Aluminum Reduction Technology: Cell Modernization (Modelling and Energy Optimization)
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Nadia Ahli, Emirates Global Aluminium; Nancy Holt, Hydro Aluminium As

Monday 2:00 PM
March 15, 2021
Room: RM 28
Location: TMS2021 Virtual

Session Chair: Jayson Tessier , ALCOA; Andre Schneider, HATCH


2:00 PM  
Introductory Comments: Aluminum Reduction Technology: Nadia Ahli1; 1Emirates Global Aluminium
    Introductory Comments

2:05 PM  
Mass Transport by Waves: Bath-metal Interface Deformation, Rafts Collision and Physical Model: Lovatiana Rakotondramanan1; László Kiss1; Sándor Poncsák1; Renaud Santerre1; Sebastien Guerard2; Jean-François Bilodeau2; Simon Richer1; 1Grips Universite Du Quebec A Chicoutimi; 2Rio Tinto
    In aluminium electrolysis cell, the interface between molten metal and electrolyte is animated by surface waves. It is well known that there is a permanent deformation of the bath-metal interface (BMI) due to the magnetohydrodynamic flow in the cell. Rafts of agglomerated alumina float on BMI. A mathematical model was developed to describe the transport of these rafts by surface waves on the BMI. In this study, we examined the impact of the BMI deformation to the mass transport by waves. The mathematical model is validated by a low temperature physical model. Laboratory experiments with rigid objects driven by regular surface waves were performed for a range of amplitude and frequencies. Two immiscible fluids are used to model the electrolysis cell, the interface between water and silicone oil is animated by regular waves. Theoretical model predictions of the object drift motion are compared with the experimental data.

2:25 PM  
Modeling Anode Current Pickup After Setting: Choon-Jie Wong1; Yuchen Yao1; Jie Bao1; Maria Skyllas-Kazacos1; Barry J. Welch1; Ali Jassim2; 1University of New South Wales; 2Emirates Global Aluminum
    With rising power costs in some countries and intermittency of power supply due to the increased penetration of renewable energy sources globally, the energy-intensive aluminum smelting process needs to adopt a power modulation strategy as a cost-saving and operational flexibility measure. However, present smelting cell control and design only allows limited flexibility for safe power modulation. With a cell distributed mass and energy balance model, this paper presents a study of the dynamics of key process variables, demonstrating the impact on ledge thickness and other cell operating conditions spatially and temporally. By better understanding the operating limits under modulation strategies, traditional voltage-based controls can be replaced with energy-based ones that reduce costs and emissions while retaining the lifespan of a smelting cell.

2:45 PM  
Superconductor Busbars – High Benefits for Aluminium Plants: Wolfgang Reiser1; Till Reek2; Carsten Räch3; Daniel Kreutzer3; 1Vision Electric Super Conductors GmbH; 2Martin Iffert Consulting; 3University of Applied Sciences Kaiserslautern
     Superconductor busbars have reached industrial readiness. Superconductors are conducting direct current with extremely high densities of more than 500A/mm˛ with zero losses. Due to their low space requirements, high current carrying capacity and utmost efficiency superconductor busbars will find their place in the aluminium industry. The paper introduces the technical basis of superconductors and continues with technical and economic advantages. Five different usecases are illustrated with information about technical limits, energy efficiency and economic performance. Experiences out of installations are shared. The presented usecases are: Main busbars between rectifiers and potroom; Interconnection busbars between potlines and to standby rectifiers; Magnetic field compensation; DC connection between potline and power plant or grid connection point; Superconducting magnetic field shielding, permanent or mobileInvestment costs are indicated as well as costs for maintenance, operation and total cost of ownership for various timelines. A breakeven can be achieved in 4 years.

3:05 PM  
Coupled SPH-DEM to Simulate the Injection of a Powder into a Liquid with Heat Transfer and Phase Change: Thomas Roger1; Laszlo Kiss1; Kirk Fraser2; Sandor Poncsak3; Sébastien Guérard3; Jean Francois Bilodeau3; Guillaume Bonneau1; 1Universite Du Quebec A Chicoutimi; 2National Research Council Canada; 3Rio Tinto Aluminium
     The optimization of powder injection is a source of concern for several fields such as the agri-food industry, metallurgy, ore extraction. Several physical mechanisms intervene during the injection of a granular material into a liquid: solid mechanics, fluid mechanics, heat transfer and phase change. Since a powder is a discrete material, the model presented in this article uses the discrete element method (DEM). It is coupled to the "smoothed particle hydrodynamics" (SPH) method to simulate the liquid. A sub-model is used to calculate the heat transfer and the associated mechanical effects (sintering, coagulation). The phase change is integrated into the model to consider the solicitation of the liquid.Validation of the results is achieved with the injection of particles cooled with liquid nitrogen in a liquid at room temperature. The experiments were filmed with a high-speed camera to track each particle during the impact with the liquid surface.

3:25 PM  
Individual Anode Current Monitoring during Aluminum Reduction Cell Power Reduction: Yuchen Yao1; Jie Bao1; Maria Skyllas-Kazacos1; Barry Welch1; Ali Jassim2; 1University of New South Wales; 2Emirates Global Aluminum
    In this work, individual anode current measurement system is installed to monitor the aluminum smelting process during several case studies involving power reduction and restoration. In these studies, anode current signals, together with the line current and cell voltage, were obtained at a high sampling rate to ensure the dynamic features in the process are captured. It is observed that the cell exhibits “battery” behaviors on stopping the electrolysis process due to the anode having surface intermediates that have not been transformed into the final gaseous products. It is also found that some anodes experience negative currents during the reduction due to the changed magnetic fields, which may make the metal pad touch the anode, forming a closed circuit with other anodes. The analysis results provide more fundamental understandings of the aluminum reduction process and can aid the cell operations such as power modulation.

3:45 PM Question and Answer Period