Biomass torrefaction in a slot-rectangular spouted bed reactor

Abstract

Sawdust was subjected to torrefaction in a “semi-batch” slot-rectangular spouted bed (SRSB) reactor at temperatures from 240 to 330°C and biomass feed rates from 220 to 710g/h. Stable spouting of the sawdust was achieved in the slot-rectangular spouted bed, although the pressure drop across the reactor was observed to oscillate. Compared to the biomass feed rate, the temperature had a greater effect on the biomass weight loss and energy yield. Increases in temperature were found to promote weight loss of the sawdust while decreasing the energy yield. The main solid product was the torrefied sawdust, which remained in the SRSB reactor and was captured by a cyclone. The ratio of the torrefied biomass removed by the cyclone to the total torrefied biomass increased along with both the feed rate and temperature. After undergoing torrefaction, 6.7%–39.2% of the original sawdust mass was lost while 67.4%–98.7% of its energy was retained. The torrefied sawdust had a higher carbon content but less oxygen, hydrogen and volatiles, along with a greater higher heating value and increased density compared to the raw sawdust. The size of the sawdust particles also decreased markedly during the torrefaction process.