Kinetic and Thermodynamic Analysis of Municipal Sludge Combustion Characteristics
To optimize municipal sludge incineration and enhance disposal efficiency, sludge from the First Sewage Treatment Plant in Chengdu was analyzed via synchronous thermal analysis (TG-DTG-DSC) in air at 20 K/min. The combustion process comprised four stages: moisture evaporation (35–150 °C), volatile combustion (150–400 °C), fixed carbon combustion (400–600 °C), and burnout (600–1000 °C). Ignition and burnout temperatures were 220.7 °C and 605.9 °C, respectively, with a comprehensive combustion characteristic index of 6.32×10⁻⁸ %²/(min²·K³), indicating good stability. Kinetic analysis using Coats-Redfern (CR) integral and Achar-Brindley-Sharp (ABS) differential methods showed deviations below 15%, confirming CR reliability. Moisture evaporation and volatile combustion followed first-order models (F1) with activation energies of 52.24 and 48.81 kJ/mol, while fixed carbon combustion and burnout followed second-order models (F2) with activation energies of 192.38 and 102.27 kJ/mol. Thermodynamic parameters (ΔH: 49.06, 43.59, 185.94, 95.00 kJ/mol; ΔS: -148.36, -211.63, -30.74, -201.38 J/mol·K; ΔG: 105.76, 176.52, 209.74, 271.04 kJ/mol) revealed negative entropy and positive Gibbs free energy across all stages, indicating external energy dependence, with the highest demand in the burnout stage. These findings provide a theoretical basis for optimizing incineration process parameters and energy recovery.