System and method for starting an electrolyzer

Abstract

A system and method for starting an electrolytic cell are disclosed. The system and method are particularly suitable for preheating an electrolytic cell or kettle having a cathode prior to installing a preheated anode in the cell for the production of metal (e.g., aluminum). The system includes one or more electric heaters installed in the cell in place of the anode assembly, and the system can be used with a dry bath or a liquid molten bath (e.g., cryolite). Preferably, the cell is preheated by as many cell preheaters as anode assemblies. Preferably, the cell preheaters are powered by the current available in the busbar of the kettle. The present invention is environmentally friendly as it is preferably suitable for preheating cells that work with inert anodes or oxygen evolving anodes. In addition, the startup method allows for optimizing / reducing the time required to start the electrolytic cell while ensuring that the material is located within the cell.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims priority to U.S. Provisional Patent Application No. 63 / 018,680, entitled “System and Method for Starting an Electrolyzer,” filed in the U.S. Patent and Trademark Office on May 1, 2020, the contents of which are incorporated herein by reference. Technical Field

[0003] The present invention generally relates to systems and methods for starting up an electrolytic cell, such as a preheating tank or kettle prior to installing an anode assembly, for example, in a preheating tank used to produce metals such as aluminum. Background Art

[0004] In a conventional Hall-Heroult cell with carbon anodes used in aluminium electrolysis, the cell is preheated before start-up using a bed of carbonaceous material between the anode and cathode, which acts as a resistor, either by gas or fuel burners (circuit open) or by the Joule effect (circuit closed).

[0005] The use of a carbon-containing resistive bed is chemically incompatible with the electrode materials used for inert electrodes, such as inert anodes or oxygen-evolving anodes. In addition, when the bath melts at the end of preheating, loose particles of the carbon-containing bed will float in the bath and can have a negative impact on anode life.

[0006] The use of direct heating by gas or fuel is not suitable for inert anode cells whose lining may include some materials sensitive to thermal shock, because, given the geometry of the electrolytic cell, it is difficult to prevent the flame from coming into contact with the material and therefore to ensure a smooth and controlled heating profile and a uniform temperature throughout the cell.

[0007] Therefore, in the production of metals, such as aluminum, there is a need for new preheating systems and methods for preheating and starting electrolytic cells that can be used with inert electrodes, such as oxygen-evolving anodes. Summary of the Invention

[0008] Generally, prior art shortcomings are alleviated by new systems and methods for preheating electrolytic cells typically used in the electrolytic production of metals, such as aluminum, and new methods for starting up electrolytic cells using such systems or methods.

[0009] The present invention first relates to a preheating system for preheating an electrolytic cell. The electrolytic cell includes at least one cathode assembly and is configured to receive at least one anode assembly and an electrolytic bath for electrolytic production of metals. The preheating system includes at least one electric heater configured to be installed in the electrolytic cell in place of the at least one anode assembly for preheating the cell prior to installation of the at least one anode assembly in the cell.

[0010] According to a preferred embodiment, the at least one electric heater is configured to, once installed in the bath, provide a resistance R AA Equal resistance R CH , whereby the electrical and thermal profiles of the electrolytic cell remain balanced during replacement of at least one electric heater by at least one anode assembly.

[0011] According to another preferred embodiment, the at least one electric heater is configured to, once installed in the bath, provide a resistance R AA Equal variable resistor R CH , whereby the electrical and thermal profiles of the electrolytic cell remain balanced during replacement of at least one electric heater by at least one anode assembly.

[0012] According to a preferred embodiment, the electrolytic cell is configured to receive N AA At least one anode assembly, where N AA ≥1, the preheating system includes N CH At least one electric heater, where N CH ≥ 1. Each of the at least one electric heater is configured to replace at least one anode assembly to be installed in the electrolytic cell, wherein N CH =N AA and each of the at least one electric heater further comprises a power supply module operably connected to each of the at least one electric heater for supplying power to the at least one electric heater through current for preheating the electrolytic cell.

[0013] According to a preferred embodiment, the power supply module is configured to connect a main busbar of the electrolysis cell to each of the at least one electric heater for providing the current available in the main busbar.

[0014] According to a preferred embodiment, the preheating system has a current intensity A and N CH The resistance R of the tank heater CH The applied power P, where P = (R CH / N CH )*A 2 , then P is greater than the power required to heat the tank, resulting in excess energy, and the tank is configured to discharge the excess heat.

[0015] According to a preferred embodiment, the preheating system further comprises at least one electrical resistor located at the top of the preheating system to discharge excess heat.

[0016] According to a preferred embodiment, the cathode assembly and the anode assembly include a plurality of vertical cathodes and vertical anodes, respectively.

[0017] According to a preferred embodiment, the preheating system as defined herein may also be used to maintain the temperature of the preheated tank.

[0018] According to a preferred embodiment, the preheating system as defined herein may also be used for replacing a defective anode assembly of at least one anode assembly of an electrolysis cell during metal production and for maintaining and / or replacing defective anode assemblies.

[0019] According to a preferred embodiment, the metal to be produced is aluminum and at least one anode assembly comprises an inert anode or an oxygen evolving anode.

[0020] The present invention also relates to a method for preheating an electrolysis cell comprising at least one cathode assembly and configured to receive at least one anode assembly and an electrolytic bath for aluminum electrolysis production. The method comprises the steps of preheating the electrolysis cell using at least one electric heater installed in the electrolysis cell, replacing the at least one anode assembly.

[0021] According to a preferred embodiment, the method as defined herein may further comprise the steps of: introducing an electrolytic bath in the electrolytic cell once a given temperature of the electrolytic cell has been reached; and replacing the at least one electric heater with the at least one anode assembly.

[0022] According to a preferred embodiment, the step of preheating the electrolytic cell may comprise the steps of providing a resistance R AA Equal or nearly equal resistance R CH , so that the electrical and thermal distribution of the cell remains balanced during replacement of the electric heater by the anode assembly.

[0023] According to a preferred embodiment, the step of preheating the electrolytic cell may include the following steps: providing a variable resistance R to at least one electric heater CH ; and once installed in the bath, adjust the variable resistor R CH Until it is equal to the resistance R of at least one anode assembly AA , whereby the electrical and thermal profiles of the electrolytic cell remain balanced during replacement of the at least one electric heater by the at least one anode assembly.

[0024] According to a preferred embodiment, the electrolytic cell is configured to receive N AA At least one anode assembly, where N AA ≥1, the method comprises the following steps: installing N in the electrolytic cell CH Electric heaters, N CH ≥1, to replace at least one anode assembly, where N CH =N AA and powering each of the at least one electric heater with electric current for heating the electrolytic cell.

[0025] According to a preferred embodiment, the step of supplying power to each of the at least one electric heater comprises the step of supplying the current available in the main busbar of the electrolysis to each of the at least one electric heater.

[0026] According to a preferred embodiment, the method as defined herein may further comprise, during preheating of the electrolysis cell, the step of removing excess heat from the cell.

[0027] According to a preferred embodiment, the method as defined herein may further comprise the step of maintaining the temperature of the preheating tank by powering at least one of at least one electric heater installed in the electrolysis tank replacing at least one anode assembly.

[0028] According to a preferred embodiment, the method as defined herein may further comprise the step of replacing a defective anode assembly of at least one anode assembly of the electrolysis cell for maintenance and / or replacement of defective anode assemblies during metal production.

[0029] According to a preferred embodiment, the metal produced by the method as defined herein is aluminium and the at least one anode assembly comprises a plurality of inert anodes or oxygen evolving anodes, more preferably according to a vertical configuration of electrodes.

[0030] The present invention also relates to a method for starting up an electrolytic cell for producing metals, the electrolytic cell comprising at least one cathode assembly and being configured to receive at least one anode assembly and an electrolytic bath for the electrolytic production of metals, the electrolytic bath being a dry bath at ambient temperature. The method comprises:

[0031] providing a dry bath in the electrolytic cell at ambient temperature;

[0032] installing at least one heating element in the electrolytic cell at ambient temperature to replace at least one anode assembly;

[0033] heating the electrolytic cell by supplying an electric current to each of the at least one heating element;

[0034] Once a given temperature has been reached in the electrolytic cell, the melting of the dry bath is controlled by at least one heating element and, optionally, a portion of the electrolytic bath is injected into the electrolytic cell in its liquid form to top up the cell;

[0035] injecting a portion of the metal to be produced into the electrolytic cell; and

[0036] One or more of the at least one heating element is replaced by the anode assembly until each of the at least one heating element is removed from the electrolytic cell.

[0037] The present invention also relates to a method for starting an electrolytic cell for producing metals, the electrolytic cell comprising at least one cathode assembly and being configured to receive at least one anode assembly and an electrolytic bath for the electrolytic production of metals, the electrolytic bath being a liquid molten bath. The method comprises:

[0038] installing at least one heating element in the electrolytic cell at ambient temperature to replace at least one anode assembly;

[0039] heating the electrolytic cell by supplying an electric current to each of the at least one heating element;

[0040] Once a given temperature has been reached in the electrolysis cell, pouring a liquid molten bath and optionally a portion of the metal to be produced into the electrolysis cell; and

[0041] One or more of the at least one heating element is replaced by the anode assembly until each of the at least one heating element is removed from the electrolytic cell.

[0042] According to the preferred embodiment of the above two methods (using dry bath or liquid bath), for an anode assembly to be installed in an electrolytic cell, N is removed from the electrolytic cell. HE Heating elements, where N HE ≥1 and N HE Depends on N HE The total resistance R provided by the heating elements is selected to be close to or nearly equal to the resistance R of at least one anode assembly. AA .

[0043] According to a preferred embodiment, each of the heating elements comprises at least one resistor, wherein when more than one at least one resistor is present, each of the at least one resistor is electrically connected in parallel.

[0044] According to a preferred embodiment, the electrolytic cell is further heated by distributing the heat generated inside the electrolytic cell to at least one cathode assembly. Preferably, the heat distribution inside the electrolytic cell is performed taking into account the temperature rise, which depends on the nature of the material heated inside the electrolytic cell.

[0045] According to preferred embodiments, the above two methods (using a dry bath or a liquid bath) may further include the step of discharging excess heat from the electrolytic cell. Preferably, this is accomplished by providing at least one additional resistor on top of at least one heating element. More preferably, excess heat may be discharged from the electrolytic cell via an electrolytic cell exhaust system located at the top of the electrolytic cell.

[0046] According to a preferred embodiment, the above two methods (using a dry bath or a liquid bath) may further include the step of protecting the side walls of the electrolytic cell from heating. Preferably, protecting the side walls from heating includes the step of forcing heat to circulate from the at least one heating element to the at least one cathode assembly by using a protective material extending from the side walls.

[0047] According to a preferred embodiment, for both methods described above (using a dry bath or a liquid bath), the given temperature of the preheated electrolytic cell is reached after a period of between 2 and 5 days and is between 700 and 1000° C. Preferably, the metal to be produced is aluminum and at least one anode assembly comprises an inert anode or an oxygen evolving anode.

[0048] The present invention is environmentally friendly as it is particularly suitable for preheating electrolytic cells using inert anodes or oxygen evolving anodes, whether with or without an electrolytic bath in the cell prior to installing the anode assembly in the bath.

[0049] Other and further aspects and advantages of the present invention will be better understood by reading the illustrative embodiments to be described in or pointed out in the appended claims, and those skilled in the art will realize various advantages not mentioned herein by actually using the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The above and other aspects, features and advantages of the present invention will become more apparent from the following description with reference to the accompanying drawings, in which:

[0051] Figure 1 is a schematic diagram of an anode assembly according to a preferred embodiment;

[0052] Figure 2 is a front view of an electrolytic cell having vertical anode and cathode assemblies according to a preferred embodiment;

[0053] Figure 3 According to a preferred embodiment, Figure 2 A cross-sectional view of the electrolytic cell shown along line AA;

[0054] Figure 4 is a schematic front view of a tank preheater according to a preferred embodiment;

[0055] Figure 5 According to a preferred embodiment, Figure 4 Schematic side view of a tank preheater shown in .

[0056] Figure 6 According to different preferred embodiments, Figure 4 and 5 Schematic bottom view of the tank preheater shown in .

[0057] Figure 7 is a schematic diagram of a tank preheater installed in an electrolytic cell or kettle and connected to a power supply loop according to a preferred embodiment;

[0058] Figure 8 is a schematic diagram of a tank preheater installed in an electrolytic tank or kettle and connected to a kettle bus bar according to another preferred embodiment;

[0059] Figure 9 is a schematic diagram of a plurality of tank preheaters installed in a tank according to another preferred embodiment;

[0060] Figure 10 is a schematic diagram of a plurality of tank preheaters installed in a tank according to another preferred embodiment, wherein a resistor is provided on top of the tank preheater to dissipate excess heat;

[0061] Figure 11 is a flow chart showing a preheating method according to a preferred embodiment;

[0062] Figure 12 According to the first preferred embodiment, Figure 11 a flow chart of the preheating step of the illustrated method;

[0063] Figure 13 According to the second preferred embodiment, Figure 11 a flow chart of the preheating step of the illustrated method;

[0064] Figure 14 is a flow chart showing a startup method using a dry bath according to a preferred embodiment; and

[0065] Figure 15 is a flow chart showing a startup method using a liquid molten bath, according to a preferred embodiment. DETAILED DESCRIPTION

[0066] The novel systems, methods and processes will be described below.While the present invention has been described with respect to specific illustrative embodiments, it should be understood that the embodiments described herein are by way of example only and are not intended to limit the scope of the invention thereby.

[0067] The following description and the embodiments described therein are provided by way of examples illustrating the principles and embodiments of the present invention. These examples are provided for the purpose of explaining, but not limiting, those principles of the present invention. In the following description, similar components and / or steps are marked and illustrated with the same respective reference numerals throughout the specification.

[0068] The terms used herein are in accordance with the definitions listed below.

[0069] "About" indicates that the time, resistance, current, volume, or temperature value may vary within the specified range based on the error limit of the method or device used to evaluate the time, resistance, current, volume, or temperature.

[0070] As used herein, the expression "anode assembly" is meant to encompass a single anode or a plurality of anodes.

[0071] As used herein, the expression "cathode assembly" is meant to encompass a single cathode or a plurality of cathodes.

[0072] As previously stated, the present invention, as disclosed herein, is primarily directed to a preheating system for preheating an electrolytic cell.

[0073] like Figure 2 and 3 As shown, an electrolytic cell 10, or simply cell or kettle hereinafter, generally includes a bottom wall 13 and side walls 15 extending therefrom, and is configured to receive an electrolytic bath 12 for the electrolytic production of a metal, such as aluminum. Bath 12 can be a dry solid bath to be melted at ambient temperature, or a liquid molten bath including an electrolyte, such as cryolite (NaAlFe). Cell 10 also includes at least one cathode assembly 20 having at least one cathode, such as, but not limited to, a vertical cathode.

[0074] The tank 10 is further configured to receive at least one corresponding anode assembly 30, such as Figure 1 The anode assembly 30 has at least one anode 32. Preferably, the anode assembly 30 comprises a plurality of vertical anodes that extend downwardly toward the cathode assembly once inserted into the cell ( Figure 2 and 3 An example of an electrolytic cell comprising a vertical cathode assembly or module and a vertical anode assembly or module is disclosed in U.S. Patent No. 10,415,147 B2 (ELYSIS LIMITED PARTNERSHIP), the contents of which are hereby incorporated herein by reference. Other electrolytic cell configurations are also contemplated to be within the scope of the present invention.

[0075] exist Figure 4 and 5 The preheating system according to a preferred embodiment of the present invention is shown above. The preheating system 100 may include at least one electric heater 110 and is configured to be installed in an electrolytic cell to replace a corresponding anode assembly, such as Figure 7 and 8 As shown, it is used to preheat the tank before installing the corresponding anode assembly in the tank. Figure 6 As shown, the electric heater 110 may include resistors (R) having different configurations.

[0076] According to a preferred embodiment, each electric heater 110 is configured to provide a resistance RAA Close or equal resistance R CH Alternatively, the resistor R CH can be variable and once installed in the bath, outsourcedly adjusted to the resistance R of the anode assembly AA In both cases, the resistance R AA The resistance R CH The electrical and thermal profiles of the cell are allowed to equilibrate during replacement of the electric heater by the anode assembly before the electrolytic bath is introduced into the cell. According to another preferred embodiment, some residual heat may be allowed to compensate for heat dissipation from the top of the preheater.

[0077] According to a preferred embodiment, the electrolytic cell 10 may include one or more cathode assemblies 20 and is configured to receive N AA The preheating system 100 may then include N CH an electric tank heater configured to be installed in the tank 10 to replace a corresponding anode assembly, wherein N CH =N AA .like Figure 9 As shown, the number of electric heaters (resistors) can also be greater than the number of anode assemblies. A power module 120 can be operably connected to each of the electric heaters 110 for powering the electric heaters with an electric current to generate heat for heating the electrolytic cell 10. The electric current can have a fixed or variable intensity.

[0078] According to a preferred embodiment, Figure 7 In one embodiment shown in FIG, the power module is configured to connect the power loop 14 of the tank 10 to each of the electric heaters for providing current.

[0079] According to a preferred embodiment, Figure 8 In one embodiment shown in FIG, a power module is configured to connect the main busbar 16 of the electrolyzer to each of the electric heaters for providing current available in the main busbar. Current can be provided to the cell preheaters from the electrolyzer series busbar with current at very low voltage (e.g., 2 to 5 volts DC) and very high amperage (e.g., 15 to 50 kA). Alternatively, all or part of the power can be provided from an external source.

[0080] According to a preferred embodiment, the preheating system has currents of current intensity A and N. CH The resistance R of the tank heater CH The applied power P, where: P = (R CH / N CH )*A 2If P is greater than the power required to heat the tank, an energy surplus is created. The tank preheater can then be configured to remove this excess energy.

[0081] As previously mentioned, and as disclosed herein, the present invention further relates to a method for preheating an electrolysis cell comprising at least one vertical cathode assembly and configured to receive at least one corresponding vertical anode assembly and an electrolytic bath for aluminum electrolysis production. Figure 11 As shown, method 1000 includes a step 1100 of preheating the electrolytic cell by replacing the corresponding anode assembly with at least one electric heater installed in the electrolytic cell. Preferably, method 1000 also includes a step 1200 of introducing an electrolytic bath into the electrolytic cell once a given temperature of the electrolytic cell has been reached; and then a step 1300 of replacing at least one electric heater with at least one anode assembly.

[0082] according to Figure 12 In the preferred embodiment shown, the preheating step 1100 of the method 1000 may consist in providing a resistance R AA Almost equal resistance R CH , so that the electrical and thermal distribution of the cell remains balanced during replacement of the electric heater by the anode assembly 1110.

[0083] According to Figure 13 In another preferred embodiment shown, the preheating step 1100 may first include providing a variable resistor R to at least one electric heater. CH Step 1120; then, once installed in the bath, adjust the variable resistor R CH Until it is equal to the resistance R of at least one anode assembly AA , so that the electrical and thermal profiles of the electrolytic cell remain balanced during the replacement of at least one electric heater by at least one anode assembly 1130. The resistor R may be implemented by adjusting the amount of current provided through the resistor CH of adjustment.

[0084] According to a preferred embodiment, the electrolytic cell is configured to receive N AA At least one anode assembly, where N AA ≥ 1. Then, method 1000 may include installing N in the electrolytic cell. CH electric heater steps, where N CH ≥1, to replace at least one anode assembly, where N CH =N AAThen, each of the at least one electric heaters is powered with current for heating the electrolytic cell. Preferably, powering each of the at least one electric heaters may include providing current available on a main busbar for the electrolysis process to each of the at least one electric heaters. The current provided to the heaters is preferably available on a main busbar for the kettle. For example, the current available on the busbar may have a very low voltage (e.g., 2 to 5 volts DC) and a very high amperage (e.g., 15 to 50 kA).

[0085] According to a preferred embodiment, the method 1000 may further comprise the step of removing excess heat from the electrolytic cell during preheating of the cell.

[0086] According to a preferred embodiment, the method 1000 may further include the step of maintaining the temperature of the preheating tank by energizing at least one of at least one electric heater installed in the electrolytic tank replacing at least one anode assembly.

[0087] According to a preferred embodiment, the method 1000 may further comprise the step of replacing a defective anode assembly in at least one anode assembly of the electrolysis cell for maintenance and / or replacement of defective anode assemblies during metal production.

[0088] According to a preferred embodiment, the method may further comprise draining excess energy from the tank. Ways of draining excess energy are provided below.

[0089] According to a preferred embodiment, the metal to be produced after cell start-up is aluminium and the anode assembly comprises an inert anode or an oxygen evolving anode.

[0090] Also disclosed herein is a method for starting an electrolytic cell for producing metal. The electrolytic cell typically includes at least one cathode assembly configured to receive at least one anode assembly and an electrolytic bath for the electrolytic production of metals, such as aluminum. The electrolytic bath can be solid or liquid. The solid bath typically includes solid cryolite and preferably other additives at ambient temperature, and the electrolytic cell is then filled with the solid bath before the next step in the method. The liquid bath typically includes cryolite and preferably other additives that have been melted at a given temperature (typically greater than 700°C).

[0091] Figure 14 The method 2000 first includes a step 2100 of providing a dry bath in an electrolytic cell at ambient temperature, and then a step 2200 of installing at least one heating element in the electrolytic cell to replace the corresponding anode assembly at ambient temperature. Figure 9 and 10 As shown, each electrolytic cell 10 may have several cell preheaters 100, each of which has an electric heater 110 having one or more resistors. Each resistor 110 may have a different geometry, such as Figure 6 Those shown in .

[0092] "Ambient temperature" means the temperature of the immediate surroundings of the hydrolysis cell, e.g., a temperature of 25°C ± 15°C. In practice, the ambient temperature surrounding the hydrolysis cell (kettle) in the electrolysis room may be higher, particularly in hot climates, due to heat generated from adjacent kettles. Alternatively, the ambient temperature may be lower, particularly in Canada, where electrolysis rooms are generally unheated and maintained by heat generated by the hydrolysis cell or kettle.

[0093] Preferably, when there is more than one resistor to form the preheating system 100, the N of the electric heater 110 is usually CH A resistor R CH Connection, such as parallel connection. In the case of multiple N CH The same resistors R in parallel CH In the system, the total resistance is R = R CH / N CH Other connection types for the resistors may be considered without departing from the scope of the present invention. Figure 9 Each heating element is preferably mounted on the top of the electrolytic cell in place of the anode assembly, with the resistor extending from the top to the cathode, which is typically located at the bottom of the electrolytic cell, as shown in FIG. 10. Other configurations are contemplated without departing from the scope of the present invention.

[0094] like Figure 14 The illustrated method 2000 may also include a step 2300 of heating the electrolytic cell by providing current to each heating element. Preferably, the current is available in a busbar of the cell. The busbar is a conductive rod, typically made of copper or aluminum, more preferably aluminum, that allows current to flow from the power source to the electrodes (e.g., reference numeral 16, Figure 8 ).

[0095] Preferably, the electrolytic cell 10 and ultimately the dry bath 12 present therein can be further heated by advantageously distributing the heat inside the electrolytic cell towards at least one cathode assembly 20. For example, the heat can be advantageously distributed inside the electrolytic cell with regard to a temperature rise, which temperature rise depends on the nature of the material being heated inside the electrolytic cell. In this sense, the electrolytic cell can have a protective material for protecting the side walls 13. For example, by using a protective material extending from the side walls or side walls of the electrolytic cell, the heat cycle is directed from the heating element 110 towards the at least one cathode assembly 20. It is noted that the cell preheater according to the present invention has side walls. Preferably, the side walls of the preheater do not need to be made of a material that is sensitive to the heating temperature rise rate, since they usually contact adjacent preheaters (see, for example, Figure 9 ).

[0096] like Figure 14As shown, the method 2000 of using a dry bath further includes a step 2400 of controlling the melting of the dry bath in the electrolytic cell due to the heating element once a given temperature is reached in the kettle, as described in detail below. The present invention is also advantageous in that it allows the cell to be preheated while the dry bath is being melted by the heating element.

[0097] like Figure 14 As shown, method 2000 may optionally include a step 2500 of injecting a portion of the liquid molten bath into the electrolytic cell to top up the electrolytic cell, if necessary, for running an electrolytic process to produce metal (e.g., aluminum). Indeed, when using a dry bath, the volume of the bath will decrease as it melts, and then a portion of the liquid bath will be added to top up the electrolytic cell.

[0098] like Figure 14 As shown, the method 2000 further comprises a step 2600 of injecting a portion of the metal to be produced, such as aluminum, into the cell 10 to wet the cathode 20 and the cell bottom 13 (see below for more details).

[0099] Finally, if Figure 14 As shown, the method 2000 further includes step 2700 of replacing each of the heating elements with the anode assembly until all heating elements are removed from the electrolytic cell. Specifically, for one anode assembly to be installed in the electrolytic cell, N HE Heating elements, where N HE ≥1 and N HE Depends on the N HE The total resistance R provided by the heating elements CH , R CH Close to or almost equal to the resistance R of an anode assembly AA .

[0100] Figure 15 A start-up method 3000 is shown when the electrolytic bath used is already a liquid, ie, hot molten, electrolytic bath.

[0101] Method 3000 first includes step 3100 of installing at least one heating element in an electrolytic cell at ambient temperature to replace at least one anode assembly, followed by step 3200 of heating the electrolytic cell by supplying current to each of the at least one heating element. Once a given temperature is reached in the electrolytic cell, method 3000 includes step 3300 of pouring a liquid molten bath and a portion of the metal to be produced into the electrolytic cell. Finally, method 3000 includes step 3400 of replacing one or more of the at least one heating element with an anode assembly until each of the at least one heating element is removed from the electrolytic cell.

[0102] The given temperatures recited herein are estimated depending on the nature of the electrolytic material used to produce the metal and may be between 700 and 1000° C. (or more), for example, when producing aluminum from alumina.

[0103] Typically, for the startup method according to the present invention, the desired temperature in the reactor is reached after a period of several days, such as between 2 and 5 days. The electrolytic bath may include aluminum oxide for aluminum production, and a portion of the metal, such as aluminum, may be used to wet the cathode. Other options for wetting the cathode are disclosed in International Patent Application No. WO 2018 / 009862 A1 (LIU, Xinghua), the contents of which are incorporated herein by reference. For example, the aluminum-wettable material may include at least one of TiB2, ZrB2, HfB2, SrB2, or a combination thereof.

[0104] Preferably, the anode assembly can be preheated outside the cell before being moved and placed in the cell. This is particularly suitable for electrolyzers using inert or oxygen-evolving electrodes. For example, reference can be made to the apparatus and method for operating an electrolyzer disclosed in International Patent Application No. WO2021 / 035356 (ELYSIS LIMITED PARTNERSHIP), the contents of which are incorporated by reference.

[0105] When the tank heater resistance R CH Close to or almost equal to R AA This may represent a significant amount of heat generation. Therefore, the method may further comprise the step of discharging excess heat from the tank. Figure 10 As shown, excess heat is removed by providing at least one additional resistor 130 on top of at least one heating element 100. Preferably, excess heat is removed from the cell by an exhaust system located at the top of the cell above the electrolysis cell. Other methods of removing excess heat may be considered without departing from the scope of the present invention.

[0106] The method as disclosed herein is particularly advantageous because it can be used to optimize (e.g., reduce) the time required to start an electrolytic cell, thereby reducing the energy required to start the electrolytic cell, thereby making the invention environmentally friendly, while ensuring that the material is located inside the cell (e.g., inert anode).

[0107] Example

[0108] Abbreviations commonly used in this manual:

[0109] AA: Anode assembly

[0110] ·GTC:Gas Treatment Center

[0111] ·HH:Hall Heroult

[0112] IA: Inert anode

[0113] CTA: Cathode Transport Assembly

[0114] PTA: Kettle curing components

[0115] The tank preheater, which is the subject of the present invention, is an electric heater installed in the tank rather than in the anode assembly. The tank is preheated by as many tank preheaters as anode assemblies. Unlike conventional heating applications, which typically use alternating current at high voltage (110-480 V) and low amperage (several hundred amperes), the tank preheater is powered by the current available in the main busbar of the kettle, i.e., using a very low voltage (e.g., 2 to 5 volts direct current) and a very high amperage (e.g., 15 to 50 kA).

[0116] Another particularity is that at the end of preheating, when the liquid bath is poured into the tank and the tank preheater is gradually replaced by hot anode assemblies, the resistance of the tank preheater is preferably equal to or almost equal to the resistance of the anode assemblies in the bath, so that the electrical and thermal distribution of the tank is not unbalanced during the replacement process and the inert anode assemblies take the desired portion of the current without being overloaded or underloaded.

[0117] Ultimately, the tank preheater power is determined by the electrolytic cell series current and the resistance requirements. This power (P = resistance * amperage^2) is greater than the power required to heat the tank. Therefore, the tank preheater needs to be able to dissipate excess energy.

[0118] The systems, methods, and startup methods disclosed herein allow for preheating of electrolytic cells using a vertical inert anode and cathode arrangement with a controlled temperature increase in a uniform manner throughout the cell.

[0119] The systems and methods disclosed herein allow for electrical distribution to remain unbalanced during the gradual replacement of the cell preheater by anode assemblies at the end of preheating, during the cell startup procedure.

[0120] Furthermore, by using an additional resistor placed on top of the preheater, excess energy can be dissipated and will not contribute to further heating of the tank.

[0121] Option 1: Connect the tank heater to the power loop ( Figure 7 ):

[0122] An alternative solution for preheating the cells is to power the cell preheaters with current at 480 V. However, given the power involved in heating the cells (e.g., approximately 500 kW-1 MW for an AP45 cell), this would mean having a generator near the cell with 34 large cables to connect to the 17 cell preheaters, which creates significant logistical problems given the limited space available around the cell. More importantly, it would create insurmountable electrical safety issues and bridging risks with 480 V AC in the electrolytic cell train, as well as the major problem of setting up the anode assemblies in a very short time to enable the electrolytic cell train current to be set up in the cells without causing the kettle to cool down.

[0123] Option 2: Tank heaters are operatively connected to the tank busbars ( Figure 8 )

[0124] Start the program:

[0125] Short-circuit the IA tank by diverting the busbar to the next kettle in series;

[0126] Configuring a first kettle maintenance assembly (PTA) to have each of the tank preheaters and inserting the tank preheaters into the interior of the IA tank;

[0127] Connect each tank heater to the kettle busbar;

[0128] ·Remove the diverter; after a predetermined period of time (for example, about 2-5 days), start kettle preheating, preheat the electrolytic cell to the desired temperature and introduce a portion of metal (for example, aluminum) and the electrolytic bath inside the cell. Each of the cell heaters is electrically disconnected and then removed by the first PTA and immediately replaced by the preheated AA using a second PTA configured to transport the preheated AA and place it in the cell while maintaining the temperature of the preheated AA. The second PTA, also called a "Transfer Box", makes it possible to avoid temperature loss of the bath and thermal shock to the equipment, especially when the AA includes an inert anode or an oxygen-evolving anode. An example of a second PTA is disclosed in No. WO2021 / 035356 cited above.

[0129] parameter:

[0130] The resistance of the tank heater and the AA in the tank must be calculated correctly to obtain the correct amperage and heat balance (R CH =R AA Alternatively, the resistance can be adjusted or modulated to obtain R CH =R AA .

[0131] Completed the connection of each AA to the equipotential anode bus.

[0132] As mentioned above, the time it takes to install all the AAs inside the electrolyzer must be short enough to avoid temperature loss and thermal shock to the equipment.

[0133] Examples of preheater systems:

[0134] like Figure 6 As shown, resistors can be made from solid rods of various configurations (e.g., made from a resistance alloy, e.g., a 40 mm diameter size). The resistor design should preferably match the characteristics at a 12,000 A level with a nominal cell voltage of 5 VDC. The resistivity tolerance covers a window of 12,500 A at 5 VDC, i.e., a nominal 200,000 A at 5 VDC for 16 heater modules. The preheater assembly can include steel and refractory material components, both resistant to the bath, refractory to the heating surface, and with insulating refractory material behind.

[0135] Cell startup will replace the cell preheater with the AA, which has been preheated separately in a preheat tank, thereby avoiding anode thermal shock, as disclosed in WO2021 / 035356 cited above.

[0136] Example: A preheater assembly (e.g., 63kW plug heater - 5VDC - 14,400 amps) may include:

[0137] ·2-1 / 2" (approximately 6.35cm) Sch.40 Pipe 600 alloy;

[0138] 1-1 / 2"*4" (approximately 6.35*10.16cm) power cord 600 alloy;

[0139] Upper plug size: 30"*58"*13-3 / 4" (76.2*147.32*34.93cm);

[0140] ·Lifting rings;

[0141] Castable refractory lined with block insulation, with refractory anchors; supports and hangers for element tubes; and

[0142] Ordinary steel transport rack

[0143] While illustrative and presently preferred embodiments of the invention have been described above in detail, it will be understood that the inventive concept may be otherwise variously embodied and used and that the appended claims are intended to be construed to encompass such variations unless limited by the prior art.

Claims

1. A preheating system for preheating an electrolytic cell and for maintaining the temperature of the preheated electrolytic cell, the electrolytic cell comprising at least one cathode assembly including a plurality of vertical cathodes located at the bottom of the electrolytic cell, and the electrolytic cell being configured to receive at least one anode assembly including a plurality of vertical inert anodes or oxygen-evolving anodes extending from the top of the electrolytic cell toward the cathodes and an electrolytic bath for the electrolytic production of aluminum, the anode assembly being preheated outside the electrolytic cell before being moved and placed in the electrolytic cell, wherein: The preheating system comprises: at least one electric heater configured to be installed in the electrolytic cell in place of the at least one anode assembly for preheating the cell prior to installing the at least one anode assembly in the cell, The electrolytic cell is configured to receive N AA At least one anode assembly, where N AA ≥1, the preheating system comprises: N CH At least one electric heater, where N CH ≥1, each of the at least one electric heater is configured to be installed in the electrolytic cell to replace the at least one anode assembly, wherein N CH =N AA ; And, the preheating system also includes: a power supply module operatively connected to each of the at least one electric heater for powering the at least one electric heater with an electric current for preheating the electrolysis cell, wherein the power supply module connects the main busbar of the electrolysis cell to each of the at least one electric heater for providing current available in the main busbar, and The preheating system has a current intensity A and N. CH The resistance R of the tank heater CH The applied power P, where P = (R CH / N CH )*A 2 , P is greater than the power required to heat the tank, thereby generating excess energy, and the tank is configured to discharge excess heat, wherein the preheating system further includes at least one resistor, and the at least one resistor is located at the top of the preheating system to discharge the excess heat.

2. The preheating system according to claim 1, wherein: The at least one electric heater is configured to, once installed in the bath, provide a resistance R AA Equal resistance R CH , whereby the electrical and thermal profiles of the electrolytic cell remain balanced during replacement of the at least one electric heater by the at least one anode assembly.

3. The preheating system according to claim 1, wherein: The at least one electric heater is configured to, once installed in the bath, provide a resistance R regulated to the at least one anode assembly. AA Equal variable resistor R CH , whereby the electrical and thermal profiles of the electrolytic cell remain balanced during replacement of the at least one electric heater by the at least one anode assembly.

4. The preheating system according to claim 1 , further for replacing a defective anode assembly of the at least one anode assembly of the electrolysis cell during metal production and for maintaining and / or replacing the defective anode assembly.

5. A method for preheating an electrolytic cell and for maintaining the temperature of the preheated electrolytic cell, the electrolytic cell comprising at least one cathode assembly including a plurality of vertical cathodes located at the bottom of the electrolytic cell, and the electrolytic cell being configured to receive at least one anode assembly including a plurality of vertical inert anodes or oxygen-evolving anodes extending from the top of the electrolytic cell toward the cathodes and an electrolytic bath for the electrolytic production of aluminum, the anode assembly being preheated outside the electrolytic cell before being moved and placed in the electrolytic cell, the method comprising: Providing a preheating system according to any one of claims 1 to 4; preheating the electrolytic cell with at least one electric heater of the preheating system installed in the electrolytic cell replacing the at least one anode assembly; removing excess heat from the tank using at least one resistor located at the top of the preheating system; as well as maintaining the temperature of the preheated electrolytic cell by energizing at least one of the at least one electric heater installed in the electrolytic cell replacing the at least one anode assembly; The electrolytic cell is configured to receive N AA the at least one anode assembly, wherein N AA ≥1, the method comprising: Install N in the electrolytic cell CH Electric heaters, N CH ≥ 1, to replace at least one anode assembly, where N CH =N AA ;as well as energizing each of the at least one electric heater with an electric current for heating the electrolytic cell; and Wherein, supplying power to each of the at least one electric heater comprises: Each of the at least one electric heater is supplied with the electric current available in the main busbar of the electrolysis cell.

6. The method according to claim 5, further comprising: introducing the electrolytic bath into the electrolytic cell once a given temperature of the electrolytic cell has been reached; as well as The at least one electric heater is replaced by the at least one anode assembly.

7. The method according to claim 5, wherein: Preheating the electrolytic cell comprises: A resistance R is provided with respect to said at least one anode assembly in said bath AA Equal or nearly equal resistance R CH , whereby the electrical and thermal profiles of the cell remain balanced during replacement of the electric heater by the anode assembly.

8. The method according to claim 5, wherein Preheating the electrolytic cell comprises: A variable resistor R is provided to the at least one electric heater CH ;as well as Once installed in the bath, adjust the variable resistor R CH until the resistance R of the at least one anode assembly is equal to AA , whereby the electrical and thermal profiles of the electrolytic cell remain balanced during replacement of the at least one electric heater by the at least one anode assembly.

9. The method according to claim 5, further comprising: A defective anode assembly of the at least one anode assembly of the electrolysis cell is replaced during the production of aluminum for maintenance and / or replacement of the defective anode assembly.

10. A method for starting an electrolytic cell for the production of aluminum, the electrolytic cell comprising at least one cathode assembly including a plurality of vertical cathodes located at the bottom of the electrolytic cell, and the electrolytic cell being configured to receive at least one anode assembly including a plurality of vertical inert anodes or oxygen-evolving anodes extending from the top of the electrolytic cell toward the cathodes and an electrolytic bath for the electrolytic production of aluminum, the anode assembly being preheated outside the electrolytic cell before being moved and placed in the electrolytic cell, wherein When the electrolytic bath is a dry bath at ambient temperature, the method comprises: providing the dry bath in the electrolytic cell at the ambient temperature; Providing a preheating system according to any one of claims 1 to 4; installing at least one heating element of the preheating system in the electrolytic cell at the ambient temperature to replace the at least one anode assembly; heating the electrolytic cell by supplying an electric current to each of the at least one heating element; Once a given temperature is reached in the electrolytic cell, controlling the melting of the dry bath due to the at least one heating element and, optionally, injecting a portion of the electrolytic bath in its liquid form into the electrolytic cell in order to top up the electrolytic cell; injecting a portion of the aluminum to be produced into the electrolytic cell; and replacing one or more of the at least one heating element with an anode assembly until each of the at least one heating element is removed from the electrolytic cell, or, Wherein, when the electrolytic bath is a liquid molten bath, the method comprises: Providing a preheating system according to any one of claims 1 to 4; installing at least one heating element of the preheating system in the electrolytic cell at ambient temperature in place of the at least one anode assembly; heating the electrolytic cell by supplying an electric current to each of the at least one heating element; pouring the liquid molten bath and a portion of the aluminum to be produced into the electrolysis cell once a given temperature has been reached in the electrolysis cell; and replacing one or more of the at least one heating element with an anode assembly until each of the at least one heating element is removed from the electrolytic cell; And wherein the method further comprises removing excess heat from the electrolytic cell; And wherein the removal of excess heat is performed by having at least one additional resistor located on top of the at least one heating element.

11. The method according to claim 10, wherein: For an anode assembly to be installed in the electrolytic cell, remove N from the electrolytic cell. HE Heating elements, where N HE ≥1 and N HE Depends on N HE The total resistance R provided by the heating elements is selected to be close to or nearly equal to the resistance R of the at least one anode assembly. AA .

12. The method according to claim 10, wherein: Each of the heating elements includes at least one resistor, wherein when more than one of the at least one resistor is present, each of the at least one resistor is electrically connected in parallel.

13. The method according to claim 10, wherein: The electrolytic cell is further heated by distributing heat generated within the electrolytic cell toward the at least one cathode assembly.

14. The method according to claim 13, wherein: The heat is distributed within the electrolysis cell taking into account the temperature increase, which depends on the properties of the material to be heated within the electrolysis cell.

15. The method according to claim 10, wherein The excess heat is removed from the cell via the cell's exhaust system located at the top of the cell.

16. The method according to claim 10, further comprising: The side walls of the electrolytic cell are protected from heat.

17. The method according to claim 16, wherein Preventing the side wall from being heated includes: Heat is forced to circulate from the at least one heating element to the at least one cathode assembly through the use of a protective material extending from the sidewall.

18. The method according to claim 10, wherein The set temperature of the preheated electrolytic cell is reached after a period of time between 2 and 5 days and is between 700 and 1000°C.

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