Aluminum Reduction Technology: Alumina Dissolution & Bath Chemistry
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Pierre Marcellin, Rio Tinto; Stephan Broek, Kensington Technology Inc
Wednesday 2:00 PM
March 22, 2023
Room: 30E
Location: SDCC
Session Chair: Daniel Marinha, Rio Tinto
2:00 PM Introductory Comments
2:10 PM
CFD Modelling of Solidification and Melting of Bath during Raft Formation: Sindre Engzelius Gylver1; Kristian Etienne Einarsrud1; 1Norwegian University of Science and Technology
The dissolution of alumina in cryolite is a complex process, and better understanding is needed to ensure stable cell conditions and high energy efficiency. Additions of cold powder result in freezing of bath that hinders dissolution, and creation of rafts.The current work aims to develop and demonstrate a CFD framework in OpenFOAM for freezing of bath on a fed dose of alumina, based on the volume of fluid (VOF) method, where appropriate source- and sink terms are applied. Essential features have been verified by comparison with a Stefan problem, while simulating the dose as a floating rigid object demonstrate that a larger layer of freeze increase the damping of its movement. When simulating the dose as an immiscible fluid, spreading will hinder enough freeze to be formed around the dose. Hence, the added source terms behave as intended, but improvements on the alumina-bath interactions are needed.
2:35 PM
Experimental Investigation of the Alumina Cloud During Alumina Injections in Low And High Temperature Conditions: Thomas Roger1; Laszlo Kiss1; Lukas Dion1; Jean Francois Bilodeau2; Sébastien Guérard2; Guillaume Bonneau1; 1Universite Du Quebec A Chicoutimi; 2Rio Tinto
Alumina injections are the most frequent discrete events occurring in aluminum reduction cells. During each feeding, a significant fraction of the mass injected will float and create a raft composed of alumina and frozen bath which hinders the dissolution rate of the alumina. However, a small fraction of the alumina sinks in the form of a cloud in the electrolyte which establish idealize dissolution conditions. Specific investigations were performed to understand the fraction of particles in each specific state and the clouds geometrical patterns. An analog experimental setup is presented to observe the cloud at low temperature. Organics particles, cooled with liquid nitrogen, were injected in water. Each experimental injection performed were analyzed during formation of the ice-particle raft to determine the surface and the density of the cloud.The results are compared with experimental injections performed in molten cryolite using a see-through cell to pinpoint the similitude and disparities.
3:00 PM
Fundamental Mass Transfer Correlations Based on Experimental and Literature Data: Jonathan Alarie1; Lukas Dion1; László Kiss1; Sébastien Guérard2; Jean-François Bilodeau2; 1University of Quebec-Chicoutimi; 2Arvida Research and Development Centre, Rio Tinto
Using a specific description of the heat transfer, and diffusion coefficients, general mass transfer theory is applied to data available in the literature to identify their respective dissolution rate. The following calculations using data from the literature are then compared to experimental work performed under laboratory conditions using a gravimetric method to evaluate the dissolution rate of alumina disks. The contrast between the data from our experimental work and the validation provided by the literature is assumed inherent to the morphology of the sample and the adequate description of the flow around it. The following discussions highlight the dominant factor affecting the mass transfer coefficients and pinpoint the theoretical challenges to overcome to achieve more precise relations for future works.
3:25 PM Break
3:40 PM
Potential of Production Al-Si Green Alloys in AP18 Aluminium Reduction Cell: Haris Salihagic Hrenko1; Anton Verdenik1; Branko Juršek1; Dragan Mikša1; Maja Vončina2; Jožef Medved2; 1Talum d.d.; 2University of Ljubljana
The market situation and environmental requirements suggest that the direct synthesis of Al-Si alloys in aluminium electrolysis cell can help to increase added value and reduce a total CO2 footprint of alloys. The aim of this paper was to determine the influence of SiO2 additives on the process control during the production of Al-Si alloy. The regulation of the process strongly depends on the electrical resistance of the electrolysis cells, so we determined the electrical conductivity of the electrolyte using the DC four-point method. The measured electrical conductivity was a guide for determining the dosing rate of SiO2. Optimization of the reduction process has been done with the process computer data and measuring the properties of the electrolyte with STARprobeTM. The promising results of direct Al-Si alloys synthesis in AP18 industrial cells could open a path to large variety of greener Al-alloys produced by electrolysis process.