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Coal Mines
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)
References:
CCO, 2017, Coal
Directory of India 2015-16, Coal Controllers Organisation, Ministry of Coal,
Kolkata.
MOSPI. 2019, Energy Statistics 2019. New Delhi: Ministry of
Statistics and Programme Implementation (MOSPI).