Laboratory Study of the CO/NH3/NO/O2System: Implications for Hybrid Reburn/SNCR Strategies

Abstract

A laboratory study of the hybrid reburning/SNCR technique has been performed under flow reactor conditions. This technique involves the use of a selective reducing agent in the presence of combustibles (mainly CO) arising from the reburning zone. The impact of CO and O 2 concentrations, NH 3 /NO ratio, as well as the presence of HCN has been investigated as a function of the temperature in the range 700-1300 K. The results show that CO in concentrations typical of the rich/lean transition in reburning shift the regime for NO reduction in the SNCR process to temperatures below 1000 K and cause a narrowing of the temperature window. The NO reduction potential is largely unaffected compared to conditions with low CO, and the effect varying the O 2 concentration in the range 0.5-4.0% as well as of adding of HCN is found to be insignificant. Synergistic effects between reburning and SNCR are only observed in a narrow range of operating conditions with very low concentrations of CO and O 2 . Model predictions using a detailed reaction mechanism generally compare favorably with the experimental results. The present results indicate that a reduction of the CO level from the reburn zone is required before the SNCR chemistry is initiated. This can be obtained either by staging the burnout air or by injecting the N-agent in an aqueous solution to delay reaction.