From Brian Wood
I have followed with interest Fred Pearce’s article on recovering coal energy in situ (15 February, p 36) and the subsequent letters on coal gasification. I think some confusion still exists.
My memory is that coal was “destructively distilled” by heating it in the absence of air. This yielded five products: coal gas, coal tar, an aqueous phase called ammoniacal liquor, coke and retort carbon. The coal gas was supplied to the consumer and comprised hydrogen, methane, carbon monoxide and other gases. Your correspondents seem to be confusing this with “producer gas”, obtained by blowing air through a thick bed of hot coke, and “water gas”, produced by blowing steam through the same. Alternately cycling air and steam kept the process productive.
When fuel for public transport was scarce in the second world war, some British buses ran on water gas generated in trailers behind the bus, with the product stored in a balloon on top of the bus. During the severe winter of 1941, Illustrated magazine had a delightful cartoon showing a bus conductor with a busy trade in roast chestnuts and baked potatoes cooked on the gas generator.
Lenzie, East Dunbartonshire, UK
