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# Fuels: What is solid liquid and gaseous fuel?

Generally, fuels are used for creating heat energy, Such energy can then put to some engineering or industrial use. Industrial fuels usually contain elements of carbon and hydrogen. When oxygen of the air chemically combines with these elements, the heat is generated. The generation of heat is seen as a flame. The fuels also contain mineral matters which, on burning, are left behind as ash. It is not desirable to have ash in fuels because it does not in any way contribute to the generation of heat.

The calorific value of the fuel is defined as the quantity of heat generated by completely burning unit weight of a given fuel, The unit of heat is gm calories and it indicates the quantity of heat required to raise 1 gm of water through 1-degree centigrade.

 Coals
• Classification of fuels:-
Fuels are divided n the basis of their state, therefore it divided into three groups:-
1. Solid fuels
2. Liquid fuels
3. Gases fuels
• Solid fuels:-
The solid fuels are mostly used for the generation of heat required in kilns, furnaces and domestic chullas. They are also used for heating of raw materials, burning of bricks and tiles, power generation, manufacture of engineering materials and good or daily use, etc. Important solid fuels are as follows:
• Charcoal: It is prepared by burning wood in a kiln with a limited quantity of air. It is used to produce gas for domestic purposes.
• Coal: It is the chief source for producing cheap power. It is formed by the bacterial decomposition of vegetable matter under great pressure and in the absence of air. Its color is black or dark brown. This is a natural solid fuel.
• Coke: It is prepared by heating the powdered coal in special ovens and then quenching the whole mass in cold water. It is better than coal and is the most important metallurgical fuel.

• Liquid fuels:-
The source of liquid fuels is crude petroleum which is recovered from oil wells in Assam, Gujrat, and Bombay high. It has a calorific value of about 11100 gm calories. The liquid fuels are mostly used for locomotion and power generation. They are required for driving automobiles, aircraft's, locomotives, generators, and lighting purposes. The important liquid fuels are:-

• Alcohol: These are of various types such as ethyl alcohol, methyl alcohol, etc. They are used to serve as fuels for motors, airplanes, etc.
• Crude oil: This occurs in nature and it can be used as fuel after giving proper treatment to it.
• Petroleum: This is the product obtained by the distillation of organic matter in nature. It is refined and its distillation yields various artificial liquid fuels such as gasoline, gas, oil, kerosene, petrol, diesel, etc.
• Gaseous fuels:-
The gaseous fuels are used for heating, burning, lighting and running gas engines. The important gaseous fuels are:-

• Coal gas: This gas is obtained by thermal decomposition of coal at high temperature in the absence of air. It is a mixture of several gases like hydrogen, methane, carbon monoxide, nitrogen, ethylene, oxygen.
• Natural gas: This is obtained from natural underground sources. It is associated with petroleum under pressure.
• Producer gas: This gas is obtained by controlled combustion of coal, coke or charcoal in the blast of air. It is more powerful, It is used in the manufacture of glass, steel, etc.