放大准则对混合澄清槽混合室中混合时间和流动特性的影响

doi:10.11949/j.issn.0438-1157.20151143

摘要/Abstract

摘要：

工业混合澄清槽混合室的放大设计多基于操作经验,缺乏理论基础。基于几何相似放大,采用计算流体力学(CFD)方法,针对间歇操作的单相体系,对4 种不同放大准则下混合室内混合时间和流场特性的变化规律进行研究。结果显示,混合时间的计算值与测量位置有关,但随转速的增加受测量位置的影响减小;充分湍流条件下,本研究体系的功率准数趋于常数N_P=1.3,且几何相似放大可以保证混合室中轴向流动的流型特征;等桨叶端面速度和等Reynolds 数准则下,所需混合时间长,且抽吸压头小;等循环时间准则下,可以得到与基准混合室相同的混合时间和较高的抽吸压头,但单位体积功耗急剧增加到基准槽的24 倍;等单位体积功耗准则下,在满足具有较低的混合时间和较高的抽吸压头的同时还保证了较低的单位体积功耗,优于其他3 种放大准则。

关键词: 放大, 混合, 计算流体力学, 混合室, 混合时间

Abstract:

The scale-up of the industrial mixer is always based on operation experience, and lacks theoretical basis. In this paper, effects of scale-up criteria on the mixing time and flow characteristic in the intermittent pump-mixer with single-phase has been studied. Three-dimensional time-dependent mixing prediction has been carried out using multi reference frames (MRF) method and standard k-ε model embodied by computational fluid dynamics (CFD) package FLUENT6.3. The results indicated that the calculated mixing time was depended on detecting location, but the dependency became weaker by increasing the impeller speed. The power number was obtained at different Reynolds number, and it tended to be a constant as 1.3 under the condition of sufficient turbulence. Geometric similarity ensured the axial flow characteristics in the mixer. The criterion of equal impeller tip speed and equal Reynolds number demanded a longer mixing time and obtained a lower suction pressure head than the benchmark mixer. The criterion of equal circulation time and geometrical similarity could obtain the same mixing time as the benchmark and high suction pressure head, but the power consumption per unit volume sharply increased to 24 times as the benchmark. The criterion of equal power consumption per unit volume and geometrical similarity could obtain a better balance of all the parameters considered, and was considered to be the best one compared with other three criteria.

Key words: scale-up, mixing, CFD, pump-mix mixer, mixing time

中图分类号:

TQ028.8

唐巧, 叶思施, 王运东. 放大准则对混合澄清槽混合室中混合时间和流动特性的影响[J]. 化工学报, 2016, 67(2): 448-457.

TANG Qiao, YE Sishi, WANG Yundong. Mixing time and flow characteristic in square pump-mix mixer under different scale-up criteria[J]. CIESC Journal, 2016, 67(2): 448-457.

参考文献 27

[1]	张庆华, 毛在砂, 杨超. 搅拌反应器中液相混合时间研究进展[J]. 化工进展, 2008, 27(10):1544-1550. ZHANG Q H, MAO Z S, YANG C. Research progress of liquid-phase mixing time in stirred tanks[J]. Chemical Industry and Engineering Progress, 2008, 27(10):1544-1550.
[2]	BUJALSKI W, JAWORSKI Z, NIENOW A W. CFD study of homogenization with dual Rushton turbines-comparison with experimental results(Ⅰ):Initial studies[J]. Chem. Eng. Res. Des., 2000, 78(3):327-333.
[3]	BUJALSKI W, JAWORSKI Z, NIENOW A W. CFD study of homogenization with dual Rushton turbines-comparison with experimental results(Ⅱ):The multiple reference frame[J]. Chem. Eng. Res. Des., 2002, 80(1):97-104.
[4]	施力田, 高正明, 闵健. 双层涡轮桨搅拌反应器内混合时间的大涡模拟[J]. 化工学报, 2010, 61(7):1747-1752. SHI L T, GAO Z M, MIN J. Large eddy simulation for mixing time in stirred tank with dual Rushton turbines[J]. CIESC Journal, 2010, 61(7):1747-1752.
[5]	周国忠, 王英琛, 施力田. 用CFD研究搅拌槽内的混合过程[J]. 化工学报, 2003, 54(7):886-890. ZHOU G Z, WANG Y C, SHI L T. CFD study of mixing process in stirred tank[J]. Journal of Chemical Industry and Engineering(China), 2003, 54(7):886-890.
[6]	ZHAGN Q H, YANG C, MAO Z S, et al. Large eddy simulation of turbulent flow and mixing time in a gas-liquid stirred tank[J]. Ind. Eng. Chem. Res., 2012, 51:10124-10131.
[7]	SHARMA A, WAN S B, PAREEK V, et al. CFD modeling of mixing/segregation behavior of biomass and biochar particles in a bubbling fluidized bed[J]. Chem. Eng. Sci., 2014, 106:264-274.
[8]	齐娜娜, 吴桂英, 王卉, 等. 半圆管曲面涡轮搅拌槽内混合特性的数值模拟[J]. 化工学报, 2010, 61(9):2305-2313. QI N N, WU G Y, WANG H, et al. CFD simulation of mixing characteristics in stirred tank by Smith turbine[J]. CIESC Journal, 2010, 61(9):2305-2313
[9]	逄启寿, 邓华军. 三层桨搅拌槽内三维流场的数值模拟[J]. 有色金属(冶炼部分), 2012, 7:40-43. FENG Q S, DENG H J. Numerical simulation of three-dimensional flow fields generated by three-layer blades in a agitation tank[J]. Nonferrous Metals(Extractive Metallurgy), 2012, 7:40-43.
[10]	赵秋月, 张廷安, 刘燕, 等. 搅拌对箱式混合澄清槽流动性能的影响[J]. 东北大学学报(自然科学版), 2012, 33(4):559-562. ZHAO Q Y, ZHANG T A, LIU Y, et al. Effect of stirring on flow characteristic of box-type mixing/clarifying tank[J]. Journal of Northeastern University (Natural Science), 2012, 33(4):559-562.
[11]	SHABANI M O, MAZAHERY A, ALIZADEH M, et al. Computational fluid dynamics (CFD) simulation of effect of baffles on separation in mixer settler[J]. Inter. J. Min. Sci. Tech., 2012, 22(5):703-706.
[12]	刘作华, 唐巧, 王运东, 等. 刚柔组合搅拌桨增强混合澄清槽内流体宏观不稳定性[J]. 化工学报, 2014, 65(1):78-86. LIU Z H, TANG Q, WAGN Y D, et al. Enhancement of macro-instability in a mixer-settler with rigid-flexible impeller[J]. CIESC Journal, 2014, 65(1):78-86.
[13]	刘作华, 孙瑞祥, 王运东, 等. 刚-柔组合搅拌桨强化流体混沌混合[J]. 化工学报, 2014, 65(9):3340-3349. LIU Z H, SUN R X, WAGN Y D, et al. Chaotic mixing intensified by rigid-flexible coupling impeller[J]. CIESC Journal, 2014, 65(9):3340-3349.
[14]	ZOU Y, SONG W Y, WAGN Y D, et al. A study on suction effect of impellers in a square pump-mixer[J]. J. Chem. Eng. Japan, 2015, 48(5):1-8.
[15]	Al-QAESSI F, ABU-FARAH L. Prediction of mixing time for miscible liquids by CFD simulation in semi-batch and batch reactors[J]. Eng. Appl. Comp. Fluid Mech., 2014, 3(1):135-146.
[16]	JAWORSKI Z, DUDCZAK J. CFD modelling of turbulent macromixing in stirred tanks. Effect of the probe size and number on mixing indices[J]. Comp. Chem. Eng., 1998, 22:S293-S298.
[17]	张庆华, 毛在砂, 杨超, 等. 一种计算搅拌槽混合时间的新方法[J]. 化工学报, 2007, 58(8):1891-1896. ZHANG Q H, MAO Z S, YANG C, et al. A new method for determining mixing time in stirred tanks[J]. Journal of Chemical Industry and Engineering(China), 2007, 58(8):1891-1896
[18]	纪风翰, 龚绍英. 液-固相釜式搅拌反应器的放大研究[J]. 化学反应工程与工艺, 1997, 13(3):61-68. JI F H, GONG S Y. The scale-up research of the liquid-solid stirred-tank reactor[J]. Chem. React. Eng. Tech., 1997, 13(3):61-68.
[19]	银建中, 程绍杰, 贾凌云, 等. 生物反应器放大因素与方法研究[J]. 化工装备技术, 2009, 30(1):22-27. YIN J Z, CHENG S J, JIA L Y, et al. A study on scale-up factors and methods of bioreactor[J]. Chem. Equip. Tech., 2009, 30(1):22-27.
[20]	刘期崇, 夏代宽, 段天平, 等. 外环流氨化反应器数学模型及其放大[J]. 化工学报, 2000, 51(1):77-84. LIU Q C, XIA D K, DUAN T P, et al. Mathematical model and scale-up of external-loop ammoniation reactor[J]. Journal of Chemical Industry and Engineering(China), 2000, 51(1):77-84.
[21]	LIU Y, RAMAN V, FOX R, et al. Scale up of gas-phase chlorination reactors using CFD[J]. Chem. Eng. Sci., 2004, 59(22/23):5167-5176.
[22]	MIDDLETON J C, PIERCE F. Computations of flow fields and complex reaction yield in turbulent stirred reactors, and comparison with experimental data[J]. Chem. Eng. Res. Des., 1986, 64:18-22.
[23]	罗运柏, 胡宗定. 烟气脱硫三相流化床反应器的数学模拟与预测放大[J]. 化工学报, 2002, 53(2):122-127. LUO Y B, HU Z D. Scale-up and modeling of countercurrent three-phase fluidized reactor for flue gas desulfurization[J]. Journal of Chemical Industry and Engineering(China), 2002, 53(2):122-127.
[24]	GAVI E, MARCHISIO D L, BARRESI A A. CFD modelling and scale-up of confined impinging jet reactors[J]. Chem. Eng. Sci., 2007, 62(8):2228-2241.
[25]	SRILATHA C, MUNDADA T P, PATWARDHAN A W. Scale-up of pump-mix mixers using CFD[J]. Chem. Eng. Res. Des., 2010, 88(1):10-22.
[26]	王凯, 虞军. 搅拌设备[M]. 北京:化学工业出版社, 2003. WANG K, YU J. Mixing Equipment[M]. Beijing:Chemical Industry Press, 2003.
[27]	马婷婷. 混合澄清槽内流动的测量与模拟[D]. 天津:天津大学, 2013. MA T T. On measurement and simulation of flow in mixer-settler[D]. Tianjin:Tianjin University, 2013.