Pyrolysis and Combustion of Regional Agro-Industrial Wastes: Thermal Behavior and Kinetic Parameters Comparison

Abstract

The thermal decomposition of six regional agro-industrial wastes under inert and oxidative atmosphere at different heating rates was studied using thermogravimetric analysis. The kinetic parameters were calculated using the DAEM (distributed activation energy model) and FWO (Flynn–Wall–Ozawa) methods. The obtained thermogravimetric and differential thermogravimetric curves show similar shapes, considering the pyrolysis and combustion phenomena. Nevertheless, the biomass weight loss is slower and smaller under inert than oxidative atmosphere. The activation energy average values (E) in inert atmosphere for the active pyrolysis stage is about 133.90–275.57 kJ/mol and 136.51–261.10 kJ/mol for DAEM and FWO, respectively. The E average values for the devolatilization stage under oxidative atmosphere are about 104.11–125.73 kJ/mol and 108.40–128.81 kJ/mol using DAEM and FWO methods, respectively. The results calculated by FWO and DAEM methods show differences between activation energies for the same waste below 8%; thus, they were reliable and predictive in this study. The variation of E values with progressing conversion for two studied processes indicated the existence of a complex multi-step mechanism that occurs during the degradation process. Moreover, during the devolatilization stage of combustion, the lower value of E indicates that the combustion is produced in parallel to pyrolysis; the oxygen reacts with the remaining solid.