JPS6156316B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrolytic apparatus used for producing aluminum by electrolyzing alumina dissolved in molten cryolite (Yell-Hall process).

In electrolyzers with prefired anodes, the position of the anode opposite the liquid aluminum layer of the cathode needs to be adjusted periodically to take into account changes in several parameters, such as:

- the height of the aluminum layer that rises uniformly and then falls sharply when removing the metal; - the gradual wear of the anode; - the occurrence of an anodic effect (packing) of the anode; - the unevenness of the current distribution at several anodes; - local variations in the temperature or composition of the electrolyte; - variations in the contact resistance between the anode rod and the current lead; - changes in the shape of the electrolyte-metal interface caused by changes in the current diagram within the electrolyte and within the metal.

Furthermore, almost all methods for adjusting electrolytic cells for aluminum production are carried out by varying the anode-to-cathode distance.

French patents FR.935350, 955688, 955689
No. 955690 (corresponding U.S. Patent No. 2545411,
2545412, 2545413) (PECHINEY)
The method and device for adjusting the electrodes of an electrolytic cell disclosed in 2002-2020 involve measuring the internal resistance of the electrolyte solution and measuring the current distribution between each anode using a ratio meter with a crossed electric field, and determining the target value for each anode. Give a lift command to correct the difference. Furthermore, the movement of the electrodes ensures a gradual descent of the alumina within the electrolytic cell and provides automatic power supply.

Newer technologies based on the same idea as these patents include, among others, U.S. Patent No. 2904490 (ARDALOG SUNNDAL), French Patent No.
No. 1325158 (ASEA) and French Patent No. 1605666 (=US Patent No. 3627666) (PECHINEY).

According to previous knowledge, in order to obtain high efficiency it is important to make the current distribution between the various anodes of the electrolytic cell as uniform as possible.

Current large electrolyzers with multiple anodes require relatively frequent adjustments at the level of one or more anodes to maintain an even current distribution as described above. Therefore, the concept of controlling these adjustment operations individually according to the value of the current flowing in each anode was reviewed, and based on this, the above-mentioned 1944 and
Pennessy and patented invention in 1946.

Alcoa (ALCOA) French Patent Publication No.
No. 2,473,194 (US Pat. No. 4,210,513) discloses a pneumatic positioning device for individual anodes. In the device, the motion of one motor is transmitted through a clutch to each jack, each jack changing the height of its corresponding anode as required. All clutches are interlocked by a common adjustment command. This system has the following drawbacks.

- The cost of the jack is high, since the jack has to have a large lifting stroke corresponding to the level of consumption of the anode, more precisely to the level of semi-depletion.

- Since the jack has a large lifting stroke, the jack becomes large. This increases the height of the electrolytic cell and increases equipment costs.

- Requires flexible and long current leads. Therefore, the conductor's stewardship will increase.

- Each jack is mechanically connected, which is more expensive than an electrical connection.

-regardless of what kind of adjustment you make;
The speed of the vertical movement is constant. Therefore, in order to make individual fine adjustments, it is necessary to reduce the duration of all other operations.

Furthermore, it is known that in electrolytic cells for the production of aluminum a phenomenon of so-called "packing" or anode effect occurs, which causes a sudden increase in the voltage at the terminals of the electrolytic cell. That is, a voltage of about 4 volts increases to 35 or 40 volts, and the current intensity decreases correlating with this increase. This is because a gas film is usually formed in the electrolyte below the anode.

Various methods are known for eliminating the anode effect, such as adding alumina (in which case no immediate effect is obtained), sucking compressed air into the electrolyte below the anode, There is the introduction of wooden sticks, or "poling", etc. "Poling" is difficult in current electrolyzers that are completely enclosed by a cover. Another method is to move the anode to separate the gas film. In U.S. Patent No. 2,061,146, filed December 3, 1934, L.
FERRAND suggests rocking the anode, which is effective but difficult to implement. Although currently commonly used methods of raising and lowering the anode are effective, they have the drawback of causing changes in the electrolyte level.

In current electrolytic cells with concentrated continuous power supply, the electrolyte level height is relatively large and the ratio between the surface area of the anode and the total surface area of the electrolyte is large.
Therefore, the level of the electrolyte changes greatly depending on the degree of immersion of the anode. This gives rise to several drawbacks.

- It is necessary to make the electrolytic cell deep to prevent the electrolyte from overflowing to the outside of the electrolytic cell. This increases the burden of capital investment.

- Some of the electrolyte solution coats the top of the anode and solidifies. Therefore, the volume of the electrolyte solution decreases, and the ability of the electrolyte to dissolve alumina decreases. Such a solidified electrolyte layer coats the anode each time the anode is lowered, and the end of the life of the anode becomes extremely long. Therefore, additional and difficult operations are required to clean these anodes and reuse the solidified electrolyte. In addition, the electrolyte coating the anode (functions as anode support and current lead).
Wetting the steel studs causes corrosion of the studs, thereby increasing the iron concentration of the aluminum produced.

It is an object of the present invention to provide an electrolytic device capable of reducing changes in the electrolyte level during removal of the anode effect in an electrolytic cell used for aluminum production by electrolysis of alumina dissolved in molten cryolite. be.

The object of the apparatus of the present invention is an electrolytic apparatus for producing aluminum, which comprises an electrolytic cell, a fixed frame placed above the electrolytic cell, and one anode means placed above the electrolytic cell. The other anode means is located above the electrolytic cell, and one end is fixed to the fixed frame and the other end is connected to the one anode means, and the one anode means is repeatedly raised and lowered. a first elevating means;
One end is fixed to the fixed frame and the other end is connected to the other anode means, and the other anode means is raised and lowered repeatedly with a phase shift of 180° with respect to the rise and fall of the one anode means. This is achieved by a device characterized in that it comprises a second elevating means.

In the device of the invention, one of the anode means may consist of a first row of horizontally arranged anodes, and the other anode means may consist of a second row of anodes arranged horizontally.

Furthermore, in the device of the present invention, the first elevating means is connected to the first common frame supported by the fixed frame so as to be movable in the vertical direction while maintaining a horizontal state, and one end is connected to the fixed frame. The other end is connected to the first common frame, and the first lifting member for raising and lowering the first common frame is connected to the first common frame. It may also include a plurality of second elevating members connected to each anode of the first anode row and for individually raising and lowering each anode of the first anode row; The means includes a second common frame supported by a fixed frame so as to be vertically movable while maintaining a horizontal state, and one end connected to the fixed frame and the other end connected to the second common frame. a third elevating member for elevating and lowering the second common frame; one end of each member is connected to the second common frame, and the other end of each member is connected to each anode of the second anode row. It may also include a plurality of fourth elevating members for individually elevating each anode of the second anode row.

In addition, the second elevating member further includes a first small frame supported by the other end of the second elevating member and electrically and detachably connected to each anode of the first anode row. and a first connection means for electrically connecting the first small frame and the anode bus bar, and the fourth elevating member may further include the other end of the fourth elevating member. for electrically connecting the second small frame to the anode busbar, which is supported by the second small frame and electrically and removably connected to each anode of the second anode row; and a second connection means.

Further, the first and second common frames may be connected to each other by a connecting means.

Incidentally, the liquid aluminum layer produced in the electrolytic cell of the device of the invention forms the cathode surface.

Thus, while the operation of the second and fourth elevating members is interrupted, the first and third elevating members that adjust the height of each rigid common frame are simultaneously and synchronously operated, and By actuating the third lifting member, the distance between the cathode surface and the anode can be changed.

In addition, in order to jointly adjust the current flowing through each anode or each anode group, it measures the intensity of the current flowing through each anode or each anode group, compares the measured value with the target value, generates a correction command, and adjusts the current intensity. The correction command may be sent to the second and fourth elevating members in order to control an anode or an anode group whose measured value and target value do not match. Further, while the second and fourth elevating members execute the correction command, power supply to the first and third elevating members that adjust the heights of the two common frames is interrupted.

Finally, if packing (i.e. "anode effect" of the electrolytic cell) occurs, the operation of the third and fourth lifting members is interrupted and the first and third lifting members adjust the height of each common frame. The members are operated separately and synchronously to raise one common frame by a predetermined height and simultaneously lower the other common frame by an equal height, and then reverse the raising and lowering operation of each common frame. Packing can be removed by repeating such alternating lifting and lowering operations a plurality of times until the packing disappears. At this time, it is preferable that each common frame is maintained in a horizontal state. Disappearance of packing is indicated by the restoration of the cell terminal voltage to a value close to 4 volts.

According to the apparatus of the present invention, since the first and second anode means are moved up and down alternately, changes in the electrolyte level due to the up and down operation of the anode means during removal of the anode effect can be reduced, and therefore the anode When the anode means is raised and lowered so that the electrolyte does not touch the steel stud supporting the means, the lifting stroke of the anode means can be increased compared to when both anode means are raised and lowered in the same phase.

The apparatus of the present invention will be explained in detail with reference to FIGS. 1 to 6.

Two horizontal rigid beams 1, 1' are arranged above the electrolytic cell as fixed frames.
The ends of each rigid beam 1, 1' are supported by two stands 2, 2' (Fig. 4), and two assemblies consisting of rods 3, 3' and levers 4, 4'. It is fixed. The levers 4, 4' are mounted on two steel tubular beams 5, as a common frame.
5', and the two tubular beams 5, 5' corresponding to each anode row are connected by a tie bar 6 as a connecting means.
are connected to each other by.

This connection means may be a rigid connection, as shown in FIG. 3, or an articulated connection. Rod 3,
3' and levers 4, 4' are connected to the first and third by means of two mechanical screws fixed to one stand 2, 2' of the rigid beam 1, 1'.
It is operated by jacks 7, 7' as lifting and lowering members. Each jack 7, 7' has an end lever 8,
The tubular beams 5, 5' are raised and lowered via the pipes 8'.

For convenience of explanation, the tubular beam 5 corresponding to one of the anode rows will be described below. The same explanation applies to the tubular beam 5' corresponding to the other anode row.

The lever 4 is connected to the rigid beam 1 via the pivot 4a.
2 via pivots 4b and 4c.
The two rods 3 are connected to each other. The lever 4 operates the tubular beam 5 via a link 40 which is connected to the lever 4 by a pivot 4d and to the tubular beam 5 by a pivot 5a.

The end lever 8 is fixed to the rigid beam 1 by a pivot 8a, to the head of the common jack 7 by a pivot 8b and to the end of the lever 3 by a pivot 8c.

The tubular beam 5 is fitted with a second screw by means of a small mechanical screw.
An individual small frame 10 as a first small frame is supported via a jack 9 as an elevating member.

The electrolytic current is normally conducted via a rigid diagonal member such as 11 to a fixed crosspiece as an anode busbar. The stationary crosspiece is made of aluminum and has two horizontal bars 12, 12' connected to each other by equipotential tie bars 13.

The current is distributed from the horizontal lever 12 to the aluminum connector terminal 14 by means of a flexible metal strip 15 as a first connection means, which connects the terminal 1
4 is fixed to a small frame 10, and an anode rod 16 is supported by the small frame 10.

As the means 17 for fastening the anode rod 16 to the small frame 10, any known type of device may be used. For example, French Patent Publication No.
No. 2039543 (D.DUCLAUX) (corresponding U.S. patent no.
3627670) may be used. In the illustrated case, the tightening screw is used in a horizontal rather than vertical position.

The first elevating means of the device of the present invention is the jack 7
, a tubular beam 5, a jack 9, and a small frame 10.

The device according to the invention has a contact strip 30 as a first auxiliary frame made of aluminum for each anode or for each group of anodes, with a horizontal bar 1
2, 12' and a flexible metal strip 31. This contact strip 30 is carried on a support rigidly connected to the rigid beams 1, 1', so that any downward movement is completely prevented.

In FIG. 6, the contact strip 30 further includes:
Contains a simple small connector. The small connector has just enough force to support the weight of a stationary anode and is therefore inexpensive. The small connector is
It includes a connecting means 32, the connecting means 32 having four
They are pivoted at points 33, 34, 35, and 36 to form a quadrilateral. The tightening and loosening movements are ensured by the rotation of the screwdriver 37, which is controlled by a suitable tool of simple construction. Each subassembly consisting of a jack 9 and a small frame 10 supports a pair of anodes 18,19. However, this configuration is not necessarily required. Each jack 9 is 1
Configurations that control one anode or more than two anodes are also within the scope of the invention.

The jacks 9 may be operated by respective electric or air motors, or the movement of only one motor may be distributed by a set of transmission shafts. In the latter case, the conductive shaft and the jack 9 are connected via clutches, each clutch controlling the activation or deactivation of the jack 9 when a common motor rotates. Furthermore, the anode rod 16
It is possible to arrange guide means of:

The device of the invention can perform four functions as described below.

(1) Common control of the anode When it is necessary to raise or lower the entire anode in order to change the distance between the anode and the cathode according to the adjustment command, the anode is moved to the tubular beam 5, by not operating the jack 9. rigidly connected to 5';
Accurate synchronization with the common jack 7, 7' is ensured by a mechanical coupling 20 which controls the jacks 7, 7' simultaneously. two tubular beams 5,5'
simultaneously rise or fall synchronously, and the anode moves parallel to itself. This mode of operation is equivalent to that obtained by conventional opportunistic means.

(2) "Unpacking" or elimination of the anode effect In conventional devices, the anode rises and falls at the same time and in the same phase, so there is a drawback that the electrolyte level changes greatly depending on the degree of immersion of the anode. This may cause the electrolyte to overflow to the outside of the electrolytic cell, with some of the electrolyte coating the upper part of the anode and solidifying, and the electrolyte covering the anode flowing into the support and current leads of the anode. Wetting the steel stud 21, which performs the function of 1, corrodes the stud 21, thereby increasing the iron concentration of the aluminum produced.

In the device of the present invention, one anode row is lowered and the other anode row is raised by the same height at the same time, so it is possible to remove the anode effect while maintaining the electrolyte level constant. .

To this end, the mechanical joint 20 between the two jacks 7 and 7' is either eliminated or replaced by a cross joint that allows these jacks to move in opposite directions by equal widths. A marking device such as a revolution counter on the motor or any known displacement measuring means may ensure synchronized adjustment of the jacks and matching of the levels of the anodes of each anode row.

If the connection between the two tubular beams 5, 5' is rigid (FIG. 3), the tubular beams 5, 5' will tilt slightly during the lifting operation and thus the anode will also tilt. However, this slope is extremely small, on the order of several degrees. By alternately raising and lowering the anode, it is possible to cause horizontal movement of the electrolyte without changing the liquid level.

When the connection between the two tubular beams 5, 5' is articulated, the plane of the anode remains perfectly horizontal during vertical lifting operations as described above.

A similar result is of course obtained when the two tubular beams 5, 5' are mechanically independent.

The small jack 9, without using the jack 7, 7' which controls the tubular beams 5, 5'.
It is also possible to remove the anodic effect while maintaining the electrolyte level constant by operating only 9'. In particular, in an electrolytic cell where an anode effect has occurred, all jacks 9 located on the right with respect to the short axis of the electrolytic cell are given a descending command, and all jacks 9' located on the left with respect to the short axis of the electrolytic cell are given a descending command. Give the command to increase the height, then continue with the reverse operation. That is, a command to ascend to the right half and a command to descend to the left half are given. Repeat this operation until the anode effect disappears.

In the conventional case and assuming that the electrolytic cell is arranged transversely to the axis of the electrolytic system, 20 downstream anodes and 20 upstream anodes are operated, but in the present case , operate the 20 anodes on the right and the 20 anodes on the left (with respect to the axis of the electrolytic system).

(3) Individual control of the anodes If the current intensity through an anode or a group of two anodes in the case shown deviates from the target value, a regulating system, usually consisting of a computer, generates a regulating command. do. This causes the corresponding jack 9 to rise or fall in the desired direction. During this operation, the jacks 7, 7' are not controlled and the tubular beams 5, 5' are stationary.

The individual movement width of each anode or anode group can be set as desired. For example, when used in a 280,000 ampere cell system containing two anode banks of 20 anodes controlled in groups of two, the magnitude of the movement is
Set to 30mm. By slowing down the moving speed of these jacks 9, extremely high adjustment accuracy can be provided, and the current flowing through each pair of anode groups can be controlled with an accuracy of ±1%.
Can be adjusted to 14000 amps. In these electrolyzers, the average distance between the anode and cathode aluminum layer is about 40 millimeters.

(4) Power supply to the anode while the frame is rising As the anode wears out, the tubular beams 5, 5' gradually descend. It is therefore necessary to periodically return these tubular frames 5, 5' to the raised position. This operation, referred to as flame raising, is typically carried out using a lift beam guided by the electrolytic bridge into the cell, with the anode maintained at its own level. The lift beam has a gripping cover for the anode rod and is supported above the electrolyzer. This kind of lift beam is especially
ALUMINUM
PECHINEY), French Patent No. 1,445,602 (corresponding U.S. Pat. No. 3,434,955).
After fixing the anode to the lift beam, loosen the connection of the fastening means 17 of the anode rod 16 to the small frame 10 and return the tubular beams 5, 5' to the top of their travel using the jacks 7, 7'. .

This method suffers from two major drawbacks:

A. During the raising operation, the current transfer from the horizontal bar 12 to the anode rod 16 takes place via the same contacts as in normal operation of the electrolyzer. This contact is therefore slippery. Furthermore, despite the use of a lift beam, the pressure exerted by the anode rod 16 on the horizontal bar 12 is small compared to the pressure exerted by the conductor, resulting in incomplete contact. This slippery and imperfect contact, along with energy loss, often results in faster deterioration of the contact surface. On the other hand,
If an anodic effect occurs, the terminal voltage of the electrolytic cell increases significantly, so that the risk of deterioration during the raising operation is even greater.

B. Since the lift beam is a large and heavy member, an energy introduction part is required to operate the mechanism. The energy introduction is therefore operated together with an electrolytic bridge. Since the raising operation takes a relatively long time, the proportion occupied by one bridge increases and thus the number of bridges in one electrolyte system decreases. Furthermore, since the lift beam and bridge are placed above the cell, it is not possible to erect another bridge above the electrolytic cell. This also becomes a restriction on use.

The presence of the auxiliary frame 30 considerably facilitates such frame raising operations. In this lifting operation, first the anode rod 16 is fastened to the auxiliary frame 30 by the connecting means 32. The anode is thus electrically connected to the horizontal bar 12 and mechanically coupled to the auxiliary frame 30 and thus to the rigid beam 1. Next, the tightening means 17 is loosened, and the tubular beam 5, jack 9, small frame 10 of the anode rod 16, and connector terminal 14 are raised. Next, the tightening means 17 is tightened again and the connecting means 32 is loosened.

Means or mechanical attachments may be provided for spacing the auxiliary frame 30 from the anode rod 16 to prevent electrical contact between the anode rod 16 and the auxiliary frame 30.

Since the necessary tools for raising the frame consist only of a manual or mechanical spanner for tightening and loosening the connecting means 32, the two disadvantages of the prior art devices as described above are eliminated. That is, the flame raising operation is carried out independently of other operational operations and the electrolytic bridge, and free direct passage of current is always ensured irrespective of what stage the flame raising operation is in.

In addition to the four main functions as described above, the device of the invention allows for easy disconnection of the connection between the jack 9 and the tubular beam 5 during start-up of the electrolytic cell, which allows the anode to be placed on the cathode. While being placed and preheated, an electrical connection is maintained between the flexible metal strip 15 and the anode rod 16, allowing the anode to expand and move freely.

Furthermore, the connection between the jack 9 and the small frame 10 can be taken to leave some freedom in the anode without impairing the electrode contact between the anode rod 16 and the aluminum connector terminal 14. Even if the anode position is inaccurate, the voltage drop at the junction between the anode and the horizontal bar 12 is maintained at a small value.

Furthermore, it is possible to slightly raise the anode immediately before the operation, prior to replacing the anode. The current through the anode is substantially reduced to prevent degradation of the connector terminal 14 due to arcing effects as the anode rod 16 separates from the connector terminal 14.

Finally, the height of the connector terminals 14 is low compared to the height of conventional crosspieces. This reduces the height of the electrolytic cell, shortens the anode rod 16, and
The length of the conductor circuit can be shortened. It is therefore possible to considerably reduce the initial capital investment and the voltage effects during operation.

After all, according to the apparatus of the present invention, since one anode means is repeatedly raised and lowered with a phase shift of 180 degrees with respect to the raising and lowering of the other anode means, the electrolyte is Compared to raising and lowering both anode means in the same phase when raising and lowering the anode means, which can reduce changes in the liquid level and therefore prevent the electrolyte from touching the steel studs supporting the anode means. Thus, the lifting stroke of the anode means can be increased.

[Brief explanation of the drawing]

1 is a schematic partial perspective view of an embodiment of the device of the invention, FIG. 2 is a cross-sectional view at the level of the anode control jack, and FIG. 3 is a connection between two rigid members of a common frame. A cross-sectional view of the rigid tie bar; Figure 4 is a side view of the two common frame control jacks;
FIG. 5 is a cross-sectional view of the position of the auxiliary frame, and FIG. 6 is a plan view of the small connector. 1, 1'...Beam, 2, 2'...Stand,
3, 3'...rod, 4,4'...lever, 5,
5'...Frame, 6...Time bar, 7,7'...
... Jacket, 8, 8' ... Lever, 9 ... Jacket, 10 ... Small frame, 12, 12' ... Horizontal bar, 13 ... Tie bar, 14 ... Connector terminal, 15 ... Metal strip, 16 ... ...Anode rod, 18, 19...Anode, 20...Joint, 30...
...Auxiliary frame.

Claims (1)

[Scope of Claims] 1. An electrolytic apparatus for producing aluminum, comprising: an electrolytic cell; a fixed frame placed on the electrolytic cell; one anode means placed above the electrolytic cell; the other anode means positioned above the tank, and a first one whose one end is fixed to the fixed frame and whose other end is connected to the one anode means, and which repeatedly raises and lowers the one anode means. elevating means having one end fixed to the fixed frame and the other end connected to the other anode means, the other anode means being oriented at a phase of 180° with respect to the elevating and lowering of the one anode means. and a second elevating means for repeatedly elevating and lowering in a staggered manner. 2. The device according to claim 1, wherein the lifting stroke of said one anode means and the lifting stroke of said other anode row are equal. 3. Claims characterized in that the one anode means consists of a first row of anodes arranged horizontally in a row, and the other anode means consists of a second row of anodes arranged horizontally in a row. The device according to item 1 or 2. 4. The first lifting means has a first common frame supported by the fixed frame so as to be vertically movable while maintaining a horizontal state, and one end of which is connected to the fixed frame, and the other end of which is connected to the fixed frame. a first elevating member connected to a first common frame and for elevating the first common frame;
One end of each is connected to the first common frame, and the other end of each is connected to each anode of the first anode row, for individually raising and lowering each anode of the first anode row. a second common frame supported by the fixed frame so that the second elevating means can move freely in the vertical direction while maintaining a horizontal state; is connected to the fixed frame, and the other end is connected to the second common frame,
a third frame for raising and lowering the second common frame;
a lifting member, each one end of which is connected to the second common frame and the other end of each of which is connected to each anode of the second anode row; Multiple fourths for individual elevation
4. The device according to claim 3, comprising a lifting member. 5. The second elevating member further includes a first small portion supported by the other end of the second elevating member and electrically and detachably connected to each anode of the first anode row. It consists of a frame and a first connection means for electrically connecting the first small frame and the anode bus bar, and the fourth elevating member is further connected to the other end of the fourth elevating member. a second small frame supported and electrically and removably connected to each anode of the second anode row;
5. The apparatus according to claim 4, further comprising a second connecting means for electrically connecting the small frame and the anode bus bar. 6. Each anode of the first anode row has one end supported by the fixed frame and the other end electrically and removably connected to each anode of the first anode row, and It has a first auxiliary frame that is electrically connected to the anode bus bar, and in addition, each anode of the second anode row has one end supported by the fixed frame and the other end supported by the first auxiliary frame. The second auxiliary frame is electrically and removably connected to each anode of the two anode rows, and the second auxiliary frame is electrically connected to the anode bus bar. Apparatus according to scope 5. 7. The device according to any one of claims 4 to 6, wherein the first and second common frames are connected to each other by a connecting means. 8. Apparatus according to claim 7, characterized in that said connecting means rigidly connects said first and second common frames. 9. The apparatus of claim 7, wherein said connecting means articulates said first and second common frames.