Different Types of Coal
There are four major types of coal. From the softest to the hardest they are:
1) Lignite coal
The softest of the four types of coal. It is a brownish black in color, very crumbly and primarily used for the generation of electricity. Because of its color, it is often referred to as "brown coal." Lignite is the result of millions of tons of plants and trees that decayed in a swampy atmosphere about 50-70 million years ago.
The heating content of lignite is approximately 4,000-8,000 Btu's per pound. The carbon content of lignite is 25%-35% and it has a very high water content - about 35 percent.
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.
Lignite with a fossil embedded
See article of Otto C. Kopp on Lignite in the Encyclopedia Britannica. 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.
The worlds biggest Lignite or Brown Coal Producers are Germany, the Russian Federation and the US.
Lignite is mined in so-called open pit mines. The Rhenish (Rhineland) lignite-mining region covers an area of some 2,500km2 to the west of Cologne and is one of the world's most important lignite-mining regions. Where Mechanised lignite mining began in the 1890s, the first bucket-wheel excavator was commissioned in 1933 and, by 1940, output was over 60Mt/y from 23 surface mines. began in the 1890s, the first bucket-wheel excavator was commissioned in 1933 and, by 1940, output was over 60Mt/y from 23 surface mines. mechanised lignite mining began in the 1890s, the first bucket-wheel excavator was commissioned in 1933 and, by 1940, output was over 60Mt/y from 23 surface mines.
2) Sub-bituminous coal
Sub-bitumous coal
Under greater pressure and heat, brown coal continued to lose moisture. The carbon content of coal increased as water was lost. The properties of sub-bituminous coal range from those of "lignite" (with a lower carbon content) to those of "bituminous coal" (with a higher carbon content). Sub-bituminous coal is primarily used for steam-electric power generation.
This is a medium soft coal that contains much less moisture than lignite and is not nearly as crumbly. Like lignite, its primary use is in the generation of electricity. The carbon content of sub-bituminous coal runs from 35%-45% and its heat value generally ranges from 8,000-13,000 Btu's per pound.
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- Peat is an accumulation of partially decayed vegetation matter. It is not yet coal, that will take a couple of million years.
- Bituminous coal contains even less moisture than the sub-bituminous type. The carbon content of bituminous coal is generally from 45%-85%. Its heat value ranges from 10,500-15,000 Btu's per pound - greater than either lignite or the sub-bituminous types. In addition to being used for electrical generation, it is also used in making coke or coking coal, an essential ingredient in making steel.
- Anthracite coal - discovered in 1769 - is the hardest of the four types. It averages 85%-95% carbon content and has the highest heating value of the four types of coal. It is not uncommon to find anthracite that produces well in excess of 15,000 Btu's per pound. To put that in perspective, that is roughly one and one-half times as much heat as the same volume of oil and four times as much as seasoned hard-maple firewood. Anthracite makes excellent home heating fuel because it burns cleanly, does not produce volatile gases and does not deteriorate. It can be stored on the ground for long periods of time without creating environmental problems.
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