Coal gas is an flammable gaseous fuel made by the destructive distillation of coal containing a variety of calorific gases including hydrogen, carbon monoxide, methane and volatile hydrocarbons together with small quantities of non-calorific gases such as carbon dioxide and nitrogen. Before natural gas became popular in 1940s and 1950s, Coal gas was the primary source of gaseous fuel for the United States and the UK. It was used for lighting, cooking, and heating and was often supplied to households via a municipally owned piped distribution system. The composition of coal gas varied according to the type of coal and the temperature of carbonisation.
Typical composition of the Coal gas is as follows:
- Hydrogen 50%
- Methane 35%
- Carbon monoxide 10%
- Ethylene 5%
During gasification, the coal is mixed with oxygen and steam while also being heated and pressurized. During the reaction, oxygen and water molecules oxidize the coal into carbon monoxide (CO), while also releasing hydrogen gas (H2). This process has been conducted in both underground coal mines.
C (as Coal) + O2 + H2O → H2 + CO
If the refiner wants to produce gasoline, the SynGas is collected at this state and routed into a Fischer-Tropsch reaction. If hydrogen is the desired end-product, however, the SynGas is fed into the water gas shift reaction, where more hydrogen is liberated.
CO + H2O → CO2 + H2