ALUMINUM SMELTER INCLUDING CELLS WITH CATHODE OUTPUT AT THE BOTTOM OF THE POT SHELL AND CELL STABILIZING MEANS

Abstract

Aluminum smelter comprising: (i) a series of electrolytic cells, comprising an anode, a cathode and a pot shell equipped with a side wall and a bottom, each cathode including at least one cathode output, (ii) a main electric circuit through which an electrolysis current passes, including an electrical conductor connected to each cathode output of a cell N, and to the anode of a cell N+1, and (iii) a means to stabilize the electrolytic cells. At least one of the cathode outputs of the cathode of N passes through the bottom of the pot shell, and during the operation of N and N+1, the electrolysis current passes, in an upstream-downstream direction only, through each electrical conductor extending from each cathode output of N in the direction of N+1.

Description

The present invention relates to a plant for producing aluminum by the electrolysis of alumina, also referred to as an aluminum smelter.

The practice is known of producing aluminum industrially by the electrolysis of alumina using the Hall-Heroult process. To this end, an electrolytic cell is used, notably made up of a steel pot shell, an interior refractory coating, and a cathode made of carbonaceous material, connected to conductors which deliver the electrolysis current. The electrolytic cell also contains an electrolytic bath notably made up of cryolite in which the alumina is dissolved. The Hall-Heroult process consists of partially immersing a carbon block, forming the anode, into the electrolytic bath, the anode being consumed as the reaction proceeds. The liquid aluminum, produced by the electrolysis reaction, is deposited in the bottom of the cell by gravity, forming a pad of liquid aluminum that completely covers the cathode.

Generally speaking, aluminum production plants have several hundreds of electrolytic cells connected in series in production halls. An electrolysis current, in the order of several hundreds of amperes, passes through these electrolytic cells creating significant magnetic fields. Depending on the distribution of the various components of the magnetic field in the cell, the pad of aluminum may be unstable, which significantly downgrades the productivity of the cell. It is notably known that the vertical composite of the magnetic field is a determining factor in the stability of an electrolytic cell.

It is known that the stability of electrolytic cells can be improved by minimizing the vertical component of the magnetic field in the cell. To do this, the vertical component of the magnetic field relative to an electrolytic cell is compensated owing to a special arrangement of the conductors conveying the electrolysis current from a cell N to a cell N+1. Part of these conductors, generally aluminum bars, circumvent the ends of the cell N. FIG. 1 is a schematic top view of an electrolytic cell 100 wherein the magnetic field is self-compensated owing to the layout of the conductors 101 connecting this cell N 100 to the next cell N+1 102 placed downstream. To this end, it is noted that conductors 101 are off-center in relation to the cell 100 and circumvent it. Such a magnetic self-compensation method is notably known from patent document FR2469475.

However, the self-compensation method of an electrolytic cell creates a significant amount of design constraints owing to its large size due to the specific arrangement of the conductors. In addition, the significant length of the conductors needed to implement this solution generates power loss online and requires a lot of material (aluminum conductors), hence high costs in terms of energy consumption and manufacturing.

Another cause of instability of the electrolytic cells, in addition to the vertical component of the magnetic field, is the presence of horizontal electric currents in the pad of aluminum. FIG. 2 shows an electrolytic cell 200 belonging to the state of the art, through which an electrolysis current I₂₀₀ passes. The electrolytic cell 200 has an anode 201, a pot shell 202 notably containing an electrolytic bath 203, a pad of liquid aluminum 204 and a cathode 205. It should be noted that there are significant horizontal currents in the particularly conductive areas. This is notably the case when the electrolysis current I₂₀₀ passes through the pad of liquid aluminum 204.

The present invention therefore aims to remedy all or part of these drawbacks, by providing an aluminum smelter in which the stability of the liquids contained in the electrolytic cells is improved, and having lower design, construction and operating costs.

In relation thereto, the subject of the present invention is an aluminum smelter comprising:

(i) a series of electrolytic cells, designed for the production of aluminum according to the Hall-Heroult process,

each electrolytic cell comprising at least one anode, a cathode and a pot shell provided with a side wall and a bottom, each cathode comprising at least one cathode output,

(ii) a main electric circuit through which electrolysis current passes, electrically connecting the electrolytic cells together,

the electrolysis current initially passing through an electrolytic cell N, placed upstream, and secondly through an electrolytic cell N+1, placed downstream,

said main electric circuit comprising an electrical conductor connected to each cathode output of the electrolytic cell N,

the electrical conductor also being connected to at least one anode of the electrolytic cell N+1, in order to conduct the electrolysis current from electrolytic cell N to electrolytic cell N+1,

characterized in that the aluminum smelter further comprises

(iii) at least a means to stabilize the electrolytic cells among at least one secondary electric circuit through which an electric current passes, so as to compensate the magnetic field created by the electrolysis current, or the use of a cathode with a grooved surface,

and such that

at least one of the cathode outputs of the cathode of the electrolytic cell N passes through the bottom of the pot shell,

during the operation of the electrolytic cells N, N+1 (2), the electrolysis current (I₁) passes, in an upstream-downstream direction only, through each electrical conductor extending from each cathode output of the electrolytic cell N in the direction of the electrolytic cell N+1.

The invention therefore makes it possible to improve the stability of the electrolytic cells in the aluminum smelter, by acting on the horizontal currents passing though the cells and on the magnetic field generated by the electrolysis current and/or the kinetic stability of the pad of aluminum contained in the cells. It simultaneously allows the conductors conveying the electrolysis current from one cell to another to be reduced in size and weight, and consequently reduces the costs associated with the design and manufacture of the aluminum smelter according to the invention. Energy loss is further reduced.

According to another characteristic of the aluminum smelter according to the invention, the electrolytic cells are aligned along an axis, and such that the electrical conductor extends in a substantially rectilinear manner and in a manner substantially parallel to the axis of alignment of the electrolytic cells.

According to another characteristic of the aluminum smelter according to the invention, each cathode further comprises at least one cathode output passing through the downstream side wall of the pot shell.

This characteristic has the advantage of further reducing the size and weight of the electrical conductors conveying the electrolysis current from one cell to another. This cathode output passes through the side wall of the pot shell of the cell N on its downstream side, in order to respect the characteristic according to which each electrical conductor extends in the direction of the cell N+1, in the upstream-downstream direction only. Owing to the proximity of the downstream side of the cell N and cell N+1, the length of the electrical conductor connecting this cathode output to the anode of the cell N+1 is less than that of an electrical conductor connecting a cathode output by the bottom of the cell N to the anode of the cell N+1. This embodiment therefore has the advantage of reducing the size and length of the electrical conductors in relation to an embodiment of the aluminum smelter according to the invention in which the cells comprise cathode outputs located only on the bottom.

Preferably, each downstream cathode output passing though the side wall of the pot shell of the electrolytic cell N comprises a metal bar, more particularly made of steel, with a copper insert or plate.

This allows the voltage at the cathode output passing through the bottom of the pot shell to be balanced in relation to that at the level of the cathode output passing through the side wall of the pot shell.

Advantageously, the pot shell of the electrolytic cell N comprises several arches secured to the side wall and to the bottom of the pot shell, the electrical conductors connected to each cathode output passing through the bottom of the pot shell of the electrolytic cell N extending between the arches.

This characteristic has the advantage of reducing the size of the electrical conductors conveying the electrolysis current from one cell to another.

Advantageously, the electrolytic cells include short-circuiting means.

The short-circuiting means allow an electrolytic cell to be short circuited so that it can be removed for maintenance, while the other cells in the series continue to operate.

Advantageously, the short-circuiting means of the electrolytic cell N+1 comprise at least a short-circuiting electrical conductor placed permanently between electrolytic cell N and electrolytic cell N+1, each short-circuiting electrical conductor being electrically connected to one of the electrical conductors connected to a cathode output of the cell passing through the bottom of the shell of the electrolytic cell N+1, and each short-circuiting electrical conductor being located a short distance from one of the electrical conductors connected to one of the cathode outputs of the electrolytic cell N.

According to another characteristic of the aluminum smelter according to the invention, the short-circuiting means of the electrolytic cell N+1 comprise at least a short-circuiting electrical conductor placed permanently between electrolytic cell N and electrolytic cell N+1, each short-circuiting electrical conductor being electrically connected to one of the electrical conductors connected to a cathode output of the cell passing through the bottom of the shell of the electrolytic cell N, and each short-circuiting electrical conductor being located a short distance from one of the electrical conductors connected to one of the cathode outputs of the electrolytic cell N+1.

The short distance between the short-circuiting conductor and the other conductor form locations for the introduction of short-circuiting blocks. These short-circuiting blocks can be introduced from above or from below in the second case.

Preferably, at least a secondary electric circuit includes electrical conductors running along the right side and/or the left side of the electrolytic cells along at least one line of electrolytic cells.

Advantageously, the at least one secondary electric circuit includes electrical conductors extending along at least one line of electrolytic cells, under said electrolytic cells.

Advantageously, the electrical conductors of the at least one secondary electric circuit are made of a superconducting material. This allows a decrease in the voltage drop to which each secondary circuit is subjected, thereby saving energy and enabling a less powerful and less expensive power substation to be used for each secondary electric circuit. This characteristic also allows material costs to be reduced in relation to aluminum or copper conductors. It allows the size of the electrical conductors to be reduced, which saves space in the aluminum smelter.

According to another characteristic of the aluminum smelter according to the invention, the electrical conductor of the at least one secondary electric circuit runs along the electrolytic cells of the line(s) at least two times.

This characteristic offers the possibility to reduce the strength of the current passing through this secondary circuit in order to save energy.

The invention will be better understood from the detailed description given below with reference to the accompanying drawings in which:

FIG. 1 is a schematic top view of an electrolytic cell of the state of the art,

FIG. 2 is a schematic view of an electrolytic cell acknowledged as belonging to the state of the art,

FIG. 3 is a schematic top view of an aluminum smelter according to a specific embodiment of the present invention,

FIG. 4 is a schematic view of a cell N and a cell N+1 of an aluminum smelter according to a specific embodiment of the invention,

FIGS. 5 and 6 are cross-sections along lines I-I and II-II of FIG. 4, respectively,

FIG. 7 is a schematic view of an electrolytic cell according to the embodiment of FIG. 4,

FIG. 8 is a schematic top view of the cell N and cell N+1 of an aluminum smelter according to a specific embodiment of FIG. 4,

FIG. 9 is a cross-sectional view along line III-III of FIG. 8,

FIG. 10 is a schematic view of a cell N and a cell N+1 of an aluminum smelter according to another specific embodiment of the invention,

FIGS. 11 and 12 are cross-sections along lines IV-IV and V-V of FIG. 10, respectively,

FIG. 13 is a schematic top view of the cell N and the cell N+1 of an aluminum smelter according to a second specific embodiment of the invention,

FIG. 14 is a cross-section along line VI-VI of FIG. 13,

FIGS. 15 and 16 are schematic top views of an aluminum smelter 1 according to specific embodiments of the invention,

FIGS. 17, 18 and 19 are schematic side views of grooved cathodes that may equip a cell of an aluminum smelter according to an embodiment of the invention,

FIG. 20 is a schematic front view of a grooved cathode block that may equip a cell of an aluminum smelter according to an embodiment of the invention,

FIG. 21 is a schematic top view of a grooved cathode block that may equip a cell of an aluminum smelter according to an embodiment of the invention.

FIG. 3 shows an aluminum smelter 1 including a plurality of electrolytic cells 2. The electrolytic cells 2 can be rectangular, for example. They thus have two long sides 2a corresponding to their length and two short sides 2b corresponding to their width.

The short sides 2b of each cell 2 can be divided into a right side and a left side. The left side and the right side are defined in relation to an observer located at the main electric circuit 4 and looking in the overall direction of the direction of the electrolysis current I₁.

The long sides 2a of each cell 2 can be divided into an upstream side and a downstream side. The upstream side corresponds to the long side 2a of a cell 2 adjacent to the preceding cell 2, i.e. that through which the electrolysis current I₁ passes first. The downstream side corresponds to the long side 2a of a cell 2 adjacent to the next cell 2, i.e. that through which the electrolysis current I₁ passes next. More generally speaking, upstream and downstream are defined in relation to the overall direction of the electrolysis current I₁.

In the example shown in FIG. 3, the cells 2 are aligned along two parallel axes, so as to form a line F and a line F′. Each line F, F′ may comprise, for example, a hundred or so cells 2. The lines F and F′ are connected electrically to each other in series. The cells 2 are connected electrically to each other in series. A series of cells 2, which may contain several files F, F′, is connected to its ends to a power substation 3. The electrolysis current I₁ passes through the cells 2 one after the other, defining a main electric circuit 4.

In the embodiment of FIG. 3, the electrolytic cells 2 are arranged so that their long sides 2a are perpendicular to their alignment axis.

As can be seen in FIG. 3, the aluminum smelter 1 comprises two secondary electric circuits 5 and 6 separate from the main electric circuit 4.

Electrical currents I₂ and I₃ pass through the secondary electric circuits 5 and 6. The strength of the electric currents I₂ and I₃ is between 20% and 100% of that of the strength of the electrolysis current I₁ and preferably between 40% and 70%, and more particularly in the order of half. The direction of flow of electrical current I₂ and I₃ is advantageously the same as the direction of the flow of the electrolysis current I₁. The secondary electric circuits 5 and 6 can both be connected to a power substation 20 and 21 respectively, separate from the power substation 3, as can be seen for example in FIG. 15 or FIG. 16.

The secondary electric circuits 5 and 6 are formed by electrical conductors arranged parallel to the axes of alignment of the cells 2. They run along the right and left sides of the electrolytic cells 2 of each line F, F′ of the series. The secondary electric circuits 5 and 6 can also pass, in whole or in part, under the electrolytic cells 2.

In order to stabilize the liquids contained in the electrolytic cells 2, it is possible to use, in an alternative or complementary manner, secondary electric circuits 5 and 6, one or more cathode blocks 8 having a grooved upper face, as can be seen in FIGS. 17 to 21. The upper face of these cathode blocks 8 comprises at least one channel 8a extending longitudinally over at least part of the length of the cathode blocks 8. When in operation, the upper surface of the grooves is covered by the pad of aluminum and the channels 8a are thus occupied by the pad 11 of aluminum that forms during the electrolysis reaction. The height of the aluminum pad above the upper surface of the grooves is notably between 3 and 20 cm. Thus, the grooves and channels 8a make it possible to limit the movements of the pad of aluminum 11 during the electrolysis reaction and contribute to stability and to a better yield of the electrolytic cells 2.

Each electrolytic cell 2 can contain a plurality of cathode blocks 8 placed next to each another. Instead of channels 8a on the upper face of one or more of these cathode blocks 8, it is possible to allow for an inclined upper face, such that the cathode blocks 8 placed next to one another form channels 8b, as is represented schematically in FIG. 19.

Such cathode blocks with a grooved upper face are notably known from patent document U.S. Pat. No. 5,683,559.

The upper face of these cathode blocks 8 having longitudinal channels 8a may also comprise a transversal central channel 8c, extending at least partially over the width of the cathode blocks 8. The central channel 8c thus crosses the channel(s) 8a extending at least partially over the length of the cathode blocks 8. In the example of FIGS. 20 and 21, the cathode block 8 comprises a central channel 8c on its upper face arranged perpendicularly to the channels 8a extending substantially parallel to the length of the cathode block 8.

Typically, as is represented on FIG. 4, an electrolytic cell 2 comprises a metal pot shell 7 made of steel, for example. The metal pot shell 7 has a side wall 7a and a bottom 7b. It is lined internally by refractory materials (non visible). The electrolytic cell 2 also comprises a cathode formed of cathode blocks 8 made of carbonaceous material and anodes 9 also made of carbonaceous material. The anodes 9 are designed to be consumed as the electrolysis reaction progresses in an electrolytic bath 13 notably comprising cryolite and alumina. The anodes 9 are connected to a load bearing structure by rods 10. A pad of liquid aluminum 11 forms during the electrolysis reaction. The cathode comprises cathode sorties 12 passing through the pot shell 7. The cathode outputs 12 are formed, for example, by metal bars secured to cathode blocks 8. The cathode outputs 12 are themselves connected to electrical conductors 14 enabling the electrolysis current I₁ to be conveyed from the cathode outputs 12 of a cell N (the one on the left in FIG. 4) to the anodes 9 of a cell N+1 (the one on the right in FIG. 4).

The electrolysis current I₁ first passes through the anode 9 of cell N, then the electrolytic bath 13, the pad of liquid aluminum 11, the cathode, the cathode outputs 12 and the electrical conductors 14 that convey it toward the anode 9 of the next cell N+1.

As is represented in FIG. 4, which illustrates a particular embodiment of the present invention, the cathode outputs 12 advantageously pass through the bottom 7b of the pot shell 7. This allows the horizontal electric currents to be reduced to improve the yield of the cells 2. Furthermore, for the same mass of steel used for the horizontal part under the anodes of the cathode output, the overall current density is reduced and thus the voltage drop. Also, the current lines tend to extend in a substantially rectilinear manner, and thus vertically in the aluminum pad as they do naturally between the anodes and the electrical conductors. For this purpose, FIG. 7 shows the current lines passing through an electrolytic cell 2. It is noted that the horizontal electric currents, particularly in the liquid aluminum pad 11, are substantially reduced in relation to those in FIG. 2.

Another remarkable point is that the electrical conductors 14 extend in a rectilinear manner and parallel to the alignment axis of the electrolytic cells 2 from the cathode outputs 12 of the cell N in the direction of the cell N+1 so that the electrolysis current passes through them only in the upstream-downstream direction when the electrolytic cells 2 N, N+1 are in operation. The upstream-downstream direction corresponds to the overall direction of flow of the electrolysis current I₁. Thus, an observer located at an electrolytic cell 2 and moving in the upstream-downstream direction can only move toward cell N+1. In particular, to reach cell N+1, this observer cannot backtrack, even partially, in the direction of the cell N−1.

In addition, the electrical conductors 14 connected to the cathode outputs 12 passing through the bottom 7b of the pot shell 7 do not extend under the full width of the pot shell 7 of the cell N; an electrical conductor 14 does not pass completely through an electrolytic cell 2 under its pot shell 7 or on the sides. In particular, they do not pass through the plane containing the upstream side wall of the pot shell 7 of the cell N.

The rectilinear extension, in the downstream direction only, parallel to the alignment axis of the electrolytic cells 2, forms the shortest electrical path connecting a cathode output of the cell N, passing through the bottom 7b of the pot shell 7 of this cell N, up to the anode 9 of the next cell N+1. Furthermore, as stated above, the electrolysis current I₁ passing through the cell N passes through the cathode outputs 12 then the electrical conductors 14 connected to the cathode outputs 12. The electrolysis current I₁, while passing through the electrical conductors 14 is conveyed in a straight line parallel to the alignment axis of the cells 2 in the direction of the next cell N+1. This notably saves energy.

In addition, this arrangement limits the overall dimensions near the electrolytic cells 2. It thus becomes possible to reduce the center-to-center distance separating two adjacent cells 2 in order to increase the available space in the aluminum smelter 1, for example to add two additional electrolytic cells 2 or to decrease the size of the buildings.

Also, making use of electrical conductors 14, extending in a rectilinear manner from one cell to another parallel to the alignment axis of the cells 2, simplifies the structure of these electrical conductors 14. Their modularity makes their fabrication more economical.

It should be noted that this specific arrangement is made possible notably by the existence of the first secondary electric circuit 5 and the second secondary electric circuit 6 which compensate the effects of the magnetic field created by the electrolysis current I₁, or that of the cathode with the grooved upper surface that stabilizes the movements of the pad of liquid aluminum 11. It is not necessary to configure the electric conducts 14 so as to obtain self-compensation of the effects of this magnetic field relative to each electrolytic cell 2.

FIGS. 5 and 6 are sectional views of an electrolytic cell 2 according to an embodiment of the invention, along line I-I and line II-II of FIG. 4, respectively. It can be seen that the pot shell 7 of a cell 2 is supported by a plurality of arches 15. The arches 15 are placed around the pot shell 7. The arches 15 are secured against the side wall 7a and the bottom 7b of the pot shell 7. They are arranged parallel in relation to each other. A space, bounded between two consecutive arches 15, is advantageously occupied by the electrical conductors 14. It will be noted that the electrical conductors 14 can connect the cathode outputs 12 in pairs.

FIG. 8 is a schematic view of the top of a cell N (to the left in FIG. 8), placed upstream, and a cell N+1 (to the right in FIG. 8), placed downstream, according to the embodiment of FIG. 4. FIG. 9 is a sectional view along line III-III of FIG. 8. The secondary electric circuits 5 and 6, arranged parallel to the short side 2b of the electrolytic cells 2, are visible. The electrical conductors 14 will also be noted, under the pot shell 7, which extend in a straight line in the direction of the cell N+1. The arches 15 are noted, mounted on the side wall 7b of the pot shell 7 of the cell N and between which the electrical conductors 14 extend. The cathode outputs 12 can be aligned according to an axis parallel to the long sides 2a of the electrolytic cell 2, as is represented as dashed lines in FIG. 8.

FIG. 10 schematically represents another embodiment of an aluminum smelter 1 according to the present invention. FIGS. 11 and 12 represent a sectional view along lines IV-IV and V-V of FIG. 10, respectively. In this embodiment, the electrolytic cells 2 have first cathode outputs 12 passing through the bottom 7b of the pot shell 7, while the second cathode outputs 12, located downstream from the first cathode outputs 12, pass through the downstream side wall 7a of the pot shell 7. The electrolytic cells 2 of the aluminum smelter 1 according to this second embodiment thus have “mixed” cathode outputs 12, as they pass through the bottom 7b and the side wall 7a.

This arrangement allows further savings to be made in terms of material, owing to the decreased length, and thus the weight, of the electrical conductors 14.

Advantageously, the second cathode outputs 12 passing through the side wall 7a can include an element made of a material that conducts electricity better, such as steel, notably copper, in the form of a plate 16 or an insert, for example. The copper plate 16 placed on a steel bar allows, by its high electrical conductivity, to rebalance the voltages on the first cathode outputs 12, passing through the bottom 7b, and the second cathode outputs 12, passing through the side wall 7a, and thus to limit the horizontal electrical currents in the aluminum pad.

FIG. 13 schematically shows the top of a cell N, placed upstream (on the left in FIG. 13), and cell N+1, placed downstream (on the right in FIG. 13), of an aluminum smelter 1 according to the embodiment presented in FIG. 10. FIG. 14 is a sectional view along line VI-VI of FIG. 13. As in the embodiment presented in FIG. 4, the electrical conductors 14 extend between the arches 15. In addition, they extend in a rectilinear manner and the electrolysis current flows through them, during operation of the electrolytic cells 2 N, N+1, only in the direction of the cell N+1 located downstream of the cell N, from the cathode outputs 12 passing through the bottom 7b of the shell of the cell N, in order to allow the electrolysis current I₁ to be conveyed from the cathode outputs 12 of cell N to the anode 9 of cell N+1.

As in the embodiment presented in FIG. 4, the secondary electric circuits 5 and 6 are parallel to the axis of alignment of the cells 2.

The aluminum smelter 1 can also advantageously include means to short circuit each cell 2. These short-circuiting means can include electrical short-circuiting conductors 17, shown in FIGS. 4, 8, 10 and 13. The electrical short-circuiting conductors 17 are arranged between two successive electrolytic cells 2. In FIGS. 4, 8, 10 and 13, the electrical conductors 17 are placed in contact with the electrical conductors 14 connected to the cathode outputs 12 passing through the bottom 7b of the pot shell 7 of the cell N+1, and at a distance from electrical conductors 14 connected to the cathode outputs 12 of the cell N, so that a narrow space separates the electrical short-circuiting conductors 17 of the electrical conductors 14 connected to the cathode outputs 12 of the cell N, as is notably shown in FIG. 10.

The electrical short-circuiting conductors 17 are designed to short circuit a cell N+1, for example in order to remove the latter for maintenance. The distance between the electrical short-circuiting conductors 17 and the electrical conductors 14 connected to the cathode outputs 12 of the cell N is thus filled by a block made of a conducting element (not represented) so as to conduct the electrolysis current I₁ from the cell N to the cell N+2 via this block, the electrical short-circuiting conductors 17 and the electrical conductors 14 normally placed under the cell N+1 (i.e. the electrical conductors 14 connected to the cathode outputs 12 passing through the bottom 7b of the shell 7 of the cell N+1 when it is in place).

It is also possible to allow for electrical short-circuiting conductors 17 placed in contact with electrical conductors 14 connected to the cathode outputs 12 of the cell N and at a distance from electrical conductors 14 connected to the cathode outputs 12 of the cell N+1 passing through the bottom 7a of the pot shell 7.

The electrical short-circuiting conductors 17 may be made of aluminum. Given that the electrolysis current I₁ passes through them only occasionally during short-circuiting (for maintenance of a cell 2, or at intervals of several years), they can be designed to work at the highest allowable current density, which allows their mass to be limited.

Finally, it should be noted that, advantageously, the electrical conductors forming the secondary electric circuits 5 and/or 6 can be made of a superconducting material.

These superconducting materials can, for example, contain BiSrCaCuO, YaBaCuO, known from patent applications WO2008011184, US20090247412 or even other materials known for their superconducting properties.

The superconducting materials are used to convey current with little or no loss through the generation of heat by the Joule effect, as their resistivity is zero when maintained below their critical temperature.

For example, a superconducting cable comprises a central copper or aluminum core, ribbons or fibers made of a superconducting material, and a cryogenic envelope. The cryogenic envelope can consist of a sleeve containing a cooling fluid, such as liquid nitrogen for example. The cooling fluid maintains the superconducting materials at a temperature below their critical temperature, for example below 100 K (Kelvin), or between 4 K and 80 K.

The use of electrical conductors made of a superconducting material to form the secondary electric circuits 5 and 6 is of particular interest owing to their length, in the order of a few kilometers. The use of electrical conductors made of superconducting materials requires less voltage in relation to that required by electrical conductors made of aluminum or copper. It is thus possible to decrease the voltage from 30 V to 1 V. This represents a 75% to 99% decrease in energy consumption in relation to electrical conductors made of aluminum. In addition, the cost of power substations 20 and 21, of the secondary electric circuit 5 and the secondary electric circuit 6 respectively, is reduced accordingly.

The electrical conductors of the secondary electric circuits 5 and 6 can be advantageously run along a line F of electrolytic cells 2 at least two times.

The small overall dimensions of the electrical conductors made of a superconducting material in relation to electrical conductors made of aluminum or copper (cross section up to 150 smaller than the cross section of a copper conductor at equal intensity, and still further in relation to an aluminum conductor) facilitates the formation of several turns in series in the loops formed by the secondary electric circuits 5 and 6.

In addition, it is possible to place the electrical conductor of a circuit inside a single cooling sleeve regardless of the number of turns made by this same conductor. In a given location, the sleeve can contain several passages of the same electrical conductor made of superconducting material.

The fact that the loop formed by the secondary electric circuits 5 and 6 contains several turns in series allows the strength of the electrical current I₂, I₃ passing through the secondary electric circuit 5 and the secondary electric circuit 6, respectively, to be divided (as many times as the number of turns made). The decrease in the value of this current strength allows energy losses due to the Joule effect to be lowered at the junctions between the electrical conductors made of superconducting material and the poles of the power substations. The decrease of the overall current strength with the electrical conductors made of superconducting material allows the power substations 20 and 21 to be reduced in size. For example, the power substation 20 or 21 of the secondary electric circuit 5 or the secondary electric circuit 6 comprising an electrical conductor made of superconducting material can deliver current in the order of 5 kA to 40 kA. This also allows conventional off-the-shelf and thus inexpensive equipment to be used.

It should be noted that the electrical conductors made of superconducting material can be placed under the electrolytic cells 2.

Thus, the aluminum smelter 1 according to the invention has a set of characteristics, the combination of which contributes, by a synergy effect, to reducing the design, construction and operating costs of this aluminum smelter 1, and to increasing its productivity.

Naturally, the invention is in no way limited to the embodiments described above, as these embodiments are provided only as examples. Modifications remain possible, notably from the point of view of forming various elements or by the substitution of equivalent techniques, without deviating from the protective scope of the invention.

Claims

1. An aluminum smelter comprising:

(i) a series of electrolytic cells, designed for the production of aluminum according to a Hall-Heroult process,

each electrolytic cell comprising at least one anode, a cathode and a pot shell provided with a side wall and a bottom, the cathode comprising at least one cathode output;

(ii) a main electric circuit through which electrolysis current passes, electrically connecting the electrolytic cells together,

the electrolysis current initially passing through an electrolytic cell N, placed upstream, and secondly through an electrolytic cell N+1, placed downstream,

said main electric circuit comprising an electrical conductor connected to each cathode output of the electrolytic cell N,

the electrical conductor also being connected to at least one anode of the electrolytic cell N+1, in order to convey the electrolysis current from electrolytic cell N to electrolytic cell N+1; and

(iii) at least one means to stabilize the electrolytic cells selected from the group consisting of at least one secondary electric circuit through which an electric current passes, so as to compensate the magnetic field created by the electrolysis current, and a cathode with a grooved surface,

such that

at least one of the cathode outputs of the cathode of the electrolytic cell N passes through the bottom of the pot shell, and

during operation of the electrolytic cells N and N+1, the electrolysis current passes, in an upstream-downstream direction only, through each electrical conductor extending from each cathode output of the electrolytic cell N in the direction of the electrolytic cell N+1.

2. The aluminum smelter according to claim 1, characterized in that the electrolytic cells are aligned along an axis, and in that the electrical conductor extends in a substantially rectilinear manner and in a manner substantially parallel to the axis of alignment of the electrolytic cells.

3. The aluminum smelter according to claim 1, wherein at least one cathode output of each cathode passes through a downstream side wall of the pot shell.

4. The aluminum smelter according to claim 3, characterized in that each cathode output passing through the downstream side wall of the pot shell of the electrolytic cell N comprises a metal bar with a copper insert or plate.

5. The aluminum smelter according to claim 1, characterized in that the pot shell of the electrolytic cell N comprises several arches secured to the side wall and to the bottom of the pot shell, the electrical conductors connected to each cathode output passing through the bottom of the pot shell of the electrolytic cell N extending between the arches.

6. The aluminum smelter according to claim 1, characterized in that the electrolytic cells include short-circuiting means.

7. The aluminum smelter according to claim 6, characterized in that the short-circuiting means of the electrolytic cell N+1 comprise at least a short-circuiting electrical conductor placed permanently between electrolytic cell N and electrolytic cell N+1, each short-circuiting electrical conductor being electrically connected to one of the electrical conductors connected to one of the cathode outputs of the electrolytic cell passing through the bottom of the shell of the electrolytic cell N+1, and each short-circuiting electrical conductor being located a short distance from the electrical conductors connected to one of the cathode outputs of the electrolytic cell N.

8. The aluminum smelter according to claim 6, characterized in that the short-circuiting means of the electrolytic cell N+1 comprise at least a short-circuiting electrical conductor placed permanently between electrolytic cell N and electrolytic cell N+1, each short-circuiting electrical conductor being electrically connected to one of the electrical conductors connected to one of the cathode outputs of the electrolytic cell passing through the bottom of the shell of the electrolytic cell N, and each short-circuiting electrical conductor being located a short distance from the electrical conductors connected to one of the cathode outputs of the electrolytic cell N+1.

9. The aluminum smelter according to claim 1, characterized in that the at least one secondary electric circuit comprises electrical conductors running along at least one line of the electrolytic cells at a right and/or left side of the electrolytic cells.

10. The aluminum smelter according to claim 1, characterized in that the at least one secondary electric circuit comprises electrical conductors extending along at least one line of the electrolytic cells, under said electrolytic cells.

11. The aluminum smelter according to claim 9, characterized in that the electrical conductors of the at least one secondary electric circuit are made of a superconducting material.

12. The aluminum smelter according to claim 11, characterized in that the electrical conductors of the at least one secondary electric circuit run along the electrolytic cells or the at least one line of the electrolytic cells at least two times.

13. The aluminum smelter according to claim 4, characterized in that the metal bar is made of steel.

14. The aluminum smelter according to claim 10, characterized in that the electrical conductors of the at least one secondary electric circuit are made of a superconducting material.

15. The aluminum smelter according to claim 14, characterized in that the electrical conductors of the at least one secondary electric circuit run along the electrolytic cells or the at least one line of the electrolytic cells at least two times.