Flow Characteristics of Dense Phase Pneumatic Conveying of Pulverized Coal through the Bend
-
摘要: 在自主搭建的工业级管径(内径50 mm)气力输送实验平台上开展了密相气力输送实验,对气固两相通过弯管的流动特性进行了研究。借助电容层析成像技术分析弯管出口截面流型特征,发现煤粉流经弯管时管道截面浓度存在明显的径向分布,外壁浓度相对较高。采用附加压降法,并结合对实验数据的回归分析,建立了精度±10%以内弯管压降模型。并基于微元分析和弯管压降分布的基本规律,获得了煤粉浓度沿弯管流动方向的分布特征。Abstract: Experiments on dense phase pneumatic conveying of pulverized coal were carried out in the self-built pneumatic conveying facility with an industrial pipe diameter of 50 mm. The gas-solid two-phase flow characteristics through the bend were studied. With the help of Enick and Klinzing model, the entrance length of gas-solid two-phase flow in a bend outlet was calculated. It was found that the fluid flow to the electrical capacitance tomography (ECT) was not fully developed, and the fluid was affected by the bend. The flow patterns of the outlet section of the bend were analyzed in the means of ECT, and it was found that the flow pattern changed from the packed bed flow to the unstable/stable plug flow with the increase of the superficial gas velocity. Due to the influence of inertial force and centrifugal force, there was an obvious radial distribution in the concentration of the pipe section when the pulverized coal flowed through the bend, while the coal concentration on lateral wall surface was relatively high. Regression analysis of experimental data was carried out using pressure drop model and dimensional analysis method, a pressure drop model of pulverized coal dense phase pneumatic conveying bend was established by providing errors most smaller than ±10%. Finally, based on micro element analysis and pressure drop distribution along the bend, the distribution characteristics of pulverized coal concentration along the bend were obtained. This work may provide important guiding significance in reducing the wear of bend.
-
Key words:
- dense phase pneumatic conveying /
- bend /
- flow pattern /
- concentration /
- pressure drop
-
表 1 煤粉的物料性质
Table 1. Material properties of pulverized coal
dv/μm ds/μm d10/μm d50/μm d90/μm ρp/(kg·m−3) Moisture mass
fraction/%40.30 4.83 2.07 17.42 115.30 1627.50 1.15 表 2 实验工况表
Table 2. Experimental condition
Case Q2/(m3·h−1) Q3/(m3·h−1) Ws/(kg·h−1) pT/kPa Ug/(m·s−1) ∆p1/kPa $ \dfrac{{\Delta {p_2}}}{{{L}}}$/(kPa·m−1) p/kPa μ/(kg·kg−1) 1 15.75 0 4659.85 68.22 1.09 10.21 5.64 39.79 328.23 2 16.34 5.73 4161.88 62.15 1.76 8.61 3.90 49.65 170.14 3 16.07 16.41 3980.70 91.63 2.20 7.30 2.94 79.34 110.92 表 3 Le计算表
Table 3. Calculation of Le
Case Ug/(m·s−1) ρg/(kg·m−3) Re Le/mm 1 1.09 1.80 5480.45 2506.37 2 1.76 1.93 9488.27 1731.07 3 2.20 2.31 14195.53 1115.49 -
[1] 马胜, 郭晓镭, 龚欣, 等. 粉煤密相气力输送流型[J]. 化工学报, 2010, 61(6): 1415-1421. [2] MOLERUS O. Overview: Pneumatic transport of solids[J]. Powder Technology, 1996, 88(3): 309-321. doi: 10.1016/S0032-5910(96)03136-1 [3] 李君, 卢洪, 郭屹, 等. 煤粉加压密相输送系统研究现状及发展方向[J]. 洁净煤技术, 2015, 21(4): 5-11. [4] 谢锴, 郭晓镭, 丛星亮, 等. 工业级水平管粉煤气力输送的最小压降速度和稳定性[J]. 化工学报, 2013, 64(6): 1969-1975. doi: 10.3969/j.issn.0438-1157.2013.06.010 [5] 代婧鑫, 丁学勇, 许海法, 等. 弯管中高浓度煤粉气力输送流动特性的模拟[J]. 钢铁研究学报, 2020, 32(5): 377-385. [6] 贺春辉, 沈湘林, 周海军. 煤粉高压密相气力输送稳定性分析[J]. 化工学报, 2014, 65(3): 820-828. doi: 10.3969/j.issn.0438-1157.2014.03.008 [7] 周云, 陈晓平, 梁财, 等. 高压密相气力输送垂直弯管阻力特性[J]. 化工学报, 2009, 60(3): 580-584. doi: 10.3321/j.issn:0438-1157.2009.03.007 [8] 杨石, 刘振宇, 王永英, 等. 稀相气力输送水平弯管与文丘里管气固流动特性[J]. 中国粉体技术, 2019, 25(1): 40-45. [9] 周云, 陈晓平, 梁财, 等. 高压密相气力输送弯管压降研究[J]. 中国电机工程学报, 2009, 29(2): 8-12. doi: 10.3321/j.issn:0258-8013.2009.02.002 [10] 周靖. 水平弯管密相输送数值研究[J]. 冶金动力, 2019(10): 16-18. [11] CHU K W, YU A B. Numerical simulation of the gas-solid flow in three-dimensional pneumatic conveying bends[J]. Industrial & Engineering Chemistry Research, 2008, 47(18): 7058-7071. [12] 丛星亮. 粉煤密相气力输送的流型与管线内压力信号关系的研究[D]. 上海: 华东理工大学, 2013. [13] 杨道业, 周宾, 王式民. 电容层析成像在高压浓相煤粉气力输送中的应用[J]. 化工学报, 2009, 60(4): 892-897. doi: 10.3321/j.issn:0438-1157.2009.04.012 [14] JIN Y, LU H, GUO X, et al. Multiscale analysis of flow patterns in the dense phase pneumatic conveying of pulverized coal[J]. AIChE Journal, 2019, 65(9): e16674. [15] ENICK R M, KLINZING G E. A correlation for the acceleration length in vertical gas-solid transport[J]. Chemical Engineering Communications, 1986(49): 127-131. [16] TSUJI Y, MORIKAWA Y. Flow pattern and pressure fluctuation in air-solid two-phase flow in a pipe at low air velocities[J]. International Journal of Multiphase Flow, 1982, 8(4): 329-341. doi: 10.1016/0301-9322(82)90046-5 [17] JAMA G A, KLINZING G E, RIZK F. An investigation of the prevailing flow patterns and pressure fluctuation near the pressure minimum and unstable conveying zone of pneumatic transport systems[J]. Powder Technology, 2000, 112(1/2): 87-93. doi: 10.1016/S0032-5910(99)00309-5 [18] GUINEY P, PAN R, CHAMBERS J. Scale-up technology in low-velocity slug-flow pneumatic conveying[J]. Powder Technology, 2002, 122(1): 34-45. doi: 10.1016/S0032-5910(01)00392-8 [19] 程克勤. 低速密相气力输送综述[J]. 硫磷设计与粉体工程, 2001(2): 22-25. [20] YILMAZ A, LEVY E K. Formation and dispersion of ropes in pneumatic conveying[J]. Powder Technology, 2001, 114(1/3): 168-185. doi: 10.1016/S0032-5910(00)00319-3 [21] 郭晓镭, 陆海峰, 陶顺龙, 等. 竖直上升管的煤粉密相气力输送阻力特性的实验研究[J]. 华东理工大学学报(自然科学版), 2014, 40(1): 16-20. doi: 10.3969/j.issn.1006-3080.2014.01.003 [22] 郭晓镭, 龚欣, 代正华, 等. 竖直上升管中密相气力输送压降特性[J]. 化工学报, 2007, 58(3): 602-607. doi: 10.3321/j.issn:0438-1157.2007.03.012 [23] 陈先梅, 春辉, 胥宇鹏, 等. CO2/N2高压密相输送弯管压降特性实验研究[J]. 西安交通大学学报, 2012, 46(9): 83-90. [24] 王秀娟, 李灿. 室内细颗粒物碰撞模型及碰撞结果讨论[J]. 应用数学和力学, 2016, 37(7): 766-774. [25] 谢锴. 工业级粉煤密相气力输送系统特性研究[D]. 上海: 华东理工大学, 2013. [26] NAVEEN M T, DMITRY P, AVI L, et al. Bend pressure drop in horizontal and vertical dilute phase pneumatic conveying systems[J]. Chemical Engineering Science, 2019, 209: 115228. doi: 10.1016/j.ces.2019.115228 [27] 蔡海峰, 熊源泉, 周海军. 水平弯管高压密相气力输送数值模拟[J]. 东南大学学报(自然科学版), 2019, 49(1): 157-166. -