Patent Description:
A busbar system is a current-conductive element of an electrolysis cell structure and consists of two parts, anodic and cathodic. Electrolysis cells arranged in rows one after another are coupled with each other by current conductors made of aluminum or copper busbars of different cross-section and connected in an electrical circuit in series: cathode busbars of one cell are connected to anode busbars of another cell. A group of electrolysis cells combined into one electrical circuit is called a potline (or cell line). The anode part of the busbar system comprises flexible straps in a stack (or flexible strap stacks), anode risers and anode buses. The current is transferred from the anode buses to aluminum anode rods, and then to prebaked carbon (anode) blocks. The cathode part of the busbar system comprises flexible straps in stacks (or flexible strap stacks) that drain current from collector bars in the bottom of the cell to main (collecting) cathode buses, and then to cathode buses.

There are many known busbar system designs for electrolysis cells. A busbar system is developed for a specific electrolysis cell design using computer-based mathematical models (or simulations) and depends on cell type, cell amperage, cell position in the pot (or cell) room and in the potline, the availability of adjacent (or neighboring) pot rooms, local climate, the remoteness of raw materials suppliers, product consumers, and the cost of electricity, raw materials and finished products.

When developing a busbar system, it is a common practice to be guided by the following conditions:.

There is a known busbar system for electrolysis cells that are arranged side-by-side in the potroom, which contains main (collecting) busbars with cathode flexibles installed along the upstream and downstream longitudinal sides of the cell, and anode risers installed on the upstream side, through which equal currents flow. The anode busbar system is connected with the previous cell by means of risers, where the outermost risers are connected to the outermost main (collecting) cathode busbars of the upstream side of the cell by busbar stacks located along the end faces of the cell and to the main (collecting) cathode busbars of the downstream side of the cell, while the middle risers are connected to the middle main (collecting) busbars of the upstream side of the cell by busbar stacks arranged symmetrically under the cathode blocks being closest to the cell ends and to the main (collecting) cathode busbars of the downstream side of the cell, wherein the busbar extending under the bottom and located closer to an adjacent (or neighboring) row of electrolysis cells carries <NUM>% of the upstream side current, while the other one carries <NUM>% of the upstream side current, and there is an intermediate busbar under the cell bottom that extends halfway between the potline axis and the cell end, on the side opposite to the adjacent (or neighboring) row of electrolysis cells, wherein <NUM>% of the upstream side current flows through this busbar (patent <CIT>, PECHINEY ALUMINIUM, IPC C25C <NUM>/<NUM>, <NUM>).

A disadvantage of the above busbar system is the impossibility of using it for electrolysis cells operating at an amperage of greater than <NUM> kA, since asymmetrical busbar systems, from a design point of view, have limitations in compensating for the magnetic field that is picked up from an adjacent row of electrolysis cells.

There is a known current supply/drainage apparatus to/from aluminium reduction cells with double-row, side-by-side arrangement in a row, which comprises an anode busbar system connected to anodes by anode rods, a cathode busbar system composed of collector bars with flexible strap stacks projecting on both sides of the cathode shell of the cell with a bottom, main (collecting) cathode busbars on the upstream and downstream sides of the cathode shell of the cell, connecting busbars, a shunt element, a connection between the cathode and anode busbar systems, and magnetic field correction (compensation) loop busbars that are located in parallel to the transversal axis of the electrolysis cell near the cathode shell ends. The connection between the cathode busbar system and the anode busbar system of the following cell in a row is made in the form of bus modules composed of two semi-risers, wherein one of the semi-risers is rigidly connected to the downstream main (colleting) cathode busbar that, in turn, is connected to four flexible strap stacks, and another semi-riser is connected by busbars located under the cathode shell bottom and coupled with the upstream (collecting) cathode busbar stacks, each of them being connected to two flexible strap stacks, wherein the connecting busbars are located under the cathode shell bottom in parallel to the transversal axis of the electrolysis cell and each other, while the current supplied to the correction (compensation) loop is supplied in the direction coincident with the current direction in the potline, and the current in the magnetic field correction (compensation) loops is preferably <NUM>-<NUM>% of the potline amperage (patent <CIT>, PECHINEY ALUMINIUM, <NUM>-<NUM>-<NUM>).

A disadvantage of this busbar system is that it uses independent magnetic field correction (compensation) busbars from two conductors extending along both ends of electrolysis cells in a circuit, in the potline amperage direction. The correction (compensation) current is <NUM>-<NUM>% of the potline amperage. For example, when the potline amperage is <NUM> kA, the correction (compensation) current can reach <NUM> kA. A current equal to <NUM> + <NUM> = <NUM> kA that flows along the potline generates a magnetic field corresponding to <NUM> kA rather than to <NUM> kA in the potroom, which primarily has an adverse effect on potroom personnel. The additional weight of the busbar system due to correction (compensation) busbars will come to about <NUM> metric tonnes per each cell of the potline. In any case, the use of a correction (compensation) circuit (loop) leads to an increase in the busbar system weight, growth in power consumption due to a voltage drop in the correction (compensation) circuit (loop), and an increase in expenditures on the floor space for the installation of the correction (compensation) circuit (loop). For example, when the correction (compensation) current is <NUM> kA, correction (compensation) busbars will be composed of <NUM> buses with a cross-section of <NUM>×<NUM> (the width of one stack is about <NUM> meters, and the width of two stacks is about <NUM> meters).

<NPL> provides a new concept of the magnetic field from an adjacent row of cells in a potline, including simultaneous optimization (magnetic field depression with respect to the Bz component in the cell ends).

The first method of the new concept provides for the use of anode risers on the upstream side of the cell only. In the simplest form of the concept, <NUM>% of the potline amperage returns back to the current supply station via additional correction (compensation) busbars located under the bottom of the cells in a potline.

According to the second version of this new concept, the upstream busbars of the cell carry half of the potline amperage under the bottom of the cell to the upstream risers of the following cell. The downstream busbars of the cell carry the second half of the potline amperage to the risers of the following cell under the bottom, to the risers located on the downstream side of the cell. As in the first concept, the total potline current of opposite direction flows in the adjacent (neighbored) additional compensation busbars under the bottoms.

A considerable disadvantage of both options of the said concept is that they are only of theoretical interest and cannot be implemented in practice. This is due to the fact that the potential difference between the poles of power supply stations of modern potlines is <NUM>,<NUM> V and higher. Since the potline's cathode busbar system and correction (compensation) busbar stacks (that return current to the power source) are located in immediate proximity, an electric arc (plasma) will inevitably emerge between them, which is unacceptable according to the Safety Rules (SR) and the Electrical Safety Code (ESC).

There are currently no industrially applicable, inexpensive and reliable methods for insulating between high-current conductors that have a potential difference of <NUM>,<NUM> V and higher between each other, considering a large conductor area, a short distance between conductors and high amperage.

Similarly, there is another known <CIT>. The application claims consist mainly of a set of technical solutions, namely:.

In the meantime, claim <NUM> states that the busbar system has at least one first compensation loop located under electrolysis cells and capable of passing through itself the first compensation current (amperage) under electrolysis cells in the direction opposite to the total electrolysis amperage direction.

The availability of two correction (compensation) lines and a potline itself implies heavy expenditures for three independent power supply stations, taking into account that an emergency margin is required for each of them, and expenditures for additional busbars of the <NUM> correction (compensation) loops, power losses in both correction (compensation) loops and their power supply stations, which is a disadvantage of the known application.

<FIG> in the said application shows electrolysis cells, whose collector bars pass through the bottom perpendicular to the metal pad. Protection against metal leakage between the collector bars and the lining is likely to be cost-consuming, since the collector bars, the lining, and the cathode shell are substantially different in terms of their physical, electrical and thermal properties. During an electrolysis cell campaign (<NUM>-<NUM> years), the probability of molten aluminum leakages, vertical collector bar dissolution and metal run-out is very high, since the said elements of the electrolysis cell constantly move relative to each other, and their geometry and physical properties change, which is another disadvantage of the application.

<CIT> discloses an arrangement for compensating detrimental magnetic influence on longitudinally oriented pots (U3) in a pot row, from the current in one or more adjacent pot rows, in plants for producing metal, for example aluminum, by electrolytic reduction of a molten bath. Two substantially symmetrical groups of cathode taps located at opposite sides of the positive end of the pot, are each connected to a separate compensation bus bar so located in relation to the pot that they form a current loop around the cathode in a clockwise or in a counter-clockwise direction, depending upon whether a positive or a negative vertical magnetic field is to be compensated for.

<CIT> discloses a method and relevant apparatus for the electric current supply to pots for the electrolytic production of metals, particularly aluminum, arranged in side-by-side or end-to-end relationship and electrically connected in series, consisting in carrying most of the electric current in the circuit of said series of pots by means of conductors all having the same cross-section and being always combined, in the individual circuit sections, in couples of the same length, all said couples of conductors being furthermore symmetrically positioned with respect to the transverse median vertical plane and or to the longitudinal median vertical plane of the single pots in the series. By the present invention, and in compliance with the objects thereof, a high compensation and the total symmetrization (with respect to the vertical median planes) of the components of the induction magnetic field in the single pots of the series and, by consequence, the minimization and the total symmetrization of the effects of the magnetic forces operating in the molten areas of said pots are achieved.

<CIT> relates to electrolytic production of non-ferrous metals in electrolyzers arranged in two rows in housing and interconnected forming series circuit and discloses a unit including two risers located on longitudinal sides symmetrically relative to its center, two other risers located symmetrically in inlet end of electrolyzer, two cathode collecting buses located on each longitudinal side of electrolyzer. Some cathode rods of electrolyzer are connected with first cathode collecting buses and some cathode rods of electrolyzer located on side of outlet end are connected with second cathode collecting buses. First cathode collecting buses of electrolyzer are connected with risers located in second end of subsequent electrolyzers; second cathode collecting buses of electrolyzer are connected with risers located on longitudinal sides of subsequent electrolyzer. Risers located in inlet end face of electrolyzer are connected with beginning of anode buses; risers located on longitudinal side of electrolyzer are connected with center of anode buses. Device is provided with bus for compensating for effect of magnetic field of adjacent row of electrolyzers which is located at level of cathode collecting buses on external side of both rows of electrolyzers; bus used for compensation is connected to individual power supply system. Device is also provided with additional bus for compensating for effect of magnetic field of adjacent row of electrolyzers located at level of cathode collecting buses on internal side of both rows of electrolyzers and is connected with compensating bus forming series circuit; direction of current in additional bus coincides with flow of current in electrolyzer series.

The known cell busbar system according to patent<CIT>, taken as prior art, has a double-row side-by-side arrangement in a line, contains an anode busbar system part connected to anodes by anode rods and a cathode busbar system part composed of collector bars with flexible strap stacks projecting on both sides of the cathode shell of the cell. The connection between the collector bars and the anode busbar system of the following cell in a row is made in the form of bus modules composed of main (collecting) cathode busbars, connecting busbars and anode risers. At least one riser in each module is located on the upstream side of the cell and at least one riser in each module is located on the downstream side of the cell.

In the meantime, the upstream anode risers are powered from the collector bars both on the upstream side and on the downstream side of the previous electrolysis cell, and the downstream anode risers are powered from the collector bars on the downstream side of the previous electrolysis cell. About <NUM>/<NUM>-<NUM>/<NUM> of the module current flows through the upstream anode risers, while about <NUM>/<NUM>-<NUM>/<NUM> of the module current flows through the downstream anode risers, the connecting busbars are located under the cell bottom, and some connecting busbars of the outermost modules can at least pass around the cell ends and be preferably located at the molten metal level.

The disadvantages of the said prior-art busbar system are:.

The objective and technical result of the invention is the formation of an optimal magnetic field in the melt of electrolysis cells arranged side-by-side in a potroom so as to develop and deploy potlines for amperage of <NUM> kA to <NUM>,<NUM> kA, preferably for <NUM> kA.

This result is achieved due to fundamental differences between the proposed application for an invention of a busbar system and the busbar system of the prior art, which are as follows:.

In the meantime, it is impossible to have an optimal magnetic field without using the technical solutions specified in the limiting (restrictive) part of the prior art, these technical solutions comprise:.

Hereinafter, a description of the drawings is provided.

The busbar system consists of two single-row lines <NUM>, <NUM>, <NUM> and <NUM>, <NUM>, <NUM> of serially connected electrolysis cells, the lines being independent with respect to power supply. The current in the potlines flows in opposite directions. Potline <NUM>, <NUM>, <NUM> is powered from independent current source <NUM>, while potline <NUM>, <NUM>, <NUM> is powered from independent current supply source <NUM>. Potline <NUM>, <NUM>, <NUM> returns current to power source <NUM> with the help of correction (compensation) busbars <NUM> extending in close proximity to the cathode busbar systems of adjacent electrolysis cell row <NUM>. Similarly, potline <NUM>, <NUM>, <NUM> returns current to power source <NUM> by means of correction (compensation) busbars <NUM> located in close proximity to the cathode busbar systems of the potline composed of electrolysis cell row <NUM>.

As an example, <FIG> shows a four-module busbar system designed for an amperage of <NUM> kA. Depending on the number of modules to be selected, it can be developed for electrolysis cells operating at any acceptable (from technical and economic points of view) amperage (<NUM>,<NUM>-<NUM>,<NUM> kA and higher; for example, <NUM>,<NUM> kA). Developing potlines composed of single-module busbar systems is not ruled out.

The busbar system shown in <FIG> and <FIG> comprises an anode busbar system <NUM> with anodes <NUM> and anode rods <NUM>, a cathode busbar system composed of collector bars <NUM> and flexible strap stacks <NUM>, and bus modules A, B, C and D. Each module includes upstream main (collecting) cathode busbars <NUM> and downstream main (collecting) cathode busbars <NUM> of the cathode shell <NUM>, connecting busbars <NUM>, and upstream anode risers <NUM> and downstream anode risers <NUM> located symmetrically with respect to the YZ symmetry plane. The connecting busbars <NUM> are located in close proximity to the cathode busbar system of potlines <NUM> and <NUM>. The upstream anode risers <NUM> are connected to the upstream cathode busbars <NUM> of the previous electrolysis cell. The downstream anode risers <NUM> are connected to the upstream cathode busbars <NUM> of the previous electrolysis cell. The correction (compensation) busbars <NUM> and <NUM> to compensate for the magnetic field from the adjacent potline are located in close proximity to the cathode busbar system.

As shown in <FIG>, <FIG> and <FIG>, the current from the collector bars <NUM> is transferred by means of the flexible strap stacks <NUM> to the main (collecting) cathode busbars <NUM> and <NUM>, then, it is transferred to the anode busbar system <NUM> via the connecting busbars <NUM> and through the anode risers <NUM> and <NUM>, and then it is transferred to the rods <NUM> and the anodes <NUM> of the following cell in a potline. The current in the correction (compensation) busbars <NUM> and <NUM> to compensate for the magnetic field from the adjacent cell rows <NUM> and <NUM> is oriented in the opposite direction to the potline amperage.

It should be noted that the technical solution of the application for an invention is based on the understanding that low-amperage electrolysis cells do not require over-complication of the busbar system in view of low magnetic field intensity, a small density of horizontal currents, and a limited volume of molten metal. Good results during electrolysis can be achieved even in the case of one-side current drainage from the cathode and one-side current supply to the anode busbar system. Such electrolysis cells can be arranged end-to-end in two or four rows within the potroom, which has no substantial effect on the mutual influence of the magnetic fields.

High-amperage electrolysis cells (up to <NUM>,<NUM> kA) are disclosed herein, which are assembled from parallel lines of low-amperage electrolysis cells (modules), whose current is unidirectional. In the meantime, adjacent (neighboring) cells (modules) of each potline are combined into one combined cell, as shown in <FIG>.

MHD instability issues in each low-amperage electrolysis cell (module) are minimal, so there will be no substantial issues related to MHD stability in a high-amperage electrolysis cell composed of low-amperage electrolysis cells (modules).

It is efficient to arrange the combined cell transversely to the cell room axis. This allows a considerable reduction in the magnetic field intensity contribution from the cathode busbar system.

The main prerequisites for the optimal character of the magnetic field in the metal for side-by-side electrolysis cells operating at an amperage of up to <NUM> kA are as follows:.

These criteria are insufficient to ensure high technical and economic performance indicators for electrolysis cells designed for an amperage of more than <NUM> kA.

When the vertical component (Bz) of the magnetic field, which acts upon a molten metal layer, has the same sign of direction (plus or minus) over a vast area of the electrolysis cell, especially along its longitudinal sides, coherent and increasing surface oscillations may occur in the melt due to the accumulation of the longitudinal moment along the cell. They cause a low MHD stability of electrolysis cells and, as a result, their poor technical and economic performance indicators. Therefore, an increase in MHD stability, as a result of magnetic field optimization in the molten metal, is achieved through frequent changes in sign for the Bz magnetic field component along the longitudinal sides of the electrolysis cell, and, as this takes place, a change in sign should be antisymmetric with respect to the YZ symmetry plane of the cell.

In this application for an invention, this problem is solved as follows. The structure of the anode and the cathode of electrolysis cells includes great-in-size ferromagnetic masses that possess substantial metal protection properties against the magnetic field of the cathode busbar system.

Unlike the magnetic field generated by the cathode busbar system, the magnetic field generated by the anode risers, through which the total potline current passes, mainly generates the vertical (Bz) magnetic field in the metal, considering that there are no ferromagnetic shields between the metal and the risers, which reduce the effect of the magnetic field from the risers upon the metal. The (Bz) field directed downward (minus) is generated in the metal on the right side along the current flow in the riser, and the field directed upward (plus) is generated on the left side from the riser. A sinusoid-like field for the (Bz) component with an amplitude of no more than <NUM>-<NUM> mT can be generated by selecting an appropriate distance and amperage in the risers on one longitudinal side. If similar anode risers are located on the opposite side, symmetrically with respect to the YZ plane, this will result in the generation of the vertical magnetic field as shown in <FIG>, which is antisymmetric with respect to the YZ and XZ planes.

However, as the cell amperage increases due to the installation of additional modules and the cell becomes longer, the value of the magnetic induction vertical component will grow, especially in the outermost cell modules A and D, see <FIG>.

Also, with an increase in the amperage, for compensating the magnetic field picked up from the adjacent row, it will be required to increase the distance between the electrolysis cell rows to transfer current to the stacks passing around the cell ends from a greater number of collector bars in order to compensate for the growing Bz component of the magnetic field. This will have a negative effect on the busbar system weight and costs per unit of the potroom area.

These two problems are solved herein by the installation of correction (compensation) busbars under the cathode busbar systems of the cell row of the adjacent line, as shown in <FIG>, <FIG>, <FIG>, within <NUM>-<NUM>% of the total number of busbars. The correction (compensation) current flows in the direction opposite to the current flowing in the cathode busbar system of the cell row of the adjacent line.

Since the potential difference between the poles of power supply stations of modern potlines can reach <NUM>,<NUM> V and higher, the correction (compensation) busbars should be connected to their own, separate current source to preclude the potential difference between the cathode busbar system and the correction (compensation) busbars in order to avoid arcing, especially in the electrolysis cells that are located near the power source.

To solve this problem, this application provides for using the second potline to be independent in terms of electrical current supply. In other words, the facility that comprises the busbar system specified in the application consists of two single-row potlines. The current in one potline is directed clockwise (in plan view), and the current in another potline is directed counter-clockwise, as shown in <FIG>, wherein the electrolysis cell rows belonging to two potlines <NUM> and <NUM> are depicted.

The second rows in each potline are replaced by the correction (compensation) busbars <NUM> and <NUM> located in close proximity, mostly, under the bottoms of the adjacent cell rows of potlines <NUM> and <NUM>. Since the currents in the cathode busbar system and the correction (compensation) busbars are equal and flow in opposite directions, then, as a rule of thumb, the current from the busbars of the cathode busbar system and the correction (compensation) busbars compensates for the magnetic field around itself. The correction (compensation) busbars, first, compensate for the vertical magnetic field in the melt of electrolysis cells to bring it to optimal values and, second, subtract the magnetic field around each of two rows <NUM> and <NUM> of the potlines, thus preventing the influence of the magnetic field on the adjacent row of electrolysis cells.

This allows installing rows of electrolysis cells in close proximity to each other, for example, in the same pot room. However, the correction busbars not only optimize the vertical field component (Bz) in the metal, but also have an effect on the longitudinal component (By) generated mainly by volume currents and currents of collector bars, namely, they subtract it on the upstream longitudinal side of the cell and increase this component, by being added to it, on the downstream side, because they coincide in direction. <FIG> shows the By field component in the metal of the cell with the risers installed only on the upstream side, provided the correction busbars are available. As can be seen, the magnetic field has a <NUM>% positive direction with respect to this component. Being equal to (-<NUM>-<NUM> mT) on the upstream side, it reaches (+<NUM>-+<NUM> mT) on the opposite longitudinal side. Upon interaction with the vertical current, Lorentz forces occur in the melt, they are being directed from the upstream longitudinal side to the downstream longitudinal side (in plan view), which causes metal heaving or, more correctly, metal shifting from the upstream longitudinal side to the downstream side. As this takes place, the upstream longitudinal side becomes "hot" and the downstream side becomes "cold". This leads to asymmetry in the thermal balance and the ledge profile, as well as in the electric field in the metal, and more specifically, to the occurrence of planar currents that, as is known, reduce the MHD stability of electrolysis cells and their technical and economic performance indicators.

In this application for an invention, this problem is solved by the availability of anode risers located on the opposite, downstream side <NUM> of the cell, as shown in <FIG> and <FIG>. In this case, the total current in the risers on the upstream side reduces by approximately <NUM> times, and thus, facilitates an increase in the magnetic field Bx component on the upstream side, since the magnetic field generated by the anode risers with respect to the By component adds to a similar field generated by the correction (compensation) busbars. To the contrary, the magnetic field from the anode risers on the downstream side subtracts the field from the correction (compensation) busbars. By selecting the amperage for the anode risers on the upstream and downstream sides of the cell, within the limits set in the application claims, it is possible to have a magnetic field to be antisymmetric with respect to the YZ plane along the longitudinal sides, and thus, symmetric metal heaving as shown in <FIG>.

<NPL>), contains the key operating parameters of a test group of <NUM>-kA electrolysis cells, whose busbar system is assembled in accordance with the prior art in this application for an invention (<CIT>). Tests have been underway for more than <NUM> years.

In case of the magnetic field shown in <FIG> and measured with respect to the Bz component, which is similar to the magnetic field according to the application for an invention (<FIG>), the test group operates with the following operating characteristics:.

Since the start of testing these electrolysis cells, it has not yet been possible to achieve MHD instability. Their noise is <NUM>-<NUM> mV under normal operating conditions and does not exceed <NUM> mV during operational disturbances.

The practical measurements and calculations point to the same qualitative and quantitative character of the magnetic field with respect to the Bz and Bx field components both in the melt of the prior-art cell and in the melt of the cell for <NUM> kA according to the application for an invention, as shown in <FIG>, <FIG> and <FIG>.

Claim 1:
A busbar system for aluminum electrolysis cells arranged side-by-side in series for developing and deploying potlines for amperage of <NUM> kA to <NUM>,<NUM> kA, consisting of an anode part (<NUM>) designed to connect anodes (<NUM>) in a cell line by means of anode rods (<NUM>), a cathode part composed of collector bars (<NUM>) with flexible strap stacks (<NUM>) and designed to connect to the anode part (<NUM>) of the next cell in a line by means of a bus module (A, B, C, D) comprising collecting cathode busbars (<NUM> and <NUM>) on the upstream and downstream sides of the cathode shell (<NUM>) of the cell, connecting busbars (<NUM>) located under the cell bottom, some of which in the outermost bus modules (A, B, C, D) are designed to pass around the cell ends and be located at the molten metal level, at least one anode riser on the upstream side (<NUM>) and at least one anode riser on the downstream side (<NUM>) of the cell, which are located symmetrically with respect to the YZ symmetry plane of the electrolysis cell and designed to be powered by the collector bars (<NUM>) on the upstream and downstream sides of the previous cell in a line and to pass <NUM>/<NUM>-<NUM>/<NUM> of the bus module (A, B, C, D) current through the anode risers on the upstream side (<NUM>) and <NUM>/<NUM>-<NUM>/<NUM> of the bus module current through the anode risers on the downstream side (<NUM>), characterized in that it is designed to supply current to two similar aluminum cell lines (<NUM> and <NUM>) composed of one row of electrolysis cells, such lines being independent from each other in terms of power supply (<NUM> and <NUM>) and having opposite current directions in plan view clockwise in one cell line and counterclockwise in the other cell line and additionally comprises compensation busbars (<NUM> and <NUM>) located in close proximity to the cathode part of the electrolysis (reduction) cell row of the adjacent cell line, including ensuring compensation for the magnetic field.