CFD EVALUATION OF OXYGEN ENHANCED COMBUSTION: IMPACTS ON NO_x EMISSIONS, CARBON-IN-FLYASH AND WATERWALL CORROSION

摘要

This paper discusses the results of a Computational Fluid Dynamics (CFD) based evaluation of the impact of oxygen enhanced combustion in a subcritical wall-fired pulverized coal (PC) utility boiler. Praxair has previously demonstrated through pilot-scale and full-scale burner testing that significant reductions in NO_x emissions can be obtained through oxygen enhancement in low-NO_x burners. CFD modeling conducted by Reaction Engineering International (REI) has predicted that similar reductions of NO_x emissions can be obtained in full-scale boilers equipped with low-NO_x firing systems. As with any low-NO_x combustion technology, it is important to evaluate not only the impact on NO_x emissions, but also the potential for increased rates of waterwall wastage and unburned carbon in the fly ash. CFD modeling has been used to evaluate these impacts in a 180 MW front wall fired boiler equipped with low-NO_x burners and overfire air. Waterwall wastage involving both gas phase and particle phase corrosion mechanisms has been considered. The predictions have indicated that oxygen enhancement for NO_x control in this unit will likely result in unchanged rates of waterwall corrosion under low-NO_x firing conditions as compared to the case of no oxygen enhancement, and potentially reduced waterwall surface area subject to high rates of corrosion. Predictions of unburned carbon in the fly ash indicate that operation under low-NO_x firing conditions with oxygen enhancement will likely have a beneficial effect.