Evaluating the Combustion Behavior and Kinetics of Çayırhan Coal: A Comprehensive Thermogravimetric and Thermodynamic Study

In this study, the combustion behavior of Çayırhan coal under an oxygen atmosphere was investigated, and its combustion kinetics and thermodynamic parameters were determined. Thermal analyses (TGA, DTG, and DSC) revealed that the combustion process occurs in two consecutive steps. The first step, in which 85% of the total weight loss takes place, requires a relatively low activation energy. Conversely, the second step, corresponding to the remaining 15% of the combustion, requires a significantly higher activation energy. Both combustion steps were analyzed using model-free isoconversional methods. The average activation energies were calculated as 139.65 ± 9.66 kJ/mol for Combustion 1 and 402.27 ± 65.53 kJ/mol for Combustion 2. Subsequent kinetic modeling studies demonstrated that both combustion reactions are highly compatible with the diffusion mechanism. Following the determination of the most suitable reaction model, the Arrhenius pre-exponential factor (A) and other thermodynamic parameters of the activated complex (ΔS‡, ΔH‡, and ΔG‡) were successfully evaluated. These thermodynamic and kinetic insights clarify the distinct combustion regimes of Çayırhan coal under laboratory conditions. Ultimately, the selected diffusion-based kinetic models offer a practical baseline framework for evaluating combustion performance and providing preliminary insights for reactor considerations in low-rank coal applications.