Definitions

lignite

lignite

[lig-nahyt]
lignite or brown coal, carbonaceous fuel intermediate between coal and peat, brown or yellowish in color and woody in texture. It contains more moisture than coal and tends to dry and crumble when exposed to the air; the flame is long and smoky and the heating power low. It is found in the United States, Canada, Germany, and elsewhere chiefly in formations formed in the Tertiary period.

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 60–70percnt 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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Lignite, often referred to as brown coal, or Rosebud coal by Northern Pacific Railroad, is a soft brown fuel with characteristics that put it somewhere between coal and peat. It is considered the lowest rank of coal, and is found in the United States, Canada, Greece, and Germany where it is used almost exclusively as a fuel for for steam-electric power generation. Up to 50% of Greece's electricity comes from lignite power plants, and 25% of Germany's electricity.

Lignite is brownish-black in color and has a carbon content of around 60%, 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 heat content of lignite ranges from 10 to 20 MJ/kg (9 to 17 million Btu per short ton) on a moist, mineral-matter-free basis. The heat content of lignite consumed in the United States averages 13 million Btu/ton (15 MJ/kg), on the as-received basis (i.e., containing both inherent moisture and mineral matter). When reacted with quaternary amine, amine treated lignite (ATL) forms. ATL is used in drilling mud to reduce fluid loss.

Lignite has a high content of volatile matter which makes it easier to convert into gas and liquid petroleum products than higher ranking coals. However, its high moisture content and susceptibility to spontaneous combustion can cause problems in transportation and storage.

Because of its low energy density, brown coal is inefficient to transport and is not traded extensively on the world market compared with higher coal grades. It is often burned in power stations constructed very close to any mines, such as in Australia's Latrobe Valley and Luminant's Monticello plant in Texas. Carbon dioxide emissions from brown coal fired plants are generally much higher than for comparable black coal plants, with the world's worst carbon dioxide polluting being the brown coal fueled Hazelwood Power Station, Victoria. The continued operation of brown coal plants, particularly in combination with strip mining and in the absence of emissions-avoiding technology like carbon sequestration, is politically contentious.

Types

Lignite can be separated into two types. The first is xyloid lignite or fossil wood and the second form is the compact lignite or perfect lignite.

Although xyloid lignite may sometimes have the tenacity and the appearance of ordinary wood it can be seen that the combustible woody tissue has experienced a great modification. It is reducible to a fine powder by trituration and if submitted to the action of a weak solution of potash it yields a considerable quantity of ulmic acid.

Production

Lignite mined in millions of metric tons
Country 1970 1980 1990 2000 2001
369,300 388,000 356,500 167,700 175,400
127,000 141,000 137,300 86,400 83,200
5,400 42,300 82,600 83,500 80,500
24,200 32,900 46,000 65,000 67,800
8,100 23,200 51,700 63,300 67,000
32,800 36,900 67,600 61,300 59,500
4,400 15,000 43,800 63,000 57,200
67,000 87,000 71,000 50,100 50,700
13,000 22,000 38,000 40,000 47,000
26,000 43,000 60,000 - -
- - - 35,500 35,500
14,100 27,100 33,500 17,900 29,800
5,700 10,000 10,000 26,000 26,500
Total 804,000 1,028,000 1,214,000 877,400 894,800

See also

References

External links

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