Combustion Characterization and Kinetic Analysis of Mixed Sludge and Lignite Combustion

To investigate the feasibility and reaction mechanism of combusting sewage sludge and brown coal in a mixture. Thermal behavior evaluation of combustion characteristics, interactions, and kinetic analysis of sludge-lignite mixture combustion by thermogravimetry (TG). The results showed that the combustion performance of the mixed samples was all in between that of the lignite and sludge samples. The combined combustion index gradually decreased with the increase in sludge mixing. The addition of sludge favors the ignition of the mixture but is not conducive to overall stable combustion. The synergies between the sludges, as assessed by the mass loss curves, are reflected in the ash removal and coke oxidation stages. When the mixture of sludge and lignite is burned at a ratio of 10 wt %, the calorific value can still reach 20.3 MJ/kg, which is only about 4.2% lower than that of burning lignite alone. Application of the kinetic models of FWO, Starink, KAS, and Friedman, in turn, determined a minimum average activation energy of only 132.50 kJ/mol. In addition, the reaction was judged to be a simple complexation reaction by analyzing the thermodynamic parameters (ΔG, ΔS, ΔH, and A), with the combustion process approaching thermodynamic equilibrium and forming stable products. The nucleation model A4.2 can be used as the best reaction mechanism model for sludge-lignite mixed combustion.