Effects of fuel-staging and reburning on NOx emissions from NH3/CH4/air swirling flames

Advanced reburning (AR) is a method utilizes the fuel-staging and thermal de-NO x to reduce the NO x emissions in modern coal fired boilers or gas turbines. Ammonia (NH 3 ) is considered a promising carbon-free fuel in the context of carbon neutrality. However, the emission characteristics of NH 3 swirling flames respond strongly to the influence of reburning and fuel staging. This study investigated the NO x and unburnt ammonia emissions of NH 3 /CH 4 /air mixtures in a fuel-staging swirling combustor. The ammonia mole fractions range from X NH3 = 0.3, 0.6 to 1.0, with the overall equivalence ratios ranging from ϕ = 0.6 to 1.0. Secondary fuel injection ratio, η ranges from 0 to the X NH3 until the blow-off of primary flame. Three different secondary fuel injection locations (H1/D = 1.7, H2/D = 2.5 and H3/D = 3.4 where D is diamter of burner exit) were adopted to represent different flame temperatures. The secondary fuel injection prevails with a thermal de-NO x effect for X NH3 = 0.3 for all η while at X NH3 = 0.6, secondary fuel injection first reduces NO emissions and then increases the NO emissions η as increases. As the fuel injection height increases, NO reduction is more favored while N 2 O emissions and unburnt ammonia gradually appears due to the lower flame temperature and shorter residence time. The comparison of fuel-staging by methane and ammonia is also conducted which shows ammonia-staging is more efficient in reducing NO emissions. NO-PLIF measurements shows a first decrease then increase trend at the highest injection location which is consistent with NO emission measurements. Chemical reactor networks (CRN) analyses indicate that increasing the residence time in the primary reaction zone and decrease the temperature in the secondary reaction zone can efficiently reduce the NO and N 2 O emissions. But too low secondary reaction zone temperature can breed large amount of N 2 O emission and unburnt ammonia slip. Combining fuel-staging and reburning may be a promising way to achieve very low NO x and unburnt ammonia emissions in the future.