Fuel properties of biochar from torrefaction of ground coffee residue: effect of process temperature, time, and sweeping gas

Abstract

© 2020, Springer-Verlag GmbH Germany, part of Springer Nature. Ground coffee residue (GCR) was torrified under nitrogen or carbon dioxide atmosphere. Effect of torrefaction parameters on fuel properties of biochar was investigated by varying process temperature, residence time, and sweeping gas flow rate over the range of 200–300 °C, 30–60 min, and 50–250 mL/min, respectively. Severe torrefaction (300 °C) short residence time (30 min) under low carbon dioxide flow rate (50 mL/min) was determined as a promising condition to produce biochar as solid fuel. H/C and O/C atomic ratios, HHV, and energy yield of the obtained biochar were 0.94 and 0.14, 31.12 MJ/kg, and 48.04%, respectively, which were comparable with the properties of sub-bituminous coal. The calculated decarbonization (DC), dehydrogenation (DH), and deoxygenation (DO) indicated that torrefaction led to major losses of oxygen and hydrogen. The analysis of thermal decomposition properties and surface chemical functional groups revealed that temperature substantially affected biochar properties, while the effect of sweeping gas was only marginal.