EP1819847B1 - Method of changing an anode of a cell for the production of aluminium by means of electrolysis, including an adjustment of the position of the anode, and device for performing the same - Google Patents

Description

Field of the invention

The invention relates to the production of aluminum by igneous electrolysis according to the Hall-Héroult method. It relates more particularly to anode changes and service units intended to effect anode changes in aluminum production plants.

State of the art

Aluminum is produced industrially by igneous electrolysis in electrolysis cells according to the well-known Hall-Héroult process. The French patent application FR 2,806,742 (corresponding to the US patent US 6,409,894 ) describes installations of an electrolysis plant for the production of aluminum.

According to the most widespread technology, the electrolysis cells comprise a plurality of so-called "precooked" anodes of carbonaceous material which are consumed during the electrolytic reduction reactions of aluminum. The gradual consumption of the anodes requires interventions on the electrolysis cells, including, in particular, the replacement of the spent anodes with new anodes.

In order to limit the disturbance of the operation of an electrolysis cell during an anode change, it is preferable to place the new anode so that its lower surface is at the same level as that of the other anodes of the anode. the cell.

It is known to operate as follows to ensure a correct leveling of the new anodes. The worn anode rod is marked with a chalk mark at a location corresponding to a specific mark on the anode frame. The spent anode is extracted from the cell and deposited on a reference surface, which is typically a metal tray. The level of the chalk line on the rod is raised, the spent anode is removed and a new anode is placed on the reference surface. A chalk line is drawn on the stem of the new anode at the raised level. The new anode is placed on the anode frame so that the chalk line is located at the determined mark on the anode frame. These operations, which are essentially manual, require the intervention of an operator in the action zone of the anode handling tools and expose him to the risks inherent to these operations, such as the risks of load shifting and the projections of liquid metal.

It is also known to provide the anode handling tool with a position sensor. In this case, the distance traveled by the tool during the taking of the spent anode is measured, the worn anode is deposited on a reference surface and the distance traveled by the tool at the moment when the anode is measured. rests on the reference surface. The spent anode is removed, a new anode is deposited on the reference surface and the distance traveled by the tool is measured at the moment when the anode rests on the reference surface. The difference between the last two measured distances is added to the first measured distance in order to determine the distance to be traveled to the handling tool when positioning the new anode in the electrolysis cell.

These different procedures require multiple anode manipulations and moving the reference surface from one work area to another. The time spent on these operations considerably lengthens the cycle times of intervention on the electrolysis cells and the period of time during which the hoods of the tanks remain open, which reduces the efficiency of the means for collecting the effluents produced by the cells. electrolysis cells.

The plaintiff has therefore sought a procedure and means to avoid these disadvantages.

Description of the invention

The subject of the invention is an anode-change method of an igneous electrolysis aluminum production cell as described by claim 1. The invention makes it possible to carry out the measurements necessary for the positioning of a replacement anode during the handling movements necessary for the replacement of an anode (namely typically the taking of an anode used on an electrolysis cell, the deposit of the used anode on a pallet or a vehicle, the prized of a replacement anode on a pallet or a vehicle and the installation of the replacement anode in the cell), which has the advantage of not not require additional handling movements. The invention thus makes it possible to avoid, in particular, an extension of the opening time of an electrolysis cell.

The sound wave or electromagnetic wave beam (s) are advantageously placed in a place which allows the passage of a worn anode or a replacement anode through the beam (s) during the normal handling movements of these anodes, by example above an electrolysis cell, a pallet, or a vehicle.

The measurements can be manual, ie an operator records the data obtained at each stage of the process, or automated in whole or in part, that is to say that a computerized device carries out automatically all or part of the measurements.

The invention also relates to a measuring system as described by claim 19. The invention also relates to a service machine for anode change operations of a series of aluminum production cells by igneous electrolysis, said machine comprising at least one anode handling tool comprising positioning member , a gripping member and a vertical position sensor of the gripping member, and being characterized in that it further comprises said measuring system.

The invention further relates to a service unit of an igneous electrolysis aluminum production plant comprising a mobile bridge and at least one service machine according to the invention.

• La figure, 1 illustre, vue en section, une salle d'électrolyse typique destinée à la production d'aluminium et comprenant une unité de service représentée de manière schématique.
• La figure 2 illustre, vue en section transversale, une cellule d'électrolyse typique destinée à la production d'aluminium.
• La figure 3 représente, de manière schématique, une machine de service vue de côté.
• Les figures 4 et 7 illustrent un mode de réalisation du procédé de changement d'anode selon l'invention.
• Les figures 8 à 10 représentent, de manière schématique, des modes de réalisation des moyens de détection de la position d'une anode selon l'invention.

The invention is described in more detail below with the aid of the appended figures.

• The figure 1 illustrates, in section, a typical electrolysis room for the production of aluminum and comprising a service unit shown schematically.
• The figure 2 illustrates, cross-sectional view, a typical electrolysis cell for the production of aluminum.
• The figure 3 schematically represents a service machine viewed from the side.
• The figures 4 and 7 illustrate an embodiment of the anode changing method according to the invention.
• The Figures 8 to 10 show, schematically, embodiments of the means for detecting the position of an anode according to the invention.

Electrolysis plants for aluminum production include a liquid aluminum production zone that includes one or more electrolysis rooms (1). As illustrated in figure 1 each electrolysis room (1) comprises electrolysis cells (2) and at least one service unit (4). Service units are often referred to as "electrolysis service machines" or "MSEs"("PTAs" or "Pot Tending Assemblies" or "PTMs" or "Pot Tending Machines" in English).

The electrolysis cells (2) are normally arranged in rows or rows, each row typically having more than one hundred cells, and electrically connected in series using connecting conductors. The cells (2) are arranged in such a way as to disengage circulation paths (3) between the cells and along the electrolysis room (1).

As illustrated in figure 2 each electrolysis cell (2) comprises a tank (2 '), a support structure (35) called a "superstructure" and a plurality of anodes (20, 20'). The vessel (2 ') comprises a steel box (26), an inner liner (27, 28), which is generally formed of blocks of refractory materials, and a cathode assembly (29, 30), which comprises carbonaceous material (29), referred to as "cathode blocks", and metal connecting bars (30) to which the electrical conductors (31) for conveying the electrolysis current are fixed. The anodes (20, 20 ') comprise at least one anode block (21, 21') of precured carbon material and a metal rod (22, 22 '). The anode blocks (21, 21 ') typically have a parallelepiped shape. The rod (22, 22 ') is typically attached to the anode block (s) (21, 21') via a fastener (22a, 22a '), generally referred to as a "multipode" which is anchored in the anode block (s) (typically using cast iron). The anodes (20, 20 ') are removably attached to a movable metal frame (23), referred to as the "anode frame", by mechanical fastening means (24, 25) typically comprising a connector (24) and hooks ( 25). The movable frame (23) is carried by the superstructure (35) and attached to electrical conductors (not shown) for routing the electrolysis current.

An electrolysis cell (2) generally comprises a cowling system (36), typically comprising a series of cowls, for confining the effluents inside the cell, and means (not shown) for discharging effluents and wastewater. direct to a treatment center.

The inner lining (27, 28) and the cathode blocks (29) form, inside the tank (2 '), a crucible adapted to contain the electrolyte bath (33) and a sheet of liquid metal (32). ) when the cell is in operation. In general, a cover of alumina and solidified bath (34) covers the electrolyte bath and all or part of the anodes.

The anodes (20, 20 '), and more precisely anode blocks (21, 21'), are partially immersed in the electrolyte bath (33), which contains dissolved alumina. The bottom surface (21a, 21a ') of the anodes is typically substantially planar and parallel to the top surface (29') of the cathode blocks (29), which is generally horizontal. The distance between the lower surface of the anodes and the upper surface of the cathode blocks, called "anode-cathode distance", is an important parameter in the regulation of the electrolysis cells. The anode-cathode distance is generally controlled with great precision.

The anode blocks (21, 21 ') are gradually consumed in use. To compensate for this wear, it is common practice to gradually lower the anodes (20, 20 ') by moving the movable frame (23) downwards regularly. In addition, as illustrated in figure 2 , the anode blocks (21, 21 ') are generally at different degrees of wear. Therefore, the position of the replacement anode (20 "), commonly referred to as" new anode ", relative to the movable frame (23) is generally adjusted at each anode change, more specifically, the position of the anodes is adjusted. so as to put on a common plane the so-called "lower" surface (21a, 21a ', 21a ") of the anode blocks (21, 21', 21"), that is to say the surface of the anode blocks which is intended to be immersed in the electrolytic bath (33) contained in the electrolysis cell (2) and to be parallel to the upper surface (29 ') of the cathode blocks (29). In practice, the replacement anode (20 ") is placed so that, after reaching its operating temperature, its lower surface (21a") is located at the lower surface (21a ') of the worn anode (20 ') that it replaces. Said lower surface (21a, 21a ', 21a ") of the anode blocks (21, 21', 21") is generally substantially planar.

The service unit (4) is used to carry out operations on the cells (2) such as the anode changes or the filling of the ground bath supply hoppers and the AlF ₃ of the electrolysis cells. It can also be used to handle various loads, such as tank members, liquid metal pockets, or anodes.

As illustrated in figures 1 and 3 the service unit (4) comprises a movable bridge (5) which can be translated over the electrolysis cells (2) and a service machine (6). The service machine (6) comprises a mobile carriage (7) and a service module (8) equipped with several handling and intervention devices (10), such as tools (shovels, keys, stitches, etc.). ). As illustrated in figure 3 , the service module (8) typically comprises a turret (8 ') mounted on the carriage (7) so as to be pivotable about a vertical axis V in use. The handling and intervention members (10) are typically attached to the turret. The service module (8) may also include a control cabin (16) for the operators.

The movable bridge (5) rests and circulates on raceways (9, 9 ') arranged parallel to each other and to the main axis of the hall (and the queue of cells). The mobile bridge (5) can thus be moved along the electrolysis room (1). The movable carriage (7) can be moved along the movable bridge (5).

As illustrated in figure 3 , the service machines (6) used for the anode changing operations are equipped with a determined set of tools (10), namely typically a drill bit (11a), a bucket shovel (12a), an organ anode gripper (called "anode gripper") (13a) and a hopper (14) provided with a retractable duct (15). The breaker (11a) serves to break the crust of alumina and bath solidified (34) which generally covers all or part of the anodes of the cell; the bucket shovel (12a) serves to clear the location of the anode, after removal of the spent anode, by removal of solids (such as pieces of crust and alumina) therein ; the anode clamp (13a) serves to grip and manipulate the anodes by their rod, in particular for the removal of spent anodes from an electrolysis cell and the placement of new anodes in the electrolysis cell; the retractable duct (15) is used to introduce alumina and / or ground bath in the electrolysis cell, so as to reform a coating layer, after the establishment of a new anode. The breaker (11a), the bucket shovel (12a) and the anode clamp (13a) are typically mounted at the lower end of a locating member (11b, 12b, 13b), such as a mast or telescopic arm. The expression "anode handling tool" (13) denotes the assembly comprising an anode gripping member (13a) and a positioning member (13b).

For the implementation of the invention, the service machine (6) comprises at least one anode handling tool (13) provided with a positioning member (13b), a gripping member (13a) and a vertical position sensor (13c) of the gripping member.

• on place une machine de service à proximité de l'anode usée déterminée (20') ;
• on retire les capots (36) situés à proximité de l'anode usée (20') ;
• on immobilise le cadre mobile (23) auquel sont fixées les anodes (20, 20') ;
• on saisit la tige métallique de l'anode usée (20') à l'aide d'un outil de manutention d'anode (13), et plus précisément à l'aide d'un organe de préhension (13a) ;
• on défait la fixation mécanique (24) de l'anode usée ;
• on retire l'anode usée (20') de la cellule d'électrolyse à l'aide dudit outil de manutention (13) ;
• on dépose l'anode usée (20') dans un endroit déterminé ;
• on saisit une anode de remplacement (20") à l'aide d'un outil de manutention (13), généralement le même outil que celui qui a servi à manutentionner l'anode usée ;
• on détermine une position verticale pour l'anode de remplacement (20") ;
• on place l'anode de remplacement (20") à la position verticale déterminée dans l'emplacement initialement occupé par l'anode usée ;
• on fixe l'anode de remplacement (20") sur le cadre mobile (23) à l'aide d'un moyen fixation mécanique (24).

The method of changing an anode of an electrolytic aluminum production cell (2) having a plurality of anodes (20, 20 ') typically comprises the following basic steps:

• placing a service machine near the determined spent anode (20 ');
• the covers (36) located near the worn anode (20 ') are removed;
• immobilizing the movable frame (23) to which the anodes (20, 20 ') are fixed;
• the metal rod of the spent anode (20 ') is grasped with the aid of an anode handling tool (13), and more precisely with the aid of a gripping member (13a);
• the mechanical fastener (24) of the spent anode is defeated;
• the spent anode (20 ') is removed from the electrolysis cell by means of said handling tool (13);
• the used anode (20 ') is deposited in a determined location;
• a replacement anode (20 ") is gripped using a handling tool (13), generally the same tool used to handle the spent anode;
• a vertical position is determined for the replacement anode (20 ");
• the replacement anode (20 ") is placed at the determined vertical position in the location initially occupied by the spent anode;
• the replacement anode (20 ") is fixed on the mobile frame (23) by means of a mechanical fixing means (24).

According to the invention, a vertical position is determined for the replacement anode (20 ") by means of measurements made during the handling of the anodes, These measurements relate, firstly, to the position of the tool. anode handling and, secondly, the passage of the anodes through a given axis or a specific plane outside the electrolysis cell.To this end, on the one hand, we create an axis or a plane immaterial reference, delimited by sound or electromagnetic waves, and the passage of the anodes through this axis or this plane is detected by means of a sound or electromagnetic wave detection system. an anode handling tool (13) comprising a vertical position sensor (13c) of the gripper (13a), and measuring the movements of the gripper during the anode handling operations. determines the vertical position of the replacement anode from the measurements of movement of the gripping member at predetermined times, namely the taking of the spent anode, the passage of the spent anode through the determined axis or plane and the passage of the replacement anode through the axis or plane determined.

• on produit au moins un faisceau d'ondes sonores ou électromagnétiques (51) dans un axe déterminé ou un plan de référence déterminé (50) (figure 4) ;
• on positionne un outil de manutention d'anodes (13) comportant un capteur de position verticale (13c) de l'organe de préhension (13a) au niveau d'une anode usée déterminée (20') et on place un organe de préhension (13a) en position de saisie de la tige métallique (22') de cette anode (20') (figure 4) ;
• on saisit la tige métallique (22') d'une anode usée déterminée (20') à l'aide de l'organe de préhension (13a) d'un outil de manutention d'anode (13) et, à l'aide du capteur de position, on mesure une première distance verticale A parcourue par l'organe de préhension (figure 4) ;
• on défait la fixation mécanique (24) de l'anode usée (20'), on retire l'anode usée (20') de la cellule d'électrolyse à l'aide dudit outil de manutention (13), on fait passer le(s) bloc(s) anodique(s) (21') de cette anode à travers ledit faisceau en un mouvement vertical et, à l'aide dudit capteur de position, on mesure une deuxième distance verticale B parcourue par l'organe de préhension au moment où la surface de référence (21a') de l'anode traverse ledit faisceau (figure 5) ;
• on saisit la tige métallique (22") d'une anode de remplacement (20") à l'aide d'un organe de préhension (13a), on fait passer le(s) bloc(s) anodique(s) (21") de cette anode à travers ledit faisceau en un mouvement vertical et, à l'aide dudit capteur de position, on mesure une troisième distance verticale C parcourue par l'organe de préhension au moment où la surface de référence (21a") de l'anode traverse ledit faisceau (figure 6) ;
• on détermine la position verticale de l'anode de remplacement (20") dans la cellule à partir des valeurs obtenues pour lesdites première, deuxième et troisième distances parcourues (A, B et C), et on place l'anode de remplacement (20") à cette position verticale dans l'emplacement initialement occupé par l'anode usée (figure 7) ;
• on fixe l'anode de remplacement (20") sur le cadre mobile (23) à l'aide d'un moyen fixation mécanique (24).

In the embodiment of the invention which is illustrated in Figures 4 to 7 we proceed as follows:

• at least one sound or electromagnetic wave beam (51) is produced in a given axis or a determined reference plane (50) ( figure 4 );
• positioning an anode handling tool (13) comprising a vertical position sensor (13c) of the gripping member (13a) at a given spent anode (20 ') and placing a gripping member ( 13a) in the gripping position of the metal rod (22 ') of this anode (20') ( figure 4 );
• the metal rod (22 ') of a given spent anode (20') is grasped by means of the gripping member (13a) of an anode handling tool (13) and, with the aid of of the position sensor, a first vertical distance A traveled by the gripping member is measured ( figure 4 );
• the mechanical fastener (24) of the spent anode (20 ') is defeated, the used anode (20') is removed from the electrolysis cell with the aid of the handling tool (13), the (s) anode block (s) (21 ') of this anode through said beam in a vertical movement and, with the aid of said position sensor, measuring a second vertical distance B traversed by the when the reference surface (21a ') of the anode passes through said beam ( figure 5 );
• the metal rod (22 ") of a replacement anode (20") is grasped by means of a gripping member (13a), the anode block (s) are passed through (21) ") of this anode through said beam in a vertical movement and, with the aid of said position sensor, a third vertical distance C traversed by the gripping member is measured at the moment when the reference surface (21a") of the anode passes through said beam ( figure 6 );
• the vertical position of the replacement anode (20 ") in the cell is determined from the values obtained for said first, second and third distances traveled (A, B and C), and the replacement anode (20) is ") at this vertical position in the location initially occupied by the spent anode ( figure 7 );
• the replacement anode (20 ") is fixed on the mobile frame (23) by means of a mechanical fixing means (24).

Said distance measurements can be made during normal operations of replacing worn anodes. The invention thus makes it possible to substantially limit the handling operations required to determine the position of the replacement anode. The same gripping member (13a) is used to handle a determined spent anode (20 ') and the replacement anode (20 ") to replace it.This variant avoids a calibration of the separate tool sensors. and differences in distance measurement inherent in the use of separate tools. Thus, the used anode (20 ') is deposited in a predetermined location before grasping the metal rod (22 ") of the replacement anode (20") with the gripping member (13a).

Said first distance (A) can be measured before or after grasping the rod (22 ') of the spent anode (20'). This distance is preferably measured after grasping the rod (22 ') and after putting the handling tool (13) under mechanical tension, in order to make up for any mechanical play and improve the accuracy of the measurement.

The reference surface (21a, 21a ', 21a ") of the anodes is preferably the so-called" lower "surface of the anode block (s) (21, 21', 21").

In order to limit anode handling movements, said vertical distance B is measured during a downward movement of a spent anode (20 '), during the deposition of the anode in the determined location, which is generally a pallet or a vehicle (40, 40 ') for its evacuation. For this purpose, said beam is disposed at a predetermined height above said determined location.

In order to limit anode handling movements, said vertical distance C is measured during an upward movement of a replacement anode (20 "), during the removal of the anode from a storage location temporary, which is usually a pallet or a vehicle (40, 40 ") used for its supply. For this purpose, said beam is disposed at a predetermined height above said storage location.

The vertical position of a replacement anode (20 ") corresponds to a vertical distance A 'traveled by the gripping member (13a) during the placement of the replacement anode in the location initially occupied by a In practice, when setting up the replacement anode, the downward movement of the gripping member is stopped when the distance traversed by it is equal to A. The vertical distance A is typically given by the relation A '= A - B + C + D, where D is a correction term to take into account the operating mode of the replacement anode in the cell.

According to one embodiment of the method according to the invention, the worn anodes (20 ') are replaced one by one by replacement anodes (20 ").

According to another embodiment of the method according to the invention, at least two worn anodes (20 ') are replaced at a time by replacement anodes (20 ") In this case, said distances A, B and C are measured. , and said determined distance A ', for each of the used anode (20') / replacement anode (20 ") pairs. This embodiment of the invention is advantageously implemented by using a service machine (6) comprising a number of anode handling tools (13) at least equal to the number of worn anodes which are replaced simultaneously.

The position sensor (13c) is used to measure the distance traveled vertically by the gripping member (13a) during handling of anodes. The distances are given with respect to a reference level N, which may be arbitrary. The reference level N is preferably the same for all the distance measurements during the same anode change in order to simplify the calculations and to avoid introducing uncertainties in the determination of the final position of the anode. of substitution.

The position sensor (13c) may be, for example, a cable encoder or a laser range finder. The position sensor is integrated with the anode handling tool (13). The position sensor (13c) is rigidly attached to the fixed part of the positioning member (13b) of the anode handling tool (13); it makes it possible to measure the relative distance of a determined point integral with the gripping member. For example, the position sensor can be attached to the sliding arm or telescopic mast which is fixed the gripping member.

In order to compensate for any gaps between the components of the anode handling tool (13) and between the anode gripping member (13a) and an anode rod (22, 22 '), it is advantageous to to perform said first measurement of distance traveled A in tension, that is to say after having tensioned the kinematic chain of the tool (before loosening of the connector (24) which holds the rod of the anode on the mobile frame (23)), because the other distance measurements are made in traction in the context of the invention (the axis or the reference plane being immaterial and the replacement anode being suspended from the gripping member when the adjustment of its position in the cell). In order to take account of said clearances, it is advantageous to provide the anode handling tool (13) with a means for measuring the tension in the tool, such as an axial dynamometer, which makes it possible to know the moment when the kinematic chain of the tool is in tension and to determine the moment when the mechanical games are all taken in the same direction.

Said sound waves are typically ultrasonic waves.

The electromagnetic waves are typically visible light, infrared or radio waves. It is advantageous to generate said beam (51) using a laser.

The lower surface (21a, 21a ', 21a ") of the anodes, in particular worn anodes, may have irregularities resulting in particular from surface defects, irregular wear of the anodes or deposits of material (such as alumina) when using the anodes In order to avoid false measurements of distance traveled from irregularities of the reference surface (21a, 21a ', 21a "), two or more (typically three) are preferably generated. sonic or electromagnetic wave beams (51) to form a determined reference plane (50). This variant of the invention is typically implemented using a generator comprising two or more sources of sound or electromagnetic waves, that is to say that each beam (51) is generated by a source of distinct waves (in the case of electromagnetic waves, each source is typically a laser). In this variant, the distances traveled (B and C) are advantageously given by the average of the distances traveled measured for each beam (after possibly eliminating one or more values deemed aberrant).

Said determined axis or the determined reference plane (50) is preferably substantially horizontal. The angle between the horizontal and said determined reference axis or plane (50) is preferably less than about 10 °, and more preferably less than about 5 °.

The moment when the reference surface (21a ', 21a'') of an anode passes through said beam can be determined in different ways: In an advantageous manner, which can be easily computerized, a generator (or emitter) is used. sonic or electromagnetic waves for producing said beam and a detector (or receiver) for detecting said beam According to a first embodiment of this method of proceeding, which is shown diagrammatically in FIG. figure 8 there is a sound or electromagnetic wave detector (54) facing a sound or electromagnetic wave beam generator (52) so that the detector can detect the beam produced by the generator ( figure 8a ). The moment when the reference surface (21a ', 21a ") of an anode (20', 20") is detected passes through said beam when the anode block (21 ', 21 ") interrupts transmission of said beam to the detector ( figure 8b ).

According to another embodiment of this way of proceeding, which is shown schematically in the figure 9 there is provided a sound or electromagnetic wave detector (54) and a sound or electromagnetic wave beam generator (52) facing a reflecting surface (55), such as a mirror, so that the detector can detect the beam produced by the generator and reflected by the reflecting surface (55) ( figure 9a ). These elements can be arranged in a triangle so as to form a plane. The moment when the reference surface (21a ', 21a ") of an anode (20', 20") is detected passes through said beam when the anode block (21 ', 21 ") interrupts transmission of said beam to the detector ( figure 9b ).

According to yet another embodiment of this manner of proceeding, which is schematically shown in FIG. figure 10 there is provided a sound or electromagnetic wave detector (54) and a sound or electromagnetic wave beam generator (52) so that the detector can detect the beam produced by the generator and reflected by the anode block ( 21 ', 21 ") ( figure 10a ). The moment when the reference surface (21a ', 21a ") of an anode (20', 20") passes through said beam is detected when the anode block (21 ', 21 ") reflects all or part of said beam towards the detector ( figure 10b ). Tests have shown that the reflectivity of the surface of a new or used anode is sufficient to allow satisfactory operation of this embodiment. This embodiment has the advantage of allowing to easily group the detector and the generator on the same positioning member (53).

The method according to the invention can be implemented using a measuring system comprising a position sensor (13c) for measuring the vertical distances traveled by a gripping member (13a) of a handling tool. anode (13) , a sound or electromagnetic wave beam generator (52), capable of producing at least one sound or electromagnetic wave beam (51) in a given reference axis or plane (50), least one sound or electromagnetic wave detector (54) capable of detecting the passage of a determined portion (21a, 21a ', 21a ") of an anode (20, 20', 20") through said beam and least one positioning member (53) to which is fixed said generator and / or said detector. The position sensor (13c) is preferably integrated with the anode handling tool (13). The generator (52) typically includes a source for each sound or electromagnetic wave beam (52). In the variant of the invention where the beams are formed of electromagnetic waves, the generator advantageously comprises at least one laser.

In one embodiment of the invention, the or each positioning member (53) of the measuring system is, directly or indirectly, attached to or placed on a traffic lane (3).

In another embodiment of the invention, the measurement system is integrated with a service unit (4) for anode change operations. This embodiment of the invention facilitates the movement and positioning of the measuring system. It also makes it possible to carry out the measurements necessary for the positioning of a replacement anode during normal handling movements of a used anode and a replacement anode. The measuring system according to the invention is preferably integrated in the service machine (6) of said service unit (4), and more preferably in the module (8) of said service machine (6). In these cases, the vertical position sensor (13c) of the gripping member (13a) of the measuring system is typically that which is provided with the anode handling tool (13). In these variants, the or each positioning member (53) of the measuring system is, directly or indirectly, fixed to a service unit (4), to a service machine (6) or to a service module (8) .

The or each positioning member (53) of the measuring system is typically an arm or a telescopic mast. When the measuring system is integrated with a service unit (4), the generator (52) and / or the detector (54) are typically fixed in the lower part of the positioning member (53).

The measurements of distance traveled (A, B, C, A ') can be carried out with or without the intervention of an operator. For example, the detector may emit an electrical, light or sound signal when the determined reference surface of an anode passes through the said beam (s) and an operator can record the distance value traveled by the gripping member given by the sensor. position at the time of transmission of said signal. Determining the distance A 'corresponding to the position of the replacement anode can also be performed by an operator using the values obtained for the first, second and third distances traveled (A, B and C). In order to lighten the task of the operators and to avoid calculation errors, the measurement of said distances (A, B, C, A ') is advantageously carried out wholly or partly in a computer manner. For example, the passage of the reference surface (21a, 21a ', 21a ") of the anodes through said beam can electrically or electronically trigger the measurement of the position sensor and the recording of the corresponding distance. The measuring system advantageously comprises a device for recording the measurements made and for determining said vertical position of the replacement anode (20 ").

The generator (52) and the detector (54) can be located on the same positioning member (53) or on separate positioning members. The generator (52) and detector (54) may optionally be integrated in the same device.

Claims (34)

1. Process for changing an anode of a cell for the production of aluminum by fused bath electrolysis (2), each anode comprising at least one anode block (21, 21', 21") and a metal rod (22, 22', 22") and being fixed removably to a mobile metal frame (23), each anode block having a reference surface (21a, 21a', 21a"), process by which at least one determined spent anode (20') is replaced by a replacement anode (20") using at least one anode handling tool (13) comprising a positioning device (13b), a gripping device (13a) and a position sensor to determine the vertical position (13c) of the gripping device, wherein the position sensor (13c) of the anode handling tool or each anode handling tool (13) is used to measure the vertical distances traveled by the gripping device or each gripping device (13a) relative to a reference level N, and wherein at least one beam of sound or electromagnetic waves (51) is produced along a determined reference axis or in a determined reference plane (50), and in that for each determined spent anode (20');
   said process comprising the following steps:

   a) said gripping device (13a) is placed in the gripping position of the metal rod (22') of said spent anode (20'), and the vertical distance A traveled by the gripping device (13a) to reach said position is measured;

   b) the spent anode (20') is withdrawn from the electrolytic cell, the anode block (21') of this anode is passed through said beam (51) in a vertical movement and the vertical distance B traveled by the gripping device (13a) at the moment at which the reference surface (21a') of this anode passes through the beam is measured;

   c) the metal rod (22") of said replacement anode (20") is gripped using said gripping device, the anode block (21") of this anode is passed through said beam (51) in a vertical movement and the vertical distance C traveled by the gripping device (13a) at the moment at which the reference surface (21a") of this anode passes through the beam is measured;

   d) the vertical position of the replacement anode (20") in the cell is determined starting from values obtained for the traveled distances A, B and C, and the replacement anode (20") is put into this position in the place initially occupied by the spent anode (20');

   said process being characterized in that said vertical position sensor (13c) is integrated into the anode handling tool (13) and in that the spent anode is laid down and the replacement anode is taken with the help of said handling tool in a determined place, said beam (51) being set at a determined height above said determined place, typically a temporary stocking area, so that said measures of the vertical distances B and C are made respectively when said spent anode is laid down and when said replacement anode is taken in said determined place.
2. Process according to claim 1, characterized in that the anode reference surface (21a, 21a', 21a") is the so-called "lower" surface of the anode block (21, 21', 21"), that is intended to be immersed in the electrolytic bath (33) contained in the electrolytic cell (2).
3. Process according to anyone of claims 1 and 2, characterized in that said vertical distance B is measured during a downwards movement of the spent anode (20').
4. Process according to anyone of claims 1-3, characterized in that said vertical distance C is measured during an upwards movement of the replacement anode (20").
5. Process according to anyone of claims 1-4, characterized in that the vertical position of the replacement anode (20") corresponds to a vertical distance A' traveled by the gripping device (13a) during placement of the replacement anode in the place initially occupied by the spent anode (20').
6. Process according to claim 5, characterized in that the vertical distance A' is given by the relation A'=A-B+C+D, where D is a correction term to take account of the replacement anode reaching its normal operating rate in the cell.
7. Process according to anyone of claims 1-6, characterized in that the anode handling tool (13) is provided with a means of measuring the tension in the tool, such as an axial dynamometer.
8. Process according to anyone of claims 1-7, characterized in that said electromagnetic waves are chosen among the visible light, infrared or radio waves.
9. Process according to anyone of claims 1-8, characterized in that said beam (51) is generated using a laser.
10. Process according to anyone of claims 1-7, characterized in that said sound waves are ultrasound waves.
11. Process according to anyone of claims 1-10, characterized in that two or several beams of sound or electromagnetic waves (51) are generated so as to form a determined reference plane (50).
12. Process according to claim 11, characterized in that each beam (51) is generated by a distinct wave source.
13. Process according to anyone of claims 1-12, characterized in that a sound or electromagnetic wave detector (54) is placed facing a sound or electromagnetic waves beam generator (52) such that the detector can detect the beam produced by the generator and in that the moment at which the reference surface (21a', 21a") of an anode (20', 20") passes through said beam is detected when the anode block (21', 21") interrupts transmission of the beam to the detector.
14. Process according to anyone of claims 1-12, characterized in that a sound or electromagnetic wave detector (54) and a sound or electromagnetic waves beam generator (52) are placed facing a reflecting surface (55) such that the detector can detect the beam produced by the generator and reflected by the reflecting surface (55) and in that the moment at which the reference surface (21a', 21a") of an anode (20', 20") passes through said beam is detected when the anode block (21', 21") interrupts transmission of the beam to the detector.
15. Process according to anyone of claims 1-12, characterized in that a sound or electromagnetic wave detector (54) and a sound or electromagnetic waves beam generator (52) are arranged such that the detector can detect the beam produced by the generator and reflected by the anode block (21', 21") and in that the moment at which the reference surface (21a', 21a") of an anode (20', 20") passes through said beam is detected when the anode block (21', 21") reflects all or part of said beam towards the detector.
16. Process according to anyone of claims 1-15, characterized in that said determined reference axis or plane (50) is substantially horizontal.
17. Process according to anyone of claims 1-16, characterized in that the spent anodes (20') are replaced one by one by replacement anodes (20").
18. Process according to anyone of claims 1-16, characterized in that at least two spent anodes (20') are replaced at the same time by replacement anodes (20").
19. Measurement system for measuring the vertical position of an anode, characterized in that it comprises:

    a) an anode gripping device (13a),

    b) a sound or electromagnetic waves beam generator (52) capable of generating at least one sound or electromagnetic waves beam (51) along a determined reference axis or in a determined reference plane (50),

    c) at least one sound or electromagnetic wave detector (54) capable of detecting the passage of a determined part (21a, 21a', 21a") of an anode(20, 20', 20") through said beam and

    d) one positioning device (53) to which said generator and/or said at least one detector is fixed, the positioning device comprising a fixed part,

    e) a position sensor (13c) rigidly attached to the fixed part of the positioning device for measuring the vertical distances traveled by said anode gripping device relative to a reference level N.
20. Measurement system according to claim 19, characterized in that the generator (52) and the detector (54) are located on a same positioning device (53).
21. Measurement system according to claim 19, characterized in that the generator (52) and the detector (54) are located on separate positioning devices.
22. Measurement system according to anyone of claims 19-21, characterized in that the anode handling tool (13) is provided with a means of measuring the tension in the tool, such as an axial dynamometer.
23. Measurement system according to anyone of claims 19-22, characterized in that the measurement system comprises a device to record measurements made and to determine the vertical position for a replacement anode (20").
24. Measurement system according to anyone of claims 19-23, characterized in that the positioning device or each positioning device (53) is a telescopic arm or mast.
25. Measurement system according to anyone of claims 19-24, characterized in that the positioning device or each positioning device (53) of the measurement system is directly or indirectly fixed to or placed on a circulation track (3).
26. Measurement system according to anyone of claims 19-25, characterized in that the positioning device or each positioning device (53) of the measurement system is directly or indirectly fixed to a tending assembly (4), a tending machine (6) or a tending module (8).
27. Measurement system according to anyone of claims 19-26, characterized in that the determined reference axis or plane (50) is substantially horizontal.
28. Measurement system according to anyone of claims 19-27, characterized in that said electromagnetic waves are chosen among visible light, infrared or radio waves.
29. Measurement system according to claim 28, characterized in that said generator (52) comprises at least one laser.
30. Measurement system according to anyone of claims 19-29, characterized in that said sound waves are ultrasound waves.
31. Measurement system according to anyone of claims 19-30, characterized in that the generator is capable of producing two or several sound or electromagnetic waves beams (51) so as to form a determined reference plane (50).
32. Measurement system according to claim 31, characterized in that the generator comprises a distinct wave source for each beam (51).
33. Tending machine (6) intended for anode replacement operations in a series of cells for the production of aluminum by fused bath electrolysis (2), comprising at least one anode handling tool (13) comprising a positioning device (13b) and a gripping device (13a), characterized in that it comprises a measurement system according to anyone of claims 19-32.
34. Tending assembly (4) in a plant for the production of aluminum by fused bath electrolysis comprising a traveling crane (5) and at least one tending machine (6) according to claim 33.

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