Schweinfurth provided in 2002 an overview of the findings of U.S. Geological Survey as recorded in Circular 1143 on the factors affecting coal quality and use in the United States (2002), with a contribution on coal quality and public health by Finkleman (pp. 33-37).
Coal is abundant in the U.S., is relatively inexpensive, and is an excellent source of energy and byproduct raw materials. Because of these factors, domestic coal is the primary source of fuel for electric power plants in the U.S., and will continue to be well into the 21st century. In addition, other U.S. industries continue to use coal for fuel and coke production and there is a large overseas market for high-quality American coal. Because humans have used coal for centuries, much is known about it. The usefulness of coal as a heat source and the myriad of byproducts that can be produced from coal are well understood. The continued and increasingly large-scale use of coal in the United States and in many other industrialized and developing nations has resulted in known and anticipated hazards to environmental quality and human health. As a result, there is still much to be learned about the harmful attributes of coal and how they may be removed, modified, or avoided to make coal use less harmful to humans and nature. These issues of coal quality have not been examined carefully until recently.
Some of the problems that accompany the mining and use of coal are well known. Acid mine drainage results when coal beds and surrounding strata containing medium to high amounts of sulfur, in the form of compounds known as sulfides, are disrupted by mining, thereby exposing the sulfides to air and water. Atmospheric sulfur oxides (SOx) and subsequent acid deposition (such as acid rain) result from the burning of medium- to high-sulfur coal. The quality of surface and ground water may be affected adversely by the disposal of the ash and sludge that result from the burning of coal and cleaning of flue gases. These are some of the serious problems requiring either improved or new remedies. Other environmental problems are associated with emissions of carbon dioxide (CO2) and nitrogen oxides (NOx), two of the so-called “greenhouse gases.” These emissions are often attributed to coal use only; however, they also result from the burning of any fossil or biomass fuel, such as wood, natural gas, gasoline, and heating oil. The greenhouse gas problem requires a broader solution than just reducing the use of coal. Research currently is being conducted in the U.S. and several other countries into the reduction and disposal of CO2 from coal combustion. An excellent review of the results of this research and the prospects for coal can be found in a publication of IEA Coal Research (1999).
Fluidized-bed combustion (FBC) of coal, which is a new method for controlling sulfur emissions, is gaining wide acceptance. In this system, finely ground coal is mixed with finely ground limestone. Both are fed together into a furnace in a constant stream onto a horizontally moving grate. Air is forced up through the grate and the entire mass is ignited at relatively low temperatures. The forced air causes the ground coal and limestone to be mixed with the hot gases of combustion, which in turn promotes the conversion of any SOx to gypsum as the burning mass moves along on the grate. According to the U.S. Department of Energy (2000), high-sulfur coal may be burned in this way while simultaneously capturing up to 95 percent of the SOx and most of the NOx emitted.
Although much is known about coal quality, much also remains to be learned. To this end, research on coal quality is being conducted in both the public and private sectors. Current studies encompass all aspects of the origin, burial history, and composition of coal in order to understand the various factors involved in determining coal quality, such as how and where to find the right coal for a specific use and how to clean coal to make its use more environmentally and industrially acceptable.
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In the past, the only consideration given to coal quality was whether coal lumps held together during shipping burned easily to produce a hot fire and didn’t produce too much ash. Today, however, concerns about human health, the environment, energy demands, and the supply of certain raw materials have broadened our concept of coal quality and our need to know much more about the origins, nature, and effects of coal quality. An extensive evaluation of coal quality must be central to coal use. Whatever coal is used for, whether for the direct production of energy, chemicals, synthetic fuels, or the recovery of useful minerals, and whatever problems and solutions accompany that use depend on the quality of the coal. Additional, sophisticated, multidisciplinary research on coal quality is required for the future. The results will help make it possible for society to continue to benefit from the good qualities of coal and to make progress in avoiding the undesirable affects of coal use.
In the near term, the most immediate advancements related to coal-quality research appear to be improvements in the efficiency of coal use (including more efficient production of synthetic fuels) and the development of methods to best understand, and thus control, the less desirable components in coal that have the potential to contribute to environmental degradation and adverse health effects. In the longer term, the recovery of useful substances from coal (such as iron, silver, sulfur, and zinc, as well as organic chemicals, gypsum, and ash) should be an exciting area for research related to coal quality.
Finkelman reported in 2002 (pp. 33-37) that prior to the widespread adoption of selective mining procedures and pollution-control technology, human health had been affected by sulfur and particulates emitted from coal combustion. This section of Circular 1143 describes several examples of how organic compounds and trace elements are still affecting the health of people in Europe, Asia, and America. The inorganic (and in some cases, organic) constituents in coal may have profound effects on the health of those people burning coal in their homes or living near coal deposits, coal mines, or coal-burning power plants. Trace elements, such as arsenic (As), emitted from coal-burning power plants in Europe and Asia have been shown to cause severe health problems. Water leaching of organic compounds from lignites may be the cause of a kidney disease that has taken the lives of more than 100,000 people in the Balkans.
Widespread health problems may be caused by domestic coal combustion in developing countries. Millions of people suffer from fluorosis, thousands from arsenism. In the southwestern U.S., many members of the Navajo Nation are dependent on coal as their primary source of energy. Many Navajo suffer from chronic respiratory problems that are attributed to emissions from the burning of coal in their hogans.[Note: the native population health issues may, to a large extent, be due to heavy smoking and other personal tobacco uses (crewing, dipping or more recently vaping. This would apply to the issues present in areas of underground uranium mining in the 1950s and 1960s]
A better knowledge of coal-quality parameters may help to minimize some of these health problems. Information on the concentrations and distributions of potentially toxic elements in coal may help us to avoid those parts of a coal deposit having undesirably high concentrations of these elements. Information on the modes of occurrence of these elements and the textural relations of the minerals and macerals in which they occur may help us to anticipate the behavior of the potentially toxic components during coal cleaning, combustion, weathering, and leaching. Coal quality characterization, therefore, offers coal scientists opportunities to contribute to important societal needs such as improved public health.
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