Torrefaction of Agricultural Wastes: Influence of Lignocellulosic Types and Treatment Temperature on Fuel Properties of Biochar

In this article, four types of agricultural waste with different amounts of each lignocellulosic type, including rice husk (RH), coconut husk (CH), cassava rhizome (CR), and corncob (CC) were torrefied under inert environment at 200 – 300°C for 30 min. Biochar properties were characterized by various techniques in order to investigate their yield, physicochemical properties, higher heating value (HHV), thermal decomposition behavior, and surface functional group. The experimental results show that yield, HHV, and energy yield (E y ) of biochar were depended significantly on both types of agricultural waste and treatment temperature. The values of those parameters ranged from 81.75 – 35.59%, 19.06 – 28.29 MJ/kg, and 51.34 – 86.22%, respectively. Fuel properties of agricultural waste were greatly enhanced by torrefaction at 300°C. Biochar from torrefied CC provides the highest fuel ratio (2.18) with lowest atomic ratios of O/C and H/C (0.18 and 0.67, respectively) and this is comparative with bituminous coal. The changes of these properties were mainly due to dehydration and deoxygenation reactions. Interestingly, agricultural wastes with high cellulose content (44.41%) could produce biochar with the maximum energy yield (86.22%). These results indicated that torrefaction was a promising technology for conversion of agricultural wastes to biochar as coal substitute material.