Co-firing technology can be a gateway to sewage sludge valorization and net CO2 emissions reduction while maintaining a stable energy supply. In this study, the combustion characteristics of sludge, Australian black coal, shiitake substrate, and their blends were analyzed via thermogravimetric analysis (TGA) coupled with Fourier transform infrared spectroscopy. The ignition temperature, burnout temperature, flammability index (C), and combustion characteristics index (S) of the fuels and their respective blends were estimated from the TGA results. Kinetic parameters were also estimated using the Coats-Redfern method. Finally, single-pellet combustion experiments were conducted simulating real furnace conditions. The TGA results showed that sludge oxidation occurred in two distinct stages, whereas coal oxidation happened in only one. The first stage was due to the release and burning of volatiles, while the second stage was due to the oxidation of air with heavier/complex components in the fuels. In stage 1, both C and S increased with sludge addition to the sludge-coal blends. Sludge addition to the blends resulted in a decrease in C and S values in stage 2. Both CO and CO2 emissions decreased with increasing sludge ratio, while CH4, NOx and SO2 emissions decreased only for a sludge ratio of 25%. The single-pellet combustion results showed that ignition delay time reduced to a certain extent with increasing sludge ratio. The volatiles combustion duration increased and, then decreased; whereas total combustion time decreased sharply with increasing sludge ratio. Overall, sludge co-firing with coal enhances combustion reactivity and may help promote using sludge as an energy resource.

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