A manufactured gas is any gas made by a manufacturing process. Raw materials used in the production of manufactured gas include coal, oil, coke, natural gas, or one of the other manufactured gases. For example, coal gas is made by distilling bituminous coal in either retorts or by-product coke ovens. Often several of these raw materials are used together as a base for the production of a manufactured gas.
The types of manufactured gases commercially available include:
1. Coal gas or by-product coke-oven gas
2. Oil gas
3. Blue water gas
4. Carbureted water gas
5. Producer gas
6. Reformed natural gas
7. Liquefied petroleum gas
Most of these gases have low caloric values (generally between 500 and 100 Btu/ft3) and are produced primarily for industrial use. Producer gas and liquefied petroleum gas are also used for domestic purposes. The former may be used alone or in combination with other gases. Of all the manufactured gases, liquefied petroleum gas enjoys the widest application in domestic heating and cooking.