EP0042815B1 - Bus-bar arrangement for electrolytic cells - Google Patents

Description

The present invention relates to a rail arrangement for conducting the direct electrical current from the cathode bar ends of a transverse electrolysis cell, in particular for the production of aluminum, to the traverse of the subsequent cell, part of the rails being arranged under the cell.

For the production of aluminum by electrolysis of aluminum oxide, it is dissolved in fluoride melt, which largely consists of cryolite. The cathodically deposited aluminum collects under the fluoride melt on the carbon bottom of the cell, the surface of the liquid aluminum forming the cathode. Anodes, which are attached to a crossbeam and are made of amorphous carbon in conventional processes, are immersed in the melt. At the carbon anodes, the electrolytic decomposition of the aluminum oxide produces oxygen, which combines with the carbon of the anodes to form CO ₂ and CO. The electrolysis generally takes place in a temperature range of about 940-970 ° C. In the course of electrolysis, the electrolyte becomes poor in aluminum oxide. With a lower concentration of 1-2% by weight of aluminum oxide in the electrolyte, there is an anode effect, which results in a voltage increase of, for example, 4 to 5 V to 30 V and above. Then, at the latest, the crust formed from solidified electrolyte material must be hammered in and the aluminum oxide concentration increased by adding new aluminum oxide (alumina).

The cathode bars are embedded in the carbon base of the electrolysis cell, the ends of which penetrate the electrolysis tank on both sides. These iron bars collect the electrolysis current, which flows via the busbars arranged outside the cell, the risers, the crossbar and the anode rods to the carbon anodes of the subsequent cell.

The ohmic resistance from the cathode bars to the anodes of the subsequent cell causes energy losses in the order of up to 1 kWh / kg of aluminum produced. Attempts have therefore repeatedly been made to optimize the arrangement of the busbars with respect to the ohmic resistance. However, the vertical components of magnetic induction formed must also be taken into account, which ^- together with the horizontal current density components ^- generate a force field in the liquid metal obtained through the reduction process.

In an aluminum smelter with transverse electrolysis cells, the current is conducted from cell to cell as follows: The direct electrical current is collected by cathode bars embedded in the carbon bottom of the cell and emerges from the upstream and downstream ends in relation to the general direction of current. The iron cathode bars are connected to aluminum busbars via flexible straps. The busbars, which are optionally combined to form busbars, direct the direct current into the area of the subsequent cell, where the current is led via other flexible belts and via risers to the crossmember carrying the anodes. Depending on the cell type, the risers are electrically conductively connected to the front and / or one long side of the traverse.

However, these rail guides, which are characteristic of aluminum smelters, have both electrical and magnetic inconveniences, which have been attempted in several prior publications.

GB-PS 1 032 810 discloses within the scope of an invention which relates to the furnace encapsulation that the busbars can be arranged below the electrolysis cell. The electrical current is fed symmetrically into the crossbar of the next cell from the long side of the furnace. According to FIG. 2, current guides 135 are carried out symmetrically below the cell with respect to the transverse direction of the furnace.

According to US Pat. No. 3,415,724, a rail guide is sought with which the magnetic effects are not increased if the current strength is increased. For this purpose, part of the current exiting the cathode bar ends upstream, but less than half, is passed under the cell. The rest of the current emerging upstream from the cathode bar ends is concentrated around the end faces of the cell. According to FIG. 3, the conductors passing the current under the cell are in the middle of the electrolysis cell and are designed as busbars. The feed into the traverse of the subsequent cell is symmetrical with respect to the furnace cross axis at four points on the longitudinal side of the traverse.

The method of DE-AS 26 13 867 discloses a rail guide, according to which a part of the furnace stream emerging upstream from the cathode bar ends, summarized in two rails, is carried out in the middle of the cell under the furnace and is fed laterally into the traverse of the subsequent furnace. The rest of the current emerging upstream is fed around the cell into the end faces of the traverse of the subsequent cell (FIG. 3). The current emerging from the downstream cathode bars is led to the other branch of the traverse of the subsequent cell and is fed in laterally.

The arrangement for compensating for harmful magnetic influences according to DE-OS 28 45 614 comprises three busbars which pass through the cell. The current is fed in laterally via three risers in the traverse of the subsequent cell. However, this current feed is asymmetrical because a small proportion of the Oven current is conducted around the short side of the cell facing the magnetically predominant adjacent row of cells.

The prior art publications and the devices disclosed therein, in which a part of the rails is arranged under the cell, have the disadvantage that the magnetic and electrical inconveniences are not optimally eliminated.

The inventor has therefore set himself the task of creating a rail arrangement for transverse electrolysis cells, which produces practically negligible magnetic and electrical effects with low investment costs and good current efficiency.

The object is achieved according to the invention in that a maximum of five rails connected to the upstream cathode bar ends are alternately arranged individually under the cell and in packets around the cell.

The rails connected to the upstream ends of the cathode bars can be passed through or around the cell in groups. It is essential that the groups that pass under and around the cell are alternating, and that each rail connected to an upstream cathode bar end that does not go around the cell is led individually under the cell.

If e.g. B. three consecutively arranged, connected to the upstream cathode bar ends rails form a group of three performing under the cell, the next three, also upstream cathode bar ends are combined into a package and guided in a rail around the cell. The next triad of rails connected to the upstream cathode bar ends then passes individually under the cell, etc.

According to the invention, the number of rails forming the groups is limited to five; on the other hand, the number of rails forming the groups can be reduced to one, with no actual groups, but individual rails alternating, i. H. in the latter case, alternate under the cell with leading rails and rails running around the cell.

If two to five rails form the alternating groups, the number of group members is preferably approximately the same. In other words, this means that preferably about a quarter of the rails connected to the cathode bar ends are carried out under the cell. The «must be added, for example, because the number of cathode bar ends is always an even number, but does not have to be a multiple of four. If the rails connected to the upstream ends of the cathode bars are passed through and around the cell alternately, this situation necessarily arises.

On the downstream side of the electrolysis cells, the rails which are carried out individually under the cell are combined to form busbars. The rails guided around the cell and / or the rails connected to a downstream cathode bar end likewise open into these busbars. The busbars are led to the traverse of the next cell.

In the case of larger electrolysis cells, for example, all the rails connected to one end of the cathode bar can be combined to form four busbars. These merge into risers and are connected in an electrically conductive manner to the nearer longitudinal side or to at least one end face of the traverse of the following cell.

In principle, the rail arrangement can be symmetrical or asymmetrical.

In the case of a symmetrical rail guide, the same number of rails connected to a cathode bar end terminates in all busbars arranged symmetrically with respect to the cell transverse axis. The busbars are connected symmetrically with respect to the cell transverse axis to the nearer long side or the two end faces of the crossbar. The connection points of the busbars with the crossbar of the following cell are preferably at the same distance.

• - Die am nächsten bei der magnetisch vorherrschenden Nachbarzellenreihe liegende Steigleitung ist mit der Stirnseite der Traverse der Folgezelle verbunden, während die übrigen Steigleitungen in die nähere Traversenlängsseite der Folgezelle münden. Die Abstände zwischen den Verbindungen der Steigleitungen mit der Traverse der Folgezelle sind vorzugsweise ungefähr gleich gross.
• - In die am nächsten bei der magnetisch vorherrschenden Nachbarzellenreihe liegende/n Sammelschiene/n münden mehr mit einem Kathodenbarrenende verbundene Schienen als in die weiter von der Nachbarzellenreihe entfernte/n Sammelschiene/n.

An asymmetrical current flow can be achieved in the following ways:

• - The riser closest to the magnetically predominant row of neighboring cells is connected to the face of the traverse of the next cell, while the other risers open into the closer longitudinal side of the traversing cell. The distances between the connections of the risers to the traverse of the following cell are preferably approximately the same.
• - The busbars closest to the magnetically predominant row of neighboring cells lead to more bars connected to a cathode bar end than to the busbar (s) further away from the row of neighboring cells.

In addition to these two most important embodiments, however, asymmetrical current routing can also be achieved, for example, by designing busbars leading to the traverse of the subsequent cell with different cross-sections and / or consisting of materials with different electrical resistances. Furthermore, the cathode bar ends can be of different lengths.

• Figur 1 eine Elektrolysezelle mit symmetrischer Schienenführung zu der Traverse der Folgezelle
• Figur 2 einen Vertikalschnitt durch zwei nebeneinanderliegende Elektrolysezellen
• Figur 3 eine Elektrolysezelle mit asymmetrischer Schienenführung zu der Traverse der Folgezelle, mit einseitiger Stirneinspeisung
• Figur 4 eine Elektrolysezelle mit asymmetrischer Stromführung zur Traverse der Folgezelle, mit Seiteneinspeisung
• Figur 5 eine stilisierte, asymmetrische Schienenführung.

The invention is explained in more detail with reference to the drawing. They show schematically:

• 1 shows an electrolysis cell with a symmetrical rail guide to the traverse of the subsequent cell
• 2 shows a vertical section through two electrolysis cells lying next to one another
• Figure 3 shows an electrolysis cell with an asymmetrical rail guide to the traverse of the subsequent cell, with one-sided end feed
• Figure 4 shows an electrolysis cell with asymmetrical current routing for traversing the subsequent cell, with side feed
• Figure 5 is a stylized, asymmetrical rail guide.

• - Im Zentrum der Zelle führen drei Aluminiumschienen 16 den Strom der drei mittleren Kathodenbarrenenden unter der Zelle 10 durch ab.
• - Die nächsten beiden Kathodenbarrenenden sind mit einer Sammelschiene 18 verbunden, welche den Strom um die Zelle herum zu der Traverse 20 der Folgezelle 22 führt.
• - Von den nächsten beiden Kathodenbarrenenden wird der Strom, wie bei den mittleren Kathodenbarrenenden, mittels Schienen 16 einzeln unter der Zelle durchgeführt.
• - Schliesslich sind die äusseren beiden Kathodenbarrenenden wiederum mit einer Sammelschiene 18 verbunden, die zu der Traverse 20 der Folgezelle 22 führt.

Fifteen cathode bars 12 are embedded in the electrolytic cell 10 of FIG. 1. The direct electrical current is discharged from the cathode bar ends 14 upstream with respect to the general current direction I as follows:

• - In the center of the cell, three aluminum rails 16 conduct the current from the three central cathode bar ends under the cell 10.
• The next two cathode bar ends are connected to a busbar 18, which leads the current around the cell to the crossbeam 20 of the subsequent cell 22.
• - From the next two cathode bar ends, the current, as with the middle cathode bar ends, is carried out individually under the cell by means of rails 16.
• - Finally, the outer two cathode bar ends are in turn connected to a busbar 18, which leads to the traverse 20 of the following cell 22.

The rails are therefore alternately arranged in groups of two individually under the cell and in packets around the cell.

The cathode bar ends 24, which are downstream with respect to the general current direction I, are connected to busbars, the outer busbars 26 uniting with the bars 18 guided around the cell and being carried up in a riser line L ₁ or L ₃ to the end faces of the cross member 20 . The middle busbar merging into the riser line L ₂ opens in the middle of the cross member 20 into the side surface facing the cell 10.

The anode pairs 28 are indicated in the area of the traverse 20.

1 is absolutely symmetrical with respect to the cell transverse axis.

In the vertical section of FIG. 2 it can be seen how the electrical current at the upstream end 14 of the iron cathode bar 12 is led via flexible conductors 30 to the aluminum rail 16 passing under the cell and again via flexible conductors 30 to the busbar 26 ^g . This busbar 26 merges into a vertical ladder L, which leads the current to the crossmember 20 of the subsequent cell 22. The anodes 28 are suspended from this cross member by means of anode rods 32.

The electrolysis cell shown in FIG. 3, arranged transversely with respect to the general current direction, has 25 cathode bars 12, or 25 cathode bar ends 14, 24 arranged upstream and downstream. The general current direction of the magnetically predominant row of neighboring cells, on the left of FIG IN designated.

From the cathode bar ends 14, the current is conducted alternately with individually arranged rails 16 under the cell 10 through or with busbars 18 around the cell.

The rail arrangement or current routing is asymmetrical with respect to the cell transverse axis in that substantially more busbars 18 are guided around the end face of the electrolytic cell 10 facing the magnetically predominant row of neighboring cells than around the opposite end face of the cell. Furthermore, the riser line L ₁ facing the magnetically predominant row of neighboring cells leads to the end face of the traverse 20 of the subsequent cell 22, while the remaining risers L ₂ , L ₃ and L _{4 are} connected to the side face of the traverse facing the cell 10. In the present case, all welded connections of the risers to the crossbeam have the same distance both from one another and from the free end face of the crossbeam.

The embodiment of the cell shown in FIG. 4 corresponds - apart from the rail guide - to that of FIG. 3. Here, however, the rails 16, 18 connected to the upstream cathode bar ends 14 are alternately in groups of five individually under the cell and in packets around the cell arranged around. Furthermore, the rail guide is asymmetrical because the busbars 18 carry the current from ten cathode bar ends 14 around the cell on the end facing the magnetically predominant cell row, but only that of five cathode bar ends 14 on the opposite end, and because the risers L ₁ and L ₂ the flow of fifteen cathode bar ends to the closer side of the traverse, the risers L ₃ and L ₄ only carry the current of ten cathode bar ends. Finally, the distance between L ₁ and L ₂ and between L ₃ and L _{4 is} smaller than the distance between L ₂ and L ₃ .

In Fig. 5, the isolated rail guides are shown stylized. From the upstream cathode bar ends 14, the current flows alternately via rails 16 under the cells and via busbars 18 around the cell. The busbars 18 which run around the cell, the flexible bands 30 which take the current off the rails 16 and the rails 26 which take the current off the downstream cathode bar ends, form three large rails which merge into risers L _{1 '} L ₂ and L ₃ and lead electricity to the traverse of the next cell. As can easily be seen from FIG. 5, this arrangement is also asymmetrical.

Claims (9)

1. Bus-bar arrangement for conducting the electric direct-current from the cathode bar ends of a transversely placed electrolytic cell, especially for the production of aluminium, to the transverse member of the following cell, one part of the bus-bars being arranged below the cell, characterised in that in each case at most five bus-bars (16, 18) connected with the upstream cathode bar ends (14) are arranged in alternation individually through (16) beneath the cell (10) and by packs around (18) the cell.

2. Bus-bar arrangement according to claim 1, characterised in that the number of the bus-bars (16) conducted through beneath the cell (10) corresponds to about one quarter of the number of cathode bar ends (14, 24).

3. Bus-bar arrangement according to claim 2, characterised in that in each case one bus-bar (16, 18) connected with the upstream cathode bar ends (14) is arranged in alternation through (16) beneath the cell (10) and by packs around (18) the cell.

4. Bus-bar arrangement according to at least one of claims 1-3, characterised in that the bus-bars (16) leading individually through beneath the cell (10) are combined on the downstream side of the cell in collector bars (26) and - preferably together with the bus-bars (18) conducted around the cell and likewise entering these collector bars and/or the bus-bars connected with a downstream cathode bar end (24) - are conducted to the transverse member (20) of the following cell.

5. Bus-bar arrangement according to claim 4, characterised in that all bus-bars (18, 26) connected with one cathode bar end (14, 24) are combined into 3-6, preferably 4, collector bars which merge into rising leads (L₁, L₂, L₃, L₄) and are electrically conductively connected with the nearer longitudinal side or at least one end side of the transverse member (20) of the following cell (22).

6. Bus-bar arrangement according to claim 4 or 5, characterised in that the same number of bus-bars connected with one cathode bar end (14, 24) enters each of all of the collector bars (26) not lying in the transverse axis of the cell and the rising leads (L) are connected symmetrically in relation to the transverse axis of the cell with the nearer longitudinal side or both end sides of the transverse member (20).

7. Bus-bar arrangement according to at least one of claims 1-5, characterised in that the rising lead (L₁) lying closest by the magnetically dominating neighbouring cell row is connected with the end side of the transverse member (20) of the following cell, while the other rising leads enter the nearer transverse member longitudinal side.

8. Bus-bar arrangement according to claim 7, characterised in that the intervals between the connections of the rising leads (L₁, L₂, L₃, L₄) with the transverse member (20) of the following cell are approximately of equal sizes.

9. Bus-bar arrangement according to at least one of claims 1-5, 7 or 8, characterised in that the rising lead/s (L₁, L2) lying closest to the magnetically dominating neighbouring cell row contain/s more bus-bars (16, 18) connected with one cathode bar end (14, 24) than in the rising lead/s (L₃, L₄) remote from the neighbouring cell row.

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