Flue gas torrefaction for solid shell biomass

Abstract

The aim of this research is to study torrefaction performance of macadamia shell under dry flue gas conditions. Effect of torrefaction temperature at 200, 250 and 300 °C and duration time of 30, 45 and 60 minutes on the mass yield, energy density, energy yield and hydrophobicity were investigated in this work. According to the results, increasing the temperature and duration time of torrefaction led to decrease in moisture and volatile content, while the fixed carbon and ash were higher under the flue gas conditions (5% oxygen by volume) due to oxidation reaction. The increasing temperature and time also resulted in lower mass yield. Calorific value and energy yield of flue gas torrefaction were improved compared with torrefaction under inert gas conditions (nitrogen gas). Torrefied macadamia shell produced 21.7-30.9 MJ/kg, which higher than of by nitrogen gas (19.5-28.6 MJ/kg). The mass yield and energy yield were in range of 39-74 % and 63.5-90.4 %, respectively. Contact angle of the torrefied fuel with the flue gas was lower than that of nitrogen gas due to the oxidation of tar on the surface of the charcoal in the oxidation reaction. Torrefaction using flue gas reduce fuel costs in thermal pretreatment process compared to the nitrogen. The optimum flue gas torrefaction conditions are 300 °C and 45 min, highest calorific value of 30.9 MJ/kg.