Computational modeling of anodic current distribution and anode shape shift in aluminium reduction cells
Abstract
In aluminium reduction cells, the profile of a new carbon anode changes with time before reaching a steady state shape, since the anode consumption rate, depending on the current density normal to anode surfaces, varies from one region to another. In this paper, a two-dimension model based on Laplace equation and Tafel equation was built up to calculate the secondary current distribution, and the shift of anode shape with time was simulated with arbitrary Lagrangian-Eulerian method. The time it takes to reach the steady shape for the anode increases with the enlargement of the width of the channels between the anodes or between the anode and the sidewall. This time can be shortened by making a sloped bottom or cutting off the lower corners of the new anode. Forming two slots in the bottom surface increases the anodic current density at the underside of the anode, but leads to the enlargement of the current at the side of the anode.
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- Fig. 1. Schematic geometry of a modern aluminum reduction cell
- Fig. 2. The channels and their typical widths in the aluminium reduction cell
- Fig. 3. Schematic cross section of a prebaked anode in the aluminium reduction cell
- Fig. 4. The anode shapes and secondary current distributions for the 15cm channel at (a) the initial time, after (b) 1 day, (c) 2 days, (d) 4 days, (e) 6 days and (f) 8 days
- Fig. 5. The anode shapes and secondary current distributions for the 2cm channel at (a) the initial time, after (b) 1 day, (c) 2 days, (d) 4 days, (e) 6 days and (f) 7 days.
- Fig. 6. The distributions of the anodic current densities at different time for the 15cm channel.
- Fig. 7. The distributions of the anodic current densities at different time for the 2cm channel
- Fig. 8. The anode shapes and secondary current distributions for the anode with chamfers (cutting off the lower corners by 4cm) at (a) the initial time, after (b) 1 day, (c) 2 days and (d) 6 days.
- Fig. 9. The changes of the maximum anodic current densities with respect to time for the normal anode and the anode with chamfers
- Fig. 10. The anode shapes and secondary current distributions for the anode with a sloped bottom (the tilted angle of 1.7 degrees) at (a) the initial time, after (b) 1 day, (c) 2 days and (d) 5.5 days
- Fig. 11. The changes of the maximum anodic current densities with respect to time for the normal anode and the anode with a sloped bottom
- Fig. 12. The anode shapes and secondary current distributions for the anode with slots (1cm width) at (a) the initial time, after (b) 1 day, (c) 4 days and (d) 7 days
- Fig. 13. The changes of the average anodic current densities with respect to time in the different regions of the undersides of the anodes
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