Marc Dupuis, Jonquière
Valdis Bojarevics, Greenwich
Daniel Richard, Montréal
[1], it was demonstrated that as far as the thermal
balance aspect of the cell design is concerned, there is
no limit to the size of cells that could be designed.
electric design of a 740 kA cell was presented. But
what about the cell MHD stability and the potshell
mechanical design for that 9 risers, 26.2 meters long
cell?
design. Results suggest that as far as the MHD cell
stability aspect of the cell design is concerned, there is
no limit to the size of cells that could be designed.
Finally, as far as the potshell mechanical design is
concerned, after taking care of the potshell thermal
deformation issue [2], there is no limit in sight to the
size of cells that could be designed either.
that, in addition to the average magnitude, it is the
gradient of the vertical component of the magnetic
field (Bz) in the longitudinal direction of the cell that
is responsible for the main instability mechanism in a
modern side by side high amperage cell.
[4], Pechiney researchers describe how they minimized
that Bz longitudinal gradient (see figure 2 of [4]) by
using compensation busbars running along both sides
of the row of cells carrying current in the same
direction as the potline (see figure 3 of [4]). According
to the Pechiney patent, this compensation busbar
configuration will work well up to 500-600 kA cells.
analyzed using MHD cell stability modeling tool [5, 6
and 7] on a 500 kA cell (see figure 1 for the busbar
configuration). It indeed reduced the Bz magnetic field
gradient in the longitudinal direction to about 40 Gauss
over 17.3 meters (from 20G to 20G, see figure 2)
despite the fact that all 6 positive busbars are running
under the cell.
gradient, the MHD model is predicting that a coupled
(2,0) and (0,1) bath metal interface deformation wave,
the exact type of wave predicted in Urata's paper, will
grow in the cell (see figure 3 and 4).
compensation busbar configuration, so for sure, a
better setup can exist. But already in order to reduce
the Bz longitudinal gradient to 40 Gauss over 17.3
meters, the compensation busbar on the side of the
return line must carry 250 kA and the compensation
busbar on the opposite side must carry 145 kA. So in
the case presented here, a total of 395 kA or 79% of
the potline current is been carry by the 2 compensation
busbars. It is very doubtful that this compensation
busbar configuration could be extend to a 740 kA cell.
compensation busbar configuration has been
(0.0003 T) that no distinctive low frequency wave can
develop in the cell (see figure 5 and 6).
is working for any length of potshell and any number
of positive busbars running under the cell. The 9 risers,
740 kA cell design presented before [1] has too a
resulting Bz so close to 0 that no distinctive low
frequency wave can develop in the cell (see figure 7
and 8).
equally well work for any reasonable length of potshell
and any number of risers, for example a 85.8 meter
long, 30 risers, 2380 kA cell [1] could too be
magnetically compensated using the same approach.
So it is possible to conclude that as far as the MHD
cell stability aspect of the cell design is concerned,
there is no limit to the size of cells that can be
designed.