Question

The calorific value of lignite is about ____ $ KJ{g^{ - 1}} $
(A) $ 90 $
(B) $ 78 $
(C) $ 87 $
(D) $ 8 $

Answer 1

Hint :Basically, coal is a solid carbon rich fossil fuel and it is utilized as a source of energy. The calorific value is defined as the energy which is obtained by the calculation of heat produced during the complete combustion of the specified quantity of coal.

Complete Step By Step Answer:
The calorific value of a fuel is also known as the heat value of the fuel. This means that the calorific value of the coal depends on the carbon content of the fuel. More the carbon content in the coal, the higher will be the calorific value.
Lignite: This is formed after the formation of peat and it is considered as the intermediate stage of coal formation. The carbon content in lignite is $ 40 - 45{\text{ }}\% $ and the moisture content is also high, that is, around $ 35\% . $ Lignite coal is also known as brown coal. The calorific value of Lignite ranges from $ 8000KJK{g^{ - 1}} $ to $ 1500KJK{g^{ - 1}} $ which means that the calorific value of Lignite ranges from $ 8 $ to $ 15KJ{g^{ - 1}} $ .
Hence, the correct answer is option (D), that is, the calorific value of lignite is about $ 8KJ{g^{ - 1}} $ .

Additional Information:
There other three main types of coal are:
Peat: This is formed during the first stage of transformation of wood to coal. It is usually light brown in colour and it is also friable. The carbon content is less than $ 40 - 55\% $ which means that it contains a high amount of impurities.
Bituminous: This coal is most widely available and also known as soft coal. The carbon content in bituminous coal is $ 40 - 80\% $ and the moisture content is around $ 15 - 40\% . $
Anthracite: The carbon content is highest in Anthracite which is around $ 85 - 90\% . $ Anthracite is ranked the top among all other types of coal as it contains the least amount of impurities.

Note :
Pay attention during the unit conversion. The unit of measurement of the calorific value is the same as the unit of measurement of energy. Their SI unit of calorific value is $ KJK{g^{ - 1}} $ .