Influence of nozzle height to width ratio on ignition and NO_x emission characteristics of semicoke/bituminous coal blends in a 300 kW pulverized coal-fired furnace

Abstract

To improve the ignition behavior and to reduce the high NO_x emissions of blended pulverized fuels (PF) of semicoke (SC), large-scale experiments were conducted in a 300 kW fired furnace at various nozzle settings, i.e., ratios (denoted by h_f/b) of the height of the rectangular burner nozzle to its width of 1.65, 2.32, and 3.22. The combustion tests indicate that the flame stability, ignition performance, and fuel burnout ratio were significantly improved at a nozzle setting of h_f/b = 2.32. The smaller h_f/b delayed ignition and caused the flame to concentrate excessively on the axis of the furnace, while the larger h_f/b easily caused the deflection of the pulverized coal flame, and a high-temperature flame zone emerged close to the furnace wall. NO_x emissions at the outlet of the primary zone decreased from 447 to 354 mg/m³ (O₂ = 6%), and the ignition distance decreased from 420 to 246 mm when the h_f/b varied from 1.65 to 3.22. Furthermore, the ratio (denoted by S_R/S_C) of the strong reduction zone area to the combustion reaction zone area was defined experimentally by the CO concentration to evaluate the reduction zone. The S_R/S_C rose monotonously, but its restraining effects on NO_x formation decreased as h_f/b increased. The results suggested that in a test furnace, regulating the nozzle h_f/b conditions sharply reduces NO_x emissions and improves the combustion efficiency of SC blends possessing an appropriate jet rigidity.

Graphical abstract

Keywords

rectangular jet burner / nozzle height to width ratio / ignition characteristics / pyrolyzed semicoke (SC) and bituminous blend / NO_x formation

References

[1] Yao H, He B, Ding G, Thermogravimetric analyses of oxy-fuel co-combustion of semi-coke and bituminous coal. Applied Thermal Engineering, 2019, 156(6): 708–721

[2] Zhang J, Jia X, Wang C, Experimental investigation on combustion and NO formation characteristics of semi-coke and bituminous coal blends. Fuel, 2019, 247(7): 87–96

[3] Smrekar J, Potočnik P, Senegačnik A. Multi-step-ahead prediction of NO_x emissions for a coal-based boiler. Applied Energy, 2013, 106(6): 89–99

[4] Xu M, Yuan J, Ding S, Simulation of the gas temperature deviation in large-scale tangential coal fired utility boilers. Computer Methods in Applied Mechanics and Engineering, 1998, 155(3–4): 369–380

[5] Vuthaluru H B, Vuthaluru R. Control of ash related problems in a large scale tangentially fired boiler using CFD modeling. Applied Energy, 2010, 87(4): 1418–1426

[6] Liu Y, Fan W, Li Y. Numerical investigation of air-staged combustion emphasizing char gasification and gas temperature deviation in a large-scale tangentially fired pulverized-coal boiler. Applied Energy, 2016, 177(9): 323–334

[7] Guo J, Liu Z, Hu F, A compatible configuration strategy for burner streams in a 200 MW_e tangentially fired oxy-fuel combustion boiler. Applied Energy, 2018, 220(6): 59–69

[8] Habib M A, Ben-Mansour R, Abualhamayel H I. Thermal and emission characteristics in a tangentially fired boiler model furnace. International Journal of Energy Research, 2010, 34(13): 1164–1182

[9] Tang G, Wu B, Johnson K, Numerical study of a tangentially fired boiler for reducing steam tube overheating. Applied Thermal Engineering, 2016, 102(6): 261–271

[10] Khatami R, Stivers C, Joshi K, Combustion behavior of single particles from three different coal ranks and from sugar cane bagasse in O₂/N₂ and O₂/CO₂ atmospheres. Combustion and Flame, 2012, 159(3): 1253–1271

[11] Riaza J, Khatami R, Levendis Y A, Single particle ignition and combustion of anthracite, semi-anthracite and bituminous coals in air and simulated oxy-fuel conditions. Combustion and Flame, 2014, 161(4): 1096–1108

[12] Khatami R, Levendis Y A. An overview of coal rank influence on ignition and combustion phenomena at the particle level. Combustion and Flame, 2016, 164(2): 22–34

[13] Zhu M, Zhang H, Tang G, Ignition of single coal particle in a hot furnace under normal and micro-gravity condition. Proceedings of the Combustion Institute, 2009, 32(2): 2029–2035

[14] Su S, Pohl J H, Holcombe D, Techniques to determine ignition, flame stability and burnout of blended coals in p.f. power station boilers. Progress in Energy and Combustion Science, 2001, 27(1): 75–98

[15] Clements B R, Zhuang Q, Pomalis R, Ignition characteristics of co-fired mixtures of petroleum coke and bituminous coal in a pilot-scale furnace. Fuel, 2012, 97(2): 315–320

[16] Zeng G, Sun S, Dong H, Effects of combustion conditions on formation characteristics of particulate matter from pulverized coal bias ignition. Energy & Fuels, 2016, 30(10): 8691–8700

[17] Zeng G, Sun S, Yang X, Effect of the primary air velocity on ignition characteristics of bias pulverized coal jets. Energy & Fuels, 2017, 31(3): 3182–3195

[18] Zeng G, Sun S, Zhang W, Effects of bias concentration ratio on ignition characteristics of parallel bias pulverized coal jets. Energy & Fuels, 2017, 31(12): 14219–14227

[19] Zhao Y, Zeng G, Zhang L, Effects of fuel properties on ignition characteristics of parallel-bias pulverized-coal jets. Energy & Fuels, 2017, 31(11): 12804–12814

[20] Qin Y, Zhang Z, Wu S, Experimental study of jet characteristics of a rectangular nozzle with different height-to-width ratios in a tangentially-fired combustion flow field. Journal of Engineering for Thermal Energy and Power, 2000, 15(2): 125–127 (in Chinese)

[21] Zhang J, Kelly K E, Eddings E G, Ignition in 40 kW co-axial turbulent diffusion oxy-coal jet flames. Proceedings of the Combustion Institute, 2011, 33(2): 3375–3382

[22] Binner E, Zhang L, Li C, Bhattacharya S. In-situ observation of the combustion of air-dried and wet Victorian brown coal. Proceedings of the Combustion Institute, 2011, 33(2): 1739–1746

[23] Molina A, Murphy J J, Winter F, Pathways for conversion of char nitrogen to nitric oxide during pulverized coal combustion. Combustion and Flame, 2009, 156(3): 574–587

[24] Yan Y, Sun L, Peng Z, Effects of pyrolyzed semi-char blend ratio on coal combustion and pollution emission in a 0.35 MW pulverized coal-fired furnace. Frontiers in Energy, 2020, online, doi: 10.1007/s11708-020-0678-z

[25] Rastko J, Aleksandra M, Bartosz S. Sensitivity analysis of different devolatilization models on predicting ignition point position during pulverized coal combustion in O₂/N₂ and O₂/CO₂ atmospheres. Fuel, 2012, (11): 23–37

[26] Ti S, Chen Z, Li Z, Influence of primary air cone length on combustion characteristics and NO_x emissions of a swirl burner from a 0.5 MW pulverized coal-fired furnace with air staging. Applied Energy, 2018, 211(2): 1179–1189

[27] Qiao Y, Zhang L, Binner E, An investigation of the causes of the difference in coal particle ignition temperature between combustion in air and in O₂/CO₂. Fuel, 2010, 89(11): 3381–3387

[28] Sung Y, Moon C, Eom S, Coal-particle size effects on NO reduction and burnout characteristics with air-staged combustion in a pulverized coal-fired furnace. Fuel, 2016, 182(10): 558–567

[29] Chen Z, Li Z, Jing J, Gas/particle flow characteristics of two swirl burners. Energy Conversion and Management, 2009, 50(5): 1180–1191

[30] Jiang X, Zheng C, Yan C, Physical structure and combustion properties of super fine pulverized coal particle. Fuel, 2002, 81(4): 793–797

[31] Li Z, Liu Y, Chen Z, Effect of the air temperature on combustion characteristics and NO_x emissions from a 0.5 MW pulverized coal-fired furnace with deep air staging. Energy & Fuels, 2012, 26(4): 2068–2074

[32] Pedel J, Thornock J N, Smith P J. Large eddy simulation of pulverized coal jet flame ignition using the direct quadrature method of moments. Energy & Fuels, 2012, 26(11): 6686–6694

[33] Yamamoto K, Murota T, Okazaki T, Large eddy simulation of a pulverized coal jet flame ignited by a preheated gas flow. Proceedings of the Combustion Institute, 2011, 33(2): 1771–1778

[34] Zhu Z, Chi Z, Pan W, Aerodynamic experimental research in corner-fired furnace with burners of different height-width ratios. Journal of Shanghai Institute of Electric Power, 1994, 10(1): 20–27 (in Chinese)

[35] Wang C, Hao Y, Wang R, Numerical simulation of influence of depth-width ratio for boiler burner on combustion. Gas & Heat. 2010, 30(12): 11–15 (in Chinese)

[36] Moon C, Sung Y, Eom S, NO_x emissions and burnout characteristics of bituminous coal, lignite, and their blends in a pulverized coal-fired furnace. Experimental Thermal and Fluid Science, 2015, 62(1): 99–108

[37] Glarborg P, Kristensen P, Dam-Johansen K, Nitric oxide reburning by non-hydrocarbon fuels: implications for reburning with gasification gases. Energy & Fuels, 2000, 14(4): 828–838

[38] Gou X, Zhou J, Zhou Z, The influence of water vapor upon formation of NO in combustion of pulverized coal. Thermal Power Generation, 2007, 10(1): 4–8 (in Chinese)

[39] Wang Z, Zhao Y, Sun R, Effects of reaction condition on NO emission characteristic, surface behavior and microstructure of demineralized char during O₂/H₂O combustion process. Fuel, 2019, 253(10): 1424–1435

[40] De Soete G, Croiset E, Richard J R. Heterogeneous formation of nitrous oxide from char-bound nitrogen. Combustion and Flame, 1999, 117(1–2): 140–154

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