Lignite

Lignite, often referred to as brown coal, is a soft brown combustible sedimentary rock formed from naturally compressed peat. It is considered the lowest rank of coal due to its relatively low heat content. It has a carbon content around 60–70%. It is mined all around the world and is used almost exclusively as a fuel for steam-electric power generation, but is also mined for its germanium content in China. As of 2014, about 12% of Germany's energy and, specifically, 27% of Germany's electricity comes from lignite power plants, while in Greece, lignite provides about 50% of its power needs.

Characteristics

Lignite is brownish-black in color and has a carbon content around 60–70%, a high inherent moisture content sometimes as high as 75%, and an ash content ranging from 6% to 19% compared with 6% to 12% for bituminous coal.

The energy content of lignite ranges from 10 to 20 MJ/kg (9–17 million BTU per short ton) on a moist, mineral-matter-free basis. The energy content of lignite consumed in the United States averages 15 MJ/kg (13 million BTU/ton), on the as-received basis (i.e., containing both inherent moisture and mineral matter). The energy content of lignite consumed in Victoria, Australia, averages 8.4 MJ/kg (6.5 million BTU/ton).