Characteristic-particle-tracked modeling for CFB boiler: Coal combustion and ultra-low NO emission

Abstract

As a preliminary application of the Type-A-choking-oriented unified model for fast fluidization dynamics proposed previously by the author and coworker, characteristic-particle-tracked modeling for CFB boiler coal combustion and ultra-low NO emission was conducted. A novel feature of the model is that a characteristic cyclone-efficiency-equivalent particle diameter for circulated shrinking chars in the combustion-assisted attrition process was determined statistically, which greatly facilitates modeling of the most complicated process in CFB combustion. Moreover, the influence of the heterogeneous ignition status on CO formation under the combustion condition of CFB boiler and the enhancement effect of CO on carbon surface NO destruction were analyzed and modeled. Demonstration calculations showed that improving the cyclone efficiency with proper matching of the feeding coal size, then increasing the circulating solids flux and consequently the contribution of falling clusters to NO destruction provide a feasible way to realize the ultra-low NO emission required.