Coal geology in China: an overview

KEYWORDS:

• Coal
• China
• editorial
• coal geology

China has abundant coal resources, and currently is and will continue to be the largest coal producer for the foreseeable future. According to the World Energy Council (2017), China holds an estimated 114.5 Bt of coal reserve as of 2016, the third largest in the world behind the United States and Russia and about 13% of the world’s total reserves. From 1949 to 2016, coal production in China increased rapidly (Figure 1), although it has decreased a bit since 2013. In 2016, coal production in China amounted to 3.21 Bt (Enerdata 2017), about half of the total global coal production. China is also the largest user of coal in the world, consuming about as much coal as the rest of the world combined. Coal consumption accounts to more than 65% of the primary energy consumption in China. Also, the coal-bearing areas in China occur in almost every region of the country (Figure 2) and coal formation occurred in many geologic periods, including Middle Devonian, Carboniferous and Early Permian (C–P₁), Late Permian (P₂), Late Triassic (T₃), Early and Middle Jurassic (J_1-2), Late Jurassic and Early Cretaceous (J₃–K₁), and Eogene and Neogene (E–N) (Han and Yang 1980; Han et al. 1996; Dai et al. 2012; Figure 2).

Figure 1. China’s coal productions (Bt) from 1949 to 2016.

Figure 2. Coal deposits in China classified by geological age (modified from Dai et al. 2012).

‘Coal’ and ‘China’ to some extent have become synonymous. The Chinese coal industry greatly contributes to the economic development in China. However, periodically ubiquitous images of smog blanketing major Chinese cities are viewed all over the world. Coal combustion is one of the important contributors to smog, which is considered to be a major environmental and human health problem for China and other countries. News stories also highlight the periodic coal mine disasters that kill hundreds of Chinese coal miners annually. The need to address these and other human health, environmental, and mine safety issues and to maximize resource recovery and use justifies a vigorous coal research effort.

Although it is widely known that China is largest coal producer and consumer in the world, what is less well known is the fact that China has quietly become the world’s leading country for research and development on coal. Although more and more papers related to coal geology have been published in international journals, many of the Chinese coal publications are found in the Chinese literature limiting access to and awareness of this literature to all but Chinese scientists. This Special Issue of International Geology Review is intended to bring this wealth of information to English-speaking audiences. This Special Issue includes 11 papers, which provide a cross-section of current research on different aspects of the coal geology in China. They represent contributions from 70 individual authors, ranging from PhD students and early-career researchers to scientists with extensive experience who are leaders in their field. Although it is a special issue for coal geology in China, some papers have been prepared by teams drawn from several different countries, reflecting the increasingly global nature of coal and coal-related research.

The Special Issue encompasses a series of review papers, drawing on the experience of the group of researchers to provide overviews of particular topics. The first of these (Li et al. 2017b) discusses the geological setting of coal deposits in China by reviewing their distribution, coal-forming ages, coal-forming environments, and characteristics of major coal deposit formed in different ages. This is followed by an overview of China’s coal production, processing, and standardization of coal quality management over the past 30 years (Bai et al. 2017); they also analyse the present situation and future projections of China’s coal production. Coal can be considered as a source for critical elements and in some cases, base metal Al (Dai and Finkelman 2017). A comprehensive review paper by Dai et al. (2016) describes the progress and future prospects of some Chinese coals as a promising source of critical elements, including Ge, rare earth elements and Y, Ga, Al, V, Se, Zr, Nb, Au, Ag, Re, and U. Coal use can result in environmental degradation and widespread and severe health problems. Some of the elements of particular concern in some coals are As, Hg, F, Se, Be, and U, largely because of their potential for adverse environmental and human health impact. Finkelman and Tian (2017) review the health problems cause by coal combustion and mining in China, including fluorosis, arsenosis, lung cancer, selenosis, and premature deaths, as well as the possible positive impact on iodine deficiency disease. In view of its dual roles in resource recovery and environmental impact, a critical review of geochemistry of uranium in Chinese coals and its atmospheric emission by coal-fired plants in China is included in this compilation (Chen et al. 2017), covering abundance and enrichment origin of U, as well as the amount released into atmosphere from Chinese coal-fired power plants.

The emission and control of toxic trace elements, especially mercury, during coal combustion have been extensively investigated in China in recent years. Zhao et al. (2017) review the emission characteristics and control strategies of mercury and other trace elements (As, F, Se, and Cr) during coal combustion. These authors also discuss the removal performance of various sorbents (e.g., activated carbon, fly ash, calcium-based sorbents, metal oxides, and mineral sorbents) for trace element removal. Coal-fired power plants in China produce large volumes of coal combustion products (CCPs), of which disposal usually occupies large areas of useful cultivated land and may cause serious environmental issues. On the other hand, these CCPs could also be utilized as recoverable resources, and this is discussed in a review paper (Li et al. 2017a), along with the potential for economic recovery of an increasingly significant group of elements from coal products for use in modern industrial applications. Following on these reviews is a paper (Liu et al. 2017) that describes mineralogy and geochemistry of ash and slag from coal gasification in China. It covers the transformation of minerals typically found in coal and the effects of operating conditions on mineral transformation and melting/slagging behaviour of minerals during gasification process, as well as trace element migration behaviour in commercialized gasifiers.

Commercial exploitation of coalbed methane (CBM) as a natural gas resource is an important milestone in the history of the global energy industry. CBM resources less than 2000 m in depth in China are estimated to be 36.81 trillion cubic meters. Qin et al. (2017) comprehensively review the distribution of CBM resources, geological factors affecting CBM enrichment, and technical challenges of economically extracting gas from low-rank coal reservoirs and stimulating economic gas flow from deep low-permeability reservoirs. Coal seams, especially deep unminable coal seams, are one of the viable geological target for CO₂ storage to mitigate greenhouse gas emissions. Although facing some technical challenges, this storage can not only reduce the cost of pumping and injection but also can enhance recovery of CBM. The paper by Pan et al. (2017) summarize the main properties of the target coal seams, the well technologies used, the injection programmes, monitoring techniques, and key findings in China.

Stone coal in China is defined as a high-ash (usually >50%), low heat value (usually 3.5–10.5 MJ/kg), anthracite-rank combustible rock. It has been widely used as a fuel in rural areas of southern China and is the source of vanadium extraction. The final paper by Dai et al. (2017) is concerned with this special rock in China, including its occurrence, uses, geochemical and mineralogical properties, and Byproduct potential, as well as its adverse effects on environment and human health during its utilization.

The editors would like to thank all of the authors who contributed papers to the Special Issue, not only for making their efforts in organizing high-level review papers available for publication but also for demonstrating the wide variety of research objectives and coal-geology applications that have been and will be incorporated into past and future studies in a number of disciplines.

Sincere thanks are expressed to colleagues who served as reviewers, some on several occasions, for the papers that were submitted. These reviewers provided numerous constructive comments that helped many of the authors to improve the quality of their papers and generally reinforced the high standard of the work submitted.

Finally, we want to say that although this volume focuses on coal issues in China, these coal-related issues are of importance to any country that mines or burns coal. Exchange of information and collaboration of scientists from different countries and different disciplines on coal-related issues are essential for the most efficient, environmentally sensitive use of this important natural resource.

Contributions to constructive comments by Professor Deyi Ren and Yiping Zhou are also gratefully acknowledged. We would also like to thank the National Key Basic Research Program of China (No. 2014CB238902), the ‘111’ Project (No. B17042), and the National Natural Science Foundation of China (No. 41420104001), which financially supported guest editors’ international travel for discussion on various aspects of this issue and supported some papers included in this Special Issue.

Disclosure statement

No potential conflict of interest was reported by the authors.