[0001] 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.
[0002] 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.
[0003] 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.
[0004] When developing a busbar system, it is a common practice to be guided by the following
conditions:
- 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 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.
[0005] 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).
[0006] 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.
[0007] 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 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).
[0008] 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 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-section of 650×70 mm (the width
of one stack is about 2 meters, and the width of two stacks is about 4 meters).
[0009] "New Busbar Network 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).
[0010] 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.
[0011] 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.
[0012] 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
between them, which is unacceptable according to the Safety Rules (SR) and the Electrical
Safety Code (ESC).
[0013] 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.
[0014] Similarly, there is another known patent application
WO 2016/128824, 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.
[0015] In the meantime, claim 1 states that the busbar system has at least one first 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.
[0016] 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.
[0017] 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 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.
[0018] 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.
[0019] 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.
[0020] 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 the spacing
between cells, thus having an adverse effect upon its competitiveness; and
- Relative complexity of the busbar system design.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] Hereinafter, a description of the drawings is provided.
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) 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.
[0025] The busbar system consists of two single-row lines 3, 5, 1 and 4, 6, 2 of serially
connected electrolysis cells, the lines being 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
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
cell row 3.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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).
[0032] 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.
[0033] 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.
[0034] These criteria are insufficient to ensure high technical and economic performance
indicators for electrolysis cells designed for an amperage of more than 500 kA.
[0035] 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.
[0036] 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.
[0037] 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
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.
[0038] 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.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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 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 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.
[0045] 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
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
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.
[0047] 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:
- Amperage - 550 kA;
- Current efficiency - 94.5%;
- Voltage - 3.8 V; and
- Specific energy consumption - 12,000 MWh/kg.
[0048] 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.
[0049] 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.
[0050] 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.