Study of the combustion behavior of wheat straw using TG–DSC under multiple heating rates

The combustion of biomass waste has become a hot research topic due to its potential for energy production and its role in addressing environmental issues caused by biomass waste accumulation. This article investigates the combustion of wheat straw using thermogravimetric analysis-differential scanning calorimetry within a wide range of temperatures up to 1073 K at various heating rates. Based on thermogravimetric analysis, the combustion process is categorized into five distinct phases: moisture evaporation, volatile matter combustion, lignin breakdown, the combustion of residual volatiles and fixed carbon, and the final burnout phase. It was observed that the combustion characteristic temperatures, maximum combustion rate, and comprehensive combustibility index all rise as the heating rate increases. Differential scanning calorimetry analysis revealed exothermic reactions for all heating rates, with three exothermic peaks identified. The activation energy of the primary combustion phase using the Kissinger–Akahira–Sunose (KAS) method was calculated as 121.4 ± 3.7 to 316.5 ± 7.9 kJ/mol, with an increasing trend as combustion proceeds. The pre-exponential factor ranged from 1.08 × 10⁹ to 2.46 × 10²⁷ s⁻¹ for KAS, varying with the heating rate. Based on the activated complex theory, the thermodynamic parameters for the conversion of reactants to the activated complex during combustion were derived. The activation enthalpy change ranges from 117.0 to 310.6 kJ/mol, while the activation Gibbs free energy change, with an average of 162.7 kJ/mol, confirms that activated complex formation during wheat straw degradation is a non-spontaneous process. The activation entropy change spans from −85 to 264 J/(mol·K), indicating molecular disorder and variations in energy efficiency. These results offer valuable theoretical insights and data for the further development of agricultural biomass utilization.