An experimental study on ignition of single coal particles at low oxygen concentrations

Abstract

An experimental study on the ignition of single coal particles at low oxygen concentrations (X_{{\mathrm{O}}_2}<21%) was conducted using a tube furnace. The surface temperature (T_s) and the center temperature (T_c) of the coal particles were obtained from the images taken by an infrared camera and thermocouples respectively. The ignition processes were recorded by a high-speed camera at different X_{{\mathrm{O}}_2} values and furnace temperatures T_w. Compared with literature experimental data obtained at a high X_{{\mathrm{O}}_2} value, the ignition delay time t_i decreases more rapidly as X_{{\mathrm{O}}_2} increases at the low X_{{\mathrm{O}}_2} region. The responses of T_s and T_c to the variation of X_{{\mathrm{O}}_2} are different: T_s decreases while T_c remains nearly constant with increasing X_{{\mathrm{O}}_2} at a low X_{{\mathrm{O}}_2} value. In addition, t_i is less sensitive to T_w while the ignition temperature T_i is more sensitive to T_w at a low X_{{\mathrm{O}}_2} value than in air. Observations of the position of flame front evolution illustrate that the ignition of a coal particle may change from a homogeneous mode to a heterogeneous or combined ignition mode as X_{{\mathrm{O}}_2} decreases. At a low X_{{\mathrm{O}}_2} value, buoyancy plays a more significant role in sweeping away the released volatiles during the ignition process.

Graphical abstract

Keywords

coal particles / low oxygen concentration / ignition / ignition temperature / ignition modes

References

[1] Lille S, Blasiak W, Jewartowski M. Experimental study of the fuel jet combustion in high temperature and low oxygen content exhaust gases. Energy, 2005, 30(2–4): 373–384

[2] Stadler H, Ristic D, Förster M, Schuster A, Kneer R, Scheffknecht G. NO_x-emissions from flameless coal combustion in air, Ar/O₂ and CO₂/O₂. Proceedings of the Combustion Institute, 2009, 32(2): 3131–3138

[3] Li P, Wang F, Tu Y, Mei Z, Zhang J, Zheng Y, Liu H, Liu Z, Mi J, Zheng C. Moderate or intense low-oxygen dilution oxy-combustion characteristics of light oil and pulverized coal in a pilot-scale furnace. Energy & Fuels, 2014, 28(2): 1524–1535

[4] Yue G, Cai R, Lu J, Zhang H. From a CFB reactor to a CFB boiler–the review of R&D progress of CFB coal combustion technology in China. Powder Technology, 2017, 316(1): 18–28

[5] Essenhigh R H, Misra M K, Shaw D W. Ignition of coal particles: a review. Combustion and Flame, 1989, 77(1): 3–30

[6] Buhre B J, Elliott L K, Sheng C D, Gupta R P, Wall T F. Oxy-fuel combustion technology for coal-fired power generation. Progress in Energy and Combustion Science, 2005, 31(4): 283–307

[7] Qiao Y, Zhang L, Binner E, Xu M, Li C Z. An investigation of the causes of the difference in coal particle ignition temperature between combustion in air and in O/CO. Fuel, 2010, 89(11): 3381–3387

[8] Shaddix C R, Molina A. Particle imaging of ignition and devolatilization of pulverized coal during oxy-fuel combustion. Proceedings of the Combustion Institute, 2009, 32(2): 2091–2098

[9] Farazi S, Attili A, Kang S, Pitsch H. Numerical study of coal particle ignition in air and oxy-atmosphere. Proceedings of the Combustion Institute, 2019, 37(3): 2867–2874

[10] Du X, Annamalai K. The transient ignition of isolated coal particle. Combustion and Flame, 1994, 97(3–4): 339–354

[11] Liu Y, Wang C, Che D. Ignition and kinetics analysis of coal combustion in low oxygen concentration. Energy Sources. Part A, Recovery, Utilization, and Environmental Effects, 2012, 34(9): 810–819

[12] Zhou K, Lin Q, Hu H, Hu H, Song L. The ignition characteristics and combustion processes of the single coal slime particle under different hot-coflow conditions in N₂/O₂ atmosphere. Energy, 2017, 136: 173–184

[13] Annamalai K, Durbetaki P. A theory on transition of ignition phase of coal particles. Combustion and Flame, 1977, 29(2): 193–208

[14] Liu B, Zhang Z, Zhang H, Zhang D. Volatile release and ignition behaviors of single coal particles at different oxygen concentrations under microgravity. Microgravity Science and Technology, 2016, 28(2): 101–108

[15] Liu B, Zhang Z, Zhang H, Yang H, Zhang D. An experimental investigation on the effect of convection on the ignition behaviour of single coal particles under various O₂ concentrations. Fuel, 2014, 116: 77–83

[16] Goshayeshi B, Sutherland J C. A comparison of various models in predicting ignition delay in single-particle coal combustion. Combustion and Flame, 2014, 161(7): 1900–1910

[17] Ponzio A, Senthoorselvan S, Yang W, Blasiak W, Eriksson O. Ignition of single coal particles in high-temperature oxidizers with various oxygen concentrations. Fuel, 2008, 87(6): 974–987

[18] Gat N, Cohen L M, Witte A. Three-color pyrometer for burning particle temperature measurement. In: JANNAF Combust Meeting, Monterrey, 1983

[19] Fletcher T H. Time-resolved temperature measurements of individual coal particles during devolatilization. Combustion Science and Technology, 1989, 63(1): 89–105

[20] Zhu M, Zhang H, Tang G, Liu Q, Lu J, Yue G, Wang S, Wan S. 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

[21] Bhattacharya S P, Wall T F. Development of emittance of coal particles during devolatilisation and burnoff. Fuel, 1999, 78(5): 511–519

[22] Fu T, Tan P, Pang C, Zhao H, Shen Y. Fast fiber-optic multi-wavelength pyrometer. Review of Scientific Instruments, 2011, 82(6): 064902

[23] Tichenor D A, Mitchell R E, Hencken K R, Niksa S. Simultaneous in situ measurement of the size, temperature and velocity of particles in a combustion environment. Proceedings of the Combustion Institute, 1985, 20(1): 1213–1221

[24] Jiang X, Wang C, Bi H, Jiang C, Liu Y, Song Z, Lin Q. Experimental investigation on combustion and gas emission of scrap tire pellet under various concentrations of CO₂/O₂ mixtures. Combustion Science & Technology, Online (Bergheim)

[25] Bu C, Leckner B, Chen X, Pallarès D, Liu D, Gómez-Barea A. Devolatilization of a single fuel particle in a fluidized bed under oxy-combustion conditions. Part A: Experimental results. Combustion and Flame, 2015, 162(3): 797–808

[26] Zhang M, Yu J, Xu X. A new flame sheet model to reflect the influence of the oxidation of CO on the combustion of a carbon particle. Combustion and Flame, 2005, 143(3): 150–158

[27] Zhou K, Lin Q, Hu H, Shan F, Fu W, Zhang P, Wang X, Wang C. Ignition and combustion behaviors of single coal slime particles in CO₂/O₂ atmosphere. Combustion and Flame, 2018, 194: 250–263

Acknowledgment

This work was supported by the National Natural Science Foundation of China (Grant No. 11872231).

RIGHTS & PERMISSIONS

2020 Higher Education Press