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

The effect of chlorine on CO, NOx and N2O emissions has been studied in an electrically heated bed of fluidized sand, Pyridine (C5H5N) was burnt as a model compound in a mixture of O-2 and N-2 to produce CO, NO, and N2O. The experiments were done at temperature 750, 825, or 900 degrees C. The concen trations of O-2 and pyridine in the fluidizing gas were maintained at 3.2 o r 11.6 mol%, and 500, 1500, or 2000 ppm, respectively. When pyridine was bu rnt in the fluidized bed, the concentrations of CO, NOx, and N2O were measu red continuously in the freeboard. Chlorine was introduced to the fluidized bed as HCl. The addition of HCl to the fluidizing gas mixture decreased the concentrati on of NOx and either decreased or increased the concentration of N2O depend ing on the temperature. At 750 degrees C, the addition of HCl reduced the c oncentration of N2O, while it increased the concentration at 825 and 900 de grees C. Temperature has a significant impact on the effect caused by the a ddition of HCl on the formation of NOx and N2O. On the other hand, the conc entrations of pyridine and O-2 do not have a significant effect on the perc entage decrease or increase in the concentrations of NOx caused by HCl. During pyridine combustion, combustion radicals (H/OH/O) play a major role in converting HCN and NCO to NOx. Thus, the decrease in NOx caused by HCl i s due to the suppression of O, H, and OH radicals. Again the increase in th e concentration of N2O at 825 and 900 degrees C is due to the suppression o f H and OH radical by HCl. However, the decrease in N2O at 750 degrees C is probably due to the inhibition of pyridine combustion by HCl. (C) 1998 by The Combustion Institute.