Advanced approach to modeling of pulverized coal boilers for SNCR process optimization - review and recommendations

Abstract

Authors undertook an effort to analyze various models presented in the literature to define the best practices, taking into consideration the requirements of models to optimize the SNCR process.This issue is particularly important concerning pulverized coal boilers and includes the determination of the location and efficiency of the reagent injection points, taking into account the temperature window, mixing and residence time in the reaction zone.In the presented study, methods used by researchers at various stages of modeling of the pulverized coal boilers were reviewed. At the stage of creating the model geometry, all simplifying assumptions, such as symmetry planes, should be carefully considered due to the possible occurrence of asymmetries and vortices in the flue gasses. In areas with high velocity or temperature gradients (e.g. furnace), the computational mesh should be refined. Heat exchangers require special treatment. It can be taken into account using the porous medium method or only zero-thickness baffles influencing the exhaust gas path can be used. The best results are achieved when determining the inlet profiles on nozzles and burners are obtained using auxiliary models including burners or even feeding channels. However, it is possible to use more effortless techniques, such as extended inlet ports. A separate chapter is devoted to the methods of validation of pulverized coal boiler models. Full validation of the boiler model in a hot- state is extremely rare due to the high costs. Thus authors usually limit their proceeding to comparing selected gas parameters at the boiler outlet.

Keywords

• Pulverized coal
• Boiler modeling
• Model validation
• CFD, SNCR optimization
• NOx emission