Thermal decomposition kinetics and thermodynamic analysis of Barapukuria bituminous coal at multi-heating rates using model-fitting approach: implications for effective reactor design

Bangladesh, a densely populated country, faces significant energy challenges, with coal playing a crucial role in enhancing energy security. To optimize coal utilization, advanced techniques like thermogravimetric analysis (TGA) are essential. This study analyzed coal samples via TGA in a N₂ environment at heating rates (HRs) of 10, 20, and 30 °C/min, revealing multi thermal degradation regions: moisture evaporation, devolatilization, and char formation. Kinetic analysis centered on devolatilization, utilizing the Coats-Redfern model (CRM) to assess 21 reaction mechanisms within four models of solid-state reactions. The devolatilization phase takes place across the following temperature ranges: 390–550 °C, 415–605 °C, and 440–680 °C at HRs of 10, 20, and 30 °C/min, respectively. The three-dimensional transport diffusion equation (DM3) exhibited the greatest regression coefficient (R²). The frequency factor (A) and activation energy (Ea) were determined as 287.13 min⁻¹ and 177.725kJ/mol, respectively. Thermodynamic properties of devolatilization were also assessed, with Gibbs free energy (ΔG) varying between 259.3 to 274.5 kJ mol⁻¹, enthalpy (ΔH) from 163.7 to 179.25 kJ mol⁻¹, and entropy (ΔS) from 0.2103 to 0.2094 kJ mol^-1K⁻¹. ICP-OES analysis detected significant transition/heavy metals (Fe, Pb, Zn, Ni, Cr, Cd) but no alkali and alkaline earth metals (AAEMs) (K, Na, Ca, Mg) in the coal. The absence of AAEMs necessitates external addition to improving char reactivity, lower ignition temperatures, and reduce activation energy. The outcome of this research offers valuable insights for designing efficient reactors, optimizing coal utilization, and advancing energy sustainability strategies.