CONTROLLING ELECTRODE CURRENT DENSITY OF AN ELECTROLYTIC CELL

Abstract

Apparatuses and methods for controlling electrode current density of an electrolytic cell during the electrolytic production of a metal, such as aluminum or aluminium, are disclosed. The cell has anodes and cathode plates vertically aligned and arranged in alternating rows. Each electrode defines a connecting region for connecting the electrode to the cell, a middle region, and an ACO (Anode-Cathode Overlap) region extending from the middle region for overlapping adjacent electrodes(s). The ratio of the ACO region's surface area to the middle region's surface area is superior to one. Alternatively, an average cross-sectional ACO region to the middle and connecting regions, is superior than one, preferably superior than 2. The present technology allows maximizing current density in the ACO region. Increasing these ratios has less impact on the environment by reducing heat generation and energy consumption, making the metal production eco-friendly, in particular when used with inert or oxygen-evolving electrodes.

Claims

1. An electrode plate for the electrolytic production of a metal using an electrolytic cell comprising a plurality of said electrodes plates defining anode and cathode plates vertically aligned and arranged in alternating rows of said anode and cathode plates, the electrode plate defining: a connecting region adjacent a first end of the electrode plate for connecting the electrode plate to the electrolytic cell; a middle region extending from the connecting region without overlapping adjacent electrode plates; and an anode-cathode overlapping (ACO) region extending from the middle region to a second end of the electrode plate opposite to the first end, and configured for overlapping adjacent electrode plate(s); wherein the electrode plate comprises two opposite surfaces for facing surfaces of electrode plates of adjacent rows; and wherein a ratio of the ACO region's surface area to the middle region's surface area is superior to one in order to maximize current density in the ACO region.

2. The electrode plate of claim 1, wherein the ACO/middle surface ratio is equal or superior to 2.

3. The electrode plate of claim 1, wherein the electrode plate has a rectangular shape, wherein a width of the electrode plate is constant from the ACO region to the middle and connecting regions.

4. The electrode plate of claim 1, wherein the electrode plate has a goal post shape wherein the middle and connecting regions define a pair of legs on either side thereof, with a central gap between the legs below the ACO region.

5. The electrode plate of claim 1, wherein the electrode plate has a paddle shape, wherein the ACO region has a first width, the middle and connecting regions have a second width, the second width being inferior to the first width.

6. The electrode plate of claim 1, wherein the electrode plate has a trapezoid shape wherein a width of the electrode plate constantly decreases from the second end to the first end of the electrode plate.

7. The electrode plate of claim 1, wherein the ACO region and the middle region of the electrode plate has a trapezoid shape with a width of the electrode plate constantly decreases from the second end of the electrode plate to a junction between the middle and connecting regions, the connecting region having a rectangular shape.

8. The electrode plate of claim 1, wherein a surrounding edge of the surfaces has round transitions between the first end of the plate and the connecting region, and/or the surrounding edge has round transitions between the second end the ACO region.

9. The electrode plate of claim 1, wherein the metal to produce is aluminum, the electrode plate being wettable by liquid aluminum metal.

10. The electrode plate of claim 1, wherein the electrode plate is a cathode plate.

11. An electrode plate for the electrolytic production of a metal using an electrolysis cell comprising a plurality of said electrodes plates defining anode and cathode plates vertically aligned and arranged in alternating rows of said anode and cathode plates, the electrode plate defining: a connecting region adjacent a first end of the electrode plate for connecting the electrode plate to the electrolytic cell; a middle region extending from the connecting region without overlapping adjacent electrode(s); and an ACO region extending from the middle region and configured for overlapping adjacent electrodes(s); wherein an average cross-sectional area ratio of the ACO region to the middle and connecting regions is superior to one in order to maximize current density in the ACO region while retaining a mechanical strength of the connecting region for supporting the electrode plate.

12. The electrode plate of claim 11, wherein the average ACO/middle cross-sectional area ratio is equal or superior to 2.

13. The electrode plate of claim 11, wherein the electrode plate has a goal post shape wherein the middle and connecting regions define a pair of legs on either side thereof, with a central gap between the legs below the ACO region.

14. The electrode plate of claim 11, wherein the electrode plate has a paddle shape, wherein the ACO region has a first width, the middle and connecting regions have a second width, the second width being inferior to the first width.

15. The electrode plate of claim 11, wherein the electrode plate has a trapezoid shape wherein a width of the electrode plate constantly decreases from the second end to the first end of the electrode plate.

16. The electrode plate of claim 11, wherein the ACO region and the middle region of the electrode plate has a trapezoid shape with a width of the electrode plate constantly decreasing from the second end of the electrode plate to a junction between the middle and connecting regions, the connecting region having a rectangular shape.

17. The electrode plate of claim 11, wherein the electrode plate comprises two opposite surfaces for facing surfaces of electrode plates of adjacent rows, and wherein a surrounding edge of the surfaces has round transitions between the first end of the plate and the connecting region, and/or the surrounding edge has round transitions between the second end the ACO region.

18. The electrode plate of claim 11, wherein the metal is aluminum, the electrode plate being wettable by liquid aluminum metal.

19. The electrode plate of claim 11, wherein the electrode plate is a cathode plate.

20. (canceled)

21. (canceled)

22. (canceled)

23. (canceled)

24. A method for controlling the current density of a plurality of electrodes plates defining anode and cathode plates vertically aligned and arranged in alternating rows in an electrolytic cell, the electrode plate defining: a connecting region for connecting the electrode plate to the electrolytic cell; an middle region extending from the connecting region without overlapping adjacent electrode(s); and an ACO region extending from the middle region and configured for overlapping adjacent electrodes(s); the method comprising the step of: providing electrode plates in which an average cross-sectional area ratio of the ACO region to the middle and connecting regions is superior to one in order to maximize current density in the ACO region while retaining a mechanical strength of the connecting region for supporting the electrode plate.

25. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above and other aspects, features and advantages of the invention will become more readily apparent from the following description, reference being made to the accompanying drawings in which:

[0031] FIG. 1A is a partially schematic cross-sectional view of an electrolytic cell known in the art;

[0032] FIG. 1B is a side view of a portion of interleaved anode and cathode modules known in the art;

[0033] FIG. 2A is a schematic view of an electrode plate in accordance with a first embodiment of the present disclosure;

[0034] FIG. 2B is a schematic view of an electrode plate in accordance with a second embodiment of the present disclosure;

[0035] FIG. 2C is a schematic view of an electrode plate in accordance with a third embodiment of the present disclosure;

[0036] FIG. 2D is a schematic view of an electrode plate in accordance with a fourth embodiment of the present disclosure;

[0037] FIG. 3 is a front view of an electrode plate in accordance with a fifth embodiment of the present disclosure;

[0038] FIG. 4 illustrates a method for controlling the current density of a plurality of electrodes plates in accordance with a preferred embodiment of the present disclosure;

[0039] FIG. 5 illustrates a method for controlling the current density of a plurality of electrodes plates in accordance with another preferred embodiment of the present disclosure; and

[0040] FIG. 6 illustrates a method for maximizing the current density of an electrolytic cell comprising a plurality of electrodes plates in accordance with a preferred embodiment of the present disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0041] Novel apparatus and method will be described hereinafter. Although the invention is described in terms of specific illustrative embodiments, it is to be understood that the embodiments described herein are by way of example only and that the scope of the invention is not intended to be limited thereby.

[0042] The terminology used herein is in accordance with definitions set out below.

[0043] By about, it is meant that the value of weight % (wt. %), time, voltage, resistance, volume or temperature can vary within a certain range depending on the margin of error of the method or device used to evaluate such weight %, time, voltage, resistance, volume or temperature. A margin of error of 10% is generally accepted.

[0044] The description which follows, and the embodiments described therein are provided by way of illustration of an example of particular embodiments of principles and aspects of the present invention. These examples are provided for the purposes of explanation and not of limitation, of those principles of the invention. In the description that follows, like parts and/or steps are marked throughout the specification and the drawing with the same respective reference numerals.

[0045] As aforesaid, the invention as disclosed herein is directed to a new configuration of an electrolytic cell, in particular the electrodes plates, for increasing the current density.

[0046] In vertical inert anode cells, cathode and anode plates are arranged in parallel, alternating rows as illustrated on FIGS. 1A and 1B from U.S. Pat. No. 10,415,147 (LIU Xinghua), the content of which is incorporated herein by reference.

[0047] FIG. 1A shows a schematic cross-section of an electrolytic cell 10 for producing a metal (e.g. aluminum) by the electrochemical reduction of an electrolyte (e.g. alumina dissolved in molten cryolite) using an anode and a cathode. The cell 10 has at least one anode module 12 comprising a plurality of vertically oriented anodes 12E suspended above at least one cathode module 14 having a plurality of vertically oriented cathodes 14E positioned in a cell reservoir 16. The vertical cathodes 14E extend upwards towards the anode module 12. While a plurality of anodes 12E and cathodes 14E of a specific number are shown FIGS. 1A and 1B, any number of anodes 12E and cathodes 14E greater than or equal to 1 may be used to define an anode module 12 or a cathode module 14, respectively. In some embodiments, the cathode module 14 is fixedly coupled to the bottom of the cell 10 with the cathodes 14E supported in a cathode support 14B which rests in the cell reservoir 16 on cathode blocks 18, e.g., made from carbonaceous material in electrical continuity with one or more cathode current collector bars 20. The cathode blocks 18 may be fixedly coupled to the bottom of the cell 10. The reservoir 16 may has a steel shell 16S and be lined with insulating material 16A, refractory material 16B and sidewall material 16C. The reservoir 16 is capable of retaining a bath of molten electrolyte (shown by dashed line 22) and a molten aluminum metal pad therein. Portions of an anode bus 24 that supplies electrical current to the anode modules 12 are shown pressed into electrical contact with anode rods 12L of the anode modules 12. The anode rods 12L are structurally and electrically connected to an anode distribution plate 12S, to which a thermal insulation layer 12B is attached. The anodes 12E extend through the thermal insulation layer 12B and mechanically and electrically contact the anode distribution plate 12S. The anode bus 24 would conduct direct electrical current from a suitable source 26 through the anode rods 12L, the anode distribution plate 12S, anode elements, electrolyte 22 to the cathodes 14E and from there through the cathode support 14B, cathode blocks 18 and cathode current collector bars 20 to the other pole of the source of electricity 26. The anodes 12E of each anode module 12 are in electrical continuity. Similarly, the cathodes 14E of each cathode module 14 are in electrical continuity.

[0048] FIG. 1B shows the anode module 12 and the cathode module 14 with their electrodes 12E and 14E in an interleaved relationship. The height of the bath 22 relative to the cathodes 14 may be called the bath-to cathode distance or BCD. The anode module 12 can be raised and lowered (i.e. selectively positionable) in height relative to the position of the cathode module 14, as indicated by double ended arrow V. In some embodiments, the anodes 12E are not completely submerged in the bath and extend across the bath-vapor interface 22 during metal production. This vertical adjustability allows the overlap Y of the anodes 12E and the cathodes 14E to be adjusted. The level of the electrolytic bath 22, the height of the anodes 12E and the cathodes 14E may require the adjustment of the anode module 12 position relative to the cathode module 14 in the vertical direction, to achieve a selected anode-cathode overlap (ACO) Y, as well as depth of submersion in the electrolyte 22. In some embodiments, as shown in FIG. 1B, the anodes 12E are at least partially immersed in the electrolyte and the cathode electrodes 14E are completely immersed in the electrolyte. Changing the ACO Y can be used to change the cell resistance and maintain stable cell temperature.

[0049] The opposed, vertically oriented electrodes 12E, 14E permit the gaseous phases (O.sub.2) generated proximal thereto to detach therefrom and physically disassociate from the anodes 12E due to the buoyancy of the O.sub.2 gas bubbles in the molten electrolyte. Since the bubbles are free to escape from the surfaces of the anode 12, they do not build up on the anode surfaces to form an electrically insulative/resistive layer allowing the build-up of electrical potential, resulting in high resistance and, high energy consumption. The anodes 12E may be arranged in rows or columns with or without a side-to side clearance or gap between them to create a channel that enhances molten electrolyte movement, thereby improving mass transport and allowing dissolved alumina to reach the surfaces of the anode module 12. The number of rows of anodes 12E can vary from 1 to any selected number and the number of anodes 12E in a row can vary from 1 to any number. The cathodes 14E may be similarly arranged in rows with or without side-to-side clearance (gaps) between them and may similarly vary in the number of rows and the number of cathodes 14E in a row from 1 to any number.

[0050] The shapes of both vertical anodes and cathodes illustrated on FIGS. 1A and 1B are generally plate shaped. Most commonly, the plates are thin and rectangular in shape. More complicated shapes, which may include sharp angles and rapidly changing cross sections can be locations of crack initiation, especially during thermal cycling periods.

[0051] New electrode shapes have then been developed and are described herein below in reference to FIGS. 2A-D and 3.

[0052] As illustrated by the double-head arrows on the left side of FIG. 2A, the electrode plates 100, 200, 300, 400 may define three regions: [0053] an ACO (Anode-Cathode Overlap) region 110 (referenced as Y in FIG. 1B), configured to be located across from anode and cathode material where the current density at the cathode plate is high or maximal for actively producing aluminum; [0054] a middle region 120 that is not across from anode or cathode material, where the surface current density at the electrode is low. The middle region is also known as the AMD (Anode-to-Metal-Distance) region when the electrode plate is a cathode, and as aforesaid, as the BCD (Bath to Cathode Distance) region when the electrode plate is an anode; and [0055] a connecting region 130 extending from the middle region 120 for connecting the electrode plate 100 to the cell. When the electrode plate 100 is a cathode plate extending from the cell's bottom 14B (FIG. 1B), this region is typically located in the metal pad 30 (see FIG. 1B), where the surface current density actively producing aluminum is zero, and this region is also known as the Metal Pad region 30.

[0056] As a consequence of using inert or oxygen-evolving anodes, there is a voltage penalty of approximately 1 volt and an energy consumption penalty of approximately 3 kWh/kg compared to conventional technology. This is because inert anodes produce oxygen gas (O.sub.2) instead of the carbon dioxide gas (CO.sub.2) produced by carbon anodes. These penalties can be compensated by decreasing the current density (both anode current density and cathode plate current density).

[0057] This decrease in current density is achieved by developing proprietary anode and cathode plate materials that are dimensionally stable. The cathode plate is preferably wettable by liquid aluminum metal. These proprietary materials are then arranged in the vertical configuration as disclosed herein that allows retaining the same current per square foot of building space at a lower current density at the active surfaces.

[0058] Minimizing the middle region 120 minimizes the impact on cell resistance and energy efficiency, since there is little amount of current in this region.

[0059] Various shapes for vertical electrodes are proposed. Complexity, difficulty in manufacturing, and concerns about cracking and inadequate strength have to be taken into account when considering the shape of the electrode plates, in particular the cathode plates where the metal is produced.

[0060] Another approach consists in decreasing the middle region 120 of the electrode plate 100 as far as its mechanical strength and stability allow. For example, for a thin electrode plate, where the thickness is much smaller than its length or width and where the length-to-average-width aspect ratio is between 5 and 10, approximately 8 in a preferred embodiment, then the ratio of cross-sectional area at the top of the electrode plate to the cross-sectional area at the bottom of the electrode plate should be superior to 1, more preferably equal or superior to 2.

[0061] As illustrated on FIG. 2A, the electrode plate 100 has a straight rectangular shape in which the average cross-sectional area ratio of the ACO region to the middle or to the lower region is 1 (one). However, the surface ratio between the ACO and middle areas can be modulated or tuned by varying the ACO region in order to have a surface ratio superior to 1.

[0062] FIG. 2B, FIG. 2C and FIG. 2D illustrate more complex shapes with a larger area of the electrode plates in regions of high current density and a smaller area in regions of low current density. One can select the electrode plate shape and dimensions that simultaneously optimize cell voltage, energy consumption, and mechanical strength of the electrode plate.

[0063] FIG. 2B illustrates an electrode plate 200 having a goal post shape with a pair of narrow legs 210 on either side with a gap 220 in the middle and connecting regions 120, 130 below the ACO region 110.

[0064] FIG. 2C illustrates an electrode plate 300 having a paddle shape wider in the ACO region 110 and narrower in the middle/connecting regions 120, 130.

[0065] FIG. 2D illustrates an electrode plate 400 having a trapezoidal shape, wherein the width of the electrode plate is continuously sizing down from the ACO region 110 to the middle region 120 and then to the connecting region 130.

[0066] The shape which results in the highest current density is the one that has the least area in the middle/connecting regions 120, 130 below the ACO region 110, such as with goal post shape 200 and the paddle shape 300.

[0067] The trapezoidal shape 400 of FIG. 2D preferably combines the advantages of maximizing the metal produced in the upper ACO region 110, with ease of manufacture (i.e., the parts can be made as net-shape without cut-outs) with lower manufacturing cost, adequate strength, and avoidance of abrupt changes in cross section or inside cuts, that be sources of crack initiation (i.e., no introduction of weak points or crack initiation sites).

[0068] Typically, the electrode plates as defined herein, when used as a cathode plate, can be made of titanium diboride (TiB.sub.2) or zirconium diboride (ZrB.sub.2). Any material that is electrically conductive, resistant to molten metal and electrolyte, and wettable to a metal, such as aluminum, can be used without departing from the scope of the present disclosure.

[0069] As illustrated on FIG. 4 and FIG. 5, it is also disclosed a method 1000 or a method 2000 respectively for controlling the current density of a plurality of electrodes plates defining anode and cathode plates vertically aligned and arranged in alternating rows in an electrolytic cell, the electrode plate defining: a connecting region for connecting the electrode plate to the electrolytic cell; a middle region extending from the connecting region without overlapping adjacent electrode(s); and an ACO region extending from the middle region and configured for overlapping adjacent electrodes(s); wherein each electrode plate comprises a surface for facing another electrode plate of the adjacent row.

[0070] As illustrated on FIG. 4, the method 1000 comprises the step of: [0071] maximizing current density in the ACO region by varying a ratio of the ACO region's surface area to the middle region's surface area such as the ACO/middle surface area ratio is superior to one 1100.

[0072] As illustrated on FIG. 5, the method 2000 comprises the step of: [0073] providing electrode plates in which an average cross-sectional area ratio of the ACO region to the middle and connecting regions is superior to one in order to maximize current density in the ACO region while retaining a mechanical strength of the connecting region for supporting the electrode plate 2100.

[0074] As illustrated on FIG. 6, it is also disclosed a method 3000 for maximizing the current density of an electrolytic cell comprising a plurality of electrodes plates defining anode and cathode plates vertically aligned and arranged in alternating rows in an electrolytic cell. The method 3000 comprising the step of: [0075] replacing each of existing electrodes plates of the cell by the electrodes plate as disclosed herein 3100.

Example

[0076] FIG. 3 shows an example of an electrode plate 500 in accordance with a preferred embodiment of the present disclosure comprising as well an ACO region 110, a connecting region 130 and a middle region 120 extending therebetween.

[0077] The electrode plate 500 and the trapezoidal electrode plate 400 of FIG. 2D differ in that the opposite edges 530a, 530b of the connecting region 130 of the plate 500 are parallel one to the other. The width of the electrode plate 500 is continuously sizing down from X1 at the top end 510 of the ACO region 110 to X2 at the bottom end 520 of the middle region 120, the bottom 530 of the plate forming the connecting region 130 having a rectangular-like shape with the parallel edges 530a, 530b.

[0078] According to a preferred embodiment, as shown on FIG. 3, the plate 500 may further have a round transition between the top end 510 and each of the two opposite edges 510a, 510b of the ACO region 110, identified with the radius R1. Furthermore, the plate 500 may have a round transition between the bottom end 530 and each of the two opposite edges 530a, 530b of the connecting region 130, identified with the radius R2. Such round transitions R1 and/or R2 allow avoiding to introduce weak points or crack initiation sites of the electrode plates 500.

[0079] Table 1 below provides some dimensions of the electrodes plates 500 illustrated on FIG. 3, with L representing the total length of the electrode plate.

TABLE-US-00001 TABLE 1 Example of electrode plate (FIG. 3) Length (L) 581.8 7.5 mm ACO region (110) 406 10 mm Connecting region (130) 78.6 1.0 mm Top end (X1) 86 1.5 mm Bottom end (X2) 53.8 1.0 mm Round transition (radius R1) 25.3 0.5 mm Round transition (radius R2) 12.6 0.5 mm

[0080] The electrode plates as disclosed herein avoids the weaknesses discussed in accordance with the previous embodiments because there are no sharp geometry changes or narrow cross sections. The parts can be made into net shapes, without cut-outs, which can introduce flaws and crack initiation sites.

[0081] The invention enables metal production with competitive energy efficiency. The invention also allows for less heat loss in the cathode plate(s).

[0082] While illustrative and presently preferred embodiments of the disclosure have been described in detail hereinabove, it is to be understood that the inventive concepts may be otherwise variously embodied and employed and that the appended claims are intended to be construed to include such variations except insofar as limited by the prior art.