Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
[0011 A Device For Compensation Of Magnetic Field Induced By A Neighboring Row
Of High-Power Reduction Cells Connected In Series
FIELD OF THE INVENTION
[002] The invention relates to the production of aluminum by electrolysis in
high-power
electrolysis cells, and more specifically it relates to devices for
compensation of magnetic
fields induced by adjacent cells.
BACKGROUND OF THE INVENTION
[003] Aluminum is often carried out by electrolysis of a solution of alumina
in cryolite,
in cells electrically connected in series brought to a current passing through
the cell.
[004] Each electrolysis cell consists of a rectangular cathode forming a
crucible. The
bottorn of the cells is formed by blocks of carbon disposed on the steel
cathode rods
which. are adapted to transmit the current from the cathode toward the anodes
of the
follovring cell. The anode system, also made of carbon, is fixed beneath an
anode bus bar
super-structure and is connected to the cathode rods of the preceding cell.
[005] The electrolysis bath in the form of solution of alumina in cryolite is
disposed
between the anode system and the cathode. The produced aluminum is deposited
on the
cathode. To provide a thermal fly-wheel effect a layer of liquid aluminum
about 20 cm
thick is permanently kept at the bottom of the cathode crucible. In view of
the rectangular
configuration of the crucible, the anode rods supporting the anodes are
generally parallel
to its large edges of the crucible, while the cathode rods are parallel to the
small edges
thereof, known as cell heads.
[006] The cells are arranged in lines in a longitudinal direction or in a
transverse
direction depending upon whether the large sides or the small sides are
parallel to the axis
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of the line. The cells are electrically connected in series with the ends of
the series being
connected to the positive and negative outputs of an electrical rectification
and regulation
sub-station. Each series of cells comprises a certain number of lines branched
in series,
the number of lines preferably being even so as to avoid needless lengths of
conductors.
[007] The flow of electric current through the various conductors such as
electrolyte,
liquid metal, anodes, cathodes and connecting conductors creates substantial
magnetic
fields.. These fields induce in the electrolysis bath and in the molten metal
contained in
the crucible forces which are harmful to the proper operation of the cell. The
cells and the
respective connecting conductors are arranged, so that the magnetic fields
created by the
different parts thereof are adapted to compensate each other. A cell having
the vertical
plane parallel to the line of cells and passing through the center of the
crucible as its plane
of syimmetry is thus obtained. However, the cells are also subjected to the
harmful
interfering magnetic fields emanating from the adjacent line or lines.
[008] U.S. Patent 3,616,317 discloses the device provided for compensation
effect of
magnetic field from neighboring reduction cells arranged the end-to-end
relationship
inclucling the direct current conductor on the outer side of the potline, the
current in it
runs, at this, in the direction opposite to the potline current direction. The
current load in
the conductor constitutes about 25% of the potline current.
[009] This prior art device is adapted for use exclusively in low-amperage
potlines where
cells are arranged in the end-to-end relationship.
[010] The magnetic field from the conductor expands hyperbolically. The
distance from
the neighboring row of cells arranged end-to-end to the longitudinal axis of
molten
aluminum layer in the cell is between 10 and 18 m, whereas the distance from
the
compensation conduction to the axis of the molten aluminum layer is between
2.5 and 3.5
m. The amperage in the compensation conductor is almost four times less than
the potline
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amperage. In this manner, the vertical magnetic fields from the neighboring
row of
electrolytic cells and similar fields from the compensation conductor busbar
are directed
opposite each other. The field in the aluminum melt from the compensation
conductor
busbai- and the magnetic field from the neighboring row electrolytic cells
changes
hyperbolically and from the compensation busbar more intensively than the
field from the
neighboring row of the cells. As a result, compensation of magnetic field from
the
neighboring row of cells is provided at a small area of the melt having the
length of only
between 3.5 and 4.5 meters. However, when the cells are arranged side-by-side
and when
it is riecessary to compensate the magnetic field in the aluminum melt over an
area
between 10 and 18 m and, the above-discussed prior art device does not provide
the
required compensation. This is because compensation of the magnetic field in
one-half of
the cell and insufficient compensation of the magnetic field in the opposite
half of the cell
does not provide the required quality compensation.
[011] U.S. Patent 4,072,597 teaches the prior art method of compensation of
the effect of
magnetic field from neighboring rows of the electrolytic cells arranged side-
by-side,
wherein the current to anode of the downstream cell is supplied from the
cathode of the
neighboring upstream cell. In this arrangement, the current from cathode is
taken from
input and output cathode bars. The upstream cathode bars on the side closer to
the
neighboring row of cells and downstream cathode bars on the side opposite to
the
neighboring row of cells form an electric loop generating an additional
magnetic field,
which. is essentially equal to that of the neighboring magnetic fields and
acting in the
opposite direction. This is due to the higher amperage in the conductor on the
side close
to the neighboring row and connected with the cathode bars of the upstream
cell.
[012] U.S. Patent 4,159,034 discloses a device provided for compensation of
the
magnetic field from the neighboring rows of cells connected in series. Each
cell
comprises a metal cathode device. Neighboring parallel rows of cells oriented
across the
longitudinal axis of the row of the cells with the cathode device carrying a
liquid
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aluminum layer on the cathode lining. This prior art device incorporates two
compensating electric conductors disposed substantially at the level of liquid
aluminum
layer and provided on both sides of each row of cells. The source of direct
current is
connected to the compensation conductors. In this arrangement, one
compensation
conductor is positioned separately on the inner side of the series of the
cells, potline (inner
conductor) and the other compensation conductor which is separately provided
on the
outer side of the cells (outer conductor). Direct current in the inner
compensation
conductor runs in the same direction as the current in the potline. On the
other hand, the
direct current in the outer conductor runs in the opposite direction relative
to the current
direction in the potline. The inner and outer compensation conductors are
connected in
series. The amperage in the compensation conductor is defined by the following
equation:
B=2i/d,
where:
B is magnetic field in 10-4 Tesla;
i is amperage in kiloamperes;
d is the distance in meters.
The compensation conductor is selected in such a manner that the average total
magnetic
field along the longer axis of the cell is to be equal to zero.
[0131 Main drawbacks of the above-discussed prior art compensation devices are
that
they cannot efficiently compensate the magnetic field induced by neighboring
rows of
high-power cells or from conductors with amperage up to 320-400 kA and more.
[014] In order to use the device of U.S. Patent 4,159,034 a line of the cells
with intensity
or amperage 350-400 kA and it is necessary to substantially increase the
distance between
the rows of the cells (potlines) more than by 150 m to maintain acceptable
magnetic field
value around the melt. This will considerably increase the cost of land use
under the
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potrooms, cost of long busbars between the potlines. Furthermore, electric
power
consumption will be substantially increased because of warming voltage in the
long
busbars. The above-discussed factors substantially decrease the income from
investments
into high-amperage potlines.
[015] Hereinafter, the terms "upstream" and "downstream" used in the
application are
related to the general direction of the electrical current flowing through the
predetermined
row of cells (the direction of the electric current in the series). The term
"adjacent line"
means the line nearest the line under consideration and the term "field of the
adjacent
line" means the resultant of the fields of all the lines apart from the line
under
consideration.
[016] Bx, By and Bz, the components of the magnetic field along the axes Ox,
Oy an Oz
in a direct right-angled trihedron, whose center 0 is the center of the
cathode plane of the
cell, Ox is the longitudinal axis in the direction of the cell, Oy is the
transversal axis and
Oz is the vertical axis directed upwards, internal side of a cell is situated
toward the
adjacent line and external side opposes the adjacent line.
SUMMARY OF THE INVENTION
[017] The present invention provides an arrangement for compensating a
magnetic field
from neighboring lines of electrolysis cells connected in series and adapted
for the
intensity or amperage of at least 350-400 kA. It relates to the compensating
arrangement
adapted for use with electrolysis cells which are situated in one potroom
under the same
roof in the side-by-side relationship in at least two lines.
[018] The object of the invention is to increase current efficiency and to
reduce fixed
expenses. It is a further object of the invention to create optimum magnetic
field in the
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melt of the electrolytic cells arranged in the potlines in the side-by-side
relationship and
installed in one electrolysis potroom, consisting of at least two lines of the
cells.
[0191 In the arrangement of the invention the magnetic field from the
neighboring lines
of cells is compensated by the current bearing independent conductors and not
by the
asymrnetric design of cell busbar as proposed by the prior art.
[0201 One aspect of the invention provides an arrangement for compensating a
magnetic
field induced in a linearly arranged series of electrolysis cells by an
adjacent generally
parallel line of cells. Each electrolysis cell contains a metal shell
extending in one
direction between top and bottom portions thereof and between inner and outer
sides in
other direction. A cathode device containing a plurality of cathode bars is
provided with
the cells.
[0211 A main inner electrical compensating conductor is provided spaced
laterally from
the inner side of said cells in the series. The device also includes a main
outer electrical
compensating electrical conductor spaced laterally from the outer side of the
cells in the
series.
At least one inner supplemental electrical compensating conductor is disposed
at
the bottom portion of the cells in the potline in the vicinity of the cathode
bars situated at
the inner side of the respective cells and along the main inner compensating
conductor.
At least first and second outer supplemental electrical compensating
conductors are
disposed at the bottom portion of the cells along the main outer compensating
conductor.
The first outer supplemental conductor is positioned in the vicinity of the
cathode bars
situated at the outer side of the respective cells. The second outer
supplemental conductor
is positioned between the first outer supplemental conductor and small axis of
the
respective cell.
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[022] As to another aspect of the invention, the main inner and outer
electrical
compensation conductors are disposed substantially at a level of the layer of
liquid
aluminum in the respective cell.
[023] As to still another aspect of the invention, the device of the invention
further
comprises a source of direct current associated with said compensation
conductors. The
direction of the direct current in the inner electrical compensation conductor
coincides
with the direction of the current in the line of cells. The direction of
current in the outer
electrical compensation conductor is opposite to the current in the line
cells, with the
inner and outer electrical compensation conductors being connected in series.
[024] The supplemental compensation conductors can be oriented substantially
parallel
to the main electrical compensation conductors.
BRIEF DESCRIPTION OF THE DRAWINGS
10251 FIG. 1 is a schematic cross-section view of an electrolysis cell
arranged
transversely to the axis of the series, the Ox axis extends substantially
perpendicular to
the plane of the figure;
[026] FIG. 2 is a schematic partial top view of a series of electrolysis cells
arranged in
two parallel lines; and
[027] FIG. 3 is a diagram illustrating interaction of the magnetic fields from
neighboring
lines of cells resulted from utilization of the compensation arrangement of
the invention.
DETAILED DESCRIPTION OF THE INVENTION
[028] Referring now to the drawings in general and Figs. 1 and 2, a
compensating
arrangement of the invention is specifically illustrated. Each electrolysis
cell 10
comprises a metal shell 15 provided with a cathode in the form of blocks of
carbon 16 and
an anode structure 14. Metal cathode rods 18 submerged in the blocks of carbon
16
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collect the current leaving the cell. Busbars conduct the current through side
riser to the
conductors of the subsequent cell forming a beam for suspension of the anodes.
The
electrolytic bath 22 and the layer of liquid aluminum 20 are contained within
the cell. In
this conventional arrangement, the cathode outputs of each cell thus supply
the
subsequent downstream cell via the upstream head.
[029] It is illustrated in Fig. 1, the electrolysis cell 10 extends
longitudinally between an
internal side 28 and an external side 30. In the vertical direction the cell
10 extends
between top 24 and bottom 26 portions. As further illustrated in Fig. 2 the
cells in the
series are oriented transverse to an axis of the series with a short or
longitudinal axis of
each cell being oriented along or substantial parallel to the axis of the
cells in the
respective line. As further illustrated in Fig. 1 in each cell 10 the vertical
axis OZ and the
short or longitudinal axis OX passes through a center 0 of the cathode plane.
[030] Referring now to FIG. 2 illustrating a part of a series of electrolysis
cells arranged
in two parallel lines 42 and 44 within the same potroom 46. The main internal
compensating conductors 32 are provided for compensation the field of the
adjacent line.
On the external side of the series the main external electrical compensating
conductors 34
are provided. Such main compensation conductors may be joined by means of the
connector 35. The dotted line represents the direction of passage of the
electrolysis
current. In each line the main internal compensating conductors 32 are
arranged along the
internal sides 28 of the cells and the main external compensating conductor 34
is arranged
along the external sides 30 of the cells. Both main compensating conductors
can be
supplied with direct current, either separately or by positioning in series by
means of the
connector 35 from an auxiliary rectifier. The total power dissipated in these
compensating conductors is relatively low relative to the energy consumed in
the
electrolysis process. As shown in FIG. 1 both main compensation conductors 32
and 34
are situated approximately at the level of the liquid aluminum metal 20 in the
electrolysis
cells.
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[031] Reference numeral 25, illustrates the direction of current in the
designated line of
electrolysis cells, line 42 for example, whereas the numeral 27 shows the
direction of
current in the neighboring line 44 of cells. Supplemental compensation
conductors 36, 38
and 40 adapted for passage of the direct current are provided under the bottom
portion 26
of the cells in each line of cells in the series the supplemental conductors
are positioned
along or substantially parallel to the respective main internal and external
compensation
conductors 32 and 34. At least one internal supplemental electrical
compensation
conductor 36 is disposed under the bottom portion 26 of the respective cells
in the series
in the vicinity of the outer cathode rods 18 on the side of the internal main
compensation
conductor 32. The direction of current in the internal supplemental
compensation
conductors 36 and the main internal compensation conductors 32 is
substantially identical.
[032] At least a pair of external electrical supplemental compensation
conductors 38 and
40 is disposed under the bottom 26 of the cell in the series along the main
external
compensation conductor 34. The first external supplemental conductor 38 is
provided at
the outer cathode rods 18 of the side of the external main electrical
compensation
conductor 34. The second external supplemental compensation conductor 40 is
disposed
between the first external supplemental compensation conductor 38 and a plane
passing
through the short axis X of the respective electrolysis cells. The direction
of current in
the main and supplemental external conductors 34, 38 and 40 is substantially
identical.
[033] The internal compensation conductors 32, 36 can be connected to the
external
compensation conductors 34, 38 and 40 by means of the busbar 35. In one
embodiment
of the invention both groups of compensation conductors are connected to one
source of
direct current. In the alternate embodiment, each compensation conductor is
connected to
an indlividual source of direct current. In the line of the electrolysis cells
42 the potline
currenit is directed in the bottom to top direction with respect to the
observer. On the
other hand, in the neighboring row of cells 44 the current is directed in the
opposite
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direction. The entire series consisting of two lines 42 and 44 of electrolysis
cells and the
compensation device of the invention are accommodated in the same potroom 46
under
the sa-ne roof.
[034] In one embodiment of the invention the first 38 and second 40 external
supplemental compensation conductors are provided between the external sides
30 of the
respective shells 15 and at a plane passing through the center 0 of the
cathode 16 and the
short or longitudinal axis OX. In the vertical plane the first and second
external
supplemental compensation conductors 38 and 40 are spaced from the bottom
portion 26
of the respective cells. The internal supplemental compensation conductors 36
are
disposed between the internal sides 28 of the respective shells 15 and the
plane passing
through the center 0 of the cathode 16 and the longitudinal axis of the cell
OX. The
supplemental internal compensation conductor 36 and the external compensation
conductors 38 and 40 are separated from each other by a substantial gap and
are
positianed on opposite sides of the vertical plane passing through the
longitudinal axis
OX.
[035] The compensation arrangement of the invention operates in the following
manner.
Each line 42, 44 of electrolysis cells in the series is adapted for the
intensity or amperage
of about 400 kA. Each line of the cells creates in the melt of the cells of
the adjacent line
a vertical or upwardly oriented magnetic field component. The distance between
the
longitudinal axes of the lines 42 and 44 is about 30 m. In the chart of Fig. 3
the curve K
illustrates the effect of the magnetic field of the adjacent line having
intensity which
varies from the inner side to outer side of the cell in an almost hyperbolic
manner from
48.9= 10 -4 Tesla to 23.2= 10 -4 Tesla.
[036] The main internal 32 and external 34 electrical compensation conductors
create in
the melt a vertically oriented, hyperbolically expanding magnetic field having
orientation
which is opposite with respect to the magnetic field of the adjacent line of
cells. The
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length. of the electrolysis cell adapted for the intensity or amperage of at
least 400 kA is
between 10-18 m. Thus, the magnetic field from the main compensation
conductors 32
and 34 does not provide optimal compensation to the magnetic field generated
in the melt
of the neighboring line of cells. However, in the device of the invention the
supplemental
compensation conductors 36, 38 and 40 interacting with the internal and
external main
compensation conductors 32 and 24 are capable of providing optimal
compensation to the
magnetic field produced by the adjacent line of cells.
[037] In the above-discussed embodiment the respective current intensity in
the
compensation conductors is as follows: the main compensation conductor 32 - 50
kA; the
main compensation conductor 34 - 35 kA; the supplemental compensation
conductor 36 -
40 kA,; the supplemental compensation conductor 38 - 40 kA; and the
supplemental
compensation conductor 40 - 15 kA. The compensation conductors of the
compensation
device: of the invention are arranged and their respective amperage is
selected by
computer programs employing the principals of Biot-Savart-Laplace taking into
consideration ferromagnetic structures.
[038] In the chart of Fig. 3 curve L reflects the total magnetic field from
the main
internal 32 and external 34 compensation conductors as well as the
supplemental
compensation conductors 36, 38 and 40. Curve K represents the magnetic field
from the
neighboring line of cells. Curve M represents the total or resulting magnetic
field from
the neighboring line of cells and the magnetic field from the compensation
conductors, it
represents the algebraic sum of the magnetic fields, i.e. M=K+L.
[039] The above-discussed examples illustrate that utilization of the
compensation device
of the invention provides optimum compensation of the magnetic field generated
by the
neighboring row of cells. In this respect, it is clearly illustrated in the
chart of FIG. 3 that
the value of the effective magnetic field from the adjacent lines of the
electrolysis cells
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represented by the curve M is minimal and close to zero, with deviation of not
more than
3. 10"4 Tesla.
[040] The device of the invention provides compensation of the magnetic field
induced
by the neighboring row of in-series connected cells and generates an optimum
magnetic
field in the operational zone of potline of high-power cells with the
intensity of at least
350-400 kA arranged side-by-side. In this manner the optimal performance of
the
electrolysis cells is provided at the reduced level of expenses.
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