Experimental and kinetic modeling study of the effect of SO2 on the reduction of NO by ammonia

The effect of SO2 addition on the reduction of NO by ammonia in simulated thermal de-NOx conditions was studied in a JSR at atmospheric pressure for various equivalence ratios (0.1-2) and initial concentrations of NO, NH3, and SO2 (0-1000 ppm). The experiments were performed at fixed residence times of 100 and 200 ms, and variable temperature, ranging from 1100 to 1450 K. It was demonstrated that the addition of SO2 inhibits the reduction of NO by ammonia from fuel-lean to fuel-rich conditions. The effect of SO2 on the extent of NO reduction was controversial in the literature. This study confirms that SO2 does not reduce the efficiency of the thermal de-NOx process but shifts the optimal temperature to higher values. A kinetic reaction mechanism was used to simulate these experiments. According to the model, the inhibiting effect Of SO2 is due to chain terminating processes (H + H + M = H-2 + M) and radical pool reduction (H + O-2 + M = HO2 + M) via the sequence of reactions SO2 + H + M double right arrow HOSO + M, HOS-O + O-2 double right arrow HO2 + SO2, and HOSO + H double right arrow SO2 + H-2. The present results confirm the validity of the previously proposed kinetic reaction sub-mechanisms for the reduction of nitric oxide by ammonia and for the inhibition of the oxidation of fuels by SO2. (c) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved.