Assessment of Kinetic and Mixing-Controlled Models for the Prediction of Fuel-NO Emissions in P.F. Burners

Abstract

Predictions of a mathematical model are compared with NO data for pulverised -coal flames. The mathematical model comprises a two-dimensional parent code for the aerodynamics and combustion to which a fuel-NO post processor is appended. The data, which include local concentrations of NO, HCN and NH₃, were obtained in a large scale laboratory cylindrical combustor for a conventional burner and for a low NO burner. Four models for the Volatiles-derived NO and two models for the char-derived NO have been tested.

While moderately satisfactory predictions were obtained for the conventional burner, this was not the case for the low NO burner. It is believed that the time scale of the secondary cracking of the primary products of pyrolysis is significant for low NO flames and that the predictive problem arises because it is not simulated by the present simulation. The fuel-NO modelling of De Soete, which has the advantages of simplicity, gives as good prediction as any of the models tested.

Notwithstanding the deficiencies of the predictions, the physical insight which they afford considered alongside the data allow useful conclusions to be drawn about the physical circumstances likely to favour low NO emission.

Key Words:

• Nitrogen oxides
• mathematical modelling
• pulverized coal combustion