EA040774B1 - ANODE FOR ELECTROLYSIS OF ALUMINUM - Google Patents

Description

Technical field

The invention relates to an anode, in particular an anode for use in aluminum electrolyzers, comprising an anode body with a first nipple socket for inserting a nipple for connection to a voltage source, the anode comprising at least a first aluminum core and a second aluminum core, which are located inside the anode body to connect to a voltage source.

Background of the invention

When a new pre-baked anode is installed in the cell, a crust of solidified electrolyte forms on the bottom surface (foot) of the anode, which is immersed in the electrolyte bath. This crust melts on the first day after installation in the electrolytic cell and an electric current begins to flow through the anode.

The anode voltage drop U(anode) can be calculated according to equation (1)

SEP (anode) * L * I

U(anode) =--------------/1 where U(anode) - voltage drop;

SER(anode) - electrical resistivity of the anode;

L is the anode height minus half the depth of the nipple seat;

I/A - current density.

For example, with SER(anode)=55 μΩ-m, L=0.6 m and 1/A=0.8 A/cm ² the voltage drop U(anode) is about 260 mV at an early stage in the life of the anode. During the electrolysis process, the anode is consumed, while its height is continuously reduced. Due to the decrease in the height of the anode, the voltage drop also decreases.

As the anode is consumed, the voltage drop across the anode continuously decreases to about 50 mV due to the decrease in the anode height to about 0.2 m. The resulting height will be about L=0.15 m. SER(anode) is reduced to about 44 µOhm-m.

In order to ensure an efficient electrolysis process, the voltage drop U(anode) should be as small as possible also at an early stage of the life of the anode.

An additional problem in the electrolysis process is to achieve an optimized current density distribution. However, due to consumption of the anode, the size of the anode changes during the electrolysis process, thus changing the current density distribution.

The essence of the invention

The object of the invention is to provide an anode belonging to the technical field mentioned at the beginning, which provides a reduced voltage drop, in particular at an early stage of the life of the anode. Furthermore, the object of the invention is to provide an anode with which an optimized current density distribution can be achieved.

The solution according to the invention is characterized by the features of claim 1 of the claims. According to the invention, the first distance between the first aluminum core and the anode base is different from the second distance between the second aluminum core and the anode base.

At an early stage in the life of the anode, the sole of the anode is immersed in an electrolyte bath. At this stage, the first aluminum core is at a first distance from the anode base and the second aluminum core is at a second distance from the anode base. Without prejudice to generalization, the first distance is less than the second distance. Current will flow from the voltage source through the nipple to the first aluminum core because the first aluminum core is closer to the anode base than the second aluminum core. Since the first aluminum core is closer to the anode base than the nipple, the voltage drop U(anode) can be significantly reduced.

As the anode is consumed in the electrolysis process, the first distance L1 between the first aluminum core and the anode sole, as well as the second distance L2 between the second aluminum core and the anode sole, decrease. As the electrode is consumed, the electrolyte bath reaches the lower end of the first aluminum core, and the molten aluminum core will exit the anode. Now the current will flow to the second aluminum core, which is located at a distance L2-L1 from the anode sole. At this point, the second aluminum core is still closer to the anode base than the nipple, whereby the voltage drop is still greatly reduced.

It will be appreciated by those skilled in the art that additional aluminum cores can be placed in the anode, whereby more than two different distances between the aluminum core and the anode sole can be obtained. In particular, 4, 6, 10 or more different distances can be provided, whereby the voltage drop can be further optimized. The main goal is to achieve at each stage of the electrolysis process the smallest possible distance between the aluminum core and the anode sole.

However, although the ideal anode contains many aluminum cores, the actual anode will have fewer aluminum cores in order to control the cost of making the anode.

- 1 040774 yes. The benefit from the reduced voltage drop should be greater than the extra cost of placing the aluminum cores in the anode. In this case, an optimized anode will probably contain about 4-20, in particular about 6-14 aluminum cores. However, more than 20 cores are also possible, in particular if the manufacturing costs of such anodes are not too high. When the anode contains N aluminum cores, there will be 2 to N different distances between the aluminum cores and the anode sole. In particular, there will be several groups of aluminum cores that differ from each other in length, with all aluminum cores from one group having the same length and/or the same distance from the anode base. Alternatively, up to all of the aluminum cores can be arranged such that the distances to the anode base differ from one another. In a further embodiment, a different distribution of aluminum core lengths may be chosen to optimize voltage drop.

Preferably, the aluminum cores are arranged equidistantly around the pin socket. In particular, the anode may contain more than one pin socket, for example 2, 3, 4, 5, 6 or more. In this case, the concentration of aluminum cores between the nipple sockets may be less than outside. The aluminum cores can be located in close proximity to the pin seat, in particular tangentially with respect to the pin seat. In a further embodiment, there may be a radial distance between the pin socket and the aluminum cores, which is bridged, for example, by cast iron or the like. In a further embodiment, the aluminum cores are evenly distributed throughout the anode. The person skilled in the art can determine the ideal arrangement of the aluminum cores in the anode either by calculation or by doing some experimentation.

The total voltage drop U(total) across an anode equipped with an aluminum core is given by equation (2) u(total) = U(Al) + u(anode) where U(Al) is the voltage drop across the aluminum core;

U(anode) - voltage drop in the anode under the aluminum core;

U(total) - total voltage drop.

For example, as in an anode without an aluminum core, with SER (anode) = 55 μΩ-m, L = 0.6 m and 1 / A = 0.8 Asm, the voltage drop U (anode) is approximately 260 mV at an early stage of life anode life, the voltage drop for an aluminum core anode can be reduced by about 120 to about 140 mV early in the life of the anode.

However, as the life of the anode progresses, the resulting difference in voltage drop progressively decreases. The average gain in voltage drop is estimated to be one third of the original gain, i.e. 40 mV for the lifetime of the anode. However, the gain in voltage drop can be even greater, in particular more than 80 mV, for example about 100 mV.

There are three options to take advantage of the average voltage drop gain:

Option 1: reduce power consumption;

Option 2: if additional energy is available, improve performance by increasing current so that the old voltage is obtained;

Option 3: if additional energy is not available, increase the current so that the original energy supply is maintained.

In the case of option 1 and an assumed gain in voltage drop of 40 mV, the reduction in power consumption is 0.13 MWh per 1 ton of Al. In case of option 2, the current can be increased by 1.5%. In case of option 3, the current can be increased by 0.5%.

When the anode is installed in the cell, the heat wave penetrates from the sole and side surfaces into the volume of the anode. When the crust of the solidified electrolyte under the anode melts, the current will predominantly pass from the nipples through the cast iron through the aluminum rods and from them through the remaining anode sole.

The heat from the operation of the cell will increase the temperature in the anode volume above the melting point of aluminum (i.e. 660 ° C), which means that the aluminum will melt, but continue to pass current.

As the anode is consumed by the electrolysis process, the remaining lower part of the anode continuously decreases until the end of the deepest aluminum-filled hole, in particular the first aluminum core, is reached. When this happens, liquid aluminum will flow out of this hole. Accordingly, the current will pass through the remaining holes filled with aluminum and having a smaller depth. This will be repeated until the end of all holes is reached and all of the aluminum has flowed out. After that, the current will pass through the rest of the anode.

As mentioned above, by using aluminum cores in the anode, the current density distribution during the electrolysis process can be optimized. Therefore, two or more aluminum cores can be made with such dimensions and located in the anode so that

- 2 040774 an optimized current density distribution is applied.

Preferably, the length of the first aluminum core is different from the length of the second aluminum core. In this case, in an anode having a cuboid-like shape, in particular a cuboid shape, all aluminum cores can be located in the anode with the same distance from the top of the anode. In this case, the electrical connection to the voltage source can be established in a simple and standardized way for each aluminum core. However, the length of both the first and second aluminum cores may be the same.

Preferably the first aluminum core is located in the first blind hole of the anode body and preferably the second aluminum core is located in the second blind hole of the anode body, the first aluminum core and the second aluminum core being particularly parallel to each other. Meanwhile, the aluminum core can be easily created through a casting process. In alternative embodiments, the implementation of the aluminum core may be located in the grooved hole.

Preferably, the first aluminum core and the second aluminum core are perpendicular to the anode base. In embodiments, in particular if the electrode base is not flat, the aluminum cores may be positioned at a different angle relative to the anode base.

Preferably, the anode has a cuboid-like outer shape, in particular a cuboid outer shape. In this case, the anode can be manufactured in a simple manner. However, the skilled person is aware of several other external shapes suitable for special electrolysis processes.

After the green anode is formed and cooled, the conical holes are plugged with a combustible plug to prevent backfill material from entering the conical hole during anode firing.

After firing, the conical or cylindrical holes are filled with liquid or solid aluminum to the point where the diameter increases (see below).

Preferably the first blind hole is conical or cylindrical. In particular, the blind hole may be formed by a molding process or a drilling process. If carried out by a drilling process, a cylindrical hole is preferred. If performed by a molding process, a tapered bore is preferred.

Preferably, the first blind hole containing the first aluminum core is plugged with a plug, in particular a plug containing cast iron. In this case, the aluminum core can be connected to a voltage source through a nipple. In the first step, the nipple can be inserted into the nipple socket and the aluminum core can be placed in the blind hole. As a second step, the nipple is poured with cast iron (into the gap between the nipple and the nipple seat), while at the same time the cast iron connects the aluminum core in the blind hole and plugs the blind hole. In this case, the electrical connection and plugging of the blind hole can be performed in one step.

The zone with an increased diameter in the upper part of the conical or cylindrical hole is filled with cast iron. When liquid aluminum is poured from the bottom of the hole, the cast iron at the top of the hole serves as a plug to prevent the draft effect in the empty hole.

The anodes are mated with the traverse assembly in the anode-mounting compartment according to the standard procedure and liquid iron is poured into the gap between the nipple sockets and nipples. When performing this operation, liquid iron also flows along an inclined groove into the upper part of the hole with an increased diameter and is fused with the underlying aluminum. To improve the iron-aluminum bond, the aluminum can alternatively be prepared with a hole at the top, which is then filled with liquid iron.

As an alternative to liquid aluminum, solid aluminum rods (rods) can be inserted into conical or cylindrical holes.

Preferably, near the anode head, the conical or cylindrical holes have an enlarged diameter. By this, improved plugging of the blind hole can be achieved.

Preferably, the opening (opening) of the first blind hole is adjacent to the opening of the first pin socket. In this way, a more efficient recycling process can be ensured, since the cast iron connection between the nipple seat and the blind hole is short and therefore more stable. In embodiments, the opening of the first blind hole may be at some distance from the opening of the first nipple seat.

Preferably, the axis of rotation of the first blind hole is parallel to the axis of rotation of the first pin socket. In this case, during the electrolysis process, the nipple is oriented parallel to the aluminum core. In particular, the axis of rotation of the first blind hole during electrolysis is preferably perpendicular to the surface of the molten cryolite/aluminum. However, the first blind hole can also be oriented differently. The orientation depends on the size of the anode, in particular if the goal is an optimized current density distribution.

Preferably, the axis of rotation of the first blind hole is located at a distance from the rotation axis.

- 3 040774 space of the first nipple seat, and this distance is less than twice the diameter of the first nipple seat, in particular, less than the diameter of the first nipple seat. However, this distance can also be greater than twice the diameter of the first pin socket. The placement in the anode depends on the size of the anode, in particular if the goal is an optimized current density distribution.

Preferably, the first groove connects the first pin socket to the first blind hole. This can simplify the pouring process for plugging the blind hole and connecting the aluminum core to the voltage source. However, such a groove can also be excluded.

Preferably, the first groove is inclined from the first pin socket to the first blind hole. Due to this, the cast iron will flow into the blind hole opening under the action of gravity. However, the slope may be rotated from a blind hole to a pin hole, or it may be omitted.

Preferably, the aluminum core contains a cavity into which the cast iron can flow to provide a tighter connection to the plug. However, the cavity can also be excluded.

Preferably, at least the second aluminum core is located inside the anode body in the second blind hole. As a result, the voltage drop can be further reduced. More aluminum cores located in the body of the anode provides a greater reduction in voltage drop. In addition, the current density distribution can be optimized in an improved manner.

Up to 18 conical holes are molded into the body of the green anode next to the nipple sockets. As an alternative to shaped conical holes, up to 18 cylindrical holes can be machined after anode firing. However, more than 18 blind holes can be made in the anode body. The number of blind holes depends on the size of the anode body and the number of nipple sockets.

The number of conical or cylindrical holes depends on the size of the anode and the number of nipple pockets.

Tapered or cylindrical blind holes have different depths up to 650 mm and different diameters up to 100 mm. The size of the blind hole depends on the size of the anode body. The anode current distribution can be optimized by adapting the blind hole diameter. However, blind holes may have large depths and/or large diameters.

Preferably, the second blind hole is connected to the first pin socket via a second groove. In embodiments, the second blind hole may be connected to the first blind hole via a second groove.

Preferably, the first blind hole is longer than the second blind hole. In embodiments, blind holes may have the same length. Preferably the first blind hole is part of a first group of blind holes having the same length and/or the same distance from the anode base. Preferably the second blind hole is part of a second group of blind holes having the same length and/or the same distance from the anode base.

Preferably, the first blind hole has a smaller diameter than the second blind hole. When the end of the first blind hole reaches the melt during the electrolysis process, the aluminum in the first blind hole will pour out. Because the remaining second blind hole of shorter length has a larger diameter, it can compensate for the loss of the aluminum core from the first blind hole. However, the diameter can also be chosen differently.

Preferably, at least one of the following is balanced to achieve an optimized current density distribution when used in an aluminum electrolysis process:

aluminum core diameter;

aluminum core length;

location of the aluminum core in the anode.

Preferably, the anode may comprise at least a second pin socket. In particular, the anode may comprise a plurality of nipples arranged in one or more rows, and the like. In embodiments, the anode may contain only one nipple socket. Preferably, each nipple is electrically connected to at least one aluminum core. In embodiments, one or more nipples are not electrically connected to the aluminum core. Preferably, each aluminum core is electrically connected to exactly one nipple. However, the aluminum core can also be electrically connected to more than one nipple.

Preferably, the length of the longest aluminum core is between 60 and 95%, in particular between 70 and 80% of the height of the anode body. In embodiments, the length of the longest aluminum core may be more than 95% or less than 60% of the height of the anode body.

Preferably, the length of the shortest aluminum core is between 30 and 60%, in particular between 40 and 50% of the height of the anode body. In embodiments, the length of the shortest aluminum core may be more than 60 or less than 30% of the height of the anode body.

In a method for manufacturing an anode comprising an anode body with a nipple seat for inserting a nipple

- 4 040774 for connection with a voltage source, an aluminum core is placed inside the anode body for connection with a voltage source.

Preferably, after making a blind hole in the anode body, the aluminum core is placed in the blind hole.

Preferably, the blind hole and the nipple seat are created in one step by means of a forming press. Alternatively, a blind hole is created through a drilling process.

Preferably the blind hole is filled with molten aluminium, preferably molten aluminium, having the same quality as that produced in the smelter where the anode is used. Alternatively, other grades of aluminum may also be used. Preferably, the blind hole is filled with high purity molten aluminum, more preferably greater than 99% by weight purity. In embodiments, the blind hole is filled with an aluminum bar, preferably a high purity aluminum bar, more preferably greater than 99% by weight purity. In addition, blind holes can be filled with aluminum granules and heated to the melting temperature. Alternatively, the purity of the aluminum may be less than 99% by weight.

In the method of producing aluminum by aluminum electrolysis, the aluminum core of the anode is electrically connected to a voltage source.

In an anode and nipple design, the nipple is inserted into a nipple socket in the anode body and the nipple is in electrical contact with the aluminum core.

Other advantageous embodiments and combinations of features will become apparent from the following detailed description and the entire claims.

Brief description of the drawings

The drawings used to explain the embodiments show FIG. 1a is a plan view of an example of an anode;

fig. 1b is a sectional view of FIG. 1a taken along the line A-A and FIG. 1c is a sectional view of FIG. 1a, made along the line B-B.

In the figures, like components are identified by like reference numerals.

Preferred Embodiments

Fig. 1a shows a plan view of an example of anode 1. Anode 1 is box-shaped. The anode 1 has a height of 650 mm, a length of 1625 mm and a width of 780 mm. It contains three nipple sockets 20, 21, 22 in a row, having a diameter of 190 mm. The nipple (not shown) has a diameter of 160 mm. The gap between the nipple and the nipple socket is filled with liquid iron.

In addition, each nipple seat 20, 21, 22 is connected to a blind hole through a groove. The pin socket 20 is connected to three blind holes 30, the pin socket 21 is connected to four blind holes 31, and the pin socket 22 is connected to three blind holes 32.

Each blind hole 30, 31, 32 has an enlarged diameter at the top of the anode 1. In a first step, the blind holes 30, 31, 32 are filled with aluminum, in particular liquid aluminum or solid aluminum bars. Then the nipples are placed in the nipple seats 20, 21, 22. Then the gaps between the nipples and the nipple seats 20, 21, 22 are filled with liquid iron. Cast iron flows along the grooves into the area of blind holes 30, 31, 32 with an increased diameter. This establishes an electrical connection between the nipple and the aluminum core. In addition, blind holes 30, 31, 32 are clogged.

Fig. 1b shows a sectional view of FIG. 1a, made along the line A-A. As can be seen, the lengths of the blind holes 30.1 and 30.2 are different. The blind hole 30.1 has a distance L1 to the bottom of the anode 1, while the blind hole 30.2 has a distance L2 to the bottom of the anode 1. During the consumption of the anode 1, the bottom of the blind hole 30.1 will be reached and an aluminum core (not shown) will flow out of the hole 30.1 . Current will now flow to the second aluminum core in blind hole 30.2. At this stage, the distance from the second blind hole 30.2 to the sole of the electrode will be L2-L1. In addition, the length of the blind holes 31 and the length of the blind holes 32 are different. During the electrolysis process, most of the current will flow to the longest aluminum cores, since there is the least resistance. The height of the anode 1 is reduced. The end of the longest blind hole will be reached first, causing the aluminum to pour out of that blind hole. Because the top of the blind hole is plugged, the draft effect can be avoided. The remaining aluminum cores will be reached and poured later. Finally, the current will pass through the nipple through the rest of the anode 1.

Fig. 1c shows a sectional view of FIG. 1a, made along the line B-B. As can be seen, the blind holes 31 associated with the pin socket 21 have three different lengths. They have lengths of 500, 400 and 300 mm.

To achieve an optimized current distribution during the electrolysis process, the number and position of pin sockets, the number and position of blind holes and aluminum cores, and the dimensions of pin sockets and blind holes can be optimized.

- 5 040774

However, in other embodiments, the implementation of the anode 1 may have other forms known to a person skilled in the art. Blind holes may have other diameters. The length of blind holes may vary. The number of blind holes per nipple socket may vary. In addition, the number of pin sockets in the anode 1 may vary.

In summary, it should be noted that an anode has been provided for the production of aluminum by means of an electrolysis process, with which the voltage drop can be reduced, at least at an early stage of the life of the anode. In addition, by adjusting the diameter and length of the blind holes, the current distribution can be influenced.

Claims (14)

1. An anode, in particular an anode for use in aluminum electrolyzers, comprising an anode body with a first nipple socket for inserting a nipple for connection to a voltage source, the anode comprising at least a first aluminum core and a second aluminum core, which are located inside the anode body for connection to a voltage source, characterized in that the first distance between the first aluminum core and the anode sole differs from the second distance between the second aluminum core and the anode sole. 2. The anode according to claim 1, characterized in that the length of the first aluminum core is different from the length of the second aluminum core. 3. The anode according to claim 1 or 2, characterized in that the first aluminum core is located in the first blind hole of the anode body and preferably the second aluminum core is located in the second blind hole of the anode body, while the first aluminum core and the second aluminum core are, in particular , parallel to each other. 4. The anode according to any one of claims 1 to 3, characterized in that the first aluminum core and the second aluminum core are perpendicular to the anode sole. 5. An anode according to any one of claims 1 to 4, characterized in that the anode has a cuboid-like shape. 6. The anode according to any one of claims 3 to 5, characterized in that the first blind hole containing the first aluminum core is plugged with a plug, in particular a plug containing cast iron. 7. The anode according to any one of claims 3 to 6, characterized in that the opening of the first blind hole is adjacent to the opening of the first nipple socket. 8. The anode according to any one of claims 3 to 7, characterized in that the axis of rotation of the first blind hole is parallel to the axis of rotation of the first nipple seat. 9. An anode according to any one of claims 3 to 8, characterized in that the first groove connects the first pin socket to the first blind hole. 10. The anode according to any one of claims 3 to 9, characterized in that at least the second aluminum core is located inside the anode body in the second blind hole. 11. The anode according to claim 10, characterized in that the first blind hole is longer than the second blind hole. 12. The anode according to claim 10 or 11, characterized in that the first blind hole has a smaller diameter than the second blind hole. 13. The anode according to any one of claims 1 to 12, characterized in that at least one of the following parameters is balanced to achieve an optimized current density distribution when used in an aluminum electrolysis process: aluminum core diameter; aluminum core length; location of the aluminum core in the anode. 14. A method for manufacturing an anode, in particular manufacturing an anode according to any one of claims 1 to 13, comprising an anode body with a nipple socket for inserting a nipple for connection to a voltage source, wherein an aluminum core is placed inside the anode body for connection to a voltage source.