Title of Invention

FOLDED CURRENT OUTFLOW SIDE BUSBAR ARRANGEMENT

Abstract

Folded Current Outflow Side Busbar Arrangement Around Electrolytic Cell A folded current outflow side busbar arrangement for an electrolytic cell, comprising a cathode busbar (1; 11) of an upstream electrolytic cell, a riser busbar (2; 12) of a downstream electrolytic cell9 and a substantially horizontally or vertically folded busbar (3; 13) connecting the cathode busbar (1; 11) with the riser busbar (2; 12), thereby respectively forming the folded busbar section extending substantially horizontally or vertically.

Full Text

FPME05140036IN Folded Current Outflow Side Busbar Arrangement Around Electrolytic Cell Technical Field of the Present Invention The present invention relates to a folded current outflow side busbar arrangement around an electrolytic cell for aluminum electrolysis production. Background Art of the Present Invention At present, as electrical current intensity of high amperage pre-baked electrolytic cells gradually increases, the influence of the magnetic environment on the molten mass within the electrolytic cell becomes more and more significant to aluminum electrolysis production. In the prior art, the magnetic environment on the molten mass within the electrolytic cell can be configured and compensated by respective cathode busbars so as to decrease the average value of the vertical component of the magnetic field to the order of magnitude of a few gausses, thus realizing the stable aluminum electrolysis production under the high current situation. However, the configuration and the design of the magnetic field are based on the presupposition that the electrical current distributed into the cells and respective conductor sections is in an ideal condition. On the contrary, if the deflection of the current distribution occurs under practical circumstances, the magnetic field on the molten mass within the electrolytic cell tends to change. It is desirable, therefore, to ensure that the electrical current distribution in respective busbar sections of the busbar system for the electrolytic cell conforms to the design requirements as much as possible. This is very important to achieve the expected magnetic field effects. In the busbar arrangements of the busbar system around the electrolytic cell, the current inflow side and the current outflow side cathode busbars are used to introduce the current flowing out of a cathode within the electrolytic cell to a riser busbar for a downstream electrolytic cell Due to the particularity on the configuration of the electrolytic cells, the current outflow side cathode busbar is positioned closer to the riser busbar for the downstream cell than the current inflow side cathode busbar, giving rise to the considerable difference in these two electrical current paths. During the aluminum production, it leads to excessive current accumulated towards the current outflow side, inducing the so called "bias current*', which is detrimental to the desired magnetic environment based on the design requirements and the stable operation of the electrolytic cell. One proposed approach to suppress the deviated current is to decrease the cross-sectional area of the current outflow side busbar. Although reducing the required material for busbars, this approach causes higher current density and temperature in the current outflow side busbar as well as higher voltage drop across the busbar system. From a veiwpoint of economical efficiency and safety for longtime operation, it has many disadvantages. Therefore, there is still a need in the aluminum electrolysis production industry to provide a improved current outflow side busbar arrangement around the electrolytic cell Summary of the Present Invention Therefore, an object of the present invention is to provide a improved current outflow side busbar arrangement for an electrolytic cell for aluminum electrolysis production, which overcomes the above problems of the prior art. Another object of the present invention is to eliminate or at least alleviate the unbalanced electrical current between the current outflow side and the current inflow side, thus ensuring the stable operation of the electrolytic cell A further object of the present invention is to provide a compact electrolytic cell and a reduced spaced distance between the electrolytic ceil rows, lowering both the investment cost and the installation cost According to the preferred aspect of the present invention, the above objects are accomplished by providing the folded current outflow side busbar arrangement for the electrolytic cell, comprising a cathode busbar of an upstream electrolytic cell, a riser busbar of a downstream electrolytic cell, and a substantially horizontally or vertically folded busbar connecting the cathode busbar with the riser busbar, thereby respectively forming the folded busbar section extending substantially horizontally or vertically. The term "folded busbar" hereby used is meant to include any suitable portion that connects the cathode busbar and the riser busbar in an indirect or non-straight way, e.g,, folded parts, bended parts, wound parts, or combinations thereof. For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims taken in conjunction with the above described drawings. Brief Introduction of the Drawings FigJ is a schematic view of the overall structure of the electrolytic cell; Fig. 2 shows the first embodiment of the current outflow side busbar arrangement according to the present invention, with the vertically folded busbar connected to the cathode and riser busbars; Fig, 3 shows the second embodiment of the current outflow side busbar arrangement according to the present invention, with the horizontally folded busbar connected to the cathode and riser busbars; Fig.4 shows a current profile for the conventional current outflow side busbar arrangement wherein the cathode busbar is directly connected to the riser busbar; and Fig. 5 shows a current profile for the current outflow side busbar arrangement of the present invention wherein the cathode busbar is connected to the riser busbar via the present horizontally folded busbar. Modes for Carrying out the Present Invention As shown in Fig. 1, an aluminum electrolytic cell generally having a rectangular shape is provided with a current inflow side of the electrolytic cell and a current outflow side of the electrolytic cell, i.e. a side A and a side B as shown. Within the electrolytic cell a molten cryolite-based electrolyte and a molten aluminum are contained at a temperature of around 900-1000 °C At the side A is disposed a riser busbar, from which an electric current flows into an anode beam positioned at upper portion of the electrolytic cell in the longitudinal axis of the electrolytic cell The anode beam evenly distributes the current into carbon anodes immersing in the electrolyte at the side A and B of the anode beam, thereby occuring the chemical reaction with the electrolyte to form the molten aluminum which at regular intervals is drawn out of the electrolytic cell by means of dedicated devices (not shown). At the lower portion of the electrolytic cell, at the side A and B the current flow out of the electrolytic cell via carbon cathodes having built-in steel rods. The current converge at a riser busbar of a neighbouring cell via cathode busbars positioned surrounding the electrolytic cell The electrolytic cells are arranged into such a side by side configuration that the current flowing from a cathode for an upstream cell to an anode for a downstream cell. The concept of the present invention is that, in order to overcome the above described disadvantages caused by the direct connection between a cathode busbar of an upstream electrolytic cell and a riser busbar of a downstream electrolytic cell, it is desirable to fold the current outflow side busbar which connect with the cathode busbar and the riser busbar around an electrolytic cell After a great deal of experiments and investigations conducted by the present inventors, they have foimd that by folding the current outflow side busbar, the bias current, which caused by the unbalanced current at the current outflow and inflow sides, within tie current outflow side busbar is significantly surppressed. Although presently it is not very exactly clear what reasons, factors, or means lead to such a favorable result, the present inventors suppose that as a result of the current outflow side busbar which is located around an electrolytic cell is structured as above folded configuration or arrangement, thereby increasing the current path length of the current outflow side busbar and thus the resistance and impedance thereof For this reason the improved distribution of the inflowing current and the outflowing current is obtained, and consequently the better balanced current flowing through the current outflow side busbar is also achieved. It should be noted that in this connection, however, the present invention is by no means bound to or limited to such an explanation. The present inventors also assume and suppose that by folding the current outflow side busbar, the current flowing therethrough is defined to the back and forth direction, the magnetic environment caused thereby in the electrolytic cells facilitates to prevent the excessive current being accumulated to the current outflow side busbar, thereby obtaining the desired current distribution. In first embodiment of the present invention, the current outflow side busbar arrangement shown in Fig. 2 comprises a cathode busbar 11 of an upstream electrolytic cell, a riser busbar 12 of a downstream electrolytic cell, and a substantially vertically folded busbar 13 connecting the cathode busbar 11 with the riser busbar 12. The direction of the current flowing through the current outflow side busbar arrangement is shown by arrows in Fig, 2, In such a busbar arrangement constructed as above, the vertically folded busbar 13 can be made as an integral body. Alternatively, the vertically folded busbar 13 can also be not formed as one piece. In this case, a plurality of substantially vertically extending busbar sections 13 can be coupled together by a connecting plate 14 by means of known methods in the art, such as welding, as shown in Fig. 2. The plurality of busbar sections 13 may be made of the same or different materials, so as to at different locations in the cell achieve the same or different degreee of preventing the bias current. Also, the resultant folded busbar 13 composed of busbar sections can be I directly coupled to the cathode busbar 11 and the riser busbar 12, alternatively can be coupled therewith via connecting plates which are located respectively between the folded busbar 13 and the cathode busbar 11, and the folded busbar 13 and the riser busbar 12. In a typical 320KA series electrolytic cell, to obtain the good performance of balancing the current between the current outflow and inflow sides, the folding number of the folded busbar 13 is 3 or 4. If the folding number is below 33 the good performance can not be attained. On the other hand, if the folding number is above 4, the size of the electrolytic cell will be disadvantageous^ increased, as described later. However, this type of the current outflow side busbar arrangement for the electrolytic cell may not be the optimum for ensuring the better performance while keeping the required space thereof minimized. It is known that the current density in the busbar is needed to set within a predetermined range. For the purpose of this, the cross-sectional area of the busbar can not be made too small, which inevitably increase the distance between the cathode busbar II and the riser busbar 12, as well as the width of the electrolytic cell viewed from the end. Such increased distance and width certainly will be added to the distance between the electrolytic cell rows. From a veiwpoint that reducing the investment cost and the installation cost, the occupied area of the electrolytic cell and the distance between the electrolytic cell rows should be kept as small as possible. Therefore, the current outflow side busbar arrangement shown in Fig, 2 is not preferable when the size and spacing requirements are more important, although it is good at preventing the bias current. According to the another aspect of the present invention, based on the experiments and the investigations made by the present inventors, they have further found that in the event of that the current outflow side busbar is substantially horizontally folded, only once folding for the current outflow side is sufficient to obtain desired result. That is to say, even though the current outflow side busbar is folded by only one time (see Fig, 3), in such a case the bias current through the current outflow side busbar can also be significantly suppressed. In the second embodiment shown in Fig. 3, the current outflow side busbar arrangement for the electrolytic cell comprises a cathode busbar 1 of an upstream electrolytic cell, a riser busbar 2 of a downstream electrolytic cell, and a substantially horizontally folded busbar 3 connecting the cathode busbar 1 with the riser busbar 2. The direction of the current flowing through the current outflow side busbar arrangement is shown by arrows in Fig. 3. In such a busbar arrangement constructed as above, the horizontally folded busbar 3 can be made as an integral body Alternatively, the horizontally folded busbar 3 can also be not formed as one piece. In this case, two horizontally extending busbar sections 3 can be coupled together by a connecting plate 42 by means of known methods in the art, such as welding. The resultant folded busbar 3 can be coupled to the cathode busbar 1 and the riser busbar 2 respectively via a connecting plate 41 and a connecting plate 42 locating therebetween. The horizontally folded length of the current outflow side busbar arrangement is 1-2 times more than that when directly connected to the riser busbar for the electrolytic cell By the current outflow side busbar arrangement constructed as above, the distance between the cathode busbar and the riser busbar, as well as the width of the electrolytic cell viewed from the end, can be reduced to the acceptable range. Such decreased distance and width certainly will make the distance between the electrolytic cell rows smaller without affecting the operation and the production of the electrolytic cell The higher cost-efficient electrolytic cell for manufacturing and installation thus can be attained. Although presently it is not very exactly clear what factors lead to such a favorable result of the horizontally folding, the present inventors assume, based on the experiments and the investigations, that for the rectangular parallelepiped electrolytic cells arranged in longitudinal direction, the magnetic environment created by the horizontally folding is more convenient or adapted to prevent the bias current. It should be noted that in this connection, however, the present invention is by no means limited to such an explanation. It should be appreciated by those ordinary skilled in the art, the connection means by which the folded busbar coupled with the cathode busbar and the riser busbar is not limited to welded connecting plates as shown and described. Other connection means can also be used, including, but not limited to, connecting busbar sections, metal parts, or conductive adhesive substance, or the combinations thereof accomplished by brazing, bonding, gluing, or combinations thereof, or other techniques. Although the current outflow side busbar arrangement in accordance with the present invention has been described and shown in the context of horizontally or vertically folding or extending, the folded busbar can extend at an inclined angle with respect to horizontal direction, but not limited to the orthogonal directions. EXAMPLES In the 320KA series electrolytic cell of 250,000 ton aluminum outcome per a year, measuring the current flowing through the current outflow and inflow sides are conducted, and results are plotted in Fig. 4 and 5. Fig.4 shows a current profile for the conventional current outflow side busbar airangement wherein the cathode busbar is directly connected to the riser busbar, while Fig. 5 shows a current profile for the current outflow side busbar arrangement of the present invention wherein the cathode busbar is connected to the riser busbar via the present horizontally folded busbar. It can be seen that, using the present folded busbar the difference between the cuiTent flowing through the outflow and inflow sides is reduced to the acceptable range, thus the balance of the current flowing through the outflow and inflow sides is significantly improved. In this electrolytic cell, when the vertically folded busbar is used, the distance between the cathode busbar and the riser busbar is 450-700 mm more than the distance when the horizontally folded busbar is used. Employing the horizontally folded busbar can reduce 600 mm from the distance between the cell rows, saving the 98X104 m of an occupied area of a workshop. While there have been shown and described what are present considered to be the preferred embodiments of the invention, it will be apparent to those ordinary skilled in the art the various changes and modifications can be made herein without departing from the scope of the invention as defined by the appended claims. Claims 1. A current outflow side busbar arrangement for an electrolytic cell, comprising a cathode busbar, a riser busbar, and a busbar connecting the cathode busbar with the riser busbar in a nonstraight way. 2. A folded current outflow side busbar arrangement for an electrolytic cell, comprising a cathode busbar (1; 11) of an upstream electrolytic cell, a riser busbar (2; 12) of a downstream electrolytic cell, and a folded busbar (3; 13) connecting the cathode busbar (1; 11) with the riser busbar (2; 12). 3. The folded current outflow side busbar for an electrolytic cell as claimed in claim 27 characterized in that, the folded busbar (13) is shaped by substantially vertically folding, thereby forming the folded busbar section extending substantially vertically 4. The folded current outflow side busbar for an electrolytic cell as claimed in claim 2, characterized in that, the folded busbar (3) is shaped by substantially horizontally folding, thereby forming the folded busbar section extending substantially horizontally. 5. The folded current outflow side busbar for an electrolytic cell as claimed in claim 2, characterized in that, the folded busbar is shaped to extend at an inclined angle with respect to horizontal direction, 6. The folded current outflow side busbar for an electrolytic cell as claimed in any one of claim 2-5, characterized in that, the folded busbar (3; 13) is made as an integral body 7. The folded current outflow side busbar for an electrolytic cell as claimed in any one of claim 2-5, characterized in that, the folded busbar (3; 13) is made of a plurality of busbar sections made of the same or different materials and assemblied together by a connecting means (4; 14). j j

Documents:

0865-che-2005-abstract.pdf

0865-che-2005-claims.pdf

0865-che-2005-correspondnece-others.pdf

0865-che-2005-description(complete).pdf

0865-che-2005-drawings.pdf

0865-che-2005-form 1.pdf

0865-che-2005-form 3.pdf

0865-che-2005-form 5.pdf

0865-che-2005-others.pdf

865-CHE-2005 CORRESPONDENCE OTHERS.pdf

865-CHE-2005 CORRESPONDENCE PO.pdf

865-CHE-2005 FORM 18.pdf

865-che-2005 other patent document 04-01-2010.pdf

865-CHE-2005 OTHER PATENT DOCUMENT 07-12-2009.pdf