Primary Exploration of Hydrogen Metallurgy [2024 ed.] 9819968267, 9789819968268

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Primary Exploration of Hydrogen Metallurgy

Jianliang Zhang · Kejiang Li · Zhengjian Liu · Tianjun Yang

Primary Exploration of Hydrogen Metallurgy

Jianliang Zhang School of Metallurgical and Ecological Engineering University of Science and Technology Beijing Beijing, China

Kejiang Li School of Metallurgical and Ecological Engineering University of Science and Technology Beijing Beijing, China

Zhengjian Liu School of Metallurgical and Ecological Engineering University of Science and Technology Beijing Beijing, China

Tianjun Yang School of Metallurgical and Ecological Engineering University of Science and Technology Beijing Beijing, China

ISBN 978-981-99-6826-8 ISBN 978-981-99-6827-5 (eBook) https://doi.org/10.1007/978-981-99-6827-5 Jointly published with Metallurgical Industry Press The print edition is not for sale in China (Mainland). Customers from China (Mainland) please order the print book from: Metallurgical Industry Press. © Metallurgical Industry Press 2024 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publishers, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publishers nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publishers remain neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore Paper in this product is recyclable.

Foreword

In 2020, at the 75th Session of the United Nations General Assembly, China announced that the country would scale up its intended national commitment to global warming by adopting more vigorous policies and measures. China aims to have CO2 emissions peak before 2030 and achieve carbon neutrality before 2060. The Ministry of Ecology and Environment of the People’s Republic of China released a guideline on coordinated and advanced measures for climate change and eco-environmental protection in January 2021. According to the official document, China has carried out the pilot demonstration of coordinated control of air pollutants and greenhouse gases in iron and steel and other industries, which indicates that China’s efforts to reduce carbon emissions in the industry will reach an unprecedented level. In recent years, globally, special attention has been paid to the development of hydrogen metallurgy technology. This book explores the function of hydrogen in iron ore reduction for different processes, blast furnace, direct reduction and smelting reduction. At present, the annual CO2 emissions of the iron and steel industry account for 6.7% of the total global emissions, and the energy consumption and emissions of the ironmaking system account for about 70%. The ironmaking industry is facing important challenges in energy conservation and emission reduction. However, most efforts to meet this challenge have been made in the traditional ironmaking processes. All countries are gradually implementing new emission reduction plans for the lowcarbon iron smelting process. Hydrogen is regarded as the future development direction as the green energy source in the 21st century globally. At present, low-carbon iron smelting processes in developed countries aim to achieve “hydrogen metallurgy”, for fundamentally reducing or even eliminating CO2 emissions. Compared with carbon metallurgy, energy consumption and carbon emissions could be greatly reduced by hydrogen metallurgy, a clean iron smelting energy and a reductant. It is currently the first choice for countries to reduce emissions from the source in the iron and steel industry. Nowadays, iron and steel enterprises around the world have taken up ‘hydrogen metallurgy’ as the development goal for the future. Hydrogen metallurgy in China has developed rapidly in recent years. China Baowu Group Corporation Limited, Tsinghua University, and China National Nuclear Corporation have signed a strategic v

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cooperation agreement to develop nuclear hydrogen production for hydrogen metallurgy jointly. HBIS Group Co., Ltd. signed a memorandum of understanding with Tenova Group in Italy to build the world’s first direct reduction shaft furnace with coke oven gas as the reducing agent based on the Energiron technology and this plant has been put into operation in May 2023. The direct reduction shaft furnace process based on hydrogen built by Baowu Group was also put into operation in December 2023. In addition, Jianlong Group has invested in constructing and developing the new ironmaking technology of Hydrogen-based smelting reduction (CISP) in Wuhai, Inner Mongolia, China. Our research group has also participated in this development. Shanxi ZhongJing Energy Group Co., Ltd. built and developed a new process of CSDRI Hydrogen-based direct reduction, and we took part in this process along with a team from the China University of Petroleum. Internationally, the COURSE50 low-carbon ironmaking project in Japan has been carried out for more than 10 years, with hydrogen reduction ironmaking at the core focus. The EU iron and steel industry launched the ULCOS project in 2004, to develop new technology for low-carbon steelmaking to reduce 50% of CO2 emissions per ton of steel by 2050. Sweden is also implementing the HYBRIT “Hydrogen Breakthrough Ironmaking Technology” project. Dillinger Hütte and Saarschmiede GmbH in Germany have invested 14 million euros to build hydrogen steelmaking plants. The government of South Korea has also designed hydrogen reduction ironmaking as the national core industrial technology, with hydrogen metallurgy as the future development direction. In summary, many iron and steel enterprises around the world are following the trend and vigorously conducting research and development of hydrogen metallurgy. This book is a monograph introducing hydrogen metallurgy technology mainly in China. It focuses on the role of hydrogen in the iron ore reduction process. The purpose is to advance the development of hydrogen metallurgy research in China, promote low-carbon processes in China’s iron and steel industry, and fill knowledge gaps in the field of hydrogen metallurgy. Chapter 1 of this book introduces the development trends in global low-carbon metallurgy and hydrogen metallurgy, discusses the need for transforming carbon metallurgy to hydrogen metallurgy, and introduces the policies and systems of carbon emissions around the world. Chapter 2 introduces various types of hydrogen and the current hydrogen production methods. With the metallurgical industry as the background, it provides an overview of hydrogen energy and application requirements of hydrogen from the perspective of its production, storage, and transportation. Chapter 3 introduces the research and development results from China’s first direct hydrogen-based reduction CSDRI process in which we participated. Chapter 4 presents industrial research and development results from first hydrogen-based smelting reduction CISP process in China, including the role, thermodynamics, and dynamic analysis of hydrogen in the smelting reduction process based on our laboratory research. Chapter 5 introduces the new process of plasma hydrogen metallurgy, the basic properties of plasma, the mechanism of plasma hydrogen reduction, and the industrial practice process of plasma hydrogen fusion reduction based on traditional hydrogen metallurgy. As per years of teaching and research experiences, Chap. 6 discusses the role of hydrogen in the current blast furnace ironmaking process, especially its role in reduction reactions in the blast

Foreword

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furnace and proposes directions for low-carbon blast furnace in the future. Based on our scientific research, Chap. 7 discusses the role of hydrogen and its reaction mechanism in the sintering process, compares the role of hydrogen with carbon in this process, and then summarizes the progress of the hydrogen-rich sintering process in China and around the world.

Beijing, China March 2024

Tianjun Yang

Acknowledgements

First of all, we would like to thank academician Yin Ruiyu for his guidance over the years. We attended lectures on engineering philosophy and carefully studied the books and papers on “metallurgical process engineering”, which inspired us to keep exploring. We would like to thank German Professor H. W. Gudenau and Japanese Professor Ariyama for their outstanding work introducing relative research in Europe and Japan. We are grateful to Prof. Johannes Schenk of Montanuniversitaet Leoben in Austria for his close cooperation with us. He also kindly provided the opportunity for the two young scholars of our team to participate in the research of plasma hydrogen metallurgy. We also acknowledge the many highly valuable and intense scientific discussions on the topic of hydrogen reduction with Prof. Dierk Raabe and his group members from the Max-Planck-Institut für Eisenforschung (MPIE). We are also very pleased and honored to thank Profs. Wang Xiaoliu, Liu Yuncai, Xiang Zhongyong, Wu Qichang, Sha Yongzhi, and other experts for their information and valuable suggestions, and many colleagues in the ironmaking industry for their assistance and suggestions. We feel thankful to Zhang Zhixiang, chairman of Jianlong Group, for supporting and guiding the research and development of the new process of hydrogen metallurgy; and the team composed of Mr. Zhou Haichuan, Mr. Zhang Xiebing, Dr. Zhang Yong, etc., led by Dr. Xu Tao, general manager of CISP Technology Co., Ltd., for their courage and perseverance. We would also like to thank Ju Shifeng, the chairman of Shanxi ZhongJing Energy Group Co., Ltd., for carefully planning and fully supporting the research and development of the new Hydrogen-based direct reduction process. Under the leadership of Lu Qing, Fan Jinfeng, and Wu Zhijun, Shanxi ZhongJing Energy Group Co., Ltd. has overcome many difficulties. Thanks to the close cooperation of Prof. Zhou Hongjun’s team at the China University of Petroleum. With our joint efforts, we have made significant progress in the first new process of hydrogen-based direct reduction in China. HBIS Group Co., Ltd., Sinosteel Construction and Development Co., Ltd., and MCC Capital Engineering and Research Co., Ltd. have made efforts in the field of ix

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hydrogen-based direct reduction in China, their work is greatly appreciated. This process will further fill the gap in hydrogen metallurgy development in China. Postgraduate students Li Yang, Jiang Chunhe, Wang Guilin, Bi Zhisheng, Li Sida, Ma Shufang, Huang Jianqiang, Liang Zeng, Bu Yushan, Liao Haotian, Wang Tengfei, and Lu Shaofeng have made significant contributions in data collection, translation, and editing. After many seminars, the students have advanced the editing of this monograph. We would like to express our gratitude to the students for their hard work. Special thanks to Prof. Alberto Conejo of USTB and Prof. Rita Khanna of UNSW for their review, comments, and valuable suggestions for this book. We wish to thank all these people and several anonymous reviewers for their helpful suggestions. We would greatly appreciate receiving any suggestions that readers may have for improving the book.

Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Low-Carbon Technologies: Global Trends and Developments . . . . . 1.1.1 The Current Situation and Impacts of Carbon Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.2 Targets and Policies of Low-Carbon Emission Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Trends in Global Hydrogen Energy Development . . . . . . . . . . . . . . . 1.3 The Transition from Carbon Metallurgy to Hydrogen Metallurgy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.1 Low-Carbonization Trends in the Iron and Steel Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.2 Proposed Concept of Hydrogen Metallurgy . . . . . . . . . . . . . . 1.4 Research Status of Hydrogen Metallurgy . . . . . . . . . . . . . . . . . . . . . . . 1.4.1 Development Status of Hydrogen Metallurgy . . . . . . . . . . . . 1.4.2 Challenges for Hydrogen Metallurgy . . . . . . . . . . . . . . . . . . . . 1.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Hydrogen Production and Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Hydrogen in Nature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.1 The Discovery of Hydrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.2 Hydrogen and Its Family of Isotopes . . . . . . . . . . . . . . . . . . . . 2.1.3 Distribution of Hydrogen in Nature . . . . . . . . . . . . . . . . . . . . . 2.2 The Method of Hydrogen Production . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 Hydrogen Production with Fossil Fuels . . . . . . . . . . . . . . . . . . 2.2.2 Hydrogen Production with Methanol . . . . . . . . . . . . . . . . . . . . 2.2.3 Biological Hydrogen Production . . . . . . . . . . . . . . . . . . . . . . . 2.2.4 Hydrogen Production by Electrolysis of Water . . . . . . . . . . . 2.2.5 Nuclear Hydrogen Production . . . . . . . . . . . . . . . . . . . . . . . . .

1 1 1 4 11 18 18 21 24 24 31 33 34 37 37 37 38 39 41 42 50 56 63 71

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2.2.6 Advantages and Disadvantages of Various Production Methods for Hydrogen Metallurgy: A Critical Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Storage and Transportation of Hydrogen . . . . . . . . . . . . . . . . . . . . . . . 2.3.1 Pipeline Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2 High-Pressure Gas Cylinders . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3 Water-Sealed Gasholder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.4 Liquid Hydrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.5 Physically Adsorbed Hydrogen Storage Materials . . . . . . . . . 2.4 Hydrogen Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.1 Potential Safety Risks of Hydrogen . . . . . . . . . . . . . . . . . . . . . 2.4.2 Basic Knowledge of Hydrogen Safety . . . . . . . . . . . . . . . . . . . 2.4.3 Hydrogen Combustion and Explosion . . . . . . . . . . . . . . . . . . . 2.4.4 High-Pressure Hydrogen and Liquid Hydrogen . . . . . . . . . . . 2.4.5 Safety Issues Caused by Hydrogen Embrittlement . . . . . . . . 2.4.6 Safety Issues of Hydrogen Storage Alloys . . . . . . . . . . . . . . . 2.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Direct Reduction of Iron Oxides with Hydrogen . . . . . . . . . . . . . . . . . . . 3.1 Thermodynamic Analysis of the Direct Reduction Process with Hydrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.1 Thermodynamic Mechanism of the Direct Hydrogen Reduction of Iron Oxides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.2 Thermodynamic Effects of Gas Components on the Reduction Reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.3 Gibbs Free Energy Principle of the Gas-Based Direct Reduction Reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.4 Thermodynamic Equilibrium in Hydrogen Reduction of Iron Oxides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.5 Constituents of Fe1–x O Under Different Temperatures . . . . . 3.2 Kinetics Analysis of the Direct Reduction Process with Hydrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1 Kinetics for the Direct Reduction of Iron Oxides with Hydrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2 Theoretical Models of Reaction Kinetics . . . . . . . . . . . . . . . . 3.2.3 Factors Affecting Rate Controlling Steps in Reduction Kinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Influence of Different Parameters on Direct Reduction Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1 Influence of Temperature on the Reduction Rate . . . . . . . . . . 3.3.2 Influence of Pressure on the Reaction Rate . . . . . . . . . . . . . . . 3.3.3 Influence of Gas Concentration on the Reduction Rate . . . . . 3.3.4 Influence of Particle Size and Porosity on the Reduction Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

77 80 81 82 84 85 87 96 96 98 99 104 107 108 110 111 117 117 117 118 120 122 125 128 128 130 134 134 134 138 139 139

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3.3.5 Influence of Ore Types on the Reduction Rate . . . . . . . . . . . . 3.3.6 Influence of Vapor Generation on the Reduction Rate . . . . . 3.4 Differences in Reduction Processes of Iron Oxides with CO and H2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.1 Thermodynamic Differences in the Reduction Process of Iron Oxides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.2 Kinetic Difference in the Reduction Process of Iron Oxides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 Analysis of Hydrogen-Carbon Coupling in Industrial Direct Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.1 Current Status of Industrial Application of Hydrogen-Carbon Coupling Direct Reduction Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.2 Chemical Reactions of the Hydrogen-Carbon Coupling Direct Reduction Technique . . . . . . . . . . . . . . . . . . . 3.5.3 Requirements of Reducing Gas in Industrial Direct Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.4 Influence of H2 /CO Volume Ratios and Reduction Temperatures on the Coal Gas Utilization Rate . . . . . . . . . . . 3.6 Industrial Practice of Hydrogen Direct Reduction . . . . . . . . . . . . . . . 3.6.1 Economic Benefit of the Hydrogen Direct Reduction Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.2 Current Status of the Direct Reduction Technique with Hydrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.3 Development Directions in DRI with Hydrogen . . . . . . . . . . 3.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4 Hydrogen Smelting Reduction of Iron Oxides . . . . . . . . . . . . . . . . . . . . . 4.1 Thermodynamic Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.1 Thermodynamic Analysis of Smelting Reduction . . . . . . . . . 4.1.2 Thermodynamic Calculations of Hydrogen Reduction at High Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.3 Calculations of Equilibrium Components of the C–H2 –O2 –H2 O–CO–CO2 System . . . . . . . . . . . . . . . . . 4.2 Kinetic Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 Kinetic Analysis of Molten Iron Oxide Reduction with Hydrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.2 Comparison Between Hydrogen and Other Reducing Agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Behavior of Hydrogen in Molten Iron Oxides . . . . . . . . . . . . . . . . . . . 4.3.1 Hydrogen Metallurgy at High Temperatures . . . . . . . . . . . . . 4.3.2 Dissolution of Hydrogen in Molten Iron Oxides . . . . . . . . . . 4.3.3 Hydrogen Dissolution in Slag . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Industrial Practice of Hydrogen Smelting Reduction . . . . . . . . . . . . .

173 173 173

146 146 147 149

149 151 152 155 158 158 162 166 168 169

175 178 182 182 196 200 200 206 208 210

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4.4.1 Semi-Industrialized Experiment . . . . . . . . . . . . . . . . . . . . . . . . 4.4.2 Industrial Practice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

210 215 216 218

5 Reduction of Iron Oxides with Hydrogen Plasma . . . . . . . . . . . . . . . . . . 5.1 Fundamental Properties of Plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.1 Definition of Plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.2 Properties of Plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.3 Classification of Plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Reduction of Metal Oxides with Hydrogen Plasma . . . . . . . . . . . . . . 5.2.1 Hot Hydrogen Plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.2 Cold Hydrogen Plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Thermodynamic Analysis of Hydrogen Plasma Reduction . . . . . . . . 5.3.1 Thermodynamics of Hot Hydrogen Plasma Reduction . . . . . 5.3.2 Thermodynamics of Cold Hydrogen Plasma Reduction . . . . 5.4 Kinetic Analysis of Hydrogen Plasma Reduction . . . . . . . . . . . . . . . . 5.4.1 Kinetics of Hot Hydrogen Plasma Reduction . . . . . . . . . . . . . 5.4.2 Kinetics of Cold Hydrogen Plasma Reduction . . . . . . . . . . . . 5.5 Industrial Practice of Hydrogen Plasma Reduction . . . . . . . . . . . . . . 5.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

219 219 219 220 224 226 226 229 232 232 241 251 251 262 268 272 273

6 The Behavior of Hydrogen in BF Ironmaking . . . . . . . . . . . . . . . . . . . . . 6.1 Progress and Challenges of Modern Blast Furnaces . . . . . . . . . . . . . . 6.1.1 Proposition of Low-Carbon Blast Furnace Ironmaking Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1.2 Development of Blast Furnace Hydrogen-Rich Metallurgy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Thermodynamics of Hydrogen Reaction in BF . . . . . . . . . . . . . . . . . . 6.2.1 Utilization Degree of CO and H2 . . . . . . . . . . . . . . . . . . . . . . . 6.2.2 Reduction Thermodynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.3 Thermodynamics of Reduction with H2 – Gas Mixtures . . . . 6.2.4 Thermodynamic Behavior of Iron Oxide Reduction for Different H2 –CO Ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 Reaction Kinetics of Hydrogen in BF . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.1 Kinetic Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.2 Mechanism of Iron Oxide Reduction with Hydrogen in BF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.3 Calculation of the Hydrogen Reduction Kinetics . . . . . . . . . . 6.3.4 Kinetic Model of Iron Oxide Reduction with H2 –CO Gas Mixture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4 Effect of Hydrogen Enrichment on the Smelting State of BF . . . . . . 6.4.1 Effect of Hydrogen Enrichment on the BF Temperature and Concentration Fields . . . . . . . . . . . . . . . . . .

277 277 278 280 282 283 283 286 288 293 293 294 294 300 306 306

Contents

6.4.2 Effect of Hydrogen Enrichment on the Performance of Blast Furnace Charge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.3 Effect of H2 Content in Coal Injection on Blast Furnace . . . 6.4.4 Effect of Hydrogen-Rich Gas Reduction on Blast Furnace Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.5 Issues in the Hydrogen-Rich Blast Furnace . . . . . . . . . . . . . . 6.5 Exploration and Practice of Hydrogen-Rich Blast Furnace Smelting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.1 COURSE50 in Japan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.2 German Blast Furnace Hydrogen Injection . . . . . . . . . . . . . . . 6.5.3 Blast Furnace Gas Injection in Russia . . . . . . . . . . . . . . . . . . . 6.5.4 Blast Furnace Gas Injection in China . . . . . . . . . . . . . . . . . . . 6.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Hydrogen Behavior in the Sintering Process . . . . . . . . . . . . . . . . . . . . . . 7.1 An Overview of Hydrogen Behavior in Sintering . . . . . . . . . . . . . . . . 7.1.1 Development of Super-SINTER . . . . . . . . . . . . . . . . . . . . . . . . 7.1.2 Technological Principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Mechanisms of Hydrogen-Rich Effects on the Sintering Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.1 Effects of Gaseous Fuel Injection Method on Sintering Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.2 Effect of Gaseous Fuel Injection on Temperature Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.3 Effect of LNG Injection on the Interlayered Pores . . . . . . . . 7.2.4 Effects of LNG Injection on Permeability . . . . . . . . . . . . . . . . 7.3 Behavior of Hydrogen and Carbon During Sintering . . . . . . . . . . . . . 7.3.1 Effect of Hydrogen and Carbon on the Sinter Bed . . . . . . . . . 7.3.2 Mineral Phases of Sinter Ore . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.3 Economic and Technical Indicators of Sintering . . . . . . . . . . 7.3.4 Reduction Behavior of Iron-Containing Charge in a Hydrogen-Rich Atmosphere . . . . . . . . . . . . . . . . . . . . . . . 7.4 Hydrogen-Rich Practice in Sintering . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.1 Hydrogen-Rich Sintering in China . . . . . . . . . . . . . . . . . . . . . . 7.4.2 Recent Developments in Hydrogen Sintering . . . . . . . . . . . . . 7.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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312 315 319 322 325 325 330 332 334 337 339 341 341 341 343 347 347 350 350 353 355 355 356 360 366 373 373 378 382 383

8 Future Prospects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385

About the Authors

Prof. Dr. Jianliang Zhang is a full professor of metallurgical engineering at the University of Science and Technology Beijing (USTB). He is currently the honorary professor of the University of Queensland. Professor Zhang was awarded the honors of Beijing Excellent Teacher, National Outstanding Scientist, and special allowance expert of the State Council. Professor Zhang is the dean of the School of Metallurgical and Ecological Engineering of USTB. He serves as chairman of the Ironmaking Branch of the Chinese Society for Metals, secretary of the World Steel Development Research Institute, deputy leader of the National Hydrogen Metallurgy Standard Working Group, director of the Key Laboratory of Metallurgical Industry Safety Risk Prevention and Control Department, deputy director of the Collaborative Innovation Center of HBIS and USTB, deputy director of the Green Low Carbon and Comprehensive Utilization of Resource Laboratory of Jianlong Group and USTB, director of Green Manufacturing Institute of Baowu Group and USTB, and director of the Wei Shoukun Award Office of USTB. Professor Zhang has long been engaged in the research on the Low-carbon Ironmaking, Hydrogen Metallurgy, Optimization Control Technology of Ironmaking Process, Reaction Mechanism of Metallurgical Process, Direct Reduction Ironmaking, Comprehensive Utilization of Resources and Metallurgical Process Expert Systems. He has presided over more than 300 research projects including National Science and Technology Major Project. Professor Zhang has maintained xvii

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About the Authors

close cooperation with RWTH Aachen University, University of Toronto, University of Leoben, University of Queensland and University of Wollongong. Professor Zhang has won one second prize of the National Science and Technology Progress Award and 37 provincial-level science and technology progress awards. He has obtained one national standard approval and one group standard approval. He has published over 1000 papers and has been selected as “Highly Cited Researchers in China” by Elsevier in 2021 and 2022. He has been granted 76 patents and published 12 monographs. Prof. Dr. Kejiang Li is a full professor at the School of Metallurgy and Ecological Engineering, University of Science and Technology Beijing (USTB). He is also the deputy secretary-general of the Metallurgical Reaction Engineering Branch of the Chinese Society of Metals (CSM), a young editorial board member of the International Journal of Minerals, Metallurgy and Materials (IJMMM) and China Metallurgy journals. He has been awarded the China Association of Science and Technology (CAST) Young Talent Support Project. Kejiang Li got his Ph.D. from the USTB and the University of Toronto (for joint study) in 2017, then joined USTB as a specially appointed associate professor in the same year, and was promoted to professor in 2021. Kejiang Li is dedicated to studying metallurgical reaction processes and improving metallurgical technology from the microscopic atomistic scale to the macroscopic process scale. He has published more than 80 SCI papers as the first/ corresponding author in recent years, with a citation rate of more than 1800 times and an H factor of 23. He has authorized more than 10 patents, published one Chinese monograph, and co-edited one English monograph. His research results promote the interdisciplinarity of metallurgical engineering, computational chemistry, highperformance computing and artificial intelligence, and at the same time provide the theoretical and technological basis for the realization of carbon neutrality in the iron and steel industry. Kejiang Li has presided two projects of the National Natural Science Foundation of China, and participated in more than 10 lowcarbon metallurgy projects of Baowu Group and other

About the Authors

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enterprises, two of which were recognized as international leading by the China Society for Metals’ technical appraisal. He has won three provincial and ministerial awards, including the Metallurgical Science and Technology Award of China Society for Metals and the China Industry-University-Research Cooperation Innovation and Promotion Award, and has served as a reviewer for more than 20 international journals.

Chapter 1

Introduction

1.1 Low-Carbon Technologies: Global Trends and Developments 1.1.1 The Current Situation and Impacts of Carbon Emissions Global warming has exacerbated the instability of the climate system. As the most important component of greenhouse gases, CO2 has become the focus of energy conservation and emission reduction. Coping with global climate change is one of the biggest challenges for China, the largest carbon emitter with the largest population in the world and for achieving socialist modernization. However, it also provides a big opportunity towards achieving green industrialization, urbanization, and modernization of agricultural and rural areas. On November 3, 2020, during the Fifth Plenary Session, the 19th Central Committee of the Communist Party of China (CPC) adopted the “Proposals of the Central Committee of the Communist Party of China on Formulating the Fourteenth Five-Year Plan for National Economic and Social Development and the Long-term Goals for 2035” (Proposal of the Central Committee of the Communist Party of China on Formulating the Fourteenth Five-Year Plan for National Economic and Social Development and the Visionary Goals for 2035 2020). It was proposed to support green technology innovation, to promote the green transformation of key industries and important fields, to reduce the intensity of carbon emissions, and to formulate action plans for peaking carbon emissions by 2030. China will follow the guidelines including establishing and improving an economic system of green, low-carbon, and circular development, promoting a comprehensive and green transformation of economic and social development, effectively controlling greenhouse gas emissions, and coordinating high-quality development and high-level protection at present and in the future.

© Metallurgical Industry Press 2024 J. Zhang et al., Primary Exploration of Hydrogen Metallurgy, https://doi.org/10.1007/978-981-99-6827-5_1

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According to the data released by the International Energy Agency (IEA) (Fig. 1.1 IEA), total amounts of global carbon emissions related to energy consumption have grown rapidly since World War II. The reduction in energy demand caused by the global epidemic in 2020 resulted in significant reduction in CO2 emissions. However, after the epidemic stabilizes and industries resume stable operation, carbon emissions worldwide are expected to inevitably rebound. In recent years, the relative proportions of industry in energy consumption and CO2 emissions are 33% and 40% respectively from a global perspective. The CO2 emissions of the iron and steel industry, about 33.8%, account for a large proportion of total industrial emissions. The relative proportion of CO2 emissions from the petrochemical industry is about 30.5%(Pei and Pengli 2018). Figures 1.2 and 1.3 show the world’s CO2 emissions as per the industrial sector and China’s share of CO2 emissions by various industries in 2018 (according to the latest data updated by the IEA in 2018). It is seen that the thermal power generation industry has always been the largest emitter of carbon dioxide, while the relative share of the industry in total emissions has tended to decrease. In terms of carbon emissions, China, the United States, and the European Union rank among the top three among all countries and regions in the world, and their total carbon emissions have exceeded half of the world’s total, accounting for 28.6%, 14.7%, and 11.9%, respectively (Total CO2 emissions 2018). China has made some progress in carbon emission reduction, thanks to the restriction policies and the transformation and upgrading of traditional industries in recent years, but the CO2 emissions from the industry still account for a large share. Scientific research has shown that carbon dioxide, methane, and other greenhouse gases could cause enormous ecological catastrophe for the planet. Figure 1.4 shows the difference between the average temperature around the world in the last 10 years and 50 years ago. The trend of global warming is obvious. With the current global warming of estimated around 1.5 °C, impacts of climate change are already significant such as extreme weather, glacial recession (Cramer et al. 2014), various changes in the timings of seasonal events such as earlier flowering of plants (Field et al. 2014), sea level rise and decrease in the Arctic sea ice (Bahgat and Khedr 2007) etc. Since the 1980s, oceans have absorbed 20–30% of the atmospheric carbon dioxide produced Fig. 1.1 Global energy-related CO2 emissions, 1900–2020

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Fig. 1.2 CO2 emissions in various sectors of the world, 1990–2018 Fig. 1.3 The proportion of CO2 emissions in various fields in China, 2018

by humans, resulting in ocean acidification (Srocc Summary and for Policymakers. 2019). Since 1970s, oceans have absorbed more than 90% of the excess heat from the climate system (Srocc Summary and for Policymakers 2019), leading to warmer oceans. These changes have severely impacted ecosystems and human livelihoods while exacerbating desertification and land degradation in many parts of the world. Food insecurity in many regions has deteriorated and the imbalance between the supply and demand of fresh water has intensified. The environmental problems caused by climate change are increasing year by year, and greenhouse gas emissions from the use of conventional energy sources are also increasing. So, the key to stabilizing the climate is to reduce the use of conventional energy sources such as coal and other carbon-based fuels to the extent possible.

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Fig. 1.4 Comparison of annual average temperature difference before and after industrialization (Data from five databases)

The “Emissions Gap Report 2020” (United Nations Environment Programme 2020) of the United Nations has pointed out that the global greenhouse gas emissions have increased by an average of 1.4% per year since 2010, and global temperatures are expected to exceed 3 °C by the end of the twenty-first century, well above the 2 °C target originally planned by the Paris Agreement. It also mentioned that in the next 10 years, global carbon emissions will need to drop by 7.6% per year. As the economic development of densely populated developing countries such as China and India have entered an energy-intensive stage in recent years, the energy demand is expected to increase further, and the environmental problems to become even more serious. With the increasing global demand for fossil energy, the development of new energy industries and low-carbon processes are in line with the concept of a low-carbon economy and environmental protection requirements.

1.1.2 Targets and Policies of Low-Carbon Emission Reduction In 1992, the Intergovernmental Panel on Climate Change (IPCC) adopted the United Nations Framework Convention on Climate Change (United Nations Environment Programme 2020), and in 1997, the Kyoto Protocol (Wei 2016), the first additional agreement to the Convention, was passed in Kyoto, Japan. In this agreement, the market mechanism was proposed as a method to solve the problem of greenhouse gas emissions. In other words, a CO2 emission right-trading system was built up, which can be shortened to carbon trading. Since January 1, 2005, the emission reduction targets of the Kyoto Protocol are allocated to each member state by the EU, and each country allocates emission quotas to enterprises according to the national plan.

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After the enterprise meets the requirements of reducing CO2 emissions, it can sell the rest of the emission rights to those enterprises that have not fulfilled the target. That is the European Union Emission Trading Scheme (EU-ETS) (EU 1009). Since the second phase of the implementation of the EU Emission Trading Scheme in 2008, the trading market has covered 45% of carbon dioxide emissions and nearly 40% of total greenhouse gases, and it has become the world’s largest carbon emissions trading market (Siqi and Jingjing 2020). At present, there are 21 carbon emissions trading schemes in operation in the world, covering about 10% of global carbon emissions. As of the end of 2019, the carbon market has raised more than US$78 billion in total, and the global carbon financial market has an annual transaction volume of more than US$60 billion. The Paris Agreement took effect in November 2016, becoming the third international legal document after the United Nations Framework Convention on Climate Change and the Kyoto Protocol. It suggested, a restraint mechanism from 2023 to conduct regular assessments on the effects of countries’ actions every five years and proposed a goal that the average temperature rise in the world should be controlled within 1.5–2.0 °C. In November 2019, Germany passed the Climate Protection Law, which for the first time sets medium and long-term goals of Germany’s greenhouse gas emission reduction in a legislative form, including net zero greenhouse gas emissions by 2050 and carbon neutrality as a special responsibility of industrial power and the strongest member state in the economy of the EU. The draft of the European Climate Law submitted by the European Commission in March 2020 also clarified the goal of achieving carbon neutrality by 2050 in a legislative form. Developed European countries have generally proposed 2050 as the target date, while Nordic countries Finland and Iceland have advanced the target year to 2035–2040. In terms of staged goals, the realization of carbon neutrality still requires countries to propose medium-term emission reduction targets. For example, the EU has proposed to strengthen its emission reduction target in 2030, from 40% in 1990 down to 55%. The impact of sudden COVID-19 epidemic has also triggered further global reflection on climate change and ecological protection. While committing themselves to achieving economic recovery, countries have also taken to revitalizing climate governance and building a sustainable society as important tasks. Table 1.1 shows the carbon neutrality goals announced by countries around the world. So far, 30 countries and regions have clarified their carbon neutrality goals. Among them, Suriname and Bhutan have already achieved carbon neutrality. Seven countries including Sweden and the United Kingdom have enacted legislation. The EU (as a whole) and three countries and regions are in a state of legislation, and 15 countries including China and Japan have published policy statement documents. In September 2009, then President Hu Jintao first proposed China’s 2020 relative emission reduction targets when he attended the United Nations Climate Change Conference (Jintao 2009). The first target was to strive to reduce carbon dioxide emissions per unit of GDP by 40–45% compared with 2005 by 2020. The second one was that non-fossil energy accounts for about 15% of primary energy consumption. The third one was to increase the forest area by 40 million hectares and the forest growing stock by 1.3 billion cubic meters compared with 2005. The fourth

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Table 1.1 Summary of carbon neutrality goals of various countries Country/ region

Target date

Types of commitment

Additional details

China

2060

Policy statement

China announced to the United Nations General Assembly on September 22, 2020, that it is striving to achieve carbon neutrality by 2060 and that it will adopt “stronger policies and measures” to achieve peak emissions by 2030

Austria

2040

Policy statement

Austria’s coalition government, sworn in January 2020, pledged to achieve climate neutrality by 2040 and 100% of clean electricity by 2030 based on binding carbon emissions targets

Bhutan

Carbon neutrality has been achieved and is now carbon negative

Voluntary emission reduction plan under the Paris Agreement

With a population of less than 1 million, low incomes, surrounding forests and hydroelectric resources, it was easier for Bhutan to balance carbon accounts than most countries. However, economic growth and growing demand for cars are putting pressure on emissions

California, USA

2045

Executive order

California’s economy is the fifth largest in the world. Former Gov. Jerry Brown signed a carbon neutrality order in September 2018, and the state passed a law almost simultaneously to make electricity 100 percent renewable by 2045. However, green policies are not yet mature in other industries

Canada

2050

Policy statement

Prime Minister Justin Trudeau was re-elected in October 2019 with policies centered on climate action, promising net-zero emissions targets, and a legally binding five-year carbon budget

Chile

2050

Legal provisions

President Piñera announced in June 2019 that Chile is working towards carbon neutrality. In April 2020, the government submitted a strengthened medium-term commitment to the United Nations, reaffirming its long-term goals. Chile has identified eight of its 28 coal-fired power plants to close by 2024 and phase out coal power by 2040 (continued)

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Table 1.1 (continued) Country/ region

Target date

Types of commitment

Additional details

Costa Rica

2050

Submitted to the United Nations

In February 2019, President Quezada laid out a climate policy package, and a plan submitted to the United Nations in December that identified net zero emissions by 2050

Denmark

2050

Legal provisions

The Danish government laid out a plan in 2018 to create a “climate-neutral society” by 2050, which includes banning the sale of new petrol and diesel cars from 2030 and supporting electric vehicles. Climate change was a major theme in parliamentary elections in June 2019, with the winning “red bloc” parties setting tougher emissions targets, and a legislation was passed six months later

European Union

2050

Submitted to the United Nations

The European Commission is working towards a 2050 net-zero emissions target across the EU under the “Green Deal” announced in December 2019, a long-term strategy presented to the UN in March 2020

Fiji

2050

Submitted to the United Nations

As the chair of 2017 UN Climate Change Conference (COP23), Fiji has gone the extra mile to demonstrate its leadership. In 2018, the Pacific Island nation submitted a plan to the United Nations that aims to achieve net carbon zero across all economic sectors

Finland

2035

Ruling party coalition agreement

Finland’s five political parties agreed in June 2019 to strengthen the climate laws. The target is to require limiting industrial logging and phasing out the burning of peat for power generation

France

2050

Legal provisions

The French National Assembly voted on June 27, 2019, to put the net-zero target into law. In its June report, the newly formed High Commission on Climate recommended that France must triple the rate of emission reductions to achieve its carbon neutrality goal

Germany

2050

Legal provisions

Germany’s first major climate law, which came into force in December 2019, says Germany will “pursue” greenhouse gas neutrality by 2050 (continued)

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Table 1.1 (continued) Country/ region

Target date

Types of commitment

Additional details

Hungary

2050

Legal provisions

Hungary pledged to achieve climate neutrality by 2050 in the climate law passed in June 2020

Iceland

2040

Policy statement

Iceland already gets nearly carbon-free electricity and heating from geothermal and hydropower, and a strategy announced in 2018 focused on phasing out fossil fuels in transport, planting trees, and restoring wetlands

Ireland

2050

Ruling party coalition agreement

In a joint agreement finalized in June 2020, the three parties agreed to legally set a net-zero emissions target for 2050, cutting emissions by 7% a year over the next decade

Japan

Early in the second half of the twenty-first century

Policy statement

The Japanese government approved a climate strategy in June 2019 ahead of hosting the G20 leaders’ summit, focusing on the capture, utilization, and storage of carbon and the development of hydrogen as a source of clean fuel. Notably, there is no plan to phase out coal, which is expected to still supply a quarter of the country’s electricity by 2030

Marshall Islands

2050

A voluntary emission reduction commitment submitted to the United Nations

The latest report, presented to the United Nations in September 2018, laid out an aspiration to achieve net-zero emissions by 2050, although there are no specific policies to make it happen

New Zealand

2050

Legal provisions

New Zealand’s largest source of emissions is agriculture. A law passed in November 2019 sets a net-zero target for all greenhouse gases except biomethane (mainly from sheep and cattle), which will reduce biomethane by 24–47% from 2017 levels by 2050

Norway

2050/2030

Policy statement

Norway’s parliament, one of the first in the world to discuss climate neutrality, is working towards carbon neutrality through international offsets by 2030 and domestically by 2050. But this commitment is a policy intent, not a binding climate law (continued)

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Table 1.1 (continued) Country/ region

Target date

Types of commitment

Additional details

Portugal

2050

Policy statement

Portugal is one of the member states calling on the EU to adopt a net-zero emissions target for 2050. It has released a roadmap to net-zero emissions in December 2018, outlining strategies for energy, transport, waste, agriculture, and forests

Singapore

Early in the second half of the twenty-first century

Submitted to the United Nations

Like Japan, Singapore has avoided committing to a clear decarbonization date but made it the goal of a long-term strategy submitted to the United Nations in March 2020. By 2040, internal combustion vehicles will be phased out and replaced by electric vehicles

Slovakia

2050

Submitted to the United Nations

Slovakia was one of the first EU member states to formally submit a long-term strategy to the United Nations, with the goal of becoming “climate neutral” by 2050

South Africa

2050

Policy statement

The South African government published the Low Emissions Development Strategy (LEDS) in September 2020, outlining its goal of becoming a net zero economy by 2050

Korea

2050

Policy statement

The Democratic Party of Korea returned to power in a landslide in the April 2020 elections. Voters back its “Green New Deal” to decarbonize the economy by 2050 and end coal financing. It was the first of its kind in East Asia and a big deal for the world’s seventh-largest carbon dioxide emitter. Korea, which generates about 40 percent of its electricity from coal, has been a major financier of overseas coal plants

Spain

2050

Draft bill

The Spanish government submitted a draft climate framework bill to parliament in May 2020, established a committee to monitor progress, and immediately banned new coal, oil, and gas exploration licenses (continued)

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Table 1.1 (continued) Country/ region

Target date

Types of commitment

Additional details

Sweden

2045

Legal provisions

Sweden set its net-zero emissions target in 2017, bringing forward carbon neutrality by five years under the Paris Agreement. At least 85% of emissions reductions will be achieved through domestic policies, with the rest made up by international emissions reductions

Switzerland 2050

Policy statement

The Swiss Federal Council announced on 28 August 2019 that it intended to achieve net-zero carbon emissions by 2050, enhancing the Paris Agreement target of a 70–85% reduction. Parliament is revising its climate legislation, including developing technology to remove carbon dioxide from the air (one of the most advanced pilot projects in this area in Switzerland)

United Kingdom

2050

Legal provisions

The UK already passed an Emissions Reduction Framework Act in 2008, so setting a net zero target is as simple as changing 80–100%. Parliament passed the amendment on June 27, 2019. Scotland’s parliament is working on a bill to achieve net-zero emissions by 2045, based on Scotland’s strong renewable energy resources and ability to store carbon dioxide in depleted North Sea fields

Uruguay

2030

Voluntary emission reduction commitments under the Paris Agreement

Uruguay is expected to become a net carbon sink by 2030, according to Uruguay’s national report to the UN Convention, coupled with policies to reduce beef farming, waste, and energy emissions

one was to vigorously develop a green, low-carbon, and circular economy. At the same time, he also pointed out that China is a developing country, and it is unable to undertake absolute quantitative emission reduction targets that exceed the country’s capacity or development level. In November 2014 and September 2015, President Xi Jinping and then U.S. President Barack Obama twice announced the China-US Joint Announcement on Climate Change (China-U et al. xxxx), announcing their respective actions on climate change after 2020. According to these statements, in November 2015, at the summit of the 21st United Nations Climate Change Conference (COP21), President Xi Jinping expressed his expectations for the Conference

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in Paris and his views on global governance on behalf of China. Here, for the second time, China put forward the 2030 relative emission reduction action targets. The first target is that China will achieve carbon peaking around 2030 and strive to reach the peak as soon as possible. The second one is to reduce carbon dioxide emissions per unit of GDP by 60–65% as compared with 2005. The third one is that non-fossil energy accounts for about 20% of primary energy consumption, and the fourth one is to increase the forest growing stock by 4.5 billion cubic meters as compared with 2005. President Xi Jinping has pointed out several times that tackling climate change is an inherent requirement for China’s sustainable development, and it is also an international obligation that a responsible major country should fulfill. This is not what others ask us to do, but what we are willing to do. The political commitment of China is reflected in the actual governance, and the results can be seen in the present. By 2019, China’s carbon dioxide emissions per unit of GDP have dropped by about 18.2% and 48.1% as compared with 2015 and 2005 respectively (Ministry of Ecology and Environment 2020). These achievements exceeded the country’s commitment to the international community and helped reverse the rapid growth of greenhouse gas emissions. China achieved and exceeded the 2020 climate action targets ahead of schedule. In addition, the proportion of nonfossil energy in primary energy consumption in China increased from 7.4% in 2005 to 15.3% in 2019. The proportion of total renewable energy consumption in the world increased from 2.3% in 2005 to 22.9% in 2019. It has exceeded the corresponding proportion of the United States, which is 20.1%. Compared with 2005, the forest area has increased by 45 million hectares, and the forest growing stock also increased by 5.1 billion cubic meters. As President Xi Jinping said, the Paris Agreement represents the general direction of the global green and low-carbon transition. It is the minimum action that we need to take to protect the earth. Actions must be taken. To this end, China took the lead in proposing new goals in September 2020 of carbon peaking by 2030 and carbon neutrality by 2060, and proposed to further improve the nationally determined contribution at the Climate Ambition Summit on December 12, 2020 (Jinping 2020). By 2030, China’s carbon dioxide emissions per unit of GDP will reduce by more than 65% as compared with 2005, the proportion of non-fossil energy in primary energy consumption will reach about 25%, the forest growing stock will increase by 6 billion cubic meters as compared with 2005, and the total installed capacity of wind power and solar power will reach more than 1.2 billion kilowatts. These are the “2030 China carbon emission reduction targets”.

1.2 Trends in Global Hydrogen Energy Development The low-carbon transformation of the energy system is an important direction of carbon neutrality from the perspective of the deployment of low-carbon technologies in various countries. As an emerging strategic energy, hydrogen energy has the characteristics of abundant sources, high thermal efficiency, and high energy density.

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It is also clean, transportable, storable, as well as renewable. It has been included in the national energy strategic deployment of many countries and has an important role in the transformation to the future structure of global energy. The guidelines (National Energy Administration 2020) issued by the National Energy Administration on June 22, 2020, pointed out that it is necessary to formulate and implement a development plan for the hydrogen energy industry, conduct key technical equipment research, and actively promote application demonstrations. Direct reduction using hydrogen is indeed expected to be more energy-efficient than coal, and the amounts of hydrogen required for steelmaking will depend on various factors, including the type of process used. A ton of finished steel will require about 3 MWh of hydrogen, which is considerably less than the 6 MWh needed for coal-based processes. However, the process of making hydrogen will incur additional energy losses, which could increase the amount of electrical energy required by up to between 4 and 4.5 MWh per ton of steel. Assuming a ton of steel requires 90 kg of H2 , the production of 1,350 million tons of steel would use about 122 million tons of hydrogen. This amount is higher than 50% current world production of hydrogen. It is also important to note that the transition to hydrogen-based steelmaking will require significant investments in new infrastructure and technology as well. Additionally, increasing hydrogen production to meet the demand of the steel industry will require significant renewable energy capacity, as expanding hydrogen production based on fossil fuels would undermine the environmental benefits of switching to hydrogen in the first place. So far, hydrogen energy has been a strategic choice for China to optimize its energy consumption structure and to ensure the security of the national energy supply. In the development of hydrogen energy and fuel cells, the country is currently following in the footsteps of developed countries around the world. At present, it has formulated a research and development system and production and manufacturing capabilities for fuel cells, piles, and hydrogen fuel cells, and has successively carried out demonstration operations focusing on commercial vehicles such as passenger transport and logistics. China is a major producer and consumer of hydrogen. In 2016, the country’s hydrogen production capacity reached 70 billion cubic meters per year. On October 28, 2016, the Blue Book jointly compiled by the China National Institute of Standardization and the National Standardization Technical Committee first proposed the strategies for infrastructure development and technological development of China’s hydrogen energy industry and put forward policy recommendations on accelerating the infrastructure development of this industry. It is predicted that the gross value of China’s hydrogen energy industry will reach about 144 billion USD in 2030, and the total hydrogen production capacity will be ~100 billion cubic meters per year. The hydrogen energy industry will become a new economic growth point and an important part of the new energy strategy. In 2050, the gross value of the hydrogen energy industry will be about 430 billion USD. Hydrogen energy will become an important part of the energy structure, and this industry will become an important part of China’s industrial structure. China attaches great importance to the development of this industry and the construction of related supporting facilities. In 2019, hydrogen energy was written in the Government Work Report for the first time which required “promoting the construction of facilities such as charging and

1.2 Trends in Global Hydrogen Energy Development

13

hydrogen refueling”. Since then, the development of the hydrogen energy industry has accelerated significantly. At the same time, from national departments to local governments, many policies and plans to promote the development of hydrogen energy have been formulated, and related management policies and goals are also being advanced (Table 1.2). The policies mainly focus on transportation, including the technological research and development of hydrogen fuel cell vehicles, key equipment manufacturing, hydrogen refueling station construction, etc., while rail transit is one of the future development priorities of hydrogen fuel cell technology. Meanwhile, hydrogen metallurgy has become a new application field of the hydrogen energy industry, and many metallurgical enterprises are introducing new advanced hydrogen metallurgy technology from abroad, which will help realize the revolutionary green transformation of China’s iron and steel industry. Chemical processing of green hydrogen and coal, green hydrogen trade, and domestic liquid hydrogen will also be important directions for the future development of the hydrogen energy industry. As for other countries, the development orientation of the hydrogen energy industry in the world’s major countries also includes a clear development strategy and industrial positioning, the division of labor in relevant government departments, the technical route of hydrogen production, the promotion of pilot demonstrations and multi-field applications of hydrogen fuel cells, support of technology research and development of these fuel cells, continuous improvements in the policy system of the hydrogen energy industry, etc. The U.S. Department of Energy released the “Road Map to a US Hydrogen Economy” in 2002, proposing a development blueprint based on the hydrogen energy economy, and proposed the goal of fully realizing the hydrogen economy by 2040. It listed hydrogen energy as one of the main energy options in 2005 and proposed to promote its large-scale production and application in 2015. The Japanese government put forward the strategic direction of building and developing a hydrogen energy society in the Fourth Energy Basic Plan in 2014. And in 2018, the Korean government released a plan for the establishment of a hydrogen energy economy and society. The goal was to use renewable energy, natural gas, water, etc. to produce hydrogen, and to build a sustainable, low-carbon society with hydrogen energy as the main energy source. On June 10, 2020, Germany finalized the national hydrogen strategies (Li 2020), confirming the priority of green hydrogen, and clarifying the main application fields of hydrogen energy. According to the German official data, Germany currently produces about 20% of the world’s hydrogen energy. In July 2019, German Minister of Economic Affairs, Peter Altmaier, announced that Germany hoped to become the leading country in hydrogen energy technology. The German government has announced an economic recovery plan of 130 billion euros and proposed to invest at least 9 billion euros for developing hydrogen energy. According to the hydrogen strategies determined, hydrogen energy in Germany will be mainly used in shipping, aviation, heavy cargo transportation, steel, and chemical industries. By 2040, Germany will build 10 gigawatts (GW) of electrolytic green hydrogen capacity domestically at the latest, half of which will be built by 2030, including the construction of additional renewable energy devices needed. In addition, most of Germany’s

14

1 Introduction

Table 1.2 National and local policies of the hydrogen energy industry from 2019 to 2020 Serial number

Region/ department

Time

Policy

1

Seven departments including the National Development and Reform Commission

February 14, 2019

Green Industry Encourage the development, Guidance Catalog construction and operation of (2019) hydrogen energy utilization facilities, fuel cell equipment, and applications in new energy vehicles and ships

2

The State Council

April 9, 2019

Implement the opinions on the division of labor of key work departments in the “Government Work Report”

Continue to implement the preferential policies for the purchase of new energy vehicles, and promote the construction of charging, hydrogenation, and other facilities

3

National Development and Reform Commission and joint 14 departments

November 15, 2019

Implementation of opinions on Promoting the Deep Integration and Development of Advanced Manufacturing and Modern Service Industry

Strengthen the green integration of new energy production and use and manufacturing, promote the innovation and cluster development of the hydrogen energy industry, and improve facilities and services such as the hydrogen energy preparation, storage, and transportation, and refueling

4

National Bureau November of Statistics 2019

Energy Statistical Hydrogen is included in the Statement System 2020 energy statistics along with coal, natural gas, crude oil, electricity, biofuels, etc

5

Ministry of Education, National Development and Reform Commission, and National Energy Administration

Action Plan for Professional Development of Energy Storage Technology (2020–2024)

January 19, 2020

Main content

Focus on promoting basic theoretical research such as fuel cells, phase change energy storage, hydrogen storage, and phase change materials

(continued)

1.2 Trends in Global Hydrogen Energy Development

15

Table 1.2 (continued) Serial number

Region/ department

Time

Policy

Main content

6

Ministry of Science and Technology

March 19, 2020

2020 project application guide for key special projects such as the National Key R&D Program “Manufacturing Basic Technology and Key Components”

A total of 38 key research tasks were deployed. In 2020, 14 to 28 projects were planned to be launched in 4 technical directions of hydrogen energy, solar energy, wind energy, and renewable energy coupling and system integration. The total budget to be allocated from the state was 606 million yuan

7

National Energy April 10, 2020 Administration

Energy Law of the Listed hydrogen energy as People’s Republic one of the energy types in the of China (Draft draft for Comments)

8

National Energy May 19, 2020 Administration

Guiding Opinions on Establishing and Improving a Long-term Mechanism for Clean Energy Consumption (Draft for Comments)

The establishment of a clean energy on-site consumption model will be explored. Encourage clean energy-rich areas to promote applications such as hydrogen production from electrolysis, take various measures to increase demand for power consumption, and expand local consumption space

9

Qinghai Province

January 15, 2020

2020 Qinghai Provincial Government Work Report

Build a national clean energy demonstration province, study and plan hydrogen, and nuclear energy utilization projects

10

Tianjin

January 21, 2020

Tianjin Action Plan on the Hydrogen Energy Industry Development (2020–2022)

By 2022, the total output value of the hydrogen energy industry to exceed 15 billion yuan; build at least 10 hydrogen refueling stations and 3 pilot demonstration areas for hydrogen fuel cell vehicles, carry out demonstration operations at 3 bus or commuter lines at least, and build at least 2 hydrogen fuel battery cogeneration demonstration projects (continued)

16

1 Introduction

Table 1.2 (continued) Serial number

Region/ department

Time

Policy

Main content

11

Maoming City

March 4, 2020

Maoming Hydrogen Energy Industry Development Plan (Draft for Comments)

The hydrogen energy industry development strategy of “one goal, two core areas, three application fields, and tens of billions of output value” was proposed. A “three-step” goal was proposed, i.e., the total output value of the hydrogen energy industry is expected to reach 3 billion yuan in 2022, 10 billion yuan in 2025, and 30 billion yuan in 2030

12

Zhangjiakou City

March 6, 2020

Implementation plan for the construction of the first phase of the Zhangjiakou hydrogen energy guarantee supply system

Hydrogen production capacity: Before the 2022 Winter Olympics, the hydrogen production capacity will reach 10,000t/a. Hydrogen refueling stations: 16 stations will be constructed in the first phase of the project, of which 10 stations will be completed by the end of 2020, and 6 stations will be completed by the end of June 2021

13

Shandong Province

March 26, 2020

Action Plan for the Construction of International Business Innovation Industrial Park in Jinan, Qingdao, and Yantai (2020–2025)

Build a “Chinese Hydrogen Valley” in Jinan and an “Oriental Hydrogen Island” in Qingdao, involving hydrogen fuel cell vehicle manufacturing and other fields

(continued)

1.2 Trends in Global Hydrogen Energy Development

17

Table 1.2 (continued) Serial number

Region/ department

Time

Policy

Main content

14

Hebei Province

April 24, 2020

Opinions of the General Office of the People’s Government of Hebei Province on Accelerating the Promotion of Key Breakthroughs in the Construction of the “Two Districts” for the Capital

To promote the construction of an innovation center for the hydrogen energy industry, formulate and revise a batch of national, industry, and enterprise standards for this industry, and promote the commissioning of hydrogen fuel cell engines, large-scale wind-solar storage complementary hydrogen production, and hydrogen fuel cell bus projects. The number of hydrogen refueling stations to reach a total of 10, and the construction of a hydrogen energy industry ecological park to be accelerated

15

Tongling City

April 28, 2020

The Outline of the Plan for the Development of the Hydrogen Energy Industry in Tongling

In 2022, more than 20 hydrogen energy enterprises will be cultivated, and the related output value of hydrogen energy to reach 1.5 billion to 3 billion yuan. In 2025, more than 30 enterprises will be cultivated, and the output value will reach 8 billion to 10 billion yuan, and by 2030, it will reach 30 billion to 50 billion yuan

green hydrogen needs will be met through imports. Among them, European countries around the North Sea and the Baltic Sea, as well as southern European countries will be potential suppliers of green hydrogen to Germany. Meanwhile, during the transition period, “blue hydrogen” made from fossil fuels but combined with carbon capture technology will be put into use. On July 9, 2020, Frans Timmermans, Vice President of the European Commission, officially announced the long-awaited “EU Hydrogen Strategy” (Li 2020; Yifan 2020). This 24-page plan is regarded as one of the important blueprints for the energy industry in Europe and an important part of the EU’s economic stimulus plan after the COVID-19 outbreak. The European Commission said that the development of its hydrogen energy will be carried out in three stages (Beiling 2020). In the first stage (2020–2024), a batch of renewable hydrogen electrolysis equipment with a

18

1 Introduction

single power of 100 MW will be built in the EU. By 2024, the total power of renewable hydrogen production in Europe will reach 6000 MW, and the annual output will exceed 1 million tons. In the second stage (2025–2030), it will continue to increase the production capacity of renewable hydrogen and several regional centers of industrial hydrogen production called “hydrogen valleys” will be built. They are also the framework of the future pan-European hydrogen energy network by supplying hydrogen at a lower price to population clusters through scaling effects. The third stage (2031– 2050) will involve the large-scale application of hydrogen energy in energy-intensive industries such as the steel and logistics industries. To ensure the implementation of this strategy, the EU plans to invest 575 billion euros in the hydrogen energy industry in the next 10 years, out of which 145 billion euros will be paid for in tax incentives, carbon permit incentives, financial subsidies, and other forms to benefit relevant hydrogen energy companies. The remaining 430 billion euros will be directly invested in the construction of the hydrogen energy infrastructure. The specific plan for the construction is that 24 billion to 42 billion euros will be invested in the construction of green hydrogen electrolysis facilities before 2030; 220 billion to 340 billion euros will be used to build 80 to 120 GW of the wind-solar hybrid power system. As a new application field of the hydrogen energy industry, hydrogen metallurgy will have a broad development space, which will have a revolutionary impact on China’s strategic goal of carbon neutrality and the green transformation of the iron and steel industry.

1.3 The Transition from Carbon Metallurgy to Hydrogen Metallurgy 1.3.1 Low-Carbonization Trends in the Iron and Steel Industry To achieve carbon neutrality in China, the CO2 gas emitted directly and indirectly by human activities, should be absorbed through carbon capture and storage, or afforestation and other carbon sequestration technologies within a certain period (usually one year). When compared with developed countries such as European countries and the United States, China is facing a daunting task and is pressed for time. China needs to achieve greater levels of carbon neutrality in shorter times than developed countries. In the context of global decarbonization, the technological transformation of traditional metallurgy of iron and steel has been centered on reducing carbon footprint; lowering carbon emissions has become the new trend in the green development of the iron and steel industry. China is the world’s largest steel producer. Over the past 10 years, the country’s crude steel output had increased year by year (Fig. 1.5). In the first quarter of 2020,

1.3 The Transition from Carbon Metallurgy to Hydrogen Metallurgy

19

Fig. 1.5 China’s crude steel production (data from the National Bureau of Statistics, 2011–2020)

steel demand had shrunk significantly under the impact of COVID-19. However, with the resumption of work and production in the country and the gradual effect of economic stimulus policies, the economy and downstream demand steadily recovered in the second quarter. These developments have reinvigorated the enthusiasm of iron and steel enterprises, resulting in the year-on-year growth of iron and steel production. The data shows that from January to December 2020, the national output of pig iron, crude steel and steel was 888 million tons, 1065 million tons, and 1325 million tons with annual growth rates of 4.3%, 5.2%, and 7.7% respectively; the crude steel output had exceeded 1 billion tons for the first time. Since the 19th National Congress of the Communist Party of China, the country’s iron and steel industry had reoriented itself from high quantities of production to high quality steel production, this alleviating the serious issue of overcapacity in China’s iron and steel industry. However, total emissions remain high due to the enormous output from the industry. The strategic focus of China’s iron and steel industry will next shift from reducing the production capacity to optimizing and upgrading the industrial structure to meet the increasingly stringent emission standard requirements for environmental pollutants and win the battle against pollution. Although the rapid development of the iron and steel industry has made great contributions to the Chinese economy, it has also caused serious environmental problems. In the process of crude steel production, 95% of the world’s crude steel is produced through three processes, namely BF-BOF, DRI-EAF, and Scrap-based EAF. 70% of the world’s total crude steel production was produced through the BFBOF process. About 89% of the energy input of the BF-BOF process comes from coal (Fig. 1.6). According to the statistics provided by the International Energy Organization, the iron and steel industry is one of the major emitters of greenhouse gases, accounting for 4–7% of the total anthropogenic emissions of global greenhouse gases (Patisson

20

1 Introduction

Fig. 1.6 Energy consumption in different iron/steelmaking processes in a Blast Furnace-Converter; b Electric Arc Furnace

and Mirgaux 2020). Relevant data shows that the iron and steel industry has become the third largest emitter of carbon dioxide in China, next only to the electricity and building materials industry, accounting for about 15% of the country’s total carbon dioxide emissions. At the same time, other air pollutant emissions from the iron and steel industry also account for a high proportion of China’s industrial pollutant emissions, such as SO2 , NOx , and particulate matter (PM) (accounting for 11.2%, 8.8%, and 29.0%, respectively) (Wang et al. 2020). The industry has been facing increasing pressure to reduce carbon dioxide emissions for some time. Reducing these emissions and developing a low-carbon economy is vital to the future development of the iron and steel industry. In May 2018, a government plan issued by the Ministry of Ecology and Environment required all new and relocated steel projects to reach ultra-low emission levels, and the emission limit was set much lower than the special emission limit standards such as the corresponding Emission Standards for Air Pollutants in Iron and Steel Sintering and Pelletizing Industries issued by the Ministry of Environmental Protection in 2012. In April 2019, China released guidelines demanding the implementation of ultra-low emissions in the iron and steel industry (Administration and of Quality Supervision, Inspection and Quarantine 2012). The guidelines, jointly issued by five ministries including the Ministry of Ecology and Environment, stated that by the end of 2020, significant progress should be made in the ultra-low emission transformation of iron and steel enterprises in key areas, and the country would strive to complete ultra-low emission transformation of about 60% of steel production capacity enterprises. By the end of 2025, the country will complete the environmental protection transformation of iron and steel enterprises in key areas and strive to make more than 80% of these enterprises meet the ultra-low emission requirement (Yi et al. 2021). In December 2017, the national carbon emission trading system was launched officially (Jiacong et al. 2018). Mandatory CO2 emission reduction will force iron and steel enterprises to develop low-carbon technologies. At present,

1.3 The Transition from Carbon Metallurgy to Hydrogen Metallurgy

21

many companies are already developing non-primary energy routes. According to the Report on Energy Conservation and Low-Carbon Development of China’s Iron and Steel Industry (2020), compiled jointly by the Metallurgical Industry Energy Conservation Professional Committee of the China Energy Conservation Association and the Metallurgical Industry Planning and Research Institute, China’s iron and steel industry has made positive progress in energy conservation and emission reduction. In 2019, the comprehensive energy consumption per ton of surveyed iron and steel enterprises was 553.7 kg of standard coal, a reduction of 3.2% compared with 2015, and the energy efficiency index task of the Industrial Green Development Plan (2016–2020) was completed ahead of schedule. On January 4, 2021, the Ministry of Industry and Information Technology issued guidelines demanding the high-quality development of the iron and steel industry. These guidelines proposed that by 2025, the iron and steel industry will form a green, low-carbon, and sustainable development platform with reasonable industrial layout, advanced technology and equipment, high quality and intelligence, and strong global competitiveness. In the green and low-carbon development goals, the completion rate of ultra-low emission transformation in the industry is expected to exceed 80% levels. All enterprises in key areas should complete ultra-low emission transformation, reducing the total pollutant emissions by more than 20%, and both total energy consumption and intensity by more than 5%. Moreover, they should also reduce water resource consumption intensity by more than 10% and achieve a water reuse rate higher than 98%. At present, low carbonization has become a major development trend and an important challenge in the China’s iron and steel industry.

1.3.2 Proposed Concept of Hydrogen Metallurgy Xu Kuangdi (Shaobo 2012) put forward the technical concept of hydrogen metallurgy at the 125th Xiangshan Science Conference in 1999 and the Metallurgical Strategy Forum in 2002. In 2018, Gan Yong (Jue et al. 2020) pointed out that “the twentyfirst century is the era of hydrogen, and hydrogen metallurgy is to replace carbon with hydrogen, it generates water instead of greenhouse gas, and it also has a very fast reaction rate”. We have devoted ourselves to hydrogen metallurgy research for several years with focus on using gaseous hydrogen as the reducing agent in the iron ore reduction and smelting process. The traditional ironmaking process uses a large amount of carbon as a heat source and a reducing agent, which are some of the key processes that emit greenhouse gas (CO2 ). Tables 1.3 shows the carbon emission intensity of crude steel produced by BF-BOF, DRI-EAF, and Scrap-based EAF. In the table, direct emissions refer to the CO2 emissions generated by the consumption of fossil fuels and fluxes by iron and steel enterprises, while indirect emissions refer to those used in steel production but emitted from sources controlled by other entities. For instance, emissions from electricity are generated by the burning of minerals in the electricity production

22

1 Introduction

sector. When iron and steel enterprises use purchased electricity, the CO2 emissions calculated are indirect. At present, more than 90% of the iron and steel industry in China uses the BF-BOF process. In addition to carbon emissions, a series of pollution problems caused by carbon in the down-stream processes, including sintering, pelletizing, coking, and other coal agglomeration processes pose a tough challenge to the ironmaking process. The key to coping with these challenges is to develop a low-carbon ironmaking technology. Relevant calculations (Hongming et al. 2019) show that carbon emissions of the ironmaking system including coking, sintering, pelletizing, and blast furnace ironmaking processes account for 82.79% of the total emissions in iron and steel enterprises. The blast furnace ironmaking accounts for 67.02% of carbon emissions, while sintering accounts for 8.54% and coking 6.13%. In addition to producing large amounts of CO2 , smelting processes in carbon metallurgy also release several harmful elements present in the carbon-containing raw material as well as harmful pollutants such as SOx , NOx , and dioxin (Sha 2020). Whereas the H2 O produced during hydrogen reduction can coexist in harmony with nature. C + Fex O → CO + Fe

(1.1)

CO + O2 → CO2

(1.2)

H2 + Fex O → H2 O + Fe

(1.3)

Moreover, in carbon metallurgy, the conversion of solid carbon such as coke into CO takes place under incomplete combustion conditions for the reduction reaction, whereas hydrogen gas directly participates in the reduction reactions without any conversion. Therefore, theoretically, hydrogen metallurgy has great advantages in reduction efficiency and reduction rate (Taiyan et al. 2005). Vigorously developing hydrogen-rich metallurgy is of great significance for reducing CO2 emissions and ensuring the sustainable development of the iron and steel industry. In the guidelines issued on January 4, 2021, the Ministry of Industry and Information Technology has pointed out that they will support the establishment of a low-carbon metallurgical innovation alliance for iron and steel, with greater efforts in hydrogen energy Table 1.3 Carbon emission intensity of crude steel produced by different processes (t/t) Source

BF-BOF

DRI-EAF

Scrap-based EAF

IEA (Direct emissions)

1.2

1.0

0.04

IEA (Indirect emissions)

1.0

0.4

0.26

IEA (Direct and indirect emissions)

2.2

1.4

0.3

World steel association

2.2

1.4

0.3

1.3 The Transition from Carbon Metallurgy to Hydrogen Metallurgy

23

smelting, non-blast furnace ironmaking, and research and development and application of low-carbon smelting technologies such as carbon capture, utilization, and storage. At present, China’s hydrogen metallurgy has gradually achieved the basic conditions for further development, and the iron and steel metallurgy industry has stepped into the transition from carbon metallurgy to hydrogen metallurgy. Currently, hydrogen metallurgy processes mainly include blast furnace hydrogenrich ironmaking technology (Guang et al. 2019; Tonglai 2015), hydrogen-based direct reduction process (Feng et al. 2019; Jiangshan and Yicheng 2007; Hanjie and Guanyong 2015), hydrogen-based smelting reduction process, and hydrogen-based plasma direct steelmaking process (Dipl and ng.Jan Friedemann 2004; Xingying et al. 2017). The hydrogen-rich reduction technology in a blast furnace involves the injection of hydrogen-containing gas into the blast furnace, thereby reducing the use of coal or coke and CO2 emissions. In terms of thermodynamics and kinetics, hydrogen as a reducing agent for ferric oxide, is more advantageous than carbon monoxide. It has therefore become a research hotspot to seek hydrogen-rich reduction by injecting a reducing medium with high hydrogen content into the blast furnace. Figure 1.7 shows a schematic diagram of hydrogen-rich reduction, a technology involving the injection of waste plastics, natural gas (NG), and coke oven gas (COG) into a blast furnace.

Fig. 1.7 A schematic representation of hydrogen-enriched reduction in blast furnace (Zhao et al. 2020)

24

1 Introduction

The metallic product of the direct reduction process is direct reduced iron (DRI), also known as sponge iron. The reduction reaction occurs via a series of gas–solid phase reactions with the reactant gases CO and H2 . The reactor of the process is usually a vertical shaft furnace. Its reducing gas, a mixture of CO and H2 , is obtained by reforming natural gas. Compared with the blast furnace process, the substitution rate will be limited when H2 is used to replace C in the blast furnace. Even though the pulverized coal (one-third of carbon injected in the tuyeres) can be largely replaced by H2 , it is still necessary to retain the role of the skeleton of coke (two-thirds of carbon used) for the distribution of blast furnace gas flow and the favorable furnace conditions. The expected gain in terms of CO2 emissions reduction is 20% (Yilmaz et al. 2017). On the other hand, if a direct reduction shaft furnace is used, the possibility of replacing 100% of the carbon (carbon monoxide) with H2 may be quite likely. That’s why a number of projects in China and overseas have given priority to the use of pure hydrogen for iron ore reduction in shaft furnaces.

1.4 Research Status of Hydrogen Metallurgy 1.4.1 Development Status of Hydrogen Metallurgy The “Hydrogen” sub-project of the European research program ULCOS (Ultra-Low Carbon Dioxide Steelmaking, 2004–2010) is the earliest known comprehensive study of hydrogen-based steelmaking. The program investigated two methods of reducing iron ore with hydrogen. The first is the reduction of mineral fines in a multi-stage fluidized bed, replacing reformed natural gas with hydrogen, which is the only direct reduction process using pure hydrogen as the reducing agent. This process was applied to commercial operations (Nuber et al. 2006). Hydrogen here is produced through natural gas steam reforming. But this process has been out of use due to economic reasons. The second project is on the direct reduction of iron ore pellets or lumps in a vertical shaft furnace. The entire steelmaking route used in these studies is shown in Fig. 1.8. The developments of hydrogen metallurgy in China and abroad in the past two years are shown in Tables 1.4 and 1.5. In terms of hydrogen-rich blast furnace ironmaking research, China Baowu Group Corporation Limited has signed the Strategic Cooperation Agreement on Nuclear Energy-Hydrogen Production-Metallurgical Coupling Technology with China National Nuclear Corporation and Tsinghua University on January 15, 2019, to jointly build a world-leading alliance of nuclear metallurgy industry (Yanli 2020). The roadmap of Baowu’s low-carbon metallurgical technology is shown in Fig. 1.10. The idea is to use nuclear energy to produce hydrogen to achieve hydrogen metallurgy, aiming to solve the problem of coal-burning restrictions in ironmaking, reduce CO2 emissions by 30%, and develop a unique low-carbon ironmaking technology of Baowu. Overseas technologies such as the COURSE50 ironmaking process in Japan

1.4 Research Status of Hydrogen Metallurgy

25

Fig. 1.8 Hydrogen-based steelmaking in the ULCOS project

(Zhenkai et al. 2018), POSCO hydrogen reduction ironmaking process in Korea (Pei and Pengli 2018), ThyssenKrupp hydrogen-based ironmaking project in Germany, etc., replace part of the coke in the blast furnace with hydrogen to carry out partial hydrogen reduction, which greatly reduces CO2 emissions. Figure 1.9 shows a schematic diagram of the COURSE50 technology in Japan, which was launched in 2008. The research was carried out in two parts (Higuchi et al. 2013). The first part was the CO2 emission reduction technology of the blast furnace that directly reduces iron ore with hydrogen. This mainly included the technology of reducing iron ore with hydrogen, the modification technology of coke oven gas was to increase the hydrogen content, and the production technology of high-strength and high-reactivity coke. The goal was to reduce CO2 emissions by 10%. The second part involved the separation and recovery technology of CO2 in blast furnace gas that uses the waste heat energy of steel mills to separate and capture CO2 . The goal of this technology was to reduce CO2 emissions by 20% (Hu et al. 2015). Japan’s New Energy and Industrial Technology Development Organization (NEDO) has commissioned five companies including Nippon Steel, JFE, Kobe Steel, Nisshin Steel, and Nippon Steel Engineering Co., Ltd. to conduct experiments. It is

26

1 Introduction

Table 1.4 Development of hydrogen metallurgy abroad (Use 2022 exchange rate) Serial number

Enterprise

Investment

Progress

Source of hydrogen

1

COURSE50 project in Japan

107 million euros

Launched in 2008, practical application in 2030

Hydrogen production from coke oven gas

2

Pohang Nuclear Energy Hydrogen Production

73 million euros

June 2010

Hydrogen production from nuclear energy

3

HYBRIT project in Sweden

90 million to 181 million euros

Established in 2016, pilot-scale research from June 2018 to 2024, commercial operation in 2035

Produced by electrolysis of water from electricity generated by clean energy generation

4

Voestalpine’s H2FUT—URE Production

18 million euros

In early 2017, research and development on breakthrough hydrogen were carried out. By 2050, carbon dioxide emissions to be reduced by 80%

Hydrogen production by electrolysis of water for use in H2 fuel cells

5

ArcelorMittal’s hydrogen ironmaking demonstration plant

65 million euros

Started in September 2019

Hydrogen production from natural gas and blast furnace top gas pressure swing adsorption (95%), future renewable hydrogen energy

6

ThyssenKrupp hydrogen ironmaking technology in Germany (Carbon2Chem project)

10 billion euros

November 2019

Provided by Air Liquide France

7

Development of hydrogen ironmaking technology in Dillingen and Saarland, Germany

14 million euros

Implemented in 2020

Hydrogen-rich coke oven gas

8

Salzgitter Low CO2 Copper Smelting Project (SALCOS)

50 million euros

Put into use in 2020

Hydrogen production from wind power. reversible solid oxide electrolysis process for hydrogen and oxygen production

1.4 Research Status of Hydrogen Metallurgy

27

Table 1.5 Development of hydrogen metallurgy in China Serial Organization number

Time

Progress

Note

1

China Baowu Group Corporation Limited, Tsinghua University, and China National Nuclear Corporation

January 15, 2019

The Strategic Cooperation Agreement on Nuclear Energy-Hydrogen Production-Metallurgical Technology

Carry out research and development of hydrogen production from ultra-high temperature gas-cooled reactor nuclear energy, coupled with the strategic cooperation framework of steel smelting and coalification technology to achieve ultra-low carbon dioxide emissions and green manufacturing in the steel industry

2

HBIS Group March 2019 Set up “Hydrogen Energy Co., Ltd., Technology and Industry Strategic Innovation Center” Consulting Center of Chinese Academy of Engineering, China Iron & Steel Research Institute Group, Northeastern University

The hydrogen energy application research and scientific and technological achievements transformation platform have become the most representative and exemplary advocate and implementer of green, environmental protection, and sustainable energy in the Beijing-Tianjin-Hebei region

3

Jiuquan Iron and steel (Group) Co., Ltd

Created the “coal-based hydrogen metallurgy theory”, “shallow hydrogen metallurgy roasting theory” and “magnetic material wind-magnetic simultaneous selection theory”, and developed corresponding cutting-edge innovations

September 2019

Hydrogen Metallurgy Research Institute

(continued)

28

1 Introduction

Table 1.5 (continued) Serial Organization number

Time

Progress

Note

4

Rongcheng October Group in 2019 Tianjin, Shaangu Group, Hanhai Hydrogen Energy Company in Xi’an, Hancheng Government

Western hydrogen city, National hydrogen energy the memory of the times, development and supply energy internet island base, hydrogen energy application technology research and development base, and international and domestic hydrogen energy technology exchange and cooperation center, China’s hydrogen energy capital

5

HBIS Group November Co., Ltd. signed 2019 a memorandum of understanding with Tenova Group of Italy

Construct the world’s first 1.2-million-ton scale hydrogen metallurgy demonstration project

6

CSDRI project Debugging Dry reforming of of China Shanxi at the end of reducing gas to produce Taihang Mining 2020 direct reduced iron CO., Ltd

Advantages of dry reforming technology: customized syngas (reasonable H2 /CO ratio)

7

CISP project of Debugging Jianlong Group in early in Wuhai, Inner 2021 Mongolia

300,000 tons of hydrogen-based smelting reduction process to produce high-purity cast iron project to realize hydrogen metallurgy

8

Plant Design for Hydrogen Energy Development and Utilization Engineering Demonstration Project

High-purity pig iron project

December 7, Hydrogen energy 2020 development and utilization

Innovative research and development of distributed green energy, low-cost hydrogen production, coke oven gas purification, gas self-reforming, hydrogen metallurgy, heat transfer of finished products, carbon oxide removal for the second-mode hydrogen metallurgy demonstration project, etc

Proposal

1.4 Research Status of Hydrogen Metallurgy

29

Fig. 1.9 The roadmap of the low-carbon metallurgical technology of China Baowu Group Corporation Limited (Xiaoming 2019)

Fig. 1.10 Technical route of COURSE50 program (Zhenkai et al. 2018)

expected that the industrial production of Unit 1 will be realized by 2030 and will be popularized in all blast furnaces in Japan by 2050. In addition, Germany’s ThyssenKrupp Group, in cooperation with Air Liquide, plans to invest 10 billion euros by 2050 to develop a hydrogen-based ironmaking technology that injects large amounts of hydrogen into blast furnaces. On November 11, 2019, ThyssenKrupp officially injected hydrogen into the No. 9 blast furnace at the Duisburg plant for testing hydrogen-based ironmaking. Hydrogen was injected

30

1 Introduction

through one of the tuyeres, marking the beginning of a series of tests for the project. Thyssenkrupp plans to gradually expand the use of hydrogen to all 28 tuyeres of the No. 9 blast furnace. In addition, the group also plans to use hydrogen for steel smelting in the plant’s other three blast furnaces from 2022 that can reduce CO2 emissions in production by as much as 20%. In August 2020, Dillinger Hütte and Saarschmiede GmbH in Germany conducted tests on the injection of hydrogen-rich coke oven gas in a blast furnace. The investment amounted to 14 million euros. They believed that it would be technically feasible to use hydrogen as a reducing agent in blast furnaces in the future with the premise that green hydrogen should be available. The longer-term technical route is that if green hydrogen can meet the demand in quantity, under the premise of cost competitiveness, the future iron and steel production in Saarland will follow the technical route of hydrogen-based direct reduction iron-electric furnace. The researchers plan to conduct experiments using pure hydrogen next in two blast furnaces. At the same time, the company announced that it planned to achieve 40% reductions in carbon emissions by 2035, subject to major initiatives in Germany to support the development of hydrogen energy. The development of gas-based direct reduction technology is also taking place. HBIS Group Co., Ltd. has signed a Memorandum of Understanding (MOU) with the Tenova Group in Italy to utilize the world’s most advanced hydrogen production and hydrogen reduction technologies. The group also cooperated with Capital Engineering & Research Incorporation Limited to jointly develop the world’s first 1.2-million-ton hydrogen metallurgy demonstration project. HBIS Group and Tenova Group signed a contract on November 23, 2020, to build a high-tech hydrogen energy development and utilization project, including an ENERGIRON direct reduction plant with an annual output of 600,000 tons, which will be the first industrial production plant in the world using hydrogen-rich gas for direct reduction of iron. At the same time, Shanxi ZhongJing Energy Group Co., Ltd. (Hu et al. 2015) announced on December 20, 2020, that its hydrogen-based reduced iron project (known as CSDRI) will run on a trial basis, marking the official start of the industrial application stage of the hydrogen-based direct reduced iron project. A schematic diagram of the CSDRI process is shown in Fig. 1.11. CSDRI has made a breakthrough in the key technologies of the coke oven gas reforming in two aspects of gas conversion and purification technology, especially low-pressure deep desulfurization purification technology. This technology enables the application of coke oven gas in direct reduction process in China. In June 2020, the GFG Alliance signed a series of agreements with the Romanian government and related organizations. The agreements included the adoption of modern steel production technology, a significant reduction in carbon dioxide emissions, an increase in the use of low-carbon energy, and the invention of a more flexible and competitive operation mode to better achieve the company’s goal of green production of steel. Their plans include building a directreduction iron plant with an annual output of 2.5 million tons. The plant will initially use natural gas as the reducing agent. As the hydrogen reduction technology gets successfully developed, hydrogen would be used as the reducing agent. The steelmaking process would shift from using a converter to an electric arc furnace to reduce

1.4 Research Status of Hydrogen Metallurgy

31

Fig. 1.11 CSDRI (China Shanxi Direct Reduced Iron) process

carbon dioxide emissions per ton of steel by 80%. Once only hydrogen is used in the direct reduced iron plant, the carbon emissions will drop to nearly zero. In addition to the above-mentioned research about the hydrogen-rich blast furnace and gas-based reduction shaft furnace, a new process of hydrogen-based smelting reduction was developed by CISP Technology of Jianlong Group in Inner Mongolia to advance the comprehensive utilization of coke oven gas. The group initiated a hydrogen-based smelting reduction project with an annual output of 300,000 tons. The cooperation between hydrogen energy and the iron and steel industry has been a win–win result till now. Hydrogen energy helps iron and steel enterprises save energy and reduce emissions, develop their business, and achieve transformation. In turn, iron and steel enterprises provide more practical applications for hydrogen energy to promote its further development. Therefore, these two constitute a mutually reinforcing industry combination. However, hydrogen metallurgy is still in its infancy, both in theory and in practice, and still faces several challenges and difficulties.

1.4.2 Challenges for Hydrogen Metallurgy Hydrogen metallurgy is a brand-new concept, and it is essential to correctly understand its core content and to avoid pursuing unrealistic and blind “hot spots”. It needs to be recognized that hydrogen metallurgy is still in its infancy and still

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faces enormous challenges in substantial research and development and industrial applications. Firstly, the economical and low-carbon technical route of hydrogen production is the first challenge for hydrogen metallurgy. The huge production scale of the iron and steel industry has forced it to face the problem of the source of hydrogen. At present, 95% of the total hydrogen production in the world is still mainly produced by petrochemical energy (Jue et al. 2020), while petroleum fuels are produced by pyrolysis conversion, oxidation, and other methods of hydrogen production and coal gasification conversion. These technologies use high-carbon energy sources, and the problem of CO2 emissions remains unavoidable. At the same time, the problem of conversion efficiency is also involved, and the use of hydrogen metallurgy is not currently viable. Besides, producing hydrogen with coal-fired power generation and water electrolysis (Shaobo 2012) is also a commonly used technical route of hydrogen production. China’s electric power is also dominated by coal-fired power generation, so the problem of CO2 emissions still cannot be solved. Therefore, these technical routes don’t have the advantages of low energy consumption and carbon emissions, and the low-cost production of green hydrogen still faces severe technical challenges. In addition, mature hydrogen storage technologies such as high-pressure gaseous hydrogen storage and cryogenic liquefaction hydrogen storage are also vital to the large-scale and efficient utilization of hydrogen energy. Secondly, the hydrogen smelting technology in China and overseas has just started at the level of project layout, research and development. Most iron and steel enterprises are only in the early stages of signing cooperation agreements and mapping out future goals. Most enterprises still use coke oven gas and chemical by-products as hydrogen sources for smelting. Only a few companies have set the goal of producing hydrogen from clean energy as the smelting energy. At the same time, the two current mainstream hydrogen-rich metallurgical technologies (including injecting hydrogen at blast furnace tuyeres instead of coal injection and coke, and non-blast furnace hydrogen direct reduction technology) are also facing some key technical problems that need to be sorted first. Finally, from the perspective of national and local policies, China’s current hydrogen energy development policies are mainly focused on the field of transportation, such as new energy vehicles, hydrogen refueling stations, hydrogen storage and transportation, fuel cells, etc. The top-level design is urgently needed for special plans, policy systems, standard systems, and safety norms that support hydrogen metallurgy. The research and development of China’s hydrogen smelting technology still requires plans and orientation at the national level to determine a feasible technology roadmap. The win–win cooperation between hydrogen energy and the steel smelting industry can only be achieved with the support of policies. In recent years, China has been committed to conserving the ecological system. The realization of carbon neutrality and breakthroughs in hydrogen metallurgy ultimately depends on scientific and technological progress. At a development forum in March 2021, Xue Qikun has emphasized the importance of developing solar energy for the energy restructuring in the future and that solar power generation will play an important role in the future hydrogen production process. For the future of hydrogen

1.5 Summary

33

metallurgy, the most ideal situation is to use clean energy (solar power generation, hydropower, nuclear power, etc.) to produce hydrogen and to solve the problems associated with the cost of hydrogen. The economic feasibility of blast furnace hydrogenation and shaft furnace full hydrogen smelting can be further considered under this premise. Till then, it is possible to partially realize hydrogen metallurgy to a certain level by decomposing coke oven gas or high volatile coal, using a two-step method to reduce iron or a gas-based reduction of coal to gas. However, the relevant reaction mechanism and pilot work of different scales will still require a lot of investment and research development.

1.5 Summary Carbon dioxide is the main constituent of greenhouse gases. Today, due to global climate change, controlling carbon emissions has become a global concern. Starting from the UN Climate Change Convention, countries and regions around the world have formulated relevant policies and development goals. China has also taken the lead in proposing ambitious emissions reduction targets to achieve carbon peaking by 2030 and carbon neutrality by 2060. In this mode of low-carbon transitions, based on its national conditions and in line with the inherent requirements of sustainable development, China has taken the initiative to shoulder part of the international responsibility for energy conservation and emission reduction, and play a leading role in achieving the world’s carbon reduction goals. As the global requirements for low-carbon development gradually become clearer, various industries have also formulated transformation and upgrading strategies. The implementation of carbon emission trading system has further forced the relevant industries to develop low-carbon technologies and promote the process of enterprise transformation. Among these, the iron and steel industry, as a major emitter, must take the lead in taking actions. The concept of hydrogen metallurgy was first proposed in the twentieth century. Using hydrogen instead of carbon to reduce iron ore will reduce the emission of pollutants and carbon dioxide from the source, one of the key routes to achieve zero carbon emissions. However, in the twentieth century, the iron and steel industry, along with China’s hydrogen energy industry, were still in the initial stages of development, and hydrogen metallurgy was not yet relevant for the local environment at that time. In recent years, the iron and steel industry has transitioned from large-scale output developments to the current environment-friendly enterprises with optimized capacity structure. During this time, the development of hydrogen energy has also received unprecedented attention. The development of hydrogen energy has been supported by government policies at all levels in China and overseas, establishing basic conditions for the developments in hydrogen metallurgy. The current mainstream technology routes of hydrogen metallurgy consist of the blast furnace hydrogen-rich smelting and the gas-based direct reduction shaft furnace. Several domestic enterprises such as China Baowu Group, HBIS Group,

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Shanxi ZhongJing Energy Group, and CISP Technology of Jianlong Group have formulated development routes and specific goals for hydrogen metallurgy. Internationally, COURSE50 in Japan, ThyssenKrupp Group in Germany, POSCO in South Korea, and other steel joint enterprises have also started relevant research and development. The biggest challenge facing hydrogen metallurgy is still the key issue of low-cost green hydrogen production. At present, most iron and steel enterprises are based on using coke oven gas as the main objective of hydrogen-source smelting projects with related research and development on the ascend. The hydrogen production process and hydrogen metallurgy technology require breakthroughs in key technologies, and the future of hydrogen metallurgy still needs to be continuously explored. At the same time, the hydrogen energy policy at the national level is primarily concentrated in the transportation field. There is a need for further developments and systematic improvements in the hydrogen metallurgy technologies.

References al people’s congress on the ratification of the united nations framework convention on climate change. State Council Gazette of the People’s Republic of China, vol 28, p 1195 (1992) Bahgat M, Khedr H (2007) Reduction kinetics, magnetic behavior and morphological changes during reduction of magnetite single crystal. Mater Sci Eng B Beiling L (2020) The EU”s “hydrogen strategy”: both for the present and for the long term development. Sinopec Mon 8:69–71 China-U.S. Joint Presidential Statement on Climate Change [N]. 2016-04-02 Cramer W, Yohe G, Field CB (2014) Detection and attribution of observed impacts [M]. Cambridge University Press CSDRI technology of reduced iron in gas-based shaft furnace [EB/OL]. Shanxi Metallurgical Engineering Technology Co., Ltd. http://www.sxyjgc.cn/?cn-about-71.html. Dipl. I, ng.Jan Friedemann. Plaul, Dipl. I, ng. Dr. mont. Wilfried Krieger (2004) Hydrogen plasma smelting reduction: a future steelmaking technology. The 1st Sino-German (European) Metallurgical Technology Seminar, Beijing, China. EU Carbon Emissions Trading System [EB/OL]. http:// www. tanpaifang.com/tanguwen/2016/ 1009/56943.html. Explore energy data by category, indicator, country or region. [DB] IEA. https://www.iea.org/ Field CB, Van aalst M, Adger WN, et al (2014) Part A: global and sectoral aspects: volume 1, global and sectoral aspects: working group ii contribution to the fifth assessment report of the intergovernmental panel on climate change [M]. Climate change 2014: impacts, adaptation, and vulnerability. IPCC, pp 1–1101 Germany officially announced that hydrogen instead of coal will be used to make iron. Foundry Eng 2020, 44(1):76 Guang W, Jingsong W, Haibin Z et al (2019) Effect of blast furnace gas recycling with hydrogen injection on low carbon development of Chinese ironmaking. China Metall 29(10):1–6 Guo T (2015) Basic research on new low-carbon ironmaking process of coke oven gas injection into blast furnace. Northeastern University, Shenyang Guo H, Sun G (2015) Future of process and equipment on non-coking coal ironmaking (II)— prospect study on process and equipment for gas-based direct reduction ironmaking (I). Metall Equip 4:1–9, 33

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Higuchi K, Matsuzaki S, Shinotake A et al (2013) Technology development for reformed-COG injection into blast furnaces to decrease CO2 emissions. World Iron Steel 13(4):5–9 Hu J, Zhou W, Dong G (2015) Innovative ironmaking process that takes into account environmental protection and economy. 2015-07-09 Hu J (2009) Join Hands to address climate challenge—at the opening plenary session of the UN summit on climate change. Resour Habitant Environ 20:14–15 IEA. Global energy-related CO2 emissions [DB]. Paris; IEA. https://www.iea.org/ IPCC SROCC Summary for Policymakers (2019) Jiacong F, Zeqing F, Huijian T et al (2018) Research on the influencing factors of the price of carbon emissions rights: an empirical analysis based on the pilot of carbon emissions rights in China. Commer Account 2:14–17 Jinping X (2020a) Building on past achievements and launching a new journey for global climate actions—speech at the climate ambition summit. In: State council gazette of the People’s Republic of China, vol 35, p 7 Jinping X (2020b) Speech at the general debate of the 75th session of the united nations general assembly. 2020-09-23 Li F, Chu M, Tang J, et al (2019) Current situation of non-blast furnace ironmaking and development direction of china iron and steel production process. Hebei Metall 10:8–15 Li Z (2020) High-quality development of global hydrogen energy is accelerating with the priority to green development. Industry City 8:28–31 Li S (2020) Analysis of measures to reduce atmospheric pollutants in iron and steel industry. Ind Saf Environ Prot 46(6):82–84 Mao X (2019) Baosteel’s low-carbon smelting technology route, report of the 12th China iron and steel annual conference on ironmaking and raw materials Meng X, Gu A, Wu X, et al (2020) Prospect of high quality development of hydrogen energy industry in China. Sci Technol Rev 38(14):77–93 Meng X, Gu A, Wu X, et al. (2019) Review of China’s hydrogen industry policy and scientific and technological development hotspots in 2019. Sci Technol Rev 38(3):172–183 Ministry of Ecology and Environment (2021). The ministry of ecology and environment held a briefing on policies to actively respond to climate change [EB/OL]. (2020-09-27) [2021-01-20]. http://www.mee.gov.cn/ywdt/hjywnews/202009/t20200927_800752.shtml Ministry of Ecology and Environment of the People’s Republic of China, General Administration of Quality Supervision, Inspection and Quarantine (2012). GB 28662–2012 industrial air pollutant emission standard for iron and steel sintered pellets. China Environmental Science Press, Beijing Na H, He J, Yuan Y, et al (2019) Analysis of carbon emissions from different production processes of iron and steel enterprises. In: The 10th national annual conference on energy and thermal engineering, Hangzhou, Zhejiang, China National Energy Administration. Guidance on energy work in 2020 [EB/OL] (2020). http://www. nea.gov.cn/2020-06/22/c_139158412.htm Nuber D, Eichberger H, Rollinger B (2006) Circored fine ore direct reduction-the future of modern electric steelmaking. Stahl Eisen 126:47–51 Patisson F, Mirgaux O (2020) Hydrogen ironmaking: how it works. Metals-Open Access Met Lurgy J 10(7):922 Pei Z, Pengli D (2018) Carbon emissions are an issue that cannot be ignored in the future of China’s steel industry. Iron Steel 53(08):1–7 Proposal of the Central Committee of the Communist Party of China on Formulating the Fourteenth Five-Year Plan for National Economic and Social Development and the Visionary Goals for 2035 [N]. [2020-11-04]. Shaobo Z (2012) Basic research on hydrogen metallurgy and new ironmaking idea-process. China Metall 22(7):1–6 Siqi Z, Jingjing C (2020) Do early-announced emission reduction policies lead to a green paradox? Evidence from the EU Carbon Emissions Trading System. J Environ Econ 5(4):11–29

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Chapter 2

Hydrogen Production and Storage

2.1 Hydrogen in Nature Hydrogen is the first element in the periodic table. Its chemical symbol is H with an atomic weight of 1.00794, and it is the lightest element in the periodic table. Monoatomic hydrogen (H) is the most common chemical substance in the universe, accounting for 75% of the total mass of the universe, and the rest is mainly helium. Heavy elements with higher atomic numbers and larger relative atomic masses constitute about 1% of the total universal mass. Hydrogen has a special status in terms of material structure, life composition, or chemical reactions.

2.1.1 The Discovery of Hydrogen Hydrogen was discovered as early as the sixteenth century by a doctor in Switzerland. “Throwing iron filings into sulfuric acid creates bubbles that rise like a cyclone,” he said. He also found that the gas could burn, but he didn’t have time to do further research. In the seventeenth century, another doctor discovered hydrogen. But at that time, it was thought that no gas could exist alone, neither could be collected nor measured. The doctor believed that hydrogen was no different from air and quickly abandoned the study. The first person to collect hydrogen and conduct serious research was a British chemist, Cavendish. In 1766, he accidentally dropped an iron piece into hydrochloric acid. While annoyed with his carelessness, he observed the formation of gas bubbles in the hydrochloric acid solution. This scene immediately attracted him. He carried out several experiments, putting a certain amount of zinc and iron into sufficient hydrochloric acid and dilute sulfuric acid (the quality of sulfuric acid and hydrochloric acid used was varied every time). He observed that a fixed amount of gas was produced every time. This showed that the generation of this new gas did not depend on the type of acid used or the concentration of the acid.

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Cavendish used the drainage method to collect the new gas, which he found could neither help light the candle nor help the animals breathe. When mixed with air, the gas will explode as sparks. After several experiments, Cavendish finally discovered the limit to which this new gas would explode when mixed with air. He wrote in the paper: When the content of this combustible gas is less than 9.5% or more than 65%; although it burns when ignited, it will not make a deafening explosion. Soon afterward, he measured the density of this gas and then found that water was produced as a result of combustion of this gas. He had undoubtedly discovered hydrogen. Cavendish’s research was already detailed enough. He only needed to announce to the outside world that he had discovered a new element and give it a name. However, Cavendish was influenced by the “phlogiston theory”, insisting that water was an element, and did not admit that he had accidentally discovered a new element. Lavoisier later heard about it, and he repeated Cavendish’s experiment, arguing that water was not an element but a compound of hydrogen and oxygen. In 1787, Lavoisier formally proposed that “hydrogen” was an element. The product of hydrogen combustion was water, so he named it “the generator of water” (Hydrogen) in Latin (Chinese Petroleum Society 1996).

2.1.2 Hydrogen and Its Family of Isotopes An isotope is an element that occupies the same position in the periodic table of elements and has the same number of protons but different numbers of neutrons (Chinese Petroleum Society 1996). The hydrogen atom H represents the most basic of atomic structures. The nucleus contains only one proton, no neutrons, and only one electron outside the nucleus, so the hydrogen atom is a model system for studying atomic structure. Seven isotopes of H that have been discovered so far and are represented by 1 H-7 H. Each isotope contains only one proton, but the number of neutrons varies from 0 to 6. The natural isotopes are hydrogen or protium (1 H), deuterium (2 H), and tritium (3 H). Their atomic structure is shown in Fig. 2.1, and their properties are compared in Table 2.1. The two isotopes, protium and deuterium, are similar in chemical properties. Deuterium can replace hydrogen atoms in any hydrogen-containing compound, but Fig. 2.1 Schematic diagram of the atomic structure of protium, deuterium and tritium

2.1 Hydrogen in Nature

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Table 2.1 Common isotopes of hydrogen Symbol

1H

English name

Protium

Deuterium

Tritium

Relative atomic mass

1.007825

2.01410

3.01005

Abundance/%

99.985

0.015

Product of a nuclear reactor

Number of protons

1

1

1

Number of neutrons

0

1

2

(P)

2H

(D)

3H

(T)

the difference in atomic mass is quite large. So, these two isotopes have large differences in reaction speed and reaction equilibrium position, but in the catalytic reaction, the reaction rates of the two isotopes are similar. Therefore, deuterium is often used as a tracer atom in the research of many reaction mechanisms. Deuterium has important applications in nuclear fusion reactions as well. Fusion reactions of deuterium and tritium are very fast and release a large amount of energy. In addition, deuterium oxide also acts as a moderator for neutrons in nuclear reactions to increase the probability of nuclear fission reactions. The isotope of H containing two neutrons in the nucleus is called tritium (T). It is an unstable isotope that can become 23 He through β decay, with a half-life of about 12.32 years. Tritium was first prepared in 1934 by Ernst Rutherford, Mark Oliphant, and Paul Harteck from deuterium. It can be obtained by the nuclear reaction of lithium isotopes with neutrons, or by the reaction of deuterium and neutrons. Tritium was used in nuclear weapons by the United States during the Cold War; it was obtained in a special heavy-water reactor at the Savannah River Site. The tritium production was restarted in 2003 by irradiating various isotopes with neutrons. The main use of tritium is in nuclear fusion, and the fusion reaction of tritium and deuterium can release 17.6 meV of energy. (31 )T + (21 )D → (42 )He + (10 )n

(2.1)

Tritium has certain radioactive hazards. But because of its short half-life, it can only exist in the human body for about 14 days, so it is less harmful to humans. Tritium is often used as a radioactive marker in some analytical chemistry studies. Before the signing of the Comprehensive Nuclear Test Ban Treaty, tritium, produced as a biproduct of several nuclear weapons tests, provided a good tracer element for oceanographers to study the marine environment and biological evolution. In addition, 4 H, 5 H, 6 H, and 7 H are unstable radioisotopes synthesized in the laboratory.

2.1.3 Distribution of Hydrogen in Nature Hydrogen accounts for about 75% of the matter in the universe. On Earth, the large amount of oxygen in the air leads to the oxidation of H to H2 O, so the amount of

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Fig. 2.2 a The mass ratio of various elements in air; b The mass ratio of each element in the universe; c The mass ratio of various element in Earth’s crust

hydrogen in the air is low (Fig. 2.2a). Figure 2.2b shows the proportion of each element in the universe. Apart from their relative proportion in the universe, heavy elements account for the main part of the substances that make up the Earth. Hydrogen still occupies an unenviable position, ranking third in reserves on the earth. It can be said that hydrogen is the most abundant element in nature. The relative amount of elemental H in the Earth’s crust is shown in Fig. 2.2c Hydrogen is one of the main components of stars and giant planets and provides energy for stars through proton-proton chain reactions and nuclear fusion reactions in the carbon–nitrogen-oxygen cycle. The star in the solar system, the sun, is composed of hydrogen and its isotopes. There is also a large amount of hydrogen on Earth. In nature, most of the hydrogen elements exist in the form of compounds, and typical hydrogen compounds include the following four. The first one is its hydroxide compound namely water: H2 O. Water is an inorganic substance composed of two elements, hydrogen and oxygen. It is a colorless, odorless liquid at ordinary temperature and pressure. It is one of the most common substances on Earth, an important resource for the survival of all life, including human beings, and the most important component of organisms. This substance has played an important role in the evolution of life. In addition to water, there are also some other hydroxide compounds such as hydrogen peroxide in plants.

2.2 The Method of Hydrogen Production

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The second one is hydrocarbons. They are organic compounds composed of two elements, carbon and hydrogen. There are a large number of hydrocarbons; more than 2,000 kinds of hydrocarbons with known structures have been identified. Hydrocarbons are parent molecules for all organic compounds. All organic compounds are formed as the result of replacing certain atoms in hydrocarbons with other atoms. These are derived from fossil fuels including coal, oil, and natural gas. The main components of biogas are methane (CH4 ) and hydrogen sulfide (H2 S); methane is also a hydrocarbon. The third one is carbon-hydrogen–oxygen polymers, including inorganic and organic substances composed of only carbon, hydrogen, and oxygen, such as proteins and carbohydrates that make up organisms. The fourth one consists of its presence in inorganic and organic acids. Hydrogen is often present as oxalate in the cell membranes of plants such as barberry, sow thistle tassel flower herb, creeping oxalis, and garden sorrel. Almost all plants contain calcium oxalate. The abundance of hydrogen in the Earth’s crust (the percentage of the composition of the crust’s weight) is relatively high. Within 1 km of the Earth’s crust (including the ocean and atmosphere), the weight of combined hydrogen accounts for about 1%, with atomic percentage of about 15.4%. The most common forms of combined hydrogen are water and organic matter (such as oil, coal, natural gas, and organisms). In a few cases (such as in volcanic gas and mineral water) it is found compounded with nitrogen, sulfur, or halogens. Elemental hydrogen is however quite rare, accounting for only about one in ten million in the atmosphere. It is often found in volcanic gases, sometimes trapped in minerals, sometimes in natural gas and some anaerobic fermentation products. Due to the high diffusion velocity of hydrogen molecules (average diffusion velocity is 1.84 km/s), hydrogen will quickly escape from the atmosphere into outer space. The gas emitted by a volcanic eruption contains a lot of hydrogen, and sometimes hydrogen is also ejected when drilling deep wells. Therefore, geologists have proposed new hypotheses about the structure of the Earth’s core. They believe that, like other planets, hydrogen is one of the most widespread substances that make up the Earth. The Earth’s core is composed of metal hydrides. Under high pressure, hydrogen can be dissolved into the metal, and the volume of the dissolved hydrogen can exceed the volume of the metal itself by hundreds to thousands of times. Not only does this generate metal hydrides, but under the ultra-high pressure of the Earth’s core, the hydrides are metalized, becoming ultra-dense and highly conductive metallic phases.

2.2 The Method of Hydrogen Production Unlike traditional fossil fuels, hydrogen cannot exist naturally through long-term accumulation. As a secondary energy source, hydrogen must be produced by certain methods. There are many methods for preparing hydrogen. The traditional methods of its production mainly include fossil fuels reforming, hydrogen production by

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electrolysis of water, and industrial by-product hydrogen. New hydrogen production methods mainly include biomass hydrogen production and photocatalytic hydrogen production.

2.2.1 Hydrogen Production with Fossil Fuels Fossil fuels (coal, oil, natural gas, etc.) are abundant primary energy sources. If these fossil fuels are used to produce hydrogen, the raw materials are abundant, and costs are low. But fossil fuels will emit large amounts of CO2 in the process. If the issue of clean and efficient utilization of fossil fuels and the capture and storage of generated CO2 could be solved, hydrogen production from fossil fuels would become the preferred process for countries with abundant primary energy reserves to realize the hydrogen economy strategy. At present, the clean and efficient utilization of fossil fuels has attracted China’s attention, and the relevant research has made some achievements. Several issues remain still. For example, it is expected that the country will introduce incentive policies and measures for the development and use of new energy. In addition, the existing fossil fuel hydrogen production technology is inadequate, with a low energy conversion rate (less than 50%) and the production costs are too high. There is also a shortage of high-level skill-base in energy technology research and development. Therefore, there is a long way to go to realize the clean and efficient utilization of fossil fuels in China.

2.2.1.1

Hydrogen Production with Coal Gasification

Hydrogen production with coal gasification uses coal as the reducing agent and water vapor as the oxidant. The coal and water vapor are converted into syngas mainly composed of CO and H2 at high temperatures. The chemical reaction process is as follows: C + H2 O → CO + H2

(2.2)

This reaction is endothermic, the reforming process requires additional heat, and the heat released by the combustion of coal and air provides the heat required for the reaction. The CO in the product is further converted into CO2 and H2 by a water–gas shift reaction: CO + H2 O → CO2 + H2

(2.3)

The technology of hydrogen production from coal gasification is quite mature. This technology first gasifies coal to obtain gaseous products with hydrogen and carbon monoxide as the main components. The technology generally includes the

2.2 The Method of Hydrogen Production

43

Fig. 2.3 The process flow of hydrogen production from coal gasification (Zhengang et al. 2001)

main production processes such as coal gasification, gas purification, CO transformation, and H2 purification. The main production equipment for preparing syngas from coal gasification is a coal gasifier, in which the raw materials are coal and gasification agents (oxygen, water vapor, etc.), and the output is crude syngas. The process flow of hydrogen production from coal gasification is shown in Fig. 2.3. Generally, coal gasification can be divided into fixed bed gasification, fluidized bed gasification, and molten bed gasification according to the different contact ways of coal and the gasification agent in the process of flowing in the gasifier. In the fixed bed gasification process, coal is added from the top of the gasifier, the gasification agent is added from the bottom, and the two are in countercurrent contact. Compared with the rising speed of gas, the falling speed of coal is very slow, and it can even be regarded as fixed, so it is called a fixed bed (Gang and Le 2011). In fluidized bed gasification, small particles of coal with a size of 0.5–5 mm are used as the raw materials of gasification. These are suspended and dispersed in the vertically rising airflow in the gasifier, and the coal particles are subjected to a gasification reaction in a boiling state. Meanwhile, the reaction temperature is generally lower than the ash melting temperature (900–1050°C). When the gas velocity is high, the entire bed will form a liquid-like interface, and the friction between the coal particles and the fluid will be balanced with their own gravity. In this state, it is called a fluidized bed. Fusion bed gasification consists of the injection of pulverized coal and a gasification agent into the furnace hearth at high temperature and at a high speed in a tangential direction and transfer part of the kinetic energy to the slags, so that the molten particles in the furnace hearth rotate in a spiral motion and gasify. Currently, this gasification process is no longer being developed further. The process of hydrogen production with coal has been investigated previously and the technology is relatively mature. Germany developed the first-generation gasification process from the 1930s to the 1950s, including the crushed coal pressurized gasification Lurgi furnace of the fixed bed, the atmospheric Winkler furnace of the fluidized bed, and the atmospheric KT furnace of the entrained-flow bed. In the 1970s, second-generation gasifiers were developed, such as BGL, HTw, Texaco, Shell, KRW, etc. The first-generation furnaces used pure oxygen as the gasification agent, which could achieve continuous operation and greatly improve the strength and efficiency of gasification. The second-generation furnaces added pressurized operation. The third-generation furnaces use different external energy sources, including catalytic gasification of coal, plasma gasification of coal, solar energy gasification of coal, and

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nuclear waste heat gasification of coal (Huaxing and Lixin 2011). Different gasification processes have different requirements based on the properties of raw materials such as coal reactivity, adhesive force, clinkering property, thermal stability, mechanical strength, particle-size distribution, and the content of moisture, ash, and sulfur. Table 2.2 shows some typical surface coal gasification processes and their key characteristics. China, being a coal producer and consumer, primarily uses coal as the main primary energy source. The clean and efficient utilization of coal is related to the overall strategy for the country’s energy sources. Although China’s coal resources are abundant, the reserves of oil and natural gas are relatively poor. Therefore, hydrogen production from coal gasification will be the main route for producing hydrogen in China. As demands increase for energy and environmental protection, hydrogen production from coal gasification needs to meet the new development requirements for output, efficiency, and environmental protection. Therefore, the Integrated Gasification Combined Cycle (IGCC), as an advanced power system that organically combines coal gasification technology with the high-efficiency combined cycle, has developed rapidly in recent years. The system can use various energy resources to produce clean fuel, hydrogen, and other by-products while realizing functions such as power generation, heating, and cooling to meet the functional needs of multiple fields. IGCC technology mainly uses coal, residual oil, petroleum coke, etc. as fuel. The fuel is converted into coal gas through a gasifier and purified by dust removal, desulfurization, and other purification processes to make it clean coal gas, which is supplied to the gas turbine for combustion and work. The waste heat from the exhaust gas of the gas turbine and the recovered heat from the sensible heat of the gasification island are heated by the waste heat boiler to produce superheated steam, which drives the steam turbine to generate electricity, thereby realizing the coal gasification combined cycle power generation process. The composition of a typical IGCC system is shown in Fig. 2.4 (Xiang 2007). The optimal configuration of energy flow and logistics in the IGCC co-production system are shown in Fig. 2.5. Due to the organic integration of coal-based material production and coal power generation, the joint production of electric energy, liquid fuels, and chemicals can be realized to achieve high-efficiency utilization of energy sources. Over the last decade, China’s utilization of advanced coal to chemicals industry (ACCI) has made rapid progress as an important approach for using coal in a clean and low carbon manner. By using coal as raw material for synthetic natural gas and conventional oil-based products such as gasoline, diesel, olefins, aromatics, and ethylene glycol through pyrolysis, gasification, liquefaction and other related processes, China has succeeded in partially replacing oil and natural gas. Four CTSNG projects have been operational since the end of 2019, including Yili Xintian Coal Chemical Industry Corporation Ltd., China Kingho Energy Group Corporation Ltd., China Datang Corporation Ltd., and Huineng Group, which utilize Topsoe Corporation’s and Davy Corporation’s methanation technologies. Although ACCI has reached the

Fixed Bed

Fixed Bed

Fixed Bed

Fixed Bed

Fluidized Bed

Fluidized Bed

Fluidized Bed

Fluidized Bed

Entrained-flow Bed

Entrained-flow Bed

Entrained-flow Bed

Entrained-flow Bed

Entrained-flow Bed

Entrained-flow Bed

Gas producer

Water gas gasifier

Lurgi

BG/L

Winkler

HTW

U-Gas

KRW

K-T

Texaco

Shell

Destee

Prenflo

GSP

Note ST is the standard temperature

Type of bed

Gasification technology

Pulverized Coal

Pulverized Coal

Coal Water Slurry

Pulverized Coal

Coal Water Slurry

Pulverized Coal

Crushed Coal

Crushed Coal

Crushed Coal

Crushed Coal

Lump Coal

Lump Coal

Lump Coal

Lump Coal

Fuel

Oxygen/Water Vapor

Oxygen/Water Vapor

Oxygen/Water Vapor

Oxygen/Water Vapor

Oxygen/Water Vapor

Oxygen/Water Vapor

Air/Water Vapor

Air/Water Vapor

Air/Water Vapor

Air/Water Vapor

Oxygen/Water Vapor

Oxygen/Water Vapor

Air/Water Vapor

Air/Water Vapor

Gasification agent

Liquid State

Liquid State

Liquid State

Liquid State

Liquid State

Liquid State

Agglomeration

Agglomeration

Solid State

Solid State

Liquid State

Solid State

Solid State

Solid State

Slag

Table 2.2 Some typical surface coal gasification processes and their main characteristics (Zhengang et al. 2001)

Pressurization

Pressurization

Pressurization

Pressurization

Pressurization

Normal Pressure

Pressurization

Pressurization

Pressurization

Normal Pressure

Pressurization

Pressurization

Normal Pressure

Normal Pressure

Pressure

> ST

> ST

> ST

> ST

> ST

> ST

> ST

> ST

< ST

< ST

> ST

< ST

< ST

< ST

Temperature

2.2 The Method of Hydrogen Production 45

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2 Hydrogen Production and Storage

Fig. 2.4 Composition of a typical IGCC system (Xiang 2007)

Fig. 2.5 Optimal configuration of energy flow and logistics in the co-production system (Xiang 2007)

highest industrial scale worldwide, coal gasification would still pave the way for clean coal utilization. In future, China expects gasification technology to be flexible, efficient, and intelligent, as well as suitable for coal with high ash and ash melting points. Moreover, the efficient directional conversion of methanol and syngas, largescale efficient catalyst preparation, and optimization and upgrading key equipment and processes will be developed. The development of high-performance catalysts for methanol synthesis remains a key focus (Xie 2021).

2.2.1.2

Hydrogen Production from Natural Gas

The production of hydrogen from natural gas mainly uses the following three different chemical processes: Steam methane reforming, Partial oxidation and autothermal reduction. A. Steam Methane Reforming (SMR) SMR was first applied in 1962 and has become the most mature hydrogen production technology in the industry. The main principle is the endothermic conversion of methane and steam into H2 and CO. The main chemical reaction processes are as follows. CH4 + H2 O → CO + 3H2

(2.4)

CO + H2 O → CO2 + H2

(2.5)

2.2 The Method of Hydrogen Production

47

The heat required for the reaction is supplied by the heat generated from the combustion of methane. The required temperature of the process of reaction (2.4) is 700–850 °C, and the reaction products are CO and H2 , of which CO accounts for about 12% of the total products. The CO is later converted into CO2 and H2 through a water–gas shift reaction. B. Partial Oxidation (POX) The process of partial oxidation of natural gas to produce hydrogen is to release CO and H2 through the partial combustion of methane and oxygen. The chemical reaction process is as follows. 1 CH4 + O2 → CO + 2H2 2

(2.6)

This process is an exothermic reaction, which needs to be carefully designed. The reactor does not need an additional heat source, and the CO produced by the reaction will be further converted into H2 , as shown in the chemical reaction process (2.5). C. Autothermal Reformer (ATR) ATR is a combination of the SMR and POX processes, and the overall reaction is exothermic. The outlet temperature of the reactor can reach 950–1100°C. The CO produced by the reaction is converted into H2 through the water–gas shift reaction (2.7). The hydrogen produced by the ATR process needs to be purified, which greatly increases the cost of hydrogen production. Table 2.3 compares the pros and cons of the three methods for producing hydrogen from fossil fuels. CO + H2 O → H2 + CO2

(2.7)

Natural gas is a petrochemical fuel resource. The world’s known natural gas reserves are 230 trillion cubic meters, and the unproven natural gas reserves are also considerable. The use of natural gas resources to optimize hydrogen production can reduce greenhouse gas emissions, which has dual significance for energy conservation and environmental protection. The methods of using methane as a raw material resource for hydrogen production include obtaining H2 by preparing a mixture of H2 and CO, obtaining H2 by directly decomposing methane. Traditional methods (SMR, POX, ATR, etc.) also produce large amounts of CO while generating hydrogen. To obtain pure H2 , the CO from the syngas needs to be removed, which is not economical for the whole process. The hydrogen can be directly obtained by a methane cracking reaction. The main product of this reaction is hydrogen, and the by-product is carbon. SMR is one of the most mature industrial hydrogen production technologies, so we will focus attention on its industrial production process. SMR involves an endothermic and reversible reaction, but its reaction rate is very slow even at 1000 °C and requires a catalyst to speed up the reaction. In the process of SMR catalytic reaction, the catalyst is one of the key factors to determine the operating conditions

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Table 2.3 Comparison of three methods for producing hydrogen from fossil fuels Hydrogen production technology

Advantages

Disadvantages

SMR

Most widely used; no oxygen required; lowest process temperature; optimum ratio of H2 / CO for hydrogen production

Too much steam is usually required; the equipment investment is large and the energy demand is high

ATR

Requires low energy; lower Limited commercial application; usually process temperature than POX; requires oxygen ratio of H2 /CO is easily affected by ratio of CH4 /O2

POX

No steam required for direct desulfurization of the materials; low natural ratio of H2 /CO; beneficial for applications with ratios less than 20

A low natural ratio of H2 /CO is disadvantageous for applications with a demand ratio greater than 20; the process operates at high temperatures, often requiring oxygen

and equipment size. Due to the high operating temperature requirements, a twostage reforming process is usually used in industry to improve the conversion rate of methane. The process temperature of the first-stage reforming is usually 600– 800 °C, and the second-stage steam reforming temperature used are 1000–1200 °C. Such high-temperature operating conditions can easily make the grains of the catalyst grow. Therefore, to obtain a highly active catalyst, it is necessary to disperse the active components on a heat-resistant carrier. In addition, it is necessary to use additives to improve the anti-sulfur and anti-carbon properties of the catalyst, and further improve the catalyst performance. Table 2.4 shows the types and properties of common catalysts. The entire process flow of steam methane reforming is shown in Fig. 2.6. The process is mainly composed of four units: feed gas treatment, steam reforming (steam methane reforming), CO removal, and hydrogen purification. After pretreatment such as desulfurization, the feed gas enters the reformer for a steam methane reforming reaction. It is a strongly endothermic reaction, and the heat required for the reaction is supplied by the combustion of natural gas. Since the reforming reaction is strongly endothermic, it needs to be carried out at high temperatures to achieve high conversion. The reforming reaction conditions require that the temperature should be maintained at 750–920 °C. The syngas obtained by steam methane reforming enters the steam shift reactor and is converted into carbon dioxide and hydrogen after two stages of shift reactions at different temperatures, that can improve the yield of hydrogen. The operating temperature of the high-temperature shift is generally 350–400 °C, and the mediumtemperature shift is lower than 300–350 °C. The methods of hydrogen purification include the condensation-low temperature adsorption method, low-temperature absorption method, pressure swing adsorption method (PSA), palladium membrane diffusion method of physical process, and methanation reaction of the chemical process.

2.2 The Method of Hydrogen Production

49

Table 2.4 Types and properties of catalysts for hydrogen production from methane Types of catalysts

Properties of catalysts

VIII B group composite metal oxides or supported catalysts on MgO, Al2 O3 , SiO2 , Yb2 O3 , and monoliths

Fe, Co, and Ni have good catalytic activity, good stability, and low costs, and are widely used in industrial production. The loading of NiO ranges from 7% to 79 Wt.%, generally ~15 Wt.%. If the content of Ni is high, it is easy to form carbon deposits during the reaction. Ni-based rare earth oxide catalysts are active at reaction temperatures ranging from 573 to 1073 K

Noble metals supported on MgO, Al2 O3 , SiO2 , ZrO2, and monoliths, and their complex oxides with rare earth metal oxides

Precious metal catalysts have higher activity than Ni-based catalysts but are more expensive. Among precious metals, Rh is better than Pt, and Ru and Rh are the most stable. Ru is cheaper in precious metals and is more stable than Ni and does not form carbonyl groups under high vapor pressures

Fig. 2.6 Process flow of steam methane reforming

The production of hydrogen with methane and natural gas has been industrialized. Internationally important hydrogen production companies include Air Products & Chemicals, Inc. in the United States, Technip in France, Lurgi, Linde, and other companies in Germany (Xiaoyan et al. 2017). China has achieved some success in the development of hydrogen production from natural gas. Especially in terms of catalysts for this process, China has made some progress in industrial applications. At present, some large and medium-sized domestic enterprises have introduced foreign technologies in the production of hydrogen with natural gas. These have mainly adopted advanced foreign technologies in core processes such as steam reforming procedures. Pressure swing adsorption (PSA) technology has been applied in the industrial field (Zhu Wenge and Jiandong. 2018). PSA utilizes the concept that high-boiling impurity components are easily adsorbed under similar pressures, and the adsorbed medium is easily desorbed under low pressure. Raw hydrogen containing impurities are sent into the adsorbed layer. When passing through the adsorbed layer under high pressure, the impurities are adsorbed in the layer. Highpurity hydrogen flows out from the outlets on the adsorbed layer. The impurities adsorbed in the adsorbed layer are desorbed and regenerated under low pressure, and thereby continue the regeneration cycle. The whole process does not require additional medium and heat exchange equipment. All operations are carried out at normal temperatures. The utilization rate of adsorbent is high, the cycle period short, and the energy consumption is low (Liyou and Maojie 2017). As some key issues of

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PSA hydrogen production technology get resolved such as stable production of highefficiency lithium-based adsorbents, research, and development of radial bed adsorbers, reliable high frequency and development of large-diameter butterfly valves, etc.), the scale of PSA hydrogen production has increased year by year in China. The power consumption of hydrogen has gradually decreased, and the reliability of the device has steadily improved. The scale of the equipment has also developed from less than 1000 m3 /h to 6000 m3 /h of a single two-tower hydrogen generator, and the scale of multiple towers in parallel can reach more than 30,000 m3 /h. The power consumption per unit of hydrogen production is reduced to somewhere below 0.32 kW·h/m3 . The annual operating rate of the hydrogen generator is over 98%. In 2018 alone, more than 70 sets of pressure swing adsorption oxygen production units with a scale of more than 1000 m3 /h were built in China. Chinese enterprises such as Peking University Pioneer Technology Co., Ltd., Shanghai Hengye Molecular Sieve Co., Ltd., and Tianyi Technology have changed the situation of relying on imports of PSA hydrogen-producing molecular sieves through continuous efforts. At the same time, breakthroughs have been made in the field of lithium molecular sieves and other products, and the industrial application of new molecular sieve products has been realized. With its development, compared with cryogenic hydrogen production technology, pressure swing adsorption hydrogen production technology has gradually formed many unique advantages, which further promotes its wide application in many industries in China (Xili 2019). Compared with the plants of hydrogen production from coal, hydrogen production with natural gas requires low investment, low CO2 emissions and water consumption, and a high yield of hydrogen. It is an ideal method in the hydrogen production routes from fossil raw materials. China is rich in coal but lacks oil and gas. In 2018, the external dependence degree on crude oil exceeded 73%, and the external dependence degree on natural gas exceeded 43%. Under the background of the current energy supply situation, it is no longer economical to use heavy oil based on petroleum resources to produce hydrogen, and it is indeed rarely used in actual production. The use of natural gas to produce hydrogen has practical issues such as the supply of natural gas cannot be guaranteed, and the price is high. But in the long run, since China has abundant unconventional natural gas resources (shale gas, coalbed methane, combustible ice, etc.). With the advancement of unconventional natural gas extraction technology and the reduction of extraction costs in the future, China is expected to usher in a period of great development of natural gas. The use of natural gas is also expected be more advantageous than coal for producing hydrogen.

2.2.2 Hydrogen Production with Methanol Methanol is synthesized from hydrogen and carbon monoxide under pressure and catalysis. Similarly, methanol can also be catalytically decomposed to produce hydrogen. To produce hydrogen with methanol, methods such as methanol steam reforming, methanol cracking, methanol partial oxidation, and methanol partial

2.2 The Method of Hydrogen Production

51

oxidation reforming can be adopted. Hydrogen production with methanol steam reforming is a process in which methanol and steam are reformed in the presence of a catalyst to produce H2 , CO2 and a small amount of CO. Hydrogen production with methanol cracking (thermal decomposition) refers to the process in which methanol vapor is directly thermally decomposed into H2 and CO under the action of a catalyst. Partial oxidation of methanol to hydrogen is a process in which methanol vapor and oxygen react to generate H2 and CO2 . Partial oxidation reforming is a process in which methanol vapor is reformed with water vapor and O2 to generate H2 and CO2 . The gases produced by the above hydrogen production processes all need to be further separated and purified by pressure swing adsorption (PSA) to obtain hydrogen.

2.2.2.1

Hydrogen Production with Methanol Steam Reforming

As early as the 1970s, the Johnson-Matthey company (Amphlett et al. 1994) began to produce hydrogen from methanol steam in the laboratory. At present, the hydrogen production technology of methanol steam reforming has become mature. Compared with other hydrogen production methods, methanol steam reforming has the following characteristics (Shuren and Yanhao 1998). First, due to the low reaction temperatures (200–300 °C) for hydrogen production with methanol steam reforming, the fuel consumption is low as well, and waste heat recovery does not need to be considered. Compared with similar levels for natural gas or light oil conversion hydrogen production units, the energy consumption of methanol steam reforming for hydrogen production is only 50% of the former. Thus, it is suitable for small and medium-scale hydrogen production. Second, compared with hydrogen production by electrolysis of water, the unit hydrogen cost of hydrogen production by methanol steam reforming is lower. Hydrogen production by electrolysis of water is generally small in scale, but its power consumption is high. Therefore, the unit hydrogen cost of methanol steam reforming hydrogen production unit is much lower than the cost required for hydrogen production by electrolysis of water. Third, since the methanol feedstock used is of high purity, no further purification is required. The reaction conditions are mild, the process is simple, and the operation easy. Fourth, methanol raw materials are readily available and are convenient for transportation and storage. Fifth, this hydrogen production device can be assembled as a movable device and is easy to transport and operate. Hydrogen production from methanol steam catalytic reforming is currently the most widely studied method and considered one of the most promising hydrogen production methods for proton exchange membrane fuel cells. From the point of view of “atomic economy”, methanol steam catalytic reforming for hydrogen production is the reaction with the highest hydrogen content in the methanol-reforming hydrogen production system. Under the action of the catalyst, equimolar methanol and water generate 1 mol CO2 and 3 mol H2 : CH3 OH + H2 O → CO2 + 3H2

(2.8)

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2 Hydrogen Production and Storage

The main advantages of the methanol steam reforming hydrogen production system are that the reaction conditions are mild, the hydrogen content in the product is high, and the CO content is low. But it still does not meet the standards required for proton membrane fuel cells. However, it has some shortcomings as well. The reaction is strongly endothermic, and both the gasification of the raw material and the progress of the reaction need to absorb heat. The heat needs to be supplied by the raw material itself or by other fuels. This results in lower overall efficiency when supplying hydrogen to the fuel cell. Therefore, the development of new reforming catalysts is essential. The process flow of methanol steam reforming for hydrogen production is shown in Fig. 2.7. Methanol and desalted water are mixed in a certain proportion and then preheated in a heat exchanger before entering the vaporization tower. The vaporized methanol steam enters the reactor passing through the heat exchanger and undergoes catalytic cracking and shift reaction in the catalyst bed. Coming out of the reactor, the gas mixture contains about 74% hydrogen and 24% carbon dioxide. After heat exchange, cooling, and condensation, it enters the water scrubber. The unconverted methanol and water are collected at the bottom of the scrubber for recycling, and the top gas is sent to the pressure swing adsorption device to purify the hydrogen. As per different requirements of hydrogen purity and trace impurity components, a pressure swing adsorption process with four scrubbers or more can be used, and the hydrogen purity can reach 99.9–99.999%. There are two main types of catalysts currently used in methanol-reforming to produce hydrogen. One is a non-noble metal catalyst, mainly including copper-based catalysts (such as CuO/ZnO/Al2 O3 ) and non-copper-based catalysts (such as Zn-Cr).

Fig. 2.7 Process flow of methanol steam reforming for hydrogen production (Shuren and Yanhao 1998)

2.2 The Method of Hydrogen Production

53

The other type is a noble metal catalyst (such as Pd/ZnO). Compared with noble metal catalysts, copper-based catalysts have better low-temperature reforming activity and can generate hydrogen and carbon dioxide with high selectivity under suitable conditions. Therefore, it is widely used in methanol steam reforming hydrogen production technology.

2.2.2.2

Hydrogen Production with Methanol Cracking

Methanol is directly decomposed into CO and H2 under the action of a catalyst. H2 accounts for about 60% and CO accounts for more than 30% of the cracked gas. CO can be further converted into H2 by low-temperature water–gas shift reaction. Then, through low-temperature selective oxidation, high-purity H2 with a CO content less than 10−4 can be obtained. The equation of methanol cracking is as follows. CH3 OH → CO + 2H2

(2.9)

Hydrogen production from methanol cracking was initially used as a fuel for automobiles, as shown in Fig. 2.8. Liquid methanol is vaporized and cracked by the waste heat generated by the engine operation, and the cracked gas enters the engine to react with O2 in the air, which is the fuel of the engine. This process makes full use of the exhaust gas emitted by the engine and achieves energy recycling. Moreover, using H2 and CO as engine fuels burns more thoroughly as compared to methanol. In recent years, research has been carried out on the reaction mechanism of methanol cracking with specific focus on the adsorption and desorption of methanol on the catalyst surface. Some researchers believe that HCOOCH3 is an intermediate product of a methanol cracking reaction. At low temperatures, CH3 OH is first dehydrogenated to form HCOOCH3 . With increasing temperatures, HCOOCH3 is further decomposed to generate CO and CH3 OH. 2CH3 OH → HCOOCH3 + 2H2

(2.10)

HCOOCH3 → CH3 OH + CO

(2.11)

Fig. 2.8 Schematic diagram of the use of methanol as fuel in automobiles (Yuanli 2009)

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2 Hydrogen Production and Storage

Fig. 2.9 Methanol cracking process (Jianzhong and Yuandong 2004)

Deluca et al. (2019) believe that CH2 O is an intermediate cracking product of methanol cracking, and CH3 OH is first dehydrogenated to form CH2 O. Then CH2 O may react in two ways. One is to directly split into H2 and CO, and the other is to generate HCOOCH3 . Then according to the above reaction, CH3 OH and CO will be generated. CH3 OH → CH2 O + H2

(2.12)

CH2 O → CO + H2

(2.13)

2CH2 O → HCOOCH3

(2.14)

CuO-based catalysts are low-temperature catalysts that catalyze methanol cracking, and the operating temperature is generally 200–275 °C. The operating temperature of the Zn/Cr catalyst is about 300°C. Pt group catalysts are hightemperature catalysts, the operating temperature is generally above 400 °C. The operating temperature of copper chloride catalysts is generally 350 °C. Cu/Cr catalysts doped with Mn, Ba, SiO2 , or alkaline earth metals have high activities at low temperatures, their catalytic activity is higher than those for ordinary Cu/ZnO catalysts (Idem and Bakhshi 1996). A typical industrial methanol cracking process is shown in Fig. 2.9.

2.2.2.3

Hydrogen Production with Methanol Partial Oxidation

Methanol Partial Oxidation (MPO) is a process in which methanol vapor and oxygen are introduced into the feed to react to generate H2 and CO2 . The reaction formula is as follows. 1 CH3 OH + O2 → CO2 + 2H2 2

(2.15)

Compared with methanol steam reforming and methanol decomposition, partial oxidation of methanol to produce hydrogen has a specific advantage. This advantage is mainly reflected in the fact that the reaction is strongly exothermic, so the time

2.2 The Method of Hydrogen Production

55

required from the start to the formal reaction is much shorter than that required for endothermic steam reforming and decomposition reactions. Murcia-Mascarós et al. (2001) studied the partial oxidation of methanol catalyzed by Cu/ZnO/Al2 O3 catalysts obtained from hydrotalcite precursors and proposed that the partial oxidation of methanol included thermal oxidation of methanol, thermal decomposition of methanol and methanol reforming reaction. Among these, methanol thermal oxidation and thermal decomposition are parallel reactions, which constitute a continuous reaction with a methanol reforming reaction. The three reaction equations are as follows. 3 CH3 OH + O2 → CO2 + 2H2 O 2

(2.16)

CH3 OH → CO + 2H2

(2.17)

CH3 OH + H2 → CO2 + 3H2

(2.18)

The molar ratio of O2 /CH3 OH in the feed gas is controlled between 0.3 and 0.4. Thermal oxidation and thermal decomposition of methanol are considered the main reactions in the initial stages of the process. When O2 is fully consumed, the methanol conversion rate increases beyond the stoichiometric amount based on partial oxidation. The chemical selectivity of H2 in the product gas (the ratio of the number of reactants consumed by H2 to the total amount of reactants) increases, but the selectivity of CO does not increase significantly. Therefore, this study proposed that the subsequent reaction was the mechanism of the reforming reaction of methanol with the by-product H2 O. Rabe and Vogel (Murcia-Mascarós et al. 2001) studied commercial Cu/ZnO/ Al2 O3 catalysts and conducted catalytic methanol partial oxidation studies using a thermal gravimetric analyzer (TGA). Fourier transform infrared spectroscopy was used for analysis. It was found that when the O2 contents in the feed were high, formaldehyde and H2 O were present in the product, and that the formaldehyde may continue to react to generate H2 and CO2 . Although the mechanism of the entire reaction is not fully clear, it could be confirmed that CO2 was the initial reaction product and was not generated by the oxidation of CO in the subsequent steps.

2.2.2.4

Hydrogen Production with Methanol Partial Oxidation Reforming

Methanol partial oxidation reforming is a reaction process that combines methanol partial oxidation and methanol steam reforming reactions. Methanol vapor and water vapor in the system react with oxygen to generate H2 and CO2 . The process is as follows.

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2 Hydrogen Production and Storage

CH3 OH + (1 − 2n)H2 O + nO2 → CO2 + (3 − 2n)H2 (0 < n < 0.5)

(2.19)

Since the reaction system is composed of endothermic methanol steam reforming and exothermic methanol partial oxidation, the system is heated by methanol partial oxidation. The theoretical molar hydrogen production of methanol is between that of methanol steam reforming and methanol partial oxidation. The main factors affecting the product gas composition are the reactor gas inlet temperature and the molar ratio of water to alcohol. A higher molar ratio and gas inlet temperature can prevent the oxidation reaction of methanol with oxygen. Moreover, the high content of H2 in the product can reduce the carbon deposition of the catalyst (Semelsberger et al. 2004), but the role of increasing energy consumption needs to be considered.

2.2.3 Biological Hydrogen Production Biological hydrogen production refers to the use of microorganisms to biodegrade organic wastewater and waste to obtain hydrogen. This process can not only obtain hydrogen but also treat the waste. So, it has drawn increasing attention in recent years, although the research on biological hydrogen production had already been initiated a long time ago. As early as the nineteenth century, it was recognized that bacteria and algae had the basic requisite characteristics for producing hydrogen molecules. Under the action of microorganisms, hydrogen can be produced from water by fermenting calcium formate. In 1942, when scientists observed the growth of some algae, it was found that by reducing the supply of CO during photosynthesis, green algae stopped releasing oxygen, but produced hydrogen instead. In 1958, scientists discovered that algae could directly produce hydrogen through photolysis without the need for the fixation of CO2 . In 1966, Lewis (1966) first proposed the subject of biological hydrogen production, and his research was mainly focused on the photolysis hydrogen production and fermentation hydrogen production of green algae, cyanobacteria, and photosynthetic bacteria. In 1974, Benemann et al. (Liyou and Maojie 2017) found that the cyanobacteria-anabaena could simultaneously produce hydrogen and oxygen after being stored in argon atmosphere for several hours. The energy crisis of the 1970s drew widespread attention to biomass hydrogen production. The initial research on biomass hydrogen production by PNL (Pacific Northwest Laboratory) in the United States mainly focused on high-temperature vaporization of biomass, extraction of liquid fuel and synthesis gas from biomass, and preliminary research on its kinetic properties and catalysts. Subsequently, PNL conducted research on the biomass vaporization system in critical water, mainly analyzing the chemical characteristics of biomass reaction in high-temperature compressed fluid and supercritical fluid, including catalyst selection, continuous flow reactor test, and carbon gasification process. In the early 1990s, the University of Hawaii began to use supercritical technology to vaporize biomass to produce hydrogen, using activated carbon as a catalyst to study the effect of vaporization of

2.2 The Method of Hydrogen Production

57

biomass in supercritical water. High-pressure water was used as a CO absorbent. It is currently working on prolonging the activity of the catalyst and completing the design and installation of the biomass reforming flow reactor, while preparing for the further pilot scale studies on the new reactor system (Antal et al. 2000; Alves et al. 2013). Biomass hydrogen production employs carbohydrates as hydrogen donors, in particular photosynthetic bacteria or anaerobic bacteria to produce hydrogen. Microbial carriers, embedding agents and other bacterial immobilization methods are applied to immobilize the bacteria to achieve hydrogen production. According to different types of microorganisms, raw materials, and mechanisms required by organisms in the process of hydrogen production, biological hydrogen production can be divided into photosynthetic hydrogen production, hydrogen production by dark anaerobic fermentation, photosynthetic-fermentation composite biological hydrogen production, and so on.

2.2.3.1

Photosynthetic Hydrogen Production

Photosynthetic bacteria can use organic matter as hydrogen donors and carbon sources under anaerobic light or aerobic dark conditions. Bacteria that carry out photosynthesis also have the property of changing their metabolic types with environmental conditions. There are three types of microorganisms that can achieve photobiological hydrogen production: aerobic green algae, blue-green algae, and anaerobic photosynthetic bacteria. These photo-oxygen organisms use sunlight as an energy source fully utilizing solar energy for hydrogen release. Photosynthetic bacteria have mild hydrogen production conditions and can use a variety of organic wastes as substrates for hydrogen production to achieve dual effects of energy production and waste utilization. Therefore, photosynthetic bacteria hydrogen production can be treated as an important pathway to a future energy resource. Photosynthetic hydrogen production includes biological hydrogen production technology with solar water splitting and biological hydrogen production technology with photo-fermentation. Gaffron and Rubin (1942) reported hydrogen and oxygen production with photobiological processes, using solar energy and photosynthetic microorganisms for efficient hydrogen production. Since Gest (1993) first demonstrated that photosynthetic bacteria could use organic matter as a hydrogen donor to achieve photosynthetic hydrogen production, the research on the mechanism of photosynthetic hydrogen production has always been a difficult and interesting topic for research. The physiological functions and metabolic roles of photosynthetic microorganisms are diverse, so they are likely to have different hydrogen production pathways. Taking the biological hydrogen production technology from solar water splitting as an example, both blue-green algae and green algae can produce hydrogen through direct and indirect photosynthesis. The hydrogen production pathway is shown in Fig. 2.10 Direct photosynthetic hydrogen production process of blue-green algae and green algae uses solar energy to directly split water to generate hydrogen and oxygen. It

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Fig. 2.10 Pathways of photosynthetic hydrogen production (Dasgupta et al. 2010) Fdox -Ferredoxin (oxidation state); Fdred -Ferredoxin (reduction state)

shows aerobic photosynthesis like higher plants in capturing solar energy, which contains two photosynthetic systems (PS I and PS II). When oxygen is insufficient, hydrogenase can also use electrons from ferredoxin to reduce protons and produce hydrogen. In a photoreactor, partial inhibition of the cell’s photosynthetic system, PS II, produces anaerobic conditions. This is because only a small amount of water is oxidized to produce oxygen, and the remaining oxygen is consumed by respiration. The chemical reaction equation is as follows. 2H2 O + hv → O2 ↑ +4H+ + Fdred 4e + 4H+ → FdOX + 2h 2

(2.20)

Indirect biological photosynthesis, the process of efficiently separating oxygen from hydrogen, is most common in blue-green algae. Stored carbohydrates are oxidized to produce hydrogen. The chemical reaction equation is as follows. 12H2 O + 6CO2 → 12H2 + 6CO2

(2.21)

C6 H12 O6 + 12H2 O → 12H2 + 6CO2

(2.22)

2.2 The Method of Hydrogen Production

59

To improve the production rate of biological hydrogen, various photobioreactors have been designed. In a photobioreactor, luminous energy is converted into biochemical energy. Some fundamental factors differentiate a bioreactor from other common reactors. The reactor is transparent, allowing light to pass through as much as possible. Energy transfer is instantaneous and cannot be stored in the reactor. The cells tend to shade themselves, resulting in a loss of extra absorbed energy. Fluorescence and heat can raise temperatures, so bioreactors require additional cooling systems. Reactors are usually thin in order to increase the ratio of reactor area to volume and avoid the effects of the self-shading of cells. Various photobioreactors have individual advantages and disadvantages. For example, a large light irradiation area can be obtained in a tubular photoreactor. However, due to the high concentration of dissolved oxygen produced by photosynthesis and the high energy input by the pump, the large-scale development of this type of reactor has been limited. In a column-type photobioreactor, the irradiation area of light is small. Since it is small and cheap, easy to operate, and can be stirred by bubbling, it is widely used in hydrogen production by microalgae and photosynthetic bacteria. In the flat plate photoreactor, the photosynthesis efficiency is high, the air pressure is controllable, and the cost is low compared with other reactors. But it is difficult to maintain a constant culture temperature and proper agitation during the hydrogen production process. In addition to the effect of the shape of the photobioreactor on the hydrogen production efficiency, the physicochemical parameters of the photobioreactor also affect the hydrogen production, such as the pH of the solution, temperature, light intensity, depth of light penetration, dissolved oxygen, dissolved CO2 , agitation, gas exchange, carbon and nitrogen sources and the ratio of the two, etc.

2.2.3.2

Hydrogen Production by Dark Anaerobic Fermentation

Hydrogen production by dark anaerobic fermentation produces hydrogen by degrading organic matter under the action of anaerobic microbial nitrogenase or hydrogenase. This process does not require luminous energy. The microorganisms capable of producing hydrogen by dark anaerobic fermentation include some obligate anaerobic bacteria, facultatively anaerobic bacteria, and a small number of aerobic bacteria. At present, there are three main types of hydrogen production by dark anaerobic fermentation. One type combines pure strains with immobilization technology. The conditions for hydrogen production by fermentation of this type are relatively harsh, and it is currently in the experimental stage. The second type uses anaerobic activated sludge to ferment organic wastewater to produce hydrogen. The third type uses highefficiency hydrogen-producing bacteria to carry out the biological fermentation of carbohydrates, proteins, and other substances to produce hydrogen. The reactors and technologies required for hydrogen production by biological fermentation are relatively simple, which greatly reduces the cost of biological

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hydrogen production. After years of research, it has been found that the hydrogenproducing bacteria species mainly include Enterobacter, Clostridium, Escherichia, and Bacillus. In addition to the research and application of traditional strains, people also try to find strains with higher hydrogen production efficiency and wider substrate utilization range. But few new hydrogen-producing organisms have been reported in the past ten years. The amount of hydrogen produced by biological fermentation has not increased significantly. The hydrogen production process of biological fermentation does not depend on the light source and has a wide range of substrates, which can be carbohydrates such as glucose and maltose, as well as garbage and wastewater. Among these, glucose is the preferred carbon source for producing hydrogen through fermentation. In this process, acetic acid, butyric acid, and hydrogen are generated. Various chemical reactions are as follows. C6 H12 O6 + 2H2 O → 2CH3 COOH + 2CO2 + 4H2

(2.23)

C6 H12 O6 + 2H2 O → CH3 CH2 COOH + 2CO2 + 2H2

(2.24)

The traditional biological fermentation hydrogen production process includes the method of biological hydrogen production by activated sludge, and the immobilized hydrogen production by fermentation bacteria. A biological hydrogen production method combining biological fermentation with microbial electrolytic cells has been studied. A. The Method of Biological Hydrogen Production by Activated Sludge The activated sludge biological hydrogen production method uses anaerobic sludge to ferment organic wastewater to produce hydrogen. The end products after fermentation are mainly ethanol and acetic acid. The equipment required for biological hydrogen production using activated sludge is relatively simple and of low-cost. But the generated hydrogen is easily consumed by the hydrogen-consuming bacteria mixed in the activated sludge, thus affecting the hydrogen production efficiency. China has made some progress in biological hydrogen production from activated sludge. In 2005, Ren Nanqi completed the world’s first demonstration project of biological hydrogen production by wastewater fermentation. The biological hydrogen production device (CSTR type) used had an effective volume of 65 m3 , and the daily hydrogen production capacity was 350 m3 . The demonstration project of coupled power generation with hydrogen fuel cells has been completed. The daily hydrogen production capacity can meet the needs of 60–80 households. B. The Method of Immobilized Hydrogen Production by Fermentation Bacteria In the study of hydrogen production by fermentation, it was found that a higher bacterial concentration can fully extend the hydrogen production capacity of bacteria. In order to increase the biological holding capacity of bacteria in the reactor, cell immobilization technology is used to make fermentation bacteria aggregate effectively. The

2.2 The Method of Hydrogen Production

61

hydrogen production method of immobilized fermentative bacteria is to immobilize the fermentative hydrogen-producing bacteria on lignocellulose, agar, alginate, and other carriers, then cultivate them and finally use them for hydrogen production. Studies have shown that, compared with non-immobilized cells, immobilized cells can tolerate a lower pH value, continue to produce hydrogen for a longer time, and can inhibit the rate of oxygen diffusion. Although the immobilization technology has greatly improved the hydrogen production rate and operation stability of the unit volume reactor, the carriers used have different degrees of toxicity to the fermentation bacteria. The large space occupied by the carriers limits the increase of the concentration of hydrogen-producing bacteria. Meanwhile, the carriers also have the disadvantages of poor mechanical strength and durability. C. The Method Combining Biological Fermentation with Microbial Electrolytic Cells Combining biological fermentation with microbial electrolytic cells can increase the hydrogen production of the overall system. First, through biological fermentation, bacteria convert biomass (such as lignocellulose) into formic acid, acetic acid, lactic acid, ethanol, carbon dioxide, and hydrogen. The acids and alcohols are then converted into hydrogen by microbial electrolytic cells. Such a combination can greatly improve the efficiency of fermentation hydrogen production. Several factors affect the operation of the bio-fermentation hydrogen production reactor, such as temperature, pH value of the solution, substrate, hydraulic retention time etc. The main factor limiting the industrial scale biological hydrogen production is the low hydrogen production rate in the process of fermentative hydrogen production. According to the current hydrogen production capacity, if industrialization is to be realized, a huge volume reactor is required. Some studies have shown that the production rate of hydrogen at room temperature is 2.7L/h by using the biological fermentation method, and the minimum volume of the bioreactor that provides 1 kW of electricity for small proton exchange membrane fuel cells is 198L. For reactors on an experimental scale, batch reactors are usually employed. They have the advantages of easy operation and flexibility. But so far, no industrial-scale reactor has been constructed. In Germany, most of the biological hydrogen production reactors are usually vertical continuous stirring reaction tanks with different types of stirrers. More than half of these types of reactors are covered by a single- or double-layered membrane to preserve biomass.

2.2.3.3

Photosynthetic-Fermentation Composite Biological Hydrogen Production

Utilizing the advantages and complementary synergy of anaerobic dark fermentation hydrogen-producing bacteria and photo-fermentation hydrogen-producing bacteria, the overall combined system is called photosynthetic fermentation composite biological hydrogen production technology.

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The photosynthetic fermentation composite technology can not only reduce the required luminous energy but also increase hydrogen production and completely degrade the organic matter. Therefore, this technology has become the development direction for the biological hydrogen production technology. Non-photosynthetic organisms can degrade macromolecular substances to produce hydrogen. Photosynthetic bacteria can utilize a variety of low-molecular-weight organic matter for photosynthetic hydrogen production. Cyanobacteria and green algae can photolyze water to produce hydrogen. Non-photosynthetic bacteria and photosynthetic bacteria can also produce hydrogen separately in different reactors. In the first phase (dark reactor, no light required), the organic matter is degraded into organic acid, and hydrogen is generated. After the discharge enters the second phase (photoreactor, light required), the photosynthetic bacteria completely degrade the organic acid to produce hydrogen. In this system, the non-photosynthetic bacteria and the photosynthetic bacteria are reacted in their respective reactors, and it is easier to control them to reach the optimum state respectively. Photosynthetic-fermentation composite biological hydrogen production includes the two-step method of dark-photo-fermentation bacteria (Fig. 2.11) and hydrogen production by the mixed culture (Fig. 2.12). The mixed cultivation of dark- photofermentation bacteria is the coexistence of microbial strains of different nutritional types and properties in a system. In this way, a hydrogen production system of the high-efficiency mixed culture is established, and the complementary functional properties of these bacteria are used to improve the hydrogen production capacity, enlarge the substrate conversion range, and advance its conversion efficiency. Compared with hydrogen production by the mixed culture, the two-step hydrogen production is easier to realize, and the two kinds of bacteria play their roles in their respective environments. The first step is the fermentation of dark fermentative bacteria to produce hydrogen, which simultaneously produces a large amount of soluble smallmolecule organic metabolites. The second step is that photo fermentative bacteria rely on luminous energy to further utilize these small molecule metabolites and release hydrogen.

Fig. 2.11 Schematic diagram of the two-step method of dark- and photo-fermentation bacteria (Sufang 2014)

Fig. 2.12 Schematic diagram of hydrogen production by the mixed culture (Sufang 2014)

2.2 The Method of Hydrogen Production

63

Hydrogen production by dark anaerobic microbial fermentation has some advantages over photosynthetic hydrogen production. Firstly, it has a high capacity for hydrogen production and a high growth rate of hydrogen-producing bacteria, without the need for a light source. Secondly, the design, operation, and management of the reaction device are simple and convenient. In addition, the sources of its raw materials are extensive and low-cost, and the bacteria are easier to be preserved and transported. Therefore, it is easier to realize large-scale industrial production through fermentation biological hydrogen production than photolysis biological hydrogen production technology. At present, the research and scale of photo-fermentation biological hydrogen production technology are still at the laboratory level, and the pilot-scale research of dark-fermentation biological hydrogen production technology has been completed (Nanqi 2001). To achieve industrial production, it is still necessary to further improve the conversion efficiency and reduce the cost of hydrogen production. There are many difficulties in the large-scale biological hydrogen production from pure strains, and the material and energy recycling process in nature, especially the degradation process of organic wastewater, scrap, and biomass, is usually conducted by two or more microorganisms in synergy.

2.2.4 Hydrogen Production by Electrolysis of Water The traditional hydrogen production technology by electrolysis of water is relatively mature as it has been used for more than 80 years. The method is to supply electricity to a water electrolysis device, so that water is electrochemically decomposed into hydrogen and oxygen. The purity of hydrogen obtained by the method of electrolysis of water is high and can reach 99.99%. But the process consumes a lot of electricity. At present, the electrolysis efficiency of this process needs to be improved from 50 to 70%. To improve the efficiency of hydrogen production, electrolysis is usually carried out in a high-pressure environment with pressures typically ~3.0–3.5 MPa. If the Solid Polymer Electrolyte (SPE) method developed in the United States is used, the electrolysis efficiency can be increased to 90% (Lu and Srinivasan 1979). Based on the current thermoelectric conversion efficiency of most nuclear power plants, which is only about 35%, the total efficiency of nuclear hydrogen production in this route is about 30%. However, the efficiency of hydrogen production by electrolysis of water is still quite low thereby limiting its large-scale application. Pure water is a weak electrolyte due to its small degree of ionization and low conductivity. Therefore, when electrolyzing water, an electrolyte needs to be added to increase the conductivity of the solution, so that water can be smoothly electrolyzed into hydrogen and oxygen. When direct current is passed into the aqueous electrolyte solution, the decomposed substances have absolutely nothing to do with the original electrolyte. The substance that is decomposed is the solvent water, while the electrolyte remains in the water. For example, sulfuric acid, sodium hydroxide, potassium hydroxide, etc. all belong to this type of electrolyte.

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With potassium hydroxide (KOH) as an example, when KOH solution is electrolyzed, direct current is passed into the electrolyzer, and the electrolyte KOH will not be electrolyzed. Water molecules react electrochemically at the electrodes, releasing oxygen at the anode and hydrogen at the cathode. Potassium hydroxide is a strong electrolyte. After it dissolves in water, the ionization process occurs. A large amount of K+ and OH− ions are produced in the aqueous solution. Water is a weak electrolyte and difficult to ionize. But when KOH is dissolved in water, polar water molecules surround the ionized K+ to form hydrated potassium ions, and the action of K+ makes the water molecules to have a polar direction. Under the action of direct current, K+ moves to the cathode together with water molecules in a polar direction. When both H+ and K+ exist in the aqueous solution, H+ will get electrons first at the cathode and become hydrogen, while K+ will remain behind in the solution. Hydrogen production by electrolysis of water has been industrialized. The core part of the equipment of water electrolysis hydrogen production is the electrolyzer. At present, the commonly used electrolyzers include alkaline electrolyzers, proton exchange membrane electrolyzers (PEM) or solid polymer electrolyzers (SPE), and solid oxide electrolyzers.

2.2.4.1

Hydrogen Production by Alkaline Water Electrolysis

Hydrogen production by alkaline water electrolysis is one of the easiest methods for producing hydrogen. At present, the technology is relatively mature and widely used in industrial fields. Figure 2.13 shows the schematic diagram of alkaline water electrolysis. The main technical problem here is the low current density due to high ohmic losses in the liquid electrolyte. In the overall alkaline water electrolysis system, Fig. 2.13 Schematic diagram of alkaline water electrolysis (Yongheng et al. 2019)

2.2 The Method of Hydrogen Production

65

the resistance comes mainly from three sources: external resistance, transfer resistance, and electrochemical resistance (Buttler and Spliethoff 2018). Gas evolution can be accelerated by circulating the electrolyte or by adding inert surfactants. New diaphragms can be developed to reduce diaphragm resistance, thereby reducing energy consumption costs, and improving its durability and safety. Most of the devices for hydrogen production by alkaline water electrolysis have a bipolar filter press structure, which can work under ordinary pressures and have the advantages of safety and reliability. However, the process of hydrogen production by electrolysis of water can be a source of potential damage to the environment. Leaks in the production process or improper disposal after use can cause pollution to the surrounding environment.

2.2.4.2

Proton Exchange Membrane (PEM) and Solid Polymer Electrolyte (SPE)

Proton exchange membrane water electrolysis technology (PEM) is a hydrogen production technology by water electrolysis developed by the General Electric Company in the 1970s. Compared with alkaline water electrolysis, PEM technology significantly reduces the size and weight of the electrolyzer. The proton exchange membrane used in PEM electrolysis is both an ion-conducting electrolyte and a gas barrier (Lili et al. 2019). The electrolysis current density of PEM technology is higher than that of alkaline electrolysis technology, and the purity of hydrogen produced is higher than that of alkaline water electrolysis. Figure 2.14 shows the schematic diagram of PEM water electrolysis. Water passes into the anode area and is oxidized to oxygen, and protons are reduced to hydrogen at the cathode through the proton exchange membrane in the form of hydrated protons. The anode and cathode are mainly noble metal catalysts. A. Hydrogen Production by PEM Water Electrolysis The main difference between the hydrogen production technology by PEM water electrolysis and the hydrogen production technology by alkaline water electrolysis is that a high molecular polymer cation exchange membrane is used in the PEM, instead of a diaphragm and liquid electrolyte in alkaline water electrolysis. It plays the role of isolating gas and ion conduction. In the PEM electrolyzer, water is decomposed into oxygen, hydrogen ions, and electrons through electrochemical reactions at the anode catalytic reaction interface through the anode chamber. The hydrogen ions generated at the anode pass through the electrolyte membrane in the form of hydronium ions (H+ ·H2 O), and electrochemically react with electrons transported through the external circuit at the reaction interface of the cathode chamber to generate hydrogen. Anodic reaction: H2 O → 2H+ + 0.5O2 + 2e−22

(2.25)

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Fig. 2.14 Schematic diagram of PEM water electrolysis (Yongheng et al. 2019)

Cathodic reaction: 2H+ + 2e− → H2

(2.26)

1 H2 O == H2 + O2 2

(2.27)

Overall reaction:

The electrolyzer of the hydrogen production technology of PEM water electrolysis is composed of PEM membrane electrodes, bipolar plates, and other components. The membrane electrode is the core component of the electrochemical reaction, which determines the performance of the electrolyzer. The membrane electrode is composed of a proton exchange membrane and a cathode and anode catalyst bonded to the proton exchange membrane, and it is the place for the water electrolysis reaction. The bipolar plate can connect multichip membrane electrodes in series and separate the membrane electrodes from each other. There are anode flow channels and cathode flow channels on both sides of the bipolar plate, which play the role of material transport, collecting, and outputting H2 , O2 , and H2 O. At the same time, they conduct electrons in the process of water electrolysis (Shuping and Song 2009). B. Hydrogen Production by SPE Water Electrolysis The electrolyzer of SPE (solid polymer electrolyte) water electrolysis is composed of several electrolysis chambers connected in series in the form of bipolar filter pressing. They consist of electrodes, proton exchange membranes sprayed with platinum-group metal catalysts, and gaskets. The proton exchange membrane is

2.2 The Method of Hydrogen Production

67

mainly composed of the perfluorosulfonic acid proton exchange membrane. Each chamber is compressed by end plates and tensioning screws. The electrolyzer is provided with an O2 /H2 O outlet, a nitrogen purge port, an H2 /H2 O outlet, and a deionized water inlet. The electrolyzer is the core component of the hydrogen production system, and auxiliary equipment includes hydrogen and oxygen separators, circulating pumps, feedwater and deionized water equipment, heat exchangers, power supplies, and control panels. When deionized water is supplied to the anode of the proton exchange membrane of the electrolysis chamber and the direct current is applied, the water is electrolyzed, and oxygen is generated on the anode. The protons generated on the anode are conducted through the proton exchange membrane and combine with the electrons generated on the cathode to form hydrogen. Anode: 2H2 O == 4H+ + O2 + 4e−

(2.28)

4H+ + 4e− == 2H2

(2.29)

Cathode:

The oxygen precipitated on the anode leaves the anode with water and enters the oxygen separator, where it is separated from the water by gravity, and the separated oxygen is stored for further use or vented. The mixed flow of hydrogen and water precipitated on the cathode also enters the hydrogen separator/cooler. The hydrogen is separated from the water by gravity, and the separated water is returned to the suction side of the circulating pump. This method has advantages that other on-site hydrogen production technologies do not have. In addition to the high purity of the product gas, it has the advantages of less maintenance, low cost, no corrosive liquid, and no pollution to the environment. With the rapid development of fuel cell vehicles and space technology, SPE technology is expected to develop rapidly (Shuping and Song 2009). The world’s first SPE electrolyzer was successfully developed by General Electric Company of the United States and used in fuel cells in NASA’s space program. In the 1970s, SPE hydrogen production technology was used for water electrolysis. In the early days, only the application of small equipment was studied, which was limited to aerospace and military. In 1975, in order to adapt to industrial development, the U.S. government, electric utilities, and General Electric Company formulated a development plan to scale up SPE hydrogen production equipment and develop advanced equipment for water electrolysis hydrogen production. Figure 2.15 shows the schematic diagram of the hydrogen production equipment. Compared with alkaline water electrolysis, the electrolyte of the proton exchange membrane electrolyzer is changed from a generally strong alkaline electrolyte to a solid polymer ion exchange membrane, which can act as a diaphragm for the cathode and anode of the electrolyzer. As an electrolyte, the proton exchange membrane has the advantages of high efficiency, good mechanical strength, high chemical stability,

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Fig. 2.15 Schematic diagram of hydrogen production equipment (Shuping and Song 2009)

fast proton conduction, good gas separation, and convenience compared with traditional electrolytes using alkaline or acidic liquids. The proton exchange membrane electrolyzer operates at a higher current without reducing the hydrogen production efficiency. Although it does not leak corrosive liquids in actual operation, the polymer ion exchange membrane is expected to decompose and produce toxic gases when operating temperatures reach 150 °C.

2.2.4.3

Hydrogen Production by Solid Oxide Water Electrolysis

According to reports (Iora et al. 2010), the power consumption (standard state) for hydrogen production on alkaline electrolyzers is 4.3–4.8 kW·h/m3 . As Proton electrolyte membrane electrolyzers cannot presently reduce the power consumption of hydrogen production, new breakthroughs are required in solid oxide electrolyzers. The operating temperature of solid oxide water electrolysis is between 700 °C and 1000 °C. Due to high temperatures of the reaction, the efficiency of this technology is higher than those of alkaline water electrolysis and PEM water electrolysis. The electrolyte of this technology is mainly solid oxide, which reduces the total loss in the electrolyzer by increasing the operating temperature (600–1000 °C), and the heat

2.2 The Method of Hydrogen Production

69

energy generated by other processes replaces part of the electrical energy required by the solid oxide electrolyzer. But such high operating temperatures require expensive materials. Therefore, high investment and operating costs will be required. From the perspective of chemical reactions or energy conversion, hydrogen production by high-temperature water electrolysis in solid oxide electrolysis cells (SOEC) is the inverse process of the reaction of hydrogen with oxygen in solid oxide fuel cells (SOFC) to generate water. As shown in Fig. 2.16 (Ge et al. 2015), when the power is turned on, water molecules on the hydrogen electrode side diffuse to the three phase boundaries (TPB) of the hydrogen electrode, electrolyte, and hydrogenwater vapor mixture and then decompose, producing adsorbed H and O. Two H atoms combine to form H2 , with diffusing hydrogen getting collected at the electrode. O atoms capture two electrons to form O2. and diffuse through the oxygen ion conductor electrolyte to the interface between the anode and the electrolyte, where the O2. ions are oxidized. The two electrons it carries flow to the outer circuit to complete the current loop, and the oxygen that loses electrons combines to form O2 , which then diffuses out of the oxygen electrode. The SOEC electrode reaction is as follows (Ben et al. 2017). Hydrogen electrode (cathode): H2 O + 2e− → H2 + O2−

Fig. 2.16 The operating principle of SOEC (Ben et al. 2017)

(2.30)

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Fig. 2.17 Concept of the IS process (Ping et al. 2005)

Fig. 2.18 GA flowsheet of the sulfur-iodine thermochemical cycle for hydrogen production (Ping et al., 2005)

Oxygen electrode (anode): O2 →

1 O2 + 2e− 2

(2.31)

2.2 The Method of Hydrogen Production

71

Overall electrode reaction: 1 H2 O → H2 + O2 2

(2.32)

It has been reported that moderate-temperature solid oxide electrolyzers consume less electricity for hydrogen production than other types of electrolyzers. According to thermodynamic principles, when the temperature increases, the Gibbs free energy of the water electrolysis reaction in the solid oxide electrolyzer decreases, which means that a part of the electrical energy can be replaced by heat energy when the temperature rises. It is therefore possible to combine solid oxide fuel cells (SOFC) with solid oxide electrolysis cells (SOEC) for hydrogen production. Natural gas is injected into the SOFC to provide electricity for the SOEC, and the heat generated by the irreversible process in the SOFC is supplied to the SOEC. Electricity and heat generated by the SOFC have been used to increase the conversion efficiency of energy. Compared with other methods for hydrogen production by water electrolysis, the solid oxide electrolyzer used for hydrogen production by solid oxide electrolysis has a high operating temperature. There is a possibility of generating oxygen at high temperatures, which can cause an explosion upon reaction with hydrogen. Table 2.5 provides a comparison between three water electrolysis technologies. It can be seen that alkaline water electrolysis technology has the advantage of long service life, but the KOH or NaOH solution used in the electrolyte will pollute the environment, and the current density of this technology is low. PEM water electrolysis technology has the advantages of high current density and hydrogen purity, and is safe and easy to operate. However, due to the cost and other reasons, it is currently only suitable for small-scale hydrogen production. The system efficiency of high-temperature solid oxide electrolysis technology is higher than that of the other two technologies, but its operating temperature is too high, and it has not yet been put into industrial production (Yongheng et al. 2019).

2.2.5 Nuclear Hydrogen Production Nuclear energy is a low-carbon, high-efficiency primary energy source, and the uranium resources it uses can be recycled. After more than half a century of development, nuclear energy is a mature technology. Nuclear hydrogen production has gradually become the best choice for large-scale industrial hydrogen production. Compared with other methods of hydrogen production, nuclear hydrogen production has advantages such as no greenhouse gas emissions, high efficiency, and large-scale hydrogen production (Lei and Ming 2019). The combination of nuclear energy and hydrogen energy can achieve clean energy production and utilization.

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Table 2.5 Comparison of water electrolysis technologies (Yongheng et al. 2019) Types of electrolysis

Alkaline electrolysis

PEM electrolysis

High-temperature solid oxide electrolysis

Electrolyte

20% ~ 30% KOH aqueous solution

polymer electrolyte

solid oxide electrolyte

Electrode

Ni

Pt, Ir

Ni-cermet

Anodic reaction

2OH− → 1/2O2 + H2 O + 2e

H2 O → 1/2O2 + 2H+ + 2e

O2− → 1/2O2 + 2e

Cathodic reaction

2H2 O + 2e → H2 + 2OH−

2H+ + 2e → H2

H2 O + 2e− → H2 + O2−

Current density/ A·cm−2

0.3 ~ 0.5

1~2

0.5 ~ 1

Operating temperature/°C

40 ~ 90

50 ~ 90

700 ~ 1000

Operating pressure/ 100 ~ 3000 kPa

100 ~ 30,000

Hydrogen purity/% 99.5 ~ 99.9998

99.9 ~ 99.9999

System efficiency/ %

68 ~ 77

62 ~ 77

System lifetime/h

> 100,000

> 40,000

89

At present, there are two main ways to produce hydrogen from nuclear energy: hydrogen production by water electrolysis and thermochemical hydrogen production. Nuclear reactors provide electricity and heat for these two methods. In addition to nuclear hydrogen production, the direct use of the high temperatures generated by the nuclear fission in the reactor for thermochemical hydrogen production has been investigated extensively. Compared with hydrogen production by water electrolysis, the thermochemical process hashigher efficiency and lower cost. However, with the efficiency of hydrogen production by water electrolysis ~80%, and the current thermoelectric conversion efficiency of light water reactors ~35%, the total efficiency of nuclear hydrogen production is estimated to be ~25%. The total efficiency of the high-temperature thermochemical process for hydrogen production is expected to reach higher than 50%. It may also be possible to raise the efficiency to ~60% by combining thermochemical hydrogen production with electric power generation. Thermochemical hydrogen production couples a nuclear reactor with a thermochemical cycle device for hydrogen production, and uses the high temperatures generated by the nuclear reactor as a heat source to catalyze the thermal decomposition of water at 800–1000 °C to produce hydrogen and oxygen. The simplest thermochemical water-splitting process involves heating the water to a high temperature and separating the hydrogen produced from the equilibrium mixture. The thermochemical properties of the water splitting reaction under standard conditions (25 °C, 1 atm) change as follows.

2.2 The Method of Hydrogen Production

1 H2 O → H2 + O2 2

73

(2.33)

θ θ ΔH298K = 285.84 kJ/mol; ΔG θ298K =237.19 kJ/mol; ΔS298K =0.163 kJ/mol. The entropy change is the negative value of the temperature derivative of ΔG, and its value is small. It can be seen from the calculation that the Gibbs free energy of the reaction cannot be zero until the temperature rises to about 4700 K. Kogan et al. (2000) have shown that the decomposition of water becomes more efficient when the temperature is higher than 2500 K. But both material and separation issues are, however, difficult to resolve under these conditions, therefore direct water decomposition is currently not feasible. Funk and Reinstrom (1964) first proposed the use of thermochemical processes to split water to produce hydrogen in 1964. By introducing a new substance that divides the water-splitting reaction into several different reactions, and forms a cycle as shown below.

H2 O + X → XO + H2

(2.34)

1 XO → X + O2 2

(2.35)

The net result is the splitting of water to produce hydrogen and oxygen. 1 H2 O → H2 + O2 2

(2.36)

The sum of the entropy change, enthalpy change, and Gibbs free energy change of each reaction is equal to the corresponding value of the direct water decomposition reaction. Each step of the reaction may be carried out at relatively low temperatures. In the whole process, only water is consumed, and other substances are recirculated in the system to achieve the purpose of thermally decomposing water to produce hydrogen. The most promising method of catalytic thermal decomposition, that has been recognized internationally, is the sulfur-iodine cycle (IS cycle) developed by the United States, in which the sulfur cycle separates oxygen from water and the iodine cycle separates hydrogen. The IS cycle was invented by the GA company in the United States in the 1970s (Norman et al. 1982), and a great deal of research has been carried out since then. This process is known as the GA process. Besides, Japan, France, China, and other countries have conducted in-depth research on the IS cycle as the preferred process for future nuclear hydrogen production (Agency October 2000; Anzieu et al. 2006). The IS cycle process is shown in Fig. 2.17. In theory, the process consists of three reactions. Bunsen reaction: SO2 + I2 + 2H2 O → 2HI + H2 SO4

(2.37)

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Sulfuric acid decomposition reaction: 1 H2 SO4 → SO2 + H2 O + O2 2

(2.38)

Hydroiodic acid decomposition reaction: 2HI → I2 + H2

(2.39)

The net overall reaction is still water splitting: 1 H2 O → H2 + O2 2

(2.40)

This process is divided into four units (I, II, III, and IV). Units I and II respectively involve the production of H2 SO4 /HI and the separation of O2 . Decomposition reaction in unit III produces I2 and H2 gases. In unit IV, the I2 from III reacts with H2 O and SO2 in a countercurrent reactor to generate two kinds of acid solutions. During the GA process, it was found that in the presence of excess I2 , HI and H2 SO4 could be separated into two liquid phases, forming the basis of the IS cycle. The lower density phase contains all H2 SO4 at a concentration of 50%, with traces of I2 and SO2 . The denser phase contains HI and a large amount of I2 in solution. H2 SO4 reacts with liquid I2 and SO2 . When its concentration increases to 57%, the two phases separate, and then the H2 SO4 goes through unit II for decomposition. The low-density phase containing HI, H2 O, I2 , and SO2 goes through a degassing step to remove all SO2 and then enters III for purification and HI separation. The mixture of SO2 and O2 produced by the decomposition of SO3 in II reacts with I2 and H2 O through a countercurrent reactor, and the remaining gas at the top of the reactor is only O2 and a small amount of I2 . The I2 is removed in the column washer to obtain the O2 . II contains the concentration and decomposition of H2 SO4 . Sulfuric acid at a concentration of 57% is concentrated in a series of flash evaporators and then decomposed into H2 O and SO3 . SO3 is then decomposed into SO2 and O2 at 1120 K and 0.86 MPa. III is the separation of HI. The HI-I2 -H2 O solution from unit I is treated with concentrated H3 PO4 , and I2 at a concentration of 95% is separated from the solution. The solution containing HI, H2 O, H3 PO4 , and a small amount of I2 is sent to the extractive distillation column, and most of the H2 O remains in the H3 PO4 . HI, I2 , and a small amount of H2 O are separated as overhead vapors and then separated by condensation. HI is purified and compressed to 5 MPa and then sent to unit IV for separation. Unit IV is the decomposition of HI. HI is catalytically decomposed at 393 K in the decomposition reactor, and the product H2 is separated from most of I2 and HI in the gas–liquid separator, and then washed with water to obtain pure H2 . I2 is returned to the main solution in unit I (Ping et al. 2005). At high iodine concentrations, the formed H2 SO4 and HI phases spontaneously separate. However, these two phases contaminate each other, which means that small

2.2 The Method of Hydrogen Production

75

amounts of HI and H2 SO4 are contained in the H2 SO4 phase and the HI phase, respectively. Under certain conditions, the operation of the Bunsen reaction and the separation of the two liquid phases at high temperatures may lead to side reactions (Sakurai et al. 2000). H2 SO4 + 6HI → S + 3I2 + 4H2 O

(2.41)

H2 SO4 + 8HI → H2 S + 4HI + 4H2 O Side reactions are more likely to occur with increasing reaction temperatures and acid concentrations, but high iodine concentrations hinder their occurrence. These side reactions can unbalance circulating materials or lead to clogged pipes. To avoid side reactions, all sulfuric acid must be removed from the HI phase solution, which is then distilled and recycled in the IS process. Similarly, hydriodic acid must be removed from the H2 SO4 solution. Ying et al.(2009) have proposed optimal operating conditions for efficient purification of H2 SO4 and HI phases in the closed loop IS process. The purification process should be carried out in a continuous operation. Then the purification process would require a lower nitrogen flow (such as 50 mL/ min) and a higher temperature (above 130 °C) to purify H2 SO4 and HI. The IS cycle is facing some challenging issues that include: (1) hydriodic acid and water form an azeotrope, and the HI concentration process using traditional distillation methods is energy-intensive and inefficient; (2) the decomposition reaction of HI is a reversible one, the equilibrium conversion rate is low, and the product H2 needs to be continuously separated from the reaction system; (3) the reaction of H2 SO4 below 400°C involves a strong corrosion process, with high material requirements. But this process has significant advantages as well. The method uses temperatures below 1000 °C to split water and to generate hydrogen; the chemical process has been well established. The process can be operated continuously. In addition, it is a closed loop process. Only water needs to be added, other materials are recycled, and there are no effluents. In addition, the expected efficiency can reach about 52%, and the efficiency of the combined process (hydrogen production and power generation) can reach 60%. Therefore, the IS cycle is still a hydrogen production method with a great potential. The hybrid sulfur cycle was originally proposed by Westinghouse Electric Corporation of the United States. It contains two main chemical reactions. The hybrid sulfur cycle is the simplest form of thermochemical water splitting for hydrogen production, involving only two reactions. One of them is a thermochemical reaction, involving the decomposition of sulfuric acid. The other reaction involves an electrochemical reaction, namely a sulfur dioxide depolarized electrolysis reaction. The chemical equations of the above two reactions are: 1 H2 SO4 → SO2 + H2 O + O2 2

(2.43)

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2H2 O + SO2 → H2 SO4 + H2

(2.44)

The overall reaction is water splitting to generate hydrogen and oxygen. At present, the main industrial hydrogen production methods include coal gasification, methane reforming, and water electrolysis. Compared with coal gasification, the carbon emissions are greatly reduced in the hybrid sulfur cycle with significant environmental benefits. Compared with methane reforming, the hybrid sulfur cycle does not need to consume the scarce natural gas resources in China. Furthermore, the standard electrode potential of SO2 depolarized electrolysis reaction is only 0.158 V, while that of the water electrolysis reaction at 25 °C is 1.229 V. The hybrid sulfur cycle for hydrogen production has significant thermodynamical advantages and a greater potential for power saving. In the traditional hybrid sulfur cycle process, SO2 depolarized electrolysis is carried out at near normal temperatures and pressure and direct current, while the sulfuric acid decomposition reaction needs to be catalyzed and decomposed by a catalyst at temperatures above 850 °C. The sulfuric acid unit has high requirements for thermal grade materials. As per the current theoretical and engineering research, the decomposition of sulfuric acid can use nuclear energy as a primary energy source. Sulfuric acid pyrolysis refers to the reaction in which sulfuric acid is decomposed into sulfur dioxide, water vapor, and oxygen at high temperatures (usually over 1000 °C) without a catalyst. Sulfuric acid can almost be completely decomposed in a few to tens of seconds at high temperatures and has the characteristics of simplicity, high efficiency, and producing high-grade steam by-product. In order to solve the current industrial application problem of the hybrid sulfur cycle, sulfur dioxide depolarized electrolysis is combined with the existing process of sulfuric acid pyrolysis to form a closed-loop hybrid sulfur cycle process. This makes the process of hydrogen production by hybrid sulfur cycle well suited to the large-scale demand for hydrogen in hydrogen-rich metallurgy and petroleum processing. Due to the requirements of high temperature and electricity, its efficiency is higher than that of conventional hydrogen production by electrolysis of water. Compared with hydrogen production by electrolysis of water, thermochemical hydrogen production has a higher efficiency. Its total efficiency at high temperatures is expected to exceed 50%. If it is combined with power generation, the efficiency can be increased to 60%. According to the operating temperature requirements of thermochemical hydrogen production, the high-temperature gas-cooled reactor of the Generation IV nuclear energy systems, which is being actively developed around the world, is suitable for heating the thermochemical hydrogen production process. The high-temperature gas-cooled reactor is recognized by international experts in the nuclear field as a reactor type with good safety characteristics. Its outlet temperature is 850–1000°C. It has the commercial application prospect for nuclear hydrogen production. At the end of 2002, the Generation IV International Forum (GIF) and the U.S. Department of Energy jointly released “A Technology Roadmap for Generation IV Nuclear Energy Systems”. They selected six types of reactors, namely gas-cooled fast reactors, lead-cooled fast reactors, molten salt reactors, sodium-cooled fast reactors,

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77

supercritical water-cooled reactors, and ultra-high/high-temperature gas-cooled reactors as the focus of GIF’s future international collaborative research. The Generation IV nuclear energy system is advanced with better safety, economic competitiveness, less nuclear waste, and can effectively prevent nuclear proliferation. It represents the development trend and technological frontier of advanced nuclear energy systems. Among the six types of reactors, the outlet temperature of the reactor core of the ultrahigh/high-temperature gas-cooled reactor is ~850–1000 °C. These have the characteristics of inherent safety, high outlet temperature, suitable power, etc., and have the commercial application prospect of nuclear hydrogen production (Yanli 2020).

2.2.6 Advantages and Disadvantages of Various Production Methods for Hydrogen Metallurgy: A Critical Comparison In the field of renewable energy, scientists have a new “definition” of the color of hydrogen. They divide H2 into gray, blue, and green according to the source of hydrogen energy. Gray hydrogen is the hydrogen produced by fossil fuels (such as natural gas, coal gas, etc.), associated with large amounts of CO2 emissions during the production process. These correspond to early stages of hydrogen energy production (2020–2030). It still currently accounts for 95% of the hydrogen produced in the world. Blue hydrogen refers to the hydrogen that meets the low carbon threshold (with CO2 separation or capture technology) but is still produced using non-renewable energy sources (such as fossil fuels, etc.). Green hydrogen refers to the hydrogen that not only meets low carbon thresholds but is produced from renewable energy sources (e.g., solar energy, wind energy). In the UK, demonstration plants have begun to conduct scale production to produce and use blue and green H2 to decarbonize carbon-intensive industries, including the cement and steel industries, thermal power plants, chemicals, and oil industries. In addition, a systematic strategy has been developed to expand the H2 distribution pipeline to support H2 -powered transport. Table 2.6 compares the limitations of various hydrogen production methods in industrial production. At present, the main method of hydrogen production in the metallurgical field is hydrogen production with coke oven gas. PSA technology is used to extract pure hydrogen and achieve the goals of adsorption and desorption by changing the pressure. Adsorption is often carried out in a high-pressure environment. Pressure swing adsorption proposes a method of combining pressurization and decompression, which is an adsorption–desorption (regeneration) cycle operation system consisting of pressurized adsorption and decompression and regeneration at a certain temperature. The adsorption capacity of the adsorbent to the adsorbate increases with increasing pressure, and vice versa. At the same time, the adsorbed

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gas is released during decompression down to ordinary pressure or vacuum to regenerate the adsorbent, and to achieve the separation or purification of the multicomponent mixed gas. Before cleaning the feed gas, the PSA must be adjusted to suit the composition of the feed gas. The whole process is divided into the following parts. (1) Impurities in the supplied gas are removed. The pressure of the supplied gas is increased to remove impurities and pure hydrocarbons with high carbon content. (2) The absorbed components are removed by the gas supply. (3) Desulfurization is completed. (4) Cleaning and delivery of the PSA are conducted (Yage and Lixia 2020). There are some requirements for the product hydrogen after using coke oven gas to produce hydrogen. The purity of H2 should not be lower than 99.99%. The pressure should not be lower than 1.6 MPa, and the temperature should not be higher than 50°C. For the traditional steel industry, the output of coke oven gas is huge. For the hydrogen production by coke oven gas, the available supply of raw materials is sufficient. However, in the production process, there are still greenhouse gas emissions, greatly polluting the environment (Yage and Lixia 2020). Since 2004, the United States has been promoting research on nuclear hydrogen production and has made some progress recently. The country announced the Table 2.6 Comparison of various hydrogen production processes Hydrogen Hydrogen production production process from gas

Hydrogen production from natural gas

Hydrogen production by ammonia decomposition

Hydrogen production by water electrolysis

Hydrogen production by methanol cracking

Technical maturity

Mature

Mature

Relatively mature

Mature

Relatively mature

Suitable scale/m3

10,000–20,000

> 5000

< 50

2–300

10 kg/cm2 , liquid hydrogen in a container, and lowtemperature hydrogen under atmospheric pressure when the gas temperature reaches 35 °C is regarded as a high-pressure gas. Operators need to be trained to obtain a high-pressure gas operation license before doing this job. Meanwhile, the usage area should be transformed as per the needs, and corresponding signs and facilities installed. In addition, the exhaust and temperature control should be carried out, and fire and ignition appliances be prohibited. The leakage of hydrogen at high pressures will be quite different. Hydrogen at ordinary pressures leaks into an open space, where it can quickly diffuse away from the ground due to the buoyancy of air. But hydrogen is often stored in high-pressure containers. The concentration of hydrogen leaked from a high-pressure container is inversely proportional to the distance from the leak and is little affected by the buoyancy of the air. So, it is easy to reach the lower limit concentration of hydrogen explosion near the leak. In addition, when the internal pressure of the high-pressure container rises rapidly, to prevent the container from exploding, it is necessary to automatically release hydrogen to reduce the pressure in the container. For safety reasons, a blasting plate or a spring-loaded safety valve is generally installed on the container It is also necessary to prevent the micro powder from clogging the valve. Hydrogen leakage at high pressures can be either instantaneous (such as compressors, and hydrogenation equipment) or continuous (such as pipeline cracks). The combustion of hydrogen leaked instantaneously can produce a fire mass. The harm caused by a continuous leakage depends on the burning time and the direction of the flame. An explosion is possible if the leak of hydrogen occurs in an enclosed space or if there are too many cracks in the pipes. The probabilities of the explosion caused by delayed combustion and spark combustion are 40% and 60%, respectively. The amplitude of the shock wave produced by the hydrogen explosion depends on hydrogen diffusion in the air and the concentration distribution. The strength of the shock wave increases with the total amount of hydrogen, and the effect of the explosion increases with the speed of flame propagation. If a large amount of hydrogen storage infrastructure is involved, a considerable distance, which is called a safety distance, needs to be set up between hydrogen storage facilities or between them and other facilities to avoid secondary hazards. It is also necessary to set the distance away from the heat source. The distance from the heat source of 9.8 kW/m2 is referred to as the effective distance (Matthijsen and Kooi 2006) corresponding to an explosion probability of 1%.

2.4 Hydrogen Safety

2.4.4.2

105

Dangers of Liquid Hydrogen

Low-temperature dangers of liquid hydrogen a Risk of frostbite Severe frostbite can occur when liquid hydrogen is splashed on bare skin or thin clothes in contact with pipelines and valves containing liquid hydrogen. It should be pointed out that the low-temperature steam of liquid hydrogen can also cause frostbite on the operator’s skin. In actual use, all personnel operating liquid hydrogen equipment must wear cotton protective clothing to minimize exposed parts of the skin. Once frostbitten by liquid hydrogen, people can soak the frostbitten part with warm water at about 40 °C, then seek medical advice, and do not rub it. The following points should be noted when operating hydrogen. People should wear cotton or asbestos gloves, cotton long-sleeved clothes, trousers, and cotton boots (synthetic fibers and woolen clothing are strictly prohibited), and a mask with protective glasses. b Low-temperature brittleness of materials and difficult handling of parts Low temperatures can have a strong influence on the properties of various metals. At liquid hydrogen temperatures, various mild steels could lose their ductility and may become brittle. Sudden temperature changes can also cause localized stresses in various metallic materials. In addition, these low temperatures can make some joints in the pipeline system lose their original flexibility, thereby increasing the risk of leakage of liquid hydrogen from these joints. c Hazards of vaporization of large quantities of liquid hydrogen Liquid hydrogen has a low boiling point, and its volume expands by more than 780 times after vaporization. Vaporization can cause the danger of overpressure. It is necessary to prevent a large amount of hydrogen from overflowing. In order to ensure the overflow caused by the vaporization pressure of hydrogen, the filling ratio of the liquid hydrogen storage tank is 0.9. Since the temperature of liquid hydrogen is very low, external substances can be additional heat sources. During the transfer or storage process, any “blind areas” where liquid hydrogen may reach (leakage or accident), such as pipelines, interlayers, valve chambers, etc., may vaporize liquid hydrogen if proper or effective heat insulation measures are not taken, resulting in an increase in system pressure and an explosion in severe cases. When designing and using equipment, strict attention should be paid to the safety of “blind areas”. If necessary, safety valves or bursting membrane devices can be added to these parts. d Solid oxygen and air Solid gaseous impurities in liquid hydrogen can destroy the normal operation of related equipment (such as valve stuck, and pipeline blockage). Air or impurities mixed into liquid hydrogen will produce solid oxygen or solid air, forming an explosive mixture similar to explosives. Therefore, the liquid hydrogen storage container

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is required to be heated (normal temperature) at least once a year, so that the solid oxygen or solid air can be emptied (Xingguo 2012). A Leakage of liquid hydrogen, fire and explosion hazards Liquid hydrogen has lower molecular weight and viscosity (2 orders of magnitude smaller than water), and with the speed of leakage being inversely proportional to viscosity, liquid hydrogen can leak very easily. If only the influence of viscosity on the speed of leakage is considered, the leakage rate is 100 times greater than hydrocarbon fuels, 50 times greater than water, and 10 times greater than liquid nitrogen. The leaked liquid hydrogen evaporates quickly to form a flammable and explosive mixture. However, this type of mixture dissipates very quickly. For example, 2273L of liquid hydrogen overflows and diffuses into a non-flammable mixture in one minute. Small leaks of liquid hydrogen do occur, but these are not very common. Because the boiling point of liquid hydrogen is very low, the range between the critical temperature and the boiling point temperature is also narrow. A small amount of liquid hydrogen is prone to liquid–gas two-phase transformation before it overflows in the system, and it might have been vaporized while overflowing. However, when the equipment is broken down or the valves or other parts of the liquid filling pipe and the discharge pipe are damaged, a large amount of liquid hydrogen may leak out. Such situations occur almost suddenly, and part of the outflowing liquid may evaporate quickly, while the other part could form a “liquid hydrogen pool” on the ground. Under the influence of surrounding air, regarded as an important heat source, the “liquid hydrogen pool” will tend to dry up at an evaporation rate of 30–170 mm/min (Liang and Guangwen 1995). When liquid hydrogen escapes and catches fire, the main danger is from the associated equipment being destroyed by the releasing heat. If the liquid hydrogen storage tank or piping cracks, the whole device could be destroyed. In the aerospace power system, the leakage of liquid hydrogen from the storage tank to the instrument compartment and the power system test site seriously threatens the safety of the aerospace power system during development stages and early stages of the launch. Therefore, leak detection and monitoring of hydrogen is an urgent issue to be solved. It is related to the production and use of hydrogen, the safety of the personnel and equipment, so multiple hydrogen concentration monitoring and automatic alarm systems are often installed. B Storage capacity and safety distance of liquid hydrogen The overflow or vaporization of a large amount of liquid hydrogen will cause overpressure, so the safety distance needs to be maintained while storing liquid hydrogen. The safe storage distance is determined by the environment and whether there is a protective wall. If there is a liquid oxidant, it must also maintain a certain safe distance from the liquid oxidant.

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107

2.4.5 Safety Issues Caused by Hydrogen Embrittlement Hydrogen is not generally corrosive and does not react with typical container materials. Under certain temperature and pressure conditions, it can diffuse into steel and other metals, reducing the strength of high-strength steel and/or cause embrittlement. To avoid this problem, appropriate materials must be chosen in the manufacture of hydrogen storage containers/cylinders to ensure that no leakage or deterioration will occur after several years of hydrogen filling. At present, austenitic stainless steel and aluminum alloy steel are mostly used in hydrogen systems. Figure 2.31 shows the temperature change of necking of various austenitic stainless sheets of steel when used in a hydrogen environment. SUS316L, SUS316NG, and SUS310S were less affected by the hydrogen environment. In addition, various stainless sheets of steel with high nickel content were also less affected by hydrogen. In addition to base metal materials, the processing technology, especially the welding process, can also cause hydrogen embrittlement. Common welding includes TIG (Tungsten Inert Gas) welding, MIG (Metal Inert Gas) welding, SAW (Submerged Arcwelding), Reduced Pressure Electron Beam welding, Friction Stir welding, CO2 laser welding, etc. The methods used in TIG, MIG, and SAW can alter the low-temperature toughness of austenitic stainless steel, while FSW and RPEB are more suitable for welding aluminum alloys. In addition to iron-based metals, other metals such as titanium alloys could also be affected. In petrochemical plants, acetic acid, acetaldehyde, purified terephthalic acid, urea, and other industries contain imported or domestic titanium equipment. In ethylene production and power generation plants, titanium is also used to make seawater coolers and condensers. Titanium equipment is often a pressure vessel, which generally operates under high temperatures, high pressures, strong corrosive

Fig. 2.31 Effect of hydrogen temperature and pressure on relative necking of austenitic stainless steel

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media, and even flammable and explosive environments. Although most of the titanium equipment has a long-expected service life, some titanium equipment and parts need to be gradually replaced after three to five years of use or after more than ten years. A few of these cannot be used and are scrapped within one to two years. The failure of titanium equipment is mostly due to corrosion and cracking, generally caused by hydrogen absorption and hydrogen embrittlement. Therefore, during regular open inspection of in-service titanium equipment, the detection of corrosion hydrogen absorption and hydrogen embrittlement is crucially important. As hydrogen can affect the properties of various materials such as steel, titanium alloys, aluminum alloys, etc., materials used in hydrogen systems need to be carefully evaluated.

2.4.6 Safety Issues of Hydrogen Storage Alloys Several safety issues need to be addressed while using hydrogen storage alloys, with focus on the following aspects.

2.4.6.1

Ignition and Combustion of Metal Hydrides

The hydrogen storage materials currently used are metal hydrides. But these metal hydrides are relatively active and often used in powder form, which can easily catch fire and burn (Ohsumi 1993). Table 2.10 shows the ignitability and combustion characteristics of hydrides of LaNi5 and TiFe, in comparison with highly reactive Ce (Lundin and Sullivan 1975; Lundin and Lynch 1975). Metal hydrides can catch fire at relatively low temperatures and have high flammability, but these do not react slowly with oxygen like Ce, and LaNi5 series hydrides. The reaction of TiFe with oxygen will form an oxide film covering the surface, which can prevent fire.

2.4.6.2

The Risk of Dust Explosion

The hydrogen storage alloy will be micronized when it adsorbs and desorbs hydrogen repeatedly, and when such micronized powder is exposed to the atmosphere, there is a danger of dust explosion. According to the powder explosion experiment, the explosion critical concentration and explosion pressure of hydrogen storage alloy and its hydride can be measured. As shown in Fig. 2.32, smaller the particle size of the powder, the stronger the explosion tendency and higher the explosion pressure. But compared with carbon powder, it is much safer.

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109

Table 2.10 Ignitability and combustion characteristics of LaNi5 hydride and TiFe hydride Atmosphere

Metal or alloy

Relative combustion energy

Ignition temperature/°C

O2

Ce

90

149

O2

La

13

376

O2

Ni

–

–

O2

LaNi5

28

323

O2

LaNi5 hydride

38

228

Air

LaNi5

4

360

Air

LaNi5 hydride

17

192

O2

Fe