The reduction of recycled-NOx in coal combustion with O2/recycled flue gas under low recycling ratio

The emission and reduction of NOx in coal combustion with O2/recycled flue gas were investigated in an electric heated up-flow-tube combustor with a high volatile bituminous coal. The recycling ratio of flue gas ranged from 0 to 0.4, and the concentrations of recycled-NO in inlet gas were 0, 500 and 1000 ppm. Reduction efficiency of the recycled-NOx changed both with equivalence ratio and recycling ratio. More than 60% recycled-NO was reduced when equivalence ratio ϕ>1.4. Less recycled-NO was reduced under lower recycling ratio than that under higher recycling ratio. HCN and NH3 were also detected with GC-FTD. The results indicated that HCN emissions decreased with the increase of recycled-NO concentration in inlet gas. No obvious influence of temperature on the reduction of recycled-NO was found. The experiments on recycled-NO2 demonstrated a consistent trend similar to the NO recycle tests.