American Flame Research Committee

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Title An Investigation of NO Reduction by Coal Reburning
Creator Yang, Y. B.; Gibbs, B. M.; Hampartsoumian, E.
Publisher Digitized by J. Willard Marriott Library, University of Utah
Date 1998
Spatial Coverage presented at Maui, Hawaii
Abstract In this paper coal reburning for the reduction of NO emission was investigated in a 0.2MWt pilot-scale furnace. Eight bituminous coals were selected for study over a wide range of operational parameters including reburn zone residence time, reburn-fuel fraction, type of coal, furnace temperature level and primary NO concentration. Three-dimensional numerical calculations were carried out in an effort to fully understand the reburning process, the related NO-chemistry and to investigate in detail the sensitivity of the reburning process to the devolatilisation behaviour of the reburn coal and mixing rates. A global NO mechanism model was employed which features the three major NO-reducing agents, i.e. hydrocarbon (CH) fragments, volatile fuel-nitrogen (HCN) species and char particles. The model predictions show that reactions between primary NO reduction and CH fragments are the dominant NO-reduction mechanism in the reburn-zone, accounting for nearly 70% of the total reduction observed. The predictions also serve to validate the experimentally observed effects of increasing the furnace temperature level and number of coal injectors. Parametric analysis shows that increased volatile yields and/or faster devolatilisation rates can lead to improved NO reduction in the reburn zone provided that the reborn zone is operated fuel-rich so as to limit the consumption of volatile gases by oxygen. As reburn zone conditions become increasingly leaner, rapid coal pyrolysis results in the earlier consumption of volatile gases by oxygen as mixing takes place, leading to less NO reduction. The experimental and predicted results highlight the differences in coal pyrolysis behaviour, even between coals of similar rank which would account for the variability observed in the extent on NO reduction for the coals investigated.
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ARK ark:/87278/s6h70jf1
Setname uu_afrc
ID 13299
Reference URL https://collections.lib.utah.edu/ark:/87278/s6h70jf1

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Title Page 17
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OCR Text maximum volatile concentration along the rebum-jet axis is higher and the volatile matter concentrated in a narrow region near to the reactor axis as a result of the impingement of the two opposing jets. This results in the overall improved performance of the four injector system. 5. Conclusions A combined experimental and theoretical approach was carried out to assess the impact of volatile release, temperature and mixing rates on N O reduction by coal reburning. Rebum performance tests using eight bituminous coals demonstrated that N O reductions of up to 6 0 % were possible depending on operating conditions and coal selection. The optimum residence time for maximum N O reduction was found to be around 450 ms for the size range of pulverised coals investigated. From a sensitivity analysis, the most important coal property was found to be the volatile matter content. The coal nitrogen content was found to be less important with regard to reducing N O in the rebum zone. The reduction of NO by hydrocarbon (CH) fragments was shown to be the dominant NO reduction route accounting for nearly 7 0 % of the total N O reduction. Higher volatile yields improved the overall N O reduction through the production of C H fragments in the rebum zone. Faster devolatilisation was also shown to be more effective for N O reduction, as a result of the earlier release of volatile gases into the surrounding primary NO-laden stream, provided that the rebum zone stoichiometry is sufficiently oxygen-lean to prevent to early oxidisation of volatile gases. Increasing the average rebum zone temperature resulted in poorer N O reduction efficiencies as a consequence of the more rapid production and consumption of hydrocarbon volatile gases before they could mix and react effectively with the primary NO-laden gases. This detrimental effect could be lessened by improving the mixing between in the rebum zone between the reburning coal jets and the primary flow. Acknowledgements The authors work like to thank the UK EPSRC for a grant in aid of this work. References 1. Chen, S. L., McCarthy, J. M., Clark, W. D., Heap, M. P., Seeker, W. R, and Pershing D. W., Twenty-first Symposium (International) on Combustion, The Combust. Institute, Pittsburgh, 1986, p.1159. 2. Wendt, J. O. L., Sternling , C. V. and Matovich, M. A., Fourteenth Symposium (International) on Combustion, p.897. The Combustion Institute, 1973. 3. Yang, Y.B., Naja, T.A., Gibbs, B. M. and Hampartsoumian, E., J. Inst. Energy, 482:9-17, (1997) 4. Liu, H., Hampartsoiirnian, E. and Gibbs, B. M , Fuel, 76:985-993 (1997) 5. Reed, R. D., Process for the Disposal of Nitrogen Oxide. John Zink Company, U.S. Patent 1,274,637, 1969. 6. Kicherer, A., Spliethoff, H., Majer, H. and Hein, K. R. G., Fuel,.73:1443-1446 (1994) 7. De Soete, G. G., Fifteenth Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, 1975, pp 1093-1102. 8. Mereb, J.B. and Wendt,J. O.L., Twenty-third Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, 1990, pp 1273-1279.
Setname uu_afrc
ID 13297
Reference URL https://collections.lib.utah.edu/ark:/87278/s6h70jf1/13297