Conference Agenda

Over the last few decades, electric power consumption has increased faster than the increase in power generation. Flexible power is a demand-driven power management strategy, based on cost and availability of energy, that has changed the aluminum cell production rate and power consumption dynamically. This can provide benefits for both the smelting industry and the power grid, particularly as intermittent renewable energy sources become more prevalent. However, power modulation poses challenges for preserving the stability and efficiency of the smelting process, which is susceptible to temporal variations of mass and thermal balances. It is complicated to follow bath temperature variation linked to current fluctuation, given that high variation is primary factor in heat imbalance in the cells. In this paper, we present a new approach to follow the cell behavior in terms of thermal balance during power modulation.

A thermo-electrical 3D transient model is used to simulate scenarios with different inputs in order to estimate the impact of power modulation on the thermal phenomena as well as the energy balance in the cells. This model was tested on Laboratoire de recherches des fabrications (LRF) prototype pots to assess its predictivity and response to energy variation compared to measurements. The simulation results, for a given amperage amplitude, show an accurate prediction of the cell temperatures across various locations, particularly in the bath, and also the ledge profile variations. Moreover, this modeling enables us to estimate the temperature evolution on the cathode block surface, which allows a precise view of the cathode thermal state.

The magnetohydrodynamic (MHD) stability of an aluminium (Al) electrolysis cell is important for overall stable operation at a lower anode-to-cathode distance (ACD). In particular, it is beneficial to understand the influence of changing cell parameters such as the ACD, metal height, and reduction current on the stability of the cell, which can be quantified by the growth or decay rate of the interfacial waves on the aluminium-electrolyte interface. This can be done by running a suite of numerical MHD simulations with different cell parameters and then using the resulting interface evolution to find the growth/decay rates. However, with many combinations of cell parameters to test, such an endeavor will often be expensive and time consuming. In this work, we utilize the mechanical model of MHD instabilities in Al cells presented in [1] to analyze the stability of an Al cell for different combinations of cell parameters. We first show that the model’s stability and growth/decay rate can be found quickly by solving a system of algebraic equations. Then, we use the model to study the stability of an Al cell at different ACD and metal height combinations and show a stability map of the growth/decay rates. Our results show the value of using the mechanical model as a complement tool to MHD simulations, where it can be used to rapidly narrow down the combinations of cell parameters to be simulated numerically.

During the process of reducing energy consumption in the SY350 potline of SPIC, challenges arose in terms of insufficient magnetohydrodynamic stability. Specifically, a noticeable decline in current efficiency was observed after reducing anode-cathode distance (ACD). To address this issue without affecting the overall production capacity of the potline, experimental pot was selected for an upgrade experiment on MHD stability by SAMI. The experimental plan involved the redesign of the busbar around the cell using the most advanced magnetic field calculation platform, coupled with the application of networked self-equalizing busbar technology to enhance the anti-interference capability. After the technological upgrade, the vertical magnetic field of the experimental pot was significantly reduced, with a decrease exceeding 70 % in the 1st quadrant and over 40 % in the 2nd and 4th quadrants. Additionally, the distribution of the magnetic field is much more uniform. Both the liquid metal velocity and the bath velocity decreased, exhibiting a more regular double-pool distribution. The interface deformation below the anode projection was reduced from approximately 4.3 cm to around 3.6 cm. The improvement of the above indicators has significantly increased the performance of the pot, and the stability of the MHD is no longer a technical bottleneck. The net voltage of the test pots is reduced from about 4.02 V to about 3.90 V, the current efficiency is no longer affected when the ACD is reduced by 3 mm, and the average DC power consumption is < 12400 kWh/t Al.

This paper extends our previous research (ICSOBA, 2023) by introducing the variation of bubble voltage drop during the slotted anode life span (~70 shifts) into the existing Computational Fluid Dynamics (CFD) model. This enhanced model investigates the gas dynamics and bubble voltage drop in an aluminium electrolysis cell. Numerical simulations for two anode slots inclinations (20 mm and 80 mm) were performed using COMSOL Multiphysics software based on the finite element method. The CFD model couples turbulent flow, phase transport, and secondary current distribution physics. The latter gives the voltage drop caused by the gas concentration and its layer thickness underneath the anode, while Navier-Stokes equations and phase transport physics give the velocity and pressure profiles as well as the gas volume fraction distribution, respectively. The standard k-ε turbulence model was used. The results reveal how different parameters vary throughout anode life span like the voltage drop penalties due to gas coverage, bath mixing efficiency caused by pushing the gases towards the central channel, and heat transfer through the side wall due to the change in flow steering corresponding to the variation of gas amount passing to the side channel. These findings can help on the optimization of slotted anode designs in industrial cells.