Electrolysis system and method for operating an electrolysis system of this type

Abstract

The invention relates to an electrolysis system (1) comprising an electrolyser (3) for producing hydrogen (H2) and oxygen (O2) as product gases, comprising a plurality of electrolysis cells which each have two half-cells separated by an ion-permeable membrane (5) so that an anode chamber (7) and a cathode chamber (9) are formed. On the anode side, an oxygen product line (11B) is connected to the anode chamber (7) and on the cathode side a hydrogen product line (11A) is connected to the cathode chamber (9), wherein the hydrogen product line (11A) leads into a first gas separator (13A) and the oxygen product line (11B) leads into a second gas separator (13B). The electrolysis system (1) has a differential pressure control device (15) which comprises a differential pressure sensor (17A) that is configured such that a differential pressure (Δp) between the anode chamber (7) and the cathode chamber (9) can be determined, the value of which can be processed in the differential pressure control device. The invention further relates to a method for operating such an electrolysis system (1).

Description

Electrolysis system and method for operating an electrolysis system of this type The invention relates to an electrolysis system comprising an electrolyzer for production of hydrogen and oxygen as product gases, having a multitude of electrolysis cells each having two half-cells separated by an ion-permeable membrane, so as to form an anode space and a cathode space. The invention further relates to a method of operating an electrolysis system. Hydrogen is nowadays produced, for example, by means of proton exchange membrane (PEM) electrolysis or alkaline electrolysis. The electrolyzers produce hydrogen and oxygen from the water supplied with the aid of electrical energy. An electrolyzer generally has here a multitude of electrolysis cells arranged adjacent to one another. By means of water electrolysis, water is split into hydrogen and oxygen in the electrolysis cells. There are various known electrolysis technologies and electrolyzers. In the case of a PEM electrolyzer, distilled water is typically supplied as reactant on the anode side and split into hydrogen and oxygen at a proton-permeable membrane (“proton exchange membrane”; PEM). It is also possible to conduct what is called an anion exchange membrane water electrolysis (AEMWE), or AEM electrolysis for short, which is analogous to PEM electrolysis to some degree, but in which the reactant used is an alkaline in aqueous solution, frequently potassium hydroxide KOH or potassium hydrogencarbonate KHCO3 in aqueous solution with a suitably chosen concentration of about 1 mol / l. At the same time, the water or the alkali in aqueous solution is oxidized at the anode to oxygen. The protons pass through the proton-permeable membrane. Hydrogen is produced on the cathode side. The water is generally conveyed from a bottom side into the anode space and / or cathode space. In the case of alkaline electrolysis too, a membrane is provided, which is formed as a semipermeable membrane or diaphragm and selectively permits passage of particular ions. The electrolyte used is potassium hydroxide solution (KOH) with a concentration of typically 20-40%. The gas-tight membrane, called the diaphragm, does permit transport of OH- ions, but at the same time prevents mixing of the product gases formed. With regard to the system, the electrolysis process takes place in what is called the electrolysis stack, composed of multiple electrolysis cells. In the electrolysis stack, which is under DC voltage, water is introduced as reactant, passes through the electrolysis cells and gives rise to two exiting fluid streams consisting of water and gas bubbles (oxygen O2 and hydrogen H2 respectively). A gas separation is therefore necessary thereafter, i.e. a phase separation of water and the respective gaseous product gas in the phase mixture. It is customary here that several electrolysis cells and also several electrolysis units are connected to one another by piping, and the respective exiting gas-water mixture is fed to a central gas separator. In practice, there are small amounts of hydrogen in the oxygen gas stream and small amounts of oxygen in the hydrogen gas stream. The quantity of the respective extraneous gas depends on the electrolysis cell design and also varies under influences including current density, catalyst composition and aging, and is dependent, moreover, on the membrane material of the electrolysis cell. It is inherent to the system that the gas stream of one product gas includes very small amounts of the respective other product gas. Later on in the process, generally in downstream gas cleaning steps, even small oxygen traces are removed from the hydrogen by cleaning steps that are very complex and costly in some cases, especially when a particularly high product gas quality is required, as is the case, for instance, when the hydrogen is being utilized for fuel cells for example. Under some circumstances, it may be necessary here to reduce the 2023405114   17 Jun 2026 extraneous gas concentration immediately in or directly downstream of the electrolysis cell or electrolysis stack, for example in gas separators downstream of the electrolyzer. The problem is aggravated in part-load operation or generally in the case of changes in load and in the case of aged membranes, and leads to restrictions in the mode of operation or even to prevention of safe continued operation and to premature safety shutdown. Particularly in the case of positive load gradients, for instance in the case of startup of the electrolysis system or in the event of a change from part-load operation to fullload operation, this gives rise to critical states for the membrane because of pressure differentials across the cell division from the anode space to the cathode space, and associated pressure gradients. It is an object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages. According to an aspect of the present invention, there is provided an electrolysis system comprising an electrolyzer for production of hydrogen and oxygen as product gases, having a multitude of electrolysis cells each having two half-cells separated by an ion-permeable membrane so as to form an anode space and a cathode space, wherein an oxygen product conduit is connected to the anode space on an anode side and a hydrogen product conduit to the cathode space on a cathode side, wherein the hydrogen product conduit opens into a first gas separator and the oxygen product conduit into a second gas separator, and having a pressure differential control device comprising a pressure differential transducer set up such that a pressure differential between the anode space and the cathode space can be ascertained, the value of which can be processed in the pressure differential control device, wherein the pressure 2023405114   17 Jun 2026 differential transducer is connected to the first gas separator and to the second gas separator at a respective sampling point, where the sampling points are in the upper region of the gas separators such that the pressure differential can be ascertained in the gas phase of the gas separators, and wherein the pressure differential transducer is connected to a respective sampling point in an anodic half-cell and a cathodic half-cell, such that the pressure differential across the halfcells can be ascertained. According to another aspect of the present invention, there is provided a method of operating an electrolysis system as claimed in any of the preceding claims, wherein hydrogen and oxygen are produced as product gases, wherein the pressure differential transducer measures a pressure differential between the anode space and the cathode space, wherein a differential pressure is determined in the gas phase of the gas separators and cellspecific over the half-cells of an anodic and a cathodic halfcell, and wherein the measurement signal is imported into the pressure differential control device and compared with a reference value, and wherein a continued operation mode is maintained when the pressure differential is smaller than the reference value. It is therefore an object of the invention to specify an electrolysis system that enables improved operation with regard to safety and plant efficiency. The object is achieved in accordance with the invention by an electrolysis system comprising an electrolyzer for production of hydrogen and oxygen as product gases, having a multitude of electrolysis cells each having two half-cells separated by an ion-permeable membrane so as to form an anode space and a cathode space, wherein an oxygen product conduit is connected to the anode space on the anode side and a hydrogen product conduit to 2023405114   17 Jun 2026 the cathode space on the cathode side, wherein the hydrogen product conduit opens into a first gas separator and the oxygen product conduit into a second gas separator, and having a pressure differential control device comprising a pressure differential transducer set up such that a pressure differential between the anode space and the cathode space can be ascertained, the value of which can be processed in the pressure differential control device. The object is also achieved in accordance with the invention by a method of operating the electrolysis system in question, wherein hydrogen and oxygen are produced as product gases, wherein the pressure differential transducer measures a pressure differential between the anode space and the cathode space, wherein the measurement signal is imported into the pressure differential control device and compared with a reference value, and wherein a continued operation mode is maintained when the pressure differential is smaller than the reference value. The advantages and preferred configurations that are cited below in relation to the method can be applied correspondingly to the electrolysis system. The invention proceeds directly from the finding that the pressure differential resistance of the ion-permeable membrane of an electrolysis system is an essential parameter for the design and operating regime of an electrolysis system. Therefore, a very substantially undistorted and reliable measurement for the current pressure differential in situ across the ion-conducting membrane is indispensable for monitoring and operational control and the mode of operation of the electrolysis system. This is of great industrial and economic interest, particularly with regard to aging-related degradation of the ion-conducting membrane, in respect of the question of whether the membrane is sufficiently stable to a pressure differential and hence safe continued operation is possible. The measurement procedures known to date and the values ascertained therefrom are indirect and hence inexact in respect of a determination of pressure differential, which leads to high measurement inaccuracies particularly in the case of higher pressure ranges. In order to avoid major or irreversible membrane damage (membrane loss), it has been necessary to date to allow generous safety reserves owing to inaccuracies, which envisage early safety shutdowns and inspections of the electrolysis plant, even though these measures would not have been physically necessary. This also relates to monitoring of the passage of hydrogen from the cathode space into the anode space through the membrane owing to the current pressure differential, i.e. the extraneous gas concentration of hydrogen on the oxygen side, which has to be kept below a maximum value for safety reasons (explosion risk). From an economic point of view, the existing concepts are inadequate and very disadvantageous. The term “ion-conducting membrane” should be interpreted here in a technically comprehensive manner, especially also in the sense of an ion-permeable membrane or ion-transporting membrane, and the ion-conducting membrane is therefore applicable to various types of electrolysis. It should be taken into account here that, on the technical and physical side, water electrolyses are constructed in cell form with a multitude of electrolysis cells. The cells in turn are structured into two half-cells with a membrane as separation between the two half-cells. The product gases are respectively released in one of the two half-cells. The ratio of the gas volume flow rates of H2 / O2, because of the stoichiometry of the electrolysis reaction, is 2:1. This asymmetry, especially in the case of positive load gradients, causes a pressure differential across the cell division, i.e. across the ion-conducting membrane, from the hydrogen half-cell side that forms a cathode space across the membrane to the oxygen half-cell side that forms an anode space. The reason for this is the additional different amount of liquid that the product gases have to displace. Significant gas formation can therefore result in formation of shock waves in the hydraulic system, which can result in localized pressure peaks that exceed the target pressure by several times and have not been reliably measurable to date, known as Joukowsky shock in hydraulic systems. With progressive aging, but also as a result of faults in the ion-conducting membrane in individual cells, these can lose their operationally necessary property of pressure differential stability. If this case occurs, the electrolysis has to be refurbished in a costly and time-consuming manner, even though it would still be utilizable for steady-state operation. The invention has recognized that currently known simple and indirect pressure differential monitoring means, for future requirements, will not be able to reliably determine the rise in hydrogen concentration in the oxygen in particular and to keep it below a still permissible limit. This will be especially true of future electrolysis systems with electrolyzers having high required system pressures of > 30 bar. The sensitivity of the sensors in the case of the customary construction with two independent absolute pressure sensors will then no longer be sufficient to ascertain and to exactly resolve pressure differences in the region of typically ± 50 mbar via difference formation: for example, an absolute pressure sensor with a 1 bar measurement range provides scaling of 10 mV / mbar in the 0-10 V voltage range. By contrast, for example, an absolute pressure sensor with a measurement range of 50 bar provides scaling of 0.2 mV / mbar. On the basis of this simple consideration alone, given a typical relative measurement accuracy of 0.1% in each case of the measurement value, this gives a measurement accuracy of ± 1 mbar and ± 50 mbar respectively, which is inadequate. By contrast, the invention for the first time directly enables a very exact in situ determination of pressure differential, specifically also in the case of high system pressures. A direct measurement of pressure differential via selected and representative measurement sites is implemented as an in situ state indicator in the electrolysis system. For this purpose, a pressure differential control device is provided, comprising a pressure differential transducer set up such that a pressure differential between the anode space and the cathode space can be ascertained, the value of which can be processed in the pressure differential control device. The pressure differential transducer is thus connected via two selected sampling sites - that are respectively representative of the anode space and the cathode space - and the pressure differential measurement signal therefrom is processible in the pressure differential control device. Direct measurement of the pressure differential enables very accurate and virtually delay-free state diagnosis and hence reliable operation of the electrolysis system. In order to ascertain and assess the pressure differential, the pressure differential control device has a pressure differential transducer that measures the pressure differential directly between the half-cells. This measurement may be made at different sampling sites as required. Further operation of the electrolysis system is thus particularly advantageously possible, since a current pressure differential can be monitored and controlled reliably with respect to a permissible maximum pressure differential. It is also possible for the maximum permissible pressure differential in the pressure differential control device to be defined and set or adjusted. The invention is applicable in an advantageous and flexible manner to various types of electrolysis system, for instance an alkaline water electrolysis or else PEM electrolysis or an anion exchange membrane water electrolysis (AEMWE), with implementation of a pressure differential control device with pressure differential transducers in the electrolysis system. What is thus minimized and monitored in particular is the risk of unwanted passage of gas from one side of the electrolysis half-cell to the other as a result of pressure differentials. Specifically for PEM electrolysis, the invention thus enables safe continued operation even if the separating membrane is subject to aging-related damage through cracks, holes or the like. Measurement directly across the half-cell spaces - anode space and cathode space - or in the immediate proximity thereof best represents the pressure differential situation during dynamic operations, for example power consumption in the course of startup of the electrolysis system or changing of operation between part-load operation and full-load operation. In a particularly preferred configuration of the electrolysis system, the pressure differential control device is designed for pressure differential limitation, with a set maximum value for the pressure differential. This achieves a particularly simple and simultaneously reliably functioning limitation of pressure differential between anode space and cathode space, and hence limits the stress caused by the pressure differential across the membrane in accordance with a set maximum pressure differential value, with simultaneous monitoring of the passage of gas. In general, a minimum pressure differential in operation is preferable. Preferably, in the electrolysis system, the pressure differential transducer is connected to the first gas separator and to the second gas separator at a respective sampling point, where the sampling points are in the upper region of the gas separators such that the pressure differential can be ascertained in the gas phase of the gas separators. In this way, a pressure differential is determinable between the gas phases of the gas separators. In this way, in operation of the electrolysis system, the pressure differential between the gas spaces of the two gas separators is measured as a reliable and representative measure of the pressure differential. The pressure differential is recordable directly and in largely undistorted form via the sampling points of the pressure differential transducer. The gas phase is in the upper vessel region of the gas separators above the liquid phase present in the lower vessel region. By virtue of the phase separation of liquid and gaseous phase in the respective product gas, the hydrogen or oxygen in the phase mixture is spatially separable. The invention has recognized that this manner of positioning and implementation of the pressure differential transducer at the specifically chosen sampling sites in the gas separator in the gas phase provides particularly reliable and representative pressure differential values that permit conclusions in situ as to the membrane state and the passage of gas through the membrane in the half-cells. In a particularly preferred configuration of the electrolysis system, the pressure differential transducer is connected to a respective sampling point in an anodic half-cell and a cathodic half-cell, such that the pressure differential across the halfcells can be ascertained. With this configuration, the measurement of pressure differential can be conducted directly via representative halfcell spaces, so as to enable a pressure differential between the anode space and the cathode space in a particularly precise and simultaneously flexible manner. At the same time, the selected half-cells need not necessarily belong to the same electrolysis cell. It is sufficient when the two sampling points measure the pressure differential between the anode space and the cathode space across a respective representative half-cell. Direct local information as to the pressure differential has been provided. This mode of measurement directly across the half-cells or in the immediate proximity thereof particularly reliably represents the local pressure differential situation during dynamic operations, for instance in the startup of the electrolysis system. It is also possible here to provide redundancies in that multiple pressure differential transducers are implemented in the electrolysis system, which permit representative in situ pressure differential measurements across the half-cells, across electrolysis stacks or segments. Redundancy increases accuracy and, moreover, dynamic changes in the electrolysis system are localizable in space and time. Local state information relating to the ion-conducting membrane with regard to the aging-related current pressure resistance thereof and passage of gas is thus also detectable within the electrolysis system via the number and arrangement of pressure differential transducers. Preferably, in the electrolysis system, the anodic half-cell and the cathodic half-cell form an electrolysis cell, such that the pressure differential can be ascertained in a cell-specific manner across an electrolysis cell. Useful half-cells here are selected half-cells of the cell assembly of an electrolysis system that are separated by a membrane and have a sampling point via which the pressure differential sensor senses the pressure differential. A cellspecific measurement of pressure differential is thus implemented, and particularly exact localization of the cell state is enabled in terms of space and time. Compared to simple measurement of the pressure differential in the gas phase between the gas separators, especially in the case of a positive load gradient, the pressure differential signal may be highly attenuated and time-delayed, since a pressure buildup is first necessary in the gas separators, which are generally of quite large dimensions. The introduction of the pressure differential transducers into the half-cells provides additional advantages here in these specific modes of operation. The measurement of pressure differential across the gas separators and locally across selected half-cells is accordingly advantageously combinable and complementary. In a particularly preferred configuration of the electrolysis system, the sampling points are at the reactant inlet of the anodic half-cell and of the cathodic half-cell. In this way, a respective sampling point is implemented on the cell entry side of the electrolysis system, such that the pressure differential is determinable directly and with high accuracy between the anode space and the cathode space, since dynamic effects are also detectable locally. In the case of PEM electrolysis, for example, a respective sampling point may be disposed at the reactant inlet of the pressure differential transducer at the cell inlet or close to the cell inlet for the water reactant on the oxygen side and the hydrogen side, which advantageously promotes particularly precise measurement of pressure differential and monitoring of pressure differential between the anode space and cathode space. In a preferred configuration of the electrolysis system, a first reactant conduit is connected to the cathode space on the cathode side and a second reactant conduit is connected to the anode space on the anode side. Possible reactants here for performance of a PEM electrolysis include water, especially demineralized water, which can be supplied on the anode side and cathode side via the two reactant conduits. In this way, two reactant circuits are formed as water circuits in the PEM electrolysis. It is also possible that, in an alternative configuration of a PEM electrolysis, water reactant can be supplied preferably only on the anode side via a reactant conduit. In this case, the cathode remains dry and is not contacted with reactant water via a reactant conduit, and so only one reactant circuit is employed. This is also referred to as dry cathode operation. Alternatively, the electrolysis system may be designed for alkaline electrolysis, in which case an electrolyte that can be supplied as reactant via a reactant conduit of the electrolysis cell is, for example, potassium hydroxide with a concentration of 20%-40%. Preferably, in the electrolysis system, the ion-permeable membrane is configured as a proton-permeable membrane, such that a PEM electrolysis is performable. In the case of a PEM electrolysis, the protein-permeable membrane is preferably designed on the basis of a gas- and liquid-tight fluoropolymer. It is thus possible for the membrane to be selectively ion-transporting for the protons. In the acidic or proton exchange membrane electrolyzer (PEM electrolyzer), distilled or demineralized water is split into hydrogen and oxygen by electrical current. The electrolyzer consists of a proton-permeable polymer membrane (“proton exchange membrane” or “polymer electrolyte membrane”, “PEM” for short). This is coated on the cathode side with a porous electrode composed of carbon-supported platinum and on the anode side with precious metals in metallic form or in oxide form (usually iridium and ruthenium). An external voltage is applied to these electrodes. Water is typically supplied as reactant on the anode side of the electrolyzer. It is also possible to flood both half-cells with water, or else only the cathode side, depending on the end use. The catalytic effect of the precious metal electrode leads to breakdown of the water on the anode side: this forms oxygen, free electrons and positively charged H+ ions. The hydrogen ions diffuse through the proton-conducting membrane onto the cathode side, where they combine with the electrons to form hydrogen as product gas. In the case of an alternatively particularly preferred anion exchange membrane (AEM), the membrane is designed to be selectively ion-transporting for hydroxide anions for the transport of hydroxide ions OH- from the anode space to the cathode space across the ion-transporting membrane. The electrolysis system with an electrolyzer is thus set up on the basis of an anion exchange membrane water electrolysis (AEMWE). In a further-preferred configuration of the electrolysis system, the ion-permeable membrane is configured as a diaphragm that selectively permits passage of hydroxide ions, such that an alkaline electrolysis is performable. In an alkaline electrolyzer, at a DC voltage of at least 1.5 volts, hydrogen is formed at the cathode and oxygen at the anode. The electrolyte used is potassium hydroxide solution (KOH) having a concentration of typically 20%-40%. The ion-permeable membrane used is a gas-tight membrane, called the diaphragm. Although this permits the transport of OH- ions, it simultaneously prevents mixing of the product gases formed. Electrodes used are called “DSA electrodes” (dimensionally stable anodes), usually titanium electrodes with a ruthenium oxide coating. These are expanded metals coated with a precious metal catalyst oxide - for example ruthenium oxide or iridium oxide. But there are also systems with Raney nickel catalysts in a gas diffusion electrode. Alkaline electrolyzers are used globally on a large scale. The invention is advantageously implementable and utilizable both in a PEM electrolysis system, in an AEM water electrolysis system, and in an alkaline electrolysis system, such that the pressure differential control device is employable in a technology-independent manner in the electrolysis system. The division of the half-cells is specifically different depending on the technology. Alkaline electrolyses use what is called a diaphragm, a semipermeable membrane which is permeable to the alkaline liquid and simultaneously less permeable up to a particular pressure differential for gas. PEM electrolysis and AEM electrolysis alike use a gas- and liquid-tight fluoropolymer, as described above. PEM technology is thus generally much less sensitive to relatively high pressure differentials or changes in pressure differential. With the invention, it is now possible to very accurately and directly determine and monitor even small changes in pressure differentials or fluctuations of < 50 mbar. This permits reliable diagnosis and conclusions in particular with regard to the membrane aging state and unwanted gas transfer through the ion-conducting membrane. It is thus possible that, in the method of operating such an electrolysis system, hydrogen and oxygen are produced as product gases, wherein the pressure differential transducer measures a pressure differential between the anode space and the cathode space, wherein the measurement signal is imported into the pressure differential control device and compared with a reference value, and wherein a continued operation mode is maintained when the pressure differential is smaller than the reference value. A defined and adjustable reference value is stored as the maximum value for the permissible pressure differential in the pressure differential control device. Because of the elevated accuracy of the pressure differential measurement and pressure differential limitation, continued operation of the electrolysis system is envisaged and advantageously possible. The continued operation may include different modes of operation, i.e., for instance, normal operation under full load or part-load or a change in load or else a startup operation. In continued operation mode too, the pressure differential is monitored continuously. Compared to existing measurement concepts with inexact absolute pressure sensors, early shutdown operation -owing to safety reserves that have to be maintained - is avoided and economic further utilization and hydrogen production is achieved. Preferably, a shutdown operation mode is initiated by the pressure differential control device when the pressure differential is greater than the reference value. By virtue of the measurement of pressure differential and the associated higher measurement accuracy, especially in the case of high system pressures, the control parameters for the initiation of the shutdown operation mode in the pressure differential control device are more precisely determinable, and a safety reserve can be made smaller. Early shutdown operation is avoided since further operation advantageously has priority as far as possible. In the method, a pressure electrolysis is preferably performed with a system pressure of at least 5 bar. Particular preference is given to high system pressures of greater than 30 bar as nominal pressure for the performance of the method with a pressure electrolyzer. Preferred system pressures are at least 10 bar up to 35 bar. The method of the invention is therefore advantageously employable in a particular manner in pressure electrolyses since the elevated measurement accuracy by virtue of the direct measurement of pressure differential via the at least two implemented pressure differential transducers achieves reliable ascertainment of pressure differential and limitation of pressure differential even at high pressures. In general, minimum pressure differentials across the ion-transporting membrane between the anode space and the cathode space are preferable; in any case, a maximum pressure differential value should regularly not be exceeded. Working examples of the invention are elucidated in detail with reference to a drawing. The figure shows, in schematic and highly simplified form: FIG an electrolysis system with, according to the invention, a pressure differential control device. The sole figure shows an electrolysis system 1 in a greatly simplified detail of plant parts and components. The electrolysis system 1 has an electrolyzer 3, designed either as a PEM electrolyzer or as an alkali electrolyzer. The electrolyzer 3 comprises a cathode space 9 and an anode space 7, divided by an ion-permeable membrane 5. The anode space 9 and the cathode space 7 are formed in each case by a multitude of respective anodic or cathodic half-cells stacked in an axial direction, which are not shown in detail in the figure, separated by the ion-conducting membrane 5. The figure therefore shows a vertically aligned electrolyzer 3 designed for electrochemical splitting of water H2O or an electrolyte as reactant into hydrogen H2 and oxygen O2 as product gases by means of electrical current. In the case of an acidic electrolysis, demineralized water H2O is used as reactant. In the case of an alkaline electrolysis, an alkali is used, for example potassium hydroxide KOH in an aqueous solution with a concentration of typically 20% to 40%. Several such electrolysis cells may be connected in series in horizontally stacked “electrolysis stacks”. In the working example shown in the figure, the electrolysis system 1 of the electrolyzer is designed as a PEM electrolyzer. Each electrolysis cell here has a proton-permeable membrane 5 based on a fluoropolymer, where a respective electrode - an anode and a cathode - adjoins the two sides, across which an external voltage is applied in operation. On the cathode side, a first reactant conduit 21A is provided for supply of water H2O to the cathode space 9. On the anode side is connected a second reactant conduit 21B for supply of water H2O to the anode space 7. As a result, two circuits are implemented in the electrolyzer 3 configured as a PEM electrolyzer. Water H2O thus circulates not only through the anode space 7, but also through the cathode space 5. But it is also possible that the electrolyzer 3 is implemented with just one anode-side circuit. In operation of the electrolysis system 1, the oxygen O2 produced from the anode space 7 in the electrolysis cell is removed via an oxygen product conduit 11B. On the cathode side, a hydrogen product conduit 11A is provided for removal of the hydrogen produced from a cathode space 5. For the respective phase separation of the phase mixture of product gas and water, a first gas separator 13A is connected downstream of the hydrogen product conduit 11A. Correspondingly, a second gas separator 13B is connected downstream of the oxygen product conduit 11B. A phase separation is thus achieved, such that a gas space containing the gas phase exists in the upper region of the gas separators 11A, 11B, whereas the liquid phase is present at the base of the gas separators 11A, 11B, i.e. a water level. The electrolysis system 1 has a pressure differential control device 15 comprising pressure differential transducers 17A, 17B. Thus, a pressure differential transducer 17A connected across the gas spaces takes readings from the first gas separator 13A and the second gas separator 13B at respective sampling points 19A, 19B, such that a pressure differential Ap with regard to the gas phases of the gas separators 13A, 13B is determinable directly. In addition, a respective pressure measurement device for the determination of an absolute pressure value is connected to the gas separators 13A, 13B, such that not only the pressure differential Ap but also an absolute pressure pA in the gas phase of the first gas separator 13A and an absolute pressure pB in the gas phase of the second gas separator 13A is determinable. By means of the pressure differential transducer 17A, the pressure differential Ap between the cathode space 9 and the anode space 7 is determinable. The measurement signals for the pressure differential and the pressure values pA and pB in the gas separators 13A, 13B are processed in the pressure differential control device 15. An input parameter which is recorded or adjustable for the pressure differential control device is a maximum pressure differential Apmax. This value for the maximum pressure differential Apmax is adjustable if required to the respective selected or typical operating conditions of the electrolyzer 3 and the aging state of the ion-permeable membrane 5. The pressure differential control device is set up for the output of control signals S1, S2, which can be transmitted to a higher-level control system (not shown in detail) of the electrolysis system 1. It is thus possible to set and adjust the physical operating parameters of the electrolysis system 1, for instance the electrolysis current, the electrolysis current density, the reactant volume flow rates, the system pressure or the pressure differential Ap < Apmax. The pressure differential control device 15 may also be designed as part of and integrated into the higher-level control system. The control system is therefore designed to control the operation of the electrolysis stack. With the aid of the control system, it is possible, for example, to set a definable absolute pressure pa as target value in the anode space 7, and to set a definable absolute pressure pk as target value in the cathode space 9, although operation is also possible, for example, where the anode-side pressure pa is set at a higher level than the pressure pk in the cathode space 9. In this way, the possible adverse consequences of membrane damage in operation of an electrolyzer 3 are minimized, since, in the case of perforation of the ion-permeable membrane 5, less hydrogen migrates through the membrane from the cathode space 9 into the anode space 7. This achieves failsafe capacity. For further improvement of the accuracy of the pressure differential measurement and pressure differential monitoring, alternatively or additionally to the pressure differential transducer 17A, a further pressure differential transducer 17B may be connected to a respective sampling site 19A, 19B of an anodic half-cell and a cathodic half-cell, such that the pressure differential Ap can be ascertained locally via the selected and representative half-cells. It is possible here that the selected half-cells form one and the same electrolysis cell. This local introduction of the pressure differential transducer 17B at the half-cell level means that the measurement signal for the pressure differential Ap is not distorted by fluid-dynamic processes, as occurs particularly in the case of changes in load or on startup. In particular, dynamic effects of the water column and the phase mixture of product gas and water across the anode space 7 and the cathode space 9 are further minimized by the local measurement, and good measurement quality is assured even in the case of high system pressures, for instance in the case of pressure electrolysis. In operation of the electrolysis system 1, reactant water H2O is fed to the electrolyzer 3 via the reactant conduits 21A, 21B, and hydrogen H2 and oxygen O2 are produced as product gases. The pressure differential transducer 17A, 17B measures a pressure differential Ap between the anode space 7 and the cathode space 9. The measurement signal is imported into the pressure differential control device 15 and compared with the reference value Apmax. When the pressure differential Ap is less than the reference value Apmax, a continued operation mode is maintained. In the case of a pressure differential Ap greater than the reference value Apmax, the pressure differential control device 15 initiates a shutdown operation mode. This can also be effected in a higher-level control unit in that corresponding control signals S1, S2 are transmitted from the pressure differential control device 15 to a higher-level control unit. Because of the more precise measurement of pressure differential, it is also possible to reliably conduct pressure electrolyses with a high system pressure of at least 30 bar. In general, the continued operation mode and the failsafe properties enable reliable continued operation of the electrolysis system and avoid premature shutdown, which brings economic benefits and increases running times. Maintenance and inspection operations can, moreover, be planned in a more anticipatory manner by continuous and exact “in situ” pressure differential diagnostics, and the service measures can be timetabled and adapted according to the aging state.

Claims

1. An electrolysis system comprising an electrolyzer for production of hydrogen and oxygen as product gases, having a multitude of electrolysis cells each having two half-cells separated by an ion-permeable membrane so as to form an anode space and a cathode space, wherein an oxygen product conduit is connected to the anode space on an anode side and a hydrogen product conduit to the cathode space on a cathode side, wherein the hydrogen product conduit opens into a first gas separator and the oxygen product conduit into a second gas separator, and having a pressure differential control device comprising a pressure differential transducer set up such that a pressure differential between the anode space and the cathode space can be ascertained, the value of which can be processed in the pressure differential control device, wherein the pressure differential transducer is connected to the first gas separator and to the second gas separator at a respective sampling point, where the sampling points are in the upper region of the gas separators such that the pressure differential can be ascertained in the gas phase of the gas separators, and wherein the pressure differential transducer is connected to a respective sampling point in an anodic half-cell and a cathodic half-cell, such that the pressure differential across the halfcells can be ascertained.

2. The electrolysis system as claimed in claim 1, in which the pressure differential control device is designed for a pressure differential limitation, with a set maximum value for the pressure differential.

3. The electrolysis system as claimed in claim 1, in which the anodic half-cell and the cathodic half-cell form an electrolysis cell, such that the pressure differential can be ascertained in a cell-specific manner across an electrolysis cell.2023405114   17 Jun 20264. The electrolysis system as claimed in claim 1, in which the sampling points are at a reactant stream inlet of the anodic half-cell and of the cathodic half-cell.

5. The electrolysis system as claimed in any one of the preceding claims, in which a reactant conduit is connected to the anode space on the anode side.

6. The electrolysis system as claimed in any one of claims 1 to 5, in which a first reactant conduit is connected to the cathode space on the cathode side and a second reactant conduit is connected to the anode space on the anode side.

7. The electrolysis system as claimed in any one of the preceding claims, in which the ion-permeable membrane is configured as a proton-permeable membrane, such that a PEM electrolysis is performable.

8. The electrolysis system as claimed in any one of claims 1 to 6, in which the ion-permeable membrane is configured as an anion-transporting membrane, such that an anion exchange membrane water electrolysis is performable.

9. The electrolysis system as claimed in any of claims 1 to 6, in which the ion-permeable membrane is configured as a diaphragm that selectively permits passage of hydroxide ions, such that an alkaline electrolysis is performable.

10. A method of operating an electrolysis system as claimed in any of the preceding claims, wherein hydrogen and oxygen are produced as product gases, wherein the pressure differential transducer measures a pressure differential between the anode space and the cathode space, wherein a differential pressure is determined in the gas phase of the gas separators and cellspecific over the half-cells of an anodic and a cathodic halfcell, and wherein the measurement signal is imported into the pressure differential control device and compared with a2023405114   17 Jun 2026reference value, and wherein a continued operation mode is maintained when the pressure differential is smaller than the reference value.

11. The method as claimed in claim 10, wherein a shutdown operation mode is initiated by the pressure differential control device when the pressure differential is greater than the reference value.

12. The method as claimed in claim 10 or 11, wherein a pressure electrolysis is performed with a system pressure of at least 5 bar.

13. The method as claimed in claim 12, wherein the pressure electrolysis is performed with the system pressure of at least 10 bar to 35 bar.Siemens Energy Global GmbH & Co. KG Patent Attorneys for the Applicant / Nominated Person SPRUSON & FERGUSON

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