AN EXPERIMENTAL AND MODELING STUDY OF THE SELECTIVE NONCATALYTIC REDUCTION OF NO BY AMMONIA IN THE PRESENCE OF HYDROCARBONS

This paper presents an experimental and modeling investigation of the NOx removal from flue gases through the SNCR process in the presence of hydrocarbon additives. The selective non-catalytic NOx reduction process was realized in a high-temperature flow reactor. A lead salt diode laser system, combined with second derivative spectroscopy, monitored the concentration of NO, NH3, N2O, NO2, and HCN downstream of the reactor. After injection of the hydrocarbon additive (methane or ethane) at concentrations of up to 1000 vppm, the shift of the temperature window of the SNCR process and the by-product formation was measured. The experimental results have then been compared with the results of the modeling study. Both experimental and theoretical results show a shift of the temperature window towards lower temperatures in the presence of additives, as well as a decreased temperature range of ammonia slip and the formation of NO2 as a by-product at the cold side of the temperature window. Nitrous oxide was neither predicted by the model nor experimentally detected. Ln oxygen-deficient gas mixtures, HCN-formation was observed up to 300 vppm. HCN-formation from NO-ethane interaction could be attributed to the reaction of HCCO with NO, but there is an additional route of HCN-production from the interaction of ethane with ammonia, possibly from the reaction of NH, with unsaturated hydrocarbons. Thus, there is a strong demand for reliable kinetic data on these reactions and on the reaction sequence HCCO + NO --> HCNO + CO, HCNO + H --> HCN + OH.