Physicochemical Properties of Thermally Treated Biomass and Energy Requirement for Torrefaction

Torrefaction is a thermal pretreatment of biomass to overcome some of the limitations of raw biomass (e.g., low heating value and hygroscopy) for power and fuel production. The objective of this study was to examine the effects of torrefaction temperature (225°C, 250°C, and 275°C), time (15, 30, and 45 min), and their interaction on the physicchemical properties of pine, sweetgum, and switchgrass. Increasing temperature and time resulted in a decrease of solids retained while increasing the heating value of the fuel for all feedstocks. In addition, absorbed moisture decreased with torrefaction. Carbon content in biomass increased while oxygen content decreased with increasing temperature and time. Elemental composition and energy content of the torrefied biomass prepared under the most severe conditions were similar to that of coal. Furthermore, the torrefaction energy requirement at different moisture contents was successfully modeled using a simple linear regression.