WO2017163154A1 - Système de barre omnibus permettant de compenser le champ magnétique dans des rangées adjacentes de cellules électrolytiques placées transversalement - Google Patents

Système de barre omnibus permettant de compenser le champ magnétique dans des rangées adjacentes de cellules électrolytiques placées transversalement Download PDF

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Publication number
WO2017163154A1
WO2017163154A1 PCT/IB2017/051529 IB2017051529W WO2017163154A1 WO 2017163154 A1 WO2017163154 A1 WO 2017163154A1 IB 2017051529 W IB2017051529 W IB 2017051529W WO 2017163154 A1 WO2017163154 A1 WO 2017163154A1
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Prior art keywords
cathode
cell
busbar
transversal
parallel
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PCT/IB2017/051529
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English (en)
Inventor
Alexander Arkhipov
Abdalla ALZAROONI
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Dubai Aluminium Pjsc
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Publication of WO2017163154A1 publication Critical patent/WO2017163154A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
    • C25C3/16—Electric current supply devices, e.g. bus bars
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
    • C25C3/20—Automatic control or regulation of cells

Definitions

  • the invention relates to the field of fused salt electrolysis, and more precisely to an electrolytic cell suitable for the Hall-Heroult process for making aluminium by fused salt electrolysis.
  • the invention relates to a particular arrangement of the cathode busbar system in an electrolysis plant in which electrolytic cells are arranged side by side, capable of counterbalancing the negative effect of high vertical magnetic field in the upstream corners of the cell as well as the vertical magnetic fields generated by adjacent rows of cells.
  • the Hall-Heroult process is the only continuous industrial process for producing metallic aluminium form aluminium oxide.
  • Aluminium oxide Al 2 0 3
  • molten cryolite Na 3 AIF 6
  • the resulting mixture typically at a temperature comprised between 940 °C and 970 °C acts as a liquid electrolyte in an electrolytic cell.
  • An electrolytic cell used for the Hall-Heroult process typically comprises a steel shell (so-called pot shell), a lining (comprising refractory bricks protecting said steel shell against heat, and cathode blocks usually made from graphite, anthracite or a mixture of both), and a plurality of anodes (usually made from carbon) that plunge into the liquid electrolyte.
  • Anodes and cathodes are connected to external busbars.
  • An electrical current is passed through the cell (typically at a voltage between 3.5 V and 5 V) which electrochemically reduces the aluminium oxide, split by the electrolyte into aluminium and oxygen ions, into aluminium at the cathode and oxygen at the anode; said oxygen reacting with the carbon of the anode to form carbon dioxyde.
  • the resulting metallic aluminium is not miscible with the liquid electrolyte, has a higher density than the liquid electrolyte and will thus accumulate as a liquid metal pad on the cathode surface from where it needs to be removed from time to time, usually by suction into a crucible.
  • the cells also called “pots" are always operated in series of several tens (up to several hundreds) of pots (such a series being also called a “potline”); within each series DC currents flow from one cell to the neighbouring cell.
  • the cells are arranged in a building, with the cells arranged in rows either side-by-side, that is to say that the long side of each cell is perpendicular to the axis of the series, or end-to-end, that is to say that the long side of each cell is parallel to the axis of the series.
  • electrolysis according to the Hall-Heroult process is a continuous process driven by the flow of electric current across the electrolyte, whereby said electric current reduces the aluminium atoms that are bounded in the alumina present in the molten electrolyte.
  • electrolysis according to the Hall-Heroult process is a continuous process driven by the flow of electric current across the electrolyte, whereby said electric current reduces the aluminium atoms that are bounded in the alumina present in the molten electrolyte.
  • Four equilibria define the optimum cell operation window, leading to the high current efficiency: electrical equilibrium, magnetic equilibrium, thermal equilibrium and chemical equilibrium. Two of these equilibria are determined by the cell design; two others can be acted upon in the process of cell operation.
  • Conditions of electrical equilibrium of the cell are attained when the distribution of the current is as uniform as possible throughout the electrolyte; the thickness of electrolyte between the anode and the cathode (inter-electrode spacing) in a typical Hall-Heroult cell is of the order of about two to five centimeters.
  • the main operating parameter by which the operator can act on this equilibrium is the inter-electrode spacing; which determines the cell voltage to a large extent.
  • the main permanent perturbation factor of the electrical equilibrium is the current path in the liquid metal, as will be explained below; this factor is determined by the cell design and cell operation. Discontinuous events such as anode change and so-called anode effects also perturb the electrical equilibrium.
  • the magnetic equilibrium and the thermal equilibrium of the cell are both determined to a large extent by the cell design.
  • the magnetic equilibrium is determined to a large extent by the busbar structure.
  • Perturbation factors are mainly related to electrical currents arising from conductors outside of the cell.
  • the thermal equilibrium is determined by the choice and thickness of materials and components, and by the lining; perturbation factors are mainly related to specific discontinuous operations (anode change, metal tapping, adding of electrolyte) or to so-called anode effects (this term and the phenomenon that it designates are known to a person skilled in the art and need not to be explained here).
  • the chemical equilibrium is determined by the chemical composition of the electrolytic bath; alumina addition is the principal operational parameter.
  • the present invention is related to the magnetic equilibrium of an electrolytic Hall-Heroult cell.
  • Such cells are of rectangular shape, and as such they are symmetric by construction. Asymmetry arises from asymmetry of the electric current flow in the cell.
  • Electrical current enters the cell through anodes which cover a large part of the surface of the cell, crosses the electrolyte and the liquid metal pad, and is collected by the cathode which forms the whole surface of the cell bottom.
  • the cathode is made from a carbonaceous material and contains steel collector bars which enable an electrical contact to be established with the cathode busbar. However, the electrical conductivity of both the cathode and the steel cathode bar is much lower than that of the liquid metal pad.
  • the current lines in the liquid metal are not vertical but have horizontal components, interacting with the vertical magnetic field and leading to magnetohydrodynamic (MHD) perturbations.
  • MHD magnetohydrodynamic
  • the cathode busbar is linked to a small number of connecting elements called anode risers, through which the current is fed into the anode beam of the downstream cell. Further perturbation of the magnetic field in the cell is due to boundary effects, the cell not having infinite dimensions.
  • the magnetic field in the cell locally has a spatial distribution which, combined with electrical currents in the cell, creates Laplace forces; these induce movement of liquid conductors (electrolyte and metal) and deform the metal-bath interface hydrostatically. Laplace forces may also induce metal-bath interface oscillations.
  • the resulting unevenness of the metal surface leads to a local variation in anode-to-metal pad distance across the length of the pot, which is represented by small fluctuations of the overall cell voltage signal; this may even lead to a short-circuit between the anode and the cathode.
  • MHD magnetohydrodynamic
  • Certain perturbative events may increase these instabilities and metal and bath velocities.
  • the perturbative effects of an event will be higher if the vertical component of the magnetic field, in particular in the upstream corners of the cell, is high.
  • B z the vertical component of the magnetic field
  • B z the coordinate running upwards from the bottom to the top of the cell
  • a root-mean square average value of about one millitesia is a usual upper limit.
  • the horizontal components B x and B y should be anti-symmetrical with respect to the longitudinal and transverse axis, respectively.
  • a required property of B z is also the anti-symmetry with respect to the cell centre, i.e. equal and opposite values in each corner of the cell.
  • Another perturbation factor of a cell operating under conditions of magnetic equilibrium is the effect of neighboring cells, as cells are usually arranged side-by-side in series of up to several hundred cells and divided in at least two potrooms.
  • This perturbation leads to local variations of the vertical component of the magnetic field B z , in the liquid metal pad which destroy the anti-symmetry of B z with respect to cell centre, required for good MHD stability of the cell.
  • the value of the vertical magnetic field should be zero in the geometrical center of the liquid metal pad, but the contribution from the adjacent rows gives a bias that can be greater than one millitesla, depending on potline current and distance to the adjacent rows of cells.
  • the magnetic effect of neighboring cells can be decreased by an appropriate design of the potline, and prior art offers a wide range of such designs.
  • the design of the cathode busbar system aims at generating a magnetic field that compensates as far as possible the local B z in the cells, and especially in the upstream corners where B z is usually the highest.
  • a much smaller perturbation factor of a cell operating under conditions of magnetic equilibrium is due to magnetic fields generated by more distant electric conductors carrying high currents. These conductors belong to the rectifiers and power station feeding the cell line, and to other lines of electric cells present in the same plant.
  • Such perturbation induces a slight magnetic dissymmetry (so-called "bias") of the cell: the local variations of the vertical component of the magnetic field are no longer symmetric over the longitudinal direction of the cell, as they would be in the absence of an external magnetic field.
  • the magnetic fields generated by adjacent rows of cells lead to a perturbation of the magnetic equilibrium of the row; this may lead to a decrease in overall efficiency of the plant.
  • These second order effects are the main focus of the present invention. It is customary to designate as the "adjacent row” the row closest to the row in question, while the "field of the adjacent row” is the resultant of the fields of all the rows other than the row in question.
  • US 4, 169,034 discloses the use of an auxiliary conductor at each end of the cell, parallel to the long axis of the pot and situated in the plane of the bath/metal interface as near as possible to the pot shell; a direct current of appropriate direction and intensity (of the order of 10 to 30 kA for a cell operating at 175 kA) is passed through this auxiliary conductor.
  • US 4,713, 161 discloses the use of two correcting conductors per potline, one on each side of the pot, that extend parallel to the axis of the potline; the total current in these corrective conductors is up to 70 % of the current through individual cells. This seems to give satisfactory results for potlines operating at very high amperage.
  • WO 2015/017924 discloses a compensation circuit parallel to the axis of the series that extends underneath the potline.
  • This circuit comprises a set of three to ten parallel conductors which carry a current of between 50 % and 150 % of the electrolysis current. It is claimed that this allows to decrease the distance between two rows of cells to less than 40 m.
  • Such a compensation circuit carrying such a high current requires a significant amount of metal, and ohmic losses will occur.
  • the main disadvantage of this solution seems to be however the high cost of the power supply station needed for supplying current to the compensation circuit.
  • the problem that the present invention endeavors to resolve is therefore to decrease the effect of interaction between magnetic fields generated by two neighboring rows belonging to the same series of electrolytic cells when decreasing the distance between the rows of cells and/or increasing the current in the cells, without using long lines of compensation conductors carrying high current that is not needed for the electrolysis process and that requires independent power supply stations.
  • a first object of the present invention is therefore a cathode busbar system for an electrolytic cell of substantially rectangular shape, suitable for the Hall-Heroult electrolysis process,
  • said electrolytic cell comprising a cathode forming the bottom of said electrolytic cell and comprising a plurality of parallel cathode blocks, each cathode block being provided with at least one current collector bar and two electrical connections points,
  • a lateral lining defining together with the cathode a volume containing the liquid electrolyte and the liquid metal resulting from the Hall-Heroult electrolysis process, said cathode and lateral lining being contained in an outer metallic shell, and said electrolytic cell further comprising a plurality of anode assemblies suspended above the cathode, each anode assembly comprising at least one anode and at least one metallic anode rod connected to an anode busbar (so- called anode beam), said cathode busbar system comprising a so called cathode ring busbar, surrounding said outer metallic shell viewed from above,
  • said ring busbar being substantially rectangular and defining a main plane, a median longitudinal plane as well as a median transversal plane, both orthogonal to said main plane,
  • said ring busbar comprising two opposite and parallel longitudinal parts each extending along the long sides of the cell, and two opposite and parallel transversal parts extending along the ends (short sides) of the cell,
  • cathode busbar system being provided with connection means for connection with both electrical connection points of each cathode block of the cell
  • said cathode busbar system being characterized in that said ring bus bar is asymmetric with respect both to said median longitudinal plane (PX) and to said median transversal plane (PY). Said two parallel longitudinal parts of the ring busbar are the downstream longitudinal part, electrically connected to the anode risers, and the upstream longitudinal part connected to the said downstream anode risers via the busbars at the ends of the cell.
  • said ring busbar substantially consists in said two opposite and parallel longitudinal parts each extending along the long sides of the cell, and two opposite and parallel transversal parts extending along the ends of the cell.
  • the parallel transversal parts of the cathode ring busbar are asymmetric with respect to said median longitudinal plane.
  • the asymmetry of the transversal parts of the ring busbar can be achieved by providing said transversal parts in their upstream section with a derivation sector, both derivation sectors being offset with respect to said median longitudinal plan and closer to the upstream cell than to the downstream cell.
  • Said derivation sector can be asymmetric with respect to main axis of said transversal part.
  • said derivation sector projects towards the bottom, with respect to the level of the liquid metal pad in the cell. Both derivation sectors face each other, along an axis parallel to the longitudinal part of the ring busbar.
  • Said derivation sector extends in a plane parallel to the median transversal plane.
  • Said derivation sector can be U-shaped, said U-shape possibly comprising rounded and/or straight sections.
  • said derivation sector is formed of straight portions.
  • at least one of the transversal parts of the ring busbar is provided in its upstream section with a derivation sector (and preferably a "U" shaped sector), projecting towards the bottom, both derivation sectors being offset with respect to said median longitudinal plane.
  • cathode blocks are symmetric and have collector bar ends coming out on each side, in side-by-side arrangements of electrolytic cells half of the current collected by the collector bars of the cathode blocks will flow directly to the downstream longitudinal part of the cathode busbar system, while the other half flows to the upstream longitudinal part (see Figure 8). It is therefore necessary to carry the cathode current collected at the upstream side of the cathode busbar system (that is to say by the upstream longitudinal parts) back to the downstream part of the cathode busbar system. This is achieved by the transversal parts of the ring busbar.
  • each anode riser collects a predefined current; if said plurality of risers comprises end risers and central risers, the end risers may collect a different current than the central risers or equal current to the one in centre risers.
  • the cathode busbar system may comprise additional electrical balancing circuits. Said electrical balancing circuits and the components thereof are not a part of the ring busbar as defined herein.
  • said cathode busbar system further comprises a downstream electrical balancing circuit comprising conductors arranged in vicinity of and parallel to the downstream longitudinal part of said ring busbar.
  • said cathode busbar system further comprises two or more conductive arms that extend between said longitudinal parts of said ring busbar, underneath said shell.
  • These conductive arms extending underneath the ring busbar system connect the upstream longitudinal part of the ring busbar to the downstream longitudinal part, thereby creating an additional path for the cathode current collected upstream. They are not part of the ring busbar system as such; they act as an upstream electrical balancing circuit, achieving preferential feeding of the cathode current collected by the upstream longitudinal parts of said ring busbar to the end risers.
  • Said conductive arms can be symmetric or asymmetric with respect to said median longitudinal planes, and/or they can be symmetric or asymmetric with respect to said median transversal plane. In an advantageous embodiment, said arms are asymmetric with respect to said median longitudinal plane.
  • each transversal part comprises at least two parallel busbars separated by an intercalary space.
  • said intercalary space is at least 10 mm, preferably at least 25 mm, and most preferably at least 50 mm.
  • said parallel busbars have conductive sections the sum of which is different in the duct end transversal busbar and in the tap end transversal busbar.
  • the outer of said parallel busbars can have a conductive section which is smaller than that of the inner of said parallel busbars.
  • the ratio of the sum of the conductive cross sections of the duct end longitudinal busbars and the sum of the conductive cross sections of the tap end longitudinal busbars is greater than 1.1 , preferably greater than 1.25, and preferably greater than 1.43.
  • Another object of the invention is an electrolytic cell of substantially rectangular shape suitable for the Hall-Heroult electrolysis process, comprising
  • a cathode forming the bottom of said electrolytic cell and comprising a plurality of parallel cathode blocks, each cathode block being provided with at least one current collector bar and two electrical connections points,
  • cathode and lateral lining being and lining being contained in an outer metallic shell
  • each anode assembly comprising at least one anode and at least one metallic anode rod connected to an anode beam
  • said electrolytic cell being characterized in that it comprises a cathode busbar system according to any of the embodiments and variants of the present invention.
  • potline comprising a plurality of electrolytic cells of substantially rectangular shape, suitable for the Hall-Heroult electrolysis process, characterized in that at least 50%, and preferably at least 80% of said cells are electrolytic cells according to claim this invention.
  • a last object is an electrolysis plant comprising at least one potline according to the invention.
  • said electrolysis plant has a potline according to the invention, said potline being arranged in a first and a second rows connected in series and operating at a current / s (In kilo-Amperes), both rows being parallel, and each row comprising a plurality of electrolytic cells connected in series, characterized in that said second row runs parallel to said first row, at a distance R (in metres) of less than / s /4.1 metres, preferably less than / s /4.5 metres, still more preferably less than / s /5 metres, and most preferably less than / s /5.6 metres.
  • This decrease in distance R between parallel rows of the same series of electrolytic cells leads to savings in investment cost, and furthermore, compared to the use of compensation conductors carrying high current according to prior art, leads also to savings in operational cost.
  • Another object of the invention is an aluminium electrolysis plant comprising at least one line of electrolysis cells of substantially rectangular shape, said cells being arranged side by side, and said plant further comprising means for electrically connecting said cells in series and for connecting the cathode busbar of a cell to the anode beam of a downstream cell, characterized in that more than 80 % of the electrolysis cells in at least one of said line, and preferably each electrolysis cell of said line, is an electrolysis cell according to the present invention.
  • a last object of the invention is a method for making aluminium by the Hall-Heroult electrolysis process using electrolytic cells of substantially rectangular shape, characterized in that said method is carried out in an aluminium electrolysis plant according to the invention.
  • FIGs 1 to 6 and 9 represent various embodiments of the present invention.
  • Figures 7 and 8 illustrate prior art.
  • Figure 1 is a schematic view, showing the global arrangement of a plant according to the invention.
  • Figure 2 is a perspective view, showing a cathode busbar according to a first embodiment of the invention, which belongs to the smelter of the figure 1.
  • Figure 3 is a bottom schematic view, showing an electrolytic cell provided with the cathode busbar of figure 2.
  • Figure 4 is a front view, showing a transversal part of cathode busbar of figure 2 with its derivation section.
  • Figures 5 and 6 are front views, similar to figure 4, showing further variants of the transversal part of a cathode busbar.
  • Figure 7 is a typical plot of the vertical magnetic field (B z ) depending on the distance from the centre point of a typical 420 kA electrolysis cell.
  • the three curves correspond to different lines parallel to the length of the cell: curve (a) corresponds to the downstream region, curve (b) to the upstream region, curve (c) to the centre.
  • Figure 8 is a schematic cross section along a transversal plane across a Hall-Heroult electrolytic cell. The arrows represent the current flow across the cell.
  • Figure 9 shows details of the transversal part of an embodiment of the busbar system according to the invention.
  • Figure 9(a) tap end
  • Figure 9(b) duct end
  • the present invention is directed to the global arrangement of a plant, or aluminium smelter, used in the Hall-Heroult process.
  • the aluminium smelter of the invention comprises a plurality of electrolytic cells C1 , C2, ... , Cn-1 , Cn, arranged the one behind the other (and side by side) along two parallel lines L1 and L2, each of which comprises n/2, i.e. m cells.
  • These cells are electrically connected in series by means of conductors, which are not shown on Figure 1.
  • the number of cells in a series is typically comprised between 50 and over 100, but this figure is not substantial for the present invention.
  • the electrolysis current therefore passes from one cell to the next, along arrow DC.
  • the cells are arranged transversally in reference of main direction D1 or D2 (axis of the row) of the line L1 or L2 they constitute.
  • main dimension, or length, of each cell is substantially orthogonal to the main direction of a respective line, i.e. the circulation direction of current.
  • Figure 1 depicts a typical "clockwise" current orientation.
  • the Hall-Heroult process as such, the way to operate the latter, as well as the cell arrangement are known to a person skilled in the art and will not be described here in more detail.
  • the terms “upper” and “lower” refer to mechanical elements in use, with respect to a horizontal ground surface.
  • conductive means “electrically conductive”.
  • cathode blocks are symmetric and have collector bar ends 806 coming out on each side, in side by side arrangements of electrolytic cells half of the current collected by the collector bars 806 of the cathode blocks 805 will flow directly to the downstream longitudinal part 2 of the cathode busbar system, while the other half flows to the upstream longitudinal part 3 (see figure 8).
  • means are provided to carry the cathode current collected at the upstream part 3 of the cathode busbar system back to the downstream longitudinal part 2 of the cathode busbar system.
  • the present invention is more particularly directed to the cathode busbars of the potline, each of which surrounds a respective cell (schematically shown on Figure 3 as reference number 11 designating the visible outer boundaries of the cell volume, i.e. the potshell).
  • reference number 11 designating the visible outer boundaries of the cell volume, i.e. the potshell.
  • the arrangement of two embodiments of the busbar associated with cell C2 will be described, in relation with Figures 2 and following.
  • the arrangement of a majority of the other busbars and, most preferably, of all the busbars of the plant is similar.
  • cathode busbar as a whole is given the general reference 1.
  • Busbar system 1 is located on about the same horizontal level as the molten aluminium metal contained within the cell.
  • the cell is designated as C2 on Figure 2.
  • Busbar system 1 comprises different mechanical elements, which will be described hereafter more in detail. It first includes a ring (called here “ring busbar”) which is generally formed by two longitudinal parts 2 and 3, parallel to axis X-X, as well as two transversal parts 4 and 5. This ring busbar defines a main plane PR, which extends horizontally.
  • the ring busbar in the sense of the present invention therefore represents a loop (like a geometrical ring), but it differs from a geometrical ring in that it is not circular but substantially rectangular in shape: the ring busbar is formed by the two longitudinal parts 2 and 3 that are opposite and parallel to each other, and by the two transversal parts 4 and 5 that are also opposite and parallel to each other.
  • the loop also differs from a geometrical ring in that the loop is open so that the downstream longitudinal part 3 is electrically insulated from other parts of the loop, usually with an air gap or some other electrical insulation.
  • the whole ring busbar 2 - 5 has a rectangular shape, the length LR of which is slightly superior to that of cell C2, whereas the width WR of which is slightly superior to that of cell C2.
  • length LR is between about 14 000 mm and about 25 000 mm
  • width WR is between about 5 000 mm and about 9 000 mm.
  • Axis X-X defines a median longitudinal direction of the cell and of the whole ring busbar 2 - 5
  • axis Y-Y defines a median transversal, or lateral direction of the cell and of the whole ring busbar 2 - 5.
  • transversal axis Y-Y of the ring busbar 2 - 5 corresponds to the main longitudinal direction D1 of the line L1 which includes cell C2.
  • PX defines a median longitudinal plane of the cell and of the whole ring busbar 2 - 5, said plane being orthogonal to main plane PR and including axis X-X.
  • PY defines a median transversal plane of the cell and of the whole ring busbar 2 - 5, said plane being orthogonal to main plane PR and including axis Y-Y.
  • the ring busbar is asymmetric with respect to plane PX; this is an essential feature of the present invention.
  • the ring busbar is asymmetric with respect to plane PY. As will be explained in more detail below, this asymmetry with respect to each of plane PX and plane PY can be obtained by different technical features.
  • Longitudinal part 2 is called upstream part, since it is on the upstream side of the cell with respect to current flow direction. It first comprises a main busbar 20, which is straight and horizontal, and which extends along the whole length of part 2.
  • This busbar 20 is rectangular in cross section, with vertical large sides. By way of example, its height H20 is between about 500 mm and about 1 100 mm, whereas its width W20 is between about 100 mm and about 300 mm.
  • Busbar 20 is provided with a row of connectors 21 , projecting downwards.
  • each connector 21 may be a flexible formed from stacked sheet and is intended to cooperate with the first end of a cathode block (not shown on the figures), that is to say to be connected with the cathode collector bar 806 protruding out of the cathode block 805 (see figure 8).
  • Busbar 20 may be manufactured in one single piece or be assembled lengthwise from two half-bars, typically by welding; the welding seams are marked with reference number 201.
  • Longitudinal part 3 is called downstream part, since it is on the downstream side of the cell with respect to current flow direction. It first comprises a main busbar 30, which is straight and horizontal, and which extends along the whole length of part 3.
  • This busbar 30 is rectangular in cross section, with vertical large sides. By way of example, its height H30 is between about 300 mm and about 700 mm, whereas its width W30 is between about 100 mm and about 150 mm.
  • Busbar 30 is provided with a row of connectors 31 , similar to those 21 , each of which is intended to cooperate with the other end of a respective cathode block (see figure 8); these connectors are known as such and will not be discussed here in more detail.
  • busbar 30 may be manufactured in one single piece or be assembled lengthwise from two half-busbars, typically by welding; the welding seams are marked with reference numbers 301 , thus creating a zig-zag and increasing its length as required by electrical equilibrium of the busbars.
  • Transversal part 4 is called duct end or duct part for a potline with current circulating clockwise; it is turned towards the line L2 of cells, facing the line L1 which includes present cell C2.
  • Duct end and tap end would be interchanged for a potline with current circulating counter-clockwise. It may be formed in full thickness by one busbar, or may be formed by two parallel "half-busbars", i.e.
  • each inner and outer busbar has the same height H41, which is between about 500 mm and about 1 100 mm, whereas each busbar has the same width W41 which is between about 200 mm and about 400 mm.
  • H41 height of busbar
  • W41 width of bus- bar
  • Transversal part 5 is called tap end or tap part in a potline with clockwise current, since it is turned opposite the other line L2 of cells.
  • the whole ring busbar is asymmetric in view of plane Y-Y.
  • the general shape of the structures of this end parts can be similar to that of duct part 4.
  • both transversal duct part 4 and tap part 5 can both have a U shape, and in this case the U- shaped part 5 may be different in lengths composing U said shape, but can be similar in shape to that on duct part 4.
  • the references of the components of part 5 are the same as those of part 4, apart from the fact that the first digit "5" replaces the first digit "4".
  • each transversal part 4 or 5 is mechanically and electrically linked to a respective end of upstream longitudinal part 2.
  • an inner junction member 81 or 91 extends between inner rod 41 or 51 and facing parts of rod 20.
  • an outer junction member 82 or 92 extends between outer rod 42 or 52 and facing parts of main rod 20.
  • Each junction member has an appropriate structure, so as to fulfil the above technical function. In the shown example, it is made of stacked sheets, the flexibility of which is sufficient to create a rounded shape.
  • Each transversal part 4, 5 is of uniform width.
  • the width and/or cross-section of the transversal duct-end part 4 is greater than that of the transversal tap-end part 5; this is one of the asymmetric means of the ring busbar system with respect to the median transversal plane PY that allows to achieve compensation of the vertical component of the magnetic field generated by distant conductors such as adjacent row of electrolytic cells.
  • Other means to achieve this compensation that are asymmetric with respect to the median transversal plane PY are related to the cross-section of the transversal parts 4, 5, as can be seen from figure 2.
  • transversal parts 4, 5 that are formed by two parallel half bars 41 , 42, 51 , 52.
  • inner half bar 41 has a cross section S41 which is smaller than the cross section S42 of outer half bar 42.
  • inner half bar 51 has a cross section S51 which is smaller than the cross section S52 of outer half bar 52.
  • both half bars have the same height and differ only by their width: at the duct end, inner half bar 41 has a width W41 which is smaller than the width W42 of outer half bar 42. At the tap end, inner half bar 51 has a width W51 which is smaller than the width W52 of outer half bar 52.
  • the cross section S51 (or in the abovementioned specific embodiment: the width W51) of tap inner half bar 51 is substantially equal to the cross section S41 (or width W41) of duct inner half bar 41.
  • the cross section S52 (or width W52) of tap outer half bar 52 is smaller than the cross section S42 (or width W42) of duct outer half bar 42.
  • the ratio of cross sections S42/S52 (or ratio (W42/W52)) is superior to 1.1 , in particular to 1.8. This ratio is typically between 1.1 and 3.
  • ratio (S41+S42)/(S51+S52) (or (W41+W42)/(W51+W52)) is superior to 1.1 , in particular to 1.43. This ratio is typically between 1.1 and 3.
  • each sum (S41 + S42) or (S51 + S52) is called “conductive cross section”) (and each sum ⁇ W41 + W42) or ⁇ W51 + W52) is called “conductive width”) of the respective part 4 or 5.
  • conductive cross section corresponds to the cross section (or width) of this bar and, if one transversal part is composed of at least three bars, its conductive cross section (or width) corresponds to the sum of the cross sections (or widths) of these bars.
  • the width of intercalary space 53 of tap part 5 is substantially equal to that of intercalary space 43 of duct part 4.
  • this width is preferably at least 10 mm, still more preferably at least 25 mm, even more preferably 50 mm.
  • the cooling effect is usually not significant below 10 mm, and little additional cooling effect is observed above 50 mm.
  • longitudinal part 2 is also split into two parallel rectangular half-bars.
  • Figure 2 also shows downstream balancing circuits 100; they do not form part of the ring bus bar as defined herein, and do not form part of the present invention.
  • the first downstream electric balancing circuit 100a connects the downstream cathode collector bars 31 n° 1 to 4 to the next anode end riser 10a
  • the second downstream electric balancing circuit 100b connects the downstream cathode collector bars n° 5 to 8 to the next anode end riser 10a
  • the third downstream electric balancing circuit 100c connects downstream cathode collector bars n° 9 to 14 to the next central anode riser 10b (the numbering of the cathode collector bars starts at the end of the pot, the reference number 31 corresponds to the connector to said cathode collector bar, said cathode collector bar itself not being represented on Figure 2).
  • the asymmetry of the ring busbar with respect to median transversal plane PY can be achieved in different ways and using different means. These include derivation sectors in the transversal parts 4,5, as well as different thicknesses of the transversal parts 4,5, or a different distribution of individual thicknesses of the half-bars 41 ,42;51 ,52 of each transversal part 4,5. Another means to achieve asymmetry with respect to median transversal plane PY is to choose a different distance between each of transversal parts 4,5 and the closest outer limit of the pot shell. These various ways and means to achieve asymmetry with respect to median transversal plane PY can be combined.
  • FIG 4 is a front view of transversal part 4. It shows an example of a transversal part 4 that is asymmetric with respect to the median longitudinal plane PX of the cell by use of derivation sectors.
  • A4 is the main direction of this transversal part 4, i.e. the axis extending between opposite ends thereof.
  • Axis A4 is parallel to axis Y-Y described hereabove.
  • Busbars 41 and 42 define a first sector 44 of part 4, adjacent downstream longitudinal part 3, as well as a second sector 46 of part 4, adjacent upstream longitudinal part 2.
  • First sector 44 which is straight and horizontal, extends along main axis A4.
  • second sector 46 is U-shaped and projects downwards this axis A4.
  • sector 46 is not symmetric with respect to axis A4.
  • Sector 46 comprises two vertical wings 461 and 461 ', as well as a horizontal core 462.
  • the height H46 of U-shaped sector 46 which is defined by the distance between the lower faces of sector 44 and core 462, is between about 1 000 mm and about 1 600 mm.
  • the straight length L46 of U- shaped sector 46 which is defined by the distance between the opposite front and rear faces of core 462, is typically between about 1 500 mm and about 3 700 mm; this length L46 is advantageously between about 20 % and about 75 % of the length L4 of the whole part 4.
  • Sector 46 forms a derivation sector of transversal part 4.
  • LD46 of this sector i.e. the sum of lengths L461, L462 and L461'.
  • the so called derivation ratio of the derivation sector is equal to the ratio (LD461 L46) between developed length and straight length.
  • this derivation ratio is superior to 2, which permits noticeable change of the magnetic field intensity and direction at the upstream corners of the cell.
  • Figures 5 and 6 show variants of the derivation sector of transversal part 4, which are referenced 46A and 46B on these further drawings.
  • the wings of the U are straight and not orthogonal to its core, like on Figure 4, but extend obliquely.
  • the wings are rounded.
  • duct part 4 differs from tap part 5, in that its U-shaped portion 46 is less high (or deep) than U-shaped portion 56 of part 5.
  • height H46 is inferior to that H56.
  • ratio (H56/H46) is superior to 1.2, in particular to 1.94. This ratio is typically between 1.2 and 2.5.
  • the ring bus bar system according to the invention can also be designed in a way that all transversal parts 4,5 are straight (i.e. in particular the transversal parts 4,5 have no sections that project out of the main horizontal plane PR).
  • duct part 5 differs from tap part 4 in that its two half bars 51 and 52 have different widths.
  • Inner half bar 51 has a width W51 which is inferior to that W52 of outer half bar 52. In embodiments in which all transversal parts 4,5 are straight this is a preferred approach to the ring bus bar design.
  • the cathode busbar system according to the invention can further comprise two arms 6,7 that extend between longitudinal parts 2,3 underneath said shell and connect said longitudinal parts 2,3 together. They act as an upstream electrical balancing circuit and are not part of the ring bus bar system as such: these arms achieve preferential feeding of the cathode current collected by the upstream longitudinal parts to the end anode risers 10a,10d.
  • said arms 6,7 are asymmetric with respect to said mean transversal plane PY and also asymmetric with respect to said median longitudinal plane PX.
  • Conductive arm 6 is called duct branch, since it is offset towards duct end 4, with respect to axis Y-Y'; it extends underneath the potshell. It comprises a main pole 61 , which extends parallel to Y-Y', under the surface of main plane PR, underneath the potshell. This pole is prolonged by two orthogonal branches 62 and 63, each of which extends under a respective longitudinal part 2 or 3 towards the head of the cell. The junctions between these branches 62, 63 and these parts 2,3 are different, depending on their downstream or upstream location.
  • upstream branch 62 is prolonged by an intermediate segment 64, which slopes both above and towards median axis Y-Y'.
  • a terminal upright portion 65 made of stacked plates, links segment 64 and longitudinal upstream part 2.
  • downstream branch 63 is directly linked to the cut-out wedge bar 32, via an upright portion 66, also made of stacked plates.
  • the main difference between upstream and downstream zones of arm 6 is intermediate segment 64.
  • Branch 7 is called tap arm, since it is offset towards tap end 5, with respect to axis Y-Y'. Although, as explained above, duct branch 6 and tap branch 7 are asymmetric with respect to axis Y-Y, the overall structure of this branch 7 is identical to that of branch 6. On the drawings, the references of the components of branch 7 are the same as those of branch 6, apart from the fact that the first digit "7" replaces the first digit "6".
  • Each of said cut-out wedge bars 32 are connected to the two anodic risers in its vicinity, as can be seen from Figure 2. It is understood here that these cut-out wedge bars 32 are not part of the ring bus bar
  • duct arm 6 substantially differs from tap arm 7, in that its main pole 61 is closer to the axis Y-Y than main pole 71 of tap arm 7.
  • both branches 62 and 63 are shorter than respectively branches 72 and 73.
  • L62, L63, L72 and L73 denote the respective lengths of branches 62, 63, 72 and 73. Since poles 61 and 71 are parallel, differences (L62 - L72) and (L63 - L 73) are equal.
  • the purpose of this asymmetry of arms 6 and 7 is to decrease the vertical magnetic field in the upstream corner and not to contribute to the compensation of the magnetic field of the adjacent row of cells.
  • FIG. 2 shows a preferred embodiment of the present invention
  • said conductive arms 6, 7 (which do not form part of the ring busbar system as defined herein) are symmetric with respect to said median transversal plane PY and asymmetric with respect to said mean longitudinal plane PX, or they are asymmetric with respect to said median transversal plane PY in such a way that its main pole 61 is further away from the axis Y-Y than the main pole 71 and asymmetric with respect to said mean longitudinal plane PX, or they have generally different shapes.
  • Table 1 Overall average (a) and maximum (b) B z bias in each quarter [millitesla] at potline current of 450 kA.
  • the first line of values represents the overall average in the liquid zone of the cell
  • the second line of values represents the downstream side
  • the third line of values represents the upstream side
  • the right-hand column represents the duct end and the left-hand column the tap end of the cell.
  • a potline operating using a ring busbar according to the present invention could either be designed to operate at the same row-to-row distance at an increased current, or could be designed to have a smaller row-to-row distance without increasing the perturbation level.
  • the current is conducted clockwise, that is to say it enters the last cell Cm of line L1 upstream, crosses it downstream and then turns clockwise (in direction of the duct end) to line L2.
  • the invention applies also to counter-clockwise structures, and a person skilled in the art can easily adapt the cathode ring busbar system according as shown on the figures to counter-clockwise potlines.
  • the cathode ring busbar system according to the invention can be manufactured from aluminium sections of appropriate cross section. In a known way, stacked aluminium sheets or plates and stacks of flexible aluminium sheets can be used for joining sections by welding.

Abstract

L'invention concerne un système de barre omnibus de cathode destiné à une cellule électrolytique de forme sensiblement rectangulaire, conçu pour le procédé d'électrolyse de Hall-Héroult, ladite cellule électrolytique comprenant une cathode formant le fond de ladite cellule électrolytique et comprenant une pluralité de blocs de cathode parallèles, chaque bloc de cathode comprenant au moins une barre de collecteur de courant et deux points de connexion électrique, un revêtement latéral définissant, conjointement avec la cathode, un volume contenant l'électrolyte liquide et le métal liquide résultant du procédé d'électrolyse de Hall-Héroult, lesdits cathode et revêtement latéral étant contenus dans une enveloppe métallique externe, et ladite cellule électrolytique comprenant en outre une pluralité d'ensembles d'anode suspendus au-dessus de la cathode, chaque ensemble d'anode comprenant au moins une anode et au moins une tige d'anode métallique reliée à une barre omnibus d'anode, ledit système de barre omnibus de cathode comprenant une barre omnibus dite en anneau, entourant ladite enveloppe métallique externe en vue depuis le dessus, ladite barre omnibus en anneau étant sensiblement rectangulaire et définissant un plan principal (PR), un plan longitudinal médian (PX) ainsi qu'un plan transversal médian (PY), ces deux derniers étant orthogonaux audit plan principal (PR), ladite barre omnibus en anneau comprenant deux parties longitudinales opposées et parallèles (2, 3) s'étendant chacune le long des côtés longs de la cellule, et deux parties transversales opposées et parallèles (4, 5) s'étendant chacune le long des extrémités de la cellule, ladite barre omnibus en anneau étant symétrique par rapport audit plan transversal médian (PY), ladite barre omnibus en anneau comprenant des moyens de connexion (21, 31) permettant une connexion avec les deux points de connexion électrique de chaque bloc de cathode de la cellule, ledit système de barre omnibus de cathode étant caractérisé en ce que ladite barre omnibus en anneau est asymétrique par rapport audit plan longitudinal médian (PX) et audit plan transversal médian (PY).
PCT/IB2017/051529 2016-03-21 2017-03-16 Système de barre omnibus permettant de compenser le champ magnétique dans des rangées adjacentes de cellules électrolytiques placées transversalement WO2017163154A1 (fr)

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GB1604679.9A GB2548565A (en) 2016-03-21 2016-03-21 Busbar system for compensating the magnetic field in adjacent rows of transversely arranged electrolytic cells
GB1604679.9 2016-03-21

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CN115125585A (zh) * 2021-03-25 2022-09-30 青海北辰科技有限公司 一种独特的镁电解直流电母线装置及使用方法
CN115125585B (zh) * 2021-03-25 2024-05-03 青海北辰科技有限公司 一种独特的镁电解直流电母线装置及使用方法

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US4683047A (en) * 1984-12-28 1987-07-28 Alcan International Limited Busbar arrangement for aluminium electrolytic cells
RU2164557C2 (ru) * 1999-04-20 2001-03-27 ОАО "Объединенная компания "Сибирский алюминий" Ошиновка электролизера для получения алюминия
WO2006033578A1 (fr) * 2004-09-23 2006-03-30 Norsk Hydro Asa Procede de connexion electrique et de compensation magnetique de cuves d'electrolyse d'aluminium, et systeme associe
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DE2709821A1 (de) * 1975-11-28 1977-09-15 Pechiney Aluminium Verfahren und vorrichtung zum kompensieren der magnetischen felder der einander benachbarten reihen von querangeordneten schmelzflusselektrolysezellen
US4683047A (en) * 1984-12-28 1987-07-28 Alcan International Limited Busbar arrangement for aluminium electrolytic cells
RU2164557C2 (ru) * 1999-04-20 2001-03-27 ОАО "Объединенная компания "Сибирский алюминий" Ошиновка электролизера для получения алюминия
WO2006033578A1 (fr) * 2004-09-23 2006-03-30 Norsk Hydro Asa Procede de connexion electrique et de compensation magnetique de cuves d'electrolyse d'aluminium, et systeme associe
US20150218718A1 (en) * 2012-07-17 2015-08-06 United Company RUSAL Engineering and Technology Centre LLC Busbar arrangement for aluminium electrolysers with a longitudinal position

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CN115125585A (zh) * 2021-03-25 2022-09-30 青海北辰科技有限公司 一种独特的镁电解直流电母线装置及使用方法
CN115125585B (zh) * 2021-03-25 2024-05-03 青海北辰科技有限公司 一种独特的镁电解直流电母线装置及使用方法

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