Effects of gas staging on the NO emission during O2/CO2 combustion with high oxygen concentration in circulating fluidized bed.

Oxy-fuel circulating fluidized bed (oxy-CFB) combustion, which combines the advantages of oxy-fuel combustion with those of CFB technology, is one of the most promising technologies to capture CO2. In this paper, experiments were carried out in a 50 kWth CFB combustor to investigate the effects of gas staging on the formation and emission of NO in the oxy-fuel CFB combustor with high oxygen concentrations by analysing the NO axial profiles along the combustor height at different conditions. The results show that the concentration of NO in the dense zone in oxy-fuel firing with high oxygen concentrations is slightly higher than that in air-firing, but the final emission of NO is lower in oxy-fuel combustion. With the secondary gas location rising, the emission of NO maximally drops from 171.2 mg/MJ to 31.9 mg/MJ in 50% O2/50% CO2 atmosphere. Gas staging is also an efficient method to reduce NO emission in oxy-fuel CFB combustion with high oxygen concentration. The decrease of the primary/secondary gas ratio leads the dropping of NO emission maximally from 171.2 mg/MJ to 66.7 mg/MJ. However the effects of gas staging lessen in oxy-fuel CFB combustion with high oxygen concentration compared with that in traditional air combustion. In addition, oxygen staging could be more effective in restricting the formation of NO in the dense zone than gas staging in oxy-fuel CFB combustion with high oxygen concentration.