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 o f hydrocarbon additives. The selective non-catalytic NOx reduction pro cess was realized in a high-temperature flow reactor. A lead salt diod e laser system, combined with second derivative spectroscopy, monitore d the concentration of NO, NH3, N2O, NO2, and HCN downstream of the re actor. After injection of the hydrocarbon additive (methane or ethane) at concentrations of up to 1000 vppm, the shift of the temperature wi ndow of the SNCR process and the by-product formation was measured. Th e experimental results have then been compared with the results of the modeling study. Both experimental and theoretical results show a shif t of the temperature window towards lower temperatures in the presence of additives, as well as a decreased temperature range of ammonia sli p and the formation of NO2 as a by-product at the cold side of the tem perature window. Nitrous oxide was neither predicted by the model nor experimentally detected. Ln oxygen-deficient gas mixtures, HCN-formati on was observed up to 300 vppm. HCN-formation from NO-ethane interacti on could be attributed to the reaction of HCCO with NO, but there is a n additional route of HCN-production from the interaction of ethane wi th ammonia, possibly from the reaction of NH, with unsaturated hydroca rbons. Thus, there is a strong demand for reliable kinetic data on the se reactions and on the reaction sequence HCCO + NO --> HCNO + CO, HCN O + H --> HCN + OH.