DE1802787A1 - Method for limiting an anode effect in an electrolytic cell for the production of aluminum - Google Patents

Description

The invention relates to a method for limiting an anode effect in an electrolytic cell Manufacture of aluminum.

The metal aluminum is obtained from aluminum oxide, such as Al ₃ O ₅ , by electrolysis from a molten bath or electrolyte. When aluminum is extracted using the conventional electrolysis process, commonly referred to as the Ha11-Heroult process, the electrolytic cell consists essentially of a steel container with a carbon lining on the inside. The bottom of the carbon lining, together with a portion of electrolytically generated molten aluminum, which accumulates in it during operation,

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the cathode. One or more consumable carbon electrodes extend from the top of the cell, which with their lower ends in a slide of molten material Immerse the electrolyte in the sieve in the cell. In operation, the electrolyte or bath is a mixture Made of an alumina and cryolite, you cell is filled, and an electric current is fed from the anode to it The cathode is passed through the cell via the sliding part of the molten electrolyte. The aluminum oxide wire! through the Stream split, leaving aluminum on top of the liquid Deposited aluminum cathode and oxygen. the carbon a node is released, the Koblenstoffraonoxid- and Carbon dioxide gas forms. On the surface of the bath It forms a crust of solidified electrolyte and aluminum oxide, and this crust is arched with additional Covered with aluminum oxide.

In the conventional electrolysis processes were two types of Slektrolysesellen used, and. was once those who work with prefabricated anodes and those who commonly known as the Söderberg cell. At seder the Cells run the reduction process exactly the same chemical Reactions. The fundamental difference is there in construction. In the prefabricated cell, the carbon anodes are burned before installation in the cell, while with the Söderberg cell the anode is in place

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ORIGINAL INSPECTED

"- 3 - ■ - ■ ■■ ■ '■■ - ■■■ - ■■' - ■ '': ■■: '-

is burned, d. i.e., it will -during operation of the Electrolytic cell burned, with part of the through the Reduction process generated heat is exploited. The present invention seeks both types of Cells.

A solvent used in conventional commercial plants typical Aluminiumelektrolysebad nos have the following composition: 1 to 10 56 alumina, 0 to 10 # Aluminiumtrif tetrafluoride, 5 to 12 id 56 calcium fluoride and 80 to 90 $ cryolite. While the electrolysis takes place, aluminum oxide is consumed in proportion to the metal produced. As the concentration of alumina in the cryolite decreases, a point is reached at which an uncomfortable phenomenon known as the anode effect occurs. > The voltage drop across the cell can e.g. B. from about 4 YoIt up to 40 YoIt and even higher. This effect is usually associated with an insufficient concentration of aluminum oxide in the bath or electrolyte of the reduction cell. The actual concentration of the aluminum oxide in the electrolyte at which this effect occurs appears to depend on the temperature of the composition of the electrolyte and the anode current diodes. The occurrence of the anode effect is the signal for the addition of more aluminum oxide. This is done by the keeper breaking through the frozen crust on top of it

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BATH ORIGINAL

he asked beforehand a pad of alumina distributed. That Adding alumina as well as stirring vigorously of the electrolyte makes the anode effect disappear, where the electrolysis continues its normal course until the next anode effect occurs.

Hit the anode effect has several adverse consequences connected, so that it is highly desirable, to terminate such an effect as soon as possible and restore normal operating conditions. During the During the normal course of electrolysis, the lower working surface of the anode is surrounded by gas bubbles which are similar in shape exude from it. They appear to form on the anode, easily peel off and leak from the electrolyte. A steady flow of gas around the anode is an indication of normal work. The moment the anode effect occurs, the lower one appears Working surface of the electrode to be completely surrounded by a film of gas. This envelops the surface of the anode and pushes the molten electrolyte or the bath away, creating a so-called non-wetting or The anode is drained. Small sparks form between the electrolyte and the anode. A complete There is no interruption in the current as a certain amount of current flows across the blob of continually displacing sparks. The sparks cause local heating, which causes something

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Bath material evaporates, but enough gas is generated, see above that individual sparks are extinguished practically immediately. Seven new sparks form because the pin is in the hub of the anode is necessarily uneven in nature, and instantaneous contacts occur between the anode and the bath. This overheating leads to a very quick one Consumption of the anode. A very significant undesirable consequence of the anode effect is a major unproductive one Power consumption

In addition to the manual method mentioned above, the prior art already contains many attempts at anode effects to settle or terminate very quickly * Some of these previously known Vereuobe were very unusual, which is an indication for the difficulty of the problem is that couple people were willing to use such extreme procedures to deal with this situation.

British patent specification 855 056 describes a method in which a sounding vibrator is used to terminate Anode effects was used. It is not specified how the anode effect should be eliminated. Louis Perrand in US Pat. No. 2,560,854 describes a method for Termination of an anode effect, according to which the anodes slowly move between a lean area in the electrolyte a raiobaran Bereioh (pure aluminum oxide) bin and hereobwlngan · Deduroh is angtbliob da · Aluminum oxide In

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mixed better in the bath, which contributes to the termination of the anode effect. It is easy to imagine the inconvenient facility required to carry out such a procedure . Presumably the swinging movement of the anode allows gas bubbles to escape from the lower side. A more uniform © current density for the cell is claimed as a result of this interesting process.

Robert J. Oooper in US Pat. No. 2,930,746 discusses the manual process described above and points to other practices that may be used "including violently breaking up the metal in the aluminum can below the anodes for brief bursts from the anode produce aluminum au. This cools the gases and distributes them, so that they can escape better. A lowering of the anode up closer to the surface of the molten aluminum is applied also to the anode effect quench. " He then proposes a control system with voltage, current and temperature control, so that the anode increases or decreases depending on the need in order to keep these variables at predetermined operating values. In the Pattntaobrlft it is asserted that these procedures also terminate anodic discharge.

With the task of unloading, a tlnfaoiar ·· uni are very effective

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^11111; · ■;.;: ;;: aiiiiniii ¹¹ : ¹ :.::; Ι is

To create termination of anode effects.

The object on which the invention is based is permanently achieved in that when the voltage across the cell drops by more than 150 j> the normal operating value, the anode of the cell is lowered, over the distance between the anode and cathode of the cell to about 30 to 60 degrees that the concentration of the available Aluminiumoxidβ is in the bath at about 2% to about 6 i "of öewiohts set, and in that the anode is raised to restore the normal distance zwieohen anode and cathode, whereby the anode effect to reduce normal Arbeltsentfernung, is terminated.

When the method according to the invention is used, more than 90% of all anode effects can be ended very easily. According to the method, it is determined when the voltage drop across the cell exceeds and when that level is reached about 150 # of normal operating value. Then, the anode of the cell is lowered to the anodes Katfaoden-removal to reduce in the cell at about 30 to about 60 i "of the normal operating distance, preferably not more than about 51 1> · The available to concentration of aluminum in the bath is reduced to about 2 to about 6 $> dee öewiohts dee bathes. The anode is raised again to restore normal anode-cathode removal, and after the raising is that

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Anode effect "ended and normal operation resumed.

The etefaeude lonaentretion. of the aluminum oxide in the bay or the electrolyte can be adjusted by placing a quantity of aluminum oxide on the knee above the electrolyte for the cell and breaking the crust so that the aluminum on it gets into the electrolyte -BohiefleaBten Yerfabrin was applied to give alumina blnsstizia. The aluminum oxide can be added to the electrolyte before lowering the anode, while lowering the anode, after lifting the anode or even after lifting the anode of the cell. An "eekiÄßigee" experience consists in adding small amounts of aluminum oxide to the bath and thus preventing the dissolution in it and the formation of silt on the cathode, in which at least one part of the aluminum oxide is close to the surface The anode of the cell is placed in the electrolyte »The expression ^B Sobliek ^w is tate a collection of aluminum oxide and other bath constituents meant, which also form the carbon dioxide and the total amount of oil and the working of the cell and the purity of the recovered metal can affect »'

A convenient facility for ending a Anodeneff @ ktee according to the present invention has

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first of all a suitable remedy, such as a voltmeter to measure the voltage drop across the cell and to signal when the voltage drop occurs above the cell about 150 # of the normal operating value exceeds. This signal initiates the function of the system.

Means, such as a lift motor for the anode, lower the anode or anodes of the cell when voltage signals occur, in order to reduce the anode-cathode distance in the cell to about 50 to about 60 $> the normal operating distance. The concentration of available alumina in the cell is adjusted to about 2 to about 6 weight percent by other means responsive to the voltage signal. Finally, means are provided to lift the anode and restore normal anode-cathode removal.

The invention is to be explained in more detail in connection with the drawing on the basis of an exemplary embodiment.

Pig. 1 is a graphic representation of FIG

Total percentages of the finished anode effects depending on the remaining ones Percentage of normal anode-to-cathode removal after lowering the anode,

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Pig. 2 shows a circuit diagram of a possible embodiment of a device for terminating anode effects, - Pig. 5 shows the Io okentakt sequence of the device according to Property 2 for the termination of anode effects.

There has been a series of attempts ssur development of the Invention carried out »3The used in the Versuohen. Cells were commercial 72,000 ampere cells, which were

"Work for about 5 volts. All the Yersohen got a ToItmeter used to measure the voltage drop across the cell. In the initial attempts, if the Voltage drop across the cell about 130 # dee normal Operating value was, a motor energized, which lowered the anode and so the anode-cathode distance to approximately 55 # normal value decreased. Feed means were activated once every ten seconds at the onset of the anode effect, so that about 30 pounds of aluminum

Were) added oxide in the cell, whereby the concentration was increased to about $ 2> to about 6 i 'weight, while the anodes were lowered within 19 seconds, naohdem the anode effect had occurred. A push-rod was actuated, after which the aluminum oxide was applied to the crust above the electrolyte of the cell, and the aluminum oxide in the electrolyte

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Iyten. or to give the bath. Then, the lifting motor for the anode -was energized to the anode to increase and the Oden A _n-Eatboden removal to be brought into the vicinity of the KormaIeInetellung · This result is shown at point A in FIG. 1.

During the next tests, the lift motor for the anodes lowered them so that the anode-cathode distance in the cell was reduced to no more than 16 ^ of the normal operating distance. This occurred within 15 seconds of the signal appearing, but the cell's voltage drop exceeded approximately 130% of normal working value. The feed means were actuated two times after the anode effect began at 10 second intervals to deposit a measured amount of alumina (approximately 60 pounds) on the stem above the electrolyte of the cell. The crowbars for breaking up the erusts were operated after six actuations of the feed and then again after twelve actuations of the feed, whereby the erusts on the electrolyte of the cell were broken and the aluminum oxide on the erusts was thus led into the electrolyte. The anode lift motor was operated 100 seconds after the anode effect began to raise the anodes and restore essentially normal anode-to-cathode removal. Of 333 recorded anode effects were

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74 % completed successfully, as shown at point B in flg. 1.

When näobeten grater τοη Try the anode Kathodea-Sntfernung was further Terri Gert, on niobt Nebraska ale about 41 i> normal Working Distance. The crowbar turn breaking the Iruete were each after three Speieeeitte! Actuations once operated. The anode-to-cathode distance was left at the reduced value for approximately 155 seconds before the anode was raised again and essentially normal anode-to-cathode distance was restored. In this and the following periods, the device was actuated when the voltage drop across the cell exceeded approximately 150 Ji of the normal operating value. Sound 81 recorded anode effects were 77 or approximately 95 1> successfully completed. This is plotted in funct .0 in FIG. 1.

In the next tests, the setting of the anode-cathode distance was the same as in the Versnoben in point B in 71g. 1 are given. The differences EWlso the experiment B and these experiments, The experiments D are the following as the food means were Press the sieve evenly to add 85 pounds of τοη aluminum oxide bineu- ■ u. The crowbar was sun breaking the crust actuated five times and the anode-cathode distance was left at the reduced value for 155 seconds.

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Yon 90 recorded anode effects were terminated jo 84 or about 93 erfolgreiob how the iet applied at the point B in Fig,. 1

Trials S doubled the features of the Versuobe C, except that the anode lift motor was operated to reduce the anode-cathode distance to about £ 51 the normal anode-cathode distance and became the crowbar for the crust actuated five times. This process ended erfolgreiob 95 f> all identified anode effects, such as at point S in Pig. 1 is applied.

During a further exploratory period to determine the desired reduction in anode-cathode distance for consistent termination of anode effects, 97 % of anode effects were terminated. The minimal reduction in anode-to-cathode distance required to successfully complete an anode effect was not more than £ 81 of the normal operating distance. Most of anode effects were terminated erfolgreiob when the anode-cathode distance as about 40 j> the normal operating distance was reduced to nioht meftr, and 99% were erfolgreiob ended when the distance nioht more "1" about £ 30 normal Working distance decreased * £ 1 · Data obtained during this period will be obtained when plotting in Tig. 1 used Joreel.

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A schematic circuit for a device for ending anode effects using the method according to the invention is shown in Hg, 2, and PIg. 3 shows the hook timing sequence of the device. Hallway means lowers the anode of the cell to the anode Katboden-Entftcnung in the cell at about 30 to about 60 ia the normal Working Distance and preferably to not more than 51 fi normal working distance to be reduced. The concentration in the lad of the available Aluminiumoxidβ is adjusted to the desired value in the range of about 2 i "to about 6 ^ weight, by feeding the alumina in quantities which are 17 individual quantities each of 5 pounds in this Ausfübrungsbeispiel wherein the first individual amount of the aluminum oxide is applied essentially on the same side as the anode is lowered onto the crust and the last amount of egg gel is added when the anode is raised. The crust on the electrolyte of the cell is broadened by a Breoh rod five times during this series of electrolytes. The device is dimensioned in such a way that sia comes into operation when the voltage drop across the cell exceeds 150% of the normal operating value. At the moment the cycle motor is activated, and IU οIge of various processes, as can be seen from the topic drawing and the nook clock sequence

■ Ind. This method at 51 £ the normal setting of Anodeu-cathode distance deletes at least 95 i "from all anode effects which occur in a normal operation of a reduction cell.

Aue of this series τοη versnoben and the data given it can be seen that the essential factor in ending τοη anode effects by reducing the anode-cathode distance is that the final anode-cathode distance is reduced enough to make the effect disappear bring to. It has geBeigt found that a reduction of the anode-cathode distance on not in 95% of cases * slg leads more than about 51 i> the normal operating distance to the south. The smallest reduction in the anode-cathode distance, which ensures an acceptable reliability, for example 95 J ^, is two-rate in order to keep the disturbance of the bath level low. You feed τοη aluminum oxide into the bath as a final step in the process supports the anode effect limits. The added aluminum oxide, when dissolved in the bath, favors the return of the cell to normal electrolysis. The amount of aluminum added to the bath should not be more than the bath can dissolve in order to prevent the formation of soils on the cathode. You device to limit the anode effect and the method described require enough aluminum oxide to return τοη

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! node tie fell to prevent. The improved regulation The aluminum oxide forms the means to free the eatbode Keeping tone Sobliok. The prevention of Sohliok at the Eatbode leads to an improved work efficiency.

The crust deposition over the bath of a cell or a crucible with an anode effect remains essentially completely intact if the anode effect is regulated very quickly and if an excessive anode setting is not thermoset. If the anode effect is immediately terminated, the heat balance remains stable over the row of reduction cells, and the cells need to be paid less attention in order to ensure that the cell functions properly. The value of the mean load on the feed line is increased when anode effects are terminated quickly and effectively. Table I shows the mean load gain on the feed line for systems and methods according to the invention for terminating anodes ff eleventh. It is ersiobtlioh that a successful son elle termination of anode effects erhöbt the value of the average) load on the supply line without increasing the power supplied · The increase in the current strength of the reduction cell without additional costs below an increased yield.

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Table I.

Enlargement of the average load on the feed lines with a device for ending the anode effect

Operating values of the feed line above the device to end the anode effect

amp ZW / crucible Anode effects / Crucible day A. 71,609 373.5 .51 B. 72.274 374.6 .47 C. 72.064 373.7 .49 D. 71.962 373.7 .47

medium 71.977

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• 485

Operating values of the feed line with device to limit the anode effect

E.
P.
G
H

amp

72,694 72,083 72,421 72,337

medium 72.451

KW / crucible

375.8 371.4 372.2 372.0

372.85

Anode effects / crucible day

.53 .40 .41 .54

.470

The increase in the ampere mean of 474 amps as shown in shown in this table is achieved with no increase in energy cost and with a decrease in labor requirements of the crucible space. This improvement in the mean load on the feed line of the crucible is therefore «Ögliob,

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because the anode effects are terminated immediately and successfully.

An immediate successful termination of the anode effect according to the invention saves the hard physical exertion normally required of the crucible people. This reduction in the need for hard labor reduces the amount of human energy required to operate a row of crucibles. "The crucible people's work position can be performed without undesired interruptions to terminate anode effects." Less than an anode effect of 20 will require manual termination. Only a few of the hand-terminated anode effects require more than a small amount of agitation as mentioned earlier in connection with the Oooper patent. The sealing people will be able to take on other tasks % u without having to stop and end an anode effect.

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Claims (10)

ri - ■ '' - ■■■■■ patent claims 1. A method for limiting an anode effect in an electrolytic cell for the production of aluminum, characterized . DAB is lowered, the anode of the cell at the voltage drops across the cell by more than 150 Jt of noraalen operating value, Utah the! distance between the anode and cathode of the cell to approximately 30 i »to 60 j> of the normal Working Distance to Terringerη that the The concentration of the available aluminum oxide in the bath is adjusted to about 2 to about 6% of the normal, and that the anode is then raised to restore the normal distance between anode and cathode, whereby the anode effect is terminated. 2. The method according to claim 1, daduroh characterized in that the concentration of the available aluminum oxide in the bath is set daduroh, dafi an amount of aluminum oxide is given on the crust above the electrolyte of the cell, and that then the crust on the electrolyte Cell is broken through, so that the aluminum oxide placed on it gets into the electrolyte. SI / Si -20- 909819/0851 3. Device for ending an anode effect in an electrolytic cell for the production of aluminum, characterized in that means are provided for measuring the voltage drop across the cell which emit a signal when the voltage drop across the cell exceeds approximately 150 # of the normal operating value, that means are provided which are responsive to the voltage signal and lower the anode of the cell accordingly in order to reduce the anode-cathode distance in the cell to about 30 # to about 60 $> the normal operating distance respond to the voltage signal and regulate the concentration of available alumina in the cell to about 2 % to about 6 # of weight, and that means are provided to raise the anode and restore normal anode-cathode removal, thereby creating the anode effect is terminated. 4. The method according to claim 2, characterized in that the aluminum oxide is added to the electrolyte before lowering the anode of the cell. 5. The method according to claim 2, characterized in that the aluminum oxide is added to the electrolyte after lowering the anode of the cell. -21- 909819/085 1 6. The method according to claim 2, characterized in that the aluminum oxide is added to the electrolyte after lifting the anode of the cell. 7. The method according to claim 2, characterized in that the aluminum oxide is added gradually to the electrolyte in order to facilitate its dissolution and to prevent the formation of silt on the cathode. 8. The method according to claim 7 » characterized in that at least part of the gradually added aluminum oxide is added to the electrolyte before lowering the anode of the cell, and that at least a further part of the gradually added aluminum oxide after lowering the anode of the cell is added to the electrolyte. 9. The method according to claim 2, characterized in that the aluminum oxide is added to the electrolyte while the anode of the cell is being lowered. 10. The method according to claim 1, characterized in that the anode of the cell is lowered so that the anode-cathode distance in the cell is reduced to no more than about 51 # of the normal operating distance. 909819/0851