Simulation of NOx formation in novel dual circulating fluidized-bed boiler

doi:10.11949/j.issn.0438-1157.20170919

Abstract

Abstract:

The NO_x formation of a novel dual circulating fluidized-bed (DCFB) boiler were numerically studied based on the detailed chemical reaction mechanism in a one dimensional chemical reaction network (1D-CRN). The sensitivity of NO_x formation and the effect of reaction temperature, excess air ratio and primary air ratio were investigated. The results indicated that the NO_x emission of traditional CFB was calculated to be 224.48 mg·m^-3, while the value of DCFB was 97.29 mg·m^-3, indicating that DCFB would reduce the NO_x formation. In addition, the sensitivity analysis showed that the reactions such as R398, R1-N-1, R569 and R17 promoted NO_x formation, while those including R411, R412, R570, R571, R5 and R6 inhibited NO_x formation. Moreover, it was revealed that oxygen in the reaction zone was one contributing factor to NO_x formation by the fact that less oxygen in the reaction zone would inhibit NO_x formation. Likewise, NO_x formation decreased with increasing reaction temperature but increased with increasing excess air ratio and primary air ratio.

Key words: circulating fluidized-bed, coal combustion, NO_x formation, detailed chemical reaction mechanism, simulation

摘要：

运用煤燃烧及NO_x生成的详细化学反应机理，通过搭建一维化学反应器网络（1D-CRN），对一个新型双流化床（DCFB）内燃料型N转化为NO_x的基元化学反应进行了敏感性分析并讨论了反应温度、过量空气系数以及一、二次风配比对燃料型NO_x生成的影响。研究发现，在相同条件下，循环流化床炉膛出口的NO_x排放值为224.48 mg·m^-3，而双流化床炉膛出口的NO_x排放值为97.29 mg·m^-3，双流化床对于燃料型NO_x的减排幅度达到了56.66%。此外，促进NO_x生成的基元反应主要有R398（NH₂+O?HNO+H）、R1-N-1（N-Vol?NH₃+HCN）、R569（NCO+O₂?NO+CO₂）、R17（H+O₂?O+OH）等反应，而抑制NO_x生成的反应包括R411（NH₂+NO?N₂+H₂O）、R412（NH₂+NO?NNH+OH）、R570（NCO+NO?N₂O+CO）、R571（NCO+NO?N₂+CO₂）以及R5（Char+NO?Char+N₂+O₂）和R6（Soot+NO?n Soot+N₂+CO）等反应。这说明反应区域氧气浓度是影响NO_x生成的关键，低氧浓度可抑制燃料N向NO_x转化。另外，NO_x生成值随着反应温度的升高而降低，但随着过量空气系数和一次风所占比例的增大而增加。

关键词: 循环流化床, 煤燃烧, NO_x生成, 详细化学反应机理, 模拟

CLC Number:

TQ517.3

ZHANG Yi, LI Jianbo, WANG Quanhai, LU Xiaofeng. Simulation of NO_x formation in novel dual circulating fluidized-bed boiler[J]. CIESC Journal, 2018, 69(4): 1703-1713.

张弋, 李建波, 王泉海, 卢啸风. 新型双流化床炉内NO_x生成特性数值模拟[J]. 化工学报, 2018, 69(4): 1703-1713.

References 42

[1]	GLARBORG P, JENSEN A D, JOHNSSON J E. Fuel nitrogen conversion in solid fuel fired systems[J]. Progress in Energy & Combustion Science, 2003, 29(2):89-113.
[2]	游卓, 周志军, 王智化, 等. 分级富氧燃烧控制NOx的一维模型和试验研究[J]. 中国电机工程学报, 2014, 34(26):4462-4468. YOU Z, ZHOU Z J, WANG Z H, et al. One-dimensional model and experimental study of NOx control by staged oxy-fuel combustion[J]. Proceedings of the CSEE, 2014, 34(26):4462-4468.
[3]	ZHOU H, HUANG Y, MO G Y, et al. Conversion of fuel-N to N2O and NOx during coal combustion in combustors of different scale[J]. Chinese Journal of Chemical Engineering, 2013, 21(9):996-1006.
[4]	欧阳子区, 朱建国, 吕清刚. 无烟煤粉经循环流化床预热后燃烧特性及NOx排放特性实验研究[J]. 中国电机工程学报, 2014, 34(11):1748-1754. OUYANG Z Q, ZHU J G, LÜ Q G. Experimental study on combustion and NOx emission of pulverized anthracite coal preheated by a circulating fluidized bed[J]. Proceedings of the CSEE, 2014, 34(11):1748-1754.
[5]	曾光, 孙绍增, 赵志强, 等. 不同温度时煤热解中HCN/NH3的析出与CFB锅炉中NOx生成的关联性研究[J]. 中国电机工程学报, 2011, 31(35):47-52. ZENG G, SUN S Z, ZHAO Z Q, et al. Correlation study of HCN/NH3 releasing during coal pyrolysis and NOx formation in a CFB boiler under different temperatures[J]. Proceedings of the CSEE, 2011, 31(35):47-52.
[6]	新井纪男. 燃烧生成物的发生与抑制技术[M]. 北京:科学出版社, 2001. ARIA N. The Occurrence and Inhabitation of Combustion Products[M]. Beijing:Science Press, 2001.
[7]	王鹏, 文芳, 步学朋, 等. 煤热解特性研究[J]. 煤炭转化, 2005, 28(1):8-13. WANG P, WEN F, BU X P, et al. Pyrolysis characteristics of coal[J]. Coal Conversion, 2005, 28(1):8-13.
[8]	崔银萍, 秦玲丽, 杜娟, 等. 煤热解产物的组成及其影响因素分析[J]. 煤化工, 2007, 35(2):10-15. CUI Y P, QIN L L, DU J, et al. Products distribution and its influencing factors for coal pyrolysis[J]. Coal Chemical Industry, 2007, 35(2):10-15.
[9]	PERSHING D W, WENDT J O L. Relative contributions of volatile nitrogen and char nitrogen to NOx emissions from pulverized coal flames[J]. Industrial & Engineering Chemistry Process Design & Development, 1979, 18(1):60-67.
[10]	BASSILAKIS R, ZHAO Y, SOLOMON P R, et al. Sulfur and nitrogen evolution in the Argonne coals. experiment and modelling[J]. Energy & Fuels, 1993, 7(6):710-720.
[11]	KAMBARA S, TAKARADA T, YAMAMOTO Y, et al. Relation between functional forms of coal nitrogen and formation of nitrogen oxide (NOx) precursors during rapid pyrolysis[J]. Energy & Fuels, 1993, 7(6):1013-1020.
[12]	SOLOMON P R, COLKET M B. Evolution of fuel nitrogen in coal devolatilization[J]. Fuel, 1978, 57(12):749-755.
[13]	HAUSSMANN G J, KRUGER C H. Evolution and reaction of coal fuel nitrogen during rapid oxidative pyrolysis and combustion[J]. Symposium on Combustion, 1991, 23(1):1265-1271.
[14]	MULLINS O C, MITRAKIRTLEY S, ELP J V, et al. Molecular structure of nitrogen in coal from XANES spectroscopy[J]. Applied Spectroscopy, 1993, 47(8):1268-1275.
[15]	KIRTLEY S M, MULLINS O C, ELP J V, et al. Nitrogen chemical structure in petroleum asphaltene and coal by X-ray absorption spectroscopy[J]. Fuel, 1993, 72(1):133-135.
[16]	DENG L, JIN X, ZHANG Y, et al. Release of nitrogen oxides during combustion of model coals[J]. Fuel, 2016, 175:217-224.
[17]	AHO M J, HAMALAINEN J P, TUMMAVUORI J L. Importance of solid fuel properties to nitrogen oxide formation through HCN and NH3, in small particle combustion[J]. Combustion & Flame, 1993, 95(1/2):22-30.
[18]	HAMALAINEN J P, AHO M J. Effect of fuel composition on the conversion of volatile solid fuel-N to N2O and NO[J]. Fuel, 1995, 74(12):1922-1924.
[19]	谢建军, 杨学民, 陈安合, 等. 煤炭解耦燃烧过程N迁移与转化(Ⅱ):单组分气相化学反应实验[J]. 燃料化学学报, 2012, 40(10):1172-1178. XIE J J, YANG X M, CHEN A H, et al. Nitrogen transformation during coal decoulping combustion (Ⅱ):NO and N2O reduction with single component of pyrolysis gas[J]. Journal of Fuel Chemistry and Technology. 2012, 40(10):1172-1178.
[20]	WU Z, OHTSUKA Y. Nitrogen distribution in a fixed bed pyrolysis of coals with different ranks: formation and source of N2[J]. Energy & Fuels, 1997, 11(2):477-482.
[21]	KILPINEN P, HUPA M. Homogeneous N2O chemistry at fluidized bed combustion conditions:a kinetic modeling study[J]. Combustion & Flame, 1991, 85(1/2):94-104.
[22]	KRAMLICH J C, LINAK W P. Nitrous oxide behavior in the atmosphere, and in combustion and industrial systems[J]. Progress in Energy & Combustion Science, 1994, 20(2):149-202.
[23]	STA?CZYK K. Temperature-time sieve a case of nitrogen in coal[J]. Energy & Fuels, 2004, 18(2):405-409.
[24]	何京东. 煤炭解耦燃烧NO抑制机理实验研究[D]. 北京:中国科学院过程工程研究所, 2006. HE J D. The experimental study into the NO inhabitation mechanisms during decoupling combustion of coal[D]. Beijing:Institute of Process Engineering, CAS, 2006.
[25]	谢建军. 循环流化床煤炭解耦燃烧过程氮转化规律研究[D]. 北京:中国科学院过程工程研究所, 2007. XIE J J. Investigation into the N conversion mechanisms during decoupling combustion in circulating fluidized bed[D]. Beijing:Institute of Process Engineering, CAS, 2006.
[26]	李静海, 郭慕孙, 白蕴茹, 等. 解耦循环流化床燃烧系统及其脱硫与脱硝方法:1203117A[P]. 1997-06-25. LI J H, GUO M S, BAI Y R, et al. Decoupling circulating fluidized-bed combustion system and its desulphurization and deNOx methods:1203117A[P]. 1997-06-25.
[27]	尚校, 高士秋, 汪印, 等. 不同煤燃烧方式降低NOx排放比较及解耦燃烧应用[J]. 燃料化学学报, 2012, 40(6):672-679. SHANG X, GAO S Q, WANG Y, et al. Comparison of NOx reduction among different coal combustion methods and the application of decoupling combustion[J]. Journal of Fuel Chemistry and Technology, 2012, 40(6):672-679.
[28]	FICHET V V, KANNICHE M, PLION P, et al. A reactor network model for predicting NOx emissions in gas turbines[J]. Fuel, 2010, 89(9):2202-2210.
[29]	HASHEMI H, HANSEN S, TOFTEGAARD M B, et al. A model for nitrogen chemistry in oxy-fuel combustion of pulverized coal[J]. Energy & Fuels, 2014, 25(10):4280-4289.
[30]	RÜDIGER H, GREUL U, SPLIETHOFF H, et al. Distribution of fuel nitrogen in pyrolysis products used for reburning[J]. Fuel, 1997, 76(76):201-205.
[31]	LEPPÄLAHTI J, KOLJONEN T. Nitrogen evolution from coal, peat and wood during gasification:literature review[J]. Fuel Processing Technology, 1995, 43(1):1-45.
[32]	KIDENA K, HIROSE Y, AIBARA T, et al. Analysis of nitrogen-containing species during pyrolysis of coal at two different heating rates[J]. Energy & Fuels, 2008, 14(1):184-189.
[33]	赵炜, 常丽萍, 冯志华, 等. 煤热解过程中生成氮化物的研究[J]. 燃料化学学报, 2002, 30(5):408-412. ZHAO W, CHANG L P, FENG Z H, et al. Formation of nitrogenous species during coal pyrolysis[J]. Journal of Fuel Chemistry and Technology, 2002, 30(5):408-412.
[34]	常丽萍, XIE Zongli, 谢克昌, 等. Loy Yang褐煤热解过程中HCN和NH3形成的主要影响因素[J]. 化工学报, 2003, 54(6):863-867. CHANG L P, XIE Z L, XIE K C, et al. Some factors influencing formation of HCN and NH3 during pyrolysis of brown coal[J]. Journal of Chemical Industry and Engineering (China), 2003, 54(6):863-867.
[35]	赵炜, 常丽萍, 谢克昌, 等. 煤燃烧过程生成氮氧化物前驱体的研究[J]. 燃料化学学报, 2004, 32(4):385-389. ZHAO W, CHANG L P, XIE K C, et al. Release of NOx precursors during coal combustion[J]. Journal of Fuel Chemistry and Technology, 2004, 32(4):385-389.
[36]	LEPPÄLAHTI J. Formation of NH3 and HCN in slow-heating-rate inert pyrolysis of peat, coal and bark[J]. Fuel, 1995, 74(9):1363-1368.
[37]	ZHANG H F, FLETCHER T H. Nitrogen transformations during secondary coal pyrolysis[J]. Energy & Fuels, 2001, 15(6):1512-1522.
[38]	FRIEBEL J, KÖPSEL R F W. The fate of nitrogen during pyrolysis of German low rank coals-a parameter study[J]. Fuel, 1999, 78(8):923-932.
[39]	MAN C K, PENDLEBURY K J, GIBBINS J R. Laboratory measurement of N release under combustion conditions and comparison with plant NOx formation[J]. Fuel Processing Technology, 1993, 36(1):117-122.
[40]	谢建军, 杨学民, 朱文魁, 等. 煤炭解耦燃烧过程N迁移与转化(Ⅰ):热解阶段煤N的释放规律[J]. 燃料化学学报, 2012, 40(8):919-926. XIE J J, YANG X M, ZHU W K, et al. Nitrogen transformation during coal decoulping combustion (Ⅰ):Release behavior of coal-nitrogen during pyrolysis stage[J]. Journal of Fuel Chemistry and Technology, 2012, 40(8):919-926.
[41]	GLARBORG P, JENSEN A D, JOHNSSON J E. Fuel nitrogen conversion in solid fuel fired systems[J]. Progress in Energy and Combustion Science, 2003, 29(2):89-113.
[42]	CHEMKIN. Reaction Design[Z]. San Diego, 2008.