Comprehensive research on the solid, liquid, and gaseous products of rice husk and rice straw torrefaction

Torrefaction is a treatment that serves to improve the fuel properties of biomass. In this study, the three-phase products of rice husk (RH) and rice straw (RS) torrefaction at five temperatures (200, 225, 250, 275, and 300 °C) were analyzed. It was noticeable that torrefaction enhanced the LHV, energy density, combustion characteristics, and hydrophobicity of RH and RS. Carbon in the raw RH and RS was more likely to be preserved in solid products than oxygen and hydrogen during torrefaction. Under the same conditions, hemicellulose in RS was degraded more than that in RH. Hemicellulose and cellulose were drastically degraded to produce CO2, CO, H2, and bio-oil (mainly phenols and ketones), and the lignin content increased during severe torrefaction (≥250 °C). Nevertheless, severe torrefaction harmed the energy recovery of solid products. This study concludes that 250 °C is the optimum torrefaction temperature for converting rice waste into valuable biofuel.