Abstract
The aim of this study is to investigate the reduction of tar produced during biomass pyrolysis by torrefaction pretreatment. In this study, various biomass feedstocks (pine, ash wood, miscanthus, and wheat straw) with different particle sizes were torrefied at 280 °C. The results indicated that both particle size and biomass composition have a significant effect on the yield and properties of the torrefied products. With increasing particle size, the yield of solid product increased, while the yield of condensable liquid and noncondensable gases decreased. The raw biomasses and torrefied biomasses were then subjected to pyrolysis at 500 °C. The results clearly showed that torrefaction had a significant effect on the yield and composition of tar generated during subsequent pyrolysis. For all biomasses, the tar yields of biomasses after torrefaction were 42–62% lower compared to direct pyrolysis of raw biomasses. However, when considering the condensable liquid produced combining torrefaction and pyrolysis, the total yield of condensable liquid produced decreased 3–12% compared to the direct pyrolysis. This suggests that not only some volatiles were released during the torrefaction process, but the thermal pretreatment also transformed the biomass structure to less favor tar production in subsequent pyrolysis step.