We don't have synonyms for coaly yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are coal, colly and cooly.
(n) :
a black rock formed from prehistoric plant remains, composed largely of carbon and burned as a fuel; a piece of coal used for burning. Note that in British English the first of the following examples would usually be used, whereas in American English the latter would
"put some coals on the fire."
(v) :
to take in coal; as, the steamer coaled at Southampton; to be converted to charcoal
"1957: As a result, particles of wood and twigs insufficiently coaled are frequently found at the bottom of such pits. — H.R. Schubert, History of the British Iron and Steel Industry, p. 18."
(n) :
a black rock formed from prehistoric plant remains, composed largely of carbon and burned as a fuel; a piece of coal used for burning. Note that in British English the first of the following examples would usually be used, whereas in American English the latter would
"put some coals on the fire."
(v) :
to take in coal; as, the steamer coaled at Southampton; to be converted to charcoal
"1957: As a result, particles of wood and twigs insufficiently coaled are frequently found at the bottom of such pits. — H.R. Schubert, History of the British Iron and Steel Industry, p. 18."