The synergistic effect during co-combustion of municipal sludge and coal: Experimental and ReaxFF molecular dynamic study

In this work, the behaviors of municipal sludge/coal co-combustion were investigated by experiments and ReaxFF molecular dynamic simulations. The molecular models of coal and sludge were constructed based on experimental characterization. The characteristics of the separately combustion of sludge and coal from ReaxFF MD simulations were consistent with that from thermostatic thermogravimetric experiments. The synergistic effect on the co-combustion characteristics were investigated via performing sludge/coal co-combustion simulations under various conditions. The results showed that the sludge/coal co-combustion has positive synergistic effects on the co-combustion characteristics such as combustion rate, consumption of O2, and yield of CO2. By using the atomic labeling method, it was found that the combustion of sludge was inhibited while the combustion of coal was promoted during co-combustion process. The carbonaceous gas was found to be an important intermediate product in the generation of CO2. The synergistic effect promoted coal combustion because some ·OH radicals produced by the sludge attacked the aromatic ring structure in coal, which accelerated the formation of carbonaceous gas during sludge/coal co-combustion. This work provided new insight into the behaviors of municipal sludge/coal co-combustion.