Note: Descriptions are shown in the official language in which they were submitted.
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A MODULAR BUSBAR SYSTEM FOR ALUMINUM POTLINES
The invention relates to aluminum smelting by the method of electrolysis of
melted cryolite salts in electrolysis cells (pots) arranged side-by-side in
the cell (pot)
room.
A busbar system is a current-conductive element of an electrolysis cell
structure
and consists of two parts, anodic and cathodic. Electrolysis cells arranged in
rows one
after another are coupled with each other by current conductors made of
aluminum or
copper busbars of different cross-section and connected in an electrical
circuit in series:
cathode busbars of one cell are connected to anode busbars of another cell. A
group of
electrolysis cells combined into one electrical circuit is called a potline
(or cell line).
The anode part of the busbar system comprises flexible straps in a stack (or
flexible
strap stacks), anode risers and anode buses. The current is transferred from
the anode
buses to aluminum anode rods, and then to prebaked carbon (anode) blocks. The
cathode part of the busbar system comprises flexible straps in stacks (or
flexible strap
stacks) that drain current from collector bars in the bottom of the cell to
main
(collecting) cathode buses, and then to cathode buses.
There are many known busbar system designs for electrolysis cells. A busbar
system is developed for a specific electrolysis cell design using computer-
based
mathematical models (or simulations) and depends on cell type, cell amperage,
cell
position in the pot (or cell) room and in the potline, the availability of
adjacent (or
neighboring) pot rooms, local climate, the remoteness of raw materials
suppliers,
product consumers, and the cost of electricity, raw materials and finished
products.
When developing a busbar system, it is a common practice to be guided by
the following conditions:
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- Compliance of design solutions with safety rules (SR) and an electrical
safety code (ESC);
- Optimal current density in a busbar system and current-carrying parts of
an
electrolysis cell;
- Balanced Lorentz forces on the melt, i.e. optimal electric and magnetic
fields
in the melt;
- Possibility to quickly and safely disconnect (cut out) and connect (cut in)
one cell or a group of cells from/to an electrical circuit without having
operational
perturbations in adjacent (or neighboring) cells and without breaking or
curtailing
the potline amperage;
- Buses in Russia are currently manufactured mainly from A7E grade aluminum
having a temperature coefficient of electrical resistance of 0.004. This means
that when
the bus temperature changes by 10 C. its resistance changes by 4%, which
should also
be taken into account. In practice, this can be taken into account only
roughly, since the
temperature of any bus depends not only on the density of current flowing
through it
(the Joule¨Lenz law), but also primarily on its thermal balance that is
determined by
busbar shape, weight and material, molecular heat dissipation or heating from
another
thermal source. heat dissipation or generation through radiation. convective
heat
exchange or the influence of sources of cold;
- When designing cathode and anode busbar systems, it is desirable to have
a more uniform current distribution in collector bars and anodes in order to
minimize planar currents in the metal that adversely affect the
magnetohydrodynamic (MHD) stability of electrolysis cells, which results in
the
degradation of their technical and economic performance indicators (TEPI);
- When designing, the flexible strap stacks of the anode busbar system
should be calculated in such a way that they do not experience mechanical
damage
during anode beam (or rack) movement up and down to the limit switches and
limit
stops within a pre-set range; and
- A potline with a busbar system should be reliably insulated from 'earth'
and from the cathode shell to reduce current leakage. Current leakages not
only
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determine direct current losses, which cannot be used in the process of
electrolysis,
but also cause the hard-to-remove MHD instability of the melt in electrolysis
cells,
in those places that are close to current leakages.
There is a known busbar system for electrolysis cells that are arranged side-
by-side in the potroom, which contains main (collecting) busbars with cathode
flexibles installed along the upstream and downstream longitudinal sides of
the
cell, and anode risers installed on the upstream side, through which equal
currents
flow. The anode busbar system is connected with the previous cell by means of
risers, where the outermost risers are connected to the outermost main
(collecting)
cathode busbars of the upstream side of the cell by busbar stacks located
along the
end faces of the cell and to the main (collecting) cathode busbars of the
downstream
side of the cell, while the middle risers are connected to the middle main
(collecting) busbars of the upstream side of the cell by busbar stacks
arranged
symmetrically under the cathode blocks being closest to the cell ends and to
the
main (collecting) cathode busbars of the downstream side of the cell, wherein
the
busbar extending under the bottom and located closer to an adjacent (or
neighboring) row of electrolysis cells carries 15% of the upstream side
current,
while the other one carries 10% of the upstream side current, and there is an
intermediate busbar under the cell bottom that extends halfway between the
potline
axis and the cell end, on the side opposite to the adjacent (or neighboring)
row of
electrolysis cells, wherein 5% of the upstream side current flows through this
busbar (patent FR2552782, PECHINEY ALUMINIUM, IPC C25C 3/08, 1985).
A disadvantage of the above busbar system is the impossibility of using it
for electrolysis cells operating at an amperage of greater than 380 kA, since
asymmetrical busbar systems, from a design point of view, have limitations in
compensating for the magnetic field that is picked up from an adjacent row of
electrolysis cells.
There is a known current supply/drainage apparatus to/from aluminium
reduction cells with double-row, side-by-side arrangement in a row, which
comprises
an anode busbar system connected to anodes by anode rods, a cathode busbar
system
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composed of collector bars with flexible strap stacks projecting on both sides
of the
cathode shell of the cell with a bottom, main (collecting) cathode busbars on
the
upstream and downstream sides of the cathode shell of the cell, connecting
busbars,
a shunt element, a connection between the cathode and anode busbar systems,
and
.. magnetic field correction (compensation) loop busbars that are located in
parallel to
the transversal axis of the electrolysis cell near the cathode shell ends. The
connection
between the cathode busbar system and the anode busbar system of the following
cell
in a row is made in the form of bus modules composed of two semi-risers,
wherein
one of the semi-risers is rigidly connected to the downstream main (colleting)
cathode
busbar that, in turn, is connected to four flexible strap stacks, and another
semi-riser
is connected by busbars located under the cathode shell bottom and coupled
with the
upstream (collecting) cathode busbar stacks, each of them being connected to
two
flexible strap stacks, wherein the connecting busbars are located under the
cathode
shell bottom in parallel to the transversal axis of the electrolysis cell and
each other,
while the current supplied to the correction (compensation) loop is supplied
in the
direction coincident with the current direction in the potline, and the
current in the
magnetic field correction (compensation) loops is preferably 20-70% of the
potline
amperage (patent FR 2583069, PECHINEY ALUMINIUM, 1986-12-12).
A disadvantage of this busbar system is that it uses independent magnetic
field correction (compensation) busbars from two conductors extending along
both
ends of electrolysis cells in a circuit, in the potline amperage direction.
The
correction (compensation) current is 20-70% of the potline amperage. For
example, when the potline amperage is 500 kA, the correction (compensation)
current can reach 350 kA. A current equal to 500 + 350 = 890 kA that flows
along
the potline generates a magnetic field corresponding to 890 kA rather than to
500 kA in the potroom, which primarily has an adverse effect on potroom
personnel. The additional weight of the busbar system due to correction
(compensation) busbars will come to about 10 metric tonnes per each cell of
the
potline. In any case, the use of a correction (compensation) circuit (loop)
leads to
an increase in the busbar system weight. growth in power consumption due to a
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voltage drop in the correction (compensation) circuit (loop), and an increase
in
expenditures on the floor space for the installation of the correction
(compensation)
circuit (loop). For example, when the correction (compensation) current is 450
kA,
correction (compensation) busbars will be composed of 16 buses with a cross-
5 section of 650x70 mm (the width of one stack is about 2 meters, and the
width of
two stacks is about 4 meters).
New Busbar Nehvork Concepts Taking Advantage of Copper Collector Bars to
Reduce Busbar Weight and Increase Cell Power Efficiency' by Marc Dupuis,
Proceedings of 34th International ICSOBA Conference, Quebec, Canada, 3-6
October,
2016, p. 883, ISSN 2518-332X, Vol. 41, No. 45 provides a new concept of the
magnetic
field from an adjacent row of cells in a potline, including simultaneous
optimization
(magnetic field depression with respect to the Bz component in the cell ends).
The first method of the new concept provides for the use of anode risers on
the upstream side of the cell only. In the simplest form of the concept, 100%
of the
potline amperage returns back to the current supply station via additional
correction
(compensation) busbars located under the bottom of the cells in a potline.
According to the second version of this new concept, the upstream busbars
of the cell carry half of the potline amperage under the bottom of the cell to
the
upstream risers of the following cell. The downstream busbars of the cell
carry the
second half of the potline amperage to the risers of the following cell under
the
bottom, to the risers located on the downstream side of the cell. As in the
first
concept, the total potline current of opposite direction flows in the adjacent
(neighbored) additional compensation busbars under the bottoms.
A considerable disadvantage of both options of the said concept is that they
are only of theoretical interest and cannot be implemented in practice. This
is due to
the fact that the potential difference between the poles of power supply
stations of
modern potlines is 1,000 V and higher. Since the potline's cathode busbar
system
and correction (compensation) busbar stacks (that return current to the power
source)
are located in immediate proximity, an electric arc (plasma) will inevitably
emerge
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between them, which is unacceptable according to the Safety Rules (SR) and the
Electrical Safety Code (ESC).
There are currently no industrially applicable, inexpensive and reliable
methods for insulating between high-current conductors that have a potential
difference of 1,000 V and higher between each other, considering a large
conductor
area, a short distance between conductors and high amperage.
Similarly, there is another known patent application W02016/128824,
C25C3/16 published on August 18, 2016. The application claims consist mainly
of a
set of technical solutions, namely:
- Claim 1 states that a side-by-side busbar system has anode risers both on
the
upstream side and on the downstream side of an electrolysis cell.
- Claim 19 states that an electrolysis cell busbar system is an electrical
modular structure.
In the meantime. claim 1 states that the busbar system has at least one first
Is compensation loop located under electrolysis cells and capable of
passing through
itself the first compensation current (amperage) under electrolysis cells in
the
direction opposite to the total electrolysis amperage direction.
- Claim 1 also states that the busbar system can have at least one second
electrical
compensation loop located at least on one side of electrolysis cells and
capable of
passing the second compensation current in the electrolysis amperage
direction.
The availability of two correction (compensation) lines and a potline itself
implies heavy expenditures for three independent power supply stations, taking
into account that an emergency margin is required for each of them, and
expenditures for additional busbars of the 2 correction (compensation) loops,
power losses in both correction (compensation) loops and their power supply
stations, which is a disadvantage of the known application.
Fig. 6 in the said application shows electrolysis cells, whose collector bars
pass
through the bottom perpendicular to the metal pad. Protection against metal
leakage
between the collector bars and the lining is likely to be cost-consuming,
since the
.. collector bars, the lining, and the cathode shell are substantially
different in terms of
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their physical, electrical and thermal properties. During an electrolysis cell
campaign
(6-7 years), the probability of molten aluminum leakages, vertical collector
bar
dissolution and metal run-out is very high, since the said elements of the
electrolysis
cell constantly move relative to each other, and their geometry and physical
properties
change, which is another disadvantage of the application.
The known cell busbar system according to patent RU 2288976, taken as
prior art, has a double-row side-by-side arrangement in a line, contains an
anode
busbar system part connected to anodes by anode rods and a cathode busbar
system
part composed of collector bars with flexible strap stacks projecting on both
sides
of the cathode shell of the cell. The connection between the collector bars
and the
anode busbar system of the following cell in a row is made in the form of bus
modules composed of main (collecting) cathode busbars, connecting busbars and
anode risers. At least one riser in each module is located on the upstream
side of
the cell and at least one riser in each module is located on the downstream
side of
the cell.
In the meantime, the upstream anode risers are powered from the collector
bars both on the upstream side and on the downstream side of the previous
electrolysis cell, and the downstream anode risers are powered from the
collector
bars on the downstream side of the previous electrolysis cell. About 1/2-3/4
of the
module current flows through the upstream anode risers, while about 1/2-1/4 of
the module current flows through the downstream anode risers, the connecting
busbars are located under the cell bottom, and some connecting busbars of the
outermost modules can at least pass around the cell ends and be preferably
located
at the molten metal level.
The disadvantages of the said prior-art busbar system are:
- A limitation in developing electrolysis cells for an amperage of more than
600 kA due to the necessity of feeding a larger amount of current via busbar
stacks
passing around the cell ends, due to the need to lengthen the cell cavity,
which will
complicate the busbar system design, increase its weight and require an
increase in
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the spacing between cells, thus having an adverse effect upon its
competitiveness;
and
- Relative complexity of the busbar system design.
The objective and technical result of the invention is the formation of an
optimal magnetic field in the melt of electrolysis cells arranged side-by-side
in a
potroom so as to develop and deploy potlines for amperage of 600 kA to 2,000
kA,
preferably for 800 kA.
This result is achieved due to fundamental differences between the proposed
application for an invention of a busbar system and the busbar system of the
prior
art, which are as follows:
1. The busbar system shall obligatorily be part of a facility comprising two
single-row lines of electrolysis cells, such lines being independent in terms
of
electrical current supply.
2. The cathode correction (compensation) busbars of each line are located in
close proximity to the cathode busbar system of the adjacent cell row.
3. The current in the lines is directed in opposite directions to each other.
4. The anode risers on the upstream and downstream sides of an electrolysis
cell
are located symmetrically with respect to the YZ plane of the cell.
In the meantime, it is impossible to have an optimal magnetic field without
using
the technical solutions specified in the limiting (restrictive) part of the
prior art, these
technical solutions comprise:
5. The availability of anode risers on both the upstream and downstream sides
of
the cell.
6. The possibility of selecting an optimal current distribution in the anode
risers on the upstream and downstream sides, in those ranges that are
specified in
the limiting (restrictive) part of the application claims.
7. The possibility of passing part of the current around the cell ends when
designing an optimal field in the melt.
Hereinafter, a description of the drawings is provided.
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Fig. 1 shows a schematic diagram for the facility composed of two lines of
electrolysis cells 3, 5, 1 and 4, 6, 2 in plan view, where the correction
(compensation)
busbars of adjacent potlines 5 and 6 extend under each row of potlines 3 and 4
in the
immediate vicinity of the cathode busbar system of the line. The potlines are
.. independent with respect to power supply and each of them is connected to
separate
power sources 1 and 2.
Fig. 2 shows an example of a 4-module busbar system according to the
application for an invention that is designed for an amperage of 800 kA, with
anode
risers 16 and 17 arranged on both sides of the cell and correction
(compensation)
to busbars 5 and 6 located in the immediate vicinity of the cathode busbar
system of
electrolysis cell rows 3 and 4 belonging to the adjacent potline,
respectively.
Fig. 3 shows a connection diagram for electrolysis cell rows 3 and 4 in cross-
section view according to the application, including upstream risers 16 and
downstream risers 17, and correction (compensation) busbars to compensate for
the magnetic field from adjacent potlines 5 and 6, respectively.
Fig. 4 shows the magnetic field, in mT, for magnetic induction vector
component Bz in the middle of the metal pad of a pilot electrolysis cell,
according
to the prior-art patent, at an amperage of 550 kA.
Fig. 5 shows the magnetic field, in mT, for magnetic induction vector
component Bz in the middle of the metal pad of an electrolysis cell, according
to
the application for an invention, at an amperage of 800 kA.
Fig. 6 shows the magnetic field, in mT, for magnetic induction vector
component By of an electrolysis cell similar to the application for an
invention, with
upstream anode risers 16 only and correction (compensation) busbars 5 and 6 to
.. compensate for the magnetic field from the adjacent potline, respectively.
Fig. 7 shows the magnetic field, in mT, for magnetic induction vector
component By of an electrolysis cell according to the application for an
invention,
with anode risers 16 and 17 located on both sides of the cell symmetrically
with
respect to the YZ plane and correction (compensation) busbars 5 and 6 to
compensate for the magnetic field from adjacent cell rows 3 and 4,
respectively.
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The busbar system consists of two single-row lines 3, 5, 1 and 4, 6, 2 of
serially
connected electrolysis cells, the lines bein2, independent with respect to
power supply.
The current in the potlines flows in opposite directions. Potline 3, 5, 1 is
powered from
independent current source 1, while potline 4, 6, 2 is powered from
independent
5 current supply source 2. Potline 3, 5, 1 returns current to power source
1 with the help
of correction (compensation) busbars 5 extending in close proximity to the
cathode
busbar systems of adjacent electrolysis cell row 4. Similarly, potline 4, 6, 2
returns
current to power source 2 by means of correction (compensation) busbars 6
located in
close proximity to the cathode busbar systems of the potline composed of
electrolysis
10 cell row 3.
As an example, Fig. 2 shows a four-module busbar system designed for an
amperage of 800 kA. Depending on the number of modules to be selected, it can
be
developed for electrolysis cells operating at any acceptable (from technical
and
economic points of view) amperage (1,000-1,500 kA and higher; for example,
2,000 kA). Developing potlines composed of single-module busbar systems is not
ruled out.
The busbar system shown in Fig. 2 and Fig. 3 comprises an anode busbar
system 7 with anodes 8 and anode rods 9, a cathode busbar system composed of
collector bars 10 and flexible strap stacks 11, and bus modules A, B, C and D.
Each
module includes upstream main (collecting) cathode busbars 12 and downstream
main (collecting) cathode busbars 13 of the cathode shell 14, connecting
busbars
15, and upstream anode risers 16 and downstream anode risers 17 located
symmetrically with respect to the YZ symmetry plane. The connecting busbars 15
are located in close proximity to the cathode busbar system of potlines 3 and
4. The
upstream anode risers 16 are connected to the upstream cathode busbars 13 of
the
previous electrolysis cell. The downstream anode risers 17 are connected to
the
upstream cathode busbars 12 of the previous electrolysis cell. The correction
(compensation) busbars 5 and 6 to compensate for the magnetic field from the
adjacent potline are located in close proximity to the cathode busbar system.
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As shown in Fig. 1, Fig. 2 and Fig. 3, the current from the collector bars 10
is transferred by means of the flexible strap stacks 11 to the main
(collecting)
cathode busbars 12 and 13, then, it is transferred to the anode busbar system
7 via
the connecting busbars 15 and through the anode risers 16 and 17, and then it
is
transferred to the rods 9 and the anodes 8 of the following cell in a potline.
The
current in the correction (compensation) busbars 5 and 6 to compensate for the
magnetic field from the adjacent cell rows 3 and 4 is oriented in the opposite
direction to the potline amperage.
It should be noted that the technical solution of the application for an
invention
is based on the understanding that low-amperage electrolysis cells do not
require
over-complication of the busbar system in view of low magnetic field
intensity, a
small density of horizontal currents, and a limited volume of molten metal.
Good
results during electrolysis can be achieved even in the case of one-side
current
drainage from the cathode and one-side current supply to the anode busbar
system.
Such electrolysis cells can be arranged end-to-end in two or four rows within
the
potroom, which has no substantial effect on the mutual influence of the
magnetic
fields.
High-amperage electrolysis cells (up to 2,000 kA) are disclosed herein,
which are assembled from parallel lines of low-amperage electrolysis cells
(modules), whose current is unidirectional. In the meantime, adjacent
(neighboring) cells (modules) of each potline are combined into one combined
cell,
as shown in Fig. 2.
MHD instability issues in each low-amperage electrolysis cell (module) are
minimal, so there will be no substantial issues related to MHD stability in a
high-
amperage electrolysis cell composed of low-amperage electrolysis cells
(modules).
It is efficient to arrange the combined cell transversely to the cell room
axis.
This allows a considerable reduction in the magnetic field intensity
contribution
from the cathode busbar system.
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The main prerequisites for the optimal character of the magnetic field in the
metal for side-by-side electrolysis cells operating at an amperage of up to
500 kA
are as follows:
- Vertical (Bz) and transverse (Bx) magnetic fields in the metal should not
exceed 1.5 mT;
- Direction of the vertical component (Bz) of the magnetic field should be
alternating in sign with respect to each quarter of the cell (propeller-like
character);
- Longitudinal component (By) of the magnetic field should be
antisymmetric with respect to the YZ symmetry plane.
These criteria are insufficient to ensure high technical and economic
performance indicators for electrolysis cells designed for an amperage of more
than
500 kA.
When the vertical component (Bz) of the magnetic field, which acts upon a
molten metal layer, has the same sign of direction (plus or minus) over a vast
area
of the electrolysis cell, especially along its longitudinal sides, coherent
and
increasing surface oscillations may occur in the melt due to the accumulation
of the
longitudinal moment along the cell. They cause a low MHD stability of
electrolysis
cells and, as a result, their poor technical and economic performance
indicators.
Therefore, an increase in MHD stability, as a result of magnetic field
optimization
in the molten metal, is achieved through frequent changes in sign for the Bz
magnetic
field component along the longitudinal sides of the electrolysis cell, and, as
this takes
place, a change in sign should be antisymmetric with respect to the YZ
symmetry
plane of the cell.
In this application for an invention, this problem is solved as follows. The
structure of the anode and the cathode of electrolysis cells includes great-in-
size
ferromagnetic masses that possess substantial metal protection properties
against
the magnetic field of the cathode busbar system.
Unlike the magnetic field generated by the cathode busbar system, the magnetic
field generated by the anode risers, through which the total potline current
passes,
mainly generates the vertical (Bz) magnetic field in the metal, considering
that there are
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no ferromagnetic shields between the metal and the risers, which reduce the
effect of
the magnetic field from the risers upon the metal. The (Bz) field directed
downward
(minus) is generated in the metal on the right side along the current flow in
the riser,
and the field directed upward (plus) is generated on the left side from the
riser. A
.. sinusoid-like field for the (Bz) component with an amplitude of no more
than 3.0-
3.5 mT can be generated by selecting an appropriate distance and amperage in
the risers
on one longitudinal side. If similar anode risers are located on the opposite
side,
symmetrically with respect to the YZ plane, this will result in the generation
of the
vertical magnetic field as shown in Fig. 4, which is antisymmetric with
respect to the
YZ and XZ planes.
However, as the cell amperage increases due to the installation of additional
modules and the cell becomes longer, the value of the magnetic induction
vertical
component will grow, especially in the outermost cell modules A and D, see
Fig. 2.
Also, with an increase in the amperage, for compensating the magnetic field
picked up from the adjacent row, it will be required to increase the distance
between
the electrolysis cell rows to transfer current to the stacks passing around
the cell ends
from a greater number of collector bars in order to compensate for the growing
Bz
component of the magnetic field. This will have a negative effect on the
busbar
system weight and costs per unit of the potroom area.
These two problems are solved herein by the installation of correction
(compensation) busbars under the cathode busbar systems of the cell row of the
adjacent
line, as shown in Figs. 1, 2, 3; within 80-100% of the total number of
busbars. The
correction (compensation) current flows in the direction opposite to the
current flowing
in the cathode busbar system of the cell row of the adjacent line.
Since the potential difference between the poles of power supply stations of
modern potlines can reach 1,000 V and higher, the correction (compensation)
busbars
should be connected to their own, separate current source to preclude the
potential
difference between the cathode busbar system and the correction (compensation)
busbars in order to avoid arcing, especially in the electrolysis cells that
are located near
the power source.
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To solve this problem, this application provides for using the second potline
to be independent in terms of electrical current supply. In other words, the
facility
that comprises the busbar system specified in the application consists of two
single-
row potlines. The current in one potline is directed clockwise (in plan view),
and
the current in another potline is directed counter-clockwise, as shown in Fig.
1,
wherein the electrolysis cell rows belonging to two potlines 3 and 4 are
depicted.
The second rows in each potline are replaced by the correction
(compensation) busbars 5 and 6 located in close proximity, mostly, under the
bottoms of the adjacent cell rows of potlines 3 and 4. Since the currents in
the
cathode busbar system and the correction (compensation) busbars are equal and
flow in opposite directions, then, as a rule of thumb, the current from the
busbars
of the cathode busbar system and the correction (compensation) busbars
compensates for the magnetic field around itself. The correction
(compensation)
busbars, first, compensate for the vertical magnetic field in the melt of
electrolysis
cells to bring it to optimal values and. second, subtract the magnetic field
around
each of two rows 3 and 4 of the potlines, thus preventing the influence of the
magnetic field on the adjacent row of electrolysis cells.
This allows installing rows of electrolysis cells in close proximity to each
other,
for example, in the same pot room. However, the correction busbars not only
optimize
the vertical field component (Bz) in the metal, but also have an effect on the
longitudinal component (By) generated mainly by volume currents and currents
of
collector bars, namely, they subtract it on the upstream longitudinal side of
the cell
and increase this component, by being added to it, on the downstream side,
because
they coincide in direction. Fig. 6 shows the By field component in the metal
of the
cell with the risers installed only on the upstream side, provided the
correction busbars
are available. As can be seen, the magnetic field has a 100% positive
direction with
respect to this component. Being equal to (-2-0 mT) on the upstream side, it
reaches
(+36¨+38 mT) on the opposite longitudinal side. Upon interaction with the
vertical
current, Lorentz forces occur in the melt, they are being directed from the
upstream
longitudinal side to the downstream longitudinal side (in plan view), which
causes
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metal heaving or, more correctly, metal shifting from the upstream
longitudinal side
to the downstream side. As this takes place, the upstream longitudinal side
becomes
"hot" and the downstream side becomes -cold". This leads to asymmetry in the
thermal balance and the ledge profile, as well as in the electric field in the
metal, and
5 .. more specifically, to the occurrence of planar currents that, as is
known, reduce the
MHD stability of electrolysis cells and their technical and economic
performance
indicators.
In this application for an invention, this problem is solved by the
availability
of anode risers located on the opposite, downstream side 7 of the cell, as
shown in
10 Fig. 2 and Fig. 3. In this case, the total current in the risers on the
upstream side
reduces by approximately 2 times, and thus, facilitates an increase in the
magnetic
field Bx component on the upstream side, since the magnetic field generated by
the
anode risers with respect to the By component adds to a similar field
generated by
the correction (compensation) busbars. To the contrary, the magnetic field
from the
15 anode risers on the downstream side subtracts the field from the
correction
(compensation) busbars. By selecting the amperage for the anode risers on the
upstream and downstream sides of the cell, within the limits set in the
application
claims, it is possible to have a magnetic field to be antisymmetric with
respect to the
YZ plane along the longitudinal sides, and thus, symmetric metal heaving as
shown
in Fig. 7.
-Light metals-2017", editor Ante P. Ratvik, p. 26, ISSN 2367-1181 ISSN
2367-1696 (electronic) The Minerals, Metals & Materials Series, ISBN 978-3-319-
51540-3 ISBN 978-3-319-51541-0 (eBook), contains the key operating parameters
of a test group of 550-kA electrolysis cells, whose busbar system is assembled
in
accordance with the prior art in this application for an invention (RU
2288976). Tests
have been underway for more than 2 years.
In case of the magnetic field shown in Fig. 4 and measured with respect to the
Bz component, which is similar to the magnetic field according to the
application for
an invention (Fig. 5), the test group operates with the following operating
characteristics:
CA 03052237 2019-07-31
16
- Amperage ¨550 kA;
- Current efficiency-94.5%;
- Voltage ________ 3.8 V; and
- Specific energy consumption ________ 12,000 MWh/kg.
Since the start of testing these electrolysis cells, it has not yet been
possible to
achieve MHD instability. Their noise is 5-6 mV under normal operating
conditions
and does not exceed 20 mV during operational disturbances.
The practical measurements and calculations point to the same qualitative and
quantitative character of the magnetic field with respect to the Bz and Bx
field
components both in the melt of the prior-art cell and in the melt of the cell
for 800 kA
according to the application for an invention, as shown in Fig. 4, Fig. 5 and
Fig. 7.
Said coincidences predict, with high confidence, that the operating parameters
of
a cell with the busbar system according to the application (up to 2,000 kA)
will be no
worse than those of the prior-art cell.
