Modelling NO formation in a swirling pulverized coal flame

Nitric oxide (NO) concentrations in a swirling pulverized coal flame were predicted from a mathematical model and compared with experimental measurements. The model consisted of a two-dimensional, axi-symmetric parent CFD code combined with a NOx post-processor. Both thermal and fuel NO are included in the NOx chemistry. The parent code is used to calculate the combustion aerodynamics within the flame, while the NOx (post-processor) model predicts the local concentrations of HCN, NH3 and NO. The volatile nitrogen is released either as HCN or NH3, depending on its functional form in the coal. Several models studying the conversion of char nitrogen to NO are tested, as well as the effect of a hydrocarbon reburn mechanism. The experimental data were obtained from a swirling pulverized coal flame (aerodynamically air staged burner) operated at the International Flame Research Foundation. A sensitivity analysis on the primary components of the NOx chemistry is included. When the only reactions considered were those involving HCN and NO, the NO concentrations were underpredicted. The full NOx chemistry model was able to achieve good NO predictions by including ammonia as a NOx precursor and incorporating a hydrocarbon mechanism to recycle NO to HCN.