Fuels, Energy, and the Environment [1 ed.] 9781466510180, 9781466510173

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Fuels, Energy, and the Environment

Ghazi A. Karim

Fuels, Energy, and the Environment

Fuels, Energy, and the Environment Ghazi A. Karim

Boca Raton London New York

CRC Press is an imprint of the Taylor & Francis Group, an informa business

CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2013 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Version Date: 20121121 International Standard Book Number-13: 978-1-4665-1018-0 (eBook - PDF) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright. com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com

To my teachers, students, and associates for all their contributions over the years

Contents Preface������������������������������������������������������������������������������������������������������������������� xiii Author���������������������������������������������������������������������������������������������������������������������xv 1. Introduction......................................................................................................1 1.1 Preamble..................................................................................................1 1.2 Different Forms of Energy....................................................................2 1.3 Primary Sources of Energy...................................................................2 1.4 Non-Fossil Fuel Based Energy.............................................................4 1.4.1 Hydropower...............................................................................4 1.4.2 Ocean/Wave Energy................................................................4 1.4.3 Wind Energy..............................................................................4 1.4.4 Solar Energy.............................................................................. 5 1.4.5 Geothermal Energy.................................................................. 9 1.4.6 Nuclear Energy......................................................................... 9 1.5 Considering the Losses of Energy from Its Production Source to Its Point of Consumption�������������������������������������������������� 10 1.6 Energy Resources Exploitation.......................................................... 11 1.7 Synopsis................................................................................................. 12 Bibliography..................................................................................................... 13 2. Fuels in General............................................................................................. 15 2.1 Introduction.......................................................................................... 15 2.2 Some of the Main Desirable Properties of Fuels............................. 16 2.3 Some Relevant Units of Measurement.............................................. 17 2.4 Some Patterns of Fuel and Energy Resources and Usage.............. 20 2.5 Definitions of Reserves........................................................................ 21 2.6 Some General Observations about Fuel and Energy Statistics........................................................................... 23 2.7 Changes in the Consumption of Different Sources of Energy...... 24 2.8 Problems................................................................................................ 26 2.9 Synopsis.................................................................................................30 Bibliography.....................................................................................................30 3. Fuels Classification........................................................................................ 33 3.1 Fossil Fuels............................................................................................ 33 3.2 Hydrocarbon Fuels.............................................................................. 33 3.2.1 Paraffinic Series, CnH2n+2 (Saturated, All with Single “C” Bonds)....................................................34

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3.2.2 Olefin Series, CnH2n (Unsaturated with One Double Bond between Two C Atoms������������������������������������������������34 3.2.3 Acetylene Series, CnH2n−2 (Unsaturated with One Triple Bond between Two C Atoms)����������������������������������� 36 3.2.4 Naphthenes or Cycloparaffins, CnH2n (Closed Chain with Single and Saturated Bonds)��������������������������������������� 36 3.2.5 Aromatics, CnH2n−6 (Unsaturated Ring Compounds)........ 37 3.3 Some Oxygenated Compounds......................................................... 38 3.4 Problems................................................................................................ 40 3.5 Synopsis................................................................................................. 41 Bibliography..................................................................................................... 41 4. Fuel-Consuming Energy Systems..............................................................43 4.1 Fuel-Consuming Work-Producing Devices.....................................43 4.2 Work and Heat......................................................................................44 4.3 Efficiency............................................................................................... 45 4.4 Fuel Energy Systems............................................................................ 47 4.4.1 Internal Combustion Engines............................................... 47 4.4.1.1 Various Types of Reciprocating Engines............. 48 4.5 Cogeneration......................................................................................... 52 4.6 Fuel Consumption...............................................................................54 4.7 Hybrid Engines.................................................................................... 56 4.8 Choice of Energy Systems................................................................... 57 4.9 Problems................................................................................................ 58 4.10 Synopsis................................................................................................. 58 Bibliography..................................................................................................... 59 5. Stoichiometry and Thermodynamics........................................................ 61 5.1 Heating Value of Fuels........................................................................ 61 5.2 Adiabatic Flame Temperature............................................................63 5.3 Procedure for Calculating the Temperature and Composition of the Products of Combustion, When Equilibrium Conditions Are Assumed............................................. 74 5.4 Calorimeters.......................................................................................... 78 5.5 Some Solved Examples........................................................................ 78 5.6 Problems................................................................................................ 86 5.7 Synopsis.................................................................................................90 Bibliography.....................................................................................................90 6. Chemical Kinetics of Fuel Combustion.................................................... 93 6.1 Chemical Reactions.............................................................................. 93 6.2 Combustion Chemical Kinetics......................................................... 96 6.3 Solved Examples................................................................................ 103 6.4 Modeling Fuel Combustion Reactions............................................ 103 6.5 Types of Chemical Reactions Relevant to Fuels and Energy ...... 106

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6.6 Problems.............................................................................................. 107 6.7 Synopsis............................................................................................... 108 Bibliography................................................................................................... 108 7. Exhaust Emissions from the Combustion of Fuels............................... 111 7.1 Products of Combustion of Fuels..................................................... 111 7.2 Air Pollution Control......................................................................... 113 7.3 Catalytic Converters.......................................................................... 119 7.4 Greenhouse Effect.............................................................................. 121 7.5 Sulfur in Fuels.................................................................................... 125 7.6 Fuel-Induced Corrosion of Metals................................................... 126 7.7 Solved Example.................................................................................. 126 7.8 Problems.............................................................................................. 127 7.9 Synopsis............................................................................................... 128 Bibliography................................................................................................... 129 8. Combustion and Flames............................................................................. 131 8.1 Combustion, Flames, and Ignition Processes................................ 131 8.2 Diffusion Flames versus Premixed Flames.................................... 135 8.3 Combustion Stability Characteristics.............................................. 142 8.4 Fuel Combustion via Burners and Orifices.................................... 145 8.5 Combustion of Solid Fuels................................................................ 146 8.6 Solid Fuels Combustion Using Fluidized Beds............................. 148 8.7 Problems.............................................................................................. 150 8.8 Synopsis............................................................................................... 151 Bibliography................................................................................................... 152 9. Fire and Safety in Relation to Fuel Installations and Handling....... 155 9.1 Fuel Fires............................................................................................. 155 9.2 Flammability Limits of Fuels........................................................... 156 9.3 Some Protective Measures................................................................ 162 9.4 Flash Point........................................................................................... 164 9.5 Some Terms Related to Fuel Fires and Safety................................ 167 9.6 Solved Example.................................................................................. 168 9.7 Problems.............................................................................................. 170 9.8 Synopsis............................................................................................... 172 Bibliography................................................................................................... 173 10. Petroleum...................................................................................................... 175 10.1 Petroleum Reservoirs........................................................................ 175 10.2 Oil Recovery....................................................................................... 177 10.3 Enhanced Oil Recovery Methods.................................................... 178 10.4 Oil Sands............................................................................................. 182 10.5 Oil Shale.............................................................................................. 186 10.6 Problems.............................................................................................. 188

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10.7 Synopsis............................................................................................... 188 Bibliography................................................................................................... 189 11. Refining of Petroleum................................................................................ 191 11.1 Need for Refining............................................................................... 191 11.2 Refining Chemical Processes........................................................... 196 11.3 Catalysts and Their Action............................................................... 197 11.4 Controls through Codes and Standards......................................... 198 11.5 Problems.............................................................................................. 199 11.6 Synopsis............................................................................................... 199 Bibliography................................................................................................... 199 12. Gasoline......................................................................................................... 201 12.1 Spark Ignition Gasoline-Fueled Engines........................................ 201 12.2 Volatility.............................................................................................. 203 12.3 Additives to Gasoline........................................................................ 206 12.4 Catalysts.............................................................................................. 207 12.5 Spark Ignition Engine Knock........................................................... 207 12.6 Some Features of Engine Knock...................................................... 209 12.7 Some Negative Effects of Knock in Spark Ignition Engines........ 210 12.8 Operational Knock Limits................................................................ 211 12.9 Octane Number.................................................................................. 213 12.10 Effects of Engine Variables for Increased Incidence of Knock.... 213 12.11 Knock Control.................................................................................... 215 12.12 Three-Way Catalyst............................................................................ 215 12.13 Problems.............................................................................................. 216 12.14 Synopsis............................................................................................... 217 Bibliography................................................................................................... 218 13. Diesel Fuels and Some Other Liquid Fuels............................................ 221 13.1 Diesel Engine Combustion Processes............................................. 221 13.2 Ignition Delay in Diesel Engines.....................................................222 13.3 Diesel Engine Fuels............................................................................223 13.4 Diesel Engine Emissions................................................................... 228 13.5 Biodiesel Fuels.................................................................................... 229 13.6 Fischer–Tropsch Diesel...................................................................... 230 13.7 Dual-Fuel Engine............................................................................... 230 13.8 Liquid Fuels for Aviation Applications.......................................... 231 13.9 Heavy Fuels for Boiler and Furnace Applications........................234 13.10 Liquid and Solid Propellants............................................................234 13.11 Solved Example.................................................................................. 235 13.12 Problems.............................................................................................. 236 13.13 Some Definitions Associated with Liquid Fuels........................... 237 13.14 Synopsis............................................................................................... 239 Bibliography................................................................................................... 239

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14. Solid Fuels..................................................................................................... 241 14.1 Combustion of Solid Fuels................................................................ 241 14.2 Coal...................................................................................................... 241 14.3 Case for Coal....................................................................................... 244 14.4 Some Properties of Coal.................................................................... 246 14.5 Classification of Coals....................................................................... 248 14.6 Solved Examples................................................................................ 249 14.7 Coal Combustion in Fluidized Beds............................................... 251 14.8 Gasification of Coal............................................................................ 252 14.9 Underground Gasification of Coal..................................................254 14.10 Other Solid Fuels................................................................................254 14.11 Coal Bed Methane.............................................................................. 257 14.12 Solid Fuels as Propellants................................................................. 257 14.13 Solved Example.................................................................................. 258 14.14 Problems.............................................................................................. 259 14.15 Synopsis............................................................................................... 260 Bibliography................................................................................................... 260 15. Natural Gas and Other Gaseous Fuels.................................................... 263 15.1 Merits of Operation on Gaseous Fuels............................................ 263 15.2 Natural Gas......................................................................................... 265 15.3 Natural Gas Transmission................................................................ 271 15.4 Flaring of Fuel Gases......................................................................... 275 15.5 Liquefied Natural Gas....................................................................... 276 15.6 LNG Safety.......................................................................................... 277 15.7 Hydrates of Methane......................................................................... 278 15.8 Comparison of Features of Natural-Gas-Fueled Gas Turbines with Those of Spark Ignition Engines��������������������������� 279 15.9 Propane and Liquefied Petroleum Gas........................................... 280 15.10 Solved Example.................................................................................. 281 15.11 LPG Safety...........................................................................................284 15.12 Some Common Non-Natural Gas Mixtures.................................. 285 15.13 Landfill Gases..................................................................................... 288 15.14 Biogas Fuels......................................................................................... 289 15.15 Hydrogen Sulfide............................................................................... 290 15.16 Solved Examples................................................................................ 291 15.17 Problems.............................................................................................. 295 15.18 Some Gaseous Fuel Mixture Terms................................................. 296 15.19 Synopsis............................................................................................... 296 Bibliography................................................................................................... 297 16. Alternative Fuels.......................................................................................... 301 16.1 Introduction........................................................................................ 301 16.2 Applications........................................................................................ 303 16.3 Alcohols as Fuels................................................................................304

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16.4 Hydrogen as a Fuel............................................................................ 306 16.5 Liquid Hydrogen................................................................................ 310 16.6 Compressed Natural Gas.................................................................. 311 16.7 Problems.............................................................................................. 313 16.8 Synopsis............................................................................................... 313 Bibliography................................................................................................... 314 Glossary................................................................................................................ 317 References............................................................................................................ 325

Preface It may be suggested that at least for the next 20–30 years, fossil fuels will remain the dominant source of energy. This is going to be in conjunction with significantly increased fractional contributions from alternative sources of energy such as solar, wind, geothermal, and nuclear energy in addition to fuels derived increasingly from biosources. It is also suggested that it will be impossible to introduce any new energy system that will manage to replace substantially the current dependence on combustible fuels in general and fossil fuels in particular. An entirely novel energy system if it were to be found, which is most unlikely, will take a relatively very long time to become sufficiently developed and widespread to have a major impact on our energy needs and consumption to replace our dependence on fossil fuels. What can be expected and we are seeing this happening increasingly lately is a gradual increase in the diversity of energy and fuel sources and the devices using them. This is accompanied by a greater tendency to use smaller size energy-consuming units, although in certain applications such as electrical power generation, there is a greater emphasis on larger size plants with much continued attention to secure more efficient and better optimized processes and devices. Throughout, the need to achieve a cleaner utilization of energy will remain of paramount importance, which will continue to drive our research, development, and capital projects for many years to come. In recent years, numerous developments made the subjects of fuels, energy, combustion, and the environment of prime importance to all our activities and economic and environmental well-being. Accordingly, some of the main motivating factors for having an engineering textbook suitable for the undergraduate or graduate levels with an up-­to-date, integrated, and balanced overview of the whole rapidly changing fields of fuel science and technology with particular reference to energy supplies, the environment, and the utilization of fuels are the following: • Ever-increasing diversity of the type, composition, and combustion characteristics of a wide range of fuels that are becoming available worldwide. • Increased prime dependence on combustion devices for the exploitation of various fuel resources for the production of heat and all forms of power. • An ever-increasing need to improve the efficiency of energy production and the utilization of fuel resources in general.

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• A mandatory need to critically control emissions and the negative impact on the environment from a variety of fuel-­consuming devices and all activities associated with fuel and energy applications worldwide. • Most burners and fuel-consuming appliances, particularly those that have been around for some time, were designed and manufactured with much reliance on empiricism. Any measures that may improve their performance are actively sought since much of the information available and widely used by industry tend to be empirical with some frequently arbitrarily chosen. • Great advances in recent years in the fields of combustion science and technology, particularly with the advent of fast computers and sophisticated diagnostic and control equipments. These could be made available in a relatively clear, economic, and simple way to benefit the student, practicing engineer, and eventually the consumer. With these important and rapidly changing developments, there is a need for an integrated simplified presentation targeting primarily engineers of the factors and processes that control the suitability of various types of fuels in combustion systems and their impact on the environment.

Author Ghazi A. Karim has a DSc, PhD, and DIC from London University and a BSc (Hons.) from Durham University, United Kingdom. He has been a university professor in engineering for well over four decades, both at the University of Calgary and earlier at Imperial College of Science and Technology—London University. Dr. Karim formulated, developed, and taught at the graduate, undergraduate, and continuing education levels numerous courses, conducted research, and published very extensively, notably in topics relating to energy conversion, fuels, combustion, and the environment. He has acted on numerous occasions as a consultant in these areas to a wide variety of public and private institutions and bodies.

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1 Introduction

1.1 Preamble Our civilization and the ever-increasing high standard of living that we have been enjoying in recent times are the direct outcome of our ability to harness all forms of energy usefully so as to achieve the physical comfort and economic benefits that we expect and demand. The quality of life and the survival of all living creatures on earth can be closely identified with the conservation of our earth’s resources while aiming to maintain a cleaner environment. We recognized that the whole fields of energy and the environment are interrelated in a complex manner with numerous influencing factors and issues. These need integration so that we can approach the problems to be faced more knowledgably and effectively. For example, the topic of “energy” cannot be considered without considering the contributions of factors that can be described not only in terms of thermodynamics, physics, and chemistry, but also in terms of other fields, including economics, sociology, ecology, and politics. Over the millennia of human existence, the main sources of energy for the production of heat or work became increasingly dependent and have been derived from fuels either in the form of fossilized resources of various types or the more recent origin derived primarily from living matter of plant, animal, or marine origin. The bulk of the controllable energy available to us at present is obtained through the combustion of fossil fuels. These fuels can be considered as non-renewable sources of ancient stored solar energy that took many millions of years to be formed. By virtue of their chemical structure they can release readily and rapidly, under the appropriate conditions, sufficient energy in the form of heat that can be converted to mechanical or electrical work in suitable work-producing devices commonly described as engines. Under exceptional circumstances their chemical energy ideally can be converted fully to electrical/mechanical work such as in the ideal fuel cell. It is important to note throughout that the main issue confronting our civilization at present and in the years to come is the adequate and economic provision of energy, while continuing to improve the quality of life and ensuring at the same time a cleaner environment. 1

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Fuels, Energy, and the Environment

1.2  Different Forms of Energy The following is a brief review of the most common forms of energy encountered in engineering systems and their processes: Internal energy is the sum of microscopic forms of energy of a system, which is related to the molecular structure and the degree of molecular activity. It is a function of the sum of the kinetic and potential energies of the molecules. Sensible energy refers to the kinetic energy of the molecules of the system and is a strong function of temperature. Latent energy is the internal energy associated with phase changes of the system, for example, from liquid to vapor. Formation energy refers to the chemical bonding energy of the system. Nuclear energy is associated with bonding within the nucleus of the atom, which is partly released during nuclear reactions.

1.3  Primary Sources of Energy The bulk of the energy resources available to us can be viewed to be solar in origin. These may be either of the direct type, arising from the present incidence of solar energy on earth, or the energy available in the form of fossil fuels, which can be considered as an indirect, ancient, and nonrenewable form of stored solar energy that may have taken millions of years to be processed into the form of common fossil fuels. As shown in Figure 1.1, the combustion of fossil fuels at the present time can be viewed to be merely a process that releases some of the solar energy and ­carbon dioxide used during the ancient photosynthesis process and stored ­m illions of years ago but with many orders of magnitude at different time periods. Other forms of indirect solar heating are also responsible for producing the following forms of energy:

1. Energy derived from bio-sources such as plants, wood, and animal waste 2. Wind energy associated with air movement from breezes to hurricanes 3. Energy derived from waves, sea currents, and hydropower

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FIGURE 1.1 Electricity-generating wind turbines.

Other forms of non-solar in origin energy mainly include the following: 1. Nuclear energy that is derived mainly from nuclear fission processes 2. Nuclear fusion energy that may become at some time in the far distant future potentially available for implementation as a usable energy resource 3. Geothermal energy derived from hot sources within the earth’s crust 4. Other sources of energy of lesser practical importance that may become available in limited and specific applications such as through the oxidation of certain metallic or non-metallic materials An estimate of the average solar power received by earth is 173 PW (173 × 1015 W). Approximately only 47% of this energy is converted directly into heat while around 30% is reflected back into space. Around 23% of the energy received is used in the evaporation of water. These fi ­ gures are absolutely huge in comparison to merely around 6 TW (6.0  × 1012) estimated to be the average power consumed in recent years for human activities.

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1.4  Non-Fossil Fuel Based Energy 1.4.1 Hydropower Electricity generated by hydropower was dominant for many decades as an economic energy resource. Dams were built all over the world to provide vast supplies of electricity at a relatively low cost. Industrialized nations have exploited most of their likely sources for hydroelectric power. Only a limited potential for further development may be still available mainly with less developed nations. The exploitation of this source of energy is subject also to the growing concerns about the negative environmental and social impacts of the development of such large scale projects. 1.4.2  Ocean/Wave Energy Harnessing the energy of the seas, such as through the tides, ocean currents, and waves, is under continued research and development, but it still requires much further effort, time, and expenditure of resources to make it sufficiently successful even in relatively small scale units. It is through the change in the potential and kinetic energy of water elevation and motion that it can be captured to produce electricity. This is done through a variety of measures that would include paddles or oscillating water columns. A major limitation associated with these systems is their tendency to disturb seriously the ecology of their surroundings such as of tidal basins due to changes to the tidal flow and silting. 1.4.3  Wind Energy Wind energy utilization represents a very small fraction of the current energy demand of virtually all countries. This fraction has been increasing, albeit slowly over the years. A wide variety of radically different designs and sizes of wind turbines are involved. Often their location is not optimum and they are far away from where there is much demand for their electrical output. Wind as a source of energy is variable, oscillatory, and unpredictable. It depends on the location, time, elevation, and direction. The rated output of a wind turbine is seldom achieved for long. The power that can be obtained ideally is proportional to the cube of the prevailing wind speed, which increases significantly with the height above the ground. Hence, wind turbines are usually mounted on very tall supporting towers. The efficiency of wind turbines at any location and for any set of equipment depends on the strength and direction of the prevailing wind. Additional losses are incurred to get the electrical output linked into the grid. Also, the transmission and

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integration of the electrical output from various units is costly because it involves a number of isolated individual units. The output voltage and frequency of the electricity generated are not constant and not optimum for transfer via the grid system. Relatively complex control and rectifying equipment and procedures are needed, with often huge-capacity batteries provided for electrical storage. These all contribute to additional losses, increased costs, and lowering of the conversion efficiency. At present, the cost of electricity produced, which is high and variable with time and seasons, is highly dependent on taxation and government subsidies. The price charged for the electricity can be artificially inflated by supportive consumers. Wind turbines are expensive, very bulky, difficult to construct and install especially in offshore sites, and maintenance is expensive and unwieldy. Very large sizes are required for acceptable load and efficiency. A typical example is a horizontal axis turbine rated at 200 kW of three blades with around 15 m blades on a 25 m tower. The efficiency of electrical power generation drops significantly at part load requiring a threshold of wind speed for activation. Also, safeguards are needed to protect against excessive wind speeds such as in storms and gales. Wind turbines tend to be considered by some to be ecologically unsightly and noisy with negative consequences to cattle, animals, birds, and farming activities. The real estate cost of a wind farm can be substantial and those installed at sea remain largely insufficiently developed. Nevertheless, harnessing the energy of the wind has grown significantly in sophistication, capacity, and distribution all over the world in recent years, since it represents in principle a relatively green form and cheap renewable source of energy. However, time is needed before wind-derived energy will be contributing a sufficiently substantial fraction of total energy requirements worldwide. A main challenge associated with the exploitation of wind energy is its variable and intermittent nature, which requires the maintenance of costly reserves of alternative power capacity to supply the energy needed during periods of low speed winds. Sufficiently extensive infrastructure is also required for the control and distribution of the generated power to points of its consumption. Mainly with the aid of measures such as government tax incentives and surcharges to consumers, wind power is being made an increasingly attractive and a viable renewable option to supplement the energy produced through the combustion of fossil fuels, particularly for electric power generation. 1.4.4  Solar Energy Solar energy’s contributions to our world are many and include the making of fossil fuels, hydropower, biofuels, wind, ocean currents, rain, thermal sea gradients, and so on. The energy available is intermittent and dependent on time of the day, time of the year, location, elevation, season, angle of incidence,

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Fuels, Energy, and the Environment

and whether cloudy or clear. On the whole, there have been relatively limited deliberate solar energy applications for direct power production or heating. High-intensity solar energy tends to be located largely in sparsely populated areas of the globe and requires for its exploitation large areas of land. Solar energy in principle is renewable, free, clean, and abundant. Its increased exploitation should contribute towards reducing the consumption of fossil fuels and associated harmful exhaust emissions including the greenhouse gases. The likelihood of such increased exploitation of solar energy is seriously governed by the cost and availability of fossil fuels. Also, tax incentives for its use with partial capital support for solar devices can be very influential in increasing its usage. Thermal energy as received on earth is of multi-wavelengths and its exploitation for the production of work is subject to Carnot cycle limitations. The energy on average is very dilute with approximately only 1 kW/m2 (or 1 mW/mm2) received. Some solar energy is absorbed as it travels into the atmosphere due to the presence of CO2, H2O, and O3, and only relatively low temperatures are achieved unless special measures are devised to have it concentrated. Solar energy may be used for air conditioning and cooling but quite less effectively than through the expenditure of electrical work. However, there are good prospects for its limited usage for desalination of sea water. Green vegetation utilizes solar energy at extremely low efficiency (e.g.,