EP1428910A1

EP1428910A1 - Method For Converting An Electrorefinery And Device For Use Therein

Info

Publication number: EP1428910A1
Application number: EP02102750A
Authority: EP
Inventors: Pascal Briol; Patrick Guillaume
Original assignee: Paul Wurth SA
Current assignee: Paul Wurth SA
Priority date: 2002-12-13
Filing date: 2002-12-13
Publication date: 2004-06-16

Abstract

A method for converting an electrorefinery comprises the steps of:

(a) short-circuiting a first section in an electrical circuit of an electrorefining unit and meanwhile:

removing all electrode sets arranged for operation at a cathode spacing d1 from the electrorefining cells in the section;
installing electrode sets with a cathode spacing d2 in the cells in the section, except the first and last cells;
installing in the first and last cells in the section a cell bypassing device so as to bypass the first and last cells;

(b) after step (a), opening the short-circuit to allow current to circulate through the section again;

(c) repeating steps (a) and (b) for each of the remaining sections in the unit; and

(d) interrupting the power supply in the electrical circuit and meanwhile replacing all head-bars configured for operating at cathode spacing d1 by head-bars configured for operating at cathode spacing d2.

A cell bypassing device is also presented.

Description

FIELD OF THE INVENTION

The present invention generally relates to a method for converting an electrorefinery and to a device for use therein.

BACKGROUND OF THE INVENTION

Electrorefining is a process that allows producing metals such as e.g. copper, lead, tin and other non-ferrous metals with a very high purity level.
Electrorefining of copper, for example, consists of electrolytically dissolving copper from relatively impure anodes of about 99.7% copper, and selectively plating the dissolved copper in pure form (99.997% and higher) onto a cathode. This reaction takes place in an electrorefining cell containing an electrolyte which is basically copper sulfate and sulphuric acid.
It is well known that for electrorefining at industrial scale, anodes and cathodes are arranged alternately at specified spacing in an open-top electrorefining cell containing the necessary electrolyte therein. The anodes and cathodes have a general sheet-form and are provided in their upper part with conductive lugs, which serve for their support in the cell and for their electrical connection. Therefore, each cell has about a top edge a number of adequately spaced anodic contacts, on which the anode lugs rest when installed in the cell. About the opposite top edge, the electrorefining cell includes a number of adequately spaced cathodic contacts on which the cathode lugs rest.
A typical layout of an electrorefining unit 10 as commonly used in electrorefineries is shown in Fig.1. Electrorefining cells are grouped by sections 14₁...14₁₀, each section 14_i containing a plurality of electrorefining cells 12₁...12₄₀. The sections 14₁...14₁₀ are connected in series in an electrical circuit 16 including a power supply 18, which provides the current necessary for the electrolytic process. Between two adjacent cells, the cathodic and anodic contacts are provided by means of a so-called equipotential bus-bar, in which anodic and cathodic contacts are connected with each other, so that the electrorefining cells 12₁...12₄₀ are connected in series. It is to be noted that the first cell 12₁ of each section 14_i is connected to the electrical circuit 16 by means of an upstream head-bar 20 and the last cell 12₄₀ of each section 14_i is connected to the electrical circuit by means of a downstream head-bar 22, these head- bars 20 and 22 being configured for operating at a cathode spacing corresponding to that of the electrodes in the cells.
An electrorefinery typically comprises a plurality of such electrorefining units. In practice, each section of an electrorefining unit is generally isolated once a week either for loading/unloading electrodes or for maintenance. The section to be isolated is disconnected from the electrical circuit by use of short-circuiting means (indicated 24 in Fig.1) situated between the head-bars of this section. As a result, current directly flows from the upstream head-bar to the downstream head-bar, so that the complete section is bypassed while still providing current to the other sections in the circuit so as not to stop production of the whole unit.
Today, there are two main practices in copper electrorefining, which both employ the above-described layout but differ by the nature of the cathode.
In a conventional process, the cathodes consist of so-called "starter sheets" of high purity copper. These starter sheets are produced by a special electrolytic treatment involving electrodeposition of copper onto either hard rolled copper or titanium blanks.
In a more recent process, permanent reusable cathode blanks (generally stainless steel blades about 3 mm thick) are used instead of the conventional, non-reusable starter sheets. This technology has in particular allowed to: (1) improve the cathode chemical quality; (2) improve productivity (3); increase the refining intensity; (4) reduce the inter-electrodes gap; and (5) improve plant automation.
In view of the advantages of the permanent cathode technology, and since electrorefineries equipped operating with starter sheets have now become relatively old, a number of conventional refineries have been converted to operate with permanent cathodes. Conversion of a conventional electrorefining unit to the permanent cathode technology is convenient since the layout remains the same, i.e. the cells with the associated piping network for the electrolyte is used in the same way in the permanent cathode technology.
It is however to be noted that in the permanent cathode technology, the inter-electrode gap is normally reduced to increase the active area for electrolysis per metre length of cell. Furthermore, the electrical current density for electrolysis is increased, and today permanent cathode refineries are typically operating at 330 A/m² whereas conventional starter sheet refineries operate at around 240 A/m². Therefore, when converting a conventional refinery, it is necessary to renovate the electrical circuit, which means in particular replacing the head-bars.
The installation of new electrode sets (i.e. couples of anodes and cathodes) at the new cathode spacing and renovation of the electrical connections in a section does not present major problems, as a section can be isolated. It will be however understood that, due to the change in cathode spacing, the first and last cells of each section cannot be charged with electrodes until the head-bars have been replaced. The renewal of the head-bars is not only due to the new electrode spacing but also to the need for higher current feed through the head-bars.
Due to the design of the electrical circuit, the renewal of the head-bars must be done for the whole unit at a time. This means that in practice one section is shut-down after the other to be converted, and these sections cannot be put back into production before the change of head-bars, which is done after all sections have been converted. Hence, the production of the unit decreases as the conversion progresses, which obviously leads to important production loss.

OBJECT OF THE INVENTION

The object of the present invention is to provide an improved method for converting a conventional electrorefinery to the permanent cathode technology with a different cathode spacing, which allows minimising production loss. This object is achieved by a method as claimed in claim 1.

SUMMARY OF THE INVENTION

According to the present invention, a method for converting an electrorefinery comprises the steps of:
(a) short-circuiting a first section in an electrical circuit of an electrorefining unit and meanwhile:
- removing all electrode sets arranged for operation at a cathode spacing d1 from the electrorefining cells in the section;
- installing electrode sets with a cathode spacing d2 in the cells in the section, except the first and last cells;
- installing in the first and last cells in the section a cell bypassing device so as to bypass the first and last cells;
(b) after step (a), opening the short-circuit to allow current to circulate through the section again;
(c) repeating steps (a) and (b) for each of the remaining sections in the unit; and
(d) interrupting the power supply in the electrical circuit and meanwhile replacing all head-bars configured for operating at cathode spacing d1 by head-bars configured for operating at cathode spacing d2.
Hence, according to the present method, the problem due to the incompatibility between the initial head-bars that are configured for operating at a cathode spacing d1 and the new electrodes that should operate at cathode spacing d2 is overcome by bypassing the first and last cells of a section. This allows to bring a partially converted section (end of step (a)) back into production, while another section is isolated for conversion. In other words, there is only one isolated section at a time in the electrorefining unit for the conversion. After all sections have been partially converted, the power supply is interrupted and the head-bars are changed, which will allow finishing the conversion by charging the first and last cells of each section with electrode sets at the spacing d2. In the present method, production is not dramatically affected by the conversion works, since only one section is stopped at a time, and the total stop of production only lasts during change of the head-bars. Although this method is particularly adapted for converting a conventional electrorefinery operating with starter sheet to the permanent cathode technology, it may advantageously be used for any type of conversion involving a change in cathode spacing.
So, at the end of step (d), the whole unit has been converted, with the exception of the first and last cells of each section. To provide maximum production capability, the method will thus advantageously include a further step (e), which consists in finishing the conversion of a given section by removing the cell bypassing devices from the first and last cells of the section and installing in these cells electrode sets at spacing d2. It will however be noted that, for reasons of homogeneity in a section, step (e) is preferably carried out for a given section at a time chosen in function of the section's anodic cycle. Indeed, it is preferable to charge the first and last cells of a section with new electrode sets at spacing d2 at the time anodes need to be replaced in the other cells of the section. This also means that, in this case, the use of cell-bypassing devices is still needed after the change of head-bars and until the end of the anodic cycle of a section (preferably the end of the first anodic cycle following the had-bars replacement). The cell bypassing device should thus preferably be capable of bypassing the first and last cells independently of the head-bar contacts spacing. Since after step (d) the circuit is equipped with head-bars configured for operating at spacing d2, the conversion can be finished at any time, since a section can be disconnected from the electrical circuit by means of the short-circuiting means without affecting production in the other sections.
It would also be possible to carry out step (d) at the time a given section in the unit comes to the end of its anodic cycle. In such a case, step (e) can be carried out for the given section directly after step (d), before current is turned back on in the electrical circuit, so that for this particular section, all cells will be charged with electrodes sets at spacing d2.
The electrorefining cells in the section will generally initially be connected in series by means of bus-bars configured for operating at cathode spacing d1 and arranged in between adjacent cells. Therefore, step (a) preferably includes replacing the bus-bars configured for operating at cathode spacing d1 with bus-bars configured for operating at a cathode spacing d2.
Furthermore, after the partial conversion at step (a), the first cell of each section will generally have on one side an upstream head-bar defining anodic contacts configured for operating at cathode spacing d1 and about its opposite side a bus-bar defining cathodic contacts configured for operation at cathode spacing d2. Similarly, the last cell of each section will generally have on one side a downstream head-bar defining cathodic contacts configured for operating at cathode spacing d1 and about its opposite side a bus-bar defining anodic contacts configured for operating at cathode spacing d2. In such a configuration, the first, respectively the last cell of the section is advantageously bypassed by means of a cell bypassing device including a rigid central part and a first contacting structure on a first side of the central part for coming into electrical contact with at least part of the head-bar. The device further includes a second contacting structure on an opposite second side of the central part for selectively coming into contact with at least part of the contacts on the bus-bar, the second contacting structure being electrically connected with the first contacting structure. It is to be noted that the first contacting structure is also capable of coming into contact with at least part of a head-bar configured for operating at spacing d2 (i.e. after the change of head-bars).
Although the use of such a cell bypassing device is preferred in the present method, other cell bypassing means -allowing current to flow in an empty electrorefining cell from the head-bar contacts to the bus-bar contacts- can also be used.
According to another aspect of the invention, a cell bypassing device for an electrorefining cell is proposed, the cell to be bypassed having about a first longitudinal side a head-bar defining a number of anodic, respectively cathodic, contacts at a spacing d1, and about an opposite longitudinal side a corresponding number of cathodic, respectively anodic, contacts at a spacing d2. It will be appreciated that the present cell bypassing device is adapted to rest on the cell and includes:
a rigid central part;
a first contacting structure on a first side of the central part for coming into electrical contact with at least part of the head-bar; and
a second contacting structure on an opposite second side of the central part for selectively coming into contact with at least part of the contacts on the bus-bar, the second contacting structure being electrically connected with the first contacting structure,
This device allows to bypass a cell that has anodic and cathodic contacts configured for operating at different cathode spacings, but its first contacting structure is not limited to a particular cathode spacing on the head-bar. Indeed, contrary to the second contacting structure which is designed to selectively engage the contacts on the bus-bar, the first contacting structure is capable of coming into electrical contact with at least part of the head-bar, that is with any part of the head-bar that allows establishing the electrical contact. When the device is installed in the cell, current flows from the head-bar into the first contacting structure to the second contacting structure and then into the contacts of the bus-bar.
The present device is particularly well suited to be used in a method for converting an electrorefining plant to a technology employing a cathode spacing different from the initial cathode spacing. In this context, it proves particularly advantageous when converting a conventional electrorefinery operating with starter sheet cathodes to the permanent cathode technology with a reduced cathode spacing. It is to be further noted that the present device, by laying across the cell, also allows covering the open-top electrorefining cell, which is interesting with regard to safety.
In practice, in case the electrorefining cell to be bypassed is the first cell of a section, the head-bar is an upstream head-bar defining anodic contacts at spacing d1 and the bus-bar defines cathodic contacts at spacing d2. In case the electrorefining cell to be bypassed is the last cell of a section, the head-bar is a downstream head-bar defining cathodic contacts at spacing d1 and the bus bar defines anodic contacts at spacing d2.
In a preferred embodiment, the cell bypassing device includes an electrically conductive central structure. The first contacting structure is an electrically conductive bar with a flat side that can be laid on the head-bar contacts when they are arranged in a plane. The second contacting structure includes a number of fingers extending away from the central part and spaced from each other by a distance corresponding to cathode spacing d2. These fingers thus engage the contacts on the bus-bar. Current thus flows from the first to the second contacting structure through the central part.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG.1: is a sketch illustrating the conventional layout of an electrorefining unit in an electrorefinery;
FIG.2: is a sketch illustrating the incompatibility between an upstream head-bar configured for a cathode spacing d1 and electrode sets arranged at a cathode spacing d2; and
FIG.3: is a sketch of the first three electrorefining cells in a section.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The typical layout of an electrorefining unit 10 is shown in Fig.1. The shown unit 10 includes ten sections 14₁...14₁₀ consisting each of two rows of twenty electrorefining cells 12₁...12₂₀ and 12₂₁ to 12₄₀. The sections 14₁...14₁₀ are connected in series in an electrical circuit 16 including a power supply 18, which provides the current necessary for the electrolytic process (the direction of current in the electrical circuit 16 is indicated by arrows 19). Within each section 14_i, the cells 12₁...12₄₀ are connected in series, so that the current flows through the section 14_i according to the path indicated by arrow 23.
Turning now to Fig.3, an electrorefining cell can be seen in more detail. As is well known, an electrorefining cell 12₂ or 12₃ conventionally consists of an open-top tank charged with electrode sets that are arranged to obtain an alternance of anodes 30 and cathodes 32 at a specified cathode spacing. The anodes 30 and cathodes 32 have a general sheet-form and are provided in their upper part with conductive lugs, which serve for their support in the cell and for their electrical connection. The cell 12_i is filled with the necessary electrolyte and electrodes 30, respectively 32, of similar polarity are connected in parallel. Therefore, each cell 12_i has about a top edge a number of adequately spaced anodic contacts (not shown), on which the anode lugs rest when the electrodes are in place in the cell. About the opposite top edge, the electrorefining cell 12_i includes a number of adequately spaced cathodic contacts (not shown) on which the cathode lugs rest.
Between two adjacent cells 12_i,i+1, the cathodic and anodic contacts are provided by means of a so-called bus-bar (not shown), in which anodic and cathodic contacts are connected with each other. Such a bus-bar installed e.g. between cells 12₂ and 12₃ thus has a number of cathodic contacts next to e.g. cell 12₂ and a number of anodic contacts next to cell 12₃, so that the electrorefining cells 12₁...12₄₀ are connected in series.
It is to be noted that the first cell 12₁ of each section 14_i is connected to the electrical circuit 16 by means of an upstream head-bar 20 and the last cell 12₄₀ of each section 14_i is connected to the electrical circuit 16 by means of a downstream head-bar 22, these head- bars 20 and 22 being configured for operating at the cathode spacing of the electrodes in the cells.
It will be understood that since the current enters a section 14_i via the upstream head-bar 20 (upstream with regard to the direction of current), this head-bar 20 is configured to define anodic contacts, which are spaced from each other by a given distance adapted to the cathode spacing.
Similarly, as the downstream head-bar 22 ends a section 14_i, it is configured to define cathodic contacts at the adapted cathode spacing.
In practice, an upstream head-bar 20 may be a copper bar that is partially covered with an insulator on areas defining cathode support zones and the non-insulated areas provide the anodic contacts. For the downstream head-bars 22, the configuration is inverted, i.e. the insulated areas define anodic support zones.
In order to be able to disconnect (isolate) a section 14_i from the circuit 16 without interrupting the production in the other sections, each section 14_i is provided with short-circuiting means 24 that allow to selectively direct the current from the section's upstream head-bar 20 directly to the downstream head-bar 22.
As a result, current does not flow through the isolated section, thereby allowing to bypass a complete section 14_i while still providing current to the other sections in the circuit 16 so as not to stop production of the whole unit 10. In Fig.1, the third section 14₃ is short-circuited (indicated by arrows 26), and thus allows maintenance or loading/unloading of electrodes in the section 14₃.
As already mentioned, the conventional electrorefining practice has used starter sheet cathodes, but the more recent permanent cathode technology proves more advantageous in terms of quality and productivity.
Since the layout of the electrorefining unit 10 is the same for both cathode technologies, some conventional electrorefineries have been converted to operate with permanent cathodes.
Although such a conversion is convenient since it allows reusing the cell tanks and associated piping network for the electrolyte, it is to be noted that in the permanent cathode technology, the cathode spacing is generally reduced with regard to the starter sheet technology. This thus leads to an incompatibility between the installed head-bars that are configured for operating with a cathode spacing d1 and new electrode sets that are to be arranged at a reduced cathode spacing d2.
This incompatibility is schematically illustrated in Fig.2, wherein an upstream head-bar 20' is partially shown from above. This upstream head-bar 20' is a copper bar selectively covered by insulating material generally indicated 34 to define anodic contacts 36 and cathodic support zones 38, an anodic contact 36 being an uncovered copper area in between two cathodic support zones 38 (i.e. areas of the copper bar covered by insulating material). The shown head-bar 20' is configured for operating at cathode spacing d1. Reference signs 30' and 32' illustrate the connecting lugs of anodes, respectively cathodes, that are arranged at a cathode spacing d2. As can be seen, head-bar 20' does not allow a proper connection of anodes 30' nor a proper insulating support of cathodes 32' at the required spacing d2.
When converting an existing electrorefinery to a permanent cathode technology with a reduced cathode spacing d2, the short-circuiting means allows to convert a section without shutting-down the power supply. However, due to the incompatibility between head- bars 20, 22 and the new electrode spacing, the first 12₁ and last 12₄₀ cells of each section 14_i cannot be charged with electrodes at the new, reduced cathode spacing until the head- bars 20, 22 have been changed.
Due to this incompatibility, the common practice for converting an existing electrorefining unit is to start by converting one section after the other. The conversion thus conventionally ends by replacing the head-bars and charging the new electrodes into the first and last cells of each sections.
As a result, in the common practice, a section is shut-down after the other as the conversion of the unit progresses, which leads to substantial production loss.
It will be appreciated that the present method for converting an electrorefinery allows minimising production loss during conversion of an electrorefining unit, in particular during conversion to the permanent cathode technology with a reduced cathode spacing.
According to a first step (a) of the present method, a first section 14_i of the unit 10 is short-circuited by closing the short-circuit 24, and meanwhile the section 14_i is converted, except for the first 12₁ and last 12₄₀ cells of the section 14_i. This conversion of the section mainly involves:

removing all existing electrode sets (i.e. anodes and cathodes) arranged at cathode spacing d1;
removing the existing bus-bars configured for operating at cathode spacing d1;
installing bus-bars configured for operating at a cathode spacing d2; and
charging the cells with electrode sets at cathode spacing d2, except for the first 12₁ and last 12₄₀ cells.

It will be appreciated that in order to be capable of bringing the partially converted section 14_i back into production, a cell bypassing device is installed at step (a) in the first 12₁ and last 12₄₀ cells in order to bypass each of these cells 12₁, resp. 12₄₀. Such a device, which will be described in more detail hereinbelow, basically includes a rigid structure apt to be laid on the cell and a first contacting structure on a first side of the central part for coming into contact with at least part of the head-bar, which defines a number of the anodic, respectively cathodic, contacts at spacing d1; and a second contacting structure on an opposite second side of the central part for selectively coming into contact with at least part of the cathodic, respectively anodic, contacts of the bus-bar (at spacing d2) arranged on the opposite side of the cell. The first electrical contacts are linked with the second electrical contacts, so that the current can flow between head-bar and bus-bar.
In the next step (b) of the method, the short-circuiting means 24 is opened to bring the section 14_i back into production. The cell bypassing devices allow the passage of current from the upstream head-bar 20 to the second cell 12₂, respectively from the penultimate cell 12₃₉ to the downstream head-bar 22. Hence, contrary to the conventional practice, the present method allows to bring a section 14_i back into production before changing the head- bars 20, 22, thereby minimising production loss due to conversion.
According to the further step (c) of the method, steps (a) and (b) are repeated for all the sections in the unit 10.
Finally, in a next step (d), the power supply is interrupted and meanwhile the existing upstream 20 and downstream 22 head-bars configured for operating at cathode spacing d1 are replaced by upstream and downstream head-bars configured for operating at cathode spacing d2.
At the end of step (d), the whole unit has been converted, with the exception of the first 12₁ and last 12₄₀ cells of each section 14_i. To provide maximum production capability, the method advantageously includes a further step (e), which consists in finishing the conversion of a given section 14_i by removing the cell bypassing devices from the first 12₁ and last 12₄₀ cells of the section and installing in these cells electrode sets at spacing d2. It will however be noted that, in order to operate a unit with homogenous sections, step (e) is preferably carried out for a given section when it reaches the end of its anodic cycle. The cell bypassing device is thus advantageously designed to be capable of bypassing the first and last cells independently of the head-bar spacing.
Fig.3 shows such a cell bypassing device 40 installed in the first cell 12₁ of a section. The device 40 includes an electrically conductive rigid central part 42. A first contacting structure for contacting the upstream head-bar 20 is provided by an electrically conductive bar 44 that is laid on the head-bar 20 so that it comes into contact with at least part of the head-bar 20. The second contacting structure includes a number of electrically conductive fingers 46 extending away from the central part 42 and spaced from each other by a distance d2, so that they selectively come into contact with the cathodic contacts on the bus-bar (not shown) in-between cells 12₁ and 12₂. The individual fingers are in electrical connection with the bar 44 through the electrically conductive central part 42. Hence, the current, instead of flowing trough the first cell 12₁, flows from the upstream head-bar 20 trough the device 40 to the opposite bus-bar.
It will be appreciated that the bar 40 allows connection to the head-bar independently of its configuration with regard to cathode spacing. Indeed, when the cell is empty, any part of the head-bar could be contacted. The bar 44 of the device 40 is thus laid on the head-bar in such a way that there is an electrical contact with at least part of the head-bar.
As already explained, the upper surface of a head-bar is typically selectively covered by an insulator, to define support areas for the electrode lugs that should not be in electrical connection with the head-bar. If desired, when the cell is empty, it is possible to remove the insulator to facilitate the contact between bar 44 and head-bar. Similarly, when installing the new head-bars, the installation of the insulator may be delayed to the moment when the devices 40 are not anymore required (i.e. when charging with new electrode sets).
In some cases, the head-bar has an embossed upper surface, which defines the zones where the insulator is to be installed. Hence, anodic contacts may e.g. be defined by raised zones of the head-bar surface and the cathodic support areas are recesses filled with insulator. It follows that all the anodic contact surfaces will substantially be in a same plane, and that when the bar 44 is laid with its flat side on the head-bar, it will contact all the anodic contact surfaces.
The device is preferably made of metal having good electrical conductivity, such as e.g. copper.
In Fig.3, the device 40 is shown as a single element laying over the whole length of the cell 12₁. However, for an easier handling, the device 40 may be designed to bypass only one region of the cell 12₁, so that e.g. two or three devices 40 will be laid next to each other to cover the whole length of the cell 12₁.

LIST OF REFERENCE SIGNS

10: electrorefining unit
12₁...12₄₀: electrorefining cells
14₁...14₁₀: sections
16: electrical circuit
18: power supply
19: direction of current
20: upstream head-bar
22: downstream head-bar
23: direction of current in the section
24: short-circuiting means
26: direction of current in short-circuit
30: anodes
32: cathodes
34: insulating material
36: anodic contacts
38: cathodic support zones
40: cell bypassing device
42: central part
44: electrically conductive bar
46: fingers

Claims

A method for converting an electrorefinery, the electrorefinery to be converted comprising:

at least one electrical circuit for supplying current to a number of sections connected in series, each section comprising a plurality of electrorefining cells connected in series, wherein each electrorefining cell comprises a number of electrode sets arranged for operating at a cathode spacing d1;

an upstream head-bar connecting the electrical circuit to the first cell of each section, the upstream head-bar defining anodic contacts configured for operating at the cathode spacing d1;

a downstream head-bar connecting the last cell of each section to the electrical circuit, said downstream head-bar defining cathodic contacts configured for operating at the cathode spacing d1; and

means for short-circuiting a section by directly connecting the upstream head-bar to the downstream head-bar;

said method comprising the following steps:

(a) short-circuiting a first section and meanwhile:

removing all electrode sets arranged for operating at cathode spacing d1 from the electrorefining cells in the section;

installing electrode sets with a cathode spacing d2 in the cells in the section, except the first and last cells;

installing in the first and last cells in the section a cell bypassing device so as to bypass the first and last cells;

(b) after step (a), opening the short-circuit to allow current to circulate through the section again;

(c) repeating steps (a) and (b) for each of the remaining sections in the unit; and

(d) interrupting the power supply in the at least one electrical circuit and meanwhile replacing all head-bars configured for operating at cathode spacing d1 by head-bars configured for operating at cathode spacing d2.
The method according to claim 1, comprising a further step (e), wherein the conversion of a given section in the unit is finished by removing the cell bypassing devices from the first and last cells of the section and installing in these cells electrode sets at spacing d2.
The method according to claim 2, wherein step (e) is carried out selectively for each section in function of the actual advancement in the section's anodic cycle.
The method according to claim 3, wherein step (e) is carried out when a section is isolated at the end of its anodic cycle to be charged with new anodes.
The method according to any one of the preceding claims, wherein the electrorefining cells in the section are initially connected in series by means of bus-bars configured for operating at a cathode spacing d1 and arranged in-between adjacent cells, and wherein step (a) includes replacing the bus-bars configured for operating at cathode spacing d1 with bus-bars configured for operating at cathode spacing d2.
The method according to any one of the preceding claims, wherein
at the end of step (a), the first cell, respectively the last cell, has on one side an upstream, respectively downstream, head-bar defining anodic, respectively cathodic, contacts configured for operating at cathode spacing d1 and about its opposite side a bus-bar defining cathodic, respectively anodic, contacts configured for operating at cathode spacing d2; and
said cell bypassing device includes:

a rigid central part;

a first contacting structure on a first side of the central part for coming into electrical contact with at least part of the head-bar; and

a second contacting structure on an opposite second side of the central part for selectively coming into contact with at least part of said contacts on the bus-bar, the second contacting structure being electrically connected with the first contacting structure.
A cell bypassing device for an electrorefining cell, said electrorefining cell having about a first longitudinal side a head-bar defining a number of anodic, respectively cathodic, contacts at spacing d1 and on an opposite longitudinal side a bus-bar defining a number of cathodic, respectively anodic, contacts at spacing d2, said device being adapted to rest on said cell and including:

a rigid central part;

a first contacting structure on a first side of said central part for coming into electrical contact with at least part of the head-bar; and

a second contacting structure on an opposite second side of said central part for selectively coming into contact with at least part of said contacts on the bus-bar, the second contacting structure being electrically connected with the first contacting structure.
The device according to claim 7, wherein
said contacts on said head-bar are arranged in a plane; and
said first contacting structure is an electrically conductive bar with a flat side that can be laid on the contacts on the head-bar.
The device according to claim 7 or 8, wherein said second contacting structure includes a number of fingers extending away from the central part and spaced from each other by a distance corresponding to cathode spacing d2.
The device according to any one of claims 7 to 9, wherein said device is made of a metal having good electrical conductivity.