- Email: [email protected]
Introduction to underground coal gasification and combustion
1
Introduction to underground coal gasification and combustion
M.S. Blinderman*, A.Y. Klimenko† *Ergo Exergy Technology Inc., Montreal, QC, Canada, †The University of Queensland, Brisbane, QLD, Australia
1.1
Coal and future of energy consumption
Global consumption of energy and hydrocarbons shows steady growth. The trend is sustained and prominent, displaying no signs of slowing down. The reasons seem obvious—the same processes are driving growth in consumption of food, water, and other necessities of human existence: Growth of the Earth’s population, most pronounced in developing countries Growing life standards, again, most prominent in developing countries
The graph in Fig. 1.1 shows world population growth according to projections published by the United Nations (UN DESA, 2017). The graph in Fig. 1.2 presents a projection of the world primary energy consumption, respectively, for more developed and less developed regions (EIA, 2016). Comparison of the two charts in Figs. 1.1 and 1.2 supports a clear conclusion that increases in the world energy consumption are driven predominantly by growth of both population and life standards in developing countries. These trends are playing out against the background of increasingly apparent climate change that, many argue, has its root causes in human activity, especially that 9.0
Population (Billions)
8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 1995
2005
2015
Less developed regions
2025
2035
2045
More developed regions
Fig. 1.1 Global population growth projections (UN DESA, 2017). Underground Coal Gasification and Combustion. https://doi.org/10.1016/B978-0-08-100313-8.00001-3 © 2018 Elsevier Ltd. All rights reserved.
Underground Coal Gasification and Combustion
Primary energy consumption (quad BTU)
2
900 800 700 600 500 400 300 200 100 0 2010
2015
2020 OECD
2025
2030
Non-OECD
2035
2040
World
Fig. 1.2 Projections of the world primary energy consumption.
related to energy production and consumption. It is the reality of the day that no discussion of a proposed energy source may avoid the issue of global warming and greenhouse gas (GHG) emissions. A widely discussed sustainability approach to the global energy supply proposes that agriculture grow energy crops that can be converted into primary energy and hydrocarbons, so that, ideally, an annual harvest cycle would cover the annual cycle of global consumption of energy and hydrocarbons, in addition to satisfying annual food and industrial needs. With rapidly growing population and practically exhausted availability of new agricultural land, it is hard to see how this strategy could be viable. Given these long-term tendencies, what are the answers to the challenge of supplying affordable clean energy to meet the ever-growing demand? There seems to be a consensus among energy policy experts that renewable sources of energy will not be able to fully meet the growing global energy demand in the foreseeable future. Energy supply from these sources is intermittent by their very nature and requires supplementing by other energy sources, e.g., a fossil-fuel power plant that can produce electricity in a load-following mode (IEA CIAB, 2013). There is also a widespread concern with strains on transmission system that should accommodate variability of renewable sources and incorporate them in a modern power supply network. Discussion of specific issues inherent in renewable power generation is beyond our scope. However favorable they may seem for the environment, they appear to be insufficient in meeting growing global power demand. Besides, solar and wind plants do not produce hydrocarbons: these come primarily from fossil-fuel processing. Few developing countries can claim oil and gas self-sufficiency; most are importing oil, gas, and petroleum products at a rising rate. Typical supply and demand trends show climbing hydrocarbon consumption increasingly fed by imported oil, gas, and petroleum products, draining hard currency reserves and increasing pressure on the finances of developing countries. The “shale revolution” appears unlikely to
Introduction to underground coal gasification and combustion
3
change the dynamics of hydrocarbon markets in developing nations. In these circumstances, coal, the most ubiquitous and affordable of fossil fuels, seems set to continue playing the key role in power generation and, increasingly so, in chemical industries of the developing world (Butler, 2017). But isn’t coal the most polluting source of energy, responsible for the highest GHG emissions, let alone emissions of particulates, mercury, SOx, and NOx? Aren’t ash dams of coal-fired power plants a major source of water and soil contamination? What would be the consequences of its rising use for the environment, for global climate change, assuming that emissions produced in the developing world are to become more and more prevalent?
1.2
Underground coal gasification
The most effective technical solution for controlling pollution while using coal is offered by its gasification (Higman and Van der Burgt, 2008). The main deficiency of conventional coal gasification that converts mined, prepared (washed, milled, or sifted) coal to synthesis gas (syngas) in large steel chemical reactors is that it is expensive and mostly unaffordable in the developing nations. Besides, conventional gasification uses mined coal and thereby perpetuates its ills—mining health and safety problems, environmental issues of open-cut and underground mines, coal market fluctuations, limited and progressively depleted minable resources, etc. Conventional gasification plants continue to use large ash dams. In terms of GHG emissions, gasification facilitates CO2 capture but does not have any advantages in terms of finding the sinks for GHG sequestration. What would be the attributes of a coal-based energy and hydrocarbon-producing technology that could make it beneficial and acceptable in the environmentally concerned and carbon-restricted world? It should be a coal gasification technology that could 1. 2. 3. 4. 5. 6. 7.
make use of unminable coal resources; be independent of the coal market price; produce syngas at a low, competitive cost; provide for efficient carbon capture; offer accessible and affordable carbon sinks; eliminate the health and safety hazards of conventional coal mining; produce a fuel for clean, efficient power generation and a feedstock for petrochemical industry.
The listed features seem to fit an existing technology, underground coal gasification (UCG), which is the primary focus of this book. Given the unique and important role that it may play in the future, one could say, paraphrasing Voltaire, “si il n’existait pas, il faudrait l’inventer.” UCG provides the means to create and maintain a coal gasification process within an unmined coal seam that can be accessed by drilling wells from the surface (Ergo Exergy, 2017). This technology does not require the presence of human operators underground; the process is controlled from the surface. Following its invention in 1868, the technology underwent a long and tortuous development and now seems
4
Underground Coal Gasification and Combustion
to be on the verge of wide commercial deployment. As the following chapters of this book set out to demonstrate, modern UCG technology can meet the seven criteria of coal-based environmentally friendly and affordable energy and hydrocarbon technology outlined above. Forty years have passed since the publication of the previous book on UCG (Lamb, 1977). These years have seen a great deal of research, development, field demonstrations, process modeling, and commercialization attempts that significantly changed UCG knowledge and understanding. Our book is intended to capture the main results achieved in recent stages of global UCG development and to provide a modern and multifaceted view of the technology. The authors of the book come from a variety of academic, industrial, and commercial backgrounds and represent a wide geographic and institutional UCG experience.
1.3
Multidisciplinary nature of UCG
The book is not restricted to presentation and analysis of mainstream UCG technology, but endeavors to cross the boundaries of conventional fields and disciplines to analyze applications where the accumulated knowledge and experience in UCG can be useful in offering viable alternatives to conventional technologies. While historically a few of these fields were seen as being a part of UCG technology, this is not necessarily the case at present. The authors, however, do not intend to bring forward methodological arguments about the right or wrong placement of disciplinary boundaries. Our approach is based on the productive tradition of practical interdisciplinary engineering: the book presents ideas and applications that are relevant to UCG technology, whether or not this implies crossing the boundaries of conventional branches of engineering and science. It is important to stress that the development of UCG technology has always been a multidisciplinary endeavor, combining, applying, and enriching knowledge from many different fields. UCG lies at the intersection of practical engineering and fundamental science, involving chemistry and physics, fluid mechanics and solid mechanics, thermodynamics and kinetics, and geology and hydrology. Intensive interactions of numerous factors make underground gasification and combustion extremely complex. These underground processes have common features but always remain site-dependent. The complexity of the processes needs to be dealt with in conditions of limited underground access, restricting opportunities for monitoring and control. Despite these difficulties, “no men underground” has become the key principle of modern UCG, which perhaps should eventually be extended to all mining operations—only implementation of this principle can eliminate the inherent danger of underground mining to workers. Historically, the state of the underground reactors in UCG operations and trials often had to be judged on the basis of secondary indicators, not direct measurements within the gasifier. Under these conditions, development of the technology was relatively slow, based on intuition and accumulated experience, often resorting to trial and error. Some of the techniques and physical effects were uncovered only by
Introduction to underground coal gasification and combustion
5
chance. The accidental discovery of reverse combustion linking at the Soviet Tula (Podmoskovnaia) UCG station in 1941 may serve as a good example. At the end, a long series of trials (some of which involved posttrial excavations) brought about new understanding of the underground processes. This statement is primarily related to UCG—our knowledge of underground fires, their configurations, extents, and evolutions to this day remains very limited and often based on guessing rather than knowing. Modern conditions, however, have brought new tools of measurements and simulations into UCG technology. Stringent environmental monitoring has become an inseparable part of good UCG practice. These tools, combined with nearly a century of accumulated UCG experience, form the basis of the modern UCG technology. It must be noted that proper operational conditions for UCG have not always been followed in the past. For example, prolonged periods of keeping excessively high pressures in the underground reactor may result in a short-lived improvement in product gas quality but lead to environmental contamination and trial failure. This book advocates environmentally responsible application of UCG technology based on best practices and solid and comprehensive scientific approach supported by sound and transparent regulatory framework. In fact, as discussed in this book, UCG-related technologies can be used to remedy environmental impact of some natural disasters or technological mistakes.
1.4
Gasification and combustion
We note that the separation between underground gasification and underground combustion of coal seams is rather nominal. Both processes, gasification and combustion, involve the same reactants and the same kinetics (see Chapter 7). Ineffective operational conditions during gasification (such as oxygen bypass) may lead to burning of syngas before it has a chance to be delivered to the surface, that is, to combustion replacing gasification. In the same way, underground coal fires usually produce a mixture of gases involving CO2, H2, and CO, and combustion is rarely complete under these conditions. The main difference between UCG and underground coal fires is in localization, depth, pressure, and, most importantly, in the level of control over these processes. The first ideas of UCG were formulated as a means of controlling underground fires. Further advancements in UCG technology have brought a much better understanding of underground processes of gasification and combustion of coals, at least because underground gasification is conducted in purposely designed conditions involving accurate measurements and analysis. It seems, however, that in the past, this acquired understanding has not been used for the purpose of controlling and extinguishing underground fires. In many cases, extinction of underground fires remains extremely difficult or impossible with the use of conventional techniques. Extinguishing attempts based on poor understanding of underground combustion may lead to apparent success in the short run and exacerbation of the problem in the long run. Under such conditions, establishing full or partial control over fire by UCG-originated
6
Underground Coal Gasification and Combustion
techniques seems to be a logical choice. Since this would allow to mitigate and reduce the environmental damage caused by the fires, it would be important to find a costeffective way to trial and implement these techniques in practice.
1.5
The scope of the book
The book deals with the history of UCG, UCG technology and applications, and possible extensions of the technology. As described in the first chapters of this book, the development of UCG in the world has been uneven, which may seem surprising given reasonable conceptual understanding achieved during the earliest stages of the technology life, which is covered in the chapter describing the early history of UCG (Chapter 2). The following chapters consider the history of UCG development with a focus on the main geographic centers that attained the highest technical and commercial advancement—the former USSR (Chapter 3), the United States (Chapter 4), Europe (Chapter 5), and, most recently, Australia (Chapter 6). The editors had hoped to include in the book an account of UCG projects in China, where the government-sponsored UCG program spanned some 30 years starting from the late 20th century, but it proved impossible within the necessary time frame due to logistic reasons. The technical aspects of UCG implementation are covered in Chapters 7–11. This part involves chapters on gasification kinetics (Chapter 7) and the role of groundwater in the gasification process (Chapter 8). Chapter 9 reviews the rock mechanics issues of UCG in terms of understanding surrounding rock deformation as a cause of potential environmental impacts and a key factor affecting processes in the gasification system. Another chapter provides a summary of the efforts to create a mathematical model of the UCG process (Chapter 10). Finally, there is a chapter concerned with environmental performance of UCG plants, concentrating on protection of groundwater with examples, primarily, from the former Soviet UCG program (Chapter 11). A special emphasis of the book has been placed on potential commercialization of UCG technology. A chapter is dedicated to considering the features of the technology that make it suitable for large-scale energy and petrochemical applications (Chapter 12). Processes, equipment, efficiencies, and costs of utilizing syngas for production of electricity, synthetic methane, fertilizers, synthetic automotive fuels, methanol, and other value-added commodities are discussed in another chapter of this book (Chapter 13). Two chapters are dedicated to consideration of commercialization issues using examples of two recent UCG projects—in South Africa and Australia (Chapters 14 and 15). A great deal of interest in recent years has been attracted to oil shale deposits, predominantly focusing on the shale gas and shale oil fracking revolution that took place in the United States in the last decade. The fracking is used to facilitate release and production of gaseous and liquid hydrocarbons from the shale matrix, while the organic matter of the matrix itself remains largely untouched. However, UCG experience offers an alternative, which is based on establishing a gasification process within the underground shale seam in situ and converting the shale organic mass into
Introduction to underground coal gasification and combustion
7
gaseous and liquid hydrocarbons, which would result in underground gasification of the shale. Our book includes a full chapter (Chapter 16) dedicated exclusively to the description of underground shale gasification research and development efforts and outcomes. As any industrial activity, UCG operation has an impact on the environment, which is minimized provided that proper operational procedures are followed. This book gives due emphasis to potential environmental impacts of UCG (see Chapter 11), which need to be compared with the environmental impacts of alternative technologies. Proper application of underground gasification and combustion technologies should reduce this impact. The closing chapters of the book deal with possible extensions of UCG technologies, especially when knowledge of underground processes accumulated in UCG operations can be useful in mitigation or reduction of environmental damage caused by various factors not related to UCG. Chapter 17 is dedicated to analysis of underground fires from the perspective of UCG technology. We must note, however, that comprehensive treatment of underground fires or discussion of even more remote topics such as fire safety in mines is not within the scope of this book. Extensive treatment of underground fires can be found in other publications (see Stracher et al., 2010). Environmental remediation of contaminated soils can be achieved very effectively through a specifically designed underground combustion process. One of the chapters in this book (Chapter 18) reports on a positive experience of such remediation. Both successful UCG operations and successful control and extinction of underground fires can be achieved only with appropriate monitoring and analysis. A spectrum of monitoring techniques is now standard in the best UCG operations. Chapter 19 of this book reviews measurement techniques that are commonly used in UCG operations and can be used in monitoring underground fires. The section also examines physical principles that may form a basis for advanced measurements and monitoring of underground gasification and combustion in the future. Once developed, these technologies may be suitable for monitoring a broad range of underground processes. In general, this book is addressed to an educated reader with some experience in the area; to people who have interest in commercial, technical, and scientific aspects of UCG; to research students; and to experienced researches who have a limited access to UCG-related information. The recent developments of the theory of key UCG processes (e.g., the theory of reverse and forward combustion linking, the theory of the flame position in the channel, and the theory of stability of evaporation fronts), which are highly mathematical and hardly suitable for general readers, are not included in the book. Readers interested in theoretical aspects of underground gasification and combustion are referred to relevant publications (Blinderman and Klimenko, 2007; Blinderman et al., 2008a,b; Saulov et al., 2010; Plumb and Klimenko, 2010).
Acknowledgments The editors would like to express their appreciation and gratitude to the Elsevier Publishing for all the support given to the editors and the authors of this book on UCG and combustion.
8
Underground Coal Gasification and Combustion
References Blinderman, M.S., Klimenko, A.Y., 2007. Theory of reverse combustion linking. Combust. Flame 150 (3), 232–245. Blinderman, M.S., Saulov, D.N., Klimenko, A.Y., 2008a. Forward and reverse combustion linking in underground coal gasification. Energy 33 (3), 446–454. Blinderman, M.S., Saulov, D.N., Klimenko, A.Y., 2008b. Optimal regimes of reverse combustion linking in underground coal gasification. J. Energy Inst. 81 (1), 7–12. Butler, Nick, 2017. Alternative truths and some hard facts about coal. Financial Times. April 3. Ergo Exergy, 2017. Welcome to Underground Coal Gasification. http://www.ergoexergy.com (accessed 22.07.17). Higman, C., Van der Burgt, M., 2008. Gasification, second ed. Elsevier, Amsterdam. IEA Coal Industry Advisory Board, 2013. 21st Century Coal: Advanced Technology and Global Energy Solution. OECD/IEA, Paris. Lamb, G.H., 1977. Underground Coal Gasification. Energy Technology Review No. 14, Noyes Data Corp. Plumb, O.A., Klimenko, A.Y., 2010. The stability of evaporating fronts in porous media. J. Porous Media 13 (2), 145–155. Saulov, D.N., Plumb, O.A., Klimenko, A.Y., 2010. Flame propagation in a gasification channel. Energy 35 (3), 1264–1273. Stracher, G., Prakash, A., Sokol, E., 2010. Coal and Peat Fires: A Global Perspective. In: CoalGeology and Combustion, vol. 1. Elsevier Science, Amsterdam/London. U.S. Energy Information Administration, 2016. International Energy Outlook 2016. Report DOE/EIA-0484(2016), DOE, Washington, DC. Unite Nations, Department of Economic and Social Affairs, Population Division, 2017. World Population Prospects: The 2017 Revision. custom data acquired via website.
Introduction to underground coal gasification and combustion
M.S. Blinderman*, A.Y. Klimenko† *Ergo Exergy Technology Inc., Montreal, QC, Canada, †The University of Queensland, Brisbane, QLD, Australia
1.1
Coal and future of energy consumption
Global consumption of energy and hydrocarbons shows steady growth. The trend is sustained and prominent, displaying no signs of slowing down. The reasons seem obvious—the same processes are driving growth in consumption of food, water, and other necessities of human existence: Growth of the Earth’s population, most pronounced in developing countries Growing life standards, again, most prominent in developing countries
The graph in Fig. 1.1 shows world population growth according to projections published by the United Nations (UN DESA, 2017). The graph in Fig. 1.2 presents a projection of the world primary energy consumption, respectively, for more developed and less developed regions (EIA, 2016). Comparison of the two charts in Figs. 1.1 and 1.2 supports a clear conclusion that increases in the world energy consumption are driven predominantly by growth of both population and life standards in developing countries. These trends are playing out against the background of increasingly apparent climate change that, many argue, has its root causes in human activity, especially that 9.0
Population (Billions)
8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 1995
2005
2015
Less developed regions
2025
2035
2045
More developed regions
Fig. 1.1 Global population growth projections (UN DESA, 2017). Underground Coal Gasification and Combustion. https://doi.org/10.1016/B978-0-08-100313-8.00001-3 © 2018 Elsevier Ltd. All rights reserved.
Underground Coal Gasification and Combustion
Primary energy consumption (quad BTU)
2
900 800 700 600 500 400 300 200 100 0 2010
2015
2020 OECD
2025
2030
Non-OECD
2035
2040
World
Fig. 1.2 Projections of the world primary energy consumption.
related to energy production and consumption. It is the reality of the day that no discussion of a proposed energy source may avoid the issue of global warming and greenhouse gas (GHG) emissions. A widely discussed sustainability approach to the global energy supply proposes that agriculture grow energy crops that can be converted into primary energy and hydrocarbons, so that, ideally, an annual harvest cycle would cover the annual cycle of global consumption of energy and hydrocarbons, in addition to satisfying annual food and industrial needs. With rapidly growing population and practically exhausted availability of new agricultural land, it is hard to see how this strategy could be viable. Given these long-term tendencies, what are the answers to the challenge of supplying affordable clean energy to meet the ever-growing demand? There seems to be a consensus among energy policy experts that renewable sources of energy will not be able to fully meet the growing global energy demand in the foreseeable future. Energy supply from these sources is intermittent by their very nature and requires supplementing by other energy sources, e.g., a fossil-fuel power plant that can produce electricity in a load-following mode (IEA CIAB, 2013). There is also a widespread concern with strains on transmission system that should accommodate variability of renewable sources and incorporate them in a modern power supply network. Discussion of specific issues inherent in renewable power generation is beyond our scope. However favorable they may seem for the environment, they appear to be insufficient in meeting growing global power demand. Besides, solar and wind plants do not produce hydrocarbons: these come primarily from fossil-fuel processing. Few developing countries can claim oil and gas self-sufficiency; most are importing oil, gas, and petroleum products at a rising rate. Typical supply and demand trends show climbing hydrocarbon consumption increasingly fed by imported oil, gas, and petroleum products, draining hard currency reserves and increasing pressure on the finances of developing countries. The “shale revolution” appears unlikely to
Introduction to underground coal gasification and combustion
3
change the dynamics of hydrocarbon markets in developing nations. In these circumstances, coal, the most ubiquitous and affordable of fossil fuels, seems set to continue playing the key role in power generation and, increasingly so, in chemical industries of the developing world (Butler, 2017). But isn’t coal the most polluting source of energy, responsible for the highest GHG emissions, let alone emissions of particulates, mercury, SOx, and NOx? Aren’t ash dams of coal-fired power plants a major source of water and soil contamination? What would be the consequences of its rising use for the environment, for global climate change, assuming that emissions produced in the developing world are to become more and more prevalent?
1.2
Underground coal gasification
The most effective technical solution for controlling pollution while using coal is offered by its gasification (Higman and Van der Burgt, 2008). The main deficiency of conventional coal gasification that converts mined, prepared (washed, milled, or sifted) coal to synthesis gas (syngas) in large steel chemical reactors is that it is expensive and mostly unaffordable in the developing nations. Besides, conventional gasification uses mined coal and thereby perpetuates its ills—mining health and safety problems, environmental issues of open-cut and underground mines, coal market fluctuations, limited and progressively depleted minable resources, etc. Conventional gasification plants continue to use large ash dams. In terms of GHG emissions, gasification facilitates CO2 capture but does not have any advantages in terms of finding the sinks for GHG sequestration. What would be the attributes of a coal-based energy and hydrocarbon-producing technology that could make it beneficial and acceptable in the environmentally concerned and carbon-restricted world? It should be a coal gasification technology that could 1. 2. 3. 4. 5. 6. 7.
make use of unminable coal resources; be independent of the coal market price; produce syngas at a low, competitive cost; provide for efficient carbon capture; offer accessible and affordable carbon sinks; eliminate the health and safety hazards of conventional coal mining; produce a fuel for clean, efficient power generation and a feedstock for petrochemical industry.
The listed features seem to fit an existing technology, underground coal gasification (UCG), which is the primary focus of this book. Given the unique and important role that it may play in the future, one could say, paraphrasing Voltaire, “si il n’existait pas, il faudrait l’inventer.” UCG provides the means to create and maintain a coal gasification process within an unmined coal seam that can be accessed by drilling wells from the surface (Ergo Exergy, 2017). This technology does not require the presence of human operators underground; the process is controlled from the surface. Following its invention in 1868, the technology underwent a long and tortuous development and now seems
4
Underground Coal Gasification and Combustion
to be on the verge of wide commercial deployment. As the following chapters of this book set out to demonstrate, modern UCG technology can meet the seven criteria of coal-based environmentally friendly and affordable energy and hydrocarbon technology outlined above. Forty years have passed since the publication of the previous book on UCG (Lamb, 1977). These years have seen a great deal of research, development, field demonstrations, process modeling, and commercialization attempts that significantly changed UCG knowledge and understanding. Our book is intended to capture the main results achieved in recent stages of global UCG development and to provide a modern and multifaceted view of the technology. The authors of the book come from a variety of academic, industrial, and commercial backgrounds and represent a wide geographic and institutional UCG experience.
1.3
Multidisciplinary nature of UCG
The book is not restricted to presentation and analysis of mainstream UCG technology, but endeavors to cross the boundaries of conventional fields and disciplines to analyze applications where the accumulated knowledge and experience in UCG can be useful in offering viable alternatives to conventional technologies. While historically a few of these fields were seen as being a part of UCG technology, this is not necessarily the case at present. The authors, however, do not intend to bring forward methodological arguments about the right or wrong placement of disciplinary boundaries. Our approach is based on the productive tradition of practical interdisciplinary engineering: the book presents ideas and applications that are relevant to UCG technology, whether or not this implies crossing the boundaries of conventional branches of engineering and science. It is important to stress that the development of UCG technology has always been a multidisciplinary endeavor, combining, applying, and enriching knowledge from many different fields. UCG lies at the intersection of practical engineering and fundamental science, involving chemistry and physics, fluid mechanics and solid mechanics, thermodynamics and kinetics, and geology and hydrology. Intensive interactions of numerous factors make underground gasification and combustion extremely complex. These underground processes have common features but always remain site-dependent. The complexity of the processes needs to be dealt with in conditions of limited underground access, restricting opportunities for monitoring and control. Despite these difficulties, “no men underground” has become the key principle of modern UCG, which perhaps should eventually be extended to all mining operations—only implementation of this principle can eliminate the inherent danger of underground mining to workers. Historically, the state of the underground reactors in UCG operations and trials often had to be judged on the basis of secondary indicators, not direct measurements within the gasifier. Under these conditions, development of the technology was relatively slow, based on intuition and accumulated experience, often resorting to trial and error. Some of the techniques and physical effects were uncovered only by
Introduction to underground coal gasification and combustion
5
chance. The accidental discovery of reverse combustion linking at the Soviet Tula (Podmoskovnaia) UCG station in 1941 may serve as a good example. At the end, a long series of trials (some of which involved posttrial excavations) brought about new understanding of the underground processes. This statement is primarily related to UCG—our knowledge of underground fires, their configurations, extents, and evolutions to this day remains very limited and often based on guessing rather than knowing. Modern conditions, however, have brought new tools of measurements and simulations into UCG technology. Stringent environmental monitoring has become an inseparable part of good UCG practice. These tools, combined with nearly a century of accumulated UCG experience, form the basis of the modern UCG technology. It must be noted that proper operational conditions for UCG have not always been followed in the past. For example, prolonged periods of keeping excessively high pressures in the underground reactor may result in a short-lived improvement in product gas quality but lead to environmental contamination and trial failure. This book advocates environmentally responsible application of UCG technology based on best practices and solid and comprehensive scientific approach supported by sound and transparent regulatory framework. In fact, as discussed in this book, UCG-related technologies can be used to remedy environmental impact of some natural disasters or technological mistakes.
1.4
Gasification and combustion
We note that the separation between underground gasification and underground combustion of coal seams is rather nominal. Both processes, gasification and combustion, involve the same reactants and the same kinetics (see Chapter 7). Ineffective operational conditions during gasification (such as oxygen bypass) may lead to burning of syngas before it has a chance to be delivered to the surface, that is, to combustion replacing gasification. In the same way, underground coal fires usually produce a mixture of gases involving CO2, H2, and CO, and combustion is rarely complete under these conditions. The main difference between UCG and underground coal fires is in localization, depth, pressure, and, most importantly, in the level of control over these processes. The first ideas of UCG were formulated as a means of controlling underground fires. Further advancements in UCG technology have brought a much better understanding of underground processes of gasification and combustion of coals, at least because underground gasification is conducted in purposely designed conditions involving accurate measurements and analysis. It seems, however, that in the past, this acquired understanding has not been used for the purpose of controlling and extinguishing underground fires. In many cases, extinction of underground fires remains extremely difficult or impossible with the use of conventional techniques. Extinguishing attempts based on poor understanding of underground combustion may lead to apparent success in the short run and exacerbation of the problem in the long run. Under such conditions, establishing full or partial control over fire by UCG-originated
6
Underground Coal Gasification and Combustion
techniques seems to be a logical choice. Since this would allow to mitigate and reduce the environmental damage caused by the fires, it would be important to find a costeffective way to trial and implement these techniques in practice.
1.5
The scope of the book
The book deals with the history of UCG, UCG technology and applications, and possible extensions of the technology. As described in the first chapters of this book, the development of UCG in the world has been uneven, which may seem surprising given reasonable conceptual understanding achieved during the earliest stages of the technology life, which is covered in the chapter describing the early history of UCG (Chapter 2). The following chapters consider the history of UCG development with a focus on the main geographic centers that attained the highest technical and commercial advancement—the former USSR (Chapter 3), the United States (Chapter 4), Europe (Chapter 5), and, most recently, Australia (Chapter 6). The editors had hoped to include in the book an account of UCG projects in China, where the government-sponsored UCG program spanned some 30 years starting from the late 20th century, but it proved impossible within the necessary time frame due to logistic reasons. The technical aspects of UCG implementation are covered in Chapters 7–11. This part involves chapters on gasification kinetics (Chapter 7) and the role of groundwater in the gasification process (Chapter 8). Chapter 9 reviews the rock mechanics issues of UCG in terms of understanding surrounding rock deformation as a cause of potential environmental impacts and a key factor affecting processes in the gasification system. Another chapter provides a summary of the efforts to create a mathematical model of the UCG process (Chapter 10). Finally, there is a chapter concerned with environmental performance of UCG plants, concentrating on protection of groundwater with examples, primarily, from the former Soviet UCG program (Chapter 11). A special emphasis of the book has been placed on potential commercialization of UCG technology. A chapter is dedicated to considering the features of the technology that make it suitable for large-scale energy and petrochemical applications (Chapter 12). Processes, equipment, efficiencies, and costs of utilizing syngas for production of electricity, synthetic methane, fertilizers, synthetic automotive fuels, methanol, and other value-added commodities are discussed in another chapter of this book (Chapter 13). Two chapters are dedicated to consideration of commercialization issues using examples of two recent UCG projects—in South Africa and Australia (Chapters 14 and 15). A great deal of interest in recent years has been attracted to oil shale deposits, predominantly focusing on the shale gas and shale oil fracking revolution that took place in the United States in the last decade. The fracking is used to facilitate release and production of gaseous and liquid hydrocarbons from the shale matrix, while the organic matter of the matrix itself remains largely untouched. However, UCG experience offers an alternative, which is based on establishing a gasification process within the underground shale seam in situ and converting the shale organic mass into
Introduction to underground coal gasification and combustion
7
gaseous and liquid hydrocarbons, which would result in underground gasification of the shale. Our book includes a full chapter (Chapter 16) dedicated exclusively to the description of underground shale gasification research and development efforts and outcomes. As any industrial activity, UCG operation has an impact on the environment, which is minimized provided that proper operational procedures are followed. This book gives due emphasis to potential environmental impacts of UCG (see Chapter 11), which need to be compared with the environmental impacts of alternative technologies. Proper application of underground gasification and combustion technologies should reduce this impact. The closing chapters of the book deal with possible extensions of UCG technologies, especially when knowledge of underground processes accumulated in UCG operations can be useful in mitigation or reduction of environmental damage caused by various factors not related to UCG. Chapter 17 is dedicated to analysis of underground fires from the perspective of UCG technology. We must note, however, that comprehensive treatment of underground fires or discussion of even more remote topics such as fire safety in mines is not within the scope of this book. Extensive treatment of underground fires can be found in other publications (see Stracher et al., 2010). Environmental remediation of contaminated soils can be achieved very effectively through a specifically designed underground combustion process. One of the chapters in this book (Chapter 18) reports on a positive experience of such remediation. Both successful UCG operations and successful control and extinction of underground fires can be achieved only with appropriate monitoring and analysis. A spectrum of monitoring techniques is now standard in the best UCG operations. Chapter 19 of this book reviews measurement techniques that are commonly used in UCG operations and can be used in monitoring underground fires. The section also examines physical principles that may form a basis for advanced measurements and monitoring of underground gasification and combustion in the future. Once developed, these technologies may be suitable for monitoring a broad range of underground processes. In general, this book is addressed to an educated reader with some experience in the area; to people who have interest in commercial, technical, and scientific aspects of UCG; to research students; and to experienced researches who have a limited access to UCG-related information. The recent developments of the theory of key UCG processes (e.g., the theory of reverse and forward combustion linking, the theory of the flame position in the channel, and the theory of stability of evaporation fronts), which are highly mathematical and hardly suitable for general readers, are not included in the book. Readers interested in theoretical aspects of underground gasification and combustion are referred to relevant publications (Blinderman and Klimenko, 2007; Blinderman et al., 2008a,b; Saulov et al., 2010; Plumb and Klimenko, 2010).
Acknowledgments The editors would like to express their appreciation and gratitude to the Elsevier Publishing for all the support given to the editors and the authors of this book on UCG and combustion.
8
Underground Coal Gasification and Combustion
References Blinderman, M.S., Klimenko, A.Y., 2007. Theory of reverse combustion linking. Combust. Flame 150 (3), 232–245. Blinderman, M.S., Saulov, D.N., Klimenko, A.Y., 2008a. Forward and reverse combustion linking in underground coal gasification. Energy 33 (3), 446–454. Blinderman, M.S., Saulov, D.N., Klimenko, A.Y., 2008b. Optimal regimes of reverse combustion linking in underground coal gasification. J. Energy Inst. 81 (1), 7–12. Butler, Nick, 2017. Alternative truths and some hard facts about coal. Financial Times. April 3. Ergo Exergy, 2017. Welcome to Underground Coal Gasification. http://www.ergoexergy.com (accessed 22.07.17). Higman, C., Van der Burgt, M., 2008. Gasification, second ed. Elsevier, Amsterdam. IEA Coal Industry Advisory Board, 2013. 21st Century Coal: Advanced Technology and Global Energy Solution. OECD/IEA, Paris. Lamb, G.H., 1977. Underground Coal Gasification. Energy Technology Review No. 14, Noyes Data Corp. Plumb, O.A., Klimenko, A.Y., 2010. The stability of evaporating fronts in porous media. J. Porous Media 13 (2), 145–155. Saulov, D.N., Plumb, O.A., Klimenko, A.Y., 2010. Flame propagation in a gasification channel. Energy 35 (3), 1264–1273. Stracher, G., Prakash, A., Sokol, E., 2010. Coal and Peat Fires: A Global Perspective. In: CoalGeology and Combustion, vol. 1. Elsevier Science, Amsterdam/London. U.S. Energy Information Administration, 2016. International Energy Outlook 2016. Report DOE/EIA-0484(2016), DOE, Washington, DC. Unite Nations, Department of Economic and Social Affairs, Population Division, 2017. World Population Prospects: The 2017 Revision. custom data acquired via website.