Natural gas: The main constituents of natural gas are methane (CH4) and ethane (C2H6). Its calorific value is nearly 21 MJ/m3. It is used as an alternate fuel for internal combustion engines as liquefied natural gas (LNG).
Coal gas: It mainly consists of hydrogen, carbon monoxide, and hydrocarbons. It is prepared by the carbonization of coal. It is also known as town gas. It is largely used in towns for street and domestic lighting, cooking, and running gas engines.
Coke–oven gas: It is obtained during the production of coke by heating bituminous coal. The volatile content of coal is driven off by heating. It is produced by the destructive distillation of coal in airtight coke ovens made of silica bricks. It is used in heating ovens. This gas must be thoroughly filtered before using in gas engines.
Blast furnace gas: It is obtained as a byproduct from the smelting operation in which air is forced through layers of coke and iron during the manufacture of pig iron. It contains about 20% carbon monoxide. The gas leaving the blast furnace has a high dust content, which must be removed by dust collectors and washing operations. It has a low calorific value. It is mainly used as a fuel for metallurgical furnaces.
Producer gas: It is obtained from the partial oxidation of coal, coke, or peat when burnt with an insufficient quantity of air. It has low heating value and in general, is suitable for large installations. It is also used in the steel industry for firing open-hearth furnaces.
Water-gas: It is produced by blowing steam into white-hot coke or coal. It is a mixture of hydrogen and carbon monoxide. It burns with a blue flame and is also known as blue water gas. It does not contain unsaturated hydrocarbons. In order to use this gas for domestic lighting, unsaturated hydrocarbons are added. In such cases, it is also known as carburetted water gas or enriched water gas. This is achieved by passing the gas through a carburetor into which a gas oil is sprayed. It is usually mixed with coal gas from town gas. It is used in furnaces and for welding.
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 is used as a fuel for gas engines which, in turn, drives plant pumps and agitators.
