Ash Deposition in Air-Blown Gasification of Peat and Woody Biomass in a Fluidized-Bed Gasifier

The ash deposition behaviors in air-blown gasification of a woody biomass and a Canadian peat were studied using a pilot-scale bubbling fluidized bed gasifier operating at an equivalence ratio (ER) of 0.2 to 0.35. An air-cooled probe was installed in the furnace of the gasifier to collect ash deposits on its surface. Four different bed materials including olivine, dolomite, limestone, and iron ore were used in this study to compare their effects on ash deposition rate during the gasification. The experimental results demonstrated that among the four bed materials, the use of olivine resulted in the lowest ash deposition rate <1.0 g^-2 h^-1, compared with ∼16 g^-2 h^-1 for limestone in the gasification of pine sawdust at an ER of 0.35. The superb performance of olivine in retarding ash deposition could be accounted for by its outstanding thermal stability and mechanical strength. The other three bed materials, in particular, limestone, were fragile during the fluidized bed gasification, and the fractured fines from the bed materials were found to deposit along with the fuel ash on the heat-transfer surface, leading on higher ash deposition rates. The ash deposition rates in the air-blown gasification process also strongly depended on the ER and the fuel type. The ash deposition rates for the peat gasification were much higher than those for the pine sawdust gasification.