap (eV) Reductants

2+

Co(bpy)3 sensitized with Ru(bpy)32+

DMF/TEOA, DMF/H2O/ TEOA

ZnO on activated carbon 3.0

Light source

Products

References

Xe

CO, H2

[91]

Xe

CO, H2

[92]

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47 Technological Options for Reducing Non-CO2 GHG Emissions Jeff Kuo Department of Civil and Environmental Engineering, California State University, Fullerton, CA, USA Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1783 Methane (CH4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1785 Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1785 Petroleum Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1786 Natural Gas Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1787 Stationary Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1790 Mobile Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1792 Agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1793 Enteric Fermentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1793 Manure Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1794 Rice Cultivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1795 Wastes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1796 Landfills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1796 Wastewater Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1798 Nitrous Oxide (N2O) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1798 Agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1799 Agricultural Soil Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1799 Manure Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1800 Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1801 Mobile Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1801 Stationary Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1802 Municipal Solid Waste Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1802 Industrial Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1802 Waste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1803 High-GWP Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1804 Substitution of Ozone-Depleting Substances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1805

Wei-Yin Chen, John Seiner, Toshio Suzuki & Maximilian Lackner (eds.), Handbook of Climate Change Mitigation, DOI 10.1007/978-1-4419-7991-9_47, # Springer Science+Business Media, LLC 2012

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Refrigeration and Air-Conditioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Technical Aerosols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Foams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fire Extinguishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sterilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electrical Transmission and Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Semiconductor Manufacture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1806 1810 1811 1812 1812 1813 1814 1815

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1816

Technological Options for Reducing Non-CO2 GHG Emissions

47

Abstract: In recent years, non-CO2 greenhouse gases (NCGGs), including methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6), have gained attention due to their higher global warming potentials (GWPs) and abundance of cost-effective and readily implementable technological options available for achieving significant emission reductions. A project titled Clearinghouse of Technological Options for Reducing Anthropogenic Non-CO2GHG Emissions from All Sectors was recently conducted. The overall objective of the project was to develop a clearinghouse of technological options for reducing anthropogenic NCGG emissions. The findings of the project help to better characterize cost-effective opportunities for emission reductions of NCGGs. Employment of an appropriate control technology for a given source would achieve a net reduction in NCGG emissions as well as its contribution to climate change. This chapter of the handbook extracts relevant data and information on the technological options for reducing non-CO2 GHG emissions from the aforementioned project report.

Introduction In the past, climate mitigation studies were focused on carbon dioxide (CO2), especially from energy-related sources. However, in recent years, non-CO2 greenhouse gases (NCGGs), including methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6), have gained attention due to their higher global warming potentials (GWPs) and abundance of cost-effective and readily implementable technological options available for achieving significant emission reductions. Studies have found that abatement options for several of the NCGG sources are relatively inexpensive. In addition, NCGG emission reductions may provide a more rapid response in avoiding climate impacts by focusing on short-lived gases [1, 2]. A project titled Clearinghouse of Technological Options for Reducing Anthropogenic Non-CO2 GHG Emissions from All Sectors was recently conducted by California State University, Fullerton under the sponsorship of the California Air Resources Board (CARB contract number 05–328 and Steve Church as the ARB Contract Manager) [3]. The overall objective of the project was to develop a clearinghouse of technological options for reducing anthropogenic NCGG emissions from sectors that are relevant to California. To achieve this goal, specific project tasks were completed, including (1) identification of sources of NCGG emissions from various sectors in California, (2) identification of available technological options for NCGG emission reductions through a comprehensive literature search, (3) evaluation of the identified technological options for their applicability in California, and (4) report preparation. Although the emission sources can be categorized into economic sectors (i.e., residential, commercial, industrial, agricultural, transportation, and electricity generation), six potential source sectors as defined by United Nations Intergovernmental Panel on Climate Change (IPCC) were used: energy, industrial processes, solvent use, agriculture, land-use change and forestry,

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Technological Options for Reducing Non-CO2 GHG Emissions

. Table 47.1 Comparison of GHG emissions in the United States and California USA (2004) Gas

MMTCO2-Eq.

California (2004) (%)

MMTCO2-Eq.

(%)

CA/USA(%)

Carbon dioxide

5,988

84.6

364

82.8

6.1

Methane Nitrous oxide HFCs, PFCs, and SF6 Total

557 387 143 7,074

7.9 5.5 2.0 100

28 33 14 439

6.4 7.6 3.2 100

5.0 8.6 9.9 6.2

and waste [4]. The findings of the project help to better characterize cost-effective opportunities for emission reductions of NCGGs. Employment of an appropriate control technology for a given source would achieve a net reduction in NCGG emissions as well as its contribution to climate change. > Table 47.1 presents a comparison of GHG emissions between the United States and California. These emission estimates were derived by using the 1996 IPCC GWP values. The CA estimates were extracted from an inventory report [5]. The NCGG emissions in the United States were 1,087 million metric tons of carbon dioxide equivalent (MMTCO2-Eq.) in 2004, approximately 15% of the total GHG emissions. Out of this 15%, 7.9% came from nitrous oxide, 5.5% from methane, and 2.0% from HFCs, PFCs, and SF6. The NCGG emissions in California were 75 MMTCO2-Eq. in 2004, approximately 18% of the total GHG emissions. Out of this 18%, 7.6% came from nitrous oxide, 6.4% from methane, and 3.2% from HFCs, PFCs, and SF6. Although the population of California was approximately 12% of the United States in 2004, it only made up 6.2% of GHG emissions of the United States. Some of the technological options identified from the literature search were already in use, but many of them were still in conceptual, bench-scale studies, or research and development (R&D) stages. To evaluate the applicability and implementability of a technological option, it is important to have data on reduction efficiency (RE), market penetration (MP), technical applicability (TA), service lifetime and costs (capital and O&M). Those options having sufficient and definite information on lifetime, RE, MP, TA, and costs were summarized in tables for easier comparison and use. The reduction efficiency tells the percentage that emission can be mitigated by a technological option. The percentage of the baseline to which a technological option is applicable is called technical applicability [6]. Market penetration is the percentage of emissions from a given source that is addressed by a given technological option [6]. The cost data were presented in year 2000 US dollars per metric ton CO2 equivalent ($/MTCO2-Eq.). There were three types of cost data presented in the aforementioned report for a given technological option. The one-time capital cost reflects the initial investment of the technological option. The annual cost reflects the yearly O&M cost needed to

Technological Options for Reducing Non-CO2 GHG Emissions

47

implement the option, while benefits refer to monetary savings, if any, resulting from the implementation of the option. In addition, lifetime data were also provided which showed the expected lifespan of the project [3]. With these cost data and the expected lifespan of a given technological option, one could easily derive an estimate for implementing an option. However, it should be noted that the data for a given option are often very general in nature and may not be applicable to all cases. Data on a given technological option could sometimes be found from various sources, such as reports of California Energy Commission (CEC), CARB, United States Environmental Protection Agency (USEPA), and some international agencies, including the United Nations (UN) and International Energy Agency (IEA). The aforementioned report used the data that were more specific to California first (e.g., from reports of CEC and CARB). If information from these sources was not available, data specific to the United States were then used, followed by the data that were developed for global perspectives or for other countries. The aforementioned report is about 400-pages long; this chapter of the handbook extracts relevant data and information on the technological options for reducing nonCO2 GHG emissions from it. The subsequent sections address each NCGG individually. > Section ‘‘Methane (CH4)’’ is dedicated to methane and > section ‘‘Nitrous oxide (N2O)’’ to nitrous oxide. Due to the similarities between PFCs, HFCs, and SF6 in their characteristics and sources, they were grouped as the high-GWP gases and covered in > section ‘‘High-GWP Gases.’’ > Section ‘‘Summary’’ presents a brief summary.

Methane (CH4) According to the IPCC, CH4 is approximately 23 times as effective as CO2 in trapping heat in the atmosphere over a 100-year time horizon [7]. The chemical lifetime of CH4 in the atmosphere is about 12 years. Since 1750, the global-average atmospheric concentrations of CH4 have changed from about 700–1,745 parts per million by volume (ppmV), a 150% increase [7]. The top contributors for CH4 emissions in California in the order of magnitude are landfills (30.2%), enteric fermentation (25.9%), manure management (21.6%), wastewater treatment (6.1%), natural gas systems (5.0%), stationary combustion (4.7%), mobile combustion (2.2%), rice cultivation (2.2%), petroleum system (1.8%), and field burning of agricultural residues (0.4%) [5]. The following subsections describe the emission sources and mitigation options for three major sectors: energy, agriculture, and waste.

Energy The major contributors for methane emissions in the energy sector in California are natural gas systems (36.8%), stationary combustion (34.2%), mobile combustion (15.8%), and petroleum systems (13.2%) [5].

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Technological Options for Reducing Non-CO2 GHG Emissions

Petroleum Systems Out of the 25.7 MMTCO2-Eq. methane emissions from petroleum systems in the United States in 2004, production field operations account for 97%, followed by 2% in refining operations and less than 1% in crude oil transportation [8]. The relative contribution of each subsector within the petroleum systems in California should be similar to the corresponding ones in the United States. The sources of methane emissions from petroleum production field operations include pneumatic device venting, tank venting, combustion and process upsets, miscellaneous venting and fugitive emissions, and wellhead fugitive emissions [8]. The measures to reduce methane emissions from the petroleum systems (as well as natural gas systems to be discussed in > section ‘‘Natural Gas Systems’’) can be grouped into the following mitigation strategies [9]: ● Prevention – improved process efficiencies and leakage reduction ● Recovery and reinjection – recovery of off-gases and reinjection into the subsystems such as oil reservoirs and natural gas transport pipeline ● Recovery and utilization – recovery and utilization of otherwise emitted gases for energy production ● Recovery and incineration – recovery, followed by incineration (flaring) without energy production > Table 47.2 summarizes the information on technological options that was found in literature with regards to cost, market penetration (in 2010), emission reduction efficiency, and technical applicability (in 2010) for emission reduction from production field operations in petroleum systems. It should be noted here that all the values in this table and the other similar tables in this chapter were directly extracted from the literature search. Factors such as new regulations, development of the technologies, and economic

. Table 47.2 Technological options for petroleum systems – production field operations Technology

Lifetime Capital Annual (years) MP (%) RE (%) TA (%) cost cost Benefits

Flaring instead of venting [10, 11]

15

100

98

5

$33.30

$1.00

$0.00

Associated gas (vented) mix with other options [10, 11] Associated gas (flared) mix with other options [10, 11] Option for flared gas (improved flaring efficiencies) [6, 12]

15

100

90

23–25

$69.54

$1.11

$3.71

15

100

95

14–15

$66.61

$2.21

$3.71

15

100

10

13

$66.61

$2.21

$0.00

MP market penetration, RE reduction efficiency, TA technical applicability; costs are in year 2000 US$/ MTCO2-Eq.

Technological Options for Reducing Non-CO2 GHG Emissions

47

conditions may affect these projected values. In addition, assessment of the current status of these technological options is beyond the scope of work of the project. The CH4 emissions from crude oil transportation and refining operations are relatively small, and their mitigation options are very similar to those of the natural gas processing and transmission (see > section ‘‘Natural Gas Systems’’).

Natural Gas Systems Out of the total 118.8 MMTCO2-Eq., methane emissions from natural gas systems in the United States are mainly associated with field production (33.1% of total), processing (11.8%), transmission and storage (32.3%), and distribution (22.8%). The methane emissions from natural gas systems in California were 1.4 MMTCO2-Eq. in 2004, composing 5.0% of its total methane emissions. Field Production

In this initial stage of natural gas systems, gas wells are used to extract raw gas from subsurface formations. Sources of emissions include wells themselves, collection pipelines, well-site gas treatment facilities such as dehydrators and separators, fugitive emissions and emissions from pneumatic devices, and emissions from routine maintenance and repair of wells and equipment [8]. In the United States and the worldwide, many efforts have been made to identify and implement mitigation options to reduce methane emissions from the natural gas sector [13]. For example, the Natural Gas STAR program is a voluntary partnership between USEPA and the oil and gas industry to identify and implement cost-effective technologies and measures to reduce methane emissions. They have identified many Best Management Practices (BMPs) that are cost-effective in reducing methane emissions (http://www.epa. gov/gasstar/techprac.htm). The program has sponsored a series of Lessons Learned Studies of these BMPs and several other practices. In addition, companies that are Natural Gas Star Partners have identified other practices referred to as Partner-Reported Opportunities (PROs) that also reduce methane emissions [14]. Since 1990, the oil and gas industry in the United States has achieved over 10 billion cubic meters of methane emission reduction [15]. Similar to the petroleum sector, the measures to reduce methane emissions from the natural gas systems can be categorized into the following mitigation strategies: prevention, recovery and reinjection, recovery and utilization, and recovery and incineration [9]. Specific technological options to reduce CH4 emissions from natural gas field operations include the following [3]: ● ● ● ● ●

Good housekeeping practices to reduce blowouts Good operational procedures with regards to well-testing Flaring of gas produced at well tests (during exploration) Green completion Installing plunger-lift systems in gas wells

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47 ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ●

Technological Options for Reducing Non-CO2 GHG Emissions

Using surge vessels for station/well venting Replacing high-bleed pneumatic devices with low-bleed pneumatic devices Replacing high-bleed pneumatic devices with compressed-air systems Reducing the glycol circulation rates in dehydrators Installing flash tank separators on dehydrators Replacing glycol dehydrators with desiccant dehydrators Minimizing strip gas in glycol dehydration Increasing the pressure of the condensate flash Rerouting glycol dehydrator vapor to vapor-recovery unit Reducing purge gas streams Using portable evacuation compressors for pipeline venting Fuel gas line retrofitting for blow-down valve and alter emergency shutdown (ESD) practices Installing electric starters on compressors Replacing gas starters with air/nitrogen Replacing ignition/reduce false starts Use of automatic air/fuel ratio control Replacing the frequency of gas start with gas Inspection and maintenance (pipeline leaks) Inspection and maintenance (equipment and facilities) Inspection and maintenance (chemical inspection pumps) Inspection and maintenance (enhanced)

> Table 47.3 summarizes the information on technological options that was found in literature for emission reduction from production activities in natural gas systems.

Processing

Subsequent to field production, ‘‘impurities’’ such as natural gas liquids and various other constituents from the extracted raw gas are removed, resulting in ‘‘pipeline quality’’ gas that is injected into transmission pipe and storage system. Fugitive emissions from compressors, including compressor seals are the primary emission source [8]. The mitigation options for methane emission during the processing of natural gas are very similar to those for transmission and storage, and they will be described in > section ‘‘Transmission and Storage.’’ Transmission and Storage

Natural gas produced from gas fields needs to be transported to distribution systems, power plants, or chemical plants through high-pressure pipelines. Compressor stations which contain large reciprocating engines and turbine compressors are used to move the gas throughout the United States. Natural gas is also injected and stored in subsurface formations or liquefied and stored in aboveground tanks to meet the fluctuations in gas demand. Sources of methane emissions include fugitive emissions and engine exhaust from the compressor stations; fugitive emission from metering and regulating stations; emissions from compressors and dehydrators in storage facilities [6].

Technological Options for Reducing Non-CO2 GHG Emissions

47

. Table 47.3 Technological options for natural gas system – production Technology

Lifetime Capital Annual (years) MP (%) RE (%) TA (%) cost cost Benefits

Installation of plunger-lift systems in gas wells [6, 10] Surge vessels for station/well venting [6, 10] Replace high-bleed with low-bleed pneumatic devices [6, 10]

10

100

4

10

100

5

Replace high-bleed pneumatic devices with compressed-air systems [6, 10] Reducing glycol circulation rates in dehydrators [6, 10] Installation of flash tank separators [6, 10] Installation of electric starters on compressors [10, 11] Portable evacuation compressor for pipeline venting [6, 10] Inspection and maintenance (pipeline leaks) [6, 10] Inspection and maintenance (facilities & equipment) [10, 11] Inspection and maintenance (chemical inspection pumps) [10, 11] Inspection and maintenance (enhanced) [10, 11]

1

$3,986

$159.42

$8.21

50

Table 47.13 summarizes the information on technological options that was found in literature for emission reduction from retail food refrigeration. > Table 47.14 summarizes the information on technological options that was found in literature for emission reduction from cold storage warehouse.

. Table 47.9 Technological options for household refrigeration Lifetime Capital (years) MP (%) RE (%) TA (%) cost

Technology Refrigerant recovery/ recycling [6] Use of hydrocarbons [11]

Annual cost Benefits

10

10

95

1–3

$26.19

$3.40

$1.69

15

–

100

2–7

$38.49

$0.00

$0.00

MP market penetration, RE reduction efficiency, TA technical applicability; costs are in year 2000 US$/ MTCO2-Eq.

. Table 47.10 Technological options for residential air conditioners and heat pumps Technology Refrigerant recovery/ recycling [6] Leak repair [11, 29]

Lifetime (years)

MP (%) RE (%)

TA (%)

Capital Annual cost cost Benefits

–

10

95

10

$26.19

$3.40

$1.69

5

5

90

0.2–0.5

$27.55

$0.00

$3.05

MP market penetration, RE reduction efficiency, TA technical applicability; costs are in year 2000 US$/ MTCO2-Eq.

1807

1808

47

Technological Options for Reducing Non-CO2 GHG Emissions

. Table 47.11 Technological options for motor vehicle air conditioners Lifetime (years)

Technology Refrigerant recovery/ recycling [6, 11] Improved HFC-134a systems [6] HFC-152a systems [6] Use of CO2 [6, 11]

Capital Annual MP (%) RE (%) TA (%) cost cost Benefits

10

10

95

10

$26.19

$3.40

$1.69

–

1

18

15

$404.80

$0.00

$168.30

– 12

0 0

89 100

15 15

$192.33 $611.97

$0.00 $0.00

$54.15 $86.03

MP market penetration, RE reduction efficiency, TA technical applicability; costs are in year 2000 US$/ MTCO2-Eq.

. Table 47.12 Technological options for chillers Technology

Lifetime (years)

Leak repair [11, 29]

5

MP (%)

RE (%)

TA (%)

Capital cost

Annual cost

Benefits

5

90

0–4

$27.55

$0.00

$3.05

MP market penetration, RE reduction efficiency, TA technical applicability; costs are in year 2000 US$/ MTCO2-Eq.

. Table 47.13 Technological options for retail food refrigeration Technology

Lifetime Capital Annual (years) MP (%) RE (%) TA (%) cost cost Benefits

Leak repair [11, 29] Alternative systems [11]

5 15

10 –

90 100

6–15 $27.55 $0.00 11–31 $188.10 $1.41

$3.05 $2.76

Ammonia secondary loop systems [11, 29] HFC secondary loop systems [11, 29]

20

10

100

11–31 $115.98 $12.89

$1.58

20

10–20

100

11–31

$30.93 $12.89

$1.58

Replacing direct expansion systems with distributed systems [11, 29]

20

10–20

100

11–31

$82.15

$1.58

$6.84

MP market penetration, RE reduction efficiency, TA technical applicability; costs are in year 2000 US$/ MTCO2-Eq.

Technological Options for Reducing Non-CO2 GHG Emissions

47

. Table 47.14 Technological options for cold storage warehouse Technology

Lifetime Capital Annual (years) MP (%) RE (%) TA (%) cost cost Benefits

Leak repair [11, 29] Alternative systems [11] Ammonia secondary loop systems [11, 29]

5 15 20

HFC secondary loop systems [11, 29] Replacing direct expansion systems with distributed systems [11, 29]

10 10

90 100 100

3–14 6–27 6–27

$27.55 $0.00 $188.10 $1.41 $115.98 $12.89

$3.05 $2.76 $1.58

20

10–20

100

6–27

$30.93 $12.89

$1.58

20

10–20

100

6–27

$82.15

$1.58

$6.84

MP market penetration, RE reduction efficiency, TA technical applicability; costs are in year 2000 US$/ MTCO2-Eq.

. Table 47.15 Technological options for refrigerated transport Technology Refrigerant recovery/ recycling [11, 29]

Lifetime (years) 10

Capital Annual MP (%) RE (%) TA (%) cost cost Benefits 10

95

10

$26.19

$3.40

$1.69

MP market penetration, RE reduction efficiency, TA technical applicability; costs are in year 2000 US$/ MTCO2-Eq.

. Table 47.16 Technological options for industrial process refrigeration Technology Leak repair [11, 29] Alternative systems [11, 32] Ammonia secondary loop systems [11, 29]

Lifetime (years) 5 15 20

Capital Annual MP (%) RE (%) TA (%) cost cost Benefits 10 – 10

90 100 100

1–5 2–9 2–9

$27.55 $0.00 $188.10 $1.41 $116 $12.89

$3.05 $2.76 $2.76

MP market penetration, RE reduction efficiency, TA technical applicability; costs are in year 2000 US$/ MTCO2-Eq.

Table 47.15 summarizes the information on technological options that was found in literature for emission reduction from refrigerated transport. > Table 47.16 summarizes the information that was found in literature for the technological options for emission reduction from industrial process refrigeration. >

1809

1810

47

Technological Options for Reducing Non-CO2 GHG Emissions

. Table 47.17 Technological options for commercial unitary air-conditioning Technology

Lifetime (years)

Refrigerant recovery/ recycling [6] Leak repair [11, 29]

MP (%) RE (%)

TA (%)

Capital Annual cost cost Benefits

–

10

95

10

$26.19

$3.40

$1.69

5

5

90

0–4

$27.55

$0.00

$3.05

MP market penetration, RE reduction efficiency, TA technical applicability; costs are in year 2000 US$/ MTCO2-Eq.

Table 47.17 summarizes the information on technological options that was found in literature for emission reduction from commercial unitary air-conditioning. >

Technical Aerosols Various HFCs, including HFC-34a, HFC-152a, and HFC-227ea, are used as propellants in aerosol applications. The emissions of high-GWP gases, mainly HFCs, from technical aerosols account for 10.7% of their emissions from the sector of ODS substitutes in the United States [8]. Out of the 11.1 MMTCO2-Eq. emissions in 2004, the end-uses that contribute most toward emissions of HFCs as technical aerosols in the United States include metered dose inhalers (MDIs), consumer products and specialty products. Although hydrocarbons can be used as propellants in many commercial aerosols, they have not been found acceptable for use in MDIs (USEPA, 2004). Nitrogen is another alternative as the propellant [32]. The main technological option for reducing HFCs from end-use of MDIs is dry powder inhalers (DPIs). DPIs have been successfully used with most antiasthma drugs. However, they may not be applicable to all patients or all drugs (e.g., applicable only to patients who can inhale robustly enough to transport powders to their lungs). In addition, the powders may aggregate under hot and humid climates [34, 35]. However, the use of DPIs in Europe is increasing; for example, DPIs account for 85% of inhaled medication [29]. > Table 47.18 summarizes the information on technological options that was found in literature for emission reduction from end-uses of MDIs. A trend is developing for novel oral treatment that would be swallowed, rather than inhaled. They may become available in the next 10–20 years, but they would not completely replace inhaled MDI therapy. It should be noted that MDIs are medical devices; substitute propellants need to meet stringent performance and toxicology specifications [31]. There are several technological options for reducing HFCs emissions from the nonMDI aerosol end-uses, mainly as consumer products and specialty products [3]: ● ● ● ●

Substitution with lower GWP HFCs Not-in-kind (NIK) alternatives Hydrocarbon aerosol propellants Use of compressed gases

Technological Options for Reducing Non-CO2 GHG Emissions

47

. Table 47.18 Technological options for end-uses of MDIs Technology

Lifetime Capital (years) MP (%) RE (%) TA (%) cost

Dry powder inhalers [11, 29, 31]

15

5

100

50

Annual cost

$294.21

$0.00

Benefits 0.00

MP market penetration, RE reduction efficiency, TA technical applicability; costs are in year 2000 US$/ MTCO2-Eq.

. Table 47.19 Technological options for end-uses of consumer products and specialty products Technology Substitution with lower GWP HFCs [11, 29, 31] VOC propellants [11, 29, 31] Not-in-kind (NIK) products [11, 29, 31]

Lifetime Capital Annual (years) MP (%) RE (%) TA (%) cost cost Benefits 10

25

91

48

$0.75

$2.52

$0.00

10 10

10 10

100 100

40 100

$0.44 $0.34

$5.60 $5.26

$0.00 $0.00

MP market penetration, RE reduction efficiency, TA technical applicability; costs are in year 2000 US$/ MTCO2-Eq. > Table 47.19 summarizes the information on technological options that was found in literature for emission reduction from end-uses of consumer products and specialty products.

Solvents HFCs (especially HFC-4310mee) and PFCs are used as solvents for various industrial cleaning applications including precision, electronics, and metal cleaning. HFC emissions from the precision and electronics cleaning end-uses currently dominate the GWP-weighted emissions from this sector [31, 36]. The emissions of these GWP gases from solvent uses account for 1.5% of their emissions from the ODS substitutes in the United States [8]. There are several technological options for reducing HFC/PFC emissions from solvent uses [3]: ● ● ● ●

Improved equipment and cleaning processes using existing solvent Recycle and recovery Not-in-kind (NIK) technologies Alternative solvents

> Table 47.20 summarizes the information on technological options that was found in literature for emission reduction from solvent uses.

1811

1812

47

Technological Options for Reducing Non-CO2 GHG Emissions

. Table 47.20 Technological options for solvent uses Technology

Lifetime (years) MP (%) RE (%) TA (%)

Capital Annual cost cost Benefits

Improved equipment and cleaning processes [11, 29, 31]

10

0

46–90

90–100 $370.37

$0.00

$27.84

Aqueous cleaning [11, 29, 31] Semi-aqueous cleaning [11, 29, 31]

10

5

100

90–100

$40.00

$0.00

$0.00

10

3

100

90–100

$22.22

$0.00

$0.00

10

30

85

5–100

$0.00

$1.29

$0.00

Alternative solvents [11, 29, 31]

MP market penetration, RE reduction efficiency, TA technical applicability; costs are in year 2000 US$/ MTCO2-Eq.

Foams Foams are used for thermal and sound insulation as well as cushioning. Various HFCs such as HFC-134a, HFC-152a, HFC-245fa and HFC-365mfc, are used as the blowing agents during the manufacture of foams. These blowing agents may be emitted to the atmosphere during foam manufacturing or on-site foam application while foams are in use and when foams are disposed of. The foams can be categorized by the composition (e.g., polyurethane, polystyrene or polyolefin), type of cell (open vs. closed), manufacturing process (spray versus extrusion; thermoset versus thermoplastic), and the properties (rigid versus flexible). Technological options to reduce HFC emissions from foams include the following [29, 31]: ● ● ● ●

Alternative blowing agents Lower GWP HFC substitution Alternative insulation materials and technologies Direct emission reduction

> Table 47.21 summarizes the information on technological options that was found in literature for emission reduction from the end-uses of foam.

Fire Extinguishing HFCs (HFC-227ea, HFC-236fa, HFC-23) and perfluromethane (CF4) are the principal greenhouse gases emitted from fire extinguishing systems. Basically, there are two types of fire-fighting systems: portable fire extinguishers and total flooding applications. Portable fire extinguishers are used widely; foam, water, CO2 or dry powder is commonly used. Market penetration of HFCs and PFCs in this sector is very limited [29]. Sensitive systems

Technological Options for Reducing Non-CO2 GHG Emissions

47

. Table 47.21 Technological options for foam sector Technology Replace HFC-134a in appliance with hydrocarbons [11, 29, 31, 35] Replace HFC-245fa in appliance with hydrocarbons [11, 29, 31, 35] Replace HFC-245fa in sprays with hydrocarbons [11, 29, 31, 35] Replace HFC-245fa in sprays with water-blown CO2 [11, 29, 31, 35] Replace HFC-134a or 152a in extruded polystyrene with water-blown CO2 [11, 29, 31, 35]

Lifetime Capital (years) MP (%) RE (%) TA (%) cost 25

25

100

25

15

25

0–2 $105.79

Annual cost Benefits $3.19

$0.00

100

0–10 $144.40 $32.35

$0.00

10

100

0–26

$7.81

$3.82

$0.00

25

5

100

0–26

$2.23 $23.97

$0.00

25

0

100

37–100

$8.89

$0.00

$0.14

MP market penetration, RE reduction efficiency, TA technical applicability; costs are in year 2000 US$/ MTCO2-Eq.

such as computer and telecommunication servers are contained in sealed rooms and equipped with fixed extinguishing systems that flood the room in case of fire (total flooding systems). To ensure that people working in this environment are not harmed, nontoxic extinguishing agents are needed; HFCs and PFCs are more commonly used. The technological options for reducing HFC and PFC emissions from the fire protection sector include the use of alternative fire protection agents and alternative technologies and practices [29, 31]: ● Alternative fire protection agents ● Alternative technologies and practices Tabl