sub-bituminous coal
{{Short description|Lower grade of coal that contains 35–45% carbon}}
File:SUB-BITUMINOUS COAL LIKE THE PIECE JOHN REDDING IS HOLDING LIES UNDER THE SURFACE OF SOME 25,000 SQUARE MILES OF... - NARA - 549121.jpg holding a lump of sub-bituminous coal]]
Sub-bituminous coal is a lower grade of coal that contains 35–45% carbon. The properties of this type are between those of lignite, the lowest grade of coal, and those of bituminous coal, the second-highest grade of coal.{{cite web |title=Coal explained |publisher=Energy Information Administration |url=https://www.eia.gov/energyexplained/coal/ |access-date=2020-09-26}} Sub-bituminous coal is primarily used as a fuel for steam-electric power generation.
Properties
Sub-bituminous coals 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. They contain 15-30% inherent moisture by weight and are non-coking (undergo little swelling upon heating).{{Cite book | author=The Babcock & Wilcox Company| title=Steam: its generation and use| year= 2005| publisher=The Babcock & Wilcox Company| isbn=0-9634570-1-2 | pages=36–5}} The heat content of sub-bituminous coals range from 8300 to 11,500 BTu/lb or 19.3 to 26.7 MJ/kg. Their relatively low density and high water content renders some types of sub-bituminous coals susceptible to spontaneous combustion if not packed densely during storage in order to exclude free air flow.
Reserves
A major source of sub-bituminous coal in the United States is the Powder River Basin in Wyoming.
Application
Sub-bituminous coals, in the United States, typically have a sulfur content less than 1% by weight, which makes them an attractive choice for power plants to reduce SO2 emissions under the Acid Rain Program.
Sub-bituminous coals release large quantities of greenhouse gases when burned, compared to higher grades of coal.{{cite news |last1=Bond |first1=Jordan |title=NZ imported more than a million tonnes of 'dirty' coal last year |url=https://www.rnz.co.nz/news/national/446845/nz-imported-more-than-a-million-tonnes-of-dirty-coal-last-year |access-date=24 September 2023 |work=RNZ |date=14 July 2021 |language=en-nz}}