EP1028083B1 - Hoisting device for the replacement of the anodes in the electrolytic cells for aluminium production - Google Patents

Description

The present invention relates generally to the change from spent anodes to within aluminum production electrolysis tanks. It concerns everything particularly a module capable of allowing the actual extraction of worn anodes and the installation using such modules.

Aluminum is produced industrially by the well-known process today of igneous electrolysis, that is to say using the electrolysis of alumina in a molten cryolite bath according to the reaction:

This highly exothermic reaction therefore sets up a molten bath comprising a mixture of cryolite and alumina, the temperature of which is generally higher than 800 ° C, and consumes a lot of electricity, so that the installations operate in continuous mode, in order to limit the energy losses inherent in the phases restart.

Regularly, the different anodes should be replaced, the more often made of carbon, at the level of each tank, without stopping the electrolysis reaction.

Due to the process used, namely igneous electrolysis, it forms on the surface top of the bath a hard crust of fluorinated cryolite and alumina, this crust with the advantage of retaining heat in the bath, and therefore of creating a heat-insulating envelope.

However, the extraction of spent anodes from the bath requires in the first step the rupture of this crust and, experience shows that the effort required to pull out a spent anode of said crust is seven to eight times the mass of a new anode.

Furthermore, this effort only lasts for a few centimeters of stroke, while the stroke lifting of the anode in each cycle is of the order of three to four meters, typically 3.50 m.

• un premier organe, constitué d'un système de levage comprenant au moins un câble, un ou deux tambours motorisés électriquement, un mouflage au niveau duquel est fixé un porte-outil, ledit ou lesdits câbles venant s'enrouler sur ledit ou lesdits tambours(s), et étant renvoyé(s) au niveau du mouflage, ledit premier organe de levage étant destiné à assurer le déplacement d'une charge au niveau du mouflage à vitesse relativement importante et selon une course étendue ;
• un second organe, dont l'un des éléments constitutifs est solidarisé à l'extrémité du ou des câbles dudit premier organe après renvoi au niveau du mouflage et comprenant des moyens permettant d'assurer en coopération avec ledit mouflage le déplacement vertical à vitesse réduite et selon une course limitée d'une charge plus importante.

To date, in existing installations, we have implemented, in order to carry out these operations, hydraulic cylinder systems, which to date only have a limited size allowing their integration into the volume available above the tanks.
Document US-A-5 816 565 describes a lifting system using two lifting members interacting with each other.
However, whatever the quality of the oil used in these hydraulic cylinders, given the high temperature of the molten bath, the risk of fire is permanent and, we wish to overcome this drawback crippling.
The solutions proposed until then to avoid the use of the hydraulic extraction system come up against a problem of space and the civil engineering of the existing installations. Indeed, these solutions, typically implementing a cable system, require a considerably larger size, incompatible with these installations or, requiring the construction of new installations, encumbering the corresponding costs too significantly before being likely to be amortized.
The object of the invention is therefore to provide an installation for changing spent anodes within a series of electrolytic cells, overcoming these drawbacks, and in particular compatible with existing factories and overcoming risks inherent in the use of hydraulic devices. It relates firstly to a tool holder module, intended in particular to receive a tool to allow the removal and transfer of the spent anodes. This tool holder can also integrate any type of tool, and in particular a device capable of breaking the upper crust which forms on the surface of the bath, but also of a shovel or the like, intended for collecting the pieces of crust from this break.
This tool holder module, intended to be used within a lifting installation, is characterized in that it is provided with two independently powered lifting members:

• a first member, consisting of a lifting system comprising at least one cable, one or two electrically motorized drums, a hauling system at the level of which a tool holder is fixed, said cable or cables being wound on said drum or pumps ( s), and being returned to the hauling level, said first lifting member being intended to ensure the displacement of a load at the hauling level at relatively high speed and over an extended stroke;
• a second member, one of the constituent elements of which is secured to the end of the cable or cables of said first member after returning to the hauling system and comprising means making it possible to ensure, in cooperation with said hauling, the vertical movement at reduced speed and according to a limited stroke of a larger load.

The invention therefore consists, firstly, in differentiating two movements, in know a movement requiring intense effort on a short run at reduced speed, and a movement requiring significantly less effort on a much longer run long, also at a much higher speed.

Mainly, this module is particularly suitable for uprooting and transfer worn anodes. In fact, the second organ is intended to allow the implementation of a intense tensile force, necessary and sufficient to allow the actual lifting of the spent anode outside the electrolysis bath, while the first organ, after removal effective of said anode, ensures the displacement thereof outside the tank.

According to an advantageous characteristic of the invention, the first member consists of a cable lifting system, carrying one or more cables wound on one or more several drums driven by an electric motor, and fitted with a hauling system level of which is fixed a tool, for example for gripping the anode, for breaking the upper crust of the electrolysis bath or of a tool acting as a shovel recovery of pieces from said layer.

In parallel, said second member consists of a mechanical or electro-mechanical jack, at the end of which are fixed the cable or cables of said first member.

In other words, the invention consists in making a system for lifting a load provided with a fixed point, said fixed point being capable of being made mobile over a race limited by means of said second member, that is to say in the present case, of a jack mechanical or electro-mechanical.

Advantageously, the module is provided with a cable slack, so as to limit the load applied by the tool, with which said module is provided, on an obstacle, and in particular in bottom of electrolytic cell. Furthermore, this slack in the cable makes it possible to maintain the turns of cables perfectly wound at the level of the drum (s), and is also designed not to not apply any effort to the level of the installation plan, as specified in a more detailed manner detailed later.

According to another characteristic of the invention, the tool holder module comprises a mast semi-rigid vertical guide, secured to the chassis of said module, and along which slides a tool carriage itself. By doing so, we limit the amplitude of the travel lateral of the haul, in particular in the vicinity of the maximum authorized maximum travel by the length of the cables.

The invention also relates to the installation for changing spent anodes of aluminum production electrolysis tanks.

This installation includes an overhead crane capable of moving above said tanks and on which moves in a direction perpendicular to the translation of the bridge a cart fitted with a tool holder module for extracting and transferring spent anodes out of the tanks, and to convey to the said tanks new anodes.

• à permettre de rompre la croûte superficielle qui se créée à la surface supérieure du bain d'électrolyse de chacune des cuves ;
• à collecter tout ou partie des morceaux provenant de la rupture de ladite croûte ;
• et à extraire et transférer les anodes usées hors des cuves et acheminer au niveau desdites cuves des anodes neuves,

lesdits modules porte-outils, et en conséquence, les outils qu'ils portent étant susceptibles de décrire des portions d'arc de cercle.This installation is characterized in that the carriage is provided with a vertical shaft receiving a plurality of coaxial rings, capable of being rotated independently of each other, each of said rings receiving one or more tool-holder modules, respectively intended :

• allowing to break the surface crust which is created on the upper surface of the electrolysis bath of each of the cells;
• collecting all or part of the pieces resulting from the rupture of said crust;
• and extracting and transferring the used anodes out of the tanks and conveying new anodes to the said tanks,

said tool-holder modules, and consequently, the tools they carry being capable of describing portions of an arc of a circle.

According to the invention, the maximum value of the angle between two extreme tool holders is ideally smaller than the size of the control cabin, located above of said vertical tree. In the absence of such a cabin, the angle separating two or two tools extreme tool holder is less than 180 °.

In this way, this installation can be implemented within existing installations, by minimizing interference and the risks of interaction with, in particular, gas evacuation pipes, in particular fluorinated and carbon monoxide and dioxide, from each of the tanks.

The manner in which the invention can be implemented and the advantages which ensue therefrom will emerge more clearly from the embodiment which follows, given by way of indication but not limiting in support of the appended figures.
Figure 1 is a schematic representation in partial section of an installation according to the invention.
FIG. 2 is a representation similar to FIG. 1, but in a view perpendicular to the view of FIG. 1.

FIGS. 3a, 3b and 3c are diagrammatic representations in plan of the different phases of movement of the tool-holder modules, in particular during a change in activation of the tool.
Figure 4 is a schematic representation relating to the principle of implementation of the tool holder modules according to the invention, of which Figure 5 is a representation of an example of a wiring system, and Figure 6 is a top view in Figure 5.
Figures 7, 8 and 9 are respectively schematic perspective representations of the tool holder module according to the invention, respectively alone and associated with two modules of the same nature, according to two different views.
Figures 10 and 11 are schematic representations of the operation of the slack cable used at said module according to the invention.

There is shown in Figure 1 a partial sectional view of the installation according to the invention. Basically, it consists of an overhead crane (1), likely to move in translation on a raceway (5) above a electrolysis cell (2), and more precisely from a series of substantially identical cells to each other within which a molten electrolysis bath is maintained, containing in a known manner cryolite and alumina.

Typically, the temperature of the bath is greater than 800 ° C., said bath being subjected to a voltage of about 4.5 volts, the intensity of the direct electric current flowing inside of it typically being of the order of 180,000 to 200,000 amperes.

According to the invention, this traveling crane (1) receives a carriage (6) capable of moving over a raceway (7) perpendicular to the translation of the crane. This cart (6) receives a platform (8), surmounting a vertical central shaft (9), at the level of which is mounted a succession of coaxial crowns one above the other, respectively (10), (11) and (12).

These different rings (10), (11) and (12) are capable of being actuated in rotation independently of each other by any appropriate means, and in particular by coupling of an electric motor to a suitable gear (not shown).

Each of these crowns has an extension, located substantially in the same plan, and at the level of which is fixed one or more modules (13, 14, 15) of the type described below.

• un outil d'acheminement d'anodes neuves, et d'arrachage et d'évacuation des anodes usées ;
• un outil de rupture de la croûte supérieure des bains d'électrolyse ;
• un outil de collecte, typiquement une pelle, de tout ou partie des morceaux issus de la rupture de la croûte.

More precisely, each crown is associated with a specific tool holder module, respectively:

• a tool for conveying new anodes, and for stripping and evacuating used anodes;
• a tool for breaking the upper crust of the electrolysis baths;
• a collecting tool, typically a shovel, of all or part of the pieces resulting from the breaking of the crust.

As can be seen in Figures 3a, 3b and 3c, for a three-way configuration tools, the maximum angle between the two extreme tools is less than 120 °. In this way, it there is always compatibility between the movement of the carriage (6) and in particular the pipes evacuation (4) of fluorinated and carbonaceous gases set up at the level of the installations existing. In particular, these angles can be defined according to the characteristics existing facilities, without causing any modification thereof.

Each of the crowns is equipped with a means of controlling the angle of rotation of the tool or the tool holder that it carries, the angle being determined from a fixed point on the support shaft of said crowns.

Typically, when the installation is equipped with a programmable controller, intended for automate its operation, an encoder (not shown) mounted on the motor shaft of the gear motor for driving the crown in question indicates the angle of rotation of the tool holder from a signal given by a fixed limit switch in rotation.

When the installation does not have such a programmable controller, an anti-collision system, proximity sensor type, mounted on each tool, is associated with the fixed limit switch in rotation, ensuring the relative angular control of the tools.

Advantageously, the platform (8) receives an upper cabin (not shown), intended to receive the user, the latter being likely to actuate the tools there considered and the corresponding tool holders while monitoring the operation.

Furthermore, the shaft (9) can also receive a number of coaxial rings additional, likely to carry other tools than those mentioned previously, and in particular a tool for opening the covers (3) of the tanks (2) by example, brushes, etc ...

We understand that, when we want to activate one of the tools, we spreads the other two by folding down the intermediate tool, i.e. the tool positioned between the tool in service and the most extreme tool, on said extreme tool, in order to allow the free operation of the tool in service desired.

Thus, in FIG. 3a, first of all, after opening the covers, the setting in work of the rupture tool of the upper crust of the electrolytic bath, also called a pricking tool, the other two tools being folded to the left.

Once the crust breaking operation has been carried out, the pricking tool is folded towards the left in the direction of the lifting tool, and the tool carrying the shovel is rotated by 270 °, until reaching the level of the tank considered (figure 3b).

To do this, and in order to avoid any interaction between the tool or the tool holder and the piping (4), the carriage (6) is first moved on the crane in order to spread the shaft (9), and starting from the tool-holder modules of the piping (4), then the rotation of the tool considered is carried out by taking care before reassembling the tool carriage (25) at its maximum travel on the stiffening mast (23), described below in more detail., When the rotation of said tool is complete, the carriage (6) is returned to its position original.

Finally, in Figure 3c, once the pieces of crust have been collected, the shovel is folded down on the stitching tool and the lifting tool, comprising for example three tools properly said to be identical, in turn undergoes a rotation of 270 °, after, prior displacement of the carriage (6) to allow the movement of said tools.

This makes it easy to use the installation according to the invention.

There will now be described in more detail the tool-holder modules implemented within this installation, and this in conjunction with FIGS. 4 to 11.

According to a fundamental characteristic of the invention, each of the tool holder modules, and in particular the anode changing modules, have two activation systems independent. They firstly comprise a system of cables (13), wound on one or more two drums (14), the latter being driven in rotation by means of an electric motor (15), via a wheel reducer (16) and worm (17), each wheel (16) being integral and coaxial with one of the drums (14) and coming to cooperate with the screw (17) collinear with the motor shaft of the motor (15). These drums are positioned at level of the upper chassis of each module.

The cable or cables (13) are wound on two pulleys constituting a hauling system (18) and go up towards a fixed point (19).

The load, and in particular the tool holder considered, is fixed at the level of hauling by any suitable means, itself being secured to a carriage (25), as described in more detail detail below.

According to the invention, the fixed point (19) is itself secured to the end of the screw (20) a mechanical jack (21), driven by an electric motor (22).

Thus, this double lifting system makes it possible to implement a conventional lifting ensuring the displacement travel of the anodes over relatively large distances at a relatively high speed for a reduced load, and lifting with lifting, likely to develop a significant effort on a reduced race with speed limited.

This device allows by its traction capacity, on the one hand to develop the effort necessary to tear off the used anode, intended to be replaced, but moreover, given the corresponding low speed, it makes it easier to set up the new anode at the level of the tank.

The organs of the kinematic chain, and in particular the wheels (16), the drums (14) and the cables (13) are dimensioned as a function of the intense force exerted by said second organ, and to which they are subject, taking into account their solicitation during the phase tear.

In addition, the choice of a wheel and screw reducer (16, 17) at the large motor speed ensuring the rotation of the drums (14), allows, using the low efficiency indirect between the reducer and the drum, to decrease the size of the brakes at the motor shaft of said motor (15), necessary when one is in the phase of uprooting, and therefore, more generally, the overall dimensions.

Advantageously, each of the tool holder modules is provided with two drums (14) synchronized by design of the reducer, and each receiving two cables (13), so that the total number of cables is four, as shown in particular in the figures 10 and 11, for example. In this way, it is possible to reduce the size of the pulleys, drums as well as that of reducers, and more generally, to decrease the size of the device.

According to an advantageous characteristic of the invention, the tool holder modules are associated change of anodes by three, as shown in Figures 8 and 9. This configuration is intended to allow the simultaneous change of three spent anodes. he it is of course nevertheless that each of the modules is likely to function independently of each other, so that, notwithstanding the implementation of a system with three modules, only one or two of them can be activated for the change of anodes.

The distance between the three tool-holder modules corresponds to the distance between the anodes. This spacing is likely to be different depending on the installation concerned and is therefore adjustable. It is determined by rods, the length of which corresponds to said center distance. This arrangement allows the system to be adapted to any type of installation.

As can be seen in Figures 7 to 9, each tool holder module is associated a vertical guide mast (23), secured to the level of the upper chassis of the module by through a pre-stress device incorporating ball joints, thus susceptible to allow a certain degree of freedom at the level of the lower part (24) of the mast. This mast (23) is intended to allow guiding, in particular of a carriage (25) containing the hauling (18) and by extension of the load suspension zone, this carriage (25) being provided with rollers (26) bearing on either side of said mast (23). This mast is semi-rigid. The threshold for adjusting the pre-stress is such that we are notably freed from risks of angular movement of said tool holder, in particular at the end of travel, in the event of limited efforts, and in particular those inherent in the intense magnetic field that prevails in the installation, and to which the metallic elements constituting a most of the elements used in the construction of the module

According to another characteristic of the invention, each module comprises a system of slack, thus limiting the vertical travel of the tool when it comes to interact with an obstacle, such as when the shovel comes into contact the bottom of the tank. In the latter case, we wish to limit such a risk as much as possible, taking into account the relative fragility of the tank. In addition, the slack in the cable allows keep the turns of cables perfectly organized on the drums (14).

This slack cable is more particularly described in connection with Figures 10 and 11. Sa implementation is obtained by securing in a non-fixed manner, the hauling (18) to the carriage (25) for moving the tool holder on the mast (23) by means of a set of two connecting rods (27, 28), capable of moving according to a deformable parallelogram, and articulated respectively on the frame (29) at which the haulage is mounted, and on said carriage (25), between two extreme positions, corresponding to the take-up stroke slack in the cable represented by the double arrow A in FIG. 10.

Thus, FIG. 10 represents the carriage (25) bearing on an object or an obstacle surrounding, the frame (29) no longer being in contact with said carriage (25). A sensor (no shown), positioned between the carriage (25) and the frame (29) will have given the order to stop the lifting motor while it was making a downward movement. The stopping distance maximum mobile hauling is represented by the double arrow A.

Figure 11 shows the carriage (25) suspended without contact with the environment, the frame (29) which carries the hauling pulleys being in contact with the carriage (25).

Advantageously, a spring can be put in place between the upper face of the frame (29) and the carriage (25), in order to reduce the apparent weight of said carriage on an object surrounding, allowing in this hypothesis, to preserve the electrolysis tank and its environment.

The tool holder module according to the invention is dimensioned to accept efforts to the neighboring load of 10 tonnes for speeds of the order of one millimeter per second. On the other hand, for speeds of the order of 15 meters per minute and longer runs significant, the displacement effort is of the order of 2 tonnes.

The implementation of such modules, activated electrically, is entirely adequate for existing aluminum electrolysis production plants, in the measure in particular by the physical separation of the functions associated with loads different, it limits the reactions of the rollers on the raceways existing buildings, and therefore does not require any engineering extension civil, while making it possible to significantly increase security conditions.

Claims (15)

1. Tool holder module intended to be used in lifting gear, equipped with two independently motorized lifting member :

   a first member, which consists of a lifting system with at least one cable (13), one or two electrically motorized drum(s) (14), a sheaving system (18), to which is secured a tool holder, said cable(s) (13) being wrapped over said one or two drums (14) and being returned at said sheaving system (18), said first lifting member being intended to displace a load at the level of the sheaving system (18) at a relatively high speed and over a relatively large distance;

   a second member, one of the constituent elements of which being secured to the end of the cable or cables (13) of said first member after return at the sheaving system (18), and comprising means which are intended, in cooperation with this system, to displace a heavier load vertically at a lower speed and over a limited distance.
2. Tool holder module according to claim 1, intended for pulling out spent anodes in a plant for producing aluminium by electrolysis and for transferring said anodes and fresh anodes which are to replace them, characterized in that :

   the first member is intended to displace an anode at a relatively high speed and over a relatively large distance ;

   the second member is intended to pull said anode out of the place in which it is inserted at a low speed and over a limited distance.
3. Tool holder module according to either of Claims 1 and 2, characterized in that said second member consists of a mechanical or electro-mechanical jack (20, 21) to the end of which the cable or cables (13) of said first member are fixed, and which is intended to exert the intense or pulling-out force.
4. Tool holder module according to one of Claims 1 to 3, characterized in that it has slack in the cable, so as to limit the load applied by the tool with which said module is fitted on an obstacle, and in particular at the bottom of an electrolysis tank.
5. Tool holder module according to one of Claims 1 to 4, characterized in that it comprises a semi-rigid vertical guide post (23) secured to the chassis of said module, and along which a carriage (25) to which the tool holder proper is secured can slide.
6. Tool holder module according to Claim 5, characterized in that the guide post (23) is secured to the module chassis via a preloading device intended to give the lower part (24) of the post a certain degree of freedom.
7. Tool holder module according to one of Claims 1 to 6, characterized in that the drums (14) are motorized by at least one electric motor (15) coupled to the drums (14) via a worm (17) and wheel (16) reduction gear set, each wheel (16) being secured to and coaxial with one of the drums (14) and cooperating with the worm (17) that is collinear with the motor drive shaft (15).
8. Tool holder module according to Claim 7, characterized in that the members of the drive line, and in particular the wheels (16), the drums (14) and the cables (13) are dimensioned as a function of the intense force exerted by said second member (20, 21) and to which they are subjected, given the stress applied to them during the pulling-out phase.
9. Installation for changing spent anodes in a works for producing aluminium by dry electrolysis, comprising a travelling crane (5) capable of moving over the electrolysis tanks (1), and on which there moves in a direction perpendicular to the translational movement of the crane, a carriage (6) equipped with a tool holder module according to any one of claims 2 to 8, characterized in that the carriage (6) has a vertical shaft (9) which takes a number of coaxial annuli (10, 11, 12) which can be rotated independently of each other, each of said annuli taking one or more tool holder modules respectively intended:

   to allow the surface crust created at the top surface of the electrolysis bath of each of the tanks to be broken;

   to collect all or some of the pieces that result from breaking said crust;

   and to extract and transfer the spent anodes from the tanks and bring fresh anodes to said tanks,

   said tool holder modules, and therefore the tools which they carry, being capable of describing portions of arcs of circles.
10. Installation for changing spent anodes according to Claim 9, characterized in that the carriage (6) is surmounted by a platform (8) intended to take an upper cab, itself intended to house the user, the latter being able therein to actuate the tools and the corresponding tool holders while at the same time monitoring the manoeuvre.
11. Installation for changing spent anodes according to Claim 10, characterized in that the maximum value of the angle between two end tools or end tool holders is smaller than the amount of space occupied by the cab.
12. Installation for changing spent anodes according to Claim 9, characterized in that the angle separating two end tools or two end tool holders is less than 180°.
13. Installation for changing spent anodes according to one of Claims 9 to 12, characterized in that each of the coaxial annuli (10-12) has an extension, located in essentially the same plane, and in the region of which one or several tool holder modules (13, 14, 15) is/are attached.
14. Installation for changing spent anodes according to one of Claims 9 to 13, characterized in that at least one of the annuli (10) comprises a number of tool holder modules mounted in parallel with one another and capable of operating independently of one another.
15. Installation for changing spent anodes according to Claim 14, characterized in that the spacing between the tool holder modules is adjustable and corresponds to the distance between centres of the anodes, said spacing being determined by link rods, the lengths of which correspond to said distance between centres.

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