EFFECT OF SO2 ON THE REDUCTION OF NOX BY REBURNING WITH METHANE

An investigation was carried out in order to find out any possible interactions between NO(x) and SO2 during reburning. The primary fuel used was methane doped with nitric oxide (600 ppm) and sulphur dioxide (1000 ppm) in order to approximately simulate the same type of conditions found in coal combustion. These concentrations were selected to simulate conditions where bituminous coal containing 1.5-1.7 wt% sulphur is used and the overall stoichiometry was fuel-air and kept constant at 1.1. Methane was also used as the reburn gas. Concentrations of NO(x) and SO2 were measured at various heights of the chamber for 0, 30 and 50% reburn. The optimum reduction of NO(x) to about 35-40% was achieved using 30% reburn. Experiments showed that there was a slight reduction in the final NO(x) concentration when SO2 was present and a small quantity of H2S was also formed in the reburn region. This reduction in NO(x) is attributed to the reaction of HS + NO = NS + OH, which is similar to the main reburn reaction of CH + NO = HCN + O.