A semi-empirical NOx model for LES in pulverized coal air-staged combustion

Abstract

Numerical simulation of pulverized coal combustion with the large eddy simulation (LES) method can provides important instructions on the design optimization of boilers. Because of its huge computational cost, a simple but reliable NOx prediction model is required in LES. Through the air-staged combustion experiments of six kinds of coals which conducted in an electric heated down-fired furnace (DFF), the relationship between NOx reduction and CO + H2 generation in the fuel-rich zone was identified. Based on this observation, a semi-empirical modeling strategy was proposed: instead of CHi which is difficult to calculate, the concentration of CO + H2 is used to quantify NO homogeneous reduction. An integrated NOx prediction model was proposed and implemented into LES simulation. The results proved the new model can accurately predict different NOx evolution characteristics under various conditions. Furthermore, the comparison indicated the LES method performs better on NOx prediction than the RANS method, especially in the area where the turbulent fluctuation is relatively stronger.