Experimental study on ignition and combustion of pulverized coal particles clouds under laminar and turbulent conditions
-
摘要: 利用Hencken型平面火焰燃烧器搭建携带流反应系统，研究了不同湍流强度下煤粉颗粒群的着火及燃烧特性。煤粉被一次风送入温度、氧含量（本文所称"氧含量"是指氧的摩尔分数，mole fraction）可调节的高温烟气中形成稳定的射流火焰，利用OH平面激光诱导荧光技术（OH-Planar Laser-Induced Fluorescence，OH-PLIF）观测煤粉射流火焰着火、群燃等阶段的瞬态结构，基于对火焰图像的处理探究煤粉颗粒群的着火及燃烧特性。OH-PLIF的测量结果表明，在煤粉射流火焰的上游，射流外围区域的煤粉首先发生脱挥发分并着火，外围已燃的煤粉释放出大量热量并不断向射流内部传递，促进了射流内部区域煤粉颗粒群挥发分的析出。在高速一次风的卷吸及扰动作用下，析出的挥发分与氧之间不断扩散、混合，燃烧的OH锋面逐渐向射流中心区域延伸并连接成片，出现挥发分群燃火焰。实验结果表明：层流状态下，煤粉射流火焰窄而明亮；随着一次风湍流强度的增强，射流中煤粉颗粒的扩散运动变得剧烈，火焰形态发生变化，着火距离显著缩短。本文定量地研究了不同湍流强度下背景烟气温度（1200~1700 K）、烟气氧含量（10%~30%）以及一次风氧含量（5%~45%）对煤粉颗粒群着火延迟的影响规律。随着背景烟气温度、送风氧含量的升高，着火延迟时间逐渐缩短，但存在阈值现象，一旦背景烟气温度或送风氧含量超出某一阈值，其对煤粉颗粒群着火延迟的影响变弱，控制煤粉颗粒群着火行为的主导因素随之发生改变。Abstract: The ignition and combustion behaviors of pulverized coal particles clouds in a jet with different levels of turbulence and primary O2 mole fractions were evaluated in a lab-scale optical entrained flow reactor. Bituminous particles were injected into the hot flue gas environment produced by a Hencken burner, with environment temperatures varying from 1200 K to 1700 K and secondary O2 mole fractions from 0.1 to 0.3. Digital photography and OH-Planar Laser-Induced Fluorescence (OH-PLIF) techniques were employed to record the coal jet flame behaviors and capture the transient structure of the flame. The coal jet flame was narrow and smooth under laminar conditions, and become wider as the turbulent intensity of the primary flow increased. The OH-PLIF data reveals that upstream of the turbulent coal jet flame, reactions occur only at the periphery of the clusters of the pulverized coal particles where the high-temperature environment provides sufficient heat and oxygen. Downstream of the turbulent coal jet flame, reactions could occur also within the clusters of the pulverized coal particles, because of the continuous coal devolatilization process along the streams, and the mixing process between the volatiles and the oxygen entrained by the secondary flow. The ignition delay time is reduced and the combustion intensity is enhanced with the increase of the environment temperature and O2 mole fraction in the primary or secondary flow. The frontal OH edge expands inward to the centerline of the clusters of the pulverized coal particles with the increase of the primary O2 mole fraction. In addition, the effects of the environmental temperature and O2 mole fraction on the ignition of pulverized coal particles clouds exhibit a threshold phenomenon. Once the environment temperature or the O2 mole fraction exceeds a certain threshold, its influence on the ignition delay of the coal jet becomes weaker and the leading factors controlling the ignition behavior of the pulverized coal particle clouds change accordingly.
-
Key words:
- pulverized coal particles clouds /
- ignition /
- combustion /
- turbulent flow /
- OH-PLIF
-
图 2 典型工况下燃烧器上方的轴向温度分布
Figure 2. The axial temperature distribution above the Hencken burner
图 4 湍流射流火焰的OH瞬态分布图和数码相机拍摄的火焰图像
Figure 4. Transient distribution of OH in the turbulent coal jet flames and typical image of flames captured by digital camera
图 6 煤粉颗粒群着火距离及延迟时间随背景烟气温度的变化
Figure 6. The ignition distance and delay time of pulverized coal particles clouds for various surrounding temperatures
图 8 不同一次风氧含量下射流火焰内部的OH瞬态分布图
Figure 8. Transient distribution of OH in the flames for various mole fractions of primary O2
图 9 煤粉颗粒群着火距离及延迟时间随一次风氧含量的变化
Figure 9. The ignition distance and delay time of pulverized coal particles clouds for various mole fractions of primary O2
图 10 背景烟气不同氧含量工况下的射流火焰图像
Figure 10. Flame images for various mole fractions of surrounding O2
图 11 煤粉颗粒群着火距离及延迟时间随背景烟气氧含量的变化
Figure 11. The ignition distance and delay time of pulverized coal particles clouds for various mole fractions of surrounding O2
表 1 煤种的工业分析和元素分析数据
Table 1. Proximate and ultimate analysis of coal sample
Items Values Proximate analysis
(wt %, dry basis)Volatile 33.39 Ash 11.95 Fixed carbon 54.66 Ultimate analysis
(wt %, dry ash free basis)Carbon 81.75 Hydrogen 4.31 Nitrogen 0.92 Sulfur 0.49 Oxygen 12.53 
下载: 导出CSV
-
[1] 国家统计局.中华人民共和国2019年国民经济和社会发展统计公报[R]. 2020.National Bureau of Statistics. Statistical communique of the people's republic of China on the 2019 national economic and social development[R]. 2020. [2] LEVENDIS Y A, JOSHI K, KHATAMI R, et al. Combustion behavior in air of single particles from three different coal ranks and from sugarcane bagasse[J]. Combustion and Flame, 2011, 158(3):452-465. http://www.wanfangdata.com.cn/details/detail.do?_type=perio&id=0c06523b0f86732423ce89f8e1a85fc6 [3] KHATAMI R, STIVERS C, LEVENDIS Y A. Ignition characteristics of single coal particles from three different ranks in O2/N2 and O2/CO2 atmospheres[J]. Combustion and Flame, 2012, 159(12):3554-3568. doi: 10.1016/j.combustflame.2012.06.019 [4] KHATAMI R, LEVENDIS Y A. An overview of coal rank influence on ignition and combustion phenomena at the particle level[J]. Combustion and Flame, 2016, 164:22-34. doi: 10.1016/j.combustflame.2015.10.031 [5] LIU Y H, GEIER M, MOLINA A, et al. Pulverized coal stream ignition delay under conventional and oxy-fuel combustion conditions[J]. International Journal of Greenhouse Gas Control, 2011, 5(s1):36-46. http://d.old.wanfangdata.com.cn/NSTLQK/NSTL_QKJJ0223662666/ [6] TANIGUCHI M, OKAZAKI H, KOBAYASHI H, et al. Pyrolysis and ignition characteristics of pulverized coal particles[J]. Journal of Energy Resources Technology, 2001, 123(1):32-38. doi: 10.1115/1.1347989 [7] MOLINA A, SHADDIX C R. Ignition and devolatilization of pulverized bituminous coal particles during oxygen/carbon dioxide coal combustion[J]. Proceedings of the Combustion Institute, 2007, 31(2):1905-1912. doi: 10.1016/j.proci.2006.08.102 [8] SHADDIX C R, MOLINA A. Particle imaging of ignition and devolatilization of pulverized coal during oxy-fuel combustion[J]. Proceedings of the Combustion Institute, 2009, 32(2):2091-2098. doi: 10.1016/j.proci.2008.06.157 [9] SUDA T, MASUKO K, SATO J, et al. Effect of carbon dioxide on flame propagation of pulverized coal clouds in CO2/O2 combustion[J]. Fuel, 2007, 86(12-13):2008-2015. doi: 10.1016/j.fuel.2006.11.038 [10] YUAN Y, LI S Q, LI G D, et al. The transition of heterogeneous-homogeneous ignitions of dispersed coal particle streams[J]. Combustion and Flame, 2014, 161(9):2458-2468. doi: 10.1016/j.combustflame.2014.03.008 [11] BALUSAMY S, KAMAL M M, LOWE S M, et al. Laser diagnostics of pulverized coal combustion in O2/N2 and O2/CO2 conditions:velocity and scalar field measurements[J]. Experiments in Fluids, 2015, 56(5):108. doi: 10.1007/s00348-015-1965-z [12] BALUSAMY S, SCHMIDT A, HOCHGREB S. Flow field measurements of pulverized coal combustion using optical diagnostic techniques[J]. Experiments in Fluids, 2013, 54(5):1534. doi: 10.1007/s00348-013-1534-2 [13] HAYASHI J, HASHIMOTO N, NAKATSUKA N, et al. Soot formation characteristics in a lab-scale turbulent pulverized coal flame with simultaneous planar measurements of laser induced incandescence of soot and Mie scattering of pulverized coal[J]. Proceedings of the Combustion Institute, 2013, 34(2):2435-2443. doi: 10.1016/j.proci.2012.10.002 [14] HAYASHI J, HASHIMOTO N, NAKATSUKA N, et al. Simultaneous imaging of Mie scattering, PAHs laser induced fluorescence and soot laser induced incandescence to a lab-scale turbulent jet pulverized coal flame[J]. Proceedings of the Combustion Institute, 2019, 37(3):3045-3052. doi: 10.1016/j.proci.2018.09.028 [15] HWANG S M, KUROSE R, AKAMATSU F, et al. Application of optical diagnostics techniques to a laboratory-scale turbulent pulverized coal flame[J]. Energy & Fuels, 2005, 19(2):382-392. doi: 10.1021/ef049867z [16] SUNG Y, LEE S, EOM S, et al. Optical non-intrusive measurements of internal recirculation zone of pulverized coal swirling flames with secondary swirl intensity[J]. Energy, 2016, 103:61-74. doi: 10.1016/j.energy.2015.12.095 [17] SUNG Y M, MOON C E, KIM J R, et al. Influence of pulverized coal properties on heat release region in turbulent jet pulverized coal flames[J]. Experimental Thermal and Fluid Science, 2011, 35(4):694-699. doi: 10.1016/j.expthermflusci.2011.01.003 [18] XU K L, WU Y X, WANG Z N, et al. Experimental study on ignition behavior of pulverized coal particle clouds in a turbulent jet[J]. Fuel, 2016, 167:218-225. doi: 10.1016/j.fuel.2015.11.027 [19] 许开龙, 俞伟伟, 吴玉新, 等.一次风速度对煤颗粒群着火特性影响的实验研究[J].燃烧科学与技术, 2014, 20(4):313-318. http://d.old.wanfangdata.com.cn/Periodical/rskxyjs201404006XU K L, YU W W, WU Y X, et al. Experimental study on effects of primary flow velocity on ignition of coal particles[J]. Journal of Combustion Science and Technology, 2014, 20(4):313-318. http://d.old.wanfangdata.com.cn/Periodical/rskxyjs201404006 [20] 许开龙, 俞伟伟, 吴玉新, 等.一次风氧浓度对煤颗粒群着火特性影响的实验研究[J].工程热物理学报, 2013, 34(10):1964-1968. http://www.wanfangdata.com.cn/details/detail.do?_type=perio&id=gcrwlxb201310040XU K L, YU W W, WU Y X, et al. Effects of primary flow oxygen concentration on ignition of group coal particles[J]. Journal of Engineering Thermophysics, 2013, 34(10):1964-1968. http://www.wanfangdata.com.cn/details/detail.do?_type=perio&id=gcrwlxb201310040 [21] 俞伟伟, 吴玉新, 许开龙, 等.湍流条件下煤粉颗粒群着火特性实验研究[J].工程热物理学报, 2016, 37(2):443-447. http://www.wanfangdata.com.cn/details/detail.do?_type=perio&id=gcrwlxb201602045YU W W, WU Y X, XU K L, et al. Experimental investigation on characteristics of coal particle stream ignition under turbulent condition[J]. Journal of Engineering Thermophysics, 2016, 37(2):443-447. http://www.wanfangdata.com.cn/details/detail.do?_type=perio&id=gcrwlxb201602045 -
点击查看大图
计量
- 文章访问数: 293
- HTML全文浏览量: 188
- PDF下载量: 27
- 被引次数: 0
