BITUMINOUS COAL

also called Soft Coal, most abundant form of coal that is intermediate between subbituminous coal and anthracite in rank (i.e., degree of coalification). In Europe some bituminous coal with higher heat value is labelled hard coal, the designation soft coal being restricted to bituminous coal with lower heat value, lignite, and brown coal. Bituminous coal is dark brown to black and usually banded. It consists of more than 95 percent vitrinite, a maceral group derived from woody plant tissue. Bituminous coal contains between 15 and 35 percent volatile matter and usually has a moisture content of less than 3 percent; it thus has a relatively high calorific, or heat, value. Because of these properties and its abundance, bituminous coal has the broadest range of commercial uses among the coals. It has long been utilized for steam generation in electric power plants and industrial boiler plants. In addition, those varieties of bituminous coal that contain a fairly small amount of sulfur and cake easily are the only coals suited for making coke, a hard substance of almost pure carbon important for smelting iron ore. Coke is produced by heating bituminous coal to approximately 1,100 C (2,000 F) in specially designed airtight ovens. The coal does not burn, because of the absence of oxygen, but the intense heat drives off much of the volatile matter in the coal in the form of gases, leaving coke. Some of the gases released during the coke-making process, moreover, condense into coal tar and liquid ammonia. One major problem associated with bituminous coal is air pollution. Burning large quantities of bituminous coals with medium to high sulfur content releases sulfur dioxide into the air. When moisture in the air reacts with this chemical compound, sulfuric acid is formed. This substance then falls to the Earth mixed with water droplets as acid rain, a pollutant that causes crop damage and water contamination. Because of such serious pollution problems, a growing number of coal-fuelled electric power plants in the United States have switched to subbituminous coal, which contains much less sulfur. See also subbituminous coal.