Bituminous coal, while having the advantage of plentiful supplies, low ash and low sulphur content, stable prices and high BTU value, is not well suited for use in conventional underfed stoker boilers fueled with anthracite coal.
Bituminous coal has its own peculiar characteristics that renders its use in such boilers less satisfactory than anthracite. This is due to the fact that the volatiles of bituminous coal are higher than those of anthracite while its fixed carbons are lower. The volatiles of bituminous coal ignite readily but if not subject to an appropriate combustion temperature and a sufficient amount of combustion air, a drop in the BTU output and a smokey fire are objectionable consequences so that the advantages of bituminous coal cannot be realized in conventional underfed stoker boilers.