Reduction of Tar and Soot Formation from Entrained-Flow Gasification of Woody Biomass by Alkali Impregnation

Tar and soot in product gas have been a major technical challenge toward the large-scale industrial installation of biomass gasification. This study aims at demonstrating that the formation of tar and soot can be reduced simultaneously using the catalytic activity of alkali metal species. Pine sawdust was impregnated with aqueous K2CO3 solution by wet impregnation methods prior to the gasification experiments. Raw and alkali-impregnated sawdust were gasified in a laminar drop-tube furnace at 900-1400 degrees C in a N-2-CO2 mixture, because that creates conditions representative for an entrained-flow gasification process. At 900-1100 degrees C, char, soot and tar decreased with the temperature rise for both raw and alkali-impregnated sawdust. The change in tar and soot yields indicated that potassium inhibited the growth of polycyclic aromatic hydrocarbons and promoted the decomposition of light tar (with 1-2 aromatic rings). The results also indicated that the catalytic activity of potassium on tar decomposition exists in both solid and gas phases. Because alkali salts can be recovered from product gas as an aqueous solution, alkali-catalyzed gasification of woody biomass can be a promising process to produce clean product gas from the entrained-flow gasification process at a relatively low temperature.