What was Coal Gas?

Coal gas was gas made by heating coal in the absence of air. Coal gas was introduced in the UK in the 1790s as an illuminating gas by the Scottish inventor William Murdoch and became very widely used for lighting, cooking, heating and powering gas engines.

The coal was heated in a retort and the crude gas was passed through a condenser to remove tar. There was a scrubber to remove other impurities. The residue remaining in the retort was coke. The composition of coal gas varied according to the type of coal and the temperature of the reaction. Typical figures were:

hydrogen 50%
methane 35%
carbon monoxide 10%
ethene 5%

The by-products of the process were valuable. They included coke, coal tar, sulphur and ammonia. They were used to manufacture dyes, medicines, and dozens of organic compounds.

Coke was used in the manufacture of iron and steel, though this has virtually ceased in the UK Coke is also used as smokeless fuel.

Coal tar was distilled to recover various products, including

tar, for roads
benzole, a motor fuel
creosote, a wood preservative
phenol, used in the manufacture of plastics
cresols, disinfectants
sulfur, for sulphuric acid
ammonia, for fertilisers.

Coal gas is no longer made in the UK. It was replaced first by gas made from oil and later by natural gas from the North Sea.

The industries it supported have been supplanted by modern developments; for example:

Petrochemicals removed much of the value of coal tar as a source of chemical feed stocks.
There has been a decline in creosote use for wood preserving.
There is less demand for metallurgical coke.
Less use for cast iron & steel; often replaced by aluminum and plastics.

N.D., habitat21

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