Numerical Analysis on the Quantitative Separation of Different NO_x Formation and Reduction Routes during MILD Oxy-Coal Combustion with the Improved Nitrogen Chemistry Model

Abstract

Moderate and intense low-oxygen dilution (MILD) oxy-coal combustion has great prospects for thermal efficiency improvement, NO x emission reduction, and CO 2 capture and sequestration. Based on the pulverized coal combustion experiments in the Hencken burner flat diffusion flame combustion facility, the improved nitrogen chemistry model incorporated into computational fluid dynamics software was proposed to numerically simulate NO x formation and reduction during MILD oxy-coal combustion. The simulated results were compared with the experimental data in the Hencken burner to validate the accuracy of the improved nitrogen chemistry model, and the difference between simulated and experimental NO yields was approximately 7%. Moreover, the improved nitrogen chemistry model was further used to numerically analyze the NO formation process of pulverized coal combustion at 1673 K−10%O 2 under O 2 /CO 2 atmosphere in the Hencken burner, and different NO formation and reduction routes were quantitatively separated to elucidate the relative contributions to the total NO formation. The results show that the catalytic reduction of NO by CO on the char surface caused by the high CO 2 concentration atmosphere has a significant effect. The reduction rate (RR) of char NO by CO is approximately 25%, the RR of volatile NO by CO is 19%, and the RR of the recycled NO by CO is 10%. The reduction of the recycled NO caused by flue gas recycle also plays an important role. The RR of the recycled NO with char nitrogen intermediates was 15%, and the RR of the recycled NO with volatile nitrogen intermediates was 8%. The results are conducive to providing more detailed quantitative information for the NO x formation mechanism and controlling methods of MILD-OCC.