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Light Metals 2006 Edited by TMS (The Minerals, Metals & Materials Society, 2006)
Marc Dupuis
and Valdis Bojarevics
GéniSim Inc.
3111 Alger St., Jonquière, Québec, Canada, G7S 2M9
University of Greenwich, School of Computing and Mathematics
30 Park Row, London, SE10 9LS, UK

Keywords: Thermo-electric models, MHD models, Aluminum electrolysis cell
The main goal of a cell stability MHD model like MHD-Valdis is
to help locate the busbars around the cell in a way that leads to the
generation of a magnetic field inside the cell that itself leads to a
stable cell operation.
Yet, as far as the cell stability is concerned, the uniformity of the
current density in the metal pad is also extremely important and can
only be achieved with a correct busbar network sizing.
This work compares the usage of a detailed ANSYS® based 3D
thermo-electric model with the one of the versatile 1D model part
of MHD-Valdis to help design a well balanced busbar network.
The problem of choosing the busbar sizing in order to obtain a
uniform current pick up in all the collector bars of a modern side by
side high amperage aluminum electrolysis cell, while known to be
critical to the cell MHD stability, is not often discussed in the
References [1 and 2] are two exceptions, each presents an in-house
computer code called respectively NEWBUS and BUSCAL
designed specifically to do such a task. Both use a simple 1D line
busbar network representation, a temperature dependent electrical
resistivity and solve for the resulting non-linear problem by
computing the voltage and temperature equations iteratively and
alternately until convergence is reached. These days, such an in-
house solver can be setup fairly rapidly in an Excel spreadsheet
(see figure 1).
Typically, the calculated collector bars current pick up distribution
and the different currents in the busbar network are then transferred
to the metal pad current density solver and the metal pad magnetic
field solver in preparation to run the MHD wave stability solver.
Much more recently, [3, 4, 5 and 6] ANSYS® based 3D full cell
and external busbar thermo-electric models have been developed in
order to very accurately compute the metal pad current density field
considering both the converged steady-state ledge profile and the
busbar design. Of course, once developed, the 3D busbar model
can also be solved stand-alone.
Figure 1. Simple 1D line network model of an anode studs, yoke
and rod implemented in an Excel spreadsheet.
So, on one hand, it is possible to develop an in-house code to solve
a simplified 1D line network busbar representation and use that
tool to perform busbar sizing optimization and, on the other hand,
it is possible to develop an ANSYS® based parametric 3D busbar
model to do the same.
Yet, there is now also a third option, using MHD-Valdis [7, 8, 9, 4,
5 and 10] which is a commercially available, fully non-linear MHD
cell stability solver. The fact that it is fully non-linear, means that it
is solving among other variables the busbar network current
distribution at each time step. It is doing so using a versatile 1D
line network busbar generator and solver called BUSNET also
available to carry out busbar sizing optimization studies.
The three above options will be compared to try to identify the
most efficient tool to carry out busbar sizing optimization studies,
but before proceeding with the comparison exercise, it is important
to take a step back and first review the background theory of the
equations that need to be solved.