Characterization of Torrefied Biomass Pellets from Agricultural Residues for Solid Fuels

Abstract

Torrefaction and densification are suitable techniques for upgrading solid biomass materials. They can improve the energy properties of solid fuels. The objective of this research was to evaluate changes in physico-chemical properties of agricultural residues (corn-cobs and rice husks) during torrefaction. Physical properties of the torrefied biomass pellets were analysed. The results showed that increasing the torrefaction temperature and time resulted in reduced moisture and volatile matter content of corn-cobs and rice husks. At the same time, fixed carbon, ash content and heating values were increased. The heating values of both torrefied fuels were in the range of 14.9–16.9 MJ/kg, increased by about 16 to 22% from the raw biomass. The optimum treatment conditions were found to be in the range 200–250 ^°C and 20 min. Physical properties of both torrefied pellet fuels were found to be enhanced, and closer to those required by the associated standard. The average bulk density and durability of torrefied pellets were between 1112 and 1226 kg/m³ and 91 and 94%, respectively. The water resistance and compressive strength were in the range 89–92% and 140–156 kg/m³, respectively. The energy densities of corn-cob and rice husk torrefiled fuels were increased by 22.5 and 15.7%, respectively, when compared to their original biomass inputs. Torrefied pellet fuel is technically feasible and can be used as a substitute for fossil fuel in the future.