Oral Presentation International Solvent Extraction Conference 2025

Introduction:

In the field of hydrometallurgy, high solid-content extraction systems often face the technical challenge of equipment blockage. Previous research on extraction equipment for such systems has primarily focused on agitated extraction columns, such as rotating disc contactors and Kühni columns[1]. These columns have simple internal structures and large flow spaces. Combined with sufficient turbulence, they can effectively prevent solid-phase sedimentation and clogging. However, due to the significant radial flow in the column, the flow field structure is easy to be distorted during scale-up, resulting in pronounced scale-up effects[2-3].

The pulsed sieve-plate column is one of the column types with the least scale-up effect. Due to limitations of the basic sieve plate structure, it faces the issue of solid-phase blockage when applied to liquid–liquid–solid three-phase systems with high solid content. Previous research has shown that dispersed-phase droplets in pulsed sieve-plate columns predominantly exhibit axial motion, along with continuous-phase vortices within each column section[4]. This contributes to a high degree maintenance of flow field during scale-up and leads to high extraction efficiency. Based on the fundamental flow field characteristics of pulsed sieve-plate columns, this study proposes a novel design concept for a disc-doughnut pulsed sieve-plate column tailored for solid-containing extraction systems as shown in Fig. 1. The design retains the axial motion of dispersed-phase droplets through the use of traditional sieve plate structure, while adopting a staggered arrangement of disc and doughnut sieve plates. This creates a zigzag slag discharge path via continuous-phase vortices, enabling both high extraction efficiency through flow field similarity and effective solid-phase discharge to prevent clogging.

Fig. 1. The deisgn concept of the disc-doughnut pulsed sieve plate column

Results and Discussion：

A CFD model of the novel disc-doughnut pulsed sieve-plate column was first developed, and its accuracy was validated through PIV experiments. The multiphase hydrodynamics of the new column were investigated by combining multiphase flow experiments with CFD simulations. The results showed that the flow field structure of the novel column was highly consistent with that of the traditional pulsed sieve-plate column. Meanwhile, the specially designed disc-doughnut sieve structure successfully created a zigzag hydrodynamic channel, enabling automatic solid-phase discharge in high-solid-content extraction systems.

Experimental results indicated that, compared with the traditional pulsed sieve-plate column, the novel disc-doughnut pulsed sieve-plate column achieved near-zero solid-phase holdup after stopping the extraction operation. Under liquid–liquid two-phase flow conditions, the key physical parameters of the novel and traditional columns including dispersed phase holdup, droplet size, and the axial dispersion coefficient of the continuous phase remained largely consistent. Meanwhile, these physical quantities exhibited similar trends with respect to changes in key operating parameters such as flow rates and pulsation intensity, indicating that the novel column retains the characteristic of high extraction efficiency.

A comparative study of liquid–liquid two-phase and liquid–liquid–solid three-phase flow in the novel disc-doughnut pulsed sieve-plate column showed that parameters such as dispersed phase holdup and average droplet diameter remained nearly unchanged under both conditions. However, due to the presence of solid-phase holdup, the residence time of the continuous phase decreased slightly, and the axial dispersion coefficient of the continuous phase increased by approximately 25%, which should be taken into consideration in the design of the column.

On this basis, the effects of key geometric parameters including the spacing between disc and doughnut plates, disc plate diameter, and doughnut inner diameter on the performance of the novel column were further investigated. It was found that the disc plate diameter and doughnut inner diameter are the most important design parameters. As the ratio of disc plate diameter to doughnut inner diameter decreases, the dispersed phase holdup shows a clear downward trend, while the axial dispersion coefficient of the continuous phase increases significantly. In the actual equipment design, the disc plate diameter to doughnut inner diameter ratio should be maintained at a value greater than 1.

[1] J. Zhu, S. Zhang, X. Zhou, X. Chen, Y. F. Su, V. Alfons. Chem. Eng. Technol., 1991, 14: 167-177.

[2] B Wang, S Ma, H Zhou, Q Zheng, W Lan, S Jing, S Li. AIChE J., 2025, 71: e18612.

[3] W. Y. Fei. CIESC J., 2013, 64: 44-51.

[4] Y.Q. Tu, H. Chen, Y. Z. Sun, J. G. Yu. Chem. Eng. Sci., 2021, 236: 116540.