WO2006030092A2 - 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 same - Google Patents

Abstract

The invention relates to a method of changing an anode of a cell for the production of aluminium by means of fused-salt electrolysis (2), said cell comprising a plurality of anodes (20, 20'). The inventive method comprises the following steps consisting in: (i) using at least one anode handling tool (13) comprising a positioning member (13b), a gripping member (13a) and a vertical position sensor for grip member and using said position sensor in order to measure the distances travelled vertically by the gripping member (13a) in relation to a reference level N; and (ii) producing at least one electromagnetic or sound wave beam (51) in an axis or a determined reference plane (50) and using the passage of the anode through said beam in order to measure the aforementioned distances. The method also consists in determining the vertical position of the replacement anode in the cell from the values obtained for said distances and placing the replacement anode in said position in the location initially occupied by the used anode (20').

Description

 METHOD FOR CHANGING ANODE IN A CELL

ALUMINUM PRODUCTION BY ELECTROLYSIS INCLUDING

ADJUSTING THE POSITION OF THE ANODE AND DEVICE FOR THE

ENFORCE

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. French patent application FR 2 806 742 (corresponding to US Pat. No. 6,409,894) describes installations of an electrolysis plant intended 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 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 extends 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 of capturing the effiuents 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 changing method of an igneous electrolysis aluminum production cell comprising a plurality of anodes, said cell containing an electrolytic bath and comprising at least one cathode block, each anode comprising at least one minus an anode block and a metal rod and being removably attached to a movable metal frame by mechanical fixing means, each anode block having a reference surface, the method of replacing at least one spent anode determined by an anode of replacing using at least one anode handling tool comprising a positioning member, a gripping member and a vertical position sensor of the gripping member, and wherein the position sensor of the or each tool is used. anode handling for measuring the distances traveled vertically by the or each gripping member with respect to a reference level Nce, characterized in that at least one sound or electromagnetic wave beam is produced in a given axis or reference plane, and in that for each determined spent anode:

a gripping member is placed in the gripping position of the metal rod of the spent anode and the vertical distance A traversed by the gripping member to reach said position is measured;

the used anode is removed from the electrolysis cell, the anode block of this anode is passed through the said beam in a vertical movement and the vertical distance B traversed by the gripping member is measured at the moment when the surface reference of this anode passes through said beam;

the metal rod of a replacement anode is grasped with the aid of a gripping member, the anode block of this anode is passed through the beam in a vertical movement and the vertical distance C traversed by the gripping member at the moment when the reference surface of this anode passes through said beam; the vertical position of the replacement anode in the cell is determined from the values obtained for said distances traveled A, B and C, and the replacement anode is placed at this position in the location initially occupied by the worn anode. 5

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 worn anode on a pallet or a vehicle, taking

10 an anode replacement on a pallet or a vehicle and the establishment of the replacement anode in the cell), ι which has the advantage of not requiring additional handling movements. The invention thus makes it possible to avoid, in particular, an extension of the opening time of an electrolysis cell.

15

The beam or beams of sound or electromagnetic waves are advantageously placed beforehand at a place that allows the passage of a worn anode or a replacement anode through the beam (s) during the movements of the

^{"*""" "Handling""normal" "of"} these ^"" anddës, ~~ by ^"example" above ^{"a" "cell}

20 electrolysis, a pallet or a vehicle.

The measurement taken can be manual, that is to say, an operator records _t data obtained at each process step, or automated in whole or in part, that is to say, a computerized device performs automatically all or part of the measurements.

The invention also relates to a measuring system comprising a position sensor for measuring the vertical distances traveled by an anode gripping member, a sonic or electromagnetic wave beam generator, capable of producing at least one beam of sound or electromagnetic waves in a given axis or reference plane, at least one sound or electromagnetic wave detector capable of detecting the passage of a determined part of an anode through said beam and at least one positioning member to which is fixed said generator and / or said detector.

The invention further 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 an organ positioning device, 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 also relates to a service unit of an igneous electrolysis aluminum production plant comprising a movable bridge and at least one

1 service machine according to the invention.

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

Figure 1 illustrates, in section, a typical electrolysis room for the production of aluminum and comprising a service unit shown schematically. ^{"""" * "} ~ ^{""""""""**""~"}

Figure 2 illustrates, in cross-sectional view, a typical electrolysis cell for the production of aluminum.

Figure 3 shows, schematically, a service machine viewed from the side.

Figures 4 and 7 illustrate an embodiment of the anode changing method according to the invention.

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 I ₃ 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 or line typically having more than one hundred cells, and electrically connected in series by means of connecting conductors. The cells (2) are arranged in such a way as to clear the circulation paths (3) between the cells and along the electrolysis room (1).

15 As shown in Figure 2, each electrolysis cell (2) comprises a tank (2 '), a support structure (35) called "superstructure" and a plurality of anodes (2O ₅

20 '). The tank (2 ') comprises a box (26) of steel, an inner lining (27,

28), which is generally formed by blocks made of refractory materials, and a

- - - Cathodic together- (29, 30) which r 'comprises blocks carbonaceous material ^* (29) /

20 referred to as "cathode blocks", and metal connecting bars (30) to which are attached the electrical conductors (31) for routing the electrolysis current. 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 ')

25 is typically attached to the anode block (s) (21, 21 ') via a fastener (22a, 22a ¹ ), generally referred to as a "multipode", which is anchored in the (s) 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 FIG. 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 ¹ , 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 (2Ia") is located at the lower surface (21a ¹ ) 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 elements, pockets of liquid metal 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 FIG. 3, the service machines (6) used for the anode changing operations are equipped with a set of tools (10), typically a picker (11a), a shovel bucket (12a), an anode gripping member (called "anode gripper") (13a) and a hopper (14) provided with a retractable duct (15). The piercer (l ia) 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 positioning member (Hb, 12b, 13b), such as a mast or a 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.

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:

a service machine is placed near the determined spent anode (20 ');

the covers (36) are removed near the worn anode (20 '); the moving 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 worn anode is undone;

the used 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; - It takes a replacement anode (20 ") with a handling tool (13), usually the same tool that used to handle the used anode;

a vertical position is determined for the replacement anode (20 ");

placing the replacement anode (20 ") 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.

In the embodiment of the invention which is illustrated in FIGS. 4 to 7, the procedure is as follows:

at least one sonic or electromagnetic wave beam (51) is produced in a given axis or a determined reference plane (50) (FIG. 4);

positioning an anode handling tool (13) comprising a vertical position sensor (13c) of the gripping member (13a) at a determined 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, at the using the position sensor, measuring a first vertical distance A traveled by the gripping member (Figure 4); the mechanical fastener (24) of the spent anode (20 ') is defeated, the used anode (20') is removed from the electrolysis cell by means of said handling tool (13), the 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 traveled by the member gripping at the moment when the reference surface (21a ¹ ) of the anode passes through said beam (FIG. 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 said anode through said beam in a vertical movement and, with the aid of said position sensor, measuring a third vertical distance C traversed by the gripping member at the moment when the reference surface (2Ia") 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 is placed ( 20 ") at this vertical position in the location initially occupied by the spent anode (FIG.

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.

Preferably, the same gripping member (13a) is used to handle a determined spent anode (20 ') and the replacement anode (20 ") intended to replace it.This variant makes it possible to avoid a calibration of the sensors. separate tools and differences in distance measurement inherent in the use of separate tools. In this case, the used anode (20 ') is deposited in a determined location before the metal rod (22 ") of the replacement anode (20") is gripped 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 preferably measured during a downward movement of a spent anode (20 '), typically during the deposition of the anode in the determined location, which is usually 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 the anode handling movements, it is preferably measured said vertical distance C during an upward movement of a replacement anode (20 "), typically during the removal of the anode of a temporary storage place, which is usually a pallet or 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 ¹ 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 advantageously integrated with the anode handling tool (13). Typically, 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 with the aid of 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 ¹ , 21a ") of an anode passes through said bundle can be determined in different ways. <br /><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/> In an advantageous manner, which can be easily computerized, a generator (or transmitter) is used. sound or electromagnetic waves to produce said beam and a detector

(or receiver) for detecting said beam. According to a first embodiment of this procedure, which is shown diagrammatically in FIG. 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 ¹ , 21a ") of an anode (20 ', 20") passes through said beam is detected when the anode block (21', 21 ") interrupts the transmission of said beam to the detector (FIG. 8b).

According to another embodiment of this procedure, which is shown diagrammatically in FIG. 9, there is a sound or electromagnetic wave detector (54) and a sound or electromagnetic wave beam generator (52) facing each other. a reflecting surface (55), such as a mirror, so that the detector can detect the beam produced by the generator and reflected by the reflective 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 ¹ , 21a ") of an anode (20 ', 20") passes through said beam is detected when the anode block (21', 21 ") interrupts the transmission of said beam to the detector (FIG. 9b). According to yet another embodiment of this manner of proceeding, which is shown diagrammatically in FIG. 10, there is provided a sound or electromagnetic wave detector (54) and a sound or electromagnetic wave beam generator (52) of in such a way 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 ¹ , 21a") of an anode (20 ', 20 ") passes through said beam 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 axis or reference plane (50), at least one sound or electromagnetic wave detector (54) adapted to detect the passage of a determined part (21a,

21a ', 21a ") of an anode (20, 20', 20") through said beam and at least one locating member (53) to which said generator and / or detector is attached. 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

A method of anode change of an igneous electrolysis aluminum production cell (2) having a plurality of anodes (20, 20 ', 20 "), said cell (2) containing an electrolytic bath (33) and comprising at least one cathode block (29), each anode comprising at least one anode block (21, 21 ', 21 ") and a metal rod (22, 22', 22") and being removably attached to a metal frame mobile (23) by mechanical fixing means (24, 25), each anode block having a reference surface (21a, 21a ', 21a "), by which method, 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 member (13b), a gripping member (13a) and a vertical position sensor (13c) of the gripping member, and wherein the position sensor (13c) of the or each anode handling tool (13) is used to measure the distances traveled vertically by the or each gripping member (13a) with respect to a reference level N, characterized in that at least one sonic or electromagnetic wave beam (51) is produced in an axis or a plane of determined reference (50), and in that, for each determined spent anode (20 ¹ ): - a gripping member (13a) is placed in the gripping position of the metal rod (22 ') of the spent anode (20); ') and measuring the vertical distance A traveled by the gripping member (13a) to reach said position; the spent anode (20 ') is removed from the electrolysis cell, the anode block (21') of this anode is passed through the beam (51) in a vertical movement and the vertical distance B traveled is measured by the gripping member (13a) at the moment when the reference surface (21a ¹ ) of this anode passes through said beam; the metal rod (22 ") of a replacement anode (20") is grasped by means of a gripping member, the anode block (21 ") of this anode is passed through the said beam (51). ) in a vertical movement and measure the distance vertical line C traversed by the gripping member (13a) at the moment when the reference surface (2Ia ") of this anode passes through said bundle; -the vertical position of the replacement anode (20") in the cell is determined; from the values obtained for said distances traveled A, B and C, and placing the replacement anode (20 ") at this position in the location initially occupied by the spent anode (20 '). 2. Method according to claim 1, characterized in that the same gripping member (13a) is used to handle the used anode (20 ') and the replacement anode (20 ") intended to replace it. 3. Method according to any one of claims 1 and 2, characterized in that the reference surface (21a, 21a ', 21a ") of the anodes is the so-called" lower "surface of the anode block (21, 21', 21 ") 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 block (s) (29). 4. Method according to any one of claims 1 to 3, characterized in that said vertical distance B is measured during a downward movement of the used anode (20 '). 5. Method according to any one of claims 1 to 4, characterized in that said vertical distance C is measured during an upward movement of the replacement anode (20 "). 6. Method according to any one of claims 1 to 5, characterized in that said vertical position of the replacement anode (20 ") corresponds to a vertical distance A 'traversed by the gripping member (13a) during placing the replacement anode in the location initially occupied by the spent anode (20 '). 7. Method according to claim 6, 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 into account the setting in operating mode of the replacement anode in the cell. 8. Method according to any one of claims 1 to 7, characterized in that the position sensor (13c) is integrated with the anode handling tool (13). 9. Method according to any one of claims 1 to 8, characterized in that the anode handling tool (13) is provided with a means for measuring the tension in the tool, such as a dynamometer axial. 10. Method according to any one of claims 1 to 9, characterized in that said electromagnetic waves are chosen from visible light, infrared or radio waves. 11. Method according to any one of claims 1 to 10, characterized in that said beam (51) is generated using a laser. 12. Method according to any one of claims 1 to 9, characterized in that said sound waves are ultrasonic waves. 13. Method according to any one of claims 1 to 12, characterized in that two or more beams of sound or electromagnetic waves (51) are generated so as to form a determined reference plane (50). 14. The method of claim 13, characterized in that each beam (51) is generated by a distinct wave source. 15. Method according to any one of claims 1 to 14, characterized in that there is a sound wave or electromagnetic wave detector (54) facing a sonic or electromagnetic wave beam generator (52) of in such a way that the detector can detect the beam produced by the generator and in that the moment when the reference surface (21a ¹ , 21a ") of an anode (20 ', 20") passes through said beam is detected when the anode block (21 ', 21 ") interrupts transmission of said beam to the detector. 16. A method according to any one of claims 1 to 14, characterized in that there is a sound wave or electromagnetic wave detector (54) and a sonic or electromagnetic wave beam generator (52) opposite a reflective surface (55) so that the detector can detect the beam produced by the generator and reflected by the reflective surface (55) and that the moment when the reference surface (21a ¹ , 21a ") is detected; ) an anode (20 ', 20 ") passes through said beam when the anode block (21', 21") interrupts transmission of said beam to the detector. Method according to one of Claims 1 to 14, characterized in that a sound or electromagnetic wave detector (54) and a sound or electromagnetic wave beam generator (52) are provided so that that the detector can detect the beam produced by the generator and reflected by the anode block (21 ', 21 ") and in that the moment when the reference surface (21a ¹ , 21a") of an anode ( 20 ¹ , 20 ") passes through said beam when the anode block (21 ', 21") reflects all or part of said beam towards the detector. 18. Method according to any one of claims 1 to 17, characterized in that said axis or the determined reference plane (50) is substantially horizontal. 19. Method according to any one of claims 1 to 18, characterized in that the worn anodes (20 ') are replaced one by one by replacement anodes (20 "). 20. Method according to any one of claims 1 to 18, characterized in that at least two worn anodes (20 ') are replaced at a time by replacement anodes (20 "). 21. Measuring system comprising a position sensor (13c) for measuring the vertical distances traveled by an anode gripping member (13a), a sound or electromagnetic wave beam generator (52), capable of producing at least a beam of sound or electromagnetic waves (51) in a given axis or reference plane (50), at least one sound or electromagnetic wave detector (54) able to detect the passage of a determined part (21a, 21a ', 21a ") of an anode (20, 20', 20") through said beam and at least one locating member (53) to which said generator and / or detector is attached. 22. Measuring system according to claim 21, characterized in that the generator (52) and the detector (54) are located on the same positioning member (53). 23. Measuring system according to claim 21, characterized in that the generator (52) and the detector (54) are located on separate positioning members. 24. Measuring system according to any one of claims 21 to 23, characterized in that the anode handling tool (13) is provided with a means for measuring the tension in the tool, such as an axial dynamometer. 25. Measuring system according to any one of claims 21 to 24, characterized in that the measuring system comprises a device for recording the measurements made and for determining the vertical position of a replacement anode (20 "). 26. Measuring system according to any one of claims 21 to 25, characterized in that the or each positioning member (53) is an arm or a telescopic mast. 27. Measuring system according to any one of claims 21 to 26, characterized in that the or each positioning member (53) of the measuring system is, directly or indirectly, attached to a traffic lane (3) or placed on this one. 28. Measuring system according to any one of claims 21 to 27, characterized in that 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 a service module (8). 29. Measuring system according to any one of claims 21 to 28, characterized in that said determined axis or reference plane (50) is substantially horizontal. 30. Measuring system according to any one of claims 21 to 29, characterized in that said electromagnetic waves are chosen from visible light, infrared or radio waves. 31. Measuring system according to claim 30, characterized in that said generator (52) comprises at least one laser. 32. Measuring system according to any one of claims 21 to 31, characterized in that said sound waves are ultrasonic waves. 33. Measuring system according to any one of claims 21 to 32, characterized in that the generator is able to produce two or more sound or electromagnetic wave beams (51) so as to form a determined reference plane (50). ). 34. Measuring system according to claim 33, characterized in that the generator comprises a distinct wave source for each beam (51). 35. Service machine (6) for the anode change operations of a series of igneous electrolysis aluminum production cells (2), comprising at least one anode handling tool (13) comprising an electrode positioning device (13b) and a gripping member (13a), characterized in that it comprises a measuring system according to any one of claims 21 to 34. 36. Service machine (6) according to claim 35, characterized in that the position sensor (13c) of the measuring system is integrated with the anode handling tool (13). 37. Service unit (4) of an igneous electrolysis aluminum production plant comprising a movable bridge (5) and at least one service machine (6) according to claim 35 or 36.