Three-phase fluid dynamics simulation of ionic liquid system in mixer-settler

doi:10.16085/j.issn.1000-6613.2020-2216

Abstract

Abstract:

As a new kind of green solvents, ionic liquids (ILs) have been widely studied in recent years and have potential application prospects in the spent fuel reprocessing technology. However, a lack of study on flow characteristics of ILs in the extraction equipment limits the practical applications of ILs extraction system. Mixer-settler widely used in extraction was taken as the research object in this paper. The deionized water and the 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C₄mim][NTf₂]) were adopted as the aqueous phase and the organic phase, respectively. The computational fluid dynamics (CFD) simulation was carried out to study the organic phase distribution, pressure field and turbulence degree, etc. at different agitation speeds, flow ratios and temperatures. Moreover, the influence of air on the flow behavior was considered. The simulation result accorded with the experiment data and the maximum error was less than 6.3%. The results showed that the mixing performance can be promoted significantly by increasing the agitation speed. The air flow rate at the outlet was increased significantly with increasing agitation speed when it exceeded 500r/min, which may affected the performance of clarifying chamber. Besides, the mixing performance of organic phase and aqueous phase can be promoted with increasing flow ratio and temperature at the agitation speed of 350r/min. The moment of agitator was effectively reduced by heating up. The organic phase velocity and the moment of agitator were not significantly affected by heating when the temperature exceeds 303K. Therefore, the actual process conditions were recommended to combine with heating and the adjustment of agitation speed for achieving better mixing performance while reducing the requirements of the clarifying chamber.A numerical simulation method for the three-phase system of ILs is set up in the study. Moreover, some reasonable suggestions are provided for optimizing the operating conditions of the mixer-settler, and a reference for further study of ILs extraction system is provided.

Key words: ionic liquids (ILs), computational fluid dynamics (CFD), mixer-settler, stirred vessel, multiphase flow

摘要：

离子液体是近年来被广泛研究的新兴绿色溶剂，其在乏燃料后处理技术中具有潜在的工业应用前景。但由于缺乏对萃取反应器中离子液体流动特性的研究，制约了离子液体萃取体系的实际应用。本文以萃取工艺中广泛应用的混合澄清槽为对象，以去离子水及1-丁基-3-甲基咪唑双(三氟甲磺酰)亚胺盐（[C₄mim][NTf₂]）分别作为水相及有机相，考虑上层空气对流动行为的影响，对其混合室进行计算流体力学（computational fluid dynamics, CFD）模拟，考察不同转速、流比及温度下的有机相分布、压力场、湍动程度等。结果表明，模拟结果较好地符合实验结果，且最大误差小于6.3%；转速能直观地提升混合性能，但当超过500r/min后，继续提高转速将显著增大出口气量，从而可能对澄清室的分相性能提出更高要求；增大流比、升温均能提升350r/min转速下的有机、水相混合能力，升温还有效减小了桨力矩，但当温度超过303K时，继续升温对于桨力矩、有机相速度的改变不明显。因此，实际工艺条件建议结合升温与转速调节，在实现较好混合性能的同时，减少对澄清室分相性能的要求。本文在建立离子液体三相体系数值模拟方法的同时，为混合澄清槽的工况优化提供合理建议，并为离子液体萃取体系的深入研究提供了参考。

关键词: 离子液体, 计算流体力学, 混合澄清槽, 搅拌容器, 多相流

CLC Number:

TB126

TANG Qi, BAO Di, SHAO Shaoxiong, XU Ping, LIU Lianwei, ZHENG Weiming. Three-phase fluid dynamics simulation of ionic liquid system in mixer-settler[J]. Chemical Industry and Engineering Progress, 2021, 40(10): 5468-5479.

汤祺, 鲍迪, 邵少雄, 徐平, 刘联伟, 郑维明. 混合澄清槽内离子液体体系的三相流体动力学模拟[J]. 化工进展, 2021, 40(10): 5468-5479.

Figures/Tables 22

（T=293K，p=101.325kPa）

离子液体［C₄mim］［NTf₂］

（纯度99%）

方程名称	方程式	序号
连续性方程	$? ? t α i ρ i + ? ? a i ρ i U i = 0$	（1）
动量方程	$? ? t a i ρ i U i + ? ? a i ρ i U i U i = - a i ? p + a i ρ i g + ? ? τ i ˉ ˉ + F i j$	（2）
RNG k-ε湍流模型	$? ? t ρ m k + ? ? x i ρ m u m k = ? ? x j α k i μ e f f, m ? k ? x j + G k - ρ m ε$	（3）
	$? ? t ρ m ε + ? ? x i ρ m u m ε = ? ? x j α ε μ e f f, m ? ε ? x j + ε k C 1 ε G k - ε 2 k C 2 ε$	（4）
曳力系数模型		（4）
曳力系数模型	$C D = 24 / R e 1 + 0.15 R e 0.687 ????? R e ≤ 1000 0.44 ???????????????????????????????????????? R e > 1000$	（5）
液滴的Sauter平均直径模型^［30-31］	$d 32 / D = 0.28 1 + 0.92 α j W e i j - 0.6$	（6）
液滴的Sauter平均直径模型^［30-31］	$W e i j = ρ i D 3 N / 60 2 / σ i j$	（7）
N-phase 体积分数方程	$α i + α j + α k = 1$	（8）
水力直径	圆形：D_H=D_i	（9）
水力直径	长方形：D_H=2HW/（H+W）	（10）
湍流强度	$I = 0.16 R e - 1 / 8$	（11）

方程名称	方程式	序号
连续性方程	$? ? t α i ρ i + ? ? a i ρ i U i = 0$	（1）
动量方程	$? ? t a i ρ i U i + ? ? a i ρ i U i U i = - a i ? p + a i ρ i g + ? ? τ i ˉ ˉ + F i j$	（2）
RNG k-ε湍流模型	$? ? t ρ m k + ? ? x i ρ m u m k = ? ? x j α k i μ e f f, m ? k ? x j + G k - ρ m ε$	（3）
	$? ? t ρ m ε + ? ? x i ρ m u m ε = ? ? x j α ε μ e f f, m ? ε ? x j + ε k C 1 ε G k - ε 2 k C 2 ε$	（4）
曳力系数模型		（4）
曳力系数模型	$C D = 24 / R e 1 + 0.15 R e 0.687 ????? R e ≤ 1000 0.44 ???????????????????????????????????????? R e > 1000$	（5）
液滴的Sauter平均直径模型^［30-31］	$d 32 / D = 0.28 1 + 0.92 α j W e i j - 0.6$	（6）
液滴的Sauter平均直径模型^［30-31］	$W e i j = ρ i D 3 N / 60 2 / σ i j$	（7）
N-phase 体积分数方程	$α i + α j + α k = 1$	（8）
水力直径	圆形：D_H=D_i	（9）
水力直径	长方形：D_H=2HW/（H+W）	（10）
湍流强度	$I = 0.16 R e - 1 / 8$	（11）

水相入口流量/mL·min^-1	有机相入口流量/mL·min^-1	流比（a∶o）
25	25	1∶1
25	20	5∶4
25	15	5∶3
25	10	5∶2

流比	水相体积/m³	有机相体积/m³	两相相比
1∶1	5.52×10^-5	4.47×10^-5	1.23
5∶4	5.57×10^-5	4.42×10^-5	1.26
5∶3	5.60×10^-5	4.39×10^-5	1.28
5∶2	5.72×10^-5	4.32×10^-5	1.33

温度/K	离子液体密度/kg·m^-3	黏度/mPa·s
293	1440.288	62.674
298	1435.433	50.069
303	1430.595	41.178
308	1425.688	34.779

温度/K	水相体积/m³	有机相体积/m³	两相相比
293	5.52×10^-5	4.47×10^-5	1.23
298	5.53×10^-5	4.47×10^-5	1.24
303	5.56×10^-5	4.45×10^-5	1.25
308	5.58×10^-5	4.44×10^-5	1.26

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