Aluminum Reduction Technology: On-Demand Oral Presentations
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Kristian Etienne Einarsrud, Norwegian University of Science and Technology; Stephan Broek, Boston Metal; Mertol Gokelma, Izmir Institute of Technology; Dmitry Eskin, Brunel University
Monday 8:00 AM
March 14, 2022
Room: Light Metals
Location: On-Demand Room
A Water Model Study of Alumina Feeding and Dispersion: Kristian Etienne Einarsrud1; Sindre Engzelius Gylver1; Simen Aase1; Simen Bekkevoll1; Sigmund Forberg1; 1Norwegian University of Science and Technology
In the Hall-Héroult process, alumina is fed periodically into a cryolite bath, typically forming so-called rafts. While rafts have been observed and sampled in industry, the governing mechanisms for raft formation are not easily assessed in this setting. In this paper, we present a parametric study of alumina feeding and dispersion, where the liquid is kept close to its freezing point, to which cooled (soluble) particles are added. The effect of temperature difference between particles and liquid, particle size distribution (PSD) and gas induced convection is considered and assessed. Results from the water model experiments show a strong impact of PSD upon the upon the raft floating time. High amounts of fines increased resulting in floating times between 240 and 550 seconds, compared to 35-135 seconds in the case of coarser particles. Increased temperature and convection contributed positively to dispersion, although less significantly than the PSD.
Managing Power Interruptions at 360 KA Smelter: Amit Jha1; Amit Gupta1; Pratap Sahu2; Kamal Pandey2; Senthil Nath2; 1Aditya Birla Science & Technology Company, Ltd; 2Hindalco Industries Ltd, Mahan Aluminum
Power interruptions as well as planned reduction can be difficult to manage due to challenges in thermal balance of the pot. At reduced internal heat, isotherms will shift inwards causing operational difficulties. Additionally, smelter also has pots with different design (standard collector bar & copper insert) and age groups, which react differently to amperage reduction. The study has been performed for a 360 kA potline to run at lower amperages, as low as 280 kA. Hence, computational & analytical models were used by smelter and R&D teams to identify the best cell operating window. The study was used to optimize pot control parameters like voltage adjustment, AlF3 feeding, forced cooling pressure, gas suction, metal/bath height, anode cover composition & height, covering/recovering practices etc. The actions taken at shop floor and control room helped to survive/recover pots during interruptions smoothly.
A Pragmatic Model for Alumina Feeding: Stein Tore Johansen1; Asbjørn Solheim1; Kurian J. Vachaparambil1; Kristian Etienne Einarsrud2; 1SINTEF Industry; 2Norwegian University of Science and Technology
In this paper we demonstrate how we can develop a coarse-grained model for alumina distribution and dissolution in an aluminium reduction cell. The model is designed to have the potential of being a part of a control system or play the role of a Digital Twin. The framework is based on the concepts of Pragmatism in Industrial Modelling.The numerical grid is the coarsest possible and special numerical techniques, presented in the manuscript, are applied to support fast simulations. The bath flow is imported into the coarse-grained model, while dispersion and dissolution is resolved in the model. The physics of particulate alumina dissolution and the electrochemical consumption of dissolved alumina at the anodes is represented, allowing for observations of alumina distribution in time and space. In demonstration simulations the model is able to run up to 20 times faster than real time, depending upon resolution and level of physical details.
Statistical Model for Forecasting the Cell Replacement Rate in an Aluminum Smelter: Sebastien Guerard1; Pascal Thibeault1; 1Rio Tinto
Aluminum reduction cells have a limited life expectancy, and a significant proportion therefore needs to be replaced each year. This is a large expense for smelters, requiring careful long-term planning. Accurate forecasts can be hard to achieve, however, as they depend on the age distribution, design and operation conditions of the cells. In this work, we present a statistical model for forecasting the cell replacement rate. Pots are split into distinct populations, and a statistical distribution is then fitted to each one and used to produce detailed predictions. Special conditions, such as amperage creep, constraints on the start-up rate, or pot euthanasia, can also be taken into account, and the complete model is easily accessible through a web interface. Potential applications include producing detailed predictions for the coming years, exploring differences across designs or periods, rapidly detecting variations in the life expectancy, and planning replacement campaigns for future cell designs.
The Survivability of Aluminum Potlines after Lengthy Electrical Power Outages: Alton Tabereaux1; 1Consultant
Electrical power outages lasting 3 to 6 hours in aluminum smelters can often result in shutting down all the cells in a potline. During the power outage the temperature of the cryolitic electrolyte decreases below 900°C thereby freezing a large volume of liquid bath which decreases the bath height and anode immersion in cells. When the potline is reenergized, there is a substantial increase in the total potline voltage due to the increase in electrical resistance combined with numerous anode effects causing rectifiers to ‘trip-out’ due to power over-load. The survivability of cells in the potlines to continue operating after the extended power outages depends largely on the corrective actions taken by potroom personnel during the first few hours after electrical power is restored.
Imaging Alumina Distribution Using Low-voltage Anode Effect Detections in Anodic Current: Joan Boulanger1; Anne Gosselin1; Simon Gaboury1; Louis Guimond1; Claude Simard1; Alexandre Blais1; Francis Lalancette1; 1Rio Tinto
From the observations in continuous anodic currents of the various patterns associated with Low-Voltage Anode Effects (LVAE) at the scale of single anodes, a signal processing approach is devised for automated detection. High precision and sensitivity are obtained from a training of the level-based change-point detection algorithm using evolutionary optimisation and data carefully screened from resistance, CF4 emissions, anodic and line current time series. The possibility of detecting a wide range of LVAEs allows one for tracking cell zones recurrently lean under the hypothesis that LVAEs are solely associated with a lack in Alumina. Detection spatial statistics shape a kind of tomography for Alumina distribution diagnostics. In the technology studied, characteristic and stable Alumina distribution inhomogeneities are reported. This capability to draw qualitative mapping of Alumina inhomogeneity paves the way to the development of enhanced feeding mechanisms with spatial intelligence to diminish Alumina variability and improve the process.
Modeling of the Heat Exchange, the Phase Change, and Dissolution of Alumina Injected in Electrolysis Cells: Thomas Roger1; László Kiss1; Lukas Dion1; Jean Francois Bilodeau2; Sébastien Guérard2; Guillaume Bonneau1; Kirk Fraser3; 1Universite Du Quebec A Chicoutimi; 2Rio Tinto Aluminium; 3Aluminum Technology Center
For the aluminum industry, understanding each step of alumina addition to the electrolysis bath is critical to reach optimal process conditions. From the injection to the complete dissolution, several physical and chemical mechanisms are interacting: solid and fluid mechanics, heat transfer, phase change and dissolution. The mathematical model presented in this article uses the discrete element method (DEM) to consider the solid alumina powder as a discrete material. It is coupled to the "smoothed particle hydrodynamics" (SPH) method to simulate the liquid electrolyte. The second layer of the model is used to calculate the heat transfer and coalescence of solid materials resulting from alumina sintering. Then, phase change is integrated into the model to consider the solidification of the bath. Sequentially, the dissolution of the alumina particles is reproduced and study to perform the injection of the alumina in the future.
Direct Production of Aluminum Titanium Alloys in Aluminum Reduction Cells, A Laboratory Test: Geir-Martin Haarberg1; Omar Awayssa1; Gudrun Saevarsdottir2; Rauan Meirbekova3; Wenting Xu1; 1Norwegian University of Science and Technology; 2Reykjavik University; 3DTE
Aluminum smelters produce pure aluminum in reduction cells by the Hall Héroult process, but supply a variety of alloys to their customers. The alloys are produced in the cast house, as desired alloying elements are added to the primary aluminum from the potroom before casting. In this paper the concept of producing titanium master alloys direcly in the aluminum reduction cells is discussed, by feeding titanium oxide to the electrolyte, along with the alumina raw material. The results in this paper are obtained by running electrolysis experiments in a laboratory cell, and the current efficiency for the alloy deposition is estimated. Results for aluminum-silicon and aluminum-manganese alloys are reported in a different paper.
Mass Transport by Waves: Physical Model with Coalescence, Fragmentation, and Displacement on a Bath-metal Interface: Thomas Richer1; Lukas Dion1; Laszlo Kiss1; Sebastien Gerard1; Jean-François Bilodeau1; Guillaume Bonneau1; Lovatianna Rakotondramanana1; Renaud Santerre1; 1GRIPS
Behavior of alumina rafts at the bath-metal interface in an electrolysis cell have been simulated by a numerical model in previous studies. Further refinements on this model led to broader application and more « cell like» scenarios with its ability to consider three distinct bath metal interface phenomena. First, the transport wave who stem from disturbance in the electrolysis process such as bubbles, alumina deposits or crust-breakers actions is considered. Second, the stationary wave produced by the magnetohydrodynamics forces in the cell is replicated and third, the well-known permanent deformation of the bath-metal interface (BMI) is reproduced in the numerical model. In addition to the aggregate’s movements and positions, the proposed model simulates the fragmentation and coalescence occurring on these alumina rafts. The purpose of this paper is to present an in-depth sensitivity analysis of the improved numerical model and identify scenarios and parameters which could affect industrial cell conditions.
Empirical Prediction of Alumina Dissolution Rate in a Cryolitic Melt: Comparison with the Existing Literature: Jonathan Alarie1; László Kiss1; Lukas Dion1; Martin Truchon2; Renaud Santerre3; Sébastien Guérard4; Jean-François Bilodeau4; 1Aluminium Research Centre – REGAL, University of Quebec at Chicoutimi; 2University of Quebec-Chicoutimi; 3Technical advisor, Retired from Rio Tinto; 4Arvida Research and Development Centre, Rio Tinto
There are numerous studies published in the literature related to alumina dissolution rate in cryolite melts. However, such studies cover a broad range of results given in various formats. A new empirical equation was developed based on the results of an extensive parametric study using the gravimetric method on alumina disks. A comparison between this model shows large differences with the existing literature. This paper describes and discusses these differences. Most of the variation is caused by three main parameters strongly influencing the alumina dissolution kinetics. First, there is the alumina content and its morphology. Secondly, there is the mass and heat flow around the sample inherent to the experimental methods that were used. And thirdly, the influence of the additives concentration in the bath was identified as a strong contributor to explain the reported differences.