Pyrolysis kinetics, physicochemical characteristics and thermal decomposition behavior of agricultural wastes using thermogravimetric analysis

Abstract

This study specifically focuses on pyrolysis kinetics and thermochemical decomposition of important nonedible agricultural wastes (orange filter cake, pomegranate filter cake, poplar branch, corn stalk, sugarcane bagasse, olive pomace, hazelnut glume, hazelnut shell, walnut shell and pistachio shell) with high renewable energy generation potentials. The novelty of this study is to analyze utilization of common agricultural wastes in Turkey for energy applications by evaluating their thermal characteristics and kinetics through pyrolysis from a holistic perspective. Pyrolysis experiments were conducted using a thermogravimetric analyzer (TGA) for the estimation of kinetic parameters by Coats–Redfern method. Differential thermogravimetric analysis (DTG) was carried out to study thermal degradation of biomass components. Ultimate analysis showed that poplar branch had the highest hydrogen/carbon atomic ratio (H/C=1.3) while hazelnut shell had the lowest H/C ratio of 0.9. Fixed carbon content was the lowest in pistachio shell (16.1%) and the highest in pomegranate filter cake (26.8%). The lowest ash content (1.4%) was found for sugarcane bagasse while the highest ash content (9%) was determined for corn stalk. Orange filter cake had the lowest activation energy (Ea) value of 17.8 kJ/mol and the lowest lignin content (4.9%). Poplar branch and sugarcane bagasse had less charring tendency in which char yields at 900 °C were 10.8 and 11.5%, respectively, suggesting that in case of fast pyrolysis where low char is favored, poplar branch and sugarcane bagasse would be better options among the other agricultural wastes studied.