Nitric oxide reduction by non-hydrocarbon fuels. Implications for reburning with gasification gases

The ability of non-hydrocarbon fuels such as CO and H-2 to reduce nitric ox ide under conditions relevant for the reburning process is investigated exp erimentally and theoretically. Flow reactor experiments on reduction of NO by CO and H-2 are conducted under fuel-rich conditions, covering temperatur es of 1200-1800 K and a range of stoichiometries and reactant levels. Bench and pilot scale results from literature on reburning with CO, H-2, and low calorific value gases are also considered. The experimental data are inter preted in terms of a detailed reaction mechanism, and the reactions respons ible for removal of NO are identified. The experimental results indicate th at under typical reburn process conditions these non-hydrocarbon fuels may remove 20-30% of the nitric oxide entering the reburn zone. However, result s indicate that the process potential increases with temperature and reburn fuel fraction, and at high temperatures and reburn fuel fractions of about 30%, the reduction efficiency approaches that of hydrocarbon gases. If dil ution effects and the lowering of the primary zone NO (maintaining the over all load) are accounted for, the reduction potential is further increased. Modeling results indicate that the mixing process may affect the NO reducti on in the reducing zone. The modeling predictions are in qualitative agreem ent with the experimental results but tend to underestimate the reduction o f NO. Conversion of NO to N-2 in the reburn zone proceeds primarily through the following sequence: H + NO + M reversible arrow HNO + M, HNO + H rever sible arrow NH + OH, NH + NO --> N-2 + .... The implications of the results for reburning with fuels with a low hydrocarbon content are discussed, wit h special emphasis on gasified fuels.