A simplified mechanism of hydrogen addition to methane combustion for the pollutant emission characteristics of a gas-fired boiler.

The reaction mechanism of hydrogen-enriched methane (HEM) combustion is significant in the combustion process. In this study, four widely used reaction mechanisms for methane combustion are simplified to investigate the pollutant emission characteristics of a gas-fired boiler used for HEM combustion. The laminar burn velocity (LBV) and ignition delay time (IDT) of the four detailed and four simplified mechanisms are compared, and the simplified San Diego mechanism is identified as the optimal mechanism using relative error and population standard deviation analysis. The temperatures and key components of the simplified San Diego mechanism are also compared with those of the detailed San Diego mechanism under various X H2. Based on the simplified San Diego mechanism, a chemical reactor network model for gas-fired boilers is further established to investigate the pollutant emissions of HEM combustion, in which the hydrogen doping ratio X H2 ranged from 0 to 80% and the inlet air and fuel temperature T in ranged from 300 K to 600 K. Results showed that at T in = 300 K with X H2 ranging from 0 to 80%, the mole fraction of NO increase by 1.94 times because of the increase in peak flame temperature; moreover, the mole fractions of N 2 O, CO, and CO 2 decrease by approximately 25%, 50%, and 52%, respectively. With X H2 ranging from 0 to 40% and T in ≥ 500 K, the mole fraction of NO decreases because the reduction reaction of NO + H = N + OH is promoted, whereas when X H2 is further increased to 80%, the increased H promotes the increase in NO again. CO emissions decreased as X H2 increased from 0 to 80%, whereas they increased by approximately 1.3 times as T in increased from 300 K to 600 K because of the CO 2 decomposition. N 2 O emissions decreased by more than 25% as X H2 increased from 0 to 80%. Additionally, CO 2 emissions decrease by 52% with an increase in X H2 and by only 5% with an increase in T in , indicating that X H2 has a larger impact on CO 2 emissions. The proposed optimal HEM combustion mechanism is conducive to improving the efficiency of numerical calculations. • Four detailed mechanisms for hydrogen-enriched methane combustion were simplified. • The simplified San Diego mechanism was optimal according to error analysis. • Emissions at various hydrogen doping ratios and inlet temperatures were studied. • NO increased, while N 2 O, CO, and CO 2 decreased with X H2 ranging from 0 to 80%. [ABSTRACT FROM AUTHOR]