An experimental study of the inhibiting effect of chlorine in a fluidized bed combustor

Abstract

The effect of chlorine on CO, NO x and N 2O emissions has been studied in an electrically heated bed of fluidized sand. Pyridine (C 5H 5N) was burnt as a model compound in a mixture of O 2 and N 2 to produce CO, NO, and N 2O. The experiments were done at temperature 750, 825, or 900°C. The concentrations of O 2 and pyridine in the fluidizing gas were maintained at 3.2 or 11.6 mol%, and 500, 1500, or 2000 ppm, respectively. When pyridine was burnt in the fluidized bed, the concentrations of CO, NO x , and N 2O were measured continuously in the freeboard. Chlorine was introduced to the fluidized bed as HCl. The addition of HCl to the fluidizing gas mixture decreased the concentration of NO x and either decreased or increased the concentration of N 2O depending on the temperature. At 750°C, the addition of HCl reduced the concentration of N 2O, while it increased the concentration at 825 and 900°C. Temperature has a significant impact on the effect caused by the addition of HCl on the formation of NO x and N 2O. On the other hand, the concentrations of pyridine and O 2 do not have a significant effect on the percentage decrease or increase in the concentrations of NO x caused by HCl. During pyridine combustion, combustion radicals (H/OH/O) play a major role in converting HCN and NCO to NO x . Thus, the decrease in NO x caused by HCl is due to the suppression of O, H, and OH radicals. Again the increase in the concentration of N 2O at 825 and 900°C is due to the suppression of H and OH radical by HCl. However, the decrease in N 2O at 750°C is probably due to the inhibition of pyridine combustion by HCl.