Numerical study on effects of devolatilization gas composition to reducing fuel-NOX in municipal solid waste incinerator using detailed chemical kinetics

Low NOX emission combustion technology is required for Municipal Solid Waste (MSW) incinerators. Comparing investigation between simplified 1D combustion experiment and 1D numerical analysis has been performed to decide detailed reaction mechanism suited for NO emission prediction in MSW combustion. Effects of H2/CO ratio and H2O/CO2 ratio in the modeled pyrolysis gas to NO formation were evaluated in the primary combustion and the subsequent secondary combustion by Premixed Laminar Burner-Stabilized Flame Model. Comparison between measured NO concentration and calculated NO concentration indicated that calculation results obtained by using Kilpinen97 reaction were within a certain error range compared with experimental results in a wider condition range of fuel composition and excess air ratio than the modified GRI-mech3.0. Increased H2/CO and H2O/CO2 led to the decrease in NO mole flux in the primary combustion, respectively by different reaction paths, which increased both H2/CO and H2O/CO2 showed an additive effect on the decrease in NO mole flux. NO conversion ratios after the secondary combustion from NH3 in the modeled pyrolysis gas were still reduced by the increased H2/CO and H2O/CO2 in the modeled pyrolysis gas although the NO conversion ratios after the secondary combustion were larger than those after the primary combustion because of the conversion to NO in the secondary combustion from HCN, NH3 and HCNO remained in the primary combustion. Conversion ratio from HCN, NH3 and HCNO to NO in the secondary combustion can be reduced by the decreased temperature at inlet of the secondary combustion area. Based on the findings above, it is possible to design lower NOX emission MSW incinerators by considering the conditions of the exhaust gas recirculation affecting H2/CO and H2O/CO2 in the primary combustion, and the cooling structure of the primary combustion flue gas.