lignite

—lignitic /lig nit"ik/, adj.

/lig"nuyt/, n.

a soft coal, usually dark brown, often having a distinct woodlike texture, and intermediate in density and carbon content between peat and bituminous coal.

[1800-10; LIGN- + -ITE¹]

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Yellow to dark brown, rarely black, coal that has been formed from peat under moderate pressure; it is one of the first products of coalification and is intermediate between peat and subbituminous coal.

Dry lignite contains about 60–70% carbon. Almost half of the world's total coal reserves contain lignite and subbituminous coal, but lignite has not been exploited to any great extent because lignite is inferior to higher-rank coals (e.g., bituminous coal) in heating value, ease of handling, and storage stability. In some areas, however, the scarcity of fuel has led to extensive developments.

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▪ coal

      generally yellow to dark brown or rarely black coal that formed from peat at shallow depths and temperatures lower than 100 °C (212 °F). It is the first product of coalification and is intermediate between peat and subbituminous coal according to the coal classification used in the United States and Canada. In many countries lignite is considered to be a brown coal. Lignite contains about 60 to 70 percent carbon (on a dry, ash-free basis) and has a calorific value near 17 megajoules per kilogram (7,000 British thermal units per pound).

      It has been estimated that nearly half of the world's total proven coal reserves are made up of lignite and subbituminous coal, but lignite has not been exploited to any great extent, because it is inferior to higher-rank coals (e.g., bituminous coal) in calorific value, ease of handling, and storage stability. In areas where other fuels are scarce, the production of brown coal far exceeds that of bituminous coal.

      Most lignites are geologically young, generally having formed during the Cenozoic (Cenozoic Era) and Mesozoic (Mesozoic Era) eras (approximately 2 to 250 million years ago). Many lignite beds lie close to the surface and are of great thickness, sometimes greater than 30 m (about 100 feet); they are easily worked, and the cost of production is low. The utilization of lignite is difficult because of its high water content, which can be as great as 75 percent in some varieties. Upon exposure and weathering, some of this water is given up, and disintegration, or crumbling, of the material occurs, which reduces the value of lignite as a fuel. Lignite also tends to disintegrate during combustion, and hence the losses through a grate may be relatively high. It requires special care in storing, is uneconomical to transport over long distances, and is subject to spontaneous combustion. Schemes for increasing the use of lignite have received attention in Australia, New Zealand, Canada, the United States, and elsewhere. The fuel is used primarily by local utilities and industries and by domestic consumers close to the mine sites.

Otto C. Kopp

 

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