Coal is a combustible sedimentary rock formed from ancient vegetation which has been consolidated between other rock strata and transformed by the combined effect of microbial action, pressure and heat over considerable time period. Coal occurs as layers or seams. It is mostly composed of carbon (50-90%)), hydrogen (3-13%) and oxygen, with smaller amounts of nitrogen, Sulphur, and other elements. (CCO, 2017))
Hard coal comprises anthracite and bituminous coal. It has a gross calorific value (moist, ash-free basis) above 24 MJ/kg, or less than 24 MJ/kg provided that the coal has a vitrinite mean random reflectance greater than or equal to 0.6%. Lignite refers to the brown coal with a gross calorific value (moist, ash-free basis) less than 20 MJ/kg. (MOSPI, 2019)
Classification of Coal in India (CCO, 2017):
Coking Coal: The coal with Coking property is referred as Coking coal or metallurgical coal. It forms coherent beads, free from volatiles, with strong and porous mass called coke, when it is heated in absence of air. It is mainly used in steel making and metallurgical industries.
Semi-Coking Coal: The coal, when heated in the absence of air, forms coherent beads that are not strong enough for use in blast furnaces, is called semi-coking coal. It is blended with coking coal in appropriate proportion to make coke.
Non-Coking Coal: It does not have coking properties and it mainly used for power generations. It is also used for cement, fertilizers, glass, ceramic, paper, chemical and brick manufacturing and for other heating purposes.
Washed Coal: Processing of coal through water separation mechanism to improve the quality of coal by removing denser materials (rocks) and high ash produces washed coal, which has less ash, higher moisture, better sizing, better consistency, less abrasive, etc.
Coal mining is the process of extracting coal from the ground. Coal is valued for its energy content and has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron from iron ore and for cement production.
Types of coal mines (CCO, 2017):
Underground mining of coal: It refers to extraction of coal from sedimentary rocks in which the overlying rock is left undisturbed, while the coal is removed through shafts or tunnels. The underground mining techniques such as Longwall Mining, Room-And-Pillar Mining etc., are applied for sub-surface mining of coal.
Opencast mining: Open-pit mining, open-cut mining or opencast mining is a surface mining technique of extracting rock or minerals from earth by their removal from an open pit or burrow. Open-pit mines are used when deposits of commercially useful minerals or rocks are found near the surface owing to relatively thin overburden or due to structurally unsuitable crust for tunneling.
Coal deposits are mainly confined to eastern and south central parts of the country. The states of Jharkhand, Odisha, Chhattisgarh, West Bengal, Madhya Pradesh, Telangana and Maharashtra account for 98.26% of the total coal reserves in the country. As on March 31, 2018, the estimated reserves of coal were 319.04 billion tonnes, whereas that of lignite is 45.66 billion tonnes. (MOSPI 2019)
Raw coal coming from mines is washed to remove the ash contents to make them fit for feeding into boilers, particularly those of steel plants. Total installed capacity of washeries in the country is around 127.56 million tonneper Year (MTY) as on 31.3.2018 (MOSPI 2019). Illustration 1 shows coal mines of Korba Coal Field in Chhatisgarh. Illustration 2 shows coal mines of Singrauli Coal Field in Madhya Pradesh.
Illustration 1: Coal Mines of Korba Coal Field, Chhatisgarh
Illustration 2: Coal Mines of Singrauli Coal Field, Madhya Pradesh
CCO, 2017, Coal Directory of India 2015-16, Coal Controller’s Organisation, Ministry of Coal, Kolkata.
MOSPI. 2019, Energy Statistics 2019. New Delhi: Ministry of Statistics and Programme Implementation (MOSPI).