On the co-combustion characteristics and kinetics of sludge, wood chips, and bituminous coal

Combustion with coal is an effective sludge disposal method, but it may weaken the combustion performance of coal. Mixing with biomass can improve the combustion characteristics of the coal-sludge mixture, yet the co-combustion kinetics remain to be studied. The combustion characteristics of sludge, wood chips (WC), and bituminous coal (BC) and their mixtures were investigated by TGA. Mixing 20 wt% sludge reduced the comprehensive combustion characteristic index (S) of BC. However, introducing WC offsets this weakening. The ignition temperature of the mixtures decreased from 430.5 to 274.0 °C, and the S indexes increased, indicating that WC enhances the combustibility of the mixtures. The optimum ratio of WC, sludge and BC blended for combustion was determined experimentally, resulting in the best ignition performance and the largest S index. The kinetic model of BC was represented by the Johnson-Mehl-Avrami (JMA) model. By adding 2–4 wt% WC, the kinetic models of mixtures shifted from JMA to the unimolecular decay law (F1) model and then to the phase boundary-controlled reaction (R3) model at 6 wt% WC content.