Experimental study on N2O emission in O2/CO2 combustion with high oxygen concentration in circulating fluidized bed

Abstract

To characterize the N2O formation and fuel nitrogen conversion in an oxy-fuel circulating fluidized bed (CFB) combustor with high oxygen concentration, tests were carried out by analysing the axial concentrations of N2O in a 50 kWth CFB combustor. The conversion ratios from fuel nitrogen to gaseous N-containing pollutants were calculated. The initial N2O concentrations in the bottom of the combustor were similar between oxy-fuel firing and air-firing. The axial N2O formation was more in oxy-fuel combustion than in air-firing, improving the N2O emission during 50% O2/50% CO2 combustion. The atmospheric variation significantly affected the conversion ratio from fuel nitrogen to N2O. In addition, the conversion from fuel nitrogen to N2O was much higher than that to NO. As a result, the N2O emission during oxy-fuel CFB combustion cannot be ignored. Gas staging little influenced the N2O emission. With the increasing ratio of secondary gas, the initial N2O formation in the dense zone increased, while the axial N2O formation along the combustor declined. By analysing the conversion ratios of fuel nitrogen, it was also found that gas staging obviously affected the conversion ratio from fuel nitrogen to NO by enhancing the NO to N2 conversion. However, gas staging did not impact the conversion ratio from fuel nitrogen to N2O.