Tar destruction and coke formation during rapid pyrolysis and gasification of biomass in a drop-tube furnace

This paper describes tar destruction and coke (or soot) formation of biomass in three different conversion processes: pyrolysis (in a pure nitrogen stream), steam gasification (in a mixture stream of steam and nitrogen), and partial oxidation (in a mixture stream of oxygen and nitrogen), over a wide temperature range from 600 to 1400 °C. A woody waste, hinoki cypress sawdust (HCS), was used as a feedstock, and an entrained drop-tube furnace (DTF) was applied to all experimental tests. It is found that raising the temperature remarkably decreases tar evolution. Steam and oxygen also have a positive effect on tar destruction. Benzene and toluene are the most difficult condensable tar species to destroy. The achievement of their complete destruction in the product gas requires extremely high temperatures above 1200 °C, regardless of the gasifying agents. The coke deposits from 900 °C and reaches a maximum formation at 1000 or 1100 °C. The results obtained in this study suggest that competition occurs between the secondary decomposition of hydrocarbon species and gasification reactions of the produced char and/or coke with gasifying agents in the temperature range of 900–1100 °C.