Modular busbar for series of aluminium electrolyzers

Abstract

The busbar system consists of an anode part designed to connect anodes in a cell line by means of anode rods, a cathode part composed of cathode rods with flexible strap stacks and designed to connect to the anode part of the next cell in a cell line by means of a bus module that comprises main (collecting) cathode busbars on the upstream and downstream sides of the cathode shell of the cell, connecting busbars located under the cell bottom, at least one anode riser on the upstream side and at least one anode riser on the downstream side of the cell. The busbar system is designed to supply current to two similar cell lines that are composed of one row of electrolysis (reduction) cells, such lines are designed to be independent from each other in terms of power supply and to have opposite current directions, and comprises correction (compensation) busbars.

Claims

1. A busbar system for aluminum electrolysis (reduction) cells arranged side-by-side in series, consisting of an anode part designed to connect anodes in a cell line by means of anode rods, a cathode part composed of collector bars with flexible strap stacks and designed to connect to the anode part of the next cell in a line by means of a bus module comprising main (collecting) cathode busbars on the upstream and downstream sides of the cathode shell of the cell, connecting busbars located under the cell bottom, some of which in the outermost bus modules 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 and at least one anode riser on the downstream side of the cell, which are located symmetrically with respect to the YZ symmetry plane of the electrolysis (reduction) cell and designed to be powered by the collector bars on the upstream and downstream sides of the previous cell in a line and to pass - of the bus module current through the anode risers on the upstream side and - of the bus module current through the anode risers on the downstream side, characterized in that it is designed to supply current to two similar aluminum cell lines composed of one row of electrolysis (reduction) cells, such lines being independent from each other in terms of power supply and having opposite current directions, in the meantime, it comprises correction (compensation) busbars 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.

2. The busbar system according to claim 1, characterized in that the correction (compensation) busbars are parallel to the busbars of the cathode busbar system.

3. The busbar system according to claim 1, characterized in that the correction (compensation) busbar stacks are designed to be partially arranged under the bottom and along the ends of electrolysis (reduction) cells.

Description

[0044] Hereinafter, a description of the drawings is provided.

[0045] FIG. 1 shows a schematic diagram for the facility composed of two lines of electrolysis cells 3, 5, 1 and 4, 6, 2 in plan view, where the correction (compensation) busbars of adjacent potlines 5 and 6 extend under each row of potlines 3 and 4 in the immediate vicinity of the cathode busbar system of the line. The potlines are independent with respect to power supply and each of them is connected to separate power sources 1 and 2.

[0046] FIG. 2 shows an example of a 4-module busbar system according to the application for an invention that is designed for an amperage of 800 kA, with anode risers 16 and 17 arranged on both sides of the cell and correction (compensation) busbars 5 and 6 located in the immediate vicinity of the cathode busbar system of electrolysis cell rows 3 and 4 belonging to the adjacent potline, respectively.

[0047] FIG. 3 shows a connection diagram for electrolysis cell rows 3 and 4 in cross-section view according to the application, including upstream risers 16 and downstream risers 17, and correction (compensation) busbars to compensate for the magnetic field from adjacent potlines 5 and 6, respectively. FIG. 4 shows the magnetic field, in mT, for magnetic induction vector component Bz in the middle of the metal pad of a pilot electrolysis cell, according to the prior-art patent, at an amperage of 550 kA.

[0048] FIG. 5 shows the magnetic field, in mT, for magnetic induction vector component Bz in the middle of the metal pad of an electrolysis cell, according to the application for an invention, at an amperage of 800 kA.

[0049] FIG. 6 shows the magnetic field, in mT, for magnetic induction vector component By of an electrolysis cell similar to the application for an invention, with upstream anode risers 16 only and correction (compensation) busbars 5 and 6 to compensate for the magnetic field from the adjacent potline, respectively.

[0050] FIG. 7 shows the magnetic field, in mT, for magnetic induction vector component By of an electrolysis cell according to the application for an invention, with anode risers 16 and 17 located on both sides of the cell symmetrically with respect to the YZ plane and correction (compensation) busbars 5 and 6 to compensate for the magnetic field from adjacent cell rows 3 and 4, respectively.

[0051] The busbar system consists of two single-row lines 3, 5, 1 and 4, 6, 2 of serially connected electrolysis cells, the lines being independent with respect to power supply. The current in the potlines flows in opposite directions. Potline 3, 5, 1 is powered from independent current source 1, while potline 4, 6, 2 is powered from independent current supply source 2. Potline 3, 5, 1 returns current to power source 1 with the help of correction (compensation) busbars 5 extending in close proximity to the cathode busbar systems of adjacent electrolysis cell row 4. Similarly, potline 4, 6, 2 returns current to power source 2 by means of correction (compensation) busbars 6 located in close proximity to the cathode busbar systems of the potline composed of electrolysis cell row 3.

[0052] As an example, FIG. 2 shows a four-module busbar system designed for an amperage of 800 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 (1,000-1,500 kA and higher; for example, 2,000 kA). Developing potlines composed of single-module busbar systems is not ruled out.

[0053] The busbar system shown in FIG. 2 and FIG. 3 comprises an anode busbar system 7 with anodes 8 and anode rods 9, a cathode busbar system composed of collector bars 10 and flexible strap stacks 11, and bus modules A, B, C and D.

[0054] Each module includes upstream main (collecting) cathode busbars 12 and downstream main (collecting) cathode busbars 13 of the cathode shell 14, connecting busbars 15, and upstream anode risers 16 and downstream anode risers 17 located symmetrically with respect to the YZ symmetry plane. The connecting busbars 15 are located in close proximity to the cathode busbar system of potlines 3 and 4. The upstream anode risers 16 are connected to the upstream cathode busbars 13 of the previous electrolysis cell. The downstream anode risers 17 are connected to the upstream cathode busbars 12 of the previous electrolysis cell. The correction (compensation) busbars 5 and 6 to compensate for the magnetic field from the adjacent potline are located in close proximity to the cathode busbar system.

[0055] As shown in FIG. 1, FIG. 2 and FIG. 3, the current from the collector bars 10 is transferred by means of the flexible strap stacks 11 to the main (collecting) cathode busbars 12 and 13, then, it is transferred to the anode busbar system 7 via the connecting busbars 15 and through the anode risers 16 and 17, and then it is transferred to the rods 9 and the anodes 8 of the following cell in a potline. The current in the correction (compensation) busbars 5 and 6 to compensate for the magnetic field from the adjacent cell rows 3 and 4 is oriented in the opposite direction to the potline amperage.

[0056] 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.

[0057] High-amperage electrolysis cells (up to 2,000 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. 2.

[0058] 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).

[0059] 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.

[0060] 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 500 kA are as follows:

[0061] Vertical (Bz) and transverse (Bx) magnetic fields in the metal should not exceed 1.5 mT;

[0062] Direction of the vertical component (Bz) of the magnetic field should be alternating in sign with respect to each quarter of the cell (propeller-like character);

[0063] Longitudinal component (By) of the magnetic field should be antisymmetric with respect to the YZ symmetry plane.

[0064] These criteria are insufficient to ensure high technical and economic performance indicators for electrolysis cells designed for an amperage of more than 500 kA.

[0065] 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.

[0066] 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.

[0067] 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 3.0-3.5 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. 4, which is antisymmetric with respect to the YZ and XZ planes.

[0068] 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. 2.

[0069] 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.

[0070] 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 FIGS. 1, 2, 3, within 80-100% 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.

[0071] Since the potential difference between the poles of power supply stations of modern potlines can reach 1,000 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.

[0072] 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. 1, wherein the electrolysis cell rows belonging to two potlines 3 and 4 are depicted.

[0073] The second rows in each potline are replaced by the correction (compensation) busbars 5 and 6 located in close proximity, mostly, under the bottoms of the adjacent cell rows of potlines 3 and 4. 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 3 and 4 of the potlines, thus preventing the influence of the magnetic field on the adjacent row of electrolysis cells.

[0074] 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. 6 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 100% positive direction with respect to this component. Being equal to (2-0 mT) on the upstream side, it reaches (+36+38 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.

[0075] In this application for an invention, this problem is solved by the availability of anode risers located on the opposite, downstream side 7 of the cell, as shown in FIG. 2 and FIG. 3. In this case, the total current in the risers on the upstream side reduces by approximately 2 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. 7.

[0076] Light metals-2017, editor Ante P. Ratvik, p. 26, ISSN 2367-1181 ISSN 2367-1696 (electronic) The Minerals, Metals & Materials Series, ISBN 978-3-319-51540-3 ISBN 978-3-319-51541-0 (eBook), contains the key operating parameters of a test group of 550-kA electrolysis cells, whose busbar system is assembled in accordance with the prior art in this application for an invention (RU 2288976). Tests have been underway for more than 2 years.

[0077] In case of the magnetic field shown in FIG. 4 and measured with respect to the Bz component, which is similar to the magnetic field according to the application for an invention (FIG. 5), the test group operates with the following operating characteristics: [0078] Amperage550 kA; [0079] Current efficiency94.5%; [0080] Voltage3.8 V; and [0081] Specific energy consumption12,000 MWh/kg.

[0082] Since the start of testing these electrolysis cells, it has not yet been possible to achieve MHD instability. Their noise is 5-6 mV under normal operating conditions and does not exceed 20 mV during operational disturbances.

[0083] 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 800 kA according to the application for an invention, as shown in FIG. 4, FIG. 5 and FIG. 7.

[0084] Said coincidences predict, with high confidence, that the operating parameters of a cell with the busbar system according to the application (up to 2,000 kA) will be no worse than those of the prior-art cell.