FR3065014B1 - METHOD FOR ESTABLISHING ANODE COVERAGE IN AN ELECTROLYSIS CELL, SERVICE MACHINE SUITABLE FOR CARRYING OUT SAID METHOD, AND COMPUTER PROGRAM PRODUCT FOR IMPLEMENTING SUCH A METHOD - Google Patents

Abstract

Method of placing an anode cover in an electrolysis cell (2) used for the production of aluminum by means of a service machine (4) comprising at least one dispensing device (23) a cover material (22) on at least one anode block (9), the process comprising at least the following steps: / 1 / layer deposition of a controlled amount of a cover product (22) on a upper surface (Ssup) of the anodic block (9, 9 '); / 2 / measuring the thickness using a sensor (26) of the deposited product layer (22); / 3 / comparison between the measured thickness and a reference thickness; / 4 / calculating a correction amount of cover product (22) to reach the reference thickness; / 5 / rectification of the thickness of the layer of the cover product (22) with the aid of the correction amount.

Description

The invention relates to the field of aluminum production by igneous electrolysis according to the Hall-Héroult process. More specifically, the invention relates to the covering by a powdery product of anodes in electrolysis cells for the production of aluminum.

The industrial production of aluminum from alumina by the Hall-Héroult process is a well-known technique. In general, it is carried out in an electrolysis installation comprising a hall, in which a plurality of electrolysis cells is installed. Each tank is filled with an electrolytic bath including cryolite in which the alumina is dissolved. Pre-baked carbon anodes are partially immersed in the electrolytic bath. The anodes are fed with current flowing through the bath to a cathode formed generally at the bottom of the tank. The document FR. 2,806,742 describes an example of such an installation.

The reactions taking place in the tank require regular interventions.

More particularly, the electrolysis reactions involve the progressive consumption of the anodes, which must be changed regularly.

An anode may be defined as comprising a metal rod which conducts the current, sealed to at least one precooked carbon block. It is this carbon block that is consumed by the electrolysis reduction reactions.

In order to protect the combustion by air of the part of the carbon block which is not immersed in the electrolytic bath, it is known to cover the carbon block with a cover product on a controlled thickness, for example of the order of 10cm. In general, the cover product is of the pulverulent type and comprises a mixture of alumina and "ground bath", that is to say of the electrolytic bath recovered, solidified and milled.

It has been proposed to place flanges on the carbonaceous blocks to form a container on the upper surface of the carbon block in which the spilled cover product is retained. The carbon block is thus covered with the cover product reliably. Document FR 2 527 229 provides an example of such an embodiment using aluminum strips. However, this embodiment does not cover the electrolytic bath. In addition, it requires to review the shape of the carbon blocks and add edges, which complicates the manufacture of carbon blocks and thus increases the production costs of aluminum.

In WO2007 / 132081, it is proposed to cover the carbon block with a layer of cover material to a controlled thickness before placing it in the tank. This solution has several disadvantages. In particular, it still does not provide a solution for depositing the covering product on the surface of the electrolytic bath. In addition, it requires giving specific properties to the cover product to prevent it from flowing when it covers the carbon block before being placed in the tank, which involves treatments and therefore additional costs.

When changing an anode, the bath crust is cut around the spent carbon block, called a "butt", and the spent anode is lifted out of the tank. Part of the crust falls to the bottom of the tank, and a part remains attached to the butt. Optionally, a cleaning operation using a shovel is carried out in order to recover the crustal portions that have fallen to the bottom of the tank. A new anode is placed so that the new carbon block is immersed in the electrolytic bath at a given height, with a portion of the new carbon block emerging out of the bath. Then, a few hours later, typically 3 or 4 hours, the time that a solid film called crust is formed on the surface of the electrolytic bath between the carbonaceous blocks, the cover product is poured into the tank to cover the new carbon block and the space between the carbon blocks.

The anode change operations require opening the tanks, which are normally closed by covers, to prevent the escape of toxic gases and fumes produced by the electrolysis reactions in the electrolysis hall. During these operations, devices can limit the escape of gases, fumes and toxic dust, but can not totally prevent it. Thus, an operator being close to an open tank, for example to ensure proper distribution of the roofing product, is exposed to these gases and fumes. The automation and mechanization of tank handling operations is therefore the subject of research and development to keep human operators as far away as possible from tanks and gases and fumes escaping from them. For this purpose, many tank handling operations are performed using a machine, called service machine in electrolysis or MSE, mobile in the electrolysis hall. The MSE carries tools to carry out the various interventions. An operator can control the MSE and tools from a cab.

However, the spill of the roofing product into the tank is a difficult operation to automate. Indeed, the cover product is generally stored in a hopper mounted on the MSE and provided with a dispensing device, typically a tube for pouring the cover product into the tank. A variable volumetric extraction device, such as a pallet dispenser or an Archimedean screw, for example, is associated with the dispensing device to control the supply of cover material. By moving the MSE, the pour point of the cover product by the spill device into the vessel is moved over the electrolytic bath and the carbon blocks.

However, the particle size properties of the cover product make difficult the precise and reliable control of the amount flowing out of the tube and its spread on the electrolytic bath and on the carbon block.

In addition, when removing a spent anode, as already mentioned above, a portion of the crust around the carbon block, and therefore a portion of the roofing product, may disappear involuntarily from the bath surface and Carbon blocks of adjacent anodes, either by sampling or falling into the bottom of the tank, creating areas of deficit of cover material around the changed anode and the surface of the carbon blocks of adjacent anodes. Such areas make it all the more difficult to control the amount of spilled roofing product to obtain a layer of controlled thickness.

Thus, the inventors have found that when the displacement of the tube is automated, certain areas of the tank are found in deficit cover product, and others in excess.

Therefore, the intervention of an operator on the tank is always necessary, to rectify manually, using tools, the distribution defects of the cover product in the tank.

There is therefore a need to increase the automation of the handling operations of the electrolysis tanks, and in particular the recovery operation by the cover product. For this purpose, a first object of the invention is to provide a method of handling tanks implemented automatically and reliably.

A second object of the invention is to provide a method of handling tanks for recovery of carbon blocks effective.

A third object of the invention is to enable the electrolytic bath to be covered in a reliable and controlled manner.

A fourth object of the invention is to preserve operators of gases and fumes that can escape the tanks.

A fifth object of the invention is to reduce the costs of tank operations.

A sixth object of the invention is to allow the acquisition and recording of data relating to the operation of the vessel for purposes including analysis and process improvement.

Thus, according to a first aspect, the invention proposes a method of placing a cover of at least one anode in an electrolysis cell used for the production of aluminum, by means of a mobile service machine. relative to the cell. The cell comprises a molten electrolytic bath in which an anode block of the anode is partially immersed, so that an upper surface of the anode block emerges out of the bath. The service machine comprises at least one device for dispensing an anodic block covering product. The method then comprises at least the following steps: / 1 / layer deposition of a controlled quantity of the cover product by the dispensing device on at least one zone to be covered with the upper surface of the anode block; / 2 / measuring the thickness of the covering product layer deposited in said area to be covered by at least one thickness sensor on board the service machine; / 3 / comparison between the thickness measured by the sensor and a reference thickness, the reference thickness being predetermined to allow the cover product to cover the upper surface of the anode block at a given height in at least said area to be covered ; / 4 / calculating a corrective amount of cover material to reach the reference thickness in said area to be covered; / 5 / rectification of the thickness of the layer of the cover product in said area to be covered with the aid of the correction amount.

According to one embodiment, the method comprises, prior to step / 1 / deposition, a mesh step of at least a portion of the upper portion of the carbon block defining a plurality of areas to be covered by the cover product . Therefore, at least a portion of the steps / 1 / deposition, / 2 / measurement, / 3 / comparison, / 4 / calculation and / 5 / rectification can be performed directly successively one after the other for an area to be covered before moving to a next area to be covered. As a variant, at least a part of the steps / 1 / deposition, / 2 / measurement, / 3 / comparison, / 4 / calculation and / 5 / rectification can be performed together in sequence, each step being applied to several areas to be covered before proceeding to the next step.

According to one embodiment, the thickness sensor may comprise a three-dimensional camera, making it possible to take measurements in one area and / or a two-dimensional laser in one image.

According to one embodiment, the rectification step comprises adding the corrective amount of cover product to the area to be covered by the dispensing device.

When a mesh is produced, and the thickness measured in step / 2 / measurement for at least a first area to be covered is greater than a threshold thickness, the correction amount determined in step / 3 / is then positive. When the thickness measured in step / 2 / measurement for at least a second area to be covered is less than the reference thickness, the correction amount determined in step / 4 / is then negative. The rectification step may then comprise distributing by a scraper device a controlled amount of the cover material from the first area to be coated to the second area to be coated.

Preferably, but not necessarily in the / 1 / deposition step, the controlled amount of the cover product may correspond to a layer thickness less than or equal to the reference thickness, i.e. at the first stage, there is a deficit of quantity of cover product to reach the reference thickness.

According to one embodiment, the method may comprise, prior to step / 1 / deposition, a step of setting a trajectory for the dispensing device which includes a recording of the movements of a controlled dispensing device by an operator. In other words, a learning step from an operator for the dispensing device is performed.

According to one embodiment, the method may comprise, prior to step / 1 / deposition, a step of development of a trajectory for the dispensing device which comprises a correction of the controlled quantity of cover product in step / 1 / deposition by taking into account the amount of additional covering product to be deposited to achieve the reference thickness in said area to be covered calculated in a step / 4 / calculation implemented for a block anodic previous. In other words, the method comprises a step of learning from the past: for two anodic blocks with similar characteristics (dimensions and position in the tank in particular), the amount of cover product to be deposited to reach the thickness of reference is substantially identical.

According to one embodiment, the method may further comprise a step of collecting and recording the data taken by the thickness sensor. This data can then be used to monitor the overall operation of an aluminum production plant.

According to a second aspect, the invention proposes a service machine of an electrolysis cell used for the production of aluminum, the machine being able to implement the method as presented above. The machine then comprises at least one device for dispensing a cover product and at least one thickness sensor for the cover product.

According to a third aspect, the invention proposes a computer program product for implementing the method as presented above, comprising a control system of the service machine receiving the measurements of the thickness sensor, the system control system comprising a calculation module comparing the thickness measured by the sensor and a reference thickness and calculating the corrective amount of covering product to be deposited to reach the reference thickness. Other effects and advantages of the invention will emerge in the light of the description of embodiments accompanied by the figures in which: FIG. 1 is a schematic representation of an electrolysis room; Figure 2 is a schematic representation of a sectional view of an electrolysis cell; Figure 3 is a detail view of Figure 2; Figure 4 is a schematic representation of two preformed anode blocks mounted on the same hexapod, seen from above.

Figure 1 shows an electrolysis room 1 such as those commonly found in electrolytic aluminum production plants. Electrolysis cells 2 are aligned in the electrolysis room. In order to intervene on the cells 2, the electrolysis room 1 is equipped with a mobile bridge 3 moving above the cells 2 and on which an electrolytic service machine, or MSE 4 can move. The MSE 4 carries tools for carrying out operations on the cells 2, such as the change of worn anodes by new anodes, the cleaning of the cell 2, the supply of alumina, or the handling of equipment. cell 2.

The cells 2 are arranged in rows in the electrolysis room 1, and are electrically connected in series with each other. A corridor 5 is arranged in the room 1 along the rows of cells 2, to allow for example the movement of an operator or a mobile machine.

FIG. 2 illustrates an electrolysis cell 2 seen in section. The cell 2 comprises a tank 6, a support structure called "superstructure" 7 and a plurality of anodes 8, 8 '. Each anode respectively 8, 8 'comprises at least one block, respectively 9, 9', of precured carbon material, called "anodic block", which is fixed on a rod respectively 10, 10 'metal, extending substantially vertically.

In what follows, the adjectives "horizontal" and "vertical" and their variants refer to the directions corresponding to the natural orientation of the figures, on which the rods 10, 10 'are substantially vertical.

As will be seen below, each anode 8, 8 'comprises in practice two blocks 9, 9' anodic each, mounted on the same rod 10, 10 'metal. The anodic blocks 9, 9 'typically have a parallelepipedal shape. Each rod 10, 10 'is held in abutment against an anodic frame 11, 11' of the superstructure 7 by means of a removable connector 12, 12 '.

More precisely, each anode block 9, 9 'is fixed to the corresponding rod 10, 10' via a fastening element 13, 13 ', called a "multipode". Each fixing element 13, 13 'comprises feet, anchored in the anode blocks 9, 9', in particular using cast iron. In the example illustrated in the figures, each element 13, 13 'of attachment comprises six feet, in which case they are called "hexapods", and allow the attachment of two anode blocks on a rod.

The tank 6 is typically formed of a steel casing 18, a liner 14, 15 generally formed of blocks of refractory materials, and a cathode assembly 16, 17 which comprises blocks 16 of carbonaceous material, called "cathode blocks" , and metal connection bars 17, to which electrical conductors, not shown, are fixed to convey the electrolysis current. More specifically, for a tank, the connecting bars 17 are fixed on one side to the connecting bars of an adjacent tank and on the other hand to the anode frames of another adjacent tank.

The electrolysis cell 2 is generally closed by removable covers 19, 19 ', making it possible to confine the gases and fumes in the cell 2. A system for evacuating and treating these gases and fumes is generally put in place. The covers 19, 19 'are removable, to give access to the interior of the cell, including the tools of the MSE 4, by two sides when interventions must be made.

Cell 2 is filled with an electrolytic bath comprising a mixture of alumina and molten cryolite. The anodic blocks 9, 9 'are partly immersed in the electrolytic bath, so that an upper portion emerges out of the bath 20. From the electrolysis stream is fed to the anodic blocks 9, 9' through the frames 11, 11 'anode, and passes through the electrolytic bath to the cathode assembly 16, 17, causing electrolysis of the alumina of the aluminum bath. The molten metal is deposited and forms a layer 21 at the bottom of the tank 6. An alumina feed system maintains the level of alumina bath 20 in a predetermined range.

During the electrolysis process, the anodic blocks 9, 9 'are gradually consumed. In Figure 2, there is shown two anode blocks, a first block 9 being new, the second block 9 'being consumed.

A determined distance must be maintained between the molten metal layer 21 and the lower end of the anodic block 9, 9 'in order to maintain the electrolysis reactions. As a result, the anode frames 11, 11 'are lowered as the corresponding anode block 9, 9' is consumed.

Once the anode block 9 'has been consumed, the corresponding anode 8' is replaced. For this purpose, several operations are implemented.

First, the cover 19 'giving access to the anode 8' to be replaced is removed. In general, a crust has formed on the surface of the bath 20 in contact with the air. Consequently, a cutting tool is actuated, for example from the MSE 4, to cut the crust around the anode block (s) 9 'of the anode 8' to be replaced. Then, a lifting system grasps the rod 10 'of the anode 8' to be replaced, and the corresponding connector 12 'is unlocked, allowing the removal of the anode 8' from the cell 2.

A new anode is then placed in the cell, with a new anode block immersed at least partially in the electrolytic bath. As presented in the introduction, a few hours, usually 3 hours, after the introduction of the new anode in cell 2, a thin solid crust has formed around the anodic block again, and a cover product 22 is spilled. on the surface of the anode block emerging out of the electrolytic bath. For this purpose, the MSE 4 is provided with at least one device 23 for dispensing a cover product for the carbonaceous blocks. For example, the dispensing device 23 comprises a hopper 24 for storing the cover product and a tube 25 for discharging the product from the hopper 24 into the cell 2. The dispensing device 23 is further provided with a device for dispensing the product. extraction for controlling the quantity, for example by controlling the flow, of covering product poured by the tube 25. The dispensing device 23 is controlled to be mobile with respect to the cell 2, since it is loaded on the MSE 4. For example, the MSE 4 is movable in translation along two horizontal axes relative to the cell 2, and the distribution device 23 is movable in translation along a third vertical axis and rotates about this third axis with respect to the cell 2 .

The MSE 4 is also equipped with at least one thickness sensor 26, shown diagrammatically in FIG. 3, making it possible to measure the thickness of the covering product layer.

The thickness sensor 26 may be, as will be the case in the embodiment described hereinafter, a three-dimensional camera, capable of measuring a thickness of the layer of the covering product over an area of a determined surface without displacement. Alternatively, the thickness sensor 26 may be a two-dimensional laser scanner, scanning an area of a given surface, for example by moving the MSE 4, to determine a thickness.

In what follows, the thickness of the roofing product is defined as a vertical dimension of the layer of the roofing product. It can correspond, for a zone of a given surface, to a maximum dimension, a minimum dimension, or an average of dimensions.

More precisely, in the case of the three-dimensional camera, the thickness sensor 26, of known position, is initially pointed at a reference zone of the anode 8. The reference zone is typically located on the rod 10 or on the fixing element 13, and is preferably a substantially horizontal surface. The sensor 26 stores a position data for a plurality of points Rf in the reference zone, typically a distance Dref between these points Rf and the sensor 26. In FIG. 3, for the sake of clarity, only one of these points Rf. However, the distance Dref can be calculated as an average distance, a minimum distance or a maximum distance between the points Rf and the sensor 26. The distance Dref can also be calculated from several reference zones, in order to limit the distance. influence on the distance measurement of the cover product that may be in place on the rod 10 or on the fastening element 13.

The reference area is chosen because it is at a known vertical distance from an upper Ssup face of the anode blocks 9 emerging out of the electrolytic bath. Thus, it is possible to deduce a distance Dsup between the upper face Ssup of the anodic blocks 9 and the sensor 26.

Then, the sensor 26 is pointed at a zone to be measured, on the surface of the cover product 22 covering the anode blocks 9 of the anode 8. The sensor 26 records a position data for a plurality of points Rp of the zone to be measured. measure, typically the distance Dp between these points Rp and the sensor 26. As previously, in Figure 3, for the sake of clarity, there is shown a single point Rp of the area to be measured. However, the distance Dp can be calculated as an average distance, a minimum distance or a maximum distance between the points Rp and the sensor 26.

Therefore, the thickness of the cover product 22 at the point Rp is given by the distance De corresponding to the difference between Dsup and Dp.

The sensor 26 can thus determine the thickness De for a plurality of points Rp on the surface of the cover product 22. The thickness of the cover product layer 22 in an area to be measured can then be defined as an average, a maximum or a minimum, for the area to be measured in question. The combination of the distribution device 23 and the thickness sensor 26 on the MSE 4, which is in connection with a control system, makes it possible to automate and control with greater precision the spill of the cover product. The control system, which will be described below with the steps of the process, can be embedded directly on the MSE 4 and be accessible remotely, or be embedded in any remote computer system of the MSE 4 and in connection with the MSE 4.

An exemplary embodiment of the method of placing a cover of an anode 8, in this case a new anode 8, with the aid of the cover product will now be described.

It is previously carried out a mesh on the surface of the electrolytic bath, and more precisely on the surface Ssup anodic blocks 9 of the anode 8, to define a plurality of areas An to cover. FIG. 4 shows a view from above of the two anode blocks 9 mounted on the same rod 10 using the same hexapode 13. Fourteen zones, denoted A 1, are then defined by way of example. ., Ai4. Each zone Ai,..., Ai4 includes at least a portion of the upper surface Ssup of at least one of the anode blocks 9. Also preferably, the areas to be covered include the space E between two adjacent anodes of the cell 2, and may also include the upper surface Ssup of an anode block 9 of an adjacent anode. However, some areas may only include the E space between two adjacent anodes. For this purpose, the control system is provided with a mesh module, defining the areas An to cover for example from calculations, from a mesh defined by an operator and recorded in the control system or to from a mesh defined on plan by an operator and configured in the control system.

In a first step, a layer of the cover product in controlled quantity is deposited by the dispensing device 23 on at least one of the areas to be covered. According to one embodiment, the amount of cover product is controlled to be less than an amount corresponding to a determined thickness of the cover product for the area of interest. In other words, in this first step of depositing the hedging product, the hedge product is deposited in deficit. However, as seen in the introduction, the flow of the cover product is difficult to control, so that it is difficult to ensure that the thickness of the deposited layer is actually less than the determined thickness. However, any surplus of roofing product constitutes an economic loss, in particular: the hopper 24 must be filled more often, inducing additional round trips increasing the intervention time on the cells 2; the surplus of roofing product involves more waste in the electrolysis bath which must then be treated; the electrolysis process itself can be impacted by the modification of the composition of the electrolytic bath.

The amount of cover material is controlled for example by mounting the hopper on load cells, and controlling the flow rate of cover product flowing through the tube with the aid of the extraction device.

The controlled quantity can be set as an overall quantity for the entire area to be covered, and then distributed among the areas to be covered according to a table of correspondence, established empirically or by calculation.

In a second step, the sensor 26 is then implemented in the at least one An area to be covered, in order to measure the thickness, as previously seen, of the layer of deposited roofing material.

As illustrated in FIG. 4, the mesh in zone An does not necessarily concern the whole of the upper surface Ssup of the anodic blocks 9. However, in practice, the covering product layer covers the entire upper surface Ssup of the anodic blocks 9, and the areas An to be covered constitute control areas.

In a third step, the thickness measured by the sensor 26 is then compared with a reference thickness. The reference thickness is predetermined to allow the cover product 22 to cover the surface Ssup of the anodic blocks 9 over a given height. The reference thickness is generally the same for all the areas to be covered, but not necessarily. The reference thickness may be a given value, or a range of given values.

More precisely, the measurements by the sensor 26 are transmitted to the control system, which records the measurements. The reference thickness or thicknesses were previously recorded in the control system. The control system then comprises a calculation module making it possible, for the area An concerned, to compare the measured thickness with the corresponding reference thickness.

In a fourth step, the calculation module deduces, from the difference, a corrective amount of cover product to be deposited again in the area An to cover concerned.

In a fifth step, a step of rectification of the layer of the cover product is implemented in the area An concerned as a function of the correction amount determined. As will be explained below, the correction amount calculated in the fourth step may be zero. In this case, the fifth rectification step may not take place.

For example, when the difference between the thickness measured by the sensor 26 and the reference thickness indicates a deficit of roofing product, the calculation module determines the corrective amount, positive, of coverage product corresponding to the deficit. The dispensing device 23 is then actuated by the control system to deposit the corrective amount of cover product on the surface Ssup of the anodic blocks 9, in the area An concerned. For example, the correction amount is translated into flow and / or time, and the dispensing device 23 is actuated accordingly to pour the cover product.

When the difference between the thickness measured by the sensor 26 and the reference thickness indicates a surplus of roofing product, beyond a threshold value, the calculation module determines the corrective, negative amount of roofing product corresponding to the surplus. In this case, a device for removing the surplus quantity in the concerned area An can be implemented. For example, consider two areas A, and Aj to cover, which may be adjacent but not necessarily. For a first zone A ,, the corrective amount is positive: the cover product is surplus. For the other zone Aj, the corrective amount is negative: the cover product is in deficit. In this case, the fifth rectification step may comprise the distribution, by means of a scraping device, of the cover product from the first zone A, in excess of the cover product to the other zone Aj in deficit of blanket. A new measurement step by the sensor 26 of the thickness in the two zones A, and Aj can then be implemented in order to verify the conformity, in each zone, of the thickness of the layer of roofing product with the corresponding reference thickness. If necessary, a new rectification step can be implemented in each zone A ,, Aj.

The steps of the method may be carried out, as a whole or in part, successively one after the other for each An area to be covered. For example, the four steps presented above are applied to the area Ai of Figure 4, before being applied to the area A2, and so on.

The process steps can also be performed, as a whole or in part, in sequence for several An areas to be covered. For example, the first step is applied to all fourteen zones Ai, ..., A14 to be covered before applying the second step to all fourteen zones Ai,..., Ai4 to be covered, and thus until the fifth step.

Alternatively, only the first, second and third steps are implemented in the first zone Ax before moving to the zone A2, in which only these three steps are also implemented, and so on until the zone Ai4 . Then, the fourth and fifth steps are applied in turn, either successively zone by zone, or one after the other for all the areas to be covered.

After the fifth grinding step, the process can be repeated from the second measurement step to ensure that the reference thickness is reached. It can then normally be expected that during the repetition of the process, the corrective amount calculated in the fourth step is zero. Other variants are also possible immediately.

In another variant, the process steps can be applied in real time. In particular, the steps of the method can be implemented substantially simultaneously. More precisely, the sensor 26 can be implemented almost continuously during the deposition of the layer of roofing product, in order to provide the control system with information about the thickness of the layer being deposit, and allow the correction of the amount of coverage product deposited during the deposit. In other words, a control loop can be implemented, in which the correction amount can be calculated regularly, at a determined frequency, while the cover product is being deposited, so as to rectify at most quickly the quantity of roofing product spilled over the quantity determined.

In order to cover with the cover product at least a given portion of the upper surface Ssup of the anode blocks 9 of the anode 8 to be covered, the distribution device 23 describes a given trajectory above the upper surface Ssup of the blocks 9 anodic. The trajectory is defined as the order of passage of the dispensing device 23 between the different zones An to be covered. The trajectory is associated with a transit time, that is to say the time that the distribution device 23 passes, for a zone A, to cover, for a determined flow, corresponding to a determined quantity of cover product to be deposited. . As already indicated above, in the first step, the determined quantity of product is less than the quantity necessary to reach the reference thickness.

According to one embodiment, the trajectory and the transit time are developed by simulation, or by theoretical calculation.

According to another embodiment, the development of the given trajectory and the passage time for each zone A to be covered by the distribution device 23 are made prior to the first depositing step, and include the recording of the movements and passage times of the same distribution device 23, or another equivalent, controlled by an operator. For example, an operator remotely controls the movements of the MSE 4 and the distribution device 23, as well as the passage time of the distribution device 23 in each zone A, to be covered, and the flow rate of the cover product, for 9 anodic blocks of a first anode 8, called test. A recording system records the data for the anode blocks 9 of the anode 8 test. Optionally, the following process steps are implemented for the anode blocks 9 of the test anode 8. Then, when the process is applied to the anode blocks 9 of another anode 8 to be covered, the trajectory given for the blocks 9 of this other anode 8 and the associated transit times are copied to the trajectory recorded for the anode 8 test. . Optionally, the trajectory and the passage times determined for the test anode 8 can be adapted to the position of the other anode, for example by considering a mirror symmetry effect on either side of the hexapod. Thus, the trajectory of the distribution device 23 is developed by learning from an operator.

According to yet another embodiment, the development of the trajectory and the passage times of the distribution device 23 for the anode blocks 9 of anode 8 include taking into account the step of calculating a quantity. correction applied prior to another anode. More specifically, the steps of the method, from the first deposition step to at least the fourth step of calculating a correction quality, are implemented for the anode blocks 9 of a first anode 8. In practice, the process in its entirety, up to the fifth step, can be implemented for the blocks 9 of the first anode 8. The correction amount for the anode blocks 9 of the first anode 8 is then recorded, and taken into account for the focusing the trajectory for the anode blocks 9 of a second anode 8, in particular to correct the amount of cover product deposited in the first step. For example, when the corrective amount calculated for the blocks 9 of the first anode 8 is positive, the controlled amount of cover material deposited in the first deposition step for the blocks 9 of the second anode 8 can be increased compared to that deposited in the first deposition step for the blocks 9 of the first anode 8. Similarly, in the opposite situation in which the corrective amount calculated for the blocks 9 of the first anode 8 is negative, the controlled quantity of deposited cover product in the first deposition step for the blocks 9 of the second anode 8 can be decreased compared to that deposited in the first deposition step for the blocks 9 of the first anode 8. The trajectory of the dispensing device can thus be corrected for each anodic block 9. Such a correction can be applied step by step: each time the process is applied, the correction amount is taken into account for the next application of the process. The corrected trajectory can also be recorded in connection with given conditions, for example temperature conditions or type of cover product used, so that when these same conditions are met for other anodes, the process is adapted automatically.

In practice, the trajectory and the passage times are furthermore associated with a given flow rate controlled by the control system acting on the extraction device. For example, the passage time on the different areas An to cover may be the same for each zone, that is to say that the speed of movement of the dispensing device 23 is constant, and the flow rate be regulated.

It may then happen that the correcting amount calculated in the fourth step is zero, indicating that the controlled amount deposited in the first step is the amount required to reach the reference thickness. The fifth rectification step is then empty.

Advantageously, the measurement data of the thickness sensor 26 are collected and recorded in order to be used, for example, to analyze the quality of coverage by the product and to monitor the operation of a cell 2.

The method thus described makes it possible to automate and mechanize the operations of placing the anode cover in the cells 2 in a reliable and repeatable manner, by increasing the safety of the human operators in the vicinity of the electrolysis cells 2 and by reducing the problems related to a bad evaluation of the quantity of anode cover product to be deposited to cover the carbon blocks.

Claims (14)

A method of placing a cover of at least one anode (8) in an electrolysis cell (2) used for the production of aluminum by means of a mobile service machine (4). to the cell (2), the cell (2) comprising a molten electrolytic bath (20) in which an anode block (9, 9 ') of the anode (8) is partially immersed, so that a surface (Ssup) upper of the anode block (9, 9 ') emerges out of the bath (20), the service machine (4) comprising at least one device (23) for dispensing a product (22) for covering the block ( 9, 9 '), the method comprising at least the following steps: / 1 / layer deposition of a controlled amount of the product (22) cover by the device (23) of distribution on at least one area (An) covering the upper surface (Ssup) of the anode block (9, 9 '); / 2 / measuring the thickness of the covering product layer (22) deposited in said area (An) to be covered by at least one thickness sensor (26) on board the machine (4) of service; / 3 / comparison between the thickness measured by the sensor (26) and a reference thickness, the reference thickness being predetermined to allow the product (22) to cover the upper surface (Ssup) of the block (9, 9 ') anode over a given height in at least said area (An) to be covered; / 4 / calculating a correction amount of cover product (22) to reach the reference thickness in said area (An) to be covered; / 5 / rectification of the layer thickness of the cover material (22) in said area (An) to be covered by the correction amount. 2. Method according to claim 1, comprising, prior to step / 1 / deposition, a step of meshing of at least a portion of the upper portion of the carbon block defining a plurality of areas (An) to be covered by the cover product. 3. Method according to claim 2, wherein at least a part of the steps of / 1 / deposition, / 2 / measurement, / 3 / comparison, / 4 / calculation and / 5 / rectification are performed directly successively l one after the other for an area (An) to be covered before moving to an area (An) to be covered next. 4. Method according to claim 2, wherein at least a part of the steps of / 1 / deposition, / 2 / measurement, / 3 / comparison, / 4 / calculation and / 5 / rectification are performed together in sequence each step being applied for several of the areas (An) to be covered before proceeding to the next step. The method of any of the preceding claims, wherein the thickness sensor (26) comprises a three-dimensional camera. The method of any of the preceding claims, wherein the thickness sensor (26) comprises a two-dimensional laser. A method as claimed in any one of the preceding claims, wherein the rectification step comprises adding the corrective amount of cover material to the area (An) to be covered by the dispensing device (23). . 8. The method of claim 2, wherein the thickness measured in step / 2 / measurement for at least a first zone (Ai) to be covered is greater than a threshold thickness, the correction amount determined in step / 3 / being positive, and the thickness measured in the measurement step / 2 / for at least one second area (Aj) to be covered is less than the reference thickness, the correction quantity determined in step / 4 / being negative, and wherein the grinding step / 5 comprises distributing by a scraping device a controlled amount of the cover product from the first area (Ai) to be covered to the second area (Aj) to be covered. The process according to any one of claims 1 to 7, wherein, in the deposition step / 1, the controlled amount of the cover product (22) corresponds to a layer thickness less than or equal to the thickness. reference. 10. Method according to any one of the preceding claims, comprising, prior to the step / 1 / deposition, a step of development of a trajectory for the device (23) of distribution which includes a record of displacements d a dispensing device controlled by an operator. 11. Method according to any one of the preceding claims, comprising, prior to step / 1 / deposition, a step of development of a trajectory for the device (23) of distribution which comprises a correction of the quantity controlled product (22) coverage in step / 1 / deposition by taking into account the amount of product (22) additional cover to be deposited to achieve the reference thickness in said area (An) to cover calculated in a step / 4 / calculation implemented for a previous block (9, 9 ') anodic. The method of any of the preceding claims, further comprising a step of collecting and recording data taken by the thickness sensor (26). 13. Machine (4) for the service of an electrolysis cell (2) used for the production of aluminum, the machine (4) being able to implement the method according to any one of the preceding claims, the machine comprising at least one device (23) for dispensing a cover product (22) and at least one thickness sensor (26) for the covering product (22). 14. Computer program product for implementing the method according to any one of claims 1 to 12, comprising a control system of the machine (4) service receiving the measurements of the sensor (26) of thickness, the control system comprising a calculation module comparing the thickness measured by the sensor (26) and a reference thickness and calculating the correction amount of product (22) to be deposited to reach the reference thickness.