Coal is a sedimentary deposit formed by the slow action of heat and pressure on forests buried in the long past.
Economic Importance of Coal: Of all known sources of energy, coal is the most important source supplying more than 55% of heat and energy in the world. Not only coal is a source of energy and heat but also it is the source of valuable products, viz., gases, tar, oils, pitch, coke, ammonia; fertilizers, synthetic dyes and numerous drugs. Nowadays, steam is used to produce electric power, which is then transmitted to the factory by means of wires. Production of electric power for moving industrial machinery is gradually increasing as such type of power has superior advantages.
The carbon derived from coke is indispensable for steel. So, coal may be said to be the basis of modern industrialization. Use of coal dates only from the eighteenth century. Countries are now trying hard to develop coal production with the object of attaining industrial progress and economic betterment. The industrial development of the north-eastern part of the USA, the rapid industrialization of the Soviet Union, the building of a sound industrial structure in U.K., Germany, etc. have all been largely possible due to domestic supplies of coal.
Coke is necessary for making iron and steel. Coal as a raw material is essential to the chemical industry. As a source of power, coal influences the location of manufacturing industries.
Classification of coal: Coals are mechanical mixtures of carbon, hydrogen, nitrogen, sulphur, etc. They are classified on the basis of their carbon content. The types are as follows: Anthracite coal: This is the best of all types of coal as the carbon content is above 92%. Once ignited it gives ample heat. it is smokeless and gives little ash. The colour is black and lustrous. The texture being hard, its mining cost is high and it is difficult to ignite. It is generally found in highly folded and faulted structures.
Pennsylvania is credited with 95% of U.S. anthracite reserve. Donetz in Ukraine, Russia produces a good amount of anthracite coal. About 5% of world's output of coal is anthracite.
Bituminous coal: It is next to anthracite in purity, Percentage of carbon varies from 74 to 85. Its colour is black, Flame is medium to long and luminous. It is mainly used in coke manufacture, steam raising, domestic heating and bunker fuel for steamships. It is extensively mined and widely used in industry and transport. About 80% of world's output of coal is of this type.
Lignite coal: It is a consolidated type having carbon content below 50%. It is smoky and brown, dull in colour. Texture is soft. It is used in steam raising and domestic heating.
Brown coal: It is powdery and usually contains less carbon than lignite. It gives excessive smoke, less heat and large amount of ash. About 15% of the world's output of coal is lignite or brown coal.
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