The thermal behavior and kinetics of co-combustion between sewage sludge and wheat straw

This study investigated the combustion characteristics and kinetics of sewage sludge (SS), wheat straw (WS) and their blends using thermogravimetric analysis, under air condition. Combustion characteristic parameters of SS blended with 5%–50% WS was enhanced, especially revealed by an increase in comprehensive combustion index. A significant synergetic interaction was found in high temperature region through experiments. When proportion of WS was 50%, the synergetic interaction was strongest. And the catalytic effect of alkali metal oxides in WS ash on the combustion of SS residues at high temperature region had a strong effect on synergetic interaction. Metal oxides circulated in different oxide forms to transport oxygen to carbon surface, leading to catalytic effect. Activation energy was evaluated by two isoconversional method: Flynn-Wall-Ozawa and Vyazovkin method. The lowest average activation energies of the blends were obtained at 50% wheat straw blending ratio (89.29 kJ/mol by FWO and 87.48 kJ/mol by V, respectively). The thermodynamic parameters (Gibbs free energy, Entropy and Enthalpy) were also obtained. And two master plots methods were utilized to determine the appropriate fit kinetic model of combustion which can be described by Avarami-Erofeve (A2).