A numerical analysis of NOx formation and control in radiatively/conductively-stabilized pulverized coal combustors

In an attempt to study ways for reducing NOx emissions from radiatively/conductively-stabilized combustors (RCSC) for pulverized coal, a comprehensive conjugate heat and mass transfer and reaction kinetics model of that combustor was developed. As compared with a much simpler three-reaction model, the radiation intensity distribution obtained by the new model shows a substantial decrease in the flame region. The analysis has shown that (1) the effect of a 10% deviation in the diffusion coefficients on the results was found to be negligible, indicating that the use of binary coefficients instead of those for a multi-component system may be good enough in such combustion modeling, (2) flame location was found to have little effect (similar to 6%), and internal wall emittance an insignificant effect, on NO emissions, (3) the mass fraction of these emissions could be lowered by lowering the flame temperature, accomplished by increasing the excess air ratio, (4) at the same time, the overall mass of NO emitted with the thicker lower-temperature flames produced by such increases in excess air was much higher, indicating that the RCSC with its capability for producing a high temperature thin flame is much more effective for the reduction of NO emissions than lower temperature combustion alternatives. (C) 1998 Elsevier Science S.A. All rights reserved.