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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 25-35%. 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. About 26.3% 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 25-35%, a high inherent moisture content sometimes as high as 66%, and an ash content ranging from 6% to 19% compared with 6% to 12% for bituminous coal.
The energy content of lignite ranges from (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 (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 (6.5 million BTU/ton).
Lignite has a high content of volatile matter which makes it easier to convert into gas and liquid petroleum products than higher-ranking coals. Unfortunately, its high moisture content and susceptibility to spontaneous combustion can cause problems in transportation and storage. It is now known that efficient processes that remove latent moisture locked within the structure of brown coal will relegate the risk of spontaneous combustion to the same level as black coal, will transform the calorific value of brown coal to a black coal equivalent fuel, and significantly reduce the emissions profile of 'densified' brown coal to a level similar to or better than most black coals.〔George, A.M.. State Electricity Victoria, Petrographic Report No 17. 1975; Perry, G.J and Allardice, D.J. Coal Resources Conference, NZ 1987 Proc.1, Sec. 4.. Paper R4.1〕 However, removing the moisture increases the cost of the final lignite fuel.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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