GASEOUS FUELS

Natural gas. The main constituents of natural gas are methane (CH4) and ethane (C2H6).

It has calorific value nearly 21000 kJ/m3. Natural gas is used alternately or simultaneously with oil for internal combustion engines.

Coal gas. Mainly consists of hydrogen, carbon monoxide and hydrocarbons. It is prepared by carbonisation of coal. It finds its use in boilers and sometimes used for commercial purposes.

Coke-oven gas. It is obtained during the production of coke by heating the bituminous coal. The volatile content of coal is driven off by heating and major portion of this gas is utilised in heating the ovens. This gas must be thoroughly filtered before using in gas engines.

Blast furnance gas. It is obtained from smelting operation in which air is forced through layers of coke and iron ore, the example being that of pig iron manufacture where this gas is produced as by product and contains about 20% carbon monoxide (CO). After filtering it may be blended with richer gas or used in gas engines directly. The heating value of this gas is very low.

Producer gas. It results from the partial oxidation of coal, coke or peat when they are burnt with an insufficient quantity of air. It is produced in specially designed retorts. It has low heating value and in general is suitable for large installations. It is also used in steel industry for firing open hearth furnaces.

Water or illuminating gas. It is produced by blowing steam into white hot coke or coal.

The decomposition of steam takes place liberating free hydrogen, and oxygen in the steam combines with carbon to form carbon monoxide according to the reaction.

The gas composition varies as the hydrogen content if the coal is used.

Sewer gas. It is obtained from sewage disposal vats in which fermentation and decay occur. It consists of mainly marsh gas (CH4) and is collected at large disposal plants. It works as a fuel for gas engines which in turn drive the plant pumps and agitators. Gaseous fuels are becoming popular because of following advantages they possess.

Advantages :

1. Better control of combustion.

2. Much less excess air is needed for complete combustion.

3. Economy in fuel and more efficiency of furnace operation.

4. Easy maintenance of oxidizing or reducing atmosphere.

5. Cleanliness.

6. No problem of storage if the supply is available from public supply line.

7. The distribution of gaseous fuels even over a wide area is easy through the pipe lines and

as such handling of the fuel is altogether eliminated.

8. Gaseous fuels give economy of heat and produce higher temperatures (as they can be preheated in regenerative furnances and thus heat from hot flue gases can be recovered).