Computational model for NOx reduction by advanced reburning

Advanced reburning is a NOx reduction process wherein injection of a hydroc arbon fuel such as natural gas downstream of the combustion zone is followe d by injection of a nitrogen-containing species such as ammonia. The author s recently reported a seven-step, Ii-species reduced mechanism for NO reduc tion by advanced reburning processes. However, inclusion of even a seven-st ep reduced mechanism into a CFD code for turbulent combustion leads to subs tantial computational demands. In this work, the authors have further simpl ified the kinetic mechanism. A simpler four-step, eight-species reduced mec hanism for NO reduction by advanced reburning has been developed from a 312 -step, 50-species full mechanism through the use of a systematic reduction method. The four-step reduced mechanism is in good agreement with the full mechanism for most laminar flow cases. It also agrees qualitatively with th ree sets of experimental data, which show the influences of temperature, CO concentration; O-2 concentration, and the ratio (NH3/NO)(in). It can be ap plied for coal-, gas-, and oil-fired combustion. The four-step reaction seq uence has been integrated into a comprehensive CFD combustion code for turb ulent combustion, PCGC-3. The method of integration is described. Several c omputations are reported with the combined code to demonstrate the predicti ve behavior of the advanced reburning mechanism in turbulent, pulverized co al combustion. The model calculations show the effects of temperature and c oncentrations of CO, O-2, and NH3 on NO reduction.