The effect of mixing model and mixing characteristics on No-x reduction during reburning

The current study is part of a broader investigation, which deals with the application of a novel concept of integrated design to combustor modeling u sing computational fluid dynamic (CFD) methods. The main objective is the r eduction of NOx emissions, The current work addresses the effects of mixing optimization and mixing model on NOx reduction during reburning Numerical simulations of the reburning process are conducted on a pilot-scale 0.5 MM Btu/h down-fired combustor (DFC)and compared with experimental data. Optimi zed mixing conditions resulted in a significant reduction,in NOx levels. A "reburn calculator" including the two-stage Lagrangian mixing model is used for predicting the NOx emissions in the DFC, and the results are compared with CFD-based simulations. Modeling results showed that for this case mixi ng is dominant over the chemistry, and hence the use of an advanced fluid d ynamics model and a simplified chemistry scheme is adequate. Validation tes ts were conducted on optimized configurations using natural gas and coal wa ter slurry as reburn fuels. The NOx reduction obtained with the optimized c onfigurations was, as high as 75%, an almost 30% increase over the previous experiments on nonoptimized configurations, This study showed that an inte grated approach, which includes mixing optimization, can be used effectivel y for a reburn case application, achieving significant NOx reduction; The e ffect of integration was demonstrated both theoretically and experimentally as applied to a pilot-sale DFC.