Industrial-scale investigations on effects of tertiary-air declination angle on combustion and steam temperature characteristics in a 350-MW supercritical down-fired boiler

Abstract

Industrial-scale experiments were conducted to study the effects of tertiary air declination angle (TDA) on the coal combustion and steam temperature characteristics in the first 350-MW supercritical down-fired boiler in China with the multiple-injection and multiple-staging combustion (MIMSC) technology at medium and high loads. The experimental results indicated that as the TDA increased from 0° to 15°, the overall gas temperature in the lower furnace rose and the symmetry of temperature field was enhanced. The ignition distance of the fuel-rich coal/air flow decreased. In near-burner region, the concentration of O₂ decreased while the concentrations of CO and NO increased. The concentration of NO decreased in near-tertiary-air region. The carbon in fly ash decreased significantly from 8.40% to 6.45% at a load of 260 MW. At a TDA of 15°, the ignition distances were the shortest (2.07 m and 1.73 m) at a load of 210 MW and 260 MW, respectively. The main and reheat steam temperatures were the highest (557.2°C and 559.4°C at a load of 210 MW, 558.4°C and 560.3°C at a load of 260 MW). The carbon in fly ash was the lowest (4.83%) at a load of 210 MW. On changing the TDA from 15° to 25°, the flame kernel was found to move downward and the main and reheat steam temperatures dropped obviously. The change of TDA has little effect on NO_x emissions(660–681 mg/m³ at 6% O₂). In comprehensive consideration of the pulverized coal combustion characteristics and the unit economic performance, an optimal TDA of 15° is recommended.

Keywords

supercritical down-fired boiler / industrial-scale experiment / tertiary air declination angle / coal combustion / steam temperature

References

[1] Kuang M, Li Z Q. Review of gas/particle flow, coal combustion, and NO_x emission characteristics within down-fired boilers. Energy, 2014, 69: 144–178

[2] Yang W, Wang B, Lei S Y, Wang K, Chen T, Song Z J, Ma C, Zhou Y D, Sun L S. Combustion optimization and NO_x reduction of a 600 MW_e down-fired boiler by rearrangement of swirl burner and introduction of separated over-fire air. Journal of Cleaner Production, 2019, 210: 1120–1130

[3] Burdett N A. The effects of air staging on NO_x emissions from a 500 MW_e down-fired boiler. Journal of the Institute of Energy, 1987, 60(444): 103–107

[4] Luo Z X, Wang F, Zhou H C, Liu R T, Li W C, Chang G Z. Principles of optimization of combustion by radiant energy signal and its application in a 660 MW_e down- and coal-fired boiler. Korean Journal of Chemical Engineering, 2011, 28(12): 2336–2343

[5] Cahill P, Beeley T J, O’Connor M, Spence J, Gibbins J R, Man C K. The assessment of low volatile fuels for downshot fired boilers. In: Proceedings of the 10th International Conference on Coal Science, Taiyuan, China, 1999

[6] Achim D, Naser J, Morsi Y S, Pascoe S. Numerical investigation of full scale coal combustion model of tangentially fired boiler with the effect of mill ducting. Heat and Mass Transfer, 2009, 46(1): 1–13

[7] Wei Y H, Kuang M, Zhu Q Y, Ling Z Q, Ti S G, Li Z Q. Alleviating gas/particle flow deflection and asymmetric combustion in a 600 MW_e supercritical down-fired boiler by expanding its furnace throat space. Applied Thermal Engineering, 2017, 123: 1201–1213

[8] Otero P, González J F, Rodríguez F, Caéadas L, Cortñs V. NO_x reduction in arch-fired boilers by parametric tuning of operating conditions. In: Proceedings of the Electric Power Research Institute (EPRI) / Environmental Protection Agency (EPA) Mega symposium, Washington D.C., USA, 1997

[9] Wang Q X, Chen Z C, Han H, Zeng L Y, Li Z Q. Experimental characterization of anthracite combustion and NO_x emission for a 300-MW_e down-fired boiler with a novel combustion system: influence of primary and vent air distributions. Applied Energy, 2019, 238: 1551–1562

[10] Song M H, Zeng L Y, Li X G, Liu Y B, Chen Z C, Li Z Q. Effects of tertiary air damper opening on flow, combustion and hopper near-wall temperature of a 600 MW_e down-fired boiler with improved multiple-injection multiple-staging technology. Journal of the Energy Institute, 2018, 91(4): 573–583

[11] Ministry of Environmental Protection of the People’s Republic of China. Emission Standard of Air Pollutants for Boiler (GB13271–2014). Beijing: China Environmental Science Press, 2014 (in Chinese)

[12] Liu G K, Li Z Q, Chen Z C,Zhu X Y, Zhu Q Y. Effect of the anthracite ratio of blended coals on the combustion and NO_x emission characteristics of a retrofitted down-fired 660-MW_e utility boiler. Applied Energy, 2012, 95: 196–201

[13] Song M H, Zeng L Y, Yang X C, Chen Z C, Li Z Q. Influence of the mass ratio of pulverized-coal in fuel-rich flow to that in fuel-lean flow on the gas/particle flow and particle distribution characteristics in a 600 MW_e down-fired boiler. Experimental Thermal and Fluid Science, 2018, 91: 363–373

[14] Plumed A, Cañadas L, Otero P, Espada M I, Castro M, Gonzálcz J F, Rodríguez F. Primary measures for reduction of NO_x in low volatile coals combustion. Coal Science and Technology, 1995, 24: 1783–1786

[15] Li Z Q, Kuang M, Zhu Q Y, Lai J P, Zhang Y. Aerodynamic characteristics within a cold small-scale model for a downfired 350 MW_e utility boiler applying a multiple-injection and multiple-staging technology: effect of the staged-air declination angle. Experimental Thermal and Fluid Science, 2012, 38: 184–194

[16] Song M H, Zeng L Y, Chen Z C, Li Z Q, Zhu Q Y, Kuang M. Industrial application of an improved multiple injection and multiple staging combustion technology in a 600 MW_e supercritical down-fired boiler. Environmental Science & Technology, 2016, 50(3): 1604–1610

[17] Zhao Y L, Wang C Y, Liu M, Chong D T, Yan J J. Improving operational flexibility by regulating extraction steam of high-pressure heaters on a 660 MW supercritical coal-fired power plant: a dynamic simulation. Applied Energy, 2018, 212: 1295–1309

[18] Dong J C, Fan H J, Wu X J, Zhou T, Zhang J, Zhang Z X. Study on the effect of flame offset on water wall tube temperature in 600°C and 700°C ultra-supercritical boiler. Combustion Science and Technology, 2019, 191(3): 472–490

[19] Zima W. Simulation of rapid increase in the steam mass flow rate at a supercritical power boiler outlet. Energy, 2019, 173: 995–1005

[20] Kuang M, Li Z Q, Ling Z Q, Chen Z F, Yuan D Y. Characterization of coal combustion and steam temperature with respect to staged-air angle in a 600 MW_e down-fired boiler. Energy & Fuels, 2014, 28(6): 4199–4205

[21] Li Z Q, Ren F, Liu G K, Shen S P, Chen Z C. Influence of angled secondary air on combustion characteristics of a 660-MW_e down-fired utility boiler. Combustion Science and Technology, 2010, 183(3): 238–251

[22] Fang Q Y, Wang H J, Zhou H C, Lei L, Duan X L. Improving the performance of a 300 MW down-fired pulverized-coal utility boiler by inclining downward the F-layer secondary air. Energy & Fuels, 2010, 24(9): 4857–4865

[23] Liang L, Hui S E, Zhao S, Zhou Q L, Xu T M, Zhao Q X. Cold modeling investigation of aerodynamic characteristics of an arch-fired boiler on particle image velocimetry (PIV): influence of momentum flux ratio of arch air to secondary air and secondary air angle. Experimental Thermal and Fluid Science, 2012, 42: 240–247

[24] Fan Q G. Subcritical and Supercritical Boiler. Beijing: China Electric Power Press, 2000 (in Chinese)

[25] Wang X H. Discussion on water wall cracking of supercritical down-fired boiler. Hunan Electric Power, 2012, 32(1): 48–52 (in Chinese)

RIGHTS & PERMISSIONS

Higher Education Press