Coal is the most important mineral product required to generate thermal electricity. It is an inflammable substance found in the form of sedimentary rocks. Combustible matter in coal consists of carbon and hydrogen.
Formation of Coal
Coal has been formed from wood. Large areas of forests were buried under the sediments and the wood decomposed due to heat from below and pressure from above.
During the process of change from wood to coal the amount of oxygen and nitrogen decreases and the proportion of carbon increase. The percentage of carbon depends upon the duration and intensity of heat and pressure on the wood.
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Varieties of Coal
India’s coal is mostly associated with Gondwana series of rocks and is mainly found in Peninsular India. The production of the new tertiary type (2%) is found in Assam and Kashmir.
India produced about 328 million tonnes of coal in 2001-2002. The coal in India is used mainly by the Railways and the Iron and Steel Industry.
Coal can be divided into four categories:
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Anthracite:
This is the best variety with 80% carbon. It is hard, black and burns slowly without much smoke. It has the highest heating value. A small quantity is found only in Jammu and Kashmir.
Bituminous:
This contains 60-80% carbon and is dense, compact and black in colour. Because of its high carbon content and less moisture, it is used for heating purposes as well as for the production of coke and gas. It is found in Bihar, Orissa, Madhya Pradesh and West Bengal.
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Lignite:
It is a low grade coal with about 60% carbon. Its colour varies from dark to black brown. It produces less heat, crumbles easily and is found in Rajasthan, Tamil Nadu, Assam and Jammu and Kashmir.
Peat:
This contains 50-60% carbon and does not make good fuel. It burns like wood, gives less heat, gives out more smoke and leaves a lot of ash after burning.