Experimental and Kinetic Study on the Oxidation of Syngas-Ammonia under Both N2 and CO2 Atmospheres in a Jet-Stirred Reactor

Although syngas combustion has been extensively investigated, previous studies did not systematically examine the fuel-NOx formation from ammonia-containing syngas in both N-2 and CO2 atmospheres. Investigations on syngas-ammonia oxidation are significant for suppressing the fuel-NOx emission from the combustion of actual syngas containing NH3. This study presents new experimental results on syngas-ammonia oxidation under both N-2 and CO2 atmospheres in a jet-stirred reactor. The effects of CO2 concentration (X-CO2: 0-60%), temperature (T: 900-1400 K), equivalence ratio (Phi: 0.4-1.65), initial CH4 concentration (X-CH4: 0-2000 ppm), CO/H-2 ratio, and residence time (tau: 0.001-10 s) are investigated. For the oxidation of syngas-ammonia, the reactant consumption is delayed and more CO is produced in high CO2 concentration. A critical temperature to obtain the peak N2O production is found, and it is slightly reduced from 1000 to 950 K with Phi increasing from 0.63 to 1.25. Moreover, the N2O concentration is basically insensitive to the concentration of CH4 and the CO/H-2 ratio in syngas. The NO production is enhanced with the increase of T, X-CH4, and the CO/H-2 ratio, while it is reduced with increasing Phi. Interestingly, the high concentration of CO2 suppresses the fuel-NO formation in fuel-lean conditions, while it significantly enhances the fuel-NO production in fuel-rich conditions. To minimize emissions of NO, N2O, and CO, it is recommended to operate the reaction at T > 1000 K and simultaneously avoid significantly high temperatures at the equivalence ratio of approximately 0.9, low values of initial CH4 concentration and the CO/H-2 ratio (e.g., <1), long residence times (tau > 2 s), and high concentrations of CO2 (X-CO2 > 30%). Furthermore, the numerical simulations agree well with the vast majority of measurements, and the dependence of NO on Phi at X-CO2 = 30% is also well predicted. The present study provides new fundamental understandings of the fuel-NOx formation from ammonia-containing syngas.

Automated summary

This study presents new experimental results on syngas-ammonia oxidation under both N-2 and CO2 atmospheres, investigating the effects of various parameters. It was found that high CO2 concentration delays reactant consumption and enhances CO production, while also affecting N2O formation. Additionally, NO production increases with temperature, initial CH4 concentration, and the CO/H2 ratio, but decreases with increasing equivalence ratio.