Pg.no. 110
29. Composition of Coal
Figure 29.1 (Coal)
Coal is a natural black mineral, which is a mixture of free carbon and compounds of carbon
containing hydrogen, oxygen, nitrogen, and sulphur.
How is coal made?
Coal is formed from dead and decaying plant matter which has been subject to heat and
pressure under the earth’s surface for millions of years. Coal is made up mainly of carbon,
along with differing quantities of other elements, chiefly hydrogen, with smaller quantities of
sulphur, oxygen, and nitrogen.
Older coal generally has higher carbon content. Younger coals have a lower carbon and
calorific content, the fuel is dirtier, and the moisture higher.
Types of Coal:
Lignite coal
Used almost exclusively for electric power generation lignite is a young type of coal. Lignite
is brownish black, has a high moisture content (up to 45 %), and a high suphur content.
Lignite is more like soil than a rock and tends to disintegrate when exposed to the weather.
Lignite is also called brown coal.
Lignite has a colorific value of less than 5 kw/kg approximately.
Sub bituminous coal
Sub bituminous coal is also called black lignite. Sub bituminous coal black and contains 20-
30 % moisture. Sub bituminous coal is used for generating electricity and space heating.
Subbitumnious coal has calorific values ranging from 5 - 6.8 kW/kG approximately.
Bituminous coal