A Parametric Study on Nox Emissions From Ammonia Containing Product Gas in Rich Quench Lean Combustion

Abstract Due to climate change, demand for fuels that can accelerate the transition from fossil fuels to clean energy has been increasing. Humidified product gas obtained from gasifying biomass is a promising candidate to replace natural gas. However, the gasification process releases nitrogen bearing compounds into the product gas, resulting in substantial increases in nitric oxides, NOx, in the exhaust. To mitigate these emissions at the source, a better understanding of the underlying kinetics is needed. In this study, a simplified CRN model for a gas turbine Rich-Quench-Lean (RQL) type combustor was developed in Cantera. The following parameters were investigated in this study: primary section equivalence ratio, overall equivalence ratio, steam dilution, postflame residence time and recirculation. Additionally, a benchmark CRN representing a Lean Burner (LB) as also developed. Results obtained from the CRN model suggest that, when comparing to LB, a RQL type combustor delivers up to a 75% reduction in emissions. Additionally, it was found that, for both the LB and RQL combustors, for temperatures between 1400-1600K it is preferable to burn lean, while for temperatures greater than 1800K it is preferable to operate at overall slightly rich equivalence ratios. This is because, at low temperatures and lean conditions, conversion of ammonia to nitrogen occurs readily. While, at moderate temperatures and rich conditions, NO reacts with ammonia to form Nitrogen in the reburn process. Finally, it was found that recirculation does not affect the emission minima, yet it allows for more flexible operational conditions.