Method for operating an electrolysis plant, and electrolysis plant

Abstract

The invention relates to a method for operating an electrolysis plant (100) in which water is converted into oxygen and hydrogen in an electrolysis unit (110). A processed fluid flow (c) is guided from an oxygen side (114) of the electrolysis unit to a gas separator (120), and the processed fluid flow (c) has water and gas. An oxygen-containing fluid flow (g, h) is discharged from the gas separator (120), said oxygen-containing fluid flow having gas, and the oxygen-containing fluid flow (h, d) is supplied to an oxygen region of the electrolysis plant (100). If necessary, ambient air (k) is supplied to the oxygen-containing fluid flow (h) at a supply point (140) before the fluid flow is supplied to the oxygen region of the electrolysis plant (100), or the oxygen-containing fluid flow (h) is replaced with ambient air (k) before the fluid flow is supplied to the oxygen region of the electrolysis plant (100). The invention also relates to a corresponding electrolysis plant (100).

Description

[0001] Description

[0002] Method for operating an electrolysis plant and electrolysis plant

[0003] The invention relates to a method for operating an electrolysis plant for water electrolysis, as well as to such an electrolysis plant which is used, for example, for the production of hydrogen.

[0004] State of the art

[0005] Hydrogen can be produced using electrolysis, in which, for example, water is split or converted into oxygen and hydrogen using electrical energy. This is also referred to as water electrolysis. Proton exchange membrane electrolysis (PEM electrolysis) is a possible method. In this context, PEM electrolysis systems or PEM electrolyzers are also referred to.

[0006] During PEM electrolysis, a large portion of the water typically remains on the oxygen side of the membrane. While the hydrogen is generated and removed on the other side of the membrane, the oxygen initially remains in the water and is then typically separated from the water in a container. The pressure at the cathode (hydrogen side or hydrogen formation) is typically over 20 barg. At the anode (oxygen side or

[0007] Water splitting), however, the pressure of the oxygen product is below the pressure on the cathode side, e.g. slightly above atmospheric pressure.

[0008] However, it can happen that a certain amount of hydrogen diffuses back to the oxygen side or gets there in some other way, e.g., due to defects or cracks in the membrane. This can create an explosive mixture that could potentially ignite and cause an explosion that could damage the electrolysis system. Against this backdrop, the task of making electrolysis systems and their operation safer arises.

[0009] The pressure difference between the electrodes can lead to a constant

[0010] Hydrogen transfer (so-called "crossover") through the membrane can occur. This can lead to hydrogen accumulation on the oxygen side of the electrolysis system in certain operating scenarios (e.g., partial load, startup, shutdown, and standstill of individual electrolysis cells or stacks) while the electrolysis units are in operation.

[0011] Hydrogen leakage from the cathode side to the anode side due to membrane perforation, for example, with pressures of more than 20 barg, can also occur as a result of undetected membrane defects while the electrolysis cells are in operation. A membrane rupture can lead to a sudden transfer of large amounts of hydrogen from the cathode side to the anode side.

[0012] All of these scenarios lead to an explosion risk. The so-called lower flammability limit (LEL) of hydrogen is approximately 4 vol. Above 50% of the LEL (2 vol.% hydrogen), the electrolysis plant must generally be shut down and brought into a safe state.

[0013] For example, EP 3 971 324 A1 discloses an electrolysis plant in which inert gas is incorporated into the oxygen product stream in order to reduce the hydrogen concentration.

[0014] Against this background, the task arises to provide a better way to reduce the explosion risk in water electrolysis, e.g. PEM electrolysis, and thus to improve the operation of the electrolysis plant.

[0015] Disclosure of the invention

[0016] This object is achieved by a method for operating an electrolysis system and an electrolysis system having the features of the independent patent claims. Further embodiments are the subject of the dependent patent claims and the following description.

[0017] Advantages of the invention The invention relates to water electrolysis and electrolysis systems, and their operation therefor. Such electrolysis systems are typically used to produce or extract hydrogen by electrolysis. In so-called water electrolysis, water is converted (split) into hydrogen and oxygen, i.e., in addition to hydrogen, oxygen is always extracted or produced at the same time. In water electrolysis, there is, for example, so-called alkaline water electrolysis (AEL, "Alkaline Electrolysis") or so-called proton exchange membrane electrolysis (PEM electrolysis, "Proton Exchange Membrane" electrolysis). The principles for this are known per se, e.g., from "Bessarabov et al: PEM electrolysis for Hydrogen production. CRC Press."

[0018] There are also so-called solid oxide electrolysis cells (SOEC) and anion exchange membrane electrolysis (AEM). Electrolysis technologies that operate at low temperatures, such as PEM, AEL, and AEM electrolysis, are particularly suitable for supporting the transition to renewable energy sources due to their flexible operation options.

[0019] In PEM electrolysis, for example, water, particularly demineralized water, is fed as the feed medium into an electrolysis unit with a proton exchange membrane (PEM), in which the feed medium, i.e. the water, is converted (split) into hydrogen and oxygen.

[0020] As mentioned, during PEM electrolysis, a large portion of the water typically remains on the oxygen side of the membrane. While the hydrogen is generated and removed on the other side of the membrane, the oxygen initially remains in the water and is then typically fed as a processed fluid stream to a vessel (used as a gas or oxygen separator). There, the oxygen is separated from the water, yielding an oxygen-containing fluid stream, or what is known as an oxygen product stream.

[0021] It can, however, happen that a certain amount of hydrogen diffuses back to the oxygen side or gets there in some other way, e.g. due to defects or cracks in the membrane, as explained at the beginning. The fluid flow to be discharged from the oxygen side (processed fluid flow) therefore contains not only water and oxygen, but possibly also hydrogen, i.e. generally water and gas; the term gas is generally understood here to mean a gaseous medium, not just a single gas, but also any gas mixture that may be present. An explosive mixture can therefore form on the oxygen side of the electrolysis unit or in the fluid flow, which could potentially ignite somewhere in the electrolysis system downstream of the electrolysis unit, be it in the fluid flow to the oxygen or gas separator or subsequently in the gas flow separated and discharged there (in this case, not only the oxygen but also anyexisting hydrogen is separated). The resulting explosion or detonation can damage the electrolysis plant.

[0022] Ignition of the mixture can occur particularly when the hydrogen content in the gas (the water content is not relevant here) exceeds a certain predetermined level, the so-called lower explosive limit (LEL); this is typically around 4%, for example, during standby operation or operation of the electrolysis plant at low load. The (lower) explosive limit of a gas indicates the concentration in a gas mixture above which ignition or explosion is possible, provided that sufficient oxygen content is present.

[0023] Since an ignition source in the electrolysis unit or somewhere downstream cannot generally be excluded or avoided, potential ignition, explosion, or detonation must always be taken into account during operation of an electrolysis plant. An explosion is the uncontrolled combustion of an ignitable gas mixture with a laminar flame front. An explosion differs from a detonation primarily in its propagation speed.

[0024] The reaction between hydrogen and oxygen takes place very quickly and produces very high flame speeds, i.e. high speeds at which the flames spread, for example, in corresponding fluid connections or fluid lines. In an explosion, this is below the speed of sound, while in a detonation it is typically above the speed of sound. Explosions and detonations of gases or gas mixtures result in a massive increase in pressure. Typically, an explosion of a hydrogen-oxygen mixture can result in a pressure increase by a factor of ten. The effects of a detonation are much more serious and less precisely predictable. Here the pressure increase factor can be 25 or even 50 or more, depending on the geometry, turbulence and other factors. An explosion can turn into a detonation after a certain run-up length and a minimum concentration of fuel and oxygen.Pressures can therefore arise that are sometimes 25, 50 or more times the actual operating pressure in the electrolysis plant, particularly on the oxygen side and the downstream, and possibly also upstream, flow.

[0025] To prevent any damage to the electrolysis system, the relevant fluid or gas lines can be designed for correspondingly high pressures, and their suitability can be verified through testing. Depending on the electrolysis system and the oxygen used, this can involve a large number of lines or even very long lines. This applies not only to the fluid lines from the electrolysis unit to the gas separator, but also to any gas lines in which the separated oxygen (and possibly hydrogen) is transported to one or more desired uses or other processing steps. This can lead to particularly high costs.

[0026] Irrespective of this, as mentioned above, it is generally intended to shut down the electrolysis plant when the hydrogen content reaches a certain value, e.g. 2 vol. %, in order to prevent possible explosions or detonations.

[0027] Against this background, it is now proposed that, in an electrolysis plant as described above, the oxygen-containing fluid stream—which, as mentioned, may contain not only oxygen but also a certain amount of hydrogen—be fed back into the oxygen section of the electrolysis plant, i.e., the processed fluid stream and / or the gas separator. A blower, for example, can be used for this purpose.

[0028] It is also proposed, if necessary, to supply ambient air before the oxygen-containing fluid stream is fed to the oxygen zone of the electrolysis system. The ambient air can be supplied at a suitable supply point, particularly before the blower. This creates a recirculation circuit that is open to the environment or can be opened to the environment if necessary, allowing ambient air to flow in.

[0029] In particular, the hydrogen concentration can be monitored, either continuously or quasi-continuously, for example, or analytically. For this purpose, a suitable safety device with a measuring device or sensor can be provided. The hydrogen concentration can be monitored, for example, in the processed fluid stream, preferably after the feed point and before the feed to the oxygen section of the electrolysis plant.

[0030] If monitoring reveals that the hydrogen concentration exceeds a predetermined threshold, e.g., the aforementioned 2 vol%, at least one safety measure can be initiated; this can also be done, for example, by the safety device. This can, in particular, include shutting down the electrolysis unit or the individual electrolysis cells, as well as interrupting the processed fluid flow from the oxygen side of the electrolysis unit to the gas separator and thus also to the recirculation circuit. As a particularly preferred safety measure, ambient air is introduced into the oxygen-containing fluid flow. For this purpose, the recirculation circuit can be opened, e.g., by means of a valve.

[0031] In this way, or with the help of this configuration, an increase in the hydrogen concentration in the oxygen part of the electrolysis process above the LEL (4 vol%) can be prevented at any time. Applicable standards and regulations for the safe operation of a hydrogen plant can thus be complied with, and the formation of an explosive atmosphere is prevented.

[0032] By opening the recirculation circuit to allow atmospheric air to flow into the oxygen product stream, there is no need to integrate an inert gas stream into the oxygen product stream. Instead, atmospheric air can be integrated into the recirculation circuit particularly easily and cost-effectively via a control valve.

[0033] By opening the oxygen product stream to the atmospheric air, the

[0034] Hydrogen concentration can be effectively limited to a level below the lower explosive limit (LEL) of 4%, i.e. the recirculation circuit in the proposed configuration only ensures that sufficient reaction time is created to prevent an increase in the hydrogen concentration in the oxygen part of the electrolysis or PEM electrolysis to above the LEL (4 vol%) and, if necessary, to ensure shutdown of the electrolysis unit at, for example, 50% of the LEL (2 vol% hydrogen).

[0035] In some embodiments, the (analytically monitored) oxygen product stream (or the oxygen-containing fluid stream) can be reintegrated into the oxygen system or the oxygen region at various positions on the anode side at the outlet of the electrolysis cells. For example, the oxygen product stream can be recirculated into a collecting line connecting different electrolysis cells or electrolysis units. This reduces the increased technical design requirements for all functional elements within the recirculation circuit, which result from an explosion risk. It is also conceivable to integrate the oxygen product stream (or the oxygen-containing fluid stream) directly into the gas separator (a so-called oxygen-water phase separator).

[0036] It has been shown that with the proposed configuration, the hydrogen concentrations at different positions within the recirculation loop, which is connected to the gas separator, for example, via the common manifold, do not exceed the LEL. Initially, a hydrogen concentration of, for example, 1% hydrogen in the recirculating oxygen stream is established within the recirculation loop as a result of the load state of the electrolyzers and thus due to the aforementioned "crossover." If a membrane failure is assumed in a stack, the associated additional amount of hydrogen is introduced into the recirculation stream in a short time and then continuously enriches the oxygen system as a constant hydrogen stream.As a result, membrane failure leads to a transfer of hydrogen from the cathode side to the anode side of the PEM and thus into the oxygen system, typically with a steep increase in the hydrogen concentration. This increase can be identified by a special fast-responding hydrogen analyzer (e.g. a continuous laser or spectral analysis) as early as 10s after membrane failure. In this way, a membrane defect and the associated increase in the hydrogen concentration in the oxygen system can be reliably detected within a few seconds, e.g. after 10s. By taking appropriate measures, namely by opening the loop (circuit) to allow fresh air to be supplied, the increase in the hydrogen concentration in the loop is then limited to below the LEL.

[0037] A safety-related circuit or, more generally, a monitoring device can then initiate the shutdown of the electrolysis cells, an interruption of the oxygen flow from the electrolysis cells to the recirculation circuit, and the opening of the recirculation circuit on the suction side of the blower for atmospheric fresh air, while the blower continues to operate, e.g., at a constant throughput. By opening the recirculation circuit for atmospheric air on the suction side of the blower, the gas stream of hydrogen and oxygen in the recirculation circuit (i.e., the oxygen-containing fluid stream) is diluted with atmospheric air or, in particular, even replaced by atmospheric air, and the increase in the hydrogen concentration is immediately limited. This results in a steep drop in the hydrogen concentration at the detector position in the recirculation circuit.

[0038] The recirculation circuit should be dimensioned such that the existing gas volume limits an increase in the hydrogen concentration in the loop of the recirculation circuit to less than (4 vol%) for the duration of one cycle.

[0039] Based on an analysis or summary of all relevant operating cases, it has been shown that the lower explosion limit (4 vol%) is not exceeded for any operating case, i.e. an explosion risk for the recirculation circuit can be excluded with the help of the proposed technical solution.

[0040] Furthermore, it has been shown that the increase in hydrogen concentration in the recirculation circuit becomes noticeable in good time, e.g., at least 10 seconds (depending on the system), before the concentration in the actual oxygen product stream exceeds the LEL. This allows sufficient time for safety measures.

[0041] The proposed configuration allows an explosion-proof system to be constructed with little equipment effort and minimal operating costs, which significantly limits the number of equipment and piping components and the like that would otherwise have to be explosion-proof in the oxygen system of the electrolysis plant, e.g. for PEM electrolysis, and makes it possible to use the by-product of PEM electrolysis, oxygen, without carrying over the explosion risks into subsequent systems, e.g. oxygen compression and / or oxygen purification and the like.

[0042] In one embodiment, the electrolysis plant also comprises a recombination reactor. The oxygen-containing fluid stream is then passed through the recombination reactor before being fed to the oxygen section of the electrolysis plant. A recombination reactor (also referred to simply as a recombiner or recombination catalyst) can catalytically convert hydrogen and oxygen into water. This can further increase the safety of the recirculation circuit.

[0043] For example, temperature monitoring of the highly exothermic reaction, e.g., using a temperature element in the reactor bed of the recombination reactor, can be used as a supplement to the hydrogen concentration analysis described below. This can, for example, reduce the requirements for the sensors and actuators within the recirculation circuit.

[0044] The arrangement of the recombination reaction reactor downstream of the blower favors the expected hydrogen conversion in the recirculation stream due to the higher temperatures resulting from the pressure increase. To protect the recombination reaction reactor from condensate, it is advisable to operate it approximately 10 to 20 K above the water dew point. Thus, if the compression heat of the recirculator is insufficient, preheating upstream of the recombination reactor may be necessary. Furthermore, it is advisable to protect the ultrapure water from catalyst dust. Condensate water accumulating in the downstream cooling section of the recombiner is discarded or purified, and suitable filters are used to protect the electrolysis process water from contamination.

[0045] Suitable recombination reaction reactors or recombination catalysts include, for example, platinum or palladium catalysts or mixed catalysts made of the above-mentioned precious metals, which are applied, for example, to ceramic or metallic supports.

[0046] In one embodiment, it is also provided to divert a portion of the oxygen-containing fluid stream for alternative use after the feed point and before it is fed into the oxygen section of the electrolysis system. For this purpose, an additional control valve can be provided, for example. This enables the use of the electrolysis by-product, namely oxygen, without carrying the risk of explosion into downstream systems, for oxygen compression or oxygen purification. If hydrogen is detected above the threshold value in the recirculation circuit for the safety shutdown, contamination of the downstream oxygen treatment by atmospheric air can then be prevented by closing the connecting valve to the oxygen post-treatment.

[0047] Although the invention is primarily described with reference to PEM electrolysis, it should be noted that the invention is suitable for all water electrolysis processes where there is a risk of an ignitable mixture of hydrogen and oxygen.

[0048] The invention will be explained in more detail below with reference to the accompanying drawing, which shows a system according to a preferred embodiment of the present invention.

[0049] Short description of the drawing

[0050] Figure 1 shows schematically an electrolysis plant according to the invention in a preferred embodiment.

[0051] Detailed description of the drawing

[0052] Figure 1 schematically shows an electrolysis plant 100 according to the invention in a preferred embodiment, in which a method according to the invention can also be carried out. This is an electrolysis plant for water electrolysis using PEM. In particular, the electrolysis plant shown here and generally described within the scope of the invention is an industrial-scale electrolysis plant, for example, for producing hydrogen on an industrial scale. A typical output of such an electrolysis plant is, for example, more than 10 MW or even more than 20 MW.

[0053] The electrolysis system 100 has an electrolysis unit (or stack) 110, which here, for example, has two so-called electrolysis cells 110.1, 110.2, each of which contains a proton exchange membrane (PEM) 112. The PEM 112 separates the electrolysis cells into an oxygen side 114 and a hydrogen side 116. The oxygen sides 114 and the hydrogen sides 116 can jointly be regarded as the oxygen side and the hydrogen side of the electrolysis unit 110, respectively. Furthermore, the electrolysis system 100 has a power supply unit 118, e.g., with one or more transformers and power converters, in order to be able to operate the electrolysis unit 110 and the electrolysis cells accordingly.

[0054] It should be noted that, depending on size and requirements, an electrolysis unit 110 may, for example, have only one or more than two electrolysis cells, e.g., four, six, eight, or more electrolysis cells. The power supply unit 118 may, for example, also have one transformer and one power converter per electrolysis cell; likewise, one transformer may be assigned to two power converters.

[0055] The electrolysis system 100 further comprises a container 120 which serves as a gas separator, here in particular as an oxygen separator or oxygen-water separator. The container 120 is connected via a fluid connection to the electrolysis unit 110 or to each of the electrolysis cells 110.1, 110.2 there. As a result, a fluid stream b can be pumped from the container 120 to the electrolysis unit, e.g. by means of a pump 124, via a suitable fluid connection 122, e.g. pipes. Depending on the type of electrolysis system and e.g. the number of electrolysis cells, several fluid connections (i.e. separate lines) can also be provided. For example, one fluid connection can be provided for two or four electrolysis cells.

[0056] The electrolysis unit 110 is also connected to the container 120 via a fluid connection 126, e.g., pipes. Through the fluid connection 126, a fluid flow c can be pumped from the electrolysis unit 110, there the oxygen side 114 or the oxygen side of each electrolysis cell, to the container 120; the pump 124 may also be sufficient for this purpose. Depending on the type of electrolysis system and, e.g., the number of electrolysis cells, several fluid connections (i.e., separate lines) can also be provided here. For example, one fluid connection can be provided for two or four electrolysis cells.

[0057] In addition, the electrolysis system 100 has a further gas separator 130, in this case a hydrogen separator or hydrogen-water separator. The electrolysis unit 110 is connected to the gas separator 130 via a fluid connection 128, e.g., pipes. Through the fluid connection 128, a fluid stream e from the electrolysis unit 110, there the hydrogen side 116 or the hydrogen side of each electrolysis cell, can be guided to the gas separator 130. Depending on the type of electrolysis system and, for example, the number of electrolysis cells, several fluid connections (i.e., separate lines) can be provided here as well. For example, one fluid connection can be provided for two or four electrolysis cells. Several gas separators are also conceivable.

[0058] Although only one electrolysis unit 110 is shown here, several of them can be provided, e.g., depending on the size and performance of the electrolysis system 100. Several electrolysis units can then, for example, still be connected to a common tank for gas or oxygen separation and / or a common hydrogen separator. However, additional tanks for gas or oxygen separation and hydrogen separators can also be provided.

[0059] During operation of the electrolysis system 100, the fluid stream b, which comprises water, is pumped from the tank 120 to the electrolysis unit 110. There, the water is converted into oxygen and hydrogen. For this purpose, an electrical voltage is applied to the electrolysis unit 110; the hydrogen is electrochemically transported through the PEM 112 to the hydrogen side 116. From there, optionally mixed with steam and a liquid water phase, it can be fed as stream e to the hydrogen separator 130. There, the hydrogen can be separated and discharged as stream f, for example, for further use or stored. Water separated in the hydrogen separator 130 can, for example, be subjected to treatment and then returned to the main water circuit. The oxygen remains on the oxygen side 114 together with the majority of the water.As mentioned, hydrogen may also be present in a certain amount on the oxygen side 114. The resulting fluid stream c thus comprises water and gas, in particular water, oxygen, and hydrogen. As mentioned, the fluid stream c is fed to the container 120.

[0060] Since water is converted into oxygen and hydrogen in the electrolysis unit 110 and the oxygen and hydrogen are removed, the amount of water becomes smaller and therefore - in order to maintain continuous operation - new water (so-called make-up water) can be supplied from outside as stream a.

[0061] This water a can, for example, be further treated beforehand, which, however, is not further relevant to the present invention. Likewise, water separated in the hydrogen separator 130 can be returned to the container 120, possibly also after prior treatment.

[0062] As mentioned, gas, in particular oxygen (and any hydrogen still present), is separated from the water in the container 120. The gas separated or separated in this way can be discharged as an oxygen-containing fluid stream g, for example, for further use and possibly stored. As mentioned, the oxygen-containing fluid stream g can contain not only oxygen but also hydrogen.

[0063] A (further) oxygen-containing fluid stream h can be separated from the oxygen-containing fluid stream g, which is then later fed back to the oxygen section of the electrolysis plant in a recirculation circuit. It is also conceivable that the entire oxygen-containing fluid stream g is fed to the recirculation circuit.

[0064] In the recirculation circuit, a blower 142 is provided, for example, by means of which the oxygen-containing fluid stream g is sucked in and then blown further to the oxygen region of the electrolysis system. For example, the oxygen-containing fluid stream g is designated d after the blower, further passed through a recombination reactor 144, and then introduced, for example, into the processed fluid stream c, e.g., in the fluid connection 126 shown, at a point where fluid streams from individual electrolysis cells are already combined.

[0065] The recombination reactor 144 can, for example, comprise, in the direction of fluid flow, the actual recombiner, an aftercooler, and a filter. Any condenser can be removed from the aftercooler, for example.

[0066] Upstream of the blower 142, i.e. upstream, a feed point 140 is provided at which ambient air k can be introduced into or fed to the oxygen-containing fluid stream if required. For this purpose, a valve 146 is provided, for example, which can be opened if required to allow the ambient air to flow in. This allows the oxygen-containing fluid stream h to be diluted with fresh air or ambient air. Furthermore, a valve feed point 164 can be provided upstream of the feed point 140, with which the oxygen-containing fluid stream h is interrupted. This allows the oxygen-containing fluid stream h to even be replaced by fresh air or ambient air, i.e. the stream d is then an ambient air stream that is fed to the oxygen region of the electrolysis system 100. The ambient air stream is then naturally still an oxygen-containing fluid stream, but without the hydrogen content.

[0067] Furthermore, a portion m of the oxygen-containing fluid stream d can be diverted for other uses downstream of the blower 142 and upstream of the recombination reactor 144. For this purpose, a valve 148 (or another control valve) is provided, for example. This enables the use of the electrolysis byproduct, namely oxygen, without carrying over the risk of explosion into downstream systems, for oxygen compression or oxygen purification.

[0068] In addition, the electrolysis system 100 has, for example, a control unit 160, by means of which, for example, the electrolysis unit 110 and / or the energy supply unit 118 can be controlled and, if necessary, also monitored.

[0069] The control unit 160 can also serve, for example, as a monitoring device for monitoring a hydrogen concentration in the oxygen-containing fluid stream. For this purpose, the electrolysis system 100 can, for example, have a suitable sensor 162 or other detector, by means of which the hydrogen concentration in the oxygen-containing fluid stream h can be determined or measured, e.g., downstream of the feed point 140 and upstream of the feed to the oxygen region of the electrolysis system. The control unit 160 or the monitoring device can then, for example, detect and evaluate measurement signals from the sensor.

[0070] If the hydrogen concentration exceeds a predetermined threshold value, e.g., 2 vol%, various safety measures can be initiated. The electrolysis unit can be switched off, e.g., by the control unit 160 controlling the energy supply unit 118 accordingly. In addition, the ambient air k can be fed into the oxygen-containing fluid stream h, e.g., by controlling a valve 146 to open. The oxygen-containing fluid stream can also be interrupted upstream of the feed point and replaced by ambient air, e.g., by controlling valve 164 to close and valve 146 to open. This then also includes the supply of fresh air. The control unit 160 or the monitoring device can, for example, be configured to control the valves accordingly.

[0071] Depending on the requirements, the oxygen-containing fluid stream can be diluted to a desired level with ambient air, up to and including complete replacement; for example, a proportion of at least 50%, at least 80%, or at least 90% ambient air can be used. However, it can also be provided that the oxygen-containing fluid stream is always replaced by ambient air by default.

Claims

Patent claims 1 . Method for operating an electrolysis plant (100) in which water is converted into oxygen and hydrogen in an electrolysis unit (110), wherein a processed fluid stream (c) is fed from an oxygen side (114) of the electrolysis unit to a gas separator (120), wherein the processed fluid stream (c) comprises water and gas, wherein an oxygen-containing fluid stream (g, h) is discharged from the gas separator (120), wherein the oxygen-containing fluid stream comprises gas, wherein the oxygen-containing fluid stream (h, d) is fed to an oxygen region of the electrolysis plant (100), and wherein, if required, ambient air (k) is fed to the oxygen-containing fluid stream (h) at a feed point (140) before being fed to the oxygen region of the electrolysis plant (100), or the oxygen-containing fluid stream (h) is aerated by Ambient air (k) is replaced.

2. The method according to claim 1, wherein the oxygen-containing fluid stream (d) is passed through a recombination reactor (144) after the feed point (140) and before it is fed to the oxygen region of the electrolysis plant (100).

3. The method according to claim 1 or 2, wherein a portion (m) of the oxygen-containing fluid stream (d) is removed for other use after the feed point (140) before being fed to the oxygen region of the electrolysis plant (100).

4. Method according to one of the preceding claims, wherein a hydrogen concentration in the oxygen-containing fluid stream (h), in particular after the feed point (140) and before the feed to the oxygen region of the electrolysis plant (100), is monitored, and wherein, if the hydrogen concentration exceeds a predetermined threshold value, in particular 2 vol %, at least one safety measure is initiated.

5. The method according to claim 4, wherein the at least one security measure comprises at least one of the following security measures: - Switching off the electrolysis unit (110), - supplying the ambient air (k) into the oxygen-containing fluid flow (h), interrupting the oxygen-containing fluid flow (h) before the supply point (140) and replacing the oxygen-containing fluid flow (h) with the ambient air (k).

6. The method according to any one of the preceding claims, wherein the electrolysis plant is configured for proton exchange membrane electrolysis.

7. The method according to any one of the preceding claims, wherein the oxygen-containing fluid stream (h, d) is fed to the oxygen region of the electrolysis plant (100) by feeding the oxygen-containing fluid stream (h, d) to the processed fluid stream (c) and / or the gas separator (120) 8. Electrolysis plant (100) with an electrolysis unit (110) in which water can be converted into oxygen and hydrogen, and with a gas separator (120), wherein the electrolysis plant (100) is configured to generate a processed fluid stream (c) from an oxygen side (114) of the electrolysis unit to the gas separator (120), wherein the processed fluid stream comprises water and gas, wherein the electrolysis plant (100) is configured to discharge an oxygen-containing fluid stream (g, h) from the gas separator (120) and to supply it to an oxygen region of the electrolysis plant (100), in particular to the processed fluid stream (c) and / or to the gas separator (120), wherein the oxygen-containing fluid stream comprises gas, and wherein the electrolysis plant (100) is configured, if required,to supply ambient air (k) to the oxygen-containing fluid stream (h) at a supply point (140) before it is fed to the oxygen region of the electrolysis plant (100) or to replace the oxygen-containing fluid stream (h) with ambient air (k) before it is fed to the oxygen region of the electrolysis plant (100).

9. Electrolysis plant (100) according to claim 8, further comprising a blower (142), wherein the electrolysis plant (100) is configured to supply the oxygen-containing fluid stream (g, h) to the oxygen region of the electrolysis plant (100) by means of the blower.

10. Electrolysis plant (100) according to claim 8 or 9, further comprising a recombination reactor (144), wherein the electrolysis plant (100) is arranged to guide the oxygen-containing fluid stream (g, h) through the recombination reactor before it is fed to the oxygen region of the electrolysis plant (100).

11. Electrolysis plant (100) according to one of claims 8 to 10, further comprising a monitoring device (160) which is configured to monitor a hydrogen concentration in the oxygen-containing fluid stream (h), in particular after the feed point (140) and before the feed to the oxygen region of the electrolysis plant (100), and to initiate at least one safety measure if the hydrogen concentration exceeds a predetermined threshold value, in particular 2 vol%.

12. Electrolysis plant (100) according to claim 11, wherein the at least one safety measure comprises at least one of the following safety measures: - Switching off the electrolysis unit (110), - supplying the ambient air (k) into the oxygen-containing fluid stream (h), in particular by opening a valve (146) of the electrolysis unit, interrupting the processed fluid stream (c) from the oxygen side (114) of the electrolysis unit to the gas separator (120) and replacing the oxygen-containing fluid stream (h) with the ambient air (k).

13. Electrolysis plant (100) according to one of claims 8 to 12, which is designed for proton exchange membrane electrolysis.

14. Electrolysis plant (100) according to one of claims 8 to 13, which is arranged to carry out a method according to one of claims 1 to 7.

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