NAFEMS International Journal of CFD Case Studies

Volume 13, September 2023

ISSN 1462-236X
ISBN 978-1-83979-059-1

Modelling of the Aluminium Electrolysis Process: Feeding and Dissolution of Alumina Particles

H Gesell, U. Janoske
University of Wuppertal

https://doi.org/10.59972/22gbute5

Keywords: CFD, Lagrangian, magnetohydrodynamic, electrolysis, dissolution

Abstract

The present numerical study describes the feeding and dissolution behaviour of alumina particles in the electrolytic bath of industrial Hall-Héroult cells. The dissolution rate is controlled by thermal and chemical conditions as well as the transport and mixing of particles in the electrolyte. The model presented is implemented in the OpenFOAM® framework using the Lagrangian approach for the coupling of continuous (electrolyte and liquid aluminium) and dispersed phase (alumina particles). The model solves the particle motion, mass transfer from dispersed to continuous phase, the energy equation, and the transport of dissolved concentration. Moreover, the influence of thermal conditions and turbulent mixing due to gas bubbles arising under the anodes is considered by the model. The velocity field is adopted from a previously executed magnetohydrodynamic (MHD) simulation. With the help of the model developed, various studies are carried out. The focus corresponding to the increased flexibility of electric power consumption is on the thermal behaviour during cold operating conditions of the electrolysis cell. It is important to ensure that all the alumina feed is dissolved. The sinking of undissolved alumina to the bottom of the cell must be prevented as it impairs cell efficiency. The results show that the dissolution rate and total dissolution time depend on the bath temperature. A greater effect is observed for the bath superheat defined by the difference of bath temperature and liquidus temperature of the bath. Furthermore, the influence of process parameters like grain size and feeding masses are studied in detail.

References

1. McIntosh, G., Metson, J., Lavoie, P., Niesenhaus, T., Reek, T., & Perander, L. (2016). The Impact of Alumina Quality on Current Efficiency and Energy Efficiency in Aluminum Reduction. Light Metals 2016.
2. Lavoie, P., & Taylor, M. (2016). Alumina Concentration Gradients in Aluminium Reduction Cells. Advances in Molten Slags, Fluxes, and Salts: Proceedings of the 10th International Conference on Molten Slags, Fluxes and Salts.
3. Bagshaw, A., & Welch, B. (2016). The Influence of Alumina Properties on its Dissolution in Smelting Electrolyte. Essential Readings in Light Metals.
4. Haverkamp, R., & Welch, B. (1998). Modelling the dissolution of alumina powder in cryolite. Chemical Engineering and Processing: Process Intensification.
5. Kuschel, G., & Welch, B. (2016). Further Studies of Alumina Dissolution under Conditions Similar to Cell Operation. Essential Readings in Light Metals.
6. Skybakmoen, E., Solheim, A., & Sterten, Å. (1997). Alumina solubility in molten salt systems of interest for aluminum electrolysis and related phase diagram data. Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science.
7. Solheim, A., Rolseth, S., Skybakmoen, E., Støen, L., Sterten, A., & Støre, T. (2016). Liquidus Temperature and Alumina Solubility in the System Na3AlF6-AlF3-LiF-CaF2-MgF2. Essential Readings in Light Metals.
8. Welch, B., & Kuschel, G. (2007). Crust and alumina powder dissolution in aluminum smelting electrolytes. JOM.
9. Bojarevics, V. (2019). Dynamic Modelling of Alumina Feeding in an Aluminium Electrolysis Cell. Communications in Computer and Information Science.
10. Yang, Y., Liu, X., Wang, Z., Yu, J., & Gao, B. (2018). Alumina Dispersion Rate in a Current Intensified Aluminium Smelting Cell. 12th Australasian Aluminium Smelting Technology Conference.
11. Witt, P., Feng, Y., Snook, G., Eick, I., & Cooksey, M. (2017). A Six Chemical Species CFD Model of Alumina Reduction in a Hall-Héroult Cell. SINTEF Academic Press.
12. Zhang, H., Yang, S., Zhang, H., Li, J., & Xu, Y. (2014). Numerical Simulation of Alumina-Mixing Process with a Multicomponent Flow Model Coupled with Electromagnetic Forces in Aluminum Reduction Cells. JOM.
13. Gutt, R., Nandana, V., & Janoske, U. (2018). A Numerical Study of Metal Pad Rolling Instability in a Simplified Hall-Heroult Cell. 6th European Conference on Computational Mechanics (ECCM 6).
14. Cubeddu, A., Nandana, V., & Janoske, U. (2019). A numerical study of gas production and bubble dynamics in a hall-héroult reduction cell. Minerals, Metals and Materials Series.
15. Thonstad, J., Solheim, A., Rolseth, S., & Skar, O. (2016). The Dissolution of Alumina in Cryolite Melts. Essential Readings in Light Metals.
16. Grjotheim, K., & Kvande, H. (2010). Introduction to aluminium electrolysis. Düsseldorf: Alumedia GmbH.
    
17. Zhan, S., Li, M., Zhou, J., Yang, J., & Zhou, Y. (2015). Analysis and modeling of alumina dissolution based on heat and mass transfer. Transactions of Nonferrous Metals Society of China (English Edition).
18. Kremser, R., Grabowski, N., Düssel, R., Mulder, A., & Tutsch, D. (2020). Anode Effect Prediction in Hall-Héroult Cells UsingTime Series Characteristics. Applied Sciences.
19. Zhan, S.-q., Jiang, M.-m., Wang, J.-f., & Yang, J.-h. (2021). Improved CFD modeling of full dissolution of alumina particles in aluminum electrolysis cells considering agglomerate formation. Transactions of Nonferrous Metals Society of China.
20. J. O’Rourke, P. (1989). Statistical Properties and Numerical Implementation of a Model for Droplet Dispersion in a Turbulent Gas. JOURNAL OF COMPUTATIONAL PHYSICS , 345-360. [21] Ranz, W., & Marshall, W. (1952). Evaporation from Drops. Chem. Eng. Prog, 141-146.

Cite this paper

H. Gesell, U. Janoske, Modelling of the Aluminium Electrolysis Process: Feeding and Dissolution of Alumina Particles, NAFEMS International Journal of CFD Case Studies, Volume 13, 2023, Pages 15-29, https://doi.org/10.59972/22gbute5