Applied Coal Petrology

The Role of Petrology in Coal Utilization

Isabel Suarez-Ruiz, John C. Crelling

• Publisher: Academic Press
• Year: 2008
• Print ISBN: 9780080450513
• eBook ISBN: 9780080951546
• Topic: Physical Sciences
• Subtopic: Geology & Earth Sciences

This book is an integrated approach towards the applications of coal (organic) petrology and discusses the role of this science in the field of coal and coal-related topics. Coal petrology needs to be seen as a continuum of organic (macerals) and inorganic (minerals and trace elements) contributions to the total coal structure, with the overprint of coal rank. All this influences the behavior of coal in utilization, the coal by-products, the properties of coal as a reservoir for methane or a sequestration site for carbon dioxide, and the relationships of coal utilization with health and environmental issues. The interaction of coal properties and coal utilization begins at the mine face. The breakage of the coal in mining influences its subsequent beneficiation. Beneficiation is fundamental to the proper combustion of coal and is vital to the preparation of the feedstock for the production of metallurgical coke. An understanding of basic coal properties is important for achieving reductions in trace element emissions and improving the efficiency of combustion and combined-cycle gasification. The production of methane from coal beds is related to the properties of the in situ coal. Similarly, coal bed sequestration of carbon dioxide produced from combustion is dependent on the reservoir properties. Environmental problems accompany coal on its way from the mine to the point of utilization and beyond. Health aspects related with coal mining and coal utilization are also included because, in planning for coal use, it is impossible to separate environmental and health issues from the discussion of coal utilization. The book is aimed at a wide audience, ranging from researchers, lecturers and students to professionals in industry and discusses issues (such as the environmental, and health) that are of concern to the general public as a whole. - This book focuses on the applications of coal (organic) petrology to our modern society - It is an integrated approach to help the reader appreciate the importance of coal quality and coal utilization. Coal composition (macerals, mineral, trace elements) and the overprint of coal rank are treated together - The book synthesises all the possibilities of the organic petrology as a tool for coal utilization in conventional applications (mining and beneficiation, coal combustion, gasification, liquefaction, carbonization), as a precursor of carbon materials and as a petroleum source and reservoir rock - The role of applied petrology in the characterization of solid by-products from coal utilization is also discussed - In addition, this book describes the present status of environmental and health problems linked to coal utilization and the ways in which such problems might be overcome in the future

Chapter 1. Introduction to Applied Coal Petrology

1.1. Fundamental Concepts

Coal is a combustible sedimentary rock, composed essentially of lithified plant debris. The plant debris was originally deposited in a swampy depositional environment to form a soft, spongy sediment called peat. However, physical and chemical processes brought about by compaction and elevated temperatures with prolonged burial at depths of up to several kilometers and over periods of up to several hundred million years then changed the peat into coal through a process referred to as coalification or rank advance.

The properties of a given coal can be related to three independent geological parameters, each of which is determined by some aspect of the coal's origin. As discussed more fully by authors such as Ward (1984), Diessel (1992a), Taylor et al. (1998), and Thomas (2002), these parameters are briefly defined as follows:

• Rank. Coal rank reflects the degree of metamorphism (or coalification) to which the original mass of plant debris (peat) has been subjected during its burial history. This depends in turn on the maximum temperature to which it has been exposed and the time it has been held at that temperature and for most coals reflects the depth of burial and geothermal gradient prevailing at the time of coalification in the basin concerned. Heat flow from nearby igneous intrusions, however, may also play a part.
• Type. Coal type reflects the nature of the plant debris from which the original peat was derived, including the mixture of plant components (wood, leaves, algae, etc.) involved and the degree of degradation to which they were exposed before burial. The individual plant components occurring in coal, and in some cases fragments or other materials derived from them, are referred to as macerals (see Chapter 2); these form the fundamental starting point for many different coal petrology studies.
• Grade. The grade of a coal reflects the extent to which the accumulation of plant debris has been kept free of contamination by inorganic material (mineral matter), including the periods before burial (i.e., during peat accumulation), after burial, and during rank advance. A high-grade coal is therefore a coal, regardless of its rank or type, with a low overall proportion of mineral matter, and hence a high organic matter content.

Although organic matter derived from marine algae occurs in very old (Precambrian) sedimentary rocks, land plants capable of forming coal did not appear until the Silurian and Devonian periods. Major coal deposits occur in the Carboniferous strata (354–290 My) of Europe and North America, and in the Permian (290–248 My) sequences of Australia, India, South America, and the other land masses that made up the former continent of Gondwanaland. Coals of Carboniferous and Permian age also occur in China. Mesozoic coal occurs in a number of areas, notably the Jurassic (205–142 My) of Australia and China and the Cretaceous (142–65 My) of North America. There are also significant resources of Palaeogene and Neogene age (65–1.8 My) in various continents, including Europe, North America, Asia, and Australia.

1.2. Coal Resources, Mining, and Utilization

Coal is a versatile fossil fuel that has long been used for a variety of domestic and industrial purposes. It currently provides around 25% of the world's total primary energy (International Energy Agency, 2007) and, although subject to some possible variation with different policy developments, is expected to provide a similar share in future years (e.g., 23–26% in 2030; International Energy Agency, 2007).

Most of the world's coal is used for the production of electric power (see Chapter 4). The other main use is for production of coke as a reducing agent in the iron and steel industry (see Chapter 7). Coal is also used as fuel for a range of manufacturing processes, such as the production of heat in cement kilns and other industrial plants, gasification and petrochemical production (see Chapter 5), and heating domestic and commercial buildings. In addition, it is used as a raw material in a range of nonenergy applications (see Chapter 8), such as the production of carbon electrodes for the aluminum industry or as a precursor for a number of other carbon-based industrial materials.

The availability of coal resources has been a major contributor to the economic growth of many countries, either directly through their own resources or indirectly through access to the international coal trade. In the late 19^th and early 20^th centuries, coal was mainly used as a transport fuel (such as for ships and railway locomotives) or as a source of heat and power for industrial and domestic applications. In the middle of the 20^th century the use of coal decreased in some areas because of low oil prices, but the oil supply crisis of the 1970s reversed this trend and led to an increase in coal consumption. Another consequence of the oil supply crisis was a significant increase in coal liquefaction research and development (see Chapter 6), although much of this work was subsequently put on hold when oil prices stabilized.

Though coal usage has continued to increase, environmental concerns and changes in the political climate have again begun to give coal an unfavorable public image. Increasing concerns about coal utilization as a contributor to greenhouse gas emissions, particularly CO², have led to more intense questioning of the role of coal and a renewed search for alternative energy sources. According to International Energy Agency data (International Energy Agency, 2007), coal became the world's principal source of anthropogenic CO² emissions in 2004, moving ahead of emissions derived from oil and natural gas sources. This has led to another change in the focus of coal research, with the emphasis shifting toward increasing the efficiency of coal utilization and to integrating coal utilization with CO² sequestration/storage processes.

1.2.1. Coal Resources and Production

According to data reported by the World Energy Council (2007), the total proven recoverable reserves of coal worldwide (all ranks) are currently estimated at 847 Mt, made up of 431 Mt of bituminous coal and anthracite, 267 Mt of subbituminous coal, and 150 Mt of lignite. The reserves are located on every continent and in over 70 countries, with major proportions identified in the United States, the Russian Federation, China, India, Australia, South Africa, Ukraine, and Kazakhstan.

World coal production in 2006 was 6,284 Mt (International Energy Agency, 2007), represented by 5,370 Mt of hard coal (bituminous coal and anthracite) and 914 Mt of subbituminous coal and lignite (brown coal; Table 1.1). This continues the trend previously reported by the World Coal Institute (2005), indicating an overall increase of about 40% in coal production during the past 20 years. China is now the largest single producer, with 2,841 Mt of hard coal in 2006. Other major producers, especially of hard coal, include the United States, India, Australia, South Africa, Russia, and Indonesia.

Table 1.1. Coal production, exports, and imports by country, 2006

Coal Production	Hard Coal (Mt)	Brown Coal (Mt)	Coal Exports	Hard Coal (Mt)	Coal Imports	Hard Coal (Mt)
People's Republic of China	2,481	(a)	Australia	231	Japan	178
United States of America	990	76	Indonesia	129	Korea	80
India	427	30	Russia	92	Taiwan	64
Australia	309	71	South Africa	69	United Kingdom	51
South Africa	244	0	People's Republic of China	63	Germany	41
Russia	233	76	Colombia	60	India	41
Indonesia	169	0	United States of America	45	People's Republic of China	37
Poland	95	61	Canada	27	United States of America	33
Kazakhstan	92	5	Kazakhstan	26	Russia	26
Colombia	64	0	Vietnam	22	Italy	25
Rest of world	266	595	Rest of world	51	Rest of world	243
Total	5,370	914	Total	815	Total	819

(a) Included with hard coal production.

Data compiled from International Energy Agency, 2007.

The size and extent of the world's coal reserves suggest that there is enough available to meet demands for the next 150–190 years at current ...

Table of contents

• Brief Table of Contents
• Table of Contents
• List of Figures
• List of Tables
• About the Editors
• Contributing Authors
• Acknowledgments
• Preface
• Chapter 1. Introduction to Applied Coal Petrology
• Chapter 2. Basic Factors Controlling Coal Quality and Technological Behavior of Coal
• Chapter 3. Mining and Beneficiation
• Chapter 4. Coal Combustion
• Chapter 5. Coal Gasification
• Chapter 6. Direct Coal Liquefaction
• Chapter 7. Coal Carbonization
• Chapter 8. Coal-Derived Carbon Materials
• Chapter 9. Coal as a Petroleum Source Rock and Reservoir Rock
• Chapter 10. Environmental and Health Impacts
• Chapter 11. Other Applications of Coal Petrology
• Bibliography