Effects of OFA Ratio on Coal Combustion and Generation of a 600-MW Downfired Boiler after Changing Air Distribution around Fuel-Rich Flow
Publication: Journal of Energy Engineering
Volume 145, Issue 1
Abstract
Both experimentation and numerical simulations were conducted to study the effects of the overfire air (OFA) ratio on the coal combustion and generation characteristics of a 600-MW downfired boiler after changing the air distribution around the fuel-rich flow. In these experiments, the arrangement of the secondary air ports close to the fuel-rich flow was adjusted to modify the air distribution around the fuel-rich flow. The air distributions in the total air duct at OFA damper openings of 30%, 40%, 50%, 70%, 80%, and 100% were calculated by numerical simulation to determine the theoretical air ratios, and these values were in good agreement with experimental results. The calculated air ratios were used as the inlet boundary conditions in subsequent simulations of the boiler thermal states. The calculated emissions, carbon in fly ash, and gas temperatures in the lower furnace were also in good agreement with experimental data. Increasing the OFA damper opening from 30% to 80% generated both good flow and temperature symmetry while gradually reducing the airflow declination angles in the tertiary air regions, indicating reduced downward airflow depth. The flame kernel was also found to move upward. The OFA was readily drawn into the lower furnace at OFA damper openings below 50%, whereas larger openings gradually enhanced the OFA penetration. The corresponding experimental work demonstrated that increasing the opening from 30% to 80% increased the concentration at the furnace exit from 3.02% to 3.51%, and emissions were decreased from 1,337 to at 6% . Reducing the outer secondary air while simultaneously increasing the secondary air ratio between the fuel-rich flow nozzles increased the carbon in fly ash from 4.93% to 5.75%. However, values of 5.94%–15.1% where obtained upon increasing the OFA damper opening from 0% to 70% in conjunction with prior secondary air distribution around the fuel-rich flow. Under these conditions, the coal burnout was greatly enhanced and the lower furnace temperature and emissions were slightly increased.
Get full access to this article
View all available purchase options and get full access to this article.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (51706054).
References
Basu, P., K. F. Cen, and L. Jestin. 2000. “Boilers and burners.” In Design and theory. New York: Springer.
Blas, J. G. 1970. “Spanish experience with burning low-grade coal.” Combustion 42 (3): 6–13.
Chui, E. H., H. N. Gao, A. Majeski, and G. K. Lee. 2007. “Reduction of emissions from coal-based power generation.” In Proc., 1st Int. Conf. on Climate Change. Hong Kong: Hong Kong Climate Change Forum.
De Soete, G. G. 1975. “Overall reaction rates of NO and formation from fuel nitrogen.” Symp. (Int.) Combust. 15 (1): 1093–1102. https://doi.org/10.1016/S0082-0784(75)80374-2.
Drosatos, P., N. Nikolopoulos, M. Agraniotis, M. Agraniotis, and E. Kakaras. 2016. “Numerical investigation of firing concepts for a flexible Greek lignite-fired power plant.” Fuel Process. Technol. 142 (2): 370–395. https://doi.org/10.1016/j.fuproc.2015.10.033.
Fang, Q. Y., H. J. Wang, Y. Wei, L. Lei, X. L. Duan, and H. C. Zhou. 2010. “Numerical simulations of the slagging characteristics in a down-fired, pulverized-coal boiler furnace.” Fuel Process. Technol. 91 (1): 88–96. https://doi.org/10.1016/j.fuproc.2009.08.022.
Fluent, Inc. 1998. Fluent user's guide, Version 5.0. Lebanon, NH: Fluent.
Garcia-Mallol, J. A., T. Steitz, C. Y. Chu, and P. Z. Jiang. 2005. “Ultra-low NOx advanced FW arch firing: Central power station applications.” In Proc., 2nd US China and Control Workshop. Washington, DC: US Dept. of Energy.
Hill, S. C., and L. D. Smoot. 2000. “Modeling of nitrogen oxides formation and destruction in combustion systems.” Prog. Energy Combust. Sci. 26 (4–6): 417–458. https://doi.org/10.1016/S0360-1285(00)00011-3.
Kouprianov, V. I., and V. Tanetsakunvatanab. 2003. “Optimization of excess air for the improvement of environmental performance of a 150 MW boiler fired with Thai lignite.” Appl. Energy 74 (3–4): 445–453. https://doi.org/10.1016/S0306-2619(02)00199-X.
Kuang, M., Z. Q. Li, C. L. Liu, and Q. Y. Zhu. 2013a. “Overall evaluation of combustion and emissions for a down-fired 600 MWe supercritical boiler with multiple injection and multiple staging.” Environ. Sci. Technol. 47 (9): 4850–4858. https://doi.org/10.1021/es304492j.
Kuang, M., Z. Q. Li, C. L. Liu, Q. Y. Zhu, and X. Zhang. 2013b. “Experimental study on combustion and emissions for a down-fired supercritical boiler with multiple-injection multiple-staging technology without overfire air.” Appl. Eng. 106 (11): 254–261. https://doi.org/10.1016/j.apenergy.2013.01.072.
Kuang, M., Z. Q. Li, S. T. Xu, and Q. Y. Zhu. 2011. “Improving combustion characteristics and NOx emissions of a down-fired 350 MWe utility boiler with multiple injection and multiple staging.” Environ. Sci. Technol. 45 (8): 3803–3811. https://doi.org/10.1021/es103598f.
Kuang, M., Z. Q. Li, L. Y. Zeng, X. J. Jing, and Q. Y. Zhu. 2014. “Effect of overfire air angle on flow characteristics within a small-scale model for a deep-air-staging down-fired furnace.” Eng. Convers. Manage. 79: 367–376. https://doi.org/10.1016/j.enconman.2013.12.012.
Leisse, A., and D. Lasthaus. 2008. “New experience gained from operating DS (swirl stage) burners.” VGB Power Tech. 88 (11): 1–7.
Li, Z. Q., M. Kuang, Q. Y. Zhu, J. P. Lai, and Y. Zhang. 2012. “Aerodynamic characteristics within a cold small-scale model for a down-fired 350 MWe utility boiler applying a multiple-injection and multiple-staging technology: Effect of the staged-air declination angle.” Exp. Therm. Fluid Sci. 38: 184–194. https://doi.org/10.1016/j.expthermflusci.2011.12.006.
Liu, C. L., Z. Q. Li, W. G. Kong, Y. Zhao, and Z. C. Chen. 2010. “Bituminous coal combustion in a full-scale start-up ignition burner: Influence of the excess air ratio.” Energy 35 (10): 4102–4106. https://doi.org/10.1016/j.energy.2010.06.023.
Liu, C. L., Q. Y. Zhu, Z. Q. Li, Q. D. Zong, Y. Q. Xie, and L. Y. Zeng. 2013. “Numerical simulation of combustion characteristics at different coal concentrations in bituminous coal ignition in a tiny-oil ignition burner.” Front. Energy 7 (2): 255–262. https://doi.org/10.1007/s11708-013-0255-9.
Liu, G. K., Z. Q. Li, Z. C. Chen, X. Y. Zhu, and Q. Y. Zhu. 2012. “Effect of the anthracite ratio of blended coals on the combustion and emission characteristics of a retrofitted down-fired 660-MWe utility boiler.” Appl. Energy 95 (2): 196–201. https://doi.org/10.1016/j.apenergy.2012.02.031.
Luo, R., N. Li, Y. Zhang, D. Y. Wang, T. S. Liu, Q. L. Zhou, and X. Chen. 2016. “Effect of the adjustable inner secondary air-flaring angle of swirl burner on coal-opposed combustion.” J. Eng. Eng. 142 (1): 04015018. https://doi.org/10.1061/(ASCE)EY.1943-7897.0000279.
Ma, L., Q. Y. Fang, D. Z. Lv, C. Zhang, Y. P. Chen, G. Chen, X. N. Duan, and X. H. Wang. 2015. “Reducing emissions for a 600 MWe down-fired pulverized-coal utility boiler by applying a novel combustion system.” Environ. Sci. Technol. 49 (21): 13040–13049. https://doi.org/10.1021/acs.est.5b02827.
Plumed, A., L. Cañadas, P. Otero, M. I. Espada, M. Castro, J. F. Gonzálcz, and F. Rodríguez. 1995. “Primary measures for reduction of in low volatile coals combustion.” Int. J. Coal Sci. Technol. 24: 1783–1786. https://doi.org/10.1016/S0167-9449(06)80161-8.
Ren, F., Z. Q. Li, Z. C. Chen, S. B. Fan, and G. K. Liu. 2010a. “Influence of the overfire air ratio on the emission and combustion characteristics of a down-fired 300-MWe utility boiler.” Environ. Sci. Technol. 44 (16): 6510–6516. https://doi.org/10.1021/es100956d.
Ren, F., Z. Q. Li, Z. C. Chen, Q. Y. Zhu, and G. H. Yang. 2010b. “Experimental investigations into gas/particle flows in a down-fired boiler: Influence of secondary air momentum.” Energy Fuels 24 (6): 3498–3509. https://doi.org/10.1021/ef100247v.
Ren, F., Z. Q. Li, G. K. Liu, Z. C. Chen, and Q. Y. Zhu. 2011. “Combustion and emissions characteristics of a down-fired 660-MWe utility boiler retro-fitted with air-surrounding-fuel concept.” Energy 36 (1): 70–77. https://doi.org/10.1016/j.energy.2010.11.010.
Shih, T. H., W. W. Liou, and A. Shabbir. 1995. “A new eddy viscosity model for high Reynolds number turbulent flows.” Comput. Fluids 24 (3): 227–238. https://doi.org/10.1016/0045-7930(94)00032-T.
Smoot, L. D., and P. J. Smith. 1985. Pulverized coal combustion and gasification. New York: Plenum.
Song, M. H., L. Y. Zeng, X. G. Li, Z. C. Chen, and Z. Q. Li. 2017. “Effect of stoichiometric ratio of fuel-rich flow on combustion characteristics in a down-fired boiler.” J. Eng. Eng. 143 (3): 04016058. https://doi.org/10.1061/(ASCE)EY.1943-7897.0000415.
Sun, X. Z., Z. Y. Gao, W. Song, and D. F. Chen. 2010. “Analysis of emission characteristics of W-flame boiler with undesigned air distribution.” [In Chinese.] J. Eng. Therm. Energy Power 25 (1): 57–60.
Tan, P., D. F. Tian, Q. Y. Fang, L. Ma, C. Zhang, G. Chen, L. J. Zhong, and H. G. Zhang. 2017. “Effects of burner tilt angle on the combustion and NOx emission characteristics of a 700 MWe deep-air-staged tangentially pulverized-coal-fired boiler.” Fuel 196: 314–324. https://doi.org/10.1016/j.fuel.2017.02.009.
Yang, W. J., W. C. Yang, Z. J. Zhou, J. H. Zhou, Z. Y. Huang, J. Z. Liu, and K. F. Cen. 2014. “A novel coal combustion technology for a down-fired boiler: Aerodynamic characteristics.” Fuel Process. Technol. 118 (1): 90–97. https://doi.org/10.1016/j.fuproc.2013.08.016.
Zhou, H., G. Y. Mo, D. B. Si, and K. F. Cen. 2012. “Experimental study on the aerodynamic and separating characteristics of a novel tiny-oil ignition cyclone burner for down-fired utility boiler.” Asia-Pac. J. Chem. Eng. 7 (4): 624–632. https://doi.org/10.1002/apj.618.
Zhu, Q. Y., L. Y. Zeng, M. Kuang, and Z. C. Chen. 2017. “Numerical optimization of tertiary-air declination angle for a 350MW W-shaped supercritical boiler with multi-injection and staging combustion.” [In Chinese.] Thermal Power Gener. 46 (1): 30–35.
Information & Authors
Information
Published In
Copyright
©2018 American Society of Civil Engineers.
History
Received: Mar 17, 2018
Accepted: Aug 20, 2018
Published online: Dec 8, 2018
Published in print: Feb 1, 2019
Discussion open until: May 8, 2019
Authors
Metrics & Citations
Metrics
Citations
Download citation
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.