High-temperature gasification of woody biomass in a drop tube reactor: A special focus on the particle size and axial temperature gradient

Abstract

Pine sawdust (PS) was gasified in a drop-tube reactor (DTR) using air as a gasifying agent. An almost complete mass balance was achieved by establishing a burning operation after gasification to determine the carbon deposits (CD) inside the reactor tube, providing an authentic depiction of the feedstock conversion. The results indicated that particle size reduction led to a significant improvement in the gasification performance. When the particle size of PS was below 0.25 mm, almost complete char gasification was achieved at 1300 °C, while soot remained a major particulate in the syngas. An experimental approach is proposed to simulate the axial temperature gradient (ATG) inside an auto-thermal entrained-flow gasifier by setting two different temperature zones in the DTR. The results revealed that char was rapidly and almost completely exhausted in the high-temperature zone (1300 °C). When the ATG between the upper and lower heater zones was above 300 °C, both homogeneous reforming and heterogeneous gasification proceeded slowly or almost stagnated in the lower temperature zone. An evident enhancement of soot formation was observed at ATG = 200 °C. After that, the soot yield monotonously decreased with decreasing ATG due to the substantial enhancement of the heterogeneous gasification kinetics, contributing more to carbon conversion and CGE than char gasification.