Predictions of NOx/N2O emissions from an ultra-supercritical CFB boiler using a 2-D comprehensive CFD combustion model

Abstract

NOx and N2O emissions from an ultra-supercritical circulating fluidized bed (CFB) boiler were predicted using a two dimensional (2-D) comprehensive computational fluid dynamics (CFD) combustion model. This model was developed from a three dimensional model for a supercritical CFB boiler previously constructed by our group. Based on an analysis of the NOx and N2O conversion processes in a CFB boiler, the primary formation and destruction reactions were introduced into the 2-D model and coupled. The resulting model was validated using data from the Baima 600 MW supercritical CFB boiler, and then applied to a 660MW ultra-supercritical CFB boiler. The effects of excess air, the secondary air (SA) to (primary air (PA) plus SA) ratio and the SA injection height on NOx and N2O emissions were investigated. The results show that a higher excess air volume increases both NOx and N2O emissions, while increasing the SA/(PA+SA) ratio somewhat reduces both the NOx and N2O concentrations. On the basis of the results of this work, optimal locations for SA injection ports so as to lower NOx and N2O emissions are recommended.