A study of hygroscopic property of biomass pretreated by torrefaction

Torrefaction is a thermochemical conversion process, and it is adopted to improve the drawbacks of raw biomass (such as high hygroscopicity, low calorific values and energy density). During this process, biomass is thermally degraded in an inert or nitrogen environment at temperature range of 200-300 degrees C for several minutes to several hours. In this study, high homogeneous torrefied wood samples were produced by torrefaction at 200, 210, 220, and 230 degrees C. The equilibrium moisture content (EMC) of raw and torrefied wood and the contact angle of sample surface are examined to evaluate the hygroscopicity changes of torrefied wood. The results indicate that the EMC of the torrefied wood decreased by 35% or more compared to the EMC of raw material. An increasing of contact angle of torrefied wood surface is observed with increasing torrefaction temperature, and it is in the range of 103-113 degrees which is correspond to hydrophobic surface (>900). Meanwhile, the detailed mechanisms about the changes of biomass hygroscopicity after torrefacion are also illustrated in the present work