Device and method for inerting an electrolysis system

Abstract

The invention presented relates to a rinsing system (100) for inerting an electrolysis system (200), wherein the rinsing system (100) comprises: - a first fluid source (101), - a second fluid source (103), - a first interface (105) configured to fluidly couple the first fluid source (101) to the electrolysis system (200), - a second interface (107) configured to fluidly couple the second fluid source (103) to the electrolysis system (200), wherein the flushing system (100) is configured to provide a first fluid from the first fluid source (101) through the first interface (105) in a first operating mode, in a second operating mode, to provide a second fluid from the second fluid source (103) through the second interface (107), in a third operating mode, to provide the first fluid at a first time with a first pressure for a predetermined rinsing duration and, after a predetermined holding duration in which a second pressure is established in the electrolysis system (200) which is lower than the first pressure, to provide the first fluid again at the first pressure for the predetermined rinsing duration at a second time.

Description

[0001] The presented invention relates to a rinsing system for inerting an electrolysis system, an electrolysis system and a method for inerting an electrolysis system according to the appended claims. State of the art

[0002] An essential element of electrolysis systems is the electrolysis stack or cell stack, which splits water into its components hydrogen (H2) and oxygen (O2) in an electrochemical process, e.g. using electricity.

[0003] Different types of cell stacks are known, such as PEM (proton exchange membrane), SOEC (solid oxide electrolysis cell), alkali and AEM (anion exchange membrane) cell stacks, which differ particularly in the type of ion transport across the membrane (H+, OH-, O2-).

[0004] The cell stacks are typically integrated into an electrolysis system in which the stacks are supplied with water, for example, by a pump. This water may also be passed through a heat exchanger and a filter. When a voltage is applied, product gases (O2 and H2), sometimes with larger amounts of reactant (water), are generated on both sides of a cell in the cell stack when a voltage is applied. These product gases are usually fed to a gas-liquid separator, where the respective gas is separated from the liquid. The hydrogen, in particular, is further processed in subsequent processes (especially drying, purification, and compression).

[0005] Since hydrogen can only be described as "green," i.e., CO2-neutral, if electricity from renewable sources, usually wind and photovoltaics, and less frequently from hydropower or geothermal energy, is used exclusively, the operation of an electrolysis system cannot generally be carried out at a constant operating point, but must be based on electricity availability. This results in the requirement for dynamic operation and intermittent downtimes during the operation of an electrolyzer.

[0006] The energy efficiency of electrolysis systems depends primarily on their power consumption relative to the amount of hydrogen produced or usable. Maintaining energy efficiency as high as possible is challenging given the varying operating conditions and, in particular, the intermittent downtimes caused by standby or extended shutdown periods.

[0007] For safety reasons, when shutting down an electrolysis system, the H2 side in particular is usually purged with an inert gas, usually nitrogen (N2). This prevents hydrogen from diffusing to the oxygen side and reacting there, and / or otherwise forming an ignitable mixture.

[0008] Plans are currently underway for the large-scale, industrial-scale production of hydrogen through electrolysis, with the goal of developing, building, and operating plants with capacities exceeding 1 GW. For this purpose, existing technologies include pressurized PEM (proton exchange membrane) electrolysis cell stacks, which use electrical energy to split water into its chemical elements, hydrogen and oxygen.

[0009] To operate, these electrolysis cell stacks must be connected to a supply line for deionized water and two separate outlets for the split gases, hydrogen and oxygen.

[0010] The discharge lines, consisting of an electrolysis system, are used to discharge a two-phase mixture of hydrogen + water and oxygen + water.

[0011] To separate the gases, these lines must be connected to separators.

[0012] Electrolysis systems are often offered as scalable modules. They are typically divided into central components, such as water treatment from drinking water to DI quality, cooling, and hydrogen post-treatment. These are usually only available once per plant (scale by size).

[0013] Cell stacks and their direct periphery, in particular a water circuit with pump and gas-liquid separator, often form a module that can be connected together as often as required depending on the system size (scale by number). Disclosure of the invention

[0014] In electrolysis systems, it is common practice to inertize the cell stacks and at least parts of the lines during certain operating conditions, especially during system shutdown, emergency shutdown, and possibly also during standby. This inerting is often carried out using nitrogen as an inert gas or with ultrapure water (DI water).

[0015] However, purging with inert gas leads to foreign contamination of the product gas and reduces the hydrogen yield, which has a negative impact on the economic efficiency of a plant.

[0016] Rinsing with ultrapure water enables inerting without the introduction of foreign media.

[0017] Within the scope of the invention presented, a flushing system for rendering an electrolysis system inert, an electrolysis system, and a method for rendering an electrolysis system inert are presented. Further features and details of the invention emerge from the respective subclaims, the description, and the drawings. Features and details described in connection with the flushing system according to the invention naturally also apply in connection with the electrolysis system according to the invention or the method according to the invention, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is always made to each other.

[0018] The invention presented serves in particular to operate an electrolysis system in an energy-efficient manner.

[0019] Thus, according to a first aspect of the invention presented, a rinsing system for inerting an electrolysis system is presented.

[0020] The proposed flushing system comprises a first fluid source, a second fluid source, a first interface configured to fluidically couple the first fluid source to the electrolysis system, and a second interface configured to fluidically couple the second fluid source to the electrolysis system. The flushing system is configured to provide a first fluid from the first fluid source through the first interface in a first operating mode, to provide a second fluid from the second fluid source through the second interface in a second operating mode, to provide the first fluid at a first time with a first pressure for a predetermined flushing duration in a third operating mode, and after a predetermined holding duration in which a second pressure is established in the electrolysis system that is lower than the first pressure,at a second time, provide the first fluid again at the first pressure for the specified flushing duration.

[0021] The presented invention is based on a flushing system that can be switched between different operating modes in order to pass different fluids through an electrolysis system, depending on the operating mode.

[0022] In particular, the purging system presented can be operated in a third operating mode for pressure swing purging such that a first fluid is provided at a first time and at a first pressure. The first fluid, which can be an inert gas, for example, is provided at a first time for a predetermined purging duration. The purging duration can, for example, be between one second and five minutes.

[0023] After the rinsing period, the supply of the first fluid is stopped and the amount of the first fluid introduced into the electrolysis system is not further increased or maintained for a predetermined holding time, e.g., between one second and five minutes.

[0024] After the holding period, the first fluid is again made available at the first pressure for the purging period. Since a second pressure at which the first fluid is present in the electrolysis system decreases relative to the first pressure during the holding period, e.g., due to outflows within and / or outflows from the electrolysis system, the first fluid can again flow into the electrolysis system at the first pressure after the holding period. The alternating pressures in the third operating mode flush the electrolysis system in a pressure swing purge.

[0025] The first pressure can be, for example, between 2 bar and 10 bar. For this purpose, the first fluid source can be, for example, a pressure vessel, in particular a pressure tank, in which the first pressure is present or is or can be adjusted via a pressure reducer at the outlet of the first fluid source.

[0026] Furthermore, the flushing system can be operated in a first operating mode in which a first fluid is provided in, for example, a continuous volume flow, i.e., is passed through the electrolysis system for flushing.

[0027] Furthermore, the flushing system can be operated in a second operating mode in which a second fluid is provided in, for example, a continuous volume flow, i.e., is passed through the electrolysis system for flushing.

[0028] The first operating mode, the second operating mode and the third operating mode can be set exclusively or in a predetermined sequence one after the other or repeatedly.

[0029] To provide the first fluid, the flushing system comprises a first fluid source, such as a pressure bottle or a line to a supply system.

[0030] To provide the second fluid, the flushing system comprises a second fluid source, such as a pressure reservoir or a line to a supply system, in particular a gas-liquid separator or a separate fluid reservoir of a respective electrolysis system. It can be provided that the first fluid is nitrogen and the second fluid is deionized water, or the first fluid is alkali and the second fluid is water, or the first fluid is nitrogen and the second fluid is alkali.

[0031] Nitrogen and deionized water or ultrapure water have proven to be particularly suitable fluids for inerting PEM electrolysis systems, whereas a suitable alkali and water, e.g. deionized water or ultrapure water, have proven to be suitable for rinsing or inerting AEM electrolysis systems.

[0032] By flushing or inerting with deionized water or fluid containing deionized water, in particular after a flushing process with nitrogen or nitrogen-containing fluid, a nitrogen concentration in the electrolysis system, in particular the cell stack of the electrolysis system, is minimized, so that an amount of fresh hydrogen-containing gas to be discarded during a restart is also minimized.

[0033] For this purpose, for example, the amount of H2-containing gas to be discarded can be selected depending on an N2 concentration or an H2 concentration in the gas, or a predetermined period of time for which freshly produced H2-containing gas is to be discarded can be selected to be correspondingly short, e.g. half as long as in an operation without the presented process.

[0034] According to a second aspect, the presented invention relates to an electrolysis system for the electrolysis of water.

[0035] The presented electrolysis system comprises a cell stack, a cathode subsystem, a hydrogen separator, a possible embodiment of the presented purging system and a computing unit, wherein the computing unit is configured to switch the purging system between the first operating mode, the second operating mode and the third operating mode.

[0036] In the context of the invention presented, a computing unit is understood to mean a computer, a processor, a control unit or any other programmable circuit.

[0037] The processing unit of the electrolysis system presented here can, for example, control or switch the flushing system depending on a state or operating point of the electrolysis system. For this purpose, the processing unit of the electrolysis system can, for example, communicate with a processing unit of the flushing system or control the flushing system directly. Accordingly, the processing unit of the electrolysis system can be connected to a communication interface of the flushing system.

[0038] In particular, the flushing system is integrated into the electrolysis system, so that the first interface, the second interface, the first fluid source, and / or the second fluid source are configured as part of the electrolysis system. For example, the first interface and / or the second interface can be configured as valves of the electrolysis system or as valves incorporated into the electrolysis system.

[0039] Furthermore, in particular the second fluid source can be designed as a gas-liquid separator or hydrogen separator or another separate fluid source of the electrolysis system.

[0040] Alternatively, the proposed rinsing system can be incorporated as a separate subsystem into an electrolysis system.

[0041] It may further be provided that the electrolysis system comprises a first pressure control valve configured to adjust a pressure at which the first fluid flows to the cathode subsystem to a predetermined cathode target pressure.

[0042] The first pressure control valve prevents pressure surges on the cathode subsystem and in particular on the membrane of the cell stack during flushing or inerting with the first fluid.

[0043] It can further be provided that the electrolysis system comprises a first closing valve arranged downstream of the first pressure control valve in the flow direction, which is open without energy.

[0044] The first shut-off valve enables the selective introduction of the first fluid into the cathode subsystem. In the event of a power outage or the failure of auxiliary energy, such as compressed air, the cathode subsystem can be flushed with the first fluid because the first shut-off valve is open without power.

[0045] It can further be provided that the electrolysis system comprises a second closing valve which is coupled to the second fluid source and is closed without energy.

[0046] The second shut-off valve enables the selective introduction of the second fluid, e.g., ultrapure water, into the cathode subsystem. For this purpose, the second shut-off valve can be located, for example, at an ultrapure water connection of the electrolysis system.

[0047] It can further be provided that the electrolysis system comprises a third closing valve arranged between two hydrogen outlets of the cell stack, which is closed when de-energized.

[0048] The third shut-off valve allows the opening of a hydrogen path, fed from the cell stack outlets, on the cathode side toward the hydrogen separator. The third shut-off valve can also be controlled for selective inerting. For example, to inert the cell stack, the third shut-off valve is closed and opened for pressure swing purging or the third operating mode of the purging system.

[0049] It can further be provided that the electrolysis system comprises a fourth closing valve arranged downstream of the third closing valve in the flow direction, which is closed without energy.

[0050] The fourth closing valve is closed without energy in order to fluidically decouple the hydrogen separator in the event of a power failure or auxiliary power failure and thus to maintain the high hydrogen quality during inerting with the first fluid.

[0051] It can further be provided that the electrolysis system comprises an outlet path arranged between the third closing valve and the fourth closing valve.

[0052] The first fluid or the second fluid can be discharged from the electrolysis system through the outlet path, for example to adjust a pressure in the electrolysis system.

[0053] It can further be provided that the electrolysis system comprises a fifth closing valve which is fluidly coupled to the outlet path and is open without energy.

[0054] The fifth shut-off valve allows for selective discharge of the first fluid from the cathode path. In the event of a power failure, the fifth shut-off valve allows for flushing of the cathode subsystem.

[0055] It can further be provided that the electrolysis system comprises a second pressure valve downstream of the fifth closing valve in the flow direction, which second pressure valve is open without energy and opens into a first partial outlet path for the first fluid.

[0056] The second pressure valve regulates, for example, an output pressure from the cathode subsystem to a pressure required in the cathode subsystem, so that pressure surges on the cathode subsystem and also in particular on the membrane of the cell stack are prevented during flushing or inerting with the first fluid.

[0057] It can further be provided that the electrolysis system comprises a sixth closing valve which is fluidically coupled to the outlet path, which is closed without energy and opens into a second partial outlet path for the second fluid.

[0058] The sixth closing valve allows selective discharge of the second fluid from the cathode subsystem.

[0059] All valves of the presented electrolysis system can include electrical, hydraulic and / or pneumatic actuators.

[0060] A check valve arranged between two hydrogen outlets of the cell stack and the fluid inlet prevents the produced hydrogen from entering a pipe system used for inerting.

[0061] It can further be provided that the computing unit is configured, when the flushing system is switched to the first operating mode, to control the second flushing valve, the third flushing valve, the fourth flushing valve and the sixth flushing valve such that they are closed, and the computing unit is further configured to control the first flushing valve and the fifth flushing valve such that they are open for a predetermined duration.

[0062] It can further be provided that the computing unit is configured, when the purging system is switched to the second operating mode, to control the first purging valve, the third purging valve, and the fifth purging valve such that they are closed, and the computing unit is further configured to control the second purging valve such that it is open in order to purge the cell stack, and, in the event that a purging pressure corresponds to an operating pressure of the electrolysis system, to carry out a purging in the direction of the hydrogen separator and to control the fourth purging valve such that it is open and the sixth purging valve such that it is closed, or, in the event that the purging pressure is lower than the operating pressure of the electrolysis system, to carry out a purging in the direction of the second partial outlet path and to control the fourth purging valve such thatthat it is closed and to control the sixth flush valve in such a way that it is open.

[0063] It can further be provided that the computing unit is configured, when the flushing system is switched to the third operating mode, to control the second flush valve, the fourth flush valve, the fifth flush valve and the sixth flush valve such that they are closed and the third flush valve is opened, and the computing unit is further configured, in a repeating sequence, to control the first flush valve such that it opens for the predetermined flushing duration in order to set the first pressure and closes after the predetermined flushing duration, and to control the fifth flush valve such that it opens after the first flush valve is closed in order to set the second pressure.

[0064] It can further be provided that the computing unit is further configured to keep the first flushing valve closed for a predetermined holding time after the predetermined flushing time.

[0065] For a predetermined holding time, e.g., between 1 second and 5 minutes, the pressure in the electrolysis system decreases, e.g., by opening the fifth shut-off valve. Accordingly, after the holding time, fresh fluid can flow into the electrolysis system by opening the first shut-off valve, resulting in multiple different pressures in the electrolysis system, which mechanically load the electrolysis system and promote the discharge of hydrogen from its cathode subsystem.

[0066] According to a third aspect, the presented invention relates to a method for inerting a possible embodiment of the presented electrolysis system.

[0067] The presented method comprises operating the purge system of the electrolysis system in the first operating mode or the second operating mode or the third operating mode.

[0068] It can further be provided that the first fluid and later the further fluid are passed simultaneously over the cell stack, connecting lines and the gas-liquid separator.

[0069] Alternatively, it can be provided that in a first rinsing step the first fluid is initially passed exclusively over the cell stack, then in a second rinsing step the second fluid is passed exclusively over the cell stack, and in a third rinsing step the second fluid is passed via connecting lines and finally over the gas-liquid separator.

[0070] By exclusively flushing the cell stack with the first fluid, safety requirements for the electrolysis system are met and nitrogen concentration in the electrolysis system is minimized.

[0071] It can further be provided that the second fluid is taken directly from the gas-liquid separator or is supplied via a supply line from an external system.

[0072] Since deionized water usually collects in the gas-liquid separators of a respective electrolysis system, this can be used to flush or inertize the electrolysis system after flushing or inerting with, for example, nitrogen or a nitrogen-containing fluid.

[0073] Advantages provided for the method for operating an electrolysis system according to the first aspect of the invention also apply correspondingly to the electrolysis system according to the second aspect or to the method for inerting a possible embodiment of the presented electrolysis system according to the third aspect of the presented invention.

[0074] Further advantages, features, and details of the invention will become apparent from the following description, which describes exemplary embodiments of the invention in detail with reference to the drawings. The features mentioned in the claims and in the description may be essential to the invention individually or in any combination.

[0075] They show schematically: Fig. 1 a possible design of the proposed rinsing system in a possible design of the proposed electrolysis system, and Fig. 2 a possible design of the presented procedure.

[0076] In Fig. 1 shows a purge system 100 as part of an electrolysis system 200. The purge system 100 comprises a first fluid source 101, a second fluid source 103, a first interface 105 configured to fluidly couple the first fluid source 101 to the electrolysis system 200, in particular to a cathode subsystem 203 of the electrolysis system 200, and a second interface 107 configured to fluidly couple the second fluid source 103 to the electrolysis system 200, in particular to the cathode subsystem 203.

[0077] The first interface 105 is integrated here, for example, into a first closing valve 221 of the electrolysis system 200.

[0078] The second interface 107 is integrated here, for example, into a second closing valve 223 of the electrolysis system 200.

[0079] In addition to the cathode subsystem 203, the electrolysis system 200 includes a cell stack 201 and a hydrogen separator 205, as well as several shut-off valves for controlling fluid flows through the electrolysis system 200.

[0080] To adjust a course of fluids provided by the first fluid source 101 or the second fluid source 103, the electrolysis system 200 or the flushing system 100 further comprises a first closing valve 221, a second closing valve 223, a third closing valve 207, a fourth closing valve 209, a fifth closing valve 211 and a sixth closing valve 213, each of which can be selectively set to an open state or a closed state by a computing unit 215.

[0081] An inlet pressure at which the first fluid flows from the first fluid source 101 into the cathode subsystem 203 can be regulated via a first pressure control valve 217, so that pressure surges on the cathode subsystem 203 and also in particular on the membrane of the cell stack 201 are prevented when the first closing valve 221 is opened.

[0082] A second pressure control valve 219 can be used to regulate an output pressure at which the first fluid flows out of the cathode subsystem 203 into a first partial outlet path 225, so that pressure surges on the cathode subsystem 203 and also in particular on the membrane of the cell stack 201 are prevented when the first closing valve 221 opens.

[0083] A second partial outlet path 227 can be opened via the sixth closing valve 213 to discharge the second fluid.

[0084] In the connection between the first closing valve 221 or the second closing valve 223 and respective hydrogen outlets of the cell stack 201, a check valve 229 is arranged, which prevents penetration of produced hydrogen into an inlet path for introducing the first fluid or the second fluid into the cell stack 201.

[0085] In Fig. 2 is a method 300 for inerting the electrolysis system 200 according to Fig. 2 shown.

[0086] The method 300 comprises an operating step 301 in which the rinsing system 100 of the electrolysis system 200 is operated in the first operating mode or the second operating mode or the third operating mode.

Claims

[1] Flushing system (100) for inerting an electrolysis system (200), the flushing system (100) comprising: - a first fluid source (101), - a second fluid source (103), - a first interface (105) configured to fluidly couple the first fluid source (101) to the electrolysis system (200), - a second interface (107) configured to fluidly couple the second fluid source (103) to the electrolysis system (200), wherein the flushing system (100) is configured to provide a first fluid from the first fluid source (101) through the first interface (105) in a first operating mode, in a second operating mode, to provide a second fluid from the second fluid source (103) through the second interface (107), in a third operating mode, to provide the first fluid at a first point in time with a first pressure for a predetermined rinsing time, and after a predetermined holding time in which a second pressure is established in the electrolysis system (200) which is lower than the first pressure, to provide the first fluid again at the first pressure for the predetermined rinsing time at a second point in time. [2] Flushing system (100) according to claim 1, characterized by that the first fluid is nitrogen and the second fluid is deionized water or the first fluid is alkali and the second fluid is water or the first fluid is nitrogen and the second fluid is alkali. [3] Electrolysis system (200) for electrolyzing water, the electrolysis system (100) comprising: - a cell stack (201), - a cathode subsystem (203), - a hydrogen separator (205), - a flushing system (100) according to claim 1 or 2, - a computing unit (215), wherein the computing unit (215) is configured to switch the flushing system (100) between the first operating mode, the second operating mode and the third operating mode. [4] Electrolysis system (200) according to claim 3, characterized by that the electrolysis system (200) further comprises: - a first pressure control valve (217) configured to adjust a pressure at which the first fluid flows to the cathode subsystem (203) to a predetermined cathode target pressure, - a first closing valve (221) downstream of the first pressure control valve (217) in the flow direction, which is open without energy, - a second closing valve (223) coupled to the second fluid source (103) and closed without energy, - a third closing valve (207) arranged between two hydrogen outlets of the cell stack (201), which is closed without energy, - a fourth closing valve (209) downstream of the third closing valve (207) in the flow direction, which is closed without energy, - an outlet path arranged between the third closing valve (207) and the fourth closing valve (209), - a fifth closing valve (211) fluidly coupled to the outlet path, which is open without energy, - a second pressure valve (219) downstream of the fifth closing valve (211) in the flow direction, which is open without energy and opens into a first partial outlet path for the first fluid, - a sixth closing valve (213) fluidly coupled to the outlet path, which is closed without energy and opens into a second partial outlet path for the second fluid. [5] Electrolysis system (200) according to claim 3 or 4, characterized by , that a closing valve (207) is arranged between two hydrogen outlets of the cell stack (201), wherein the computing unit (215) is configured to control the check valve such that the closing valve (207) is closed when the flushing system (100) is switched to the first operating mode or the second operating mode, and the check valve is open when the flushing system (100) is switched to the third operating mode. [6] Electrolysis system (200) according to one of claims 3 to 5, characterized by , that the computing unit (215) is configured to, when the flushing system (100) is switched to the first operating mode, to control the second flushing valve (223), the third flushing valve (207), the fourth flushing valve (209) and the sixth flushing valve (213) in such a way that they are closed, and the computing unit (215) is further configured to to control the first flush valve (221) and the fifth flush valve (211) such that they are open for a predetermined duration. [7] Electrolysis system (200) according to one of claims 3 to 6, characterized by , that the computing unit (215) is configured to, when the flushing system (100) is switched to the second operating mode, to control the first purge valve (221), the third purge valve (207) and the fifth purge valve (211) such that they are closed, and the computing unit (215) is further configured to control the second purge valve (223) such that it is open in order to purge the cell stack (201), and in the event that a flushing pressure corresponds to an operating pressure of the electrolysis system (100), to carry out a flushing in the direction of the hydrogen separator (205) and to control the fourth flushing valve (209) in such a way that it is opened and to control the sixth flushing valve (223) in such a way that it is closed, or in the event that the flushing pressure is lower than the operating pressure of the electrolysis system (200), to carry out a flushing in the direction of the second partial outlet path and to control the fourth flushing valve (209) in such a way that it is closed and to control the sixth flushing valve (213) in such a way that it is open. [8] Electrolysis system (200) according to one of claims 3 to 7, characterized by , that the computing unit (215) is configured to, when the flushing system (100) is switched to the third operating mode, to control the second flushing valve (223), the fourth flushing valve (209), the fifth flushing valve (211) and the sixth flushing valve (213) in such a way that they are closed, and to control the third flushing valve (207) in such a way that it is open, and the computing unit (215) is further configured to control, in a repeating sequence, the first flushing valve (221) in such a way that it opens for the predetermined flushing duration in order to set the first pressure and closes after the predetermined flushing duration, and to control the fifth flushing valve (211) in such a way that it opens after the first flushing valve (221) is closed in order to set the second pressure. [9] Electrolysis system (200) according to claim 8, characterized by that the computing unit (215) is further configured to keep the first flushing valve (221) closed for a predetermined holding time after the predetermined flushing time. [10] A method (300) for inerting an electrolysis system (200) according to any one of claims 3 to 9, wherein the method (300) comprises: - Operating (301) the rinsing system (100) of the electrolysis system (200) in the first operating mode or the second operating mode or the third operating mode.

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