We don't have synonyms for coalgas yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are coal gas and coal-gas.
(n) :
(petrochemistry) The poisonous gas, used domestically for cooking etc and formerly for lighting, prepared by heating coal with steam (gasification); it is a mixture of hydrogen and carbon monoxide; sometimes synonymous with synthesis gas or town gas.
(n) :
(petrochemistry) The poisonous gas, used domestically for cooking etc and formerly for lighting, prepared by heating coal with steam (gasification); it is a mixture of hydrogen and carbon monoxide; sometimes synonymous with synthesis gas or town gas.