A Reduced Reaction Scheme for Volatile Nitrogen Conversion in Coal Combustion

In pulverised coal flames, the most important volatile nitrogen component forming NOx is HCN. To be able to model the nitrogen chemistry in coal flames it is necessary to have an adequate model for HCN oxidation. The present work was concerned with developing a model for HCN/NH3/NO conversion based on systematic reduction of a detailed chemical kinetic model.

Models of different complexity were developed and tested under conditions similar to those in a pulverised coal flame. Comparisons of the models were made for ideal chemical reactors simulations (plug Bow reactor and well-stirred reactor). Provided that the CO/H-2 chemistry was described adequately, the reduced HCN/NH3/NO model compared very well with the detailed model over a wide range of stoichiometries.

Decoupling of the HCN chemistry from the CO/H-2 chemistry resulted in over-prediction of the HCN oxidation rate under fuel rich conditions, but had negligible effect on the CO/H-2 chemistry. Comparison with simplified HCN models from the literature revealed significant differences, indicating that these models should be used cautiously in modelling volatile nitrogen conversion.