Kinetics modeling of NOx emissions characteristics of a NH3/H2 fueled gas turbine combustor

Abstract

The two major challenges for ammonia combustion in gas turbines are its high NOx emission and low burning velocity. Recently, while H2 doping has been proved as an effective means of improving the NH3 burning velocity, there is a knowledge gap on the emissions characteristics of NH3/H2 fuel mixture in gas turbine conditions. This paper presents a kinetics modeling study on the NOx emission characteristics of a staged rich-lean combustor cofiring NH3/H2 mixture. A chemical reaction network was set up to model the staged combustor. Emission characteristics were obtained at various operating parameters, including equivalence ratio, residence time, and H2 doping ratio. The rich-burn stage equivalence ratio was found to be the primary factor influencing NOx emissions. The key to reduce NOx emissions is to balance the NO production and the unburnt NH3 in the rich-burn stage. Extending the residence time of its post-flame zone and increasing H2 doping ratio also benefit NOx reduction by decreasing unburnt NH3 content, but with a secondary impact. NO reaction pathway analyses showed that NO is formed mainly through the HNO pathway in the flame zone of the rich-burn stage, while NHi decomposition in the post-flame zone plays a key role in NO reduction. Depending on the NHi concentration, different mechanisms dominate NO reduction in the post-flame zone.