Effect of circulating ash from CFB boilers on NO and N₂O emission

Abstract

NO and N₂O emissions from circulating fluidized bed (CFB) boilers are determined by their formation and destruction rates in the furnace. The effect of circulating ash from a CFB boiler on NO and N₂O emissions were investigated in a laboratory-scale fluidized bed reactor. The results show that the residue char in circulating ash and the CO generated from the char play an important role in NO reduction and N₂O formation; however, active components of circulating ash such as CaO, Fe₂O₃ accelerate the decomposition of N₂O. Experiment was also conducted on a 75 t/h CFB boiler fueled with the mixture of anthracite and biomass. The lower residue carbon content of circulating ash in this experiment is lower; therefore, the reacting rate of NO deoxidize is limited. This result verified the conclusion of laboratory research.

Keywords

CFB boiler / circulating ash / NO reduction / N₂O thermal decomposition / biomass

References

[1] Feng Junkai, Yue Guangxi, Lv Junfu. Circulating Fluidized Bed Combustion Boiler. Beijing: China Electric Power Press, 2003 (in Chinese)

[2] Gani A, Naruse I. NO and N₂O formation/decomposition characteristics during co-combustion of coal with biomass. In: Lia L, ed. Proceedings of the 18th International Conference on Fluidized Bed Combustion. Toronto: ASME, 2005, FBC2005-78024

[3] Zhang H, Lu J F, Chen K Y, . An experimental study on N₂O reduction over circulating ashes of CFB boilers. In: Lia L, ed. Proceedings of the 18th International Conference on Fluidized Bed Combustion. Toronto: ASME, 2005, FBC2005-78047

[4] x000c5;mend L, Leckner B. Reduction of N₂O in a circulating fluidized-bed combustor. Fuel, 1994, 73(9): 1389-1397

[5] Armesto L, Boerrigter H, Bahillo H, . N₂O emission from fluidized bed combustion– The effect of fuel characteristics and operating conductions. Fuel, 2003, 82(15-17): 1845-1850

[6] Zhang Yi, Chen Biao, Ding Yanjun, . Experimental investigation of operating strategy of low NO_x, high efficiency coal-fired utility boilers. J Tsinghua Univ (Sci & Tech), 2006, 46(5): 666-669 (in Chinese)

[7] Zhao Zongbing, Li Wen, Li Baoqing. Catalytic reduction of NO by chars loaded with Ca and Fe. Environmental Science, 2001, 22(5): 17-20(in Chinese)

[8] Molina A, Eddings E G, Pershing D W, . Char nitrogen conversion: implication to emissions from coal-fired utility boilers. Progress in Energy and Combustion Science, 2000, 26(6): 507-531

[9] Ren Wei, Xiao Xianbing, Lv Junfu. Research on conversion of nitrogen in char during combustion under fluidized bed conditions. Journal of China University of Mining & Technology, 2003, 32(3): 259-262 (in Chinese)

[10] Hayhurst A N, Lawrence A D. The reduction of the nitrogen oxides NO and N₂O to molecular nitrogen in the presence of iron, its oxides, and carbon monoxide in a hot fluidized bed. Combustion and Flame, 1997, 110(3): 351-365

[11] Löffler G, Wargadalam V J, Winter F, . Decomposition of nitrous oxide at medium temperature. Combustion and Flame, 2000, 120(4): 427-438

[12] Barišic V, Neyestanaki A K, Klingstedt F, . Catalytic decomposition of N₂O over the bed material from circulating fluidized-bed (CFB) boilers burning biomass fuels and wastes. Energy & Fuels, 2004, 18(6): 1909-1920

[13] Hou Xiangsong, Li Jinping, Zhang Hai, . Limestone effects on N₂O emission in CFB combustor. Power System Engineering, 2005, 21(3): 1-3 (in Chinese)

[14] Winter F, Wartha C, Hofbauer H. NO and N₂O formation during the combustion of wood, straw, malt waste and peat. Bioresource Technology, 1999, 70(1): 39-49

[15] Kilpinen P, Kallio S, Konttinen J, . Towards a quantitative understanding of NO_x and N₂O emission formation in full-scale circulating fluidized combustors. In: Geiling D W ed. Proceedings of the 16th International Conference on Fluidized Bed Combustion. Reno: ASME, 2001, FBC01-0079

[16] Yang Shi, Hou Xiangsong, Yang Hairui, . Mixing ratio influence on co-combustion of biomass and coal. In: 6th Asia-Pacific Conference on Combustion. Nagoya, Japan, 2007

[17] Liu Hao, Gibbs B M. Modeling of NO and N₂O emissions from biomass-fired circulating fluidized bed combustors. Fuel, 2002, 81(3): 271-280

RIGHTS & PERMISSIONS

2014 Higher Education Press and Springer-Verlag Berlin Heidelberg