Impact of SO2 and NO on CO oxidation under post-flame conditions

Abstract

An experimental and theoretical study on the effect of SO2 on moist CO oxidation with and without NO present has been carried out. The experiments were performed in an isothermal quartz flow reactor at atmospheric pressure in the temperature range 800–1300 K. Inlet concentrations of SO2 ranged from 0 to 1800 ppmv, while the NO ranged between 0, 100, or 1500 ppm. SO2 inhibits CO oxidation under the conditions investigated, shifting the fast oxidation regime 20–40 K towards higher temperatures at 1500 ppm SO2. The inhibition is most pronounced at high O atom levels. The experimental data supported by model analysis suggest that SO2 primarily reacts with O atoms forming SO3, which is subsequently consumed mainly by reaction with O and HO2. Addition of NO significantly diminishes the effect of SO2. Since NO is usually present in combustion flue gases, the impact of SO2 on CO burnout in most practical systems is projected to be small. The H/S/O thermochemistry and reaction subset has been revised based on recent experimental and theoretical results, and a chemical kinetic model has been established. The model provides a reasonable overall description of the effect of SO2 and NO on moist CO oxidation, while the SO3/SO2 ratio is well predicted over the range of conditions investigated. In order to enhance model performance further, rate constants for a number of SO2 and SO3 reactions need to be determined with higher accuracy. © 1996 John Wiley & Sons, Inc.