Thermal behavior of hydrochar from co-hydrothermal carbonization of swine manure and sawdust: effect of process water recirculation

Abstract

Effect of process water recirculation during co-hydrothermal carbonization (co-HTC) of swine manure (SM) and sawdust (SD) on the thermal behavior of hydrochar was investigated in this study. The results showed that process water recirculation promoted the dehydration and decarboxylation reactions, and increased the mass and energy yields of hydrochar during co-HTC. The combustion behavior of hydrochar was changed by the recirculation process with decreased ignition temperature and increased burnout temperature. Additionally, the first process water recirculation decreased the average activation energy (E_a) value of the hydrochar from 156.46 and 154.16 kJ mol⁻¹ to 136.95 and 133.67 kJ mol⁻¹ by Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose methods, respectively, and further recirculation had a slight effect on the E_a value. The thermodynamic parameter of entropy change verified that combustion reactivity of the hydrochar was enhanced by process water recirculation. The present study demonstrated that process water recirculation was feasible and environment-friendly for fuel production during co-HTC of SM and SD.