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THERMAL SCIENCE
International Scientific Journal
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INFLUENCE OF PRIMARY AIR CONE GEOMETRY ON NEAR-FIELD FLOW, FUEL-AIR MIXING AND NOX PERFORMANCE OF A CENTRALLY FUEL-RICH SWIRL BURNER WITH 600 MWE BOILER VALIDATION
ABSTRACT
Under deep air-staged combustion, the secondary air flow rate of swirl burners is greatly reduced, making outlet recirculation structure, gas-solid mixing and early ignition behavior critical for stable combustion and low NOx emissions. This work examines the effects of primary air cone geometry on aerodynamic fields, fuel-air mixing and gas-solid flow in a centrally fuel-rich swirl burner for a 600 MWe wall-fired boiler. A cold model is employed for single-phase flow visualization, temperature-tracer mixing and three-dimensional phase-Doppler anemometry (PDA), validated on a 600 MWe industrial unit. As the primary air cone length decreases from 49 mm to 0 mm, the central recirculation zone (CRZ) length increases from 0.57d to 1.51d and its maximum diameter from 0.68d to 0.91d, while the axial onset of recirculation shifts ~70 mm toward the burner outlet. Shorter cones intensify the CRZ, promote earlier and stronger primary-secondary air mixing, increase radial and tangential mixing velocities, and drive fine particles outward, whereas longer cones preserve axial momentum, weaken the CRZ and maintain a strongly fuel-rich core near the centerline. PDA results further indicate that particle back-flow, concentration stratification and size segregation are highly sensitive to cone geometry. Industrial tests show that moving the primary-air outlet 0.1 m away from the burner wall shifts ignition downstream, reduces burner-throat gas temperatures (e.g. from 747°C and 823°C to 451°C and 714°C at two representative burners), and lowers NOx emissions from 344 to 313 mg/m³ at 6% O₂; compared with the pre-retrofit level of 663 mg/m³, this corresponds to an overall reduction of 52.8%. These findings demonstrate that optimizing primary air cone length and outlet position effectively coordinates ignition stability and ultra-low NOx emissions, providing practical design guidance for large wall-fired boilers under deep air-staged combustion and flexible load conditions.
KEYWORDS
PAPER SUBMITTED: 2026-01-23
PAPER REVISED: 2026-03-25
PAPER ACCEPTED: 2026-04-08
PUBLISHED ONLINE: 2026-05-17
DOI REFERENCE: https://doi.org/10.2298/TSCI260123058T
REFERENCES
[1] Ma, Dafu, et al. "Combustion stability and NOX emission characteristics of a 300 MWe tangentially fired boiler under ultra-low loads with deep-air staging." Energy 269 (2023): 126795., 10.1016/j.energy.2023.126795
[2] Gu, Wenbo, et al. "Combustion characteristics of a 660 MW tangentially fired pulverized coal boiler considering different loads, burner combinations and horizontal deflection angles." Case Studies in Thermal Engineering 64 (2024): 105520., 10.1016/j.csite.2024.105520
[3] Liu, Tao, et al. "Numerical investigation of stable combustion at ultra-low load for a 350 MW wall tangentially fired pulverized-coal boiler: Effect of burner adjustments and methane co-firing." Applied Thermal Engineering 246 (2024): 122980., 10.1016/j.applthermaleng.2024.122980
[4] Wang, Qingxiang, et al. "Achievement in ultra-low-load combustion stability for an anthracite-and down-fired boiler after applying novel swirl burners: From laboratory experiments to industrial applications." Energy 192 (2020): 116623., 10.1016/j.energy.2019.116623
[5] Li, Zhengqi, et al. "Influence of staged-air on combustion characteristics and NO x emissions of a 300 MWe down-fired boiler with swirl burners." Energy & fuels 24.1 (2010): 38-45., 10.1021/ef900476c
[6] Fan, Weidong, et al. "Impact of air staging along furnace height on NOx emissions from pulverized coal combustion." Fuel Processing Technology 91.6 (2010): 625 -634., 10.1016/j.fuproc.2010.01.009
[7] Staiger, B., et al. "Development of an air staging technology to reduce NOx emissions in grate fired boilers." Energy 30.8 (2005): 1429-1438., 10.1016/j.energy.2004.02.013
[8] Liang, Zengying, et al. "The energy consumption and environmental impacts of SCR technology in China." Applied energy 88.4 (2011): 1120-1129., 10.1016/j.apenergy.2010.10.010
[9] Ti, Shuguang, et al. "Influence of primary air cone length on combustion characteristics and NOx emissions of a swirl burner from a 0.5 MW pulverized coal-fired furnace with air staging." Applied Energy 211 (2018): 1179-1189., 10.1016/j.apenergy.2017.12.014
[10] Ti, Shuguang, et al. "Effects of the outer secondary air cone length on the combustion characteristics and NOx emissions of the swirl burner in a 0.5 MW pilot-scale facility during air-staged combustion." Applied Thermal Engineering 86 (2015): 318 -325., 10.1016/j.applthermaleng.2015.04.021
[11] Sung, Yonmo, et al. "Coal-particle size effects on NO reduction and burnout characteristics with air-staged combustion in a pulverized coal-fired furnace." Fuel 182 (2016): 558-567., 10.1016/j.fuel.2016.05.122
[12] Shen, Jun, et al. "NOx emission characteristics of superfine pulverized anthracite coal in air-staged combustion." Energy conversion and management 74 (2013): 454 -461., 10.1016/j.enconman.2013.06.048
[13] Li, Sen, et al. "NOx and SOx emissions of a high sulfur self-retention coal during air-staged combustion." Fuel 87.6 (2008): 723-731., 10.1016/j.fuel.2007.05.043
[14] Spliethoff, Hartmut, et al. "Basic effects on NOx emissions in air staging and reburning at a bench-scale test facility." Fuel 75.5 (1996): 560-564., 10.1016/0016-2361(95)00281-2
[15] Xue, Shan, et al. "Experimental investigation on NOx emission and carbon burnout from a radially biased pulverized coal whirl burner." Fuel Processing Technology 90.9 (2009): 1142-1147., 10.1016/j.fuproc.2009.05.011
[16] Xue, Shan, et al. "Experimental study on NO x emission and unburnt carbon of a radial biased swirl burner for coal combustion." Energy & fuels 23.7 (2009): 3558 -3564., 10.1021/ef900055s
[17] Ma, Dafu, et al. "Combustion stability and NOx emission characteristics of three combustion modes of pulverized coal boilers under low or ultra-low loads." Applied Energy 353 (2024): 121998., 10.1016/j.apenergy.2023.121998
[18] Li, Zhengqi, et al. "Effect of angle of arch-supplied overfire air on flow, combustion characteristics 18 and NOx emissions of a down -fired utility boiler." Energy 59 (2013): 377-386., 10.1016/j.energy.2013.06.020
[19] Ti, Shuguang, et al. "Influence of different swirl vane angles of over fire air on flow and combustion characteristics and NOx emissions in a 600 MWe utility boiler." Energy 74 (2014): 775-787., 10.1016/j.energy.2014.07.049
[20] Li, Zhengqi, et al. "Influence of staged-air flow on flow characteristics in a scale model of a down-fired utility boiler with swirl burners: An experimental study." Fuel 93 (2012): 160-166., 10.1016/j.fuel.2011.09.039
[21] Liu, Chunlong, et al. "Gas/particle two-phase flow characteristics of a down-fired 350 MWe supercritical utility boiler at different tertiary air ratios." Energy 102 (2016): 54-64., 10.1016/j.energy.2016.02.016
[22] Ribeirete, A., and M. Costa. "Detailed measurements in a pulverized-coal-fired large-scale laboratory furnace with air staging." Fuel 88.1 (2009): 40-45., 10.1016/j.fuel.2008.07.033
[23] Wang, Qingxiang, et al. "Detailed gas/particle flow characteristics of an improved down-fired boiler with respect to a critical factor affecting coal burnout: Vent-air inclination angle." Energy 182 (2019): 570-584., 10.1016/j.energy.2019.06.057
[24] Liu, Yacheng, Weidong Fan, and Yu Li. "Numerical investigation of air-staged combustion emphasizing char gasification and gas temperature deviation in a large-scale, tangentially fired pulverized-coal boiler." Applied en ergy 177 (2016): 323 -334., 10.1016/j.apenergy.2016.05.135
[25] Huang, Chunchao, et al. "Gas-solid flow and numerical simulation of novel deep peak-shaving swirl burner burning faulty coal." Applied Thermal Engineering 280 (2025): 128594., 10.1016/j.applthermaleng.2025.128594
[26] Sun, Wenjing, Wenqi Zhong, and Aibing Yu. "Gas-particle turbulent flow of foursquare tangential jets in a simplified pulverized-coal firing boiler." Advanced Powder Technology 29.6 (2018): 1463-1473., 10.1016/j.apt.2018.03.010
[27] Shang, Manxia, et al. "Characterization of the lateral gas-solid flow in a circulating fluidized bed boiler using simple mathematical model based on CPFD simulation data." Chemical Engineering Science 314 (2025): 121773., 10.1016/j.ces.2025.121773
[28] Cui, Ying, et al. "Simulation of gas-solid combustion characteristics in a 1000 MW CFB boiler for supercritical CO2 cycle." Advanced Powder Technology 34.8 (2023): 104104., 10.1016/j.apt.2023.104104
[29] Lee, Byoung-Hwa, et al. "Application of the CPFD method to analyze the effects of bed material density on gas-particle hydrodynamics and wall erosion in a CFB boiler." Fuel 342 (2023): 127878., 10.1016/j.fuel.2023.127878
[30] Ma, Lun, et al. "A novel low-NOx swirl burner with coal-ammonia co-firing: effect of ammonia ratio in the dual channels on combustion and NOx formation." Process Safety and Environmental Protection 191 (2024): 85-93., 10.1016/j.psep.2024.08.128
[31] Liu, Jingwen, et al. "Experimental study on pollutant emissions and fly ash characteristics in ammonia-bituminous coal co-firing under different ammonia injection modes in a swirl burner." Journal of the Energy Institute 123 (2025): 102265., 10.1016/j.joei.2025.102265
[32] Liu, Mingyu, et al. "Numerical investigation of ammonia/coal co-combustion in a low NOx swirl burner." Energy 282 (2023): 128358., 10.1016/j.energy.2023.128358
[33] Li, Dezheng, et al. "Effect of swirl number and oxygen mole fraction on the ignition characteristics of ammonia-coal co-firing." Fuel 407 (2026): 137544., 10.1016/j.fuel.2025.137544
[34] Hu, Heng, et al. "Numerical simulation of a novel hydrogen blending pulverized coal burner: central and annular hydrogen blending." International Journal of Hydrogen Energy 185 (2025): 151651., 10.1016/j.ijhydene.2025.151651
[35] Wen, Xu, et al. "Carrier-phase direct numerical simulation and flamelet modeling of NOx formation in a pulverized coal/ammonia co-firing flame." Combustion and Flame 269 (2024): 113722., 10.1016/j.combustflame.2024.113722
[36] Hu, Jie, Shiliang Yang, and Hua Wang. "Flue gas-dust two-phase heat transfer characteristics and corrosion behavior in industrial-scale waste heat boilers." Energy 308 (2024): 132830., 10.1016/j.energy.2024.132830
[37] Ghosh, M. "Effect of flue gas constituents on boiler tube failure of a captive power plant." Engineering Failure Analysis 151 (2023): 107416., 10.1016/j.engfailanal.2023.107416
[38] Jafarihonar, Farzad, et al. "Deposit sintering in modern Kraft recovery boilers− The role of NaOH?." Fuel 371 (2024): 132138., 10.1016/j.fuel.2024.132138
[39] Ma, Honghe, et al. "Design of porous wall air coupling with air staged furnace for preventing high temperature corrosion and reducing NOx emissions." Applied Thermal Engineering 124 (2017): 865-870., 10.1016/j.applthermaleng.2017.06.029
[40] Li, Song, et al. "Effect of outer secondary-air vane angle on the flow and combustion characteristics and NOx formation of the swirl burner in a 300-MW low-volatile coal-fired boiler with deep air staging." Journal of the Energy Institute 90.2 (2017): 239 -256., 10.1016/j.joei.2016.01.005
[41] Wen, Xu, et al. "Flamelet LES of a swirl-stabilized multi-stream pulverized coal burner in air and oxy-fuel atmospheres with pollutant formation." Proceedings of the Combustion Institute 38.3 (2021): 4141-4149., 10.1016/j.proci.2020.05.061
[42] Wen, Xu, et al. "Detailed analysis of early-stage NOx formation in turbulent pulverized coal combustion with fuel-bound nitrogen." Proceedings of the Combustion Institute 38.3 (2021): 4111-4119., 10.1016/j.proci.2020.06.317
© 2026 Society of Thermal Engineers of Serbia. Published by the Vinča Institute of Nuclear Sciences, National Institute of the Republic of Serbia, Belgrade, Serbia. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International licence