| Nitrogen oxides (NOx) are precursors to acid rain. Controlling NOx, emissions from fossil fuel combustion has been required by implementation of stringent clean air regulations. Modeling of NOx, control becomes very important for industrial design. Nitric oxide (NO) submodels were previously developed and incorporated into PCGC-3, a comprehensive CFD (Computational Fluid Dynamics) combustion code, to predict NO formation from fuel-nitrogen and nitrogen molecules in air, and its reduction through reburning technology. However, these NO submodels did not account for NO reduction by advanced reburning, which has been demonstrated experimentally to reduce NO by up to 95%. Advanced reburning is a NOx, reduction process wherein injection of a hydrocarbon fuel aft of the combustion zone is followed by injection of a nitrogen containing species such as ammonia.; The objective of this research effort has been to expand the NO submodel set in PCGC-3 to include the chemistry of advanced reburning. A four-step, eight-species reduced mechanism for NO reduction by ammonia has been developed from a 312-step, 50-species full mechanism through use of a systematic reduction method. This reduced mechanism has been shown to be in good agreement with the full mechanism within the application window of interest. It has also been shown to agree reasonably well with three sets of laminar flow data, which show the influences of temperature, (NH3/No)in, CO and O2 concentrations. Based on this reduced mechanism, a new NO submodel element has been formulated and integrated into PCGC-3.; Illustrative calculations with PCGC-3 for turbulent, pulverized coal combustion showed that the predictions are realistic, including effects of temperature and concentrations of CO, O2 and NH 3. Measured NO concentrations with advanced reburning obtained independently from a laboratory combustor are compared with model calculations. Further, parametric studies, including the change of swirl number, (NH3/NO) in, and NH3 injection location, showed that the experimental trends can be predicted. A limitation of this new submodel is its dependence not only on reliable turbulent combustion flow-field predictions, but also on the quality of upstream NO combustion predictions arising from other required NO submodel elements. |
