Oxidative torrefaction of spruce-pine-fir sawdust in a slot-rectangular spouted bed reactor

Abstract

A slot-rectangular spouted bed (SRSB) reactor was employed to torrefy spruce-pine-fir sawdust in an oxidative atmosphere. The effects of torrefaction temperature (240–300 °C) and feed-gas oxygen concentration (3–9 vol.%) on torrefaction performance and solid product properties were investigated. Adding oxygen in the feed-gas led to more uniform temperature distributions in the SRSB reactor, and was a promising way to achieve stable continuous operation. The mass fraction of cyclone-caught torrefied biomass increased, whereas the mass fraction of torrefied biomass remaining in the reactor decreased, with increasing oxygen concentration and temperature. In oxidative torrefaction, biomass weight loss was 15.4–46.4%, while energy yield was 61.2–99.4%. The effects of oxygen concentration on the weight loss, energy yield and torrefied biomass properties were more significant at 300 °C than at 240 °C. The torrefied sawdust also had greater HHV and contained less volatiles, more carbon, less oxygen and less hydrogen than the raw biomass.