A KINETIC-STUDY OF AN ADVANCED REBURNING PROCESS

The possibility of a positive synergism among flue gas recirculation, staged combustion and selective non-catalytic reduction technologies t o achieve N-containing emission reductions has been investigated by si mulating a 320 MW industrial-scale furnace boiler. A detailed chemical kinetic scheme coupled with a simplified fluid dynamic of the system has allowed us to compare the effectiveness of ammonia and isocyanic a cid in removing N-containing pollutant emitted (NPE) with hot exhausts . By keeping the same flue gas composition for both cases, the effect of temperature and the impact of different amounts of NH3 and HNCO inj ected in the final combustion stage has been analysed. Ammonia was the most effective reducing agent for the particular conditions examined. Due to its high reactivity, the maximum effectiveness of the NH3-prom oted process occurs at 940 K and an NH3/NOx, molar ratio of about 1.25 . NH2 dominates the process mainly following two paths: N-2 can be pro duced from direct interaction between NH2 and NO or via intermediate f ormation of NNH. On the other hand, HNCO is less effective than ammoni a, owing to the influence of the particular radical environment within the boiler. HNCO oxidation is influenced by the amine radical pool wh ich partly contributes to N-2 formation but is, at the same time, an i mportant source of NOx in the conditions analysed.