Effects of Mixing and Thermal Quenching on NO Reduction by Selective Non-Catalytic Reduction in the Presence of CO

The effects of thermal environment (injection temperature and quench rate), reactant ratios (initial NO and NH3/NO) and reagent mixing on the selective non-catalytic reduction (SNCR) of NO by ammonia have been investigated in a pilot scale facility in the presence and absence of CO. A reduced chemical kinetic mechanism for the prediction of SNCR chemistry has been developed and incorporated into a two-dimensional, CFD-based turbulent reacting flow model for the prediction and investigation of thermal and mixing effects on the reduction process in the presence of CO. The experiments and modeling show that with rapid mixing and near isothermal conditions, very low NO emissions are achievable (around 50 ppm) independent of inlet NO levels (ranging from 250 to 500 ppm). Chemical kinetic modeling is in agreement with this finding but overpredicts the reduction efficiencies achieved in the experiment since it ignores the effects of turbulence, mixing and heat transfer. With less rapid mixing and a thermally quenched zone, NO reduction efficiencies were much lower than those predicted by homogeneous chemical kinetics. However, predictions of SNCR performance made by the fully coupled turbulent reacting flow and reduced SNCR chemical kinetic mechanism model quantitatively predict trends and magnitudes of NO reduction. The presence of CO was found experimentally and computationally to shift and narrow the temperature window for effective reduction of NO; hence, CO was found to both increase and decrease NO reduction efficiencies depending on injection temperature and quench rate.