Production of Solid Fuel from Rice Straw through Torrefaction Process

Abstract

Torrefaction tests were carried out on rice straw samples in order to understand the changes in chemical composition at temperatures of 200–300°C and residence times of 30 and 60 minutes. The raw material chemical composition has moisture content of 14.75%, carbon (C) 48.70%, hydrogen (H) 6.59%, nitrogen (N) 1.39%, sulphur (S) 0.36%, volatiles (V) 17.13%, and calorific value (CV) 19639.3 KJ/kg. The raw biomass also has a bulk density of 73 kg/m3. Torrefaction at temperatures of 250°C and residence time of 30 minutes resulted in a significant decrease in moisture by about 83.94%, but the other components, C, H, N, O, S, and V changed only marginally. Increasing the torrefaction temperature to 300°C and residence time to 60 minutes further reduced the moisture to a final value of 0.00% (a 100% reduction compared to original) and also resulted in a decrease in the other components, H, S, and O by 23.07%, 75.00%, and 22.32%, respectively. The carbon content at 300°C and 60 minutes increased by about 12.55% while N content increased by 91.37%. The calorific values increased by about 6.25% at 250°C and 30 minutes, whereas at 300°C and 60 minutes, the increase was higher (about 11.11%) and resulted in a maximum degree of carbonization of 1.111. The H/C ratio decreased with increase in torrefaction temperature, where a minimum value of 0.093 was observed at 300°C and 60 minute while bulk density decreased with increase in temperature with the lowest value of 66 kg/m3which represents 9.59% decrease at 300°C and 60 minutes residence time.