Welcome to Coal Online

Coal Online is a major free resource providing comprehensive information on the technology of coal utilisation. The information is based on published reports from the IEA Clean Coal Centre presented as chapters on specific topics related to coal and its use in Clean Coal Technologies. Each chapter contains up to several hundred pages illustrated with figures and tables.

About Us

Coal produces around 40% of the world's power and so underpins much of global economic activity. Many major economies are dependent on coal. Coal has various advantages - there are diverse sources of supply and it is less susceptible to price volatility than oil or gas. Thus, coal can play an important role in energy security.

Established in 1975, the IEA Clean Coal Centre ( is a major provider of impartial information, analysis and research on all aspects of coal. A team of experienced professionals gather, analyse and distribute information and knowledge on the efficient and clean use of coal.

The Centre publishes technical reports and reviews, facilitates R&D, assists in the provision of networks, organises workshops and conferences and builds and maintains a number of databases. We are also available to provide expert advice for our members on any aspect of the coal chain.

There is no political or commercial influence on the research and information provided - the IEA Clean Coal Centre is a non-profit organisation funded primarily by member subscriptions. Located in London we employ approximately 20 staff, largely made up of engineers, scientists and information specialists.

The IEA Clean Coal Centre is governed by representatives of member countries (Australia, Austria, Canada, Germany, Italy, Japan, Republic of Korea, Poland, South Africa, the UK and the USA), the European Commission, and industrial sponsors (Australian Coal Industry Consortium; Banpu, Thailand; Beijing Research Institute of Coal Chemistry, China; BHEL, India; Coal Association of New Zealand; Eskom & Anglo Coal, South Africa; SUEK, Russia).

The IEA was established in 1974 within the framework of the Organisation for Economic Co-operation and Development (OECD). A basic aim of the IEA is to foster co-operation among the twenty-four IEA participating countries in order to increase energy security through diversification of energy supply, cleaner and more efficient use of energy, and energy conservation. This is achieved, in part, through a programme of collaborative research and development of which IEA Clean Coal Centre is by far the largest and the longest established single project.

Studying the structural chemistry of coal

Author: Robert M Davidson

This Chapter is intended to provide an update of Molecular structure of coal (Davidson, 1980). Since 1980 there have been other reviews of the topic including those by Wender and others (1981), Green and others (1982), Gorbaty and others (1986), Derbyshire (1991), Haenel (1992), Gorbaty (1994), and Marzec (2002). In 1981, a reprint of van Krevelen’s book, Coal – Typology – Chemistry – Physics – Constitution was published, with a preface that stated that no attempts to make the book ‘up-to-date’ had been made to this classic text. Nevertheless, in 1993, a third, completely revised edition appeared, since the ‘amazing extension’ of the instrumental techniques of observation and analysis necessitated a total revision and updating.

Coal resources

Author: Paul S Baruya, Sarah Benson, Juliet Broadbent. Anne M Carpenter, Lee B Clarke, Martin Daniel, Yoshimitsu Ishihara, Alessandra McConville, Leonora McConville, Olivier Montfort, Katerina Rousaki, Simon Walker

This Chapter contains basic information about the coal resources of most of the world’s major coalproducing counties. The concept is not to provide a definitive and detailed breakdown of world coal resources, but rather to establish an appropriate overview as a foundation for subsequent, more technologically orientated chapters.

The Chapter firstly reviews the processes of formation of both hard coal and lignite deposits, noting the differences in physical and chemical characteristics that may be encountered with coals formed at different time periods. It then introduces the topic of coal macerals, variations in which are fundamental to understanding these coal-specific behaviour characteristics, and which have an important bearing on utilisation practice.

The bulk of the Chapter is given over to descriptions of the coal resources of individual countries. The level of information included varies from country to country, reflecting both the relative importance of each in terms of production or potential production, and the accessibility of reliable data on individual coal resources. In each case, the quantification of accessible coal is based on a consideration of geological, mining and economic criteria pertaining to the specific coalfield or country. The amount of coal in place (the resource base), and in some cases the amount of mineable coal (the reserve), as quoted for each of the countries reviewed, has been provided by relevant local sources, accompanied by corresponding definitions. It should be remembered that, despite international moves towards commonly accepted practice, these definitions can still vary substantially, depending on the structural complexity of a deposit, amongst other criteria.

Greenhouse gases - emissions and control

Author: Deborah M B Adams, Katerina Rousaki, Irene M Smith, Jan L Vernon

This Chapter reviews the main climate-change issues as they relate to coal, with particular emphasis on the application of current and future technologies as a means of reducing greenhouse-gas emissions with normes bbc & rt2012 from coal production and utilisation. It also covers topics such as carbon dioxide capture and sequestration, set in the context of reducing the impact of greenhouse gases on the Earth's climate. viewView the Flash version online

Trace elements - occurrence, emissions and control

Author: Robert M Davidson, David A Reeve, Lesley L Sloss, Irene M Smith

This Chapter addresses the occurrence of trace elements and organic compounds in coal, and their emission during coal utilisation, with particular emphasis on mercury, given the long-established links between mercury and its accumulation in both the environment and in food chains. Trace elements are, of course, released from natural sources as well as from human activities.

Effects of coal ash on combustion systems

Author: Anne M Carpenter, Stephen Niksa, David H Scott, Zhangfa Wu

All coals have a significant content of ash-forming inorganic material that cannot be economically removed before combustion. This amount can range from below 3% in a clean low-ash feedstock, to over 40% in some low-grade coals. Most commonly, the ash-forming material represents between 10% and 25% of the feed coal. This Chapter reviews coal ash and the detrimental effects that it can have on combustion equipment through the formation of unwanted deposits. Following a brief overview of the types of problem that can be encountered in coal-fired boilers of all types, the Chapter provides an insight into the mineral matter that forms the basis for ash, and into the analytical methods available for the identification of the mineral species contained in it. A section on the methods of ash formation in coal-fired boilers is followed by a review of the transformations undergone by inorganic mineral particles during the combustion processes, and the Module then looks at ash deposition. Slagging and fouling can occur in all types of coal-combustion equipment, and the next three sections focus on potential ash problems in pulverised-coal, fluidised-bed and gasification systems. The Chapter includes a section on recent innovations in the development of more accurate predictive systems for identifying coals with a particular risk of causing ash deposition problems, and concludes with a review of testwork procedures available for identifying deposit accumulations and for investigating the suitability of specific coals for individual combustion systems.

Coal preparation

Author: Gordon R Couch

Preparation is the term used to describe the production of sized coals for different markets, with the use of separation processes to minimise the presence of mineral matter. Cleaning implies optimising the separation processes to remove the maximum amount of unwanted impurities. Raw coal is a complex and heterogenous fuel that contains a variety of impurities, many of which have a negative impact on the mine-to-end-user chain. Coals may contain from below 3% to over 40% of ash-forming constituents and from below 0.5% to over 5% of sulphur, and while in the past, the principal focus has been on the behaviour and treatment of the ash-forming mineral matter and sulphur, in the USA in particular there is increasing interest in the role of coal cleaning in the removal of other perceived contaminants, such as mercury and other trace elements. Water can be regarded as a major impurity in the sense that it reduces the heating value of a coal. Some low-rank coals can contain as much as 60% water. However, technologies for drying and water removal are only considered in this Chapter in the context of conventional coal-cleaning procedures. Impurities present in coal may increase the cost of transport; cause operating problems in end-users’ plants or harm the environment if released in an uncontrolled way. The materials are mainly inorganics that are present either as mineral matter or as chemically combined elements within the organic structure. In higher-rank coals, the inorganics are mainly present as mineral matter, but in lower-rank coals there is an increasing proportion of organically bound elements. Tiny amounts may be held in water in the pore structure. Some impurities may be picked up during the handling or treatment of coal before its use and, for example, there will be small quantities of magnetite left after dense-medium washing. Sulphur is present in varying proportions in both mineral matter and organically-bound forms.

Utilisation of slags, ash and residues

Author: Deborah M B Adams, Lee B Clarke, Charlotta Nilsson, Lesley L Sloss, Irene M Smith

This Chapter reviews the characteristics, and utilisation and disposal options for the residues generated from coal combustion. Until fairly recently these residues, consisting mainly of ash of various types, were usually considered to be waste products. However, over the past 20 years there has been an increasing appreciation of the potential of coal-use residues as usable products in their own right, and a considerable amount of research has been undertaken into potential markets for these materials. Some, such as fly ash from conventional pulverised coal combustion, have already become well-established, principally in construction-industry applications. In other cases, especially where new combustion technologies are still under evaluation, potential uses for combustion by-products still have to be ascertained. The clear trend is, nonetheless, towards regarding coal-use residues as a valuable byproduct capable of generating revenues, rather than as waste material that incurs disposal costs.

Transport, storage and handling of coal

Author: Anne M Carpenter, Darrell Porter, David H Scott, Simon Walker

This Chapter covers various aspects of the transportation, storage and handling of coal, predominantly between the producer and the end-user. Thus the descriptions begin with transport, which for coal (as a bulk commodity) typically encompasses road haulage, railways and seaborne delivery. The use of barges on inland waterways and as an interconnecting link between land- and sea-freight is also locally important, and is addressed here, while brief mention is also made of the infrastructure and technology involved at coal-handling ports.

The Chapter continues with a review of stockpiling philosophy and the technology used, not only for handling incoming coal and then reclaiming it for onward shipment or for use as fuel, but also in terms of the minimisation of the environmental impact of stockyards. As well as acting as storage capacity, either as a buffer or for the longer term, stockyards also have an important role in helping to achieve the most appropriate blend of coals for particular end uses. In this context, the module contains detailed information on various stacking and reclaiming methods, with particular emphasis on their advantages and disadvantages in relation to coal blending.

Aside from the bulk materials-handling systems used during coal transport and storage, one of the most widely used coal-handling technologies throughout the world is pulverisation. Pulverised coal is one of the major fuels for power generation, and the module contains extensive information about the design, application and operation of pulverisers, together with the safety issues involved with their use. Finally, the Chapter addresses spontaneous combustion during coal transport and storage. Fire is a major potential hazard at all stages of the coal production, transport and utilisation cycle, and special care has to be taken to ensure that coals that are susceptible to spontaneous combustion are handled in such as way as to minimise this risk.

Carbon products and organic chemicals from coal

Author: Chunshan Song, Harold S Schobert, John M Andresen

Coal is the most abundant hydrocarbon resource and has several positive attributes when considered as a feedstock for aromatic chemicals, and carbon-based materials. While coal continues to be used as an energy source in electric power plants, materials and chemicals from coal have been recognised as an important area for future coal utilisation research and development. This Chapter covers an area that involves chemical processing of coal and coal-derived substances for making carbon materials and organic chemicals. The objectives are to critically review the publications in open literature on carbon materials and organic chemicals from coal and to identify approaches and strategies as well as new directions for research. The technical discussions focus on both the unique, premium carbon products as materials, and the phenolic and aromatic compounds that can be converted to value-added organic chemicals. The review of chemicals from coal is directed towards those that make use of structural features of coal, rather than ‘alternative chemicals’ that are already produced from petroleum and natural gas as commodity chemicals in large quantities in industry worldwide.

NOx emissions and control

Author: Anne M Carpenter, Robert M Davidson, Kazunori Fukasawa, Lotte Garner, Stuart C Mitchell. Ruksana Moreea-Taha, David H Scott, Lesley L Sloss, Irene M Smith, Herminé Nalbandian Soud, Mitsuru Takeshita, Zhangfa Wu

Oxides of nitrogen are among the major environmental pollutants that have a significant detrimental effect on the atmosphere. Fossil-fuel combustion is responsible for over half the total global emissions of nitrogen oxides, and up to two-thirds of the emissions from human activities. Although the contribution from coal combustion alone is not known, it is evident that oil combustion in the transport sector commonly contributes over 50% of emissions from human activities in individual countries. Other sources from human activities include biomass burning and the use of ertilisers. During coal combustion, nitrogen present in both the coal and the combustion air is converted to nitric oxide (NO) and nitrogen dioxide (NO2) (together commonly referred to as NOx). These are the two most important oxides of nitrogen with respect to air pollution, and while nitrous oxide (N2O) is also an oxide of nitrogen, its role in the environment is distinct from that of NO and NO2. NOx emissions are of concern because they are associated with the increased acidity of aerosol particles, cloud water and precipitation (acid rain), causing damage to aquatic and terrestrial ecosystems, as well as being responsible for the corrosion of building materials and affecting human health. NOx can act as a fertiliser in soils but, in excess quantities, leads to eutrophication (an overabundance in nutrients leading to oxygen depletion) in many environments. Furthermore, NOx emissions are of crucial importance in the formation of photochemical smog and oxidants, especially ozone (O3), in the lower atmosphere.

SOx emissions and control

Author: Deborah M B Adams, Anne M Carpenter, Lee B Clarke, Robert M Davidson, Rohan Fernando, Kazunori Fukasawa, David H Scott, Irene M Smith, Lesley L Sloss, Herminé Nalbandian Soud, Mitsuru Takeshita, Zhangfa Wu

Sulphur occurs in coal in three forms:

Environmental legislation to control SO2 emissions has been adopted in more than 30 countries, while fuel switching to lower-sulphur coal had been chosen by many power generators in order to achieve compliance. However, where fuel switching is not an option or is inadequate, FGD is used to control SO2 emissions in pulverised coal-fired power plants. In commercial use since the early 1970s, FGD has become the most widely used technique to control SO2 emissions, next to the firing of low-sulphur coal. Numerous FGD systems are currently in use, with additional systems under development.

Coal combustion technology for a competitive power market

Author: Anne M Carpenter, R Coade, R Coldham, Rohan Fernando, Alexander Fleming, David Foster, G Goonan, Colin Henderson, D Holmes, T Johnson, S D Mann, M Mason, D McNabb, Ruksana Moreea-Taha, D Pham, David H Scott, Herminé Nalbandian Soud, D Swainsbury

The coal-combustion technologies that are currently in use are reviewed in detail in the Module on the Fundamentals of coal combustion. As is noted there, technological development is largely aimed at improving the efficiency of coal combustion (extracting more of the contained energy) and at reducing the emissions of greenhouse gases and other environmentally deleterious materials such as sulphur dioxide, oxides of nitrogen, trace elements and particulates from coal usage. More information about these aspects is contained in the respective Chapters of CoalOnline.

The world’s generating capacity has grown 15 times since 1950 (at roughly twice the rate of world economic output), whilst the cost of buying a unit of electricity has dropped by 75% in real terms since the 1940s. However, the century-old power industry has recently undergone a series of major changes driven by deregulation, technological improvements and stricter environmental legislation. As a result, today’s power generation industry is becoming increasingly dynamic, and this trend is expected to become more evident in the future.

As of the end of 1999, there were over 1600 pulverised coal fired power plants in the world, comprising more than 4000 units with a total capacity of more than 1000 GWe. This accounted for almost 40% of total electricity production. Coal’s share in the fuel market, especially for power generation, is expected to continue at the same level over the next two decades.

This Chapter looks at how coal can be used more effectively for electricity generation under today’s much more competitive market conditions, and reviews the different routes that are currently available for achieving low operational costs whilst ensuring the maximum efficiency of existing power plants.

Cofiring coal with other fuels

Author: Robert M Davidson, Alison Doig, James M Ekmann, Rohan Fernando, N Stanley Harding, Ruksana Moreea-Taha, Geoffrey F Morrison, Massood Ramezan, Katerina Rousaki, Irene M Smith, Scott M Smouse, John C Winslow

This Chapter of CoalOnline looks at the opportunities for, and the technology involved in, the use of coal in conjunction with other fuels: cofiring. There are a number of reasons why this may be economically attractive, principal amongst which are the availability of cheap alternative fuels, such as wood, biomass, refuse-derived fuel, solid municipal waste, plastics, natural gas or petroleum coke, and the need to reduce greenhouse-gas emissions in order to meet treaty obligations. The main focus of the Chapter is on the cofiring of coal with other fuels for power generation, although other coal-utilisation aspects, such as combined heat and power (cogeneration) and cement production, are also covered. Cogasification, which presents an alternative means of using other fuels with coal, either directly or indirectly, is not covered here, and reference should be made to the Chapter on Gasification fundamentals and processes or to Davidson (1997). Neither does the Chapter address any issues associated with fuels such as natural gas or oil that are used exclusively as an aid to starting-up pulverised-coal-fired boilers or in maintaining low-load operations; in these cases, the use of the alternative fuel is limited both in duration and quantity, and is not intended to provide a significant contribution to the overall thermal input to the boiler.

Fundamentals of coal combustion

Author: Anne M Carpenter, Stephen Niksa, SRI International, David H Scott, Zhangfa Wu

This Chapter looks at the fundamental processes involved in coal combustion, focusing on both pulverised coal and fluidised bed combustion technologies. It does not address gasification, information about which can be found in the Chapter dedicated to that topic. This Chapter is more theoretically based than the others that deal with the use of combustion technologies in practice, and as such forms a foundation for them. Practical applications relating to the use of coal, mainly in power generation, are discussed in detail in the Chapter on Coal-combustion technologies, while advanced coal-combustion systems that can be implemented as a means of increasing efficiencies are covered in the Chapter on Coal-combustion technology for a competitive power market. The technologies used for burning coal in conjunction with fuels such as natural gas, bio-fuels and petroleum coke are reviewed in the Chapter on Cofiring coal with other fuels.

Coal to liquids

Author: Gordon Couch

There is considerable current interest in the use of coal as a feedstock for making liquid fuels which can potentially replace imported oil and oil products. In some places, this could increase the security of supply of these liquid fuels which are mainly used for transportation.

There are major drivers which support a CTL programme in countries that have substantial coal resources, are net importers of oil and which have a policy framework encouraging energy independence. There are, however, significant cost implications if coal is used as the feedstock for providing transport fuels, and unless appropriate actions are taken, the CTL route has a much greater environmental footprint than conventional oil recovery and refining.

The various forecasts and projections indicate steadily increasing demand for liquid transport fuels, and tend to boost the perceived need for their production from different sources. However, active demand side management could reduce the increase, and even achieve a reduction in use in some countries, thus balancing an increase in others.

This study discusses both direct and indirect coal liquefaction and looks at proposals for hybrid plants. It considers the effects of coal rank and type and the range and properties of the liquid products produced. Research, pilot and demonstration programmes are reviewed, together with a description of current production units – and of plants which are planned or under construction. The review discusses potential developments, some of which have links with polygeneration. It includes country-by-country reviews of current CTL plans, together with a review of the potential environmental footprint of CTL activities. Finally there is a consideration of demand side aspects of the use of liquid transport fuels, and an economic overview of the implications of the large-scale use of CTL technologies.

Coal combustion technology

Author: Deborah M B Adams, Anne M Carpenter, Gordon R Couch, Rohan Fernando, Colin Henderson, Ruksana Moreea-Taha, Herminé Nalbandian, Stephen Niksa, Per-Axel Nilsson, Katerina Rousaki, David H Scott

This Chapter addresses the technology used in coal-combustion systems, focusing principally on systems used for electric-power generation since this accounts for a greater proportion of coal utilisation than any other individual end use. The Chapter builds on the concepts introduced in the Chapter on the Fundamentals of coal combustion, reviewing the combustion technologies that are currently in most common use. Advanced coal-combustion systems that can be implemented as a means of increasing efficiencies are covered in the Chapter on Coal-combustion technology for a competitive power market, while the technologies used for burning coal in conjunction with fuels such as natural gas, bio-fuels and petroleum coke are handled in the Chapter on Cofiring coal with other fuels.

Underground coal gasification

Author: Couch, Gordon

The report describes progress with the development of underground coal gasification (UCG), which has the potential to increase the world’s resource of useable coal. The technologies involving the drilling of injection and production wells into the coal seam are described, together with the methods for linking the wells. With advances in methods for directional drilling in-seam, new techniques for UCG have proved to be possible. The test and trial work carried out in the former USSR, in China, Europe and the USA up to 2000 is described, along with current efforts to commercialise the technology. With the power of modern computers, the modelling of various aspects of the process has become possible, and current work should facilitate the validation of some of these models. Geological and hydrogeological issues are discussed, as the single most important decision that will determine the technical and economic performance of UCG is site selection. The report covers environmental issues, including carbon management, and discusses the options for the use of the syngas formed. The recent pilot-scale tests in Australia, Canada, China and South Africa are reviewed, together with other current proposals for further trials in a wide range of countries including India, Russia, the UK and the USA.

Metallurgical uses of coal

Author: Anne Carpenter, Gordon Couch, Herminé Nalbandian, David A Reeve, David H Scott, Lesley Sloss, Irene M Smith, Jan L Vernon

Following this introduction, the Chapter provides an overview of coal utilisation in metallurgy, including a detailed description of blast-furnace operation in ironmaking. It also includes a review of coke properties that are critical to successful blast-furnace operation as well as some of the standard tests used in their determination, before looking at iron- and steel-production processes that use coal rather than coke, and coal use in non-ferrous metal smelting.