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Hydrodynamic Performance of a Pulsed Solvent Extraction Column with Novel Ceramic Internals: Holdup and Drop Size Heng Yi, Yong Wang, Kathryn H. Smith, Weiyang Fei, and Geoffrey W Stevens Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b03324 • Publication Date (Web): 28 Dec 2016 Downloaded from http://pubs.acs.org on December 30, 2016
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Highlights 1.
Two types of novel anti-corrosive ceramic internals have been designed for extraction of lithium and rare earths, and their hydrodynamic performance was investigated.
2.
Holdup of hybrid ceramic internal was higher than that of ceramic plate by around 50%. Correlations were proposed to predict holdup for both types of internal with AARD of 5.9% and 9.3% respectively.
3.
Sauter mean diameter of hybrid ceramic internal is smaller than that of ceramic plate by around 30%. Correlations were proposed to predict d with AARD of 13.6% and 4.2% respectively.
Graphical abstract
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Hydrodynamic Performance of a Pulsed Solvent Extraction Column with Novel Ceramic Internals: Holdup and Drop Size Heng Yia,b, Yong Wangb, Kathryn H. Smithb, W.Y. Feia, * and Geoffrey W. Stevensb,* a
b
Department of Chemical Engineering, Tsinghua University, Beijing, 100084, China
Department of Chemical and Biomolecular Engineering, The University of Melbourne, Parkville, Victoria 3010, Australia
ABSTRACT: Chloride in the extraction of lithium from brine in salt lakes and the separation of rare earth elements are both very corrosive to stainless steel extraction column internals, which is a significant problem in large scale production. The hydrodynamics of two types of novel anti-corrosive ceramic internals, the hybrid ceramic internal and ceramic plate, are designed and tested under pilot plant conditions in order to be considered for application to these industries. The results show that holdup decreases first and then increases with an increase of pulsation intensity. Increasing dispersed phase velocity also increases holdup. Sauter mean diameter, d , decreases with an increase of pulsation intensity, while superficial velocities of both phases have little effect. A range of correlations for holdup and d from literature are compared to the data, and it is shown that new correlations are needed to accurately predict the performance of the two internal types. Characteristic velocity, which is key parameter in calculating column throughput in the emulsion regime, is also investigated as part of the holdup correlation. Results show that characteristic velocities for both internals decrease with an
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increase of pulsation intensity, while that of ceramic plate are larger. The experimental results show higher holdup and smaller d when using the hybrid ceramic internal which indicates that this novel internal will provide a larger mass transfer area and hence better mass transfer efficiency.
Key words: Solvent extraction column, Hydrodynamics, Ceramic internal, Holdup, Drop size
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1. Introduction Liquid-liquid extraction is an important separation process. Various types of solvent extraction columns have been used for a range of applications in chemical, petroleum, nuclear, hydrometallurgical industries and other fields for many years1-3. Extraction columns have advantages over other devices such as its high volume efficiency, small footprint and environmentally friendly features. However, the design of extraction columns is still difficult due to the complexity of two phase interaction and mass transfer inside the column4. Therefore pilot plant experiments are still required for large scale design and implementation in an industrial field. Extraction of lithium from chloride brine in salt lakes5 and separation of rare earth elements6 are separation processes of great importance. They are also promising industry fields where solvent extraction columns are likely to be used. However the extraction solutions are very corrosive to stainless steel column internals because of their high chloride content, thus the development of novel anti-corrosive internal is necessary. In order to solve this problem, two types of novel ceramic internals have been designed and manufactured. Hydrodynamic performance parameters of the internals, including holdup and drop size, are important in the design of the column as they determine the column diameter and the mass transfer area between the phases which determines the column height. In this study pilot plant experiments are performed to measure and compare the hydrodynamic performance of the two types of ceramic internals including a novel hybrid ceramic internal. Correlations for both holdup and drop size are chosen from the literature and refitted to predict the experimental data with good agreement. 2. Previous studies 2.1. Holdup
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The dispersed phase holdup, xd, is defined as the volume fraction of the active section of the column that is occupied by the dispersed phase: x =
v v + v Equation 1
where vd represents the volume of the dispersed phase and vc represents the volume of the continuous phase. In a pulsed extraction column, when pulsation intensity is increased, holdup usually decreases at first and then increases. Previous researchers proposed different kinds of correlations in order to characterize this trend. Some researchers suggested splitting the range of pulsation intensity, i.e. energy input, into several regions including mixer-settler region, transition region and emulsion region and use a different correlation for each region. A typical example of this kind is the correlation proposed by Miao7 : x = 2.87 × 10 χ. V / for χ < 0.0013m / s Mixer-settler x = 4.09 × 10 χ . V / for 0.0013m / s < χ < 0.0044m / s Transition x = 8.46 × 10 χ." V / for χ > 0.0044m / s Emulsion Equation 2 where χ =
%$* &'()+
, .
3.
- / &/∆1 ) , β = & 3)& 3. )
Later Kumar and Hartland collected previously published holdup data for pulsed perforated plate columns and proposed a unified correlation which could be used in all the three operating regions8: A.KC A.KC 4 5 = 6 7 896 : |
