Experimental and ReaxFF molecular dynamic study of NO emission during municipal sludge/coal co-combustion

In this work, the emission behavior of NO during the co-combustion of municipal sludge (MS) and Meihuajing bituminous coal (MHJ) was studied using experiments and ReaxFF molecular dynamics methods. Both experimental and ReaxFF MD results indicated that there has negative synergistic effect on NO emission during MS/ MHJ co-combustion. In addition, there has positive synergistic effect on N2 and NO2 emission during MS/MHJ co-combustion. Using the atomic labeling method, it was observed that the yield of MS-NO decreased, while the yield of MHJ-NO was almost unchanged during co-combustion. Moreover, the yields of MS-N2 and MS-NO2 during co-combustion were increased. It indicated that MHJ has a significant effect on the MS-NO emission during co-combustion, while MS has little effect on the MHJ-NO emission. It attributed to the fact that MHJ consumed more oxygen, which resulted in more OH radicals generated during co-combustion, accelerating the cleavage of pyrrolic and pyridinic structures in MS to form more nitrogen-containing compounds. As combustion proceeds, the nitrogen-containing compounds from MS were gradually converted to HCN. Subsequently, HCN was oxidized to NCO, which increased the yield of MS-NCO during co-combustion. Then, the increase in MS-NCO during co-combustion promoted the reduction reaction between MS-NCO and MS-NO, increasing MS-N2 yield. In addition, the increased yield of O radicals also promoted the oxidation of MS-NO to MS-NO2 during cocombustion.