Coal
Coal and Petroleum of Class 8
COAL
Coal is a combustible black or brownish black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. Coal is composed primarily of carbon along with variable quantities of other elements, chiefly hydrogen, with smaller quantities of sulphur, oxygen and nitrogen.
Coal is one of the fuels used to cook food. Earlier, it was used in railway engines to produce steam to run the engine. It is also used in thermal power plants to produce electricity. Coal is also used as a fuel in various industries.
FORMATION OF COAL
Coal forms in swampy areas as the result of the decay of plants in the absence of oxygen. Biochemical changes produced by bacteria release oxygen and hydrogen and concentrate carbon. Coal goes through several changes during formation. With increased pressure and time, impurities and moisture are removed. In swamps where coal forms, other sediment, such as sand, clay, and silt, also deposited. The weight of the sediment compresses the underlying organic matter. During this process, moisture and other materials are squeezed out, leaving a high carbon concentration.
TYPES OF COAL
The rank of coal is based on the degree to which the original plant material has been transformed into carbon and can be seen as a rough indication of how old the coal is: the older the coal the higher the carbon content (generally). The ranks of coal (from most to least carbon content) are as follows: anthracite, bituminous coal, sub-bituminous coal, and lignite.
The coal with the highest carbon content is the best and cleanest type of coal to use. As you move down the coal rank the heat given out decreases and the dirtiness of the fuel and moisture content increases.
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Types of coal |
Description |
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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 sulphur 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 calorific value of less than 5 kw/kg approximately. |
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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. Sub bitumnious coal has calorific values ranging from 5 - 6.8 kW/kG approximately. |
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Bituminous coal |
Bituminous coal is a soft, dense, black coal. Bituminous coal often has bands of bright and dull material in it. Bituminous coal is the most common coal and has a moisture content less than 20 %. Bituminous coal is used for generating electricity, making coke, and space heating. Bituminous coal has calorific values ranging from 6.8 - 9 kW/kG approximately. |
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Anthracite coal |
Often referred to as hard coal, anthracite is hard, black and lustrous. Anthracite is low in sulphur and high in carbon. It is the highest rank of coal. moisture content generally is less than 15 %. Anthracite has a calorific values of around 9 kW/kG or above. |
Coal is processed in industry to get some useful products such as coke, coal tar and coal gas.To score More in your class 8 refer NCERT solutions for class 8 .
