TG-FTIR/MS study on the combustion kinetics and gas emission characteristics of forest duff under different oxygen concentrations

The thermal degradation behavior of forest fuels is crucial to optimize the environmental conditions before processing it for energy utilization. The ambient oxygen concentration affects the combustion kinetics and gas emissions during thermal degradation. In this study, the effects of oxygen concentration on the combustion kinetics and gas emission characteristics of forest duff (FD) were investigated by the coupling technique of thermogravimetric analysis—Fourier transform infrared spectrometry/mass spectrometry (TG-FTIR/MS). TG results reveal that thermal degradation rate was enhanced by increasing oxygen concentration. FTIR/MS results show that oxygen facilitated the generation of CO, CO₂, H₂O, carboxylic acids [COOH]+, and ester group [OCOH]+ but was not conducive to the formation of pyrolyzates of H₂, –CH₂–/–CH₃, CH₄, aldehyde groups [COH]+, acetaldehyde groups [CH₂COH]+, and aryl groups [C₇H₇]+. The generation of a small amount of pyrolyzates except for [C₇H₇]+ at higher temperatures (> 400 °C) in oxidative atmospheres was confirmed to be attributed to the char volatilization. According to the integrated findings from TG-FTIR/MS analysis, a comprehensive six-step reaction scheme including drying, FD pyrolysis, FD oxidation, char volatilization, and the oxidation of char and char residue was proposed for the kinetic analysis. A favorable agreement between the experimental and simulated TG and derivative thermogravimetric (DTG) curves was obtained. The kinetic model reveals that secondary char oxidation (i.e., the oxidation of char residue) is more pronounced in conditions of oxygen deficiency and high heating rates. The results of this study are conductive to understanding the thermal degradation behavior of FD in different atmospheres.