Synergistic effects on co-pyrolysis and co-combustion of sludge and coal investigated by thermogravimetric analysis

Thermal characteristics and kinetics of sewage sludge (SS), lignite coal, and their blends (25 and 50% of SS) in pyrolysis and combustion processes were investigated by using thermogravimetric analysis (TGA). TGA was carried out at different heating rates of 10, 20, and 40 K min−1 under inert and air atmospheres. Kinetics were calculated by Flynn–Wall–Ozawa, Starink, and Vyazovkin models by using TGA data. The deviation between the experimental and calculated values of mass loss, residual fraction, and activation energy was determined to highlight the synergistic effect between SS and coal. The results indicated that both mixtures influenced the initial and final temperatures of reactions. Mass loss of the mixtures during pyrolysis was not significantly influenced by the SS proportion, however, the residual fraction was influenced by the mixtures during pyrolysis and combustion. Blend of 50% SS with the smaller activation energy (Ea) compared to 25% SS was the most suitable for bioenergy production in pyrolysis, whereas in combustion 25% SS with small Ea was the most promising. On the other hand, 100% SS had the smallest Ea in both processes, indicating the optimum bioenergy source.