Electrolysis system and method for operating an electrolysis unit

Abstract

The disclosure relates to a method for operating an electrolysis unit, the unit comprising at least one solid oxide electrolysis cell. The electrolysis cell comprises: a process electrode; an oxy electrode; a solid electrolyte providing ionic contact between the process and oxy electrodes; a process chamber interfacing the process electrode; a first process opening coupled to the process chamber for supplying a process feed gas; a second process opening coupled to the process chamber for discharging a product gas; an oxy chamber interfacing the oxy electrode; a first oxy opening coupled to the oxy chamber for supplying a flush gas; and a second oxy opening coupled to the oxy chamber for discharging oxygen. The method comprises the steps of: operating the electrolysis unit to produce oxygen in the oxy chamber; and discharging said oxygen from the oxy chamber through both the first oxy opening and the second oxy opening.

Description

[0001] ELECTROLYSIS SYSTEM AND METHOD FOR OPERATING AN ELECTROLYSIS UNIT

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a method for operating an electrolysis unit. The present invention further relates to an electrolysis system.

[0004] BACKGROUND OF THE INVENTION

[0005] The field of solid-oxide electrolysis cell systems has seen significant advancements in recent years, with state-of-the-art technologies relying on innovative material choices and operational strategies to optimize efficiency and longevity. For example, many contemporary solid-oxide electrolysis cell (SOEC) stacks employ perovskite materials in the oxygen chamber (commonly referred to as the "oxy chamber") due to their advantageous properties in high-temperature environments. Additionally, steel interconnects are widely used to provide structural integrity and ensure efficient gas flow distribution in cell stacks.

[0006] It is common practice to utilize flush gas in the oxy chamber, in operation, but particularly also during transient operation when oxygen is not actively produced by the SOEC stack. This approach has proven effective in maintaining material integrity and ensuring stable system performance during specific operational phases. In particular, supplying flush gas can dilute off-gas such that it does not contain 100% oxygen, provide oxygen to the oxy-electrode during transient operation, decrease humidity, reduce pressure difference between the oxy and process side, or any combination thereof. During transient operation, the process electrode is commonly flushed with a reducing gas (forming gas) containing e.g. hydrogen to keep the oxygen partial pressure low, preventing an oxidation of the Nickel containing process electrode. Such low oxygen partial pressures are detrimental to the commonly used perovskite oxy electrode materials, so the oxy electrode has to be flushed with flush gas such as, e.g., air to protect it, as a small gas crossover will always occur.

[0007] Despite these advancements, significant challenges persist. A significant issue arises from the infiltration of humidity into the oxy chamber, often due to leakage from the process chamber. Such leakage can, for example, occur via the manifolds that supply the flush gas. This humidity exposure can lead to the degradation of both perovskite materials and steel interconnects, shortening the operational lifespan of the system. Moreover, mitigating these leaks requires large volumes of flush gas to be supplied during transient operations, which, in turn, necessitates the use of extensive heating systems and heat exchangers to preheat saidflush gas. This increases both the energy consumption and the system complexity, undermining the efficiency gains provided by the solid-oxide electrolysis technology.

[0008] Further complications arise during a production mode when no flush gas is supplied.

[0009] Operation without a flush gas is desirable to avoid heating of the flush gas and / or to have 100% oxygen as a second product of the electrolyser unit. However, under such conditions, a pressure drop often develops across the oxy chamber, which places substantial mechanical stress on the solid-oxide electrolysis cells. This strain can lead to performance degradation or, in extreme cases, mechanical failure of the cells, jeopardizing the overall reliability and economic viability of the system. These shortcomings highlight a critical need to address humidity infiltration, excessive flush gas requirements, and pressure imbalances without compromising the core functionality of the solid-oxide electrolysis system.

[0010] It is therefore an object of the present invention to reduce the exposure of the oxy chamber to humidity during operation. It is further an objective to minimize the pressure drop across the oxy chamber, as well as to reduce the amount of flush gas required and the heating thereof during transient operation.

[0011] SUMMARY OF THE INVENTION

[0012] On the above background, it is an object of preferred embodiments of the present disclosure to reduce exposure of the oxy chamber to humidity during operation. It is further an object of preferred embodiments of the present disclosure to minimize the pressure drop across the oxy chamber during production. It is additionally an object of some embodiments to provide flush gas to the oxy side and to reduce the amount of flush gas required and the heating thereof during transient operation. Preferably, one or more of these objectives are achieved without the need for supplying flush gas to the oxy chamber during production.

[0013] A first aspect of the present disclosure relates to a method for operating an electrolysis unit, the electrolysis unit comprising at least one solid oxide electrolysis cell, each of the at least one solid oxide electrolysis cell comprising:

[0014] a process electrode; an oxy electrode; a solid electrolyte providing ionic contact between the process electrode and the oxy electrode; a process chamber having an interface with the process electrode; a first process opening fluidly coupled to the process chamber for supplying a process feed gas to the process chamber; a second process opening fluidly coupled to the process chamber for discharging a product gas from the process chamber; an oxy chamber havingan interface with the oxy electrode; a first oxy opening fluidly coupled to the oxy chamber for supplying a flush gas to the oxy chamber; and a second oxy opening fluidly coupled to the oxy chamber for discharging oxygen from the oxy chamber,

[0015] wherein the method comprises the steps of:

[0016] operating the electrolysis unit to produce oxygen in the oxy chamber of the solid oxide electrolysis cell; and

[0017] discharging said oxygen from the oxy chamber through both the first oxy opening and the second oxy opening.

[0018] In solid oxide electrolysis cells, the oxy chamber is typically flushed by supplying flush gas through a first oxy opening coupled to the oxy chamber and discharging said flush gas through a second oxy opening, the second oxy opening being used to discharge oxygen during production of the electrolysis unit.

[0019] By discharging oxygen from the oxy chamber through both the first oxy opening and the second opening, preferably during production, several advantageous effects can be achieved.

[0020] Humidity from both the first oxy opening and the second oxy opening can be reduced, in contrast to operation in which oxygen is only discharged through one of these openings. In turn, this reduces humidity in oxy chamber as well as in relevant manifolds fluidly coupled to the oxy chamber.

[0021] By generally reducing humidity in the oxy side of the electrolysis unit, the need for flushing this part of the unit during transient operation can be reduced. In turn, this can also reduce the amount of heat which is required to supply to the flush gas during transient operation.

[0022] Further, by discharging oxygen through both the first and second oxy openings, the pressure drop across the oxy chamber during production can be reduced or even eliminated. Such a pressure drop can in particular be prominent during operation without supplying a flush gas, but can also be present while supplying a flush gas during production.

[0023] Distributing the oxygen produced in the oxy chamber across two outlets can also potentially reduce oxygen leaking from the oxy side into the process side. Since the process side can be vulnerable to high oxygen partial pressures, the technology disclosed herein can therebypotentially also reduce oxidization and cracking of materials on the process gas side, for example a nickel-based material, such as a nickel-based material forming a surface in the process chamber or forming a surface fluidly coupled to the process chamber.

[0024] The first oxy opening and the second oxy opening are separate openings into the oxy chamber.

[0025] In practice, discharging oxygen (simultaneously) through both the first oxy opening and the second oxy opening can be facilitated by a valve arrangement controlling fluid communication via the first oxy opening. Such a valve arrangement can have a first configuration in which the first oxy opening and an oxygen outlet are fluidly coupled, thereby allowing oxygen to be discharged via the first oxy opening, and a second configuration in which a flush gas supply and the first oxy opening are fluidly coupled, thereby allowing flush gas to be supplied to the oxy chamber via the first oxy opening. The valve arrangement can then be switched between the first and second configuration as desired or required, for example in combination with switching operation of the electrolysis unit between production and transient operation. In practice, a valve arrangement can be implemented as a controllable three-way valve, two two-way valves, or other known arrangements of one or more valves capable of controlling flow between three openings.

[0026] Typically, an electrolysis unit may have several different modes of operation, for example production mode (also referred to herein as 'production mode of operation' or simply 'production') and transient mode (also referred to herein as 'transient operation'). In production, electrolysis takes place, for example to split water into hydrogen and oxygen. Thereby, oxygen gas and hydrogen gas are produced in the oxy chamber and in the process chamber, respectively. In transient operation, typically little or no substantial electrolysis takes place. At least less electrolysis takes place in transient operation than during production.

[0027] During transient operation, a flush gas may also be supplied to the process chamber, which commonly is a different flush gas from the one being supplied to the oxy chamber.

[0028] Optionally, the electrolysis cell may have additional openings, such as an additional second process opening fluidly coupled to the process chamber for discharging the product gas from the process chamber, or an additional second oxy opening fluidly coupled to the oxy chamber for discharging oxygen from the oxy chamber.

[0029] According to examples of the present disclosure, the process feed gas comprises steam, carbon dioxide, or a mixture thereof. According to examples of the present disclosure, theproduct gas comprises hydrogen, carbon monoxide, or a mixture thereof. In case the process feed gas comprises steam, this steam is reduced into hydrogen, the product gas comprising said hydrogen. Correspondingly, in case the process feed gas comprises carbon dioxide, this carbon dioxide is reduced into carbon monoxide, the product case comprising said carbon monoxide.

[0030] According to examples of the present disclosure, the steps of operating the electrolysis unit and discharging said oxygen are performed in a production mode of operation.

[0031] According to examples of the present disclosure, the method comprises a step of supplying flush gas to the oxy chamber via the first oxy opening.

[0032] That is, at one point during operation, the first oxy opening is used for supplying flush gas, whereas at another point during operation, the first oxy opening is used for discharging oxygen from the oxy chamber.

[0033] According to examples of the present disclosure, the step of supplying a flush gas to the oxy chamber is performed separately from the step of discharging said oxygen from the oxy chamber through both the first oxy opening and the second oxy opening.

[0034] According to examples of the present disclosure, the flush gas is air, such as atmospheric air, preferably air or atmospheric air which has been subjected to air drying.

[0035] Atmospheric air is well-suited as a flush gas, in particular if it has been subjected to air drying.

[0036] According to examples of the present disclosure, the steps of operating the electrolysis unit and discharging said oxygen are performed in a first mode of operation, wherein the step of supplying the flush gas to the oxy chamber is performed in a second mode of operation, wherein the method comprises a step of switching between the first mode of operation and the second mode of operation.

[0037] Preferably, no flush gas is supplied through the oxy chamber in the first mode of operation.

[0038] According to examples of the present disclosure, the first mode of operation is a production mode wherein the second mode of operation is a transient mode, wherein less oxygen is produced in the transient mode than in the production mode by the at least one solid oxide electrolysis cell.According to examples of the present disclosure, no flush gas is supplied through the oxy chamber in the production mode of operation.

[0039] According to examples of the present disclosure, said oxygen discharged from the oxy chamber through both the first oxy opening and the second oxy opening is supplied to an oxygen storage, such as an oxygen storage which receives oxygen discharged through the first oxy opening and the second oxy opening.

[0040] According to examples of the present disclosure, the step of discharging said oxygen is a step of discharging said oxygen from the oxy chamber simultaneously through both the first oxy opening and the second oxy opening.

[0041] A second aspect of the present disclosure relates to an electrolysis system comprising:

[0042] an electrolysis unit, the electrolysis unit comprising at least one solid oxide electrolysis cell, each of the at least one solid oxide electrolysis cells comprising: a process electrode; an oxy electrode; a solid electrolyte providing ionic contact between the process electrode and the oxy electrode; a process chamber having an interface with the process electrode; a first process opening fluidly coupled to the process chamber for supplying a process feed gas to the process chamber; a second process opening fluidly coupled to the process chamber for discharging a product gas from the process chamber; an oxy chamber having an interface with the oxy electrode; a first oxy opening fluidly coupled to the oxy chamber for supplying a flush gas to the oxy chamber; and a second oxy opening fluidly coupled to the oxy chamber for discharging oxygen from the oxy chamber,

[0043] the electrolysis system further comprising:

[0044] a flush gas supply;

[0045] an oxygen outlet; and

[0046] a valve arrangement for controlling fluid communication between the flush gas supply, the oxygen outlet, and the first oxy opening, wherein the valve arrangement has:a first configuration in which the first oxy opening and the oxygen outlet are fluidly coupled, and

[0047] a second configuration in which the flush gas supply and the first oxy opening are fluidly coupled.

[0048] In the first configuration, the flush gas supply and the first oxy opening may preferably be fluidly decoupled, and in the second configuration, the first oxy opening and the oxygen outlet may preferably be fluidly decoupled.

[0049] The oxygen outlet may, for example, be connected to an oxygen storage.

[0050] The disclosed valve arrangement may be an automated valve arrangement which is controlled by a controlling arrangement, or it may be a passive valve arrangement which autonomously couples and decouples the oxy opening depending on, e.g., pressures in the system.

[0051] Switching between the first and second configurations may be thus typically be performed automatically. However, in principle, manual switching can also be performed.

[0052] Preferably, in the first configuration, the first oxy opening and the oxygen outlet are fluidly connected via said valve arrangement, preferably separately from a fluid connection via the second oxy opening. Preferably, in the second configuration, the flush gas supply and the first oxy opening are fluidly coupled via said valve arrangement.

[0053] According to examples of the present disclosure, the electrolysis system has a first mode of operation in which oxygen is produced in the oxy chamber of the solid oxide electrolysis cell and a second mode of operation in which flush gas is supplied to the oxy chamber via the first oxy opening.

[0054] According to examples of the present disclosure, the electrolysis system further comprises a controlling arrangement configured to control the valve arrangement between the first configuration and the second configuration.

[0055] According to examples of the present disclosure, the controlling arrangement is configured to set the valve arrangement in the first configuration while the electrolysis system is operating in the first mode of operation and configured to set the valve arrangement in the second configuration while the electrolysis system is operating in the second mode of operation.According to examples of the present disclosure, said oxygen is discharged from the oxy chamber simultaneously through both the first oxy opening and the second oxy opening in the first mode of operation.

[0056] According to examples of the present disclosure, the flush gas is supplied to the oxy chamber from the flush gas supply via the first oxy opening in the second mode of operation.

[0057] According to examples of the present disclosure, said oxygen is discharged through the oxygen outlet in the first mode of operation.

[0058] According to examples of the present disclosure, the first mode of operation is a production mode, and / or wherein the second mode of operation is a transient mode.

[0059] According to examples of the present disclosure, the electrolysis system comprises one or more pumps respectively configured to discharge oxygen through the first oxy opening and the second oxy opening in the first mode of operation and / or to supply the flush gas to the oxy chamber in the second mode of operation.

[0060] According to examples of the present disclosure, the at least one solid oxide electrolysis cell is a plurality of solid oxide electrolysis cells arranged in a solid oxide electrolysis cell stack,

[0061] wherein the valve arrangement is a common valve arrangement for controlling fluid communication between the flush gas supply, the oxygen outlet, and the first oxy opening of each cell of the plurality of solid oxide electrolysis cells,

[0062] wherein the first oxy opening of each cell of the plurality of solid oxide electrolysis cells and the oxygen outlet are fluidly coupled in the first configuration,

[0063] wherein the flush gas supply and the first oxy opening of each cell of the plurality of solid oxide electrolysis cells are fluidly coupled in the second configuration.

[0064] The first oxy opening of each cell of the stack may for example be fluidly coupled to the valve arrangement via a manifold.

[0065] According to examples of the present disclosure, the oxy chamber comprises at least one surface formed by a perovskite material, and / or the oxy chamber is fluidly coupled to at least one surface formed by a perovskite material.Perovskite materials are vulnerable to low oxygen partial pressures, for example partial pressures below 10-4bar or below 1010bar of oxygen partial pressure. Perovskite materials can be prone to disintegration below such partial pressures. Further, such perovskite materials, for example (La, Sr)CoO3-s, can be damaged or aged by humidity, since humidity enhances, e.g., Sr(OH) evaporation. Generally, perovskite materials are materials of the formula ABX3with a structure similar to the mineral perovskite, which has the formula of CaTiO3.

[0066] According to examples of the present disclosure, the process chamber comprises at least one surface formed by a nickel-based material, and / or the process chamber is fluidly coupled to at least one surface formed by a nickel-based material.

[0067] Nickel-based materials, which are often used on the process gas side, are vulnerable to high oxygen partial pressures, for example partial pressures above 1010bar or above 1018bar of oxygen partial pressure (for example, at 720°C). Nickel-based materials can oxidize and crack above such partial pressures. Examples of Nickel-based materials are nickel / yttria-stabilized zirconia (Ni-YSZ), nickel-samarium-doped ceria (Ni-SDC), and Ni-BaZro.iCeo.7Yo.203(Ni-BZCY), each of which is suitable for use as material for the process electrode.

[0068] According to examples of the present disclosure, the electrolysis unit comprises at least two solid oxide electrolysis cells connected by a steel interconnect, such as a steel interconnect comprising chromium.

[0069] Steel materials used in steel interconnect, such as a steel comprising chromium, can be damaged or aged by humidity, since humidity enhances chromium evaporation. The steel material is preferably ferritic stainless steel. The steel preferably comprises at most 35 % chromium by weight, for example in a range from 10 % to 26 % by weight, such as from 14 % to 20 % by weight.

[0070] The steel interconnect may connect neighbouring solid oxide electrolysis cells mechanically and / or electrically.

[0071] According to examples of the present disclosure, the electrolysis system comprises an auxiliary valve arrangement for controlling fluid communication between the oxygen outlet, a flush gas outlet, and any of the first oxy opening and the second oxy opening, wherein the auxiliary valve arrangement has:a first auxiliary configuration in which the oxygen outlet is fluidly coupled with any of the first oxy opening and the second oxy opening, and

[0072] a second auxiliary configuration in which the flush gas outlet is fluidly coupled with any of the first oxy opening and the second oxy opening.

[0073] The controlling arrangement may be configured to control the auxiliary valve arrangement between the first auxiliary configuration and the second auxiliary configuration. Preferably, the controlling arrangement is configured to set the auxiliary valve arrangement in the first auxiliary configuration while the electrolysis system is operating in the first mode of operation or while the valve arrangement is in the first configuration, and preferably the controlling arrangement is configured to set the auxiliary valve arrangement in the second auxiliary configuration while the electrolysis system is operating in the second mode of operation or while the valve arrangement is in the second configuration.

[0074] BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Embodiments of the invention will now be further described by reference to the accompanying drawings, in which:

[0076] Fig. 1 illustrates a solid oxide electrolysis cell and gas flows therein according to the prior art,

[0077] Fig. 2a-b illustrate gas flows in a solid oxide electrolysis cell according to examples of the present disclosure,

[0078] Fig. 3 illustrates an electrolysis system according to an example of the present disclosure,

[0079] Fig. 4 illustrates an electrolysis system according to another example of the present disclosure, and

[0080] Fig. 5 illustrates method steps according to an example of the present disclosure.

[0081] DETAILED DESCRIPTION

[0082] Fig. 1 illustrates a solid oxide electrolysis cell 2 and gas flows 12-15b therein according to the prior art.The solid oxide electrolysis cell 2 comprises a process electrode 3, an oxy electrode 4, and a solid electrolyte 5 providing ionic contact between the process electrode 3 and the oxy electrode 4.

[0083] The electrolyte 5 is made from an oxygen-conducting ceramic material, such as yttria-stabilized zirconia (YSZ) or gadolinium-doped ceria (GDC). It provides a gas-tight membrane between the process electrode 3 and the oxy electrode 4, as well as between the respective chambers 6, 9 of these, while allowing transport of oxygen ions under the influence of an applied voltage.

[0084] The process electrode 3 is formed from a porous, electronically conductive material capable of catalysing, e.g., the reduction of water according to the reaction H2O + 2e_— ► H2+ O2-. Another example of applicable catalysis is the reduction of carbon dioxide according to the reaction CO2+ 2 e-— ► CO + O2-. The process electrode 3 may, for example, be formed of a composite of nickel and YSZ (Ni-YSZ).

[0085] The oxy electrode 4 is formed from a porous, electronically conductive material capable of catalyzing the oxidation of oxygen ions to gaseous oxygen according to the reaction O2-->■1 / 2O2+ 2e_.

[0086] The process electrode 3 is positioned in a process chamber 6 having a first process opening 7 and a second process opening 8, while the oxy electrode 4 is positioned within an oxy chamber 9 having a first oxy opening 10 and a second oxy opening 11.

[0087] As an example of operation, the electrolysis cell 2 is supplied with a steam flow 12 to the process chamber 6 via the first process opening 7, which is also indicated in Fig. 1 by an arrow. Within the process chamber 6, the steam of the steam flow 12 is at least partly converted into hydrogen gas (H2) and oxygen ions (O2) at the process electrode 3. The hydrogen gas is then discharged from the process chamber via the second process opening 8 to provide a hydrogen flow 13 which is also indicated in Fig. 1 by an arrow. Further, a steam flow is also typically present. Under the influence of an applied electrical potential, oxygen ions (O2) generated at the process electrode 3 migrate through the electrolyte 5 to the oxy electrode 4. In the oxy chamber 9, oxygen ions release electrons and combine to form oxygen gas (O2). This generated oxygen is then discharged through the second oxy opening 11 to provide an oxygen flow 14 as indicated in Fig. 1. In the illustrated example, a flush gas flow may also be present simultaneously with the oxygen flow.

[0088] While no substantial electrolysis takes place, i.e., during transient operation, a flush gas is supplied to the oxy chamber 9 through the first oxy opening 10 to provide a first flush gasflow 15a as indicated by an arrow at the first oxy opening 10. The flush gas is discharged through the second oxy opening 11 to provide a second flush gas flow 15b also indicated in the figure.

[0089] The electrolysis cell is designed to operate at elevated temperatures, typically in the range of 600°C to 1000°C.

[0090] Fig. 2a-b illustrate gas flows 12-15b in a solid oxide electrolysis cell 2 according to examples of the present disclosure. The two subfigures illustrate the same solid oxide electrolysis cell 2, which is part of an electrolysis unit which may optionally comprise additional cells similar or identical to the illustrated electrolysis cell 2.

[0091] Generally, the electrolysis cell illustrated in Fig. 2a-b has the same structure as the one illustrated in Fig. 1. However, according to examples of the present disclosure, it is operated differently.

[0092] As for the operation explained in relation to Fig. 1, during transient operation, a flush gas is supplied to the oxy chamber 9 through the first oxy opening 10 to provide a first flush gas flow 15a and the flush gas is discharged through the second oxy opening 11 to provide a second flush gas flow 15b. This is illustrated in Fig. 2a.

[0093] However, while electrolysis takes place and oxygen is produced, for example in a production mode of operation, the oxygen produced in the oxy chamber 9 is discharged from the oxy chamber 9 through both the first oxy opening 10 and the second oxy opening 11. This is illustrated in Fig. 2b, where a first oxygen flow 14a is illustrated at the first oxy opening 10 and a second oxygen flow 14b is illustrated at the second oxy opening 11.

[0094] Fig. 3 illustrates an electrolysis system 29 according to an example of the present disclosure. The system 29 comprises a plurality of solid oxide electrolysis cells 2a, 2b, ... 2n arranged in a solid oxide electrolysis stack 16. Each of the cells 2a, 2b, ... 2n in the stack 16 may, for example, be substantially similar to the cell illustrated in and described in relation to Fig. 2.

[0095] Interconnects 17 are positioned between adjacent cells 2a, 2b, ... 2n in the stack 16. The interconnects 17 enable the connection of multiple cells while maintaining gas separation between the process and oxy sides, and can be made from oxidation-resistant materials, such as ferritic stainless steels or ceramic-based materials.The stack 16 or the system 29 may further comprise high-temperature sealing materials, such as glass-ceramics used to ensure gas-tight operation and to reduce leakage between the process side and oxy side.

[0096] The electrolysis system 29 further comprises a valve arrangement 24, a flush gas supply 21, and an oxygen outlet 20. A (first) oxy manifold 18 of the system 29 fluidly couples this valve arrangement 24 with the first oxy opening 10a, 10b, ... lOn of each of the electrolysis cells 2a, 2b, ... 2n. Thereby, the valve arrangement 24 can control the fluid connection between these first oxy openings 10a, 10b, ... lOn, the oxygen outlet 20, and the flush gas supply 21.

[0097] The valve arrangement 24 has at least two configurations. In a first configuration, the oxygen outlet 20 is fluidly coupled with the first oxy opening 10a, 10b, ... lOn of each of the electrolysis cells 2a, 2b, ... 2n. Thereby, oxygen produced in oxy chamber of each of the electrolysis cells 2a, 2b, ... 2n can be discharged from these oxy chambers to the oxygen outlet 20 via the valve arrangement 24. The resulting flow of oxygen in the valve arrangement 24 is indicated by an arrow as a first valve flow 22 in the figure. In the first configuration, the valve arrangement may be arranged to facilitate a flow of oxygen discharged from the oxy chamber through both the first oxy opening and the second oxy opening of the of the electrolysis cells.

[0098] In a second configuration of the valve arrangement 24, the flush gas supply 21 is fluidly coupled with the first oxy opening 10a, 10b, ... lOn of each of the electrolysis cells 2a, 2b, ...

[0099] 2n. Thereby, flush gas from the flush gas supply 21 can be supplied to the oxy chamber of each of the electrolysis cells 2a, 2b, ... 2n via the valve arrangement 24 and the respective first oxy openings 10a, 10b, ... lOn of the electrolysis cells 2a, 2b, ... 2n.

[0100] The valve arrangement 24 is controlled between the two different configurations by a controlling arrangement 28. This controlling arrangement 28 may, for example, be implemented as a computer system. The process controlling arrangement may comprise one or more processing units (such as CPUs) and one or more digital storages. Such digital storages may store a computer program, such as a computer program configured to control the valve arrangement between the first and second configurations. Such digital storages may further be arranged to receive and store data upon which the valve arrangement is controlled, for example data regarding operational status, electrolysis / hydrogen demand, or grid electricity supply. The controlling arrangement may further be communicatively connected with relevant control and sensor systems of the electrolysis system 29.

[0101] The controlling arrangement 28 can, for example, control the valve arrangement 24 fully automatically, for example as part of a control scheme in which electrolysis is performedbased on hydrogen demand and / or grid electricity supply, or control the valve arrangement 24 based on input from a human operator. In practice, control of the valve arrangement may further be implemented using, e.g., a mechanical motor operated via electricity configured to mechanically change the valve arrangement between the first configuration and the second configuration. The valve arrangement 24 may also be operated via, e.g., air or electromagnetic means.

[0102] Thereby, the controlling arrangement 28 can facilitate control and operation of the valve arrangement 24.

[0103] Fig. 4 illustrates an electrolysis system 29 according to another example of the present disclosure.

[0104] In this example, the electrolysis system additionally comprises a second oxy manifold 19, an auxiliary valve arrangement 25, an oxygen storage 26, and a flush gas outlet 27.

[0105] As for the system illustrated in Fig. 3, the first oxy opening of each of the electrolysis cells 2a, 2b, ... 2n is fluidly connected to the valve arrangement 24 via a first oxy manifold 18. In addition, the second oxy opening 11a, lib, ... lln of each of the electrolysis cells 2a, 2b, ...

[0106] 2n is fluidly connected to the auxiliary valve arrangement 25 via the second oxy manifold 19.

[0107] The auxiliary valve arrangement 25 controls fluid connection between the second oxy openings 11a, lib, ... lln, the oxygen outlet 20, and the flush gas outlet 27. The oxygen outlet 20 supplies oxygen to the oxygen storage 26.

[0108] The valve arrangement 24 is fluidly coupled to the oxygen outlet 20 via the auxiliary valve arrangement 25. However, alternatively, the valve arrangement 24 can be fluidly connected to the oxygen outlet 20 independently from the auxiliary valve arrangement 25. In the present illustration, such an alternative configuration corresponds to a connection from the valve arrangement 24 to the right-hand side of the auxiliary valve arrangement 25, instead of to the left-hand side of the auxiliary valve arrangement 25.

[0109] The auxiliary valve arrangement 25 has two configurations. In a first auxiliary configuration, the oxygen outlet 20 is fluidly coupled with the second oxy openings 11a, lib, ... lln of each of the electrolysis cells 2a, 2b, ... 2n. Thereby, oxygen produced in the oxy chamber of each of the electrolysis cells 2a, 2b, ... 2n can be discharged both from the oxy chambers to the oxygen outlet 20 via the second oxy openings 11a, lib, ... lln and the auxiliary valve arrangement 25, as well as via the first oxy openings and the valve arrangement 24 (and theauxiliary valve arrangement 25). Via both of these flow paths, the oxygen is thus provided to the oxygen outlet 20.

[0110] In the second configuration of the auxiliary valve arrangement 25, the flush gas outlet 27 is fluidly coupled with the second oxy opening 11a, lib, ... lln of each of the electrolysis cells 2a, 2b, ... 2n. Thereby, flush gas supplied from the flush gas supply 21 to the first oxy openings of the electrolysis cells 2a, 2b, ... 2n can be discharged via the second oxy openings 11a, lib, ... lln to the flush gas outlet 27.

[0111] Thus, generally, when the valve arrangement 24 is in the first configuration, the auxiliary valve arrangement 25 is preferably in the first auxiliary configuration, and when the valve arrangement 24 is in the second configuration, the auxiliary valve arrangement 25 is preferably in the second auxiliary configuration.

[0112] As for the valve arrangement 24, the auxiliary valve arrangement 25 may also be controlled from the controlling arrangement 28. The controlling arrangement 28 may control the auxiliary valve arrangement 25 using substantially the same means and principles as used for controlling the valve arrangement 24.

[0113] Fig. 5 illustrates method steps S1-S4 according to an example of the present disclosure.

[0114] The method is directed at operating an electrolysis unit as those illustrated and described as part of the present disclosure. The electrolysis unit may be part of an electrolysis system as those illustrated and described as part of the present disclosure.

[0115] The method comprises a step SI of operating the electrolysis unit to produce oxygen in the oxy chamber of the solid oxide electrolysis cell.

[0116] The method further comprises a step S2 of discharging said oxygen from the oxy chamber through both the first oxy opening and the second oxy opening. Preferably, the oxygen is discharged simultaneously through the first oxy opening and the second oxy opening. In case the electrolysis unit comprises several solid oxide electrolysis cells, the discharge through both the first oxy opening and the second oxy opening preferably occurs in each of the electrolysis cells.

[0117] These two steps S1-S2 may be part of a first mode of operation Ml, such as a production mode.The method may further comprise a second mode of operation M2 different from the first mode of operation Ml, such as a transient mode.

[0118] The method may comprise a step S4 of supplying flush gas to the oxy chamber via the first oxy opening as part of the second mode of operation. This flush gas is then discharged through the second oxy opening.

[0119] The method may further comprise a step S3 of switching between the first mode of operation and the second mode of operation. Such switching may be performed based on manual input or automatically, for example based on electrolysis demand, grid electricity supply, or maintenance.

[0120] The dashed lines in Fig. 5 indicate that the steps S3-S4 and modes of operation M1-M2 are optional. The production mode Ml may be performed without necessarily having or utilizing another mode. Preferably, no flush gas is supplied through the oxy chamber in the production mode Ml. The step S4 of supplying the flush gas is performed separately from the step S2 of discharging oxygen from the oxy chamber and separately from the step SI of operating the electrolysis unit to produce oxygen.

[0121] List of figure references:

[0122] 1 electrolysis unit

[0123] 2 solid oxide electrolysis cell, SOEC

[0124] 3 process electrode

[0125] 4 oxy electrode

[0126] 5 electrolyte

[0127] 6 process chamber

[0128] 7 first process opening

[0129] 8 second process opening

[0130] 9 oxy chamber

[0131] 10 first oxy opening

[0132] 11 second oxy opening

[0133] 12 steam flow

[0134] 13 hydrogen flow

[0135] 14 oxygen flow

[0136] 15 flush gas flow

[0137] 16 solid oxide electrolysis cell stack

[0138] 17 interconnect

[0139] 18 first oxy manifold

[0140] 19 second oxy manifold20 oxygen outlet

[0141] 21 flush gas supply

[0142] 22 first valve flow

[0143] 23 second valve flow

[0144] 24 valve arrangement

[0145] 25 auxiliary valve arrangement 26 oxygen storage

[0146] 27 flush gas outlet

[0147] 28 controlling arrangement 29 electrolysis system

[0148] S1-S4 method steps

[0149] M1-M2 mode of operationLIST OF NUMBERED EMBODIMENTS

[0150] 1. A method for operating an electrolysis unit, the electrolysis unit comprising at least one solid oxide electrolysis cell, each of the at least one solid oxide electrolysis cell comprising:

[0151] a process electrode; an oxy electrode; a solid electrolyte providing ionic contact between the process electrode and the oxy electrode; a process chamber having an interface with the process electrode; a first process opening fluidly coupled to the process chamber for supplying a process feed gas to the process chamber; a second process opening fluidly coupled to the process chamber for discharging a product gas from the process chamber; an oxy chamber having an interface with the oxy electrode; a first oxy opening fluidly coupled to the oxy chamber for supplying a flush gas to the oxy chamber; and a second oxy opening fluidly coupled to the oxy chamber for discharging oxygen from the oxy chamber,

[0152] wherein the method comprises the steps of:

[0153] operating the electrolysis unit to produce oxygen in the oxy chamber of the solid oxide electrolysis cell; and

[0154] discharging said oxygen from the oxy chamber through both the first oxy opening and the second oxy opening.

[0155] 2. A method according to embodiment 1, wherein the steps of operating the electrolysis unit and discharging said oxygen are performed in a production mode of operation.

[0156] 3. A method according to any of the preceding embodiments, wherein the method comprises a step of supplying flush gas to the oxy chamber via the first oxy opening.

[0157] 4. A method according to embodiment 3, wherein the step of supplying a flush gas to the oxy chamber is performed separately from the step of discharging said oxygen from the oxy chamber through both the first oxy opening and the second oxy opening.

[0158] 5. A method according to any of embodiments 3-4, wherein the flush gas is air, such as atmospheric air, preferably air or atmospheric air which has been subjected to air drying.6. A method according to any of embodiments 3-5, wherein the steps of operating the electrolysis unit and discharging said oxygen are performed in a first mode of operation, wherein the step of supplying the flush gas to the oxy chamber is performed in a second mode of operation, wherein the method comprises a step of switching between the first mode of operation and the second mode of operation.

[0159] 7. A method according to embodiment 6, wherein the first mode of operation is a production mode wherein the second mode of operation is a transient mode, wherein less oxygen is produced in the transient mode than in the production mode by the at least one solid oxide electrolysis cell.

[0160] 8. A method according to embodiment 2 or 7, wherein no flush gas is supplied through the oxy chamber in the production mode of operation.

[0161] 9. A method according to any of the preceding embodiments, wherein said oxygen discharged from the oxy chamber through both the first oxy opening and the second oxy opening is supplied to an oxygen storage, such as an oxygen storage which receives oxygen discharged through the first oxy opening and the second oxy opening.

[0162] 10. A method according to any of the preceding embodiments, wherein the step of discharging said oxygen is a step of discharging said oxygen from the oxy chamber simultaneously through both the first oxy opening and the second oxy opening.

[0163] 11. An electrolysis system comprising:

[0164] an electrolysis unit, the electrolysis unit comprising at least one solid oxide electrolysis cell, each of the at least one solid oxide electrolysis cell comprising: a process electrode; an oxy electrode; a solid electrolyte providing ionic contact between the process electrode and the oxy electrode; a process chamber having an interface with the process electrode; a first process opening fluidly coupled to the process chamber for supplying a process feed gas to the process chamber; a second process opening fluidly coupled to the process chamber for discharging a product gas from the process chamber; an oxy chamber having an interface with the oxy electrode; a first oxy opening fluidly coupled to the oxy chamber for supplying a flush gas to the oxy chamber; and a second oxy opening fluidly coupled to the oxy chamber for discharging oxygen from the oxy chamber,

[0165] the electrolysis system further comprising:a flush gas supply;

[0166] an oxygen outlet; and

[0167] a valve arrangement for controlling fluid communication between the flush gas supply, the oxygen outlet, and the first oxy opening, wherein the valve arrangement has:

[0168] a first configuration in which the first oxy opening and the oxygen outlet are fluidly coupled, and

[0169] a second configuration in which the flush gas supply and the first oxy opening are fluidly coupled.

[0170] 12. An electrolysis system according to embodiment 11, wherein the electrolysis system has a first mode of operation in which oxygen is produced in the oxy chamber of the solid oxide electrolysis cell and a second mode of operation in which flush gas is supplied to the oxy chamber via the first oxy opening.

[0171] 13. An electrolysis system according to any of embodiments 11-12, wherein the electrolysis system further comprises a controlling arrangement configured to control the valve arrangement between the first configuration and the second configuration.

[0172] 14. An electrolysis system according to embodiment 13, wherein the controlling arrangement is configured to set the valve arrangement in the first configuration while the electrolysis system is operating in the first mode of operation and configured to set the valve arrangement in the second configuration while the electrolysis system is operating in the second mode of operation.

[0173] 15. An electrolysis system according to any of embodiments 12-14, wherein said oxygen is discharged from the oxy chamber simultaneously through both the first oxy opening and the second oxy opening in the first mode of operation.

[0174] 16. An electrolysis system according to any of embodiments 12-15, wherein the flush gas is supplied to the oxy chamber from the flush gas supply via the first oxy opening in the second mode of operation.17. An electrolysis system according to any of embodiments 12-16, wherein said oxygen is discharged through the oxygen outlet in the first mode of operation.

[0175] 18. An electrolysis system according to any of embodiments 12-17, wherein the first mode of operation is a production mode, and / or wherein the second mode of operation is a transient mode.

[0176] 19. An electrolysis system according to any of embodiments 12-18, wherein the electrolysis system comprises one or more pumps respectively configured to discharge oxygen through the first oxy opening and the second oxy opening in the first mode of operation and / or to supply the flush gas to the oxy chamber in the second mode of operation.

[0177] 20. An electrolysis system according to any of embodiments 11-19, wherein the at least one solid oxide electrolysis cell is a plurality of solid oxide electrolysis cells arranged in a solid oxide electrolysis cell stack,

[0178] wherein the valve arrangement is a common valve arrangement for controlling fluid communication between the flush gas supply, the oxygen outlet, and the first oxy opening of each cell of the plurality of solid oxide electrolysis cells,

[0179] wherein the first oxy opening of each cell of the plurality of solid oxide electrolysis cells and the oxygen outlet are fluidly coupled in the first configuration,

[0180] wherein the flush gas supply and the first oxy opening of each cell of the plurality of solid oxide electrolysis cells are fluidly coupled in the second configuration.

[0181] 21. An electrolysis system according to any of embodiments 11-20, wherein the oxy chamber comprises at least one surface formed by a perovskite material, and / or the oxy chamber is fluidly coupled to at least one surface formed by a perovskite material.

[0182] 22. An electrolysis system according to any of embodiments 11-21, wherein the process chamber comprises at least one surface formed by a nickel-based material, and / or the process chamber is fluidly coupled to at least one surface formed by a nickel-based material.

[0183] 23. An electrolysis system according to any of embodiments 11-22, wherein the electrolysis unit comprises at least two solid oxide electrolysis cells connected by a steel interconnect, such as a steel interconnect comprising chromium.24. An electrolysis system according to any of embodiments 11-23, wherein the electrolysis system comprises an auxiliary valve arrangement for controlling fluid communication between the oxygen outlet, a flush gas outlet, and any of the first oxy opening and the second oxy opening, wherein the auxiliary valve arrangement has:

[0184] a first auxiliary configuration in which the oxygen outlet is fluidly coupled with any of the first oxy opening and the second oxy opening, and

[0185] a second auxiliary configuration in which the flush gas outlet is fluidly coupled with any of the first oxy opening and the second oxy opening.

[0186] 25. An electrolysis system according to any of embodiments 11-24, wherein the electrolysis system or the electrolysis unit is configured to be operated according to the method of any of embodiments 1-10.

Claims

CLAIMS1. A method for operating an electrolysis unit (1), the electrolysis unit (1) comprising at least one solid oxide electrolysis cell (2), each of the at least one solid oxide electrolysis cell (2) comprising:a process electrode (3); an oxy electrode (4); a solid electrolyte (5) providing ionic contact between the process electrode (3) and the oxy electrode (4); a process chamber (6) having an interface with the process electrode (3); a first process opening (7) fluidly coupled to the process chamber (6) for supplying a process feed gas to the process chamber (6); a second process opening (8) fluidly coupled to the process chamber (6) for discharging a product gas from the process chamber (6); an oxy chamber (9) having an interface with the oxy electrode (4); a first oxy opening (10) fluidly coupled to the oxy chamber (9) for supplying a flush gas to the oxy chamber (9); and a second oxy opening (11) fluidly coupled to the oxy chamber (9) for discharging oxygen from the oxy chamber (9),wherein the method comprises the steps of:operating (SI) the electrolysis unit (1) to produce oxygen in the oxy chamber (9) of the solid oxide electrolysis cell (2); anddischarging (S2) said oxygen from the oxy chamber (9) simultaneously through both the first oxy opening (10) and the second oxy opening (11), wherein the steps of operating (SI) the electrolysis unit (1) and discharging (S2) said oxygen are performed in a production mode of operation (Ml), wherein no flush gas is supplied through the oxy chamber (9) in the production mode of operation (Ml).

2. A method according to claim 1, wherein the method comprises a step of supplying flush gas to the oxy chamber (9) via the first oxy opening (10), wherein the step of supplying a flush gas to the oxy chamber (9) is preferably performed separately from the step of discharging said oxygen from the oxy chamber (9) simultaneously through both the first oxy opening (10) and the second oxy opening (11).

3. A method according to claim 2, wherein the flush gas is air, preferably air which has been subjected to air drying.

4. A method according to any of claims 2-3, wherein the production mode of operation is a first mode of operation (Ml), wherein the step of supplying the flush gas to the oxy chamber (9) is performed in a second mode of operation (M2), wherein the method comprises a step of switching between the first mode of operation (Ml) and the second mode of operation (M2).

5. A method according to claim 4, wherein the second mode of operation (M2) is a transient mode, wherein less oxygen is produced in the transient mode (M2) than in the production mode (Ml) by the at least one solid oxide electrolysis cell (2).

6. A method according to any of the preceding claims, wherein said oxygen discharged from the oxy chamber (9) through both the first oxy opening (10) and the second oxy opening (11) is supplied to an oxygen storage (26), such as an oxygen storage which receives oxygen discharged through the first oxy opening (10) and the second oxy opening (11).

7. An electrolysis system (29) comprising:an electrolysis unit (1), the electrolysis unit (1) comprising at least one solid oxide electrolysis cell (2), each of the at least one solid oxide electrolysis cell (2) comprising: a process electrode (3); an oxy electrode (4); a solid electrolyte (5) providing ionic contact between the process electrode (3) and the oxy electrode (4); a process chamber (6) having an interface with the process electrode (3); a first process opening (7) fluidly coupled to the process chamber (6) for supplying a process feed gas to the process chamber (6); a second process opening (8) fluidly coupled to the process chamber (6) for discharging a product gas from the process chamber (6); an oxy chamber (9) having an interface with the oxy electrode (4); a first oxy opening (10) fluidly coupled to the oxy chamber (9) for supplying a flush gas to the oxy chamber (9); and a second oxy opening (11) fluidly coupled to the oxy chamber (9) for discharging oxygen from the oxy chamber (9),the electrolysis system (29) further comprising:a flush gas supply (21);an oxygen outlet (20); anda valve arrangement (24) for controlling fluid communication between the flush gas supply (21), the oxygen outlet (20), and the first oxy opening (10), wherein the valve arrangement (24) has:a first configuration in which the first oxy opening (10) and the oxygen outlet (20) are fluidly coupled, anda second configuration in which the flush gas supply (21) and the first oxy opening (10) are fluidly coupled;wherein the electrolysis system (29) has a first mode of operation (Ml) in which oxygen is produced in the oxy chamber (9) of the solid oxide electrolysis cell (2) and a second mode of operation (M2) in which flush gas is supplied to the oxy chamber (9) via the first oxy opening (10), wherein said oxygen is discharged from the oxy chamber (9) simultaneously through both the first oxy opening (10) and the second oxy opening (11) in the first mode of operation (Ml),wherein the electrolysis system (29) further comprises:a controlling arrangement (28) configured to control the valve arrangement (24) between the first configuration and the second configuration, wherein the controlling arrangement (28) is configured to set the valve arrangement (24) in the first configuration while the electrolysis system (29) is operating in the first mode of operation (Ml) and configured to set the valve arrangement (24) in the second configuration while the electrolysis system (29) is operating in the second mode of operation (M2).

8. An electrolysis system (29) according to claim 7, wherein the at least one solid oxide electrolysis cell (2) is a plurality of solid oxide electrolysis cells arranged in a solid oxide electrolysis cell stack (16),wherein the valve arrangement (24) is a common valve arrangement for controlling fluid communication between the flush gas supply (21), the oxygen outlet (20), and the first oxy opening (10) of each cell of the plurality of solid oxide electrolysis cells,wherein the first oxy opening (10) of each cell of the plurality of solid oxide electrolysis cells and the oxygen outlet (20) are fluidly coupled in the first configuration,wherein the flush gas supply (21) and the first oxy opening (10) of each cell of the plurality of solid oxide electrolysis cells are fluidly coupled in the second configuration.

9. An electrolysis system (29) according to any of claims 7-8, wherein the oxy chamber (9) comprises at least one surface formed by a perovskite material, and / or the oxy chamber (9) is fluidly coupled to at least one surface formed by a perovskite material.

10. An electrolysis system (29) according to any of claims 7-9, wherein the process chamber (6) comprises at least one surface formed by a nickel-based material, and / or the process chamber (6) is fluidly coupled to at least one surface formed by a nickel-based material.

11. An electrolysis system (29) according to any of claims 7-10, wherein the electrolysis unit (1) comprises at least two solid oxide electrolysis cells connected by a steel interconnect (17), such as a steel interconnect comprising chromium.

12. An electrolysis system (29) according to any of claims 7-11, wherein the electrolysis system (29) comprises an auxiliary valve arrangement (25) for controlling fluid communication between the oxygen outlet (20), a flush gas outlet (27), and any of the first oxy opening (10) and the second oxy opening (11), wherein the auxiliary valve arrangement (25) has:a first auxiliary configuration in which the oxygen outlet (20) is fluidly coupled with any of the first oxy opening (10) and the second oxy opening (11), anda second auxiliary configuration in which the flush gas outlet (27) is fluidly coupled with any of the first oxy opening (10) and the second oxy opening (11).

13. An electrolysis system (29) according to any of claims 7-12, wherein the flush gas is supplied to the oxy chamber (9) from the flush gas supply (21) via the first oxy opening (10) in the second mode of operation (M2).

14. An electrolysis system (29) according to any of claims 7-13, wherein said oxygen is discharged through the oxygen outlet (20) in the first mode of operation (Ml).

15. An electrolysis system (29) according to any of claims 7-14, wherein the first mode of operation (Ml) is a production mode, and / or wherein the second mode of operation is a transient mode (M2).

16. An electrolysis system (29) according to any of claims 7-15, wherein the electrolysis system (29) comprises one or more pumps respectively configured to discharge oxygen through the first oxy opening (10) and the second oxy opening (11) in the first mode of operation (Ml) and / or to supply the flush gas to the oxy chamber (9) in the second mode of operation (M2).

17. An electrolysis system (29) according to any of claims 7-16, wherein the electrolysis system or the electrolysis unit (1) is configured to be operated according to the method of any of claims 1-6.

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