Intrinsic reactivity of biomass-derived char under steam gasification conditions-potential of wood ash as catalyst

Abstract

The influence of ash on the steam gasification rate of pine wood derived char particles in the temperature range 600–800°C is investigated. Ash derived from pine wood or specific ash components were added to the pine-wood (before pyrolysis) or to the produced char (after pyrolysis) via physical mixing or impregnation. The addition method and the amount and type of ash/ash component have been studied and the obtained gasification rates are compared. Impregnation of ash/ash components by ∼10wt% or more (in the original pine wood) always resulted in a significant increase in the (initial) gasification rate. At 700°C, e.g., impregnating 9.5wt% KOH in pine wood resulted in complete char conversion within 12min, corresponding to an increase in (initial) gasification rate by a factor 30 compared to char without impregnation. SEM images of the chars showed that impregnating the wood with concentrations up to 14wt% resulted in unevenly distributed ash (components) in the particles. Based on this, the hypothesis is that besides the overall amount of ash also its distribution among and inside the char particles is important for enhancement of the reaction rate. A biomass gasification concept in which the steam gasification reaction of char is catalyzed by concentrating the ashes in the biomass is feasible.