Study on mixing and settling characteristics in mixer-settler

doi:10.11949/0438-1157.20190533

Abstract

Abstract:

Mix-settler is the earliest extraction equipment which is still widely used at present. This paper studies on mixing and settling characteristics in a mixer-settler according to the limitation. The research process uses the SOPAT droplet measurement platform to measure the droplet size. The relationship between the droplet size distribution, the average droplet size, the liquid holding capacity, the size of the dispersion belt and the entrainment amount of different system mixing chambers, clarification chambers is discussed. The results show that Sauter diameter of droplet, D ₃₂, is linear with the agitation speed. D ₃₂ and liquid holdup were satisfied with the Calderbank model in the mixing chamber. And in the settling chamber, the settling performance was mainly affected by droplet size, organic/aqueous phase density difference, viscosity, mass transfer, temperature and interfacial tension. The drop studies will lay the foundation for optimizing or improving the structure of the mixer-settler.

Key words: mixer-settler, SOPAT measurement platform, drop diameter, extraction, equilibrium, interfacial tension

摘要：

混合澄清槽是最早也是目前依然被广泛使用的萃取设备，针对混合澄清槽存在的局限性对其混合与澄清特性进行规律性研究。研究过程采用SOPAT液滴测量平台测量液滴尺寸，针对不同体系混合室、澄清室液滴尺寸分布、平均液滴粒径、持液量、分散带尺寸、夹带量之间的关系探讨达到研究目的。实验结果表明，在混合过程中，大部分体系的等比表面积平均直径D ₃₂与转速呈指数关系，与持液量的关系符合Calderbank模型。而在澄清过程中，澄清效果主要受到液滴尺寸、密度差、黏度、质量传递、温度、界面张力的影响，其中界面张力的增加会增强分相效果。通过对液滴测量影响因素进行系统的研究，为具体的操作下优化或改进混合澄清槽的结构打下基础。

关键词: 混合澄清槽, SOPAT测量平台, 液滴尺寸, 萃取, 平衡, 界面张力

CLC Number:

TQ 028.8

Yuxin WU, Qiao TANG, Jiyizhe ZHANG, Yundong WANG. Study on mixing and settling characteristics in mixer-settler[J]. CIESC Journal, 2019, 70(10): 3932-3940.

吴雨馨, 唐巧, 张姬一哲, 王运东. 混合澄清槽混合与澄清特性的规律研究[J]. 化工学报, 2019, 70(10): 3932-3940.

Figures/Tables 25

Fig.1 Structure of mixer-settler

Fig.2 Structure of paddle[19]

Fig.3 SOPAT droplet measurement platform

Fig.4 Relationship between D 32 and rotation speed and surfactant concentration[22]

Fig.5 Structure of dispersion band

Fig.6 Effects of droplet size on droplet number density at different holdup in kerosene/water

Fig.7 Effects of droplet size on droplet number density at different rotation speed in kerosene/water

Fig.8 Variation of droplet size with rotation speed and oil/water ratio(FR) in kerosene/water system

Fig.9 Effects of rotation speed on D 32

Table 1 Fitness results of four systems

System	n	R ²
kerosene/water	-1.51	0.9996
P507/kerosene-water	-1.59	0.9595
P507/kerosene-NaCl	-0.56	0.9538
P507/kerosene-NdCl₃	-0.53	0.9404

Fig.10 Relationship between D 32 and holdup at different rotation speed

Fig.11 Relationship between D 32 and holdup at different phase ratio

Table 2 Fitness results of four systems

System	a	b
kerosene/water	1.31	-0.76
P507/kerosene-water	0.59	-0.76
P507/kerosene-NaCl	0.59	1.71
P507/kerosene-NdCl₃	0.77	1.32

Fig.12 Relationship between D 32 and liquid holdups

Fig.13 Relationship between D 32 and rotation speed in different surfactant concentration

Fig.14 Relationship between D 32 and liquid holdups at different surfactant concentration of P507/kerosene-water system

Fig.15 Droplet size distribution at 150 r/min of non-saponified/saponified oil phase

Fig.16 Droplet measurement position of dispersion band

Fig.17 D 32 at 300 r/min of kerosene/water system

Fig.18 D 32 at 400 r/min of kerosene/water system

Table 3 Interfacial tension(same oil phase)

System	Interfacial tension
P507/kerosene-water	18.34
P507/kerosene-NaCl	15.87
P507/kerosene-NdCl₃	25.49
P507/kerosene(saponification)-NdCl₃	8.03

Fig.19 Dispersion band size at different systems

Fig.20 Dispersion band size in different surfactant concentration

Fig.21 Phenomenon of clarification chamber of non-saponified oil phase

Fig.22 Phenomenon of clarification chamber of saponified oil phase

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