674 / 2019-04-29 20:15:38

Experimental and Numerical Study on Fuel-NOx Formation under High CO2 Concentration in a Jet Stirred Reactor

fuel-NOx, oxy-fuel combustion, jet stirred reactor (JSR), HCN, NH3

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New experimental results on fuel-NOx formation characteristics under high CO2 concentrations are obtained in a jet stirred reactor. NH3 is selected as the N element source. Effects of the CO2 concentration (0-97.4%), reaction temperature (873- 1323 K), equivalence ratio (0.56-1.61) on the production and destruction of fuel-NOx are experimentally and numerically investigated under both N2 and CO2 atmospheres. The experimental results are predicted by detailed reaction mechanisms.
The fuel-NO is found to be produced mainly through the reaction pathway of NH3→NH2→HNO→NO, regardless of N2 or CO2 as diluent. The NO-reburning chemistry (NH2+NO↔N2+H2O and NH2+NO↔NNH+OH) cannot be ignored and can even reduce the majority of NO at fuel-rich conditions. Moreover, under fuel-lean conditions, the NO emission is reduced with the increase of equivalence ratio, or the CO2 concentration. Under the stoichiometric condition, the NO productions from the N2 and CO2 atmospheres are nearly the same, irrespective of the temperature. However, under fuel-rich conditions and temperatures above 1200 K, the high CO2 concentration enhances the NO production due to the reduced NO-reburning chemistry. Moreover, the CHx radical is found to be significant for the HCN production and the HCN formation cannot be neglected under fuel-rich conditions and temperature above 1100 K, although the HCN produced from the O2/N2 combustion is higher. The N2O formation is significant at 1170 K of fuel-lean conditions and at approximately 1275 K of the stoichiometric condition, while its production is insignificant under fuel-rich conditions due to the reduced reaction rate of N2+O(+M)↔N2O(+M). Interestingly, although the fuel oxidation is slightly delayed under high CO2 concentrations, the N2O formation is basically insensitive to the CO2 concentration, because the main N2O formation reactions are insensitive to the variation of the CO2 concentration, irrespective of temperature, equivalence ratio. In addition, the numerical results are consistent well with the vast majority of the present experiments and important reactions are identified for future development of the fuel-NO formation under high CO2 concentrations.