Sub-bituminous coal

From Freepedia

Sub-bituminous coal is a coal whose properties range from those of lignite to those of bituminous coal and are used primarily as fuel for steam-electric power generation.

It may be dull, dark brown to black, soft and crumbly at the lower end of the range, to bright, jet-black, hard, and relatively strong at the upper end. Subbituminous coal contains 20 to 30 percent inherent moisture by weight. The heat content of subbituminous coal ranges from 17 to 24 million Btu per short ton (20 to 28 MJ/kg) on a moist, mineral-matter-free basis. The heat content of subbituminous coal consumed in the United States averages 17 to 18 million Btu/ton (20 to 21 MJ/kg), on the as-received basis (i.e., containing both inherent moisture and mineral matter). A major source of subbituminous coal in the United States is the Powder River Basin in Wyoming.

Its relatively low density and high water content renders some types of sub-bituminous coal susceptible to spontaneous combustion if not packed densely during storage in order to exclude free air flow.