Subbituminous

Subbituminous coal is a rank of coal that lies between lignite and bituminous coal in the conventional coalification scale. It generally has higher moisture content and lower carbon content than bituminous coal, while offering more energy per unit than lignite. Its exact properties vary by deposit.

Formation and composition: Subbituminous coal forms from peat through progressive burial and heating. It typically has moderate volatile matter and ash content and a lower carbon concentration than bituminous coal. The higher moisture content lowers its calorific value on a weight basis, and its sulfur content ranges from low to medium depending on the source.

Uses and distribution: Subbituminous coal is widely used for electricity generation in power plants designed for low- to mid-rank coals. It is often mined by surface methods in shallow deposits (for example, in the Powder River Basin in the United States) but is also recovered underground in other regions. While not typically used for metallurgical coke, it may be blended in some industrial applications and as a fuel in cement kilns.

Environmental and economic considerations: The moisture-rich nature of subbituminous coal reduces heating efficiency and increases transportation energy per unit of delivered energy. Sulfur content can influence sulfur dioxide emissions, though some deposits are relatively low in sulfur. Market costs depend on regional supply, demand, and transport distances.