Elsevier

Hydrometallurgy

Volume 181, November 2018, Pages 82-90
Hydrometallurgy

Prediction of holdup and drop size distribution in a disc-doughnut pulsed column with tenova kinetics internals for the water-Alamine 336 system

https://doi.org/10.1016/j.hydromet.2018.08.017Get rights and content

Abstract

Tenova Pulsed Column Kinetics Internals (TPC-KIs) are a newly designed type of pulsed column internals with a novel structure that is expected to achieve less back-mixing, higher holdup and improved mass transfer. This study compared the hydrodynamic performance of TPC-KIs with standard disc and doughnut internals in a 2 m high, 76 mm diameter pulsed solvent extraction column with the water-Alamine 336-Shellsol 2046 system. The effects of the wettability of column internals have also been considered. Dispersed phase holdup and Sauter mean droplet diameter were measured under various pulsation intensities and velocities of both phases, and empirical correlations for holdup and drop size have been refitted within absolute average relative errors of 15%. Tenova kinetics internals have a lower holdup and larger Sauter-mean drop size compared to standard disc and doughnut internals, and these hydrodynamic parameters are predictable using the correlation developed in this study.

Introduction

Pulsed solvent extraction columns are an efficient liquid-liquid contactor design and have been studied with various types of column internals, such as the Kühni column, pulsed packed column, pulsed perforated column and pulsed disc and doughnut column. As fixed components inside the pulsed column, the column internals can be produced at a low cost and operated with minimal ongoing maintenance. However, the design of these internals can significantly impact column performance and hence optimising their design is important. Additionally, when compared to other liquid-liquid separation apparatus such as mixer-settlers, pulsed column use can reduce evaporation loss, entrainment and solvent inventory to a large extent.

This study aims to compare the hydrodynamic performance of pulsed columns with Tenova Pulsed Column – Kinetics Internals (TPC-KIs) and standard disc and doughnut internals using the water – Alamine 336 in Shellsol 2046 liquid-liquid system (either with aqueous continuous or organic continuous operation). Wang et al. (Wang et al., 2016a) recently reported the hydrodynamic performance of a 1 m high 72.5 mm diameter pulsed solvent extraction column with Teflon standard disc and doughnut internals using tap water – Alamine 336 in Shellsol 2046. The study found an increase in dispersed phase holdup with dispersed phase flowrate and high pulsation intensity. However, there is very limited study on the performance of pulsed columns with TPC-KIs internals. As novel column internals with improved structure, TPC-KIs are expected to improve overall mass transfer performance by producing a larger dispersed phase holdup and less axial dispersion under comparable operating conditions (Tenova Advanced Technologies, 2014). Due to the presence of a sawtooth edging of Tenova kinetics internals, its flood point is expected to be higher than for standard disc and doughnut internals, thus a much higher throughput can be achieved.

In the present study, polyvinylidene fluoride (PVDF) was used for both standard disc and doughnut internals and the TPC-KIs, but the surface roughness of the PVDF sheets was different for the two types of internals resulting in variation in surface wettability (Li et al., 2017). The wettability of these internals indicates that liquid-liquid systems can be efficiently operated under both organic continuous and aqueous continuous. The present study investigates both the influence of which phase is continuous and the internal structures on the hydrodynamic performance of a pulsed solvent extraction column.

Section snippets

Background

Hydrodynamics is crucial for the assessment of solvent extraction column performance as it directly influences the interfacial area available for mass transfer. A larger liquid-liquid interfacial area results in higher mass transfer fluxes according to the two-film theory (Lewis & Whitman, 1924). In the present study, two significant hydrodynamics parameters, dispersed phase holdup and Sauter mean diameter are investigated. The dispersed phase holdup can be easily calculated as the ratio of the

Liquid-liquid system

The liquid-liquid system used in this study was tap water as the aqueous phase and 3 v/v % Alamine® 336 (tri-octyl/decyl amine, BASF), and 1 v/v % Isodecanol (ExxonMobil), diluted with Shellsol® 2046 (Shell) as the organic phase. No mass transfer of the solute occurred in this hydrodynamic study. The physical properties of each phase including density, ρ, viscosity, μ, and interfacial tensions γq-org were measured and results are shown in Table 3. Densities of aqueous and organic phases were

Dispersed phase holdup

For the newly designed TPC-KIs, the effect of pulsation intensity on the dispersed phase holdup was studied and the results are plotted on Fig. 2 for both aqueous continuous and organic continuous operation. To enable comparison between the standard disc and doughnut internals and TPC-KIs, the effect of pulsation intensity on the dispersed phase holdup with organic continuous for both internals is shown in Fig. 3. The aqueous phase flow rates were varied from 7.35 × 10−4 to 1.47 × 10−3 m/s and

Conclusions

  • 1.

    Slightly higher dispersed phase holdup can be achieved with standard disc and doughnut internals compared with Tenova Pulsed Column – Kinetics Internals (TPC-KIs).

  • 2.

    Due to the inner structure and surface property, the dispersed phase droplet diameters were scattered across a wide range at low pulsing intensities with the TPC-KIs. The internal edge and wettability of internal surface is key factor for the dispersed phase droplet formation. The Sauter mean diameter is likely independent of

Acknowledgements

The authors would like to acknowledge the funding provide by the Australian Research Council through Linkage grant LP130100305 and BHP Billiton, Olympic Dam, for this project, and would also like to thank the Particulate Fluids Processing Centre for the resources provided for this project.

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