Investigating combustion kinetics and combustion behavior of low-grade Pakistani coal: isothermal and non-isothermal analyses using thermogravimetric analysis (TGA)

Herein, the combustion kinetics of low-grade coal through isothermal and non-isothermal analysis was investigated using thermogravimetric analysis in both N₂ and O₂ atmospheres. In the non-isothermal method, ignition temperature decreased from (236.45–202.11 °C) and burnout temperature (283.12–281.21 °C) was determined. The low-grade coal samples that underwent kinetic studies were initially treated with alkali and acid treatments. Experimental data were analyzed using the shrinking core model (SCM) and volume model (VM) using the isothermal method. As per results, the combustion curve shifted to higher temperature zones (600 °C, 700 °C, 800 °C, and 900 °C), resulting in an increased peak combustion rate. Higher combustion temperatures corresponded to elevated combustion rates and reduced total combustion times, indicating an improved coal combustion process. Among the models considered, the SCM emerged as the preferred choice for establishing conversion–time relationships and estimating reaction rate constants (k) across a spectrum of temperatures. Predictions based on apparent activation energy (E) and pre-exponential factor (A) were made using the Arrhenius equation. The apparent activation energy for isothermal combustion before and after chemical treatment using SCM (161.57–131.26 kJ/mol) and VM (179.67–138.52 kJ/mol) was determined. This study contributes valuable insights into the intricate dynamics of low-grade coal combustion, particularly emphasizing the significance of temperature variations on combustion characteristics.