AU2018251178B2

AU2018251178B2 - Process for installing an anode cover in an electrolytic cell, service machine capable of implementing such a process and computer program product for the implementation of such a process

Info

Publication number: AU2018251178B2
Application number: AU2018251178A
Authority: AU
Inventors: Philippe DEGLAVE; Alain Rose
Original assignee: Fives ECL SAS
Current assignee: Fives ECL SAS
Priority date: 2017-04-10
Filing date: 2018-04-06
Publication date: 2023-11-16
Anticipated expiration: 2038-04-06
Also published as: FR3065014B1; EP3610054B1; WO2018189463A1; FR3065014A1; CN110637106B; EP3610054A1; CN110637106A; CA3058228A1; AU2018251178A1

Abstract

Process for installing an anode cover in an electrolytic cell (2) used for the production of aluminium, by means of a service machine (4) comprising at least one device (23) for dispensing a covering product (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 covering product (22) on an upper surface (Ssup) of the anode block (9, 9'); /2/ measurement, with the aid of a sensor (26), of the thickness of the layer of covering product (22) deposited; /3/ comparison between the measured thickness and a reference thickness; /4/ calculation of a corrective amount of covering product (22) in order to attain the reference thickness: /5/ correction of the thickness of the layer of the covering product (22) with the aid of the corrective amount.

Description

Method for installing an anode cover in an electrolysis cell, service machine capable of implementing such method, and computer program product for the implementation of such method

TECHNICAL FIELD

The invention relates to the field of aluminium production by igneous electrolysis using the Hall-Hroult method. More specifically, the invention relates to the coverage by a powdery product over the anodes in electrolytic tanks for the production of aluminium.

BACKGROUND

The industrial production of aluminium from alumina by the Hall-H6roult method is a well-known technique. Generally speaking, it is carried out within an electrolysis installation comprising a hall, in which a plurality of electrolytic cells is installed. Each tank is filled with an electrolytic bath including cryolite in which alumina is dissolved. Pre-baked carbon anodes are partially immersed in the electrolytic bath. The anodes are supplied with current that flows through the bath to a cathode, which is usually formed at the bottom of the tank. The document FR 2 806 742 describes an example of such installation. Reactions taking place in the tank require regular interventions. More specifically, electrolysis reactions involve the progressive consumption of the anodes, which require to be changed regularly. An anode can be defined as comprising a metal rod that conducts current, sealed on at least one pre-baked carbon block. It is this carbon block that is consumed by electrolysis reduction reactions. In order to protect the combustion by air of the part of the carbon block that is not immersed in the electrolytic bath, it is known to cover the carbon block with a covering product over a controlled thickness, for example in the order of 10cm. In general, the covering product is of the powder type and includes a mixture of alumina and "crushed bath", i.e. recovered, solidified, and crushed electrolytic bath. The

20259689_1 (GHMatters) P112082.AU covering product solidifies over the carbon block, but also over the electrolytic bath, forming a crust. Thus, the crust protects the carbon block on the one hand, but also the surface of the electrolytic bath on the other hand. The composition of the covering product can be monitored so as to ensure that the crust which is formed over the carbon block has the required properties, and specifically that it does not allow air to reach the carbon bloc, or to ensure that it minimizes leakage of the electrolytic bath out of the tank. The document W02009/055645 thus proposes an imaging system for obtaining images of the materials entering in a hopper 40 where the alumina and the particles of the electrolytic bath composing the covering product are mixed, and/or once the covering material has been applied on one or more of the electrolytic cells. The images are then processed to predict the amount of aluminia and/or electrolytic bath particles in the covering product and thus to determine if the covering material has the required composition for obtaining the targeted quality for the crust. The quantities of alumina and of electrolytic bath particles feeding the hopper are adjusted accordingly. Such system involves the processing of the images with the aim of determining the composition of the covering product and ultimately of the crust, which is complex and costly to implement. A parameter other than the composition of the covering product also allows to ensure that air does not reach the carbon block: the thickness of the layer of covering product covering the carbon block. Several solutions have been proposed in order to control the thickness of the covering product: For example, it has been proposed to install flanges on the carbon blocks to form a container on the upper surface of the carbon block in which the discharged covering material is retained. The carbon block is thus reliably covered with the covering product. The document FR 2 527 229 provides an example of such embodiment using aluminium strips. However, this embodiment does not allow the electrolytic bath to be covered. In addition, it requires a redesign of the shape of the carbon blocks and the addition of flanges, which makes the manufacture of carbon blocks more complex and therefore increases the costs of aluminium production. In the document W02007/132081, it is proposed to cover the carbon block with

20259689_1 (GHMatters) P112082.AU a layer of covering 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 the deposition of the covering product on the surface of the electrolytic bath. In addition, it requires specific properties to be given to the covering product in order to prevent it from flowing out when it covers the carbon block before being placed in the tank, which involves additional treatment and therefore additional costs. When changing an anode, the bath crust is cut around the used carbon block, called the "butt", and the used anode is lifted in order to be removed from the tank. Part of the crust falls to the bottom of the tank, and part remains attached to the butt. If necessary, a cleaning operation using a shovel is carried out in order to collect the crust parts 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 part of the new carbon block emerging from the bath. Then, a few hours later, typically 3 or 4 hours, until a solid film called a crust forms on the surface of the electrolytic bath between the carbon blocks, the covering product is discharged into the tank so as to cover the new carbon block and the space between the carbon blocks. Anode changing operations require opening the cells, which are usually closed by covers, in order to prevent the escape of toxic gases and fumes produced by the electrolysis reactions in the electrolysis hall. During these operations, some devices allow to limit the escape of toxic gases, fumes, and dust, but cannot completely prevent it. Thus, an operator that is located in the vicinity of an open tank, for example to ensure the proper distribution of the covering product, is exposed to these gasesand fumes. The automation and mechanization of handling operations on tanks is therefore the subject of research and development in order to keep human operators as far away as possible from the tanks and from the gases and fumes that escape from them. To this end, many operations of handling tank are carried out using a machine, called an electrolysis service machine, or ESM, which can be moved in the electrolysis hall. The ESM carries tools to perform the various interventions. An operator can control the ESM and tools from a cabin. However, the discharge of the covering product into the tank is an operation

20259689_1 (GHMatters) P112082.AU that is difficult to automate. Indeed, the covering product is generally stored in a hopper that is mounted on the ESM and equipped with a dispensing device, typically a tube to discharge the covering product into the tank. A variable volumetric extraction device, such as a pallet batcher or an Archimedes screw for example, is associated with the dispensing device in order to control the supply of covering product. By moving the ESM, the point of discharge of the covering product by the device for discharging into the tank is moved above the electrolytic bath and the carbon blocks. Yet, the granulometric properties of the covering product make it difficult to accurately and reliably control the amount flowing out of the tube and its spreading over the electrolytic bath and the carbon block. In addition, when removing a used anode, as already mentioned above, part of the crust around the carbon block, and therefore part of the covering product, may inadvertently disappear from the bath surface and the carbon blocks of the adjacent anodes, either due to sampling or by falling to the bottom of the tank, creating areas with a shortage of covering product around the changed anode and on the surface of the carbon blocks of the adjacent anodes. Such areas make it even more difficult to control the amount of covering material discharged in order to obtain a layer of controlled thickness. Thus, the inventors found that when the tube movement is automated, some areas of the tank show are in shortage of covering product, and others are in excess. Therefore, the intervention of an operator on the tank is always necessary, in order to manually rectify, using tools, the defects in the distribution of the covering product in the tank. There is therefore a need to increase the automation of electrolysis tank handling operations, and in particular the covering operation with the covering product. It is to be understood that, if any prior art is referred to herein, such reference does not constitute an admission that the prior art forms a part of the common general knowledge in the art, in Australia or any other country

SUMMARY

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In some forms, the invention proposes a method for handling tanks that is implemented automatically and reliably. In some forms, the invention also proposes a method for handling the tanks that will allow the carbon blocks to be covered efficiently. The invention may also allow the electrolytic bath to be covered in a reliable and controlled manner. The invention may enable protection of operators from gases and fumes that may escape from the tanks. The invention may also reduce the costs of tank operations. In some forms, the invention also allows the acquisition and recording of data relating to the operation of the tank for uses such as analysis and improvement of the method. According to a first aspect, the invention proposes a method for installing a cover on at least one anode in an electrolysis cell used for the production of aluminium, by means of a service machine which is movable in relation 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 from the bath. The service machine comprises at least one device for dispensing a product for covering the anode block. The method then comprises at least the following steps: /1/ depositing in layered form a controlled amount of covering product using the dispensing device on at least one area to be covered on the upper surface of the anode block; /2/ measuring the thickness of the covering product layer deposited in said area to be covered using at least one thickness sensor embedded on the service machine; /3/ comparing the thickness measured by the sensor with a reference thickness, the reference thickness being predetermined to allow the covering product to cover the upper surface of the anode block at a given height at least in said area to be covered; /4/ calculating a corrective amount of covering product to reach the reference thickness in said area to be covered; /5/ correcting the thickness of the layer of covering product in said area to be covered using the corrective amount, wherein prior to the deposition step /1/, a step

20259689_1 (GHMatters) P112082.AU of meshing at least a part of the upper portion of the carbon block defining a plurality of areas to be covered by the covering product;wherein at least part of the steps /1/ of deposition, /2/ of measurement, /3/ of comparison, /4/ of calculation and /5/ of rectification can be performed together in sequence, each step being applied for several of the areas to be covered before proceeding to the next step. Therefore, at least part of the steps /1/ of deposition, /2/ of measurement, /3/ of comparison, /4/ of calculation and /5/ of rectification can be carried out directly successively one after the other for an area to be covered before proceeding to a subsequent area to be covered and wherein, when the difference between the thickness measured by the sensor and the reference thickness indicates a shortage of covering product in said area, the step /4/ of calculation determines a positive corrective amount of covering product, corresponding to the shortage, to deposit on the upper surface of the anode block in said area during the step /5/ of rectification, and when the difference between the thickness measured by the sensor and the reference thickness indicates an excess of covering product in said area, beyond a threshold value, the step /4/ of calculation determines a negative corrective amount of covering product, corresponding to the excess, to remove in said area during the step /5/ of rectification. According to one embodiment, the thickness sensor can include a three dimensional camera, allowing measurements to be made on an area with a single image, and/or a two-dimensional laser. According to one embodiment, the rectification step /5/ involves adding the corrective amount of covering product to the area to be covered by the dispensing device. When a mesh is produced, and the thickness measured in the measurement step /2/ for at least one first area to be covered is greater than a threshold thickness, the corrective amount determined in step /3/ is then positive. When the thickness measured in the measurement step /2/ for at least one second area to be covered is less than the reference thickness, the corrective amount determined in step /4/ is negative. The rectification step /5/ can then include the distribution by a scraping device of a controlled amount of covering product from the first area to be covered to the second area to be covered.

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Advantageously, but not necessarily in the deposition step /1/, the controlled amount of covering product can correspond to a layer thickness that is less than or equal to the reference thickness, in other words a shortage of covering product amount is anticipated from the first step to reach the reference thickness. According to one embodiment, the method may include, prior to the deposition step /1/, a step of developing a trajectory for the dispensing device that includes recording the movements of a dispensing device controlled by an operator. In other words, a step of learning from an operator for the dispensing device is carried out. According to one embodiment, the method may include, prior to the deposition step /1/, a step of developing a trajectory for the dispensing device that includes correcting the controlled amount of covering product in the deposition step /1/ by taking into account the amount of additional covering product to be deposited in order to reach the reference thickness in said area to be coated calculated in a calculation step /4/ implemented for a previous anode block. In other words, the method comprises a step of learning from the past: for two anode blocks with similar characteristics (dimensions and position in the tank in particular), the amount of covering material to be deposited in order to reach the reference thickness is substantially identical. According to one embodiment, the method may further comprise a step of collecting and recording data collected by the thickness sensor. This data can then be used to monitor the overall functioning of a factory producing aluminum. According to a second aspect, the invention provides a service machine for an electrolysis cell used for producing aluminum, the machine being adapted to implement the method as outlined above. The machine thus comprises at least one device for dispensing a covering product and at least one thickness sensor for the covering material. According to a third aspect, the invention provides a computer program product for the implementation of the method as outlined above, comprising a control system for a service machine of an electrolysis cell used for the production of aluminium, the machine being able to carry out the method according to any of the previous claims, the machine comprising at least one device for dispensing a covering product and at least one sensor for measuring the thickness of the covering product receiving the

20259689_1 (GHMatters) P112082.AU measurements from the thickness sensor, the control system comprising a calculating module comparing the thickness measured by the sensor to a reference thickness and calculating the corrective amount of covering material to deposit in order to reach the reference thickness. Other effects and advantages of the invention will appear in the light of the description of embodiments together with the figures in which:

BRIEF DESCRIPTION OF FIGURES - Figure 1 is a schematic representation of an electrolysis chamber; - Figure 2 is a schematic representation of a sectional view of an electrolysis cell; - Figure 3 is a detailed view of Figure 2; - Figure 4 is a schematic representation of two pre-baked anode blocks mounted on the same hexapod, seen from above.

DETAILED DESCRIPTION

Figure 1 shows an electrolysis chamber 1 such as those commonly found in plants producing aluminum by electrolysis. Electrolysis cells 2 are aligned in the electrolysis chamber. In order to operate on the cells 2, the electrolysis chamber 1 is equipped with a mobile bridge 3 moving over the cell 2 and on which an electrolysis machine service, or ESM, 4 can move. The ESM 4 carries tools for performing operations on the cell 2, such as replacing used anodes with new anodes, cleaning the cell 2, supplying alumina, or handling equipment of the cell 2. The cells 2 are arranged in rows in the electrolysis chamber 1, and are electrically connected in series to each other. A passageway 5 is formed in the chamber 1 along the rows of cells 2, in order to allow for example the movement of an operator or a mobile device. Figure 2 illustrates an electrolysis cell 2 in sectional view. The cell 2 comprises a tank 6, a supporting structure called "superstructure" 7, and a plurality of anodes 8, 8 '. Each anode 8, 8' respectively comprises at least one block, 9, 9' respectively, made of pre-baked carbon material, called "anode block", which is respectively

20259689_1 (GHMatters) P112082.AU attached to a rod 10, 10' made of metal, extending substantially vertically. In the following, the adjectives "horizontal" and "vertical" and variations thereof refer to the directions corresponding to the natural orientation of the figures, in which the rods 10, 10' are substantially vertical. As will be seen below, each anode 8, 8' comprises in practice two anode blocks 9, 9', mounted on the same metallic rod 10, 10'. The anode blocks 9, 9' typically have a parallelepiped shape. Each rod 10, 10' is maintained in abutment against a frame 11, 11' of the anode superstructure 7 by means of a removable connector 12, 12'. More specifically, each anode block 9, 9' is fixed to the corresponding rod 10, 10 via a fixing element 13, 13', called "multipode". Each fixing element 13, 13' comprises feet, which are anchored in the anode blocks 9, 9', in particular using cast iron. In the example illustrated in the figures, each fixing element 13, 13' comprises six feet, in which case they are called "hexapods", and allow the fixing of two anode blocks on a rod. The tank 6 is typically formed of a housing 18 made of steel, an inside lining 14, 15, generally formed of blocks made of refractory materials, and a cathode assembly 16, 17 that comprises blocks 16 made of carbon material, called "cathode blocks", and metallic connection bars 17, to which electrical conductors, which are not shown, are attached for supplying the electrolysis current. More specifically, for one tank, the connecting bars 17 are fixed on one side to the connecting bars of an adjacent tank, and also 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 processing these gases and fumes is generally established. The covers 19, 19' are removable, so as to give access to the interior of the cell, including to the tools of the ESM 4, on two sides when interventions are to be made. The cell 2 is filled with an electrolytic bath 20, comprising a mixture of alumina and molten cryolite. The anode blocks 9, 9' are partially immersed in the electrolytic bath 20, so that an upper portion emerges from the bath 20. An electrolysis current is supplied to the blocks 9, 9' via the anode frames 11, 11', and passes through the electrolytic bath 20 until it reaches the cathode assembly 16, 17, causing the electrolysis of alumina in the aluminum bath 20. The molten metal is deposited and

20259689_1 (GHMatters) P112082.AU forms a layer 21 at the bottom of the tank 6. An alumina feed system makes it possible to maintain the alumina content of the bath 20 within a predetermined range. During the electrolysis process, the anode blocks 9, 9' are gradually consumed. In Figure 2, two anode blocks are shown, a first block 9 being new, the second block 9' being consumed. A determined distance must be maintained between the layer of molten metal 21 and the lower end of the anode block 9, 9' so as to maintain the electrolysis reactions. Consequently, the anode frames 11, 11' are gradually lowered as the corresponding anode block 9, 9' is being consumed. Once the anode block 9' has been consumed, the corresponding anode 8' is replaced. To this end, several operations are implemented. Firstly, the cover 19' providing access to the anode 8' which has to be replaced is removed. Generally, a crust has been formed on the surface of the bath 20 in contact with air. Consequently, a cutting tool is actuated, for example from the ESM 4, in order to cut the crust around the anode block or blocks 9' of the anode 8' which has to be replaced. Then, a lifting device catches the rod 10' of the anode 8' which has to be replaced, and the corresponding connector 12 is unlocked, allowing the removal of the anode 8' out of the cell 2. A new anode is then placed in the cell with a new anode block, which is at least partially immersed in the electrolytic bath 20. As shown in the introduction, a few hours, generally 3 hours, after installing the new anode in the cell 2, a thin solid crust is again formed around the anode block, and a covering product 22 is discharged on the surface of the anode block emerging from the electrolytic bath. To this end, the ESM 4 is provided with at least one device 23 for dispensing a covering product for the carbon blocks. For example, the dispensing device 23 comprises a hopper 24 for storing the covering material and a tube 25 allowing the discharge of the product from the hopper 24 into the cell 2. The dispensing device 23 is further provided with an extraction device allowing to control the amount, for example by controlling the flow rate, of covering material that is discharged through the tube 25. The delivery device 23 is controlled so as to be movable in relation to the cell 2, as it is embedded on the ESM 4. For example, the ESM 4 is movable in translation along two horizontal axes relative to the cell 2, and the dispensing device

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23 is movable in translation along a third vertical axis and in rotation about this third axis relative to cell 2. The ESM 4 is also equipped with at least one thickness sensor 26, represented schematically in Figure 3, making it possible to measure the thickness of the covering material layer. The thickness sensor 26 may be, as will be the case in the embodiment described in the following, a three-dimensional camera, capable of measuring a thickness of the layer of covering material over an area of a given surface without displacement. Alternatively, the thickness sensor 26 may be a two-dimensional laser scanner, sweeping an area of a given surface, for example by moving the ESM 4, so as to determine a thickness. In the following, the thickness of the covering material is defined as being a vertical dimension of the layer of covering material. It may correspond, for an area of a determined surface, to a maximum dimension, a minimum dimension, or an average of dimensions. More specifically, in the case of the three-dimensional camera, the thickness sensor 26, with a known position, is initially pointing to a reference area of the anode 8. The reference area is typically located on the rod 10 or on the fixing element 13, and is advantageously a substantially horizontal surface. The sensor 26 records a position data for a plurality of points Rf in the reference area, typically a distance Dre between these points Rf and the sensor 26. In Figure 3, for clarity purposes, only one of these points Rf is shown. However, the distance Dref may be calculated as being an average distance, a minimum distance, or a maximum distance between the points Rf and the sensor 26. The distance Dref may also be calculated from a plurality of reference areas, in order to limit the influence on the distance measurement of the covering material which may be found in some places on the rod 10 or on the fixing element 13. The reference area is chosen because it is at a known vertical distance from an upper face Ssup of the anode blocks 9 emerging from the electrolytic bath 20. Thus, it is possible to derive a distance Dsup between the upper face Ssup of the anode blocks 9 and the sensor 26. Then, the sensor 26 is pointed to an area to be measured, on the surface of the

20259689_1 (GHMatters) P112082.AU covering product 22 covering the anode blocks 9 of the anode 8. The sensor 26 records a position data for a plurality of points Rp in the area to be measured, typically the distance Dp between these points Rp and the sensor 26. As above, in Figure 3, for clarity purposes, a single point Rp in the area to be measured is shown. However, the distance Dp may be calculated as an average distance, a minimum distance, or a maximum distance between the points Rp and the sensor 26. Consequently, the thickness of the covering product 22 at the point Rp is given by the distance De corresponding to the difference between Dsup and Dp. The sensor 26 may thus determine the thickness De for a plurality of points Rp on the surface of the covering product 22. The thickness of the layer of covering product 22 in an area to be measured can then be defined as being an average, a maximum, or a minimum, for the area to be measured in question. As a variant, the sensor 26 may measure the distance in relation to the upper surface Ssup of the anode block 9 in the tank 6 before the discharge of covering product thereon. Thus, the distance Dsup between the upper face Ssup of the anode block 9 and the sensor 26 is directly measured, and not calculated as before. Measuring the distance Dsup instead of deducing it from the measurement of the distance Dref increases the reliability of determining the thickness De of the layer of covering product 22. Indeed, Drefis measured on a surface of the rod 8 or the fixing element 13, which may involve measurement errors that are due, for example, to erosion, to the presence of covering product over it, or to positioning gaps of the ESM 4. The extent of the surface Ssup of the anode block 9 is larger than that available of the rod 8 or the fixing element 13, such that the sensor 26 may point to the surface Ssup in an easier manner. Furthermore, measuring Dsup makes it possible to take into account the thickness of a possible residual of covering product at the periphery of the new anode block 9. The real thickness of covering product 22 covering the anode block 9 is therefore evaluated more precisely. Thus, the amount of covering product 22 to be discharged in order to reach a targeted thickness may also be determined with increased precision. The combination of the dispensing device 23 and the thickness sensor 26 on the ESM 4, which is connected to a control system, makes it possible to automate

20259689_1 (GHMatters) P112082.AU and control with increased precision the discharge of the covering material. The control system, which will be described below with the method steps, may be embedded directly on the ESM 4 and be accessed remotely, or be embedded in any computer system that is remote from the ESM 4 and in connection with the ESM 4. An embodiment of the method for installing a cover for an anode 8, in this case a new anode 8, using the covering material will now be described as an example. Previously, a mesh is produced on the surface of the electrolytic bath 20, and more specifically on the surface Ssup of the anode blocks 9 of the anode 8, so as to define a plurality of areas An to be covered. In Figure 4, a top view of the two anode blocks 9 is shown, mounted on the same rod 10 with the same hexapod 13. Fourteen areas are then defined as examples, denoted A, ... , A14. Each area A1, ... , A14 encompasses at least a portion of the upper surface Ssup of at least one of the anode blocks 9. Also advantageously, the areas An to be covered encompass the space E between two adjacent anodes of the cell 2, and may also encompass the upper surface Ssup of an anode block 9 of an adjacent anode. However, some areas may include only the space E between two adjacent anodes. To this end, the control system is provided with a meshing module, defining the areas An to be covered from calculations for example, based on a mesh defined by an operator and recorded in the control system, or from a mesh defined on a plot by an operator and configured in the control system. In a first step, a layer of covering material is deposited in a controlled amount by the dispensing device 23 in at least one of the areas An to be covered. According to one embodiment, the amount of covering material is controlled so as to be less than an amount corresponding to a determined thickness of covering material for the area concerned. In other words, in this first step of depositing the covering product, the covering product is deposited in shortage. However, as seen in the introduction, the outflow of covering product is difficult to control, making it difficult to ensure that the thickness of the deposited layer is actually less than the determined thickness. Yet, all covering material excess is an economic loss, in particular since: the hopper 24 requires to be filled more often, leading to additional roundtrips increasing the intervention time of the cells 2; the covering material excess means more waste in the electrolysis bath 20 which then requires to be treated; the electrolysis process as

20259689_1 (GHMatters) P112082.AU such may be impacted due to the change in the composition of the electrolytic bath. The amount of covering material is controlled for example by mounting the hopper on weight indicators, and by controlling the flow rate of covering material flowing through the tube 25 using the extraction device. The controlled amount may be set as an overall amount for the entire surface to cover, and then be distributed to the areas An to be covered according to a correspondence table, established empirically or by calculation. In a second step, the sensor 26 is then implemented in the at least one area(s) An to be covered, in order to measure the thickness, as seen above, of the deposited covering material layer. As illustrated in Figure 4, the meshing of the area An does not necessarily relate to the entire upper surface Ssup of the anode blocks 9. However, in practice, the covering material layer covers the entire upper surface Ssup of the anode blocks 9, and the areas An to be covered represent 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 so as to allow the covering product 22 to cover the surface Ssup of the anode blocks 9 up to a given height. The reference thickness is generally the same for all areas An to be covered, but not necessarily. The reference thickness may be a given value, or a given value range. More specifically, the measurements by the sensor 26 are transmitted to the control system, which records the measurements. The reference thickness or thicknesses have previously been recorded in the control system. The control system then comprises a calculation module allowing, for the relevant area An, to compare the measured thickness with the corresponding reference thickness. In a fourth step, the calculation module deduces, based on the difference, a corrective amount of covering material to deposit again into the relevant area An to be covered. In a fifth step, a step of rectification of the covering material layer is implemented in the relevant area An based on the determined corrective amount. As explained below, the corrective amount calculated in the fourth step may be zero. In this case, the fifth step of rectification may not take place.

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For example, when the difference between the thickness measured by the sensor 26 and the reference thickness indicates a shortage of covering material, the calculation module determines the positive corrective amount of covering product corresponding to the shortage. The dispensing device 23 is then actuated by the control system to deposit the corrective amount of covering material on the surface Ssup of the anode blocks 9 in the relevant area An. For example, the corrective amount is reflected in flow rate and/or time, and the dispensing device 23 is actuated accordingly in order to discharge the covering material. When the difference between the thickness measured by the sensor 26 and the reference thickness indicates an excess of covering product, beyond a threshold value, the calculation module determines the negative corrective amount of covering material corresponding to the excess. In this case, a device for removing the excess amount in the relevant area An can be implemented. For example, let us consider two areas Ai and Aj to be covered, which may be adjacent but not necessarily. For a first area Ai, the corrective amount is positive: the covering product is in excess. In the other area Aj, the corrective amount is negative: the covering material is in shortage. In this case, the fifth step of correction may comprise the distribution, using a scraping device, of the covering material from the first area A, with an excess of covering material, to the other area Aj that has a cover shortage. A new step of measuring, using the sensor 26, the thickness in both areas Ai and Aj may then be implemented to verify the compliance, in each area, of the thickness of the layer of covering product with the corresponding reference thickness. If necessary, a new rectification step may be implemented in each area Ai, A. The steps of the method may be carried out, in whole or in part, successively one after the other for each area An to be covered. For example, the four steps presented above are applied to the area Ai in Figure 4, before being applied to the area A2, and so on. The steps of the method may also be carried out, in whole or in part, in sequence for several areas An to be covered. For example, the first step is applied to all fourteen areas Ai, . . , A14 to be covered before applying the second step to all fourteen areas Ai, . . , A14 to be covered, and so on until the fifth step. As a variant, only the first, second, and third steps are implemented in the first

20259689_1 (GHMatters) P112082.AU area Ai before moving on to the area A2, where only these three steps are also implemented, and so on until the area A14 is reached. Then, the fourth and fifth steps are applied in turn, either successively area by area, or one after the other for all the areas An to be covered. After the fifth rectification step, the method may be repeated from the second measurement step in order to ensure that the reference thickness is reached. It may then usually be expected that when the method is repeated, the corrective amount calculated in the fourth step is zero. Other variants are also possible immediately. As another variant, the steps of the method may be applied in real time. In particular, the steps of the method may be implemented substantially simultaneously. More precisely, the sensor 26 may be used almost continuously during the deposition of the layer of covering material, in order to almost continuously provide the control system with information regarding the thickness of the layer being deposited, and in order to allow the rectification of the amount of covering material deposited during the deposition. In other words, a control loop can be implemented, in which the corrective amount can be calculated regularly, at a specified frequency, while the covering product is being deposited, so as to rectify as quickly as possible the amount of covering product that is discharged in relation to the determined amount. In order to cover with the covering product at least one given portion of the upper surface Ssup of the anode blocks 9 of the anode 8 to be covered, the dispensing device describes a given trajectory above the upper surface Ssup of the anode blocks 9. The trajectory is defined as the order in which the dispensing device 23 passes between the different areas An to be covered. The trajectory is associated with a passage time, in other words the time that the dispensing device spends, for a area Ai to be covered, for a given flow rate, corresponding to a given amount of covering product to be deposited. As already indicated previously, in the first step, the determined amount of product is less than the amount that is required to reach the reference thickness. According to one embodiment, the trajectory and the passage time are developed by simulation, or by theoretical calculation. According to another embodiment, the development of the given trajectory and

20259689_1 (GHMatters) P112082.AU the passage time for each area Ai to be covered of the dispensing device 23 is carried out prior to the first stage of deposition, and comprises the recording of movements and passage times of the same dispensing device, or another equivalent, controlled by an operator. For example, an operator remotely controls the movements of the ESM 4 and the dispensing device 23, as well as the time of passage of the dispensing device in each area Ai to be covered, and the flow rate of the covering product, for the anode blocks 9 of a first anode 8, called the test. A recording system records the data for the anode blocks 9 of the test anode 8. Potentially, the next steps of the method are carried out for the anode blocks 9 of the test anode 8. Then, when the method 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 passage times are copied onto the trajectory recorded for the test anode 8. Optionally, the trajectory and passage times determined for the test anode may 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 dispensing device is set through learning from an operator. According to another embodiment, the development of the trajectory and passage times of the dispensing device for the anode blocks 9 of an anode 8 comprises taking into account the step of calculating a corrective amount applied beforehand to another anode. More precisely, the steps of the method, from the first step of deposition to at least the fourth step of calculation of a corrective quantity, are implemented for the anode blocks 9 of a first anode 8. In practice, the entire method, up to the fifth step, can be implemented for the blocks 9 of the first anode 8. The corrective amount for the anode blocks 9 of the first anode 8 is then recorded, and taken into account for the development of the trajectory for the anode blocks 9 of a second anode 8, in particular to correct the amount of covering material 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 covering material deposited in the first deposition step for the blocks 9 of the second anode 8 may be increased compared to the one deposited in the first deposition step for the blocks 9 of the first anode 8. Similarly, in the opposite situation where the corrective amount calculated for the blocks 9 of the first anode 8 is negative, the controlled amount of covering

20259689_1 (GHMatters) P112082.AU material deposited in the first deposition step for the blocks 9 of the second anode 8 may be reduced compared to that deposited in the first deposition step for the blocks 9 of the first anode 8, thus allowing the trajectory of the dispensing device to be corrected for each anode block 9. Such a correction can be applied from close to close: each time the method is applied, the corrective amount is taken into account for the next application of the method. The corrected trajectory can also be recorded in relation to given conditions, for example temperature conditions or the type of covering product used, in such a way that when these same conditions are met for other anodes, the method is automatically adapted. In practice, the trajectory and passage times are also associated with a given flow rate controlled by the control system acting on the extraction device. For example, the passage time over the different areas An to be covered may be the same for each area, in orther words the movement speed of the dispensing device is constant, and the flow rate may be regulated. It may then happen that the corrective amount calculated in the fourth step is zero, indicating that the controlled amount deposited in the first step corresponds to 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 the product cover and to monitor the operation of a cell 2. The method thereby described makes it possible to automate and mechanize the operations of installing a cover for the anodes in the cells 2 in a reliable and repeatable manner, increasing the safety of human operators in the vicinity of the electrolysis cells 2 and reducing the problems associated with a poor evaluation of the amount of anode covering product to be applied to cover the carbon blocks. In the claims which follow and in the preceding description of the disclosure, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the disclosure.

20259689_1 (GHMatters) P112082.AU

Claims

1. Method for installing a cover for at least one anode in an electrolysis cell used for the production of aluminium, by means of a service machine which is movable relative to the cell , the cell comprising a molten electrolytic bath in which an anode block of the anode is partially immersed, in such a way that an upper surface of the anode block emerges from the bath , the service machine comprising at least one device for dispensing a product for covering the anode block, the method comprising at least the following steps: /1/ depositing in layered form a controlled amount of the covering product by the dispensing device over at least one area of the upper surface of the anode block to be covered; /2/ measuring the thickness of the layer of covering product deposited over said area to be covered by at least one thickness sensor that is embedded on the service machine; /3/ comparing the thickness measured by the sensor with a reference thickness, the reference thickness being predetermined so as to allow the covering product to cover the upper surface of the anode block over a given height in at least said area to be covered ; /4/ calculating a corrective amount of covering product to reach the reference thickness in said area to be covered; /5/ rectifying the thickness of the layer of covering product in said area to be covered using the corrective amount; wherein, prior to the deposition step /1/, a step of meshing at least a part of the upper portion of the anode block defining a plurality of areas to be covered by the covering product; and

wherein at least part of the steps /1/ of deposition, /2/ of measurement, /3/ of comparison, /4/ of calculation and /5/ of rectification are carried out together in sequence, each step being applied for several of the areas to be covered before proceeding to the subsequent step; and wherein, when the difference between the thickness measured by the sensor and

20259689_1 (GHMatters) P112082.AU the reference thickness indicates a shortage of covering product in said area, the step /4/ of calculation determines a positive corrective amount of covering product, corresponding to the shortage, to deposit on the upper surface of the anode block in said area during the step /5/ of rectification, and when the difference between the thickness measured by the sensor and the reference thickness indicates an excess of covering product in said area, beyond a threshold value, the step /4/ of calculation determines a negative corrective amount of covering product, corresponding to the excess, to remove in said area during the step /5/ of rectification.

2. The method according to claim 1, wherein the thickness sensor comprises a three-dimensional camera.

3. The method according to claim 1, wherein the thickness sensor comprises a two dimensional laser.

4. The method according to claim 1, wherein the rectification step /5/ comprises adding the corrective amount of covering product in the area to be covered by the dispensing device.

5. The method according to Claim 1, wherein the thickness measured in the measurement step /2/ for at least a first area to be covered is greater than a threshold thickness, the corrective amount determined in step /3/ being positive, and the thickness measured in the measurement step /2/ for at least one second area to be covered is less than the reference thickness, the corrective amount determined in step /4/ being negative, and wherein the rectification step /5/ comprises the distribution by a scraper device of a controlled amount of covering product from the first area to be covered to the second area to be covered.

6. The method according to any of Claims 1 to 4, wherein in the deposition step /1/, the controlled amount of covering product corresponds to a layer thickness that is lower than or equal to the reference thickness.

20259689_1 (GHMatters) P112082.AU

7. The method according to claim 1, comprising, prior to the deposition step /1/, a step for developing a trajectory for the dispensing device which includes recording of the movements of a dispensing device controlled by an operator.

8. The method according to claim 1, comprising, prior to the deposition step /1/, a step of developing a trajectory for the dispensing device which includes correcting the controlled amount of covering product in the deposition step /l/ by taking into account the amount of additional covering product to be deposited in order to reach the reference thickness in said area to be covered calculated in a calculation step /4/ carried out for a previous anode block.

9. The method according to claim 1, further comprising a step of collecting and recording data taken by the thickness sensor.

10. A computer program product for carrying out the method according to any of Claims 1 to 9, comprising a control system of a service machine of an electrolysis cell used for the production of aluminium, the machine being able to carry out the method according to any of the previous claims, the machine comprising at least one device for dispensing a covering product and at least one sensor for measuring the thickness of the covering product receiving the measurements of the thickness sensor , the 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 in order to reach the reference thickness.

20259689_1 (G HMatters) P1 12082.AU

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