A microscopic study of ash deposits in a two-stage entrained-bed coal gasifier

Deposits adhering to the wall of a 50 t d(-1) two-stage entrained-bed coal gasifier were analysed for morphology, structure, composition and sintering strength. Deposits were classified into three types: powder, lump, and fused slag. Of these, the powdery deposit consisted of melted ash particles, soot and char. Char considered as unmelted particles was produced at a lower oxygen/coal ratio. It served as a dispersive material in the deposit and prevented complete sintering even at high temperature. Because the two-stage gasifier operates with a lower oxygen/coal ratio at the gas exit zone and a higher oxygen/coal ratio at the molten slag exit zone, the slagging problem at the gas exit zone was decreased by the production of an adequate amount of char during gasification.