Kinetic and Thermodynamic Analysis of Municipal Sludge Combustion Characteristics

• • The sludge combustion process is divided into four distinct stages with activation energies of 52.24, 48.81, 192.38, and 102.27 kJ/mol for moisture evaporation, volatile combustion, fixed carbon combustion, and burnout, respectively; the high activation energy for fixed carbon combustion (192.38 kJ/mol) indicates a significant energy barrier, necessitating optimized temperature control to ensure complete combustion. • • The ignition temperature of 220.7 °C and burnout temperature of 605.9 °C, combined with a comprehensive combustion characteristic index of 6.32×10⁻⁸ %²/(min²·K³), demonstrate good ignitability and burnout performance, supporting the feasibility of incineration for energy recovery from high-ash municipal sludge. • • Kinetic analysis validated by two independent methods (CR and ABS) with deviations <15% confirms that moisture evaporation and volatile combustion follow first-order kinetics (F1), while fixed carbon combustion and burnout follow second-order kinetics (F2); this mechanistic distinction is critical for accurate reactor design and residence time estimation. • • Thermodynamic analysis shows negative entropy changes (ΔS: -148.36 to -30.74 J/mol·K) and positive Gibbs free energy (ΔG: 105.76 to 271.04 kJ/mol) across all stages, indicating that the incineration process is non-spontaneous and requires continuous external energy input, with the highest energy demand (ΔG=271.04 kJ/mol) in the burnout stage, which must be addressed to improve energy efficiency.