Kinetics modeling of NOx emission of oxygen-enriched and rich-lean-staged ammonia combustion under gas turbine conditions

Abstract

Though the oxygen enrichment combustion and fuel-rich/quick-mix/fuel-lean (RQL) combustion are respectively effective to improve burning velocity and reduce NOx emissions respectively, their combination feasibility and characteristics for burning ammonia (NH3) need further investigation as oxygen enrichment could increase NOx production. Thus, a kinetic modeling study was conducted on the NOx emission characteristics of an oxygen-enriched and RQL-staged NH3-fired combustor under gas turbine conditions by using the chemical reaction network (CRN) method. The results revealed that NOx emission could be minimized as long as the equivalence ratio (ϕ) in the fuel-rich stage was kept at a certain value according to the oxygen enrichment degree (Ω) in the fuel-rich stage oxidizer, regardless of the Ω in the fuel-lean stage oxidizer. At a higher Ω, low NOx emission was achieved in a wider ϕ range, while the optimal ϕ in the fuel-rich stage became higher and the corresponding NOx emission was lower. This mainly benefited from the stronger NH3 consumption in the fuel-rich stage due to the higher temperature and higher concentration of OH/H radicals. However, a higher Ω in the fuel-rich stage enhanced the thermal NOx formation in the fuel-lean stage. Based on the results of the present study, oxygen-enriched NH3 combustion with a proper ϕ setting in the fuel-rich stage could simultaneously improve the burning intensity and reduce NOx emission for burning NH3 in a gas turbine.