Method for operating an electrolysis plant, and electrolysis plant

Abstract

The invention relates to a method for operating an electrolysis plant (10) comprising an electrolyzer (1) having a plurality of electrolysis cells (5) electrically connected in series, wherein process water (H2O) is supplied to the electrolysis cells (5) and a current is applied to the electrolysis cells (5), wherein hydrogen (H2) and oxygen (O2) are generated as product gases, and wherein the process water (H2O) is routed in a process water circuit (31). The temperature (TP) of the process water (H2O) is controlled by specifying a temperature setpoint value (TSET) for the inlet temperature (TIN) of the process water (H2O), wherein the operating hours (OH) of the electrolyzer (1) are recorded and an efficiency loss (Δη) caused by the operation is determined. The temperature setpoint value (TSET) for the inlet temperature (TIN) is set as a function of the efficiency loss (Δη). The invention also relates to an electrolysis plant (10) designed to carry out the method.

Description

[0001] 2024PF00353

[0002] 1

[0003] Description

[0004] Methods for operating an electrolysis plant and electrolysis plant

[0005] The invention relates to a method for operating an electrolysis plant and to an electrolysis plant comprising a plurality of electrically connected electrolysis cells in series, which is set up for carrying out the method.

[0006] The importance of hydrogen in the pursuit of climate neutrality will increase significantly, and a substantial rise in demand is expected. Currently, hydrogen is predominantly produced from fossil fuels. Therefore, low-carbon production technologies are becoming increasingly important. These include not only blue hydrogen but, above all, so-called green hydrogen, produced using renewable energy sources. In the long term, green hydrogen is intended to replace hydrogen produced from fossil fuels. However, this depends on its competitiveness in production. Production costs depend significantly on electricity costs and prices, the investment in electrolyzers, the electrolyzer efficiency, and the electrolyzer's operating hours.

[0007] Hydrogen is now produced particularly efficiently using methods such as proton exchange membrane (PEM) electrolysis or alkaline electrolysis. These electrolyzers use electrical energy to produce hydrogen and oxygen from the supplied water. A PEM electrolyzer is characterized by high current density, a compact design, and good dynamic performance. The ability to operate a PEM electrolyzer under pressure is a further advantage.

[0008] An electrolyzer typically has a large number of electrolysis cells arranged adjacent to each other. 2024PF00353

[0009] 2

[0010] Water electrolysis is a process in which water is split into hydrogen and oxygen in electrolysis cells. Various electrolysis technologies and electrolyzers are known. In a PEM electrolyzer, distilled water is typically supplied as the reactant at the anode and split into hydrogen and oxygen at a proton-exchange membrane (PEM). It is also possible to perform an anion-exchange membrane water electrolysis (AEMWE), or AEM electrolysis for short. In this process, similar to PEM electrolysis, an alkali in aqueous solution is usually used as the reactant, often potassium hydroxide (KOH) or potassium bicarbonate (KHCO3) in an aqueous solution with a suitably chosen concentration of approximately 1 mol / L. The water or alkali in aqueous solution is oxidized to oxygen at the anode. The protons pass through the proton-exchange membrane.Hydrogen is produced on the cathode side. The water is typically pumped from one side into the anode compartment and / or cathode compartment. Alkaline electrolysis also utilizes a membrane, designed as a semipermeable membrane or diaphragm, which selectively allows the passage of certain ions. The electrolyte is potassium hydroxide solution (KOH) with a typical concentration of 20-40%. The gas-tight membrane, the diaphragm, permits the transport of OH- ions but simultaneously prevents the mixing of the resulting product gases.

[0011] In terms of plant technology, the electrolysis process takes place in the so-called electrolysis stack or electrolysis module, composed of several electrolysis cells connected in series. Water is introduced as the reactant into the electrolysis stack, which is under DC voltage. After passing through the electrolysis cells, two fluid streams emerge, consisting of water and gas bubbles (oxygen O2 and hydrogen H2, respectively). Subsequently, gas separation is necessary, i.e., a phase separation of water and the respective gaseous product gas in the phase mixture. [Here- 2024PF00353]

[0012] 3

[0013] It is common practice to connect several electrolysis cells and further electrolysis units via piping, with the gas-water mixture exiting each unit being fed to a central gas separator. It is possible for several electrolysis stacks or modules to be electrically connected in series to form an electrolysis line or string.

[0014] Electrolysis plants scale by multiplying electrolysis cells, which are bundled into electrolysis stacks or modules, and these in turn scale further by multiplying into electrolysis strings. To monitor operating conditions during normal operation of the electrolysis cells and to detect faults, a multitude of sensors are implemented. These sensors are attached to the cells, stacks, modules, or strings and measure physical parameters such as pressure, temperature, conductivity, process water flow rate, cell voltage, and current. This complexity of the sensor system results in significant manufacturing and operating costs for an electrolysis plant, as well as potential maintenance expenses. On the other hand, certain sensors are essential for operation and safety, which must be taken into account.Therefore, especially in large electrolysis plants, there is an urgent need to reduce the cost of sensors as much as possible in order to reduce costs, without losing necessary information on operating data of the electrolysis plant, critical operating conditions and the resulting necessary control interventions for both economical and safe plant operation.

[0015] The object of the invention is therefore to provide a method for operating an electrolysis plant that reduces the required sensor technology while maintaining sufficient operational reliability and efficiency. A further object is to provide an electrolysis plant configured to carry out the method. 2024PF00353

[0016] 4

[0017] The problem directed towards a method is solved according to the invention by a method for operating an electrolysis plant, which has an electrolyzer with a plurality of electrolysis cells connected electrically in series, wherein process water is supplied to the electrolysis cells and the electrolysis cells are supplied with a current, wherein hydrogen and oxygen are produced as product gases, and wherein the process water is circulated in a process water circuit, wherein the temperature of the process water is controlled by specifying a temperature setpoint for the supply temperature of the process water, wherein the operating hours of the electrolyzer are recorded and an efficiency loss caused by the operation is determined, and wherein the temperature setpoint for the supply temperature is adjusted as a function of the efficiency loss.

[0018] The invention is based on the understanding that, in the operation of known electrolysis plants, the sensors for temperature control and monitoring of the electrolysis process represent a significant cost factor. As described above, electrolysis plants scale by multiplying electrolysis cells, which are bundled into electrolysis stacks to form an electrolyzer, and the latter scale through further multiplication. Thus, a large-scale electrolysis plant can have multiple electrolyzers. Typically, each electrolysis stack, comprising multiple axially stacked electrolysis cells, incorporates a large number of temperature sensors to provide reliable and fail-safe functions.In some sensor topologies, the temperature sensors are also used on both sides of the electrolysis cells, i.e., on the anode side and the cathode side of an electrolysis cell, so that, for example, up to twelve temperature measuring points, each with its own temperature sensor, are possible per electrolysis module or electrolysis stack.

[0019] For industrially applied temperature measurements, temperature sensor systems based on a 2024PF00353 are typically used.

[0020] 5

[0021] A thermocouple or a resistance temperature sensor is used, typically equipped with a transmitter and an input / output module (“I / O module”). Input / output (I / O) modules are essential components in industrial automation systems, as they act as an interface between control systems and devices such as sensors, actuators, and machines. These modules help convert and process signals from the controller into signals usable by the devices, and vice versa. Various types of I / O modules are available to meet different application requirements, such as analog input, digital output, analog output, safety, IO-Link, and fieldbus modules. Therefore, the provision, installation, and operation of such a temperature measurement point incur significant costs.The operational requirement for temperature measurements is to optimize the temperature of the electrolysis stack. While a high temperature is important for the efficiency of the electrochemical reaction, it also negatively impacts cell aging. Fail-safe measurements—if implemented—primarily protect the integrity of the electrolysis stacks and prevent critical conditions to protect operating personnel. In industrial settings, these measurement functions are typically separate. Technically, a combination of operational and fail-safe functions is also possible, for example, transmitters that output both an operational analog signal and a fail-safe binary signal.

[0022] The invention proposes eliminating the need for multiple direct temperature measurements of the process water at the electrolysis cells and replacing the temperature information with calculations that utilize other available measured values. This significantly reduces the costs for sensors and temperature control in an electrolysis plant. The operating method of the invention indirectly controls the temperature of the electrolysis cells by adjusting the inlet temperature of the process water at the operating point. 2024PF00353

[0023] 6

[0024] The efficiency loss is adjusted to account for hourly and thus age-related efficiency losses. Operating hours are counted using an operating hours counter, and the electrical power used is recorded as a function of the load. These values ​​can optionally be included as equivalent operating hours in the calculation of the operational efficiency loss. Full-load hours or equivalent operating hours (EOH) are a calculated reference value for the operating hours that would result if the electrolyzer were operated at full load within one year, taking into account its operating hours at partial load. The full-load hours are calculated as the quotient of the amount of electricity actually used in the electrolyzer (MWh). el / a) and its rated power (MW) el The rated power is the maximum electrical power consumption of the electrolyzer in continuous operation, i.e., operation at full load.

[0025] The inlet temperature control of the invention advantageously exploits the fact that electrolysis operation, depending on the operating mode, leads to a corresponding degradation of the electrolysis cells and thus greater heat losses, e.g., due to higher electrical resistances of the electrolysis cells, electrolysis modules, or electrolysis series. Consequently, higher voltages are required to achieve a comparable hydrogen yield to that at the start of operation. In the proposed control system, the temperature setpoint for the inlet temperature is adjusted solely or predominantly based on the efficiency loss as a characteristic degradation parameter. It has been shown that the efficiency loss is a good and comparatively simple measure for reliably determining the cooling requirement due to aging.to determine the required cooling capacity to dissipate the heat generated by the electrolysis process and thereby maintain the electrolysis cells at a predetermined operating temperature, e.g., 60 °C for PEM electrolysis. Thus, by considering the efficiency loss, an aging-based temperature control can be achieved. 2024PF00353.

[0026] 7

[0027] The operation of electrolysis systems is possible via the adjustment of the flow temperature, which is particularly simple and robust.

[0028] The process water is circulated in a closed-loop system, with its temperature controlled by setting the target temperature solely based on the inlet temperature of the process water. The cooling requirements or heat dissipation for the electrolysis process are then determined by calculating the efficiency loss. Direct temperature measurement of the process water at the electrolysis stacks can be largely or completely eliminated. These direct temperature measurements are advantageously replaced by calculations that utilize other existing parameters, such as cell voltage, current, and the electrolysis efficiency derived from the heat dissipated (loss heat).Knowing these measured values ​​allows for a good approximation of the efficiency at the stage of an electrolysis cell, module, or series (electrolysis string) as a function of the operating load, and this efficiency can be converted to other values, possibly averaged. The efficiency, or rather the efficiency loss, can be used to determine the amount of heat that must be dissipated from the stacks through cooling during operation, i.e., adjusted for operating hours. This efficiency-based approach inherently takes into account factors such as heat radiation, enthalpy of vaporization, the heat capacity of the produced gases and process water, and the efficiency of the electrolysis itself.The proposed operating procedure and underlying methodology thus represent a fundamental departure from the previously established operating and sensor concept, in which either a multiple of appropriately equipped temperature sensors are installed downstream of an electrolysis stack or electrolysis module, or are provided directly on the electrolysis stacks. Both approaches involve, in particular, a considerable number of temperature sensors, interfaces, cabling effort, and potentially galvanic isolation – 2024PF00353.

[0029] 8

[0030] The electrolysis stacks are associated with operating at electrical potential, as well as confined space and poor accessibility or high wiring costs.

[0031] In a particularly preferred embodiment of the method, the operational load of the electrolyzer is plotted as a function of time, whereby equivalent operating hours are determined.

[0032] It has proven particularly practical and advantageous to measure and record the respective electrolysis load over the operating hours (OH) of the electrolysis plant. Equivalent full-load hours (EOH) are then determined as a standardized reference value and used to control the flow temperature in order to determine the efficiency loss and the resulting cooling requirement. The corresponding amount of heat to be dissipated is thus known, allowing a predetermined operating temperature to be maintained within the electrolysis cells, electrolysis modules, and / or electrolysis series, for example, a value between 55 °C and 65 °C, typically 60 °C for PEM electrolysis.The target temperature in the inlet to the electrolysis cells is therefore set slightly below the desired operating temperature for the age-related control of the flow temperature, depending on the state of aging, approximately in a temperature range of 5 °C to 25 °C below the respective operating temperature.

[0033] In a particularly preferred embodiment of the process, the cooling capacity required for the electrolysis process is determined and the supply temperature is adjusted to the aging-related loss of efficiency.

[0034] It has been shown that the efficiency loss is a suitable parameter for the degree of degradation and the aging state of the electrolysis plant, so that the cooling requirement over the operating period can be determined in-situ from the efficiency loss compared to an initial value. The 2024PF00353

[0035] 9

[0036] Efficiency loss is determined relative to a starting value at the time of commissioning of the electrolysis plant and is periodically calculated and plotted based on operating time or equivalent full-load hours. This allows for the creation of an efficiency curve based on operational measurements and empirical data from comparable electrolysis plants. Advantageously, partial efficiencies characteristic of degradation at the electrolysis cell, module, and / or electrolysis series stage can also be determined. This increases the accuracy of the control system. These partial efficiencies can then be considered and converted into an overall system efficiency for the electrolysis plant or a specific stage.

[0037] In a particularly preferred embodiment of the method, an efficiency characteristic curve is provided which shows the efficiency as a function of the operating hours, wherein the flow temperature is controlled in an efficiency-dependent manner such that an efficiency-dependent temperature setpoint is specified according to the efficiency characteristic curve.

[0038] Therefore, the efficiency curve allows for the simple control of the process water supply temperature as a function of efficiency, or rather the efficiency loss compared to a starting value, over the operating lifetime. Using the efficiency curve of the electrolysis system provided in this way, the supply temperature can be controlled in an efficiency-dependent manner, such that an efficiency-dependent temperature setpoint is specified according to the curve. The efficiency loss correlates – as described above – with the aging state (degradation) and thus with the cooling capacity required to maintain an operating temperature within the electrolysis cells.

[0039] The characteristic curve or characteristic curve field is predefined and stored in a storage medium. A preset flow temperature or an active characteristic curve is then used. 2024PF00353

[0040] 10

[0041] The flow temperature cannot be adjusted or changed over the course of operation. Adjusting the flow temperature based on the efficiency loss of the electrolysis process is particularly advantageous because, for example, under partial load, only a fraction of the heat from the electrolysis process needs to be dissipated. This means that less cooling capacity is required and a higher flow temperature is possible. In this specific case, this could be achieved with a fixed efficiency curve or a set of curves, such as a flow temperature-efficiency curve stored in a memory, configured for a specific flow temperature and operating efficiency. It is advantageous to provide a set of curves that comprehensively covers full-load as well as medium to low partial-load operating conditions.

[0042] In this simplified operating mode with a fixed, efficiency-based control of the flow temperature, the averaging process deliberately avoids the complexity of the sensors, thus likely resulting in a slight reduction in efficiency. However, the complexity and process engineering effort, as well as the associated costly sensor technology for temperature measurements, can be significantly reduced compared to previous temperature control methods. The proposed operating method, with constant yet efficiency-adjustable control of the process water flow temperature, achieves a particularly robust, cost-effective, and low-error operation of an electrolysis plant.This control based solely on the flow temperature using an efficiency curve can, due to its simplicity, also serve as a possible fallback or emergency running option for potentially more complex temperature control systems that may be present and specifically designed for normal or controlled operation in the event of sensor / control loop failures, particularly to increase their availability. This can be of great economic advantage in the event of sensor failures or maintenance work at the measuring points, since the methods of the invention allow continued operation of the electrolyzer. 2024 PF00353.

[0043] 11

[0044] It is lieh. Therefore, switching between two operating modes within the temperature control would be possible.

[0045] In a preferred embodiment of the method, a voltage and a current are measured and the efficiency of the electrolysis process is determined from this, whereby the cooling power required for the electrolysis process is determined from the efficiency thus determined.

[0046] In the operation of an electrolysis plant, the cell voltage and / or the stack voltage and / or the string voltage (as a series connection of several electrolysis stacks), as well as the electrolysis current, are typically already being recorded. Knowing these values ​​allows the efficiency of the electrolysis to be determined at the string level of each electrolysis cell, stack, or string, and this efficiency can be converted to the respective (averaged) other values. Thus, the existing sensor system can be used to implement indirect temperature control of the electrolysis process. The necessary cooling capacity for dissipating the process heat (loss heat) from the electrolysis process can advantageously be determined based on the efficiency, thereby enabling the setting of the required supply temperature for a given mass or volume flow rate of the process water.This approach takes into account loss mechanisms such as heat radiation, enthalpy of evaporation, the heat capacity of the produced product gases (hydrogen and oxygen) and the process water, as well as the efficiency of the electrolysis. A key advantage is that operational measurements allow for the calibration, verification, and, if necessary, adjustment of the stored efficiency curve, or a switch to a different operating point or efficiency curve within the curve field.

[0047] In a particularly preferred embodiment of the method, a cell voltage, a module voltage, and / or a string voltage are optionally measured. 2024 PF00353

[0048] 12

[0049] The string voltage results from the series connection of several electrolysis stacks or electrolysis modules. An electrolysis module can, for example, consist of fifty axially stacked electrolysis cells. An electrolysis string can consist of, for example, five electrolysis modules or electrolysis stacks. In large electrolysis systems, several electrolysis strings can be connected in parallel.

[0050] In a preferred embodiment of the method, temperature control can be carried out, which optionally intervenes at the stage of an electrolysis cell, an electrolysis module or an electrolysis string, wherein the temperature of the process water at one of the stages is determined indirectly from the current strength and the efficiency of the electrolysis process and from electrical measured variables optionally the cell voltage, the module voltage and / or the string voltage.

[0051] In a further preferred embodiment of the method, the temperature setpoint (T) SET ) is formed indirectly as a result from characteristic temperature quantity derived from determined partial efficiencies of a stage, whereby a selection of the maximum, the minimum, the median, the mean, or sorting and selection of the nth result of a series of results or after a quantity sorting is carried out.

[0052] Typically, in practice, several results derived from the partial efficiencies are continuously or periodically determined as measured values ​​or results in the form of temperature measurements at each stage. Different evaluation procedures or data analyses can be used, from which one result serves as a characteristic starting point for defining a temperature setpoint. Thus, at least one representative and suitable setpoint or target value for the pre- 2024 PF00353 can be derived from the measured values ​​for the temperature at each stage.

[0053] 13

[0054] The flow temperature is determined and read into the temperature control system, where it is processed. In particular, this allows the flow temperature of the process water to be set to the desired temperature setpoint, depending on the required efficiency-dependent cooling capacity, and to be readjusted in-situ during operation of the electrolysis plant or adjusted periodically.

[0055] The selection method is the result of optimization and also depends on the efficiency distribution function or the stage-specific partial efficiencies at each stage of an electrolysis string, as well as its aging behavior over the operating period. The optimum can therefore be adjusted over time throughout the operating period.

[0056] In a particularly advantageous embodiment of the process, the mass flow rate of process water in the upstream section of the process water circuit is kept constant.

[0057] If, in addition, the quantity of process water or cooling water supplied, i.e., the mass or volume flow rate, is kept constant in the process water circuit, a frequency-controlled pump can potentially be omitted, saving costs. Furthermore, the temperature control is advantageously limited to regulating only the supply temperature of the process water or cooling water. Depending on the process engineering design of the electrolysis plant, the temperature control can be implemented at the electrolysis stack or electrolysis string level. Combinations are also possible in principle. It is also possible to integrate a temperature sensor at selected measuring points of an electrolysis cell, electrolysis module, or electrolysis string, for example, to perform calibration measurements and verification of the indirect temperature control and the evaluation model, or for other purposes.to also be able to carry out a regular inspection in order to detect unacceptably high deviations or changes over time in efficiency and that- 2024 PF00353.

[0058] 14

[0059] to detect unexpected or unusual efficiency losses early on. This allows for timely adjustment and tracking to a different operating point on a stored efficiency curve, or a switch to a different efficiency curve to define a modified target temperature for the flow temperature. In each case, a significant cost reduction can be achieved compared to conventional temperature control of an electrolysis plant, as operation with considerably fewer temperature measuring points is possible. For example, for operational temperature measurement, a temperature measuring point with a temperature sensor in the return line, i.e., downstream of the electrolysis modules or an electrolysis series comprising several electrolysis modules, is advantageous.

[0060] This allows not only the flow temperature in the supply line of the electrolysis storage system, but also the output temperature in the return line of the electrolysis system to be measured and monitored.

[0061] An electrolysis plant according to the invention, which is set up accordingly for carrying out the process, comprises a plurality of electrolysis cells connected electrically in series and integrated into a process water circuit, as well as a temperature control device which is designed to regulate the flow temperature of the process water to a temperature setpoint.

[0062] The control system is designed to use a predetermined, constantly set target temperature for the flow temperature, depending on the current efficiency of the electrolysis system.

[0063] In a particularly preferred embodiment of the electrolysis plant, the temperature setpoint of the temperature control device can be determined as a function of the operating hours using an efficiency characteristic curve, wherein the efficiency characteristic curve shows the efficiency as a function of the operating hours and is stored as a data set in a programmable memory. 2024 PF00353

[0064] 15

[0065] is stored in the memory or can be read into it.

[0066] A characteristic curve array with a multitude of appropriately parameterized efficiency curves can be stored in the memory to react to changing operating conditions and degradation phenomena of the electrolysis cells due to operating time, and to make adjustments. It is possible to update and extend the efficiency curves, so that long-term experience from operating data can be taken into account to further refine an efficiency curve and thereby optimize the operation of the electrolysis plant according to the conditions, so that the temperature of the electrolysis cells can be controlled particularly efficiently based solely on the specified inlet temperature. Control of the stack / cell temperature is generally not provided for in this operating mode and is also unnecessary.

[0067] In a further preferred embodiment of the electrolysis plant, a programmable control and regulating device is provided, into which the temperature control device is integrated.

[0068] This advantageously enables comprehensive operation and control of the electrolysis plant. In particular, the efficiency-based control with constant flow temperature according to the invention is also advantageously possible with indirect temperature control based on temperature values ​​indirectly derived from measured values, i.e., combinations of different operating modes. The invention is advantageously and flexibly applicable to various types of electrolysis plants, such as alkaline water electrolysis, PEM electrolysis, or anion-exchange membrane water electrolysis (AEMWE), wherein a temperature control device is implemented in the electrolysis plant. 2024 PF00353

[0069] 16

[0070] Exemplary embodiments of the invention are explained in more detail with reference to a drawing. This drawing schematically and in a highly simplified manner shows the

[0071] FIG 1 an electrolyzer with a plurality of axially stacked electrolysis cells;

[0072] FIG 2 shows a schematic representation of a process diagram of an electrolysis plant with a temperature control device;

[0073] FIG 3 simplified representation of efficiency characteristic curves of an electrolysis plant in qualitative form;

[0074] FIG 4 shows a schematic representation of a process diagram of an electrolysis plant with an extended temperature control device.

[0075] FIG 1 shows an example of an electrolyzer 1 comprising four electrolysis stacks 3, which are sometimes also referred to as electrolysis modules or electrolysis segments. Each electrolysis module 3 comprises several electrolysis cells 5, so that a group of four electrolysis modules A, B, C, D is connected in series. A plurality of electrolysis cells 5 stacked along the horizontal axis are arranged as a group between two pressure plates 7 and connected together to form an electrolysis module 3. The pressure plates 7 press the electrolysis cells 5, which, for example, comprise a proton exchange membrane (PEM), together in a pressure-resistant and fluid-tight manner, ensuring a tight and precise fit. The design with pressure plates 7 is shown here only as an example. Alternative designs as end plates, cell plates, or bipolar plates are also possible.The pressure plates 7, which are arranged at the axial ends of the electrolyzer 1, are electrically connected via an electrical connection 9. Three electrical switching devices 11 are arranged in parallel with the electrolysis modules B, C and D of the electrolyzer. The 2024 PF00353.

[0076] 17

[0077] Switching devices 11 are arranged electrically in parallel to the electrolysis modules 3. In this example, each switching device 11 bridges one electrolysis module 3. Thus, each switching device 11 is electrically connected to the pressure plates 7 that define one electrolysis module 3.

[0078] In this example, electrolysis, specifically the splitting of water (H₂O) into hydrogen (H₂) and oxygen (O₂), takes place in all electrolysis modules 3, since all switching devices 11 are open. Electrolysis is carried out with direct current. Therefore, the switching devices 11 are designed as DC switching devices. A diode 13 is connected in series with the switching device 11 in the forward direction. Advantageously, this maintains the polarity and a protective voltage for the electrolysis stack 3. In this example, the electrolyzer 1 is operated at full load. If the electrical power in the grid decreases, particularly due to low wind and solar power, at least one switching device 11 can be closed. Thus, electrolysis modules B, C, and D can be switched off or bypassed as needed. In this example, electrolysis module A is always operated when the electrolysis system 1 is running.If the other modules are switched off depending on the available electrical power, electrolysis module A can be operated at a constant power density. This advantageously prevents electrolysis modules 3 or electrolysis cells 5 from operating at partial load. It is particularly advantageous to bridge the electrolysis modules 3 sequentially. Specifically, module A can be bridged first for a fixed period. Subsequently, module B or module C can be bridged for a similar period. This ensures that the modules are operated and loaded evenly. Bridging prevents the electrolysis cells 5 from aging rapidly. Furthermore, it ensures that the product gas quality, especially of the hydrogen, remains constant over a long period. 2024 PF00353.

[0079] 18

[0080] In addition to the electrical supply and connection of an electrolyzer 1 with electrolysis current, the hydraulic supply of reactant water H₂O and the discharge of the product streams obtained from the electrolysis process are crucial for safe operation. While the electrolysis cells 5 are electrically connected in series, the hydraulic conveyance of the reactant water H₂O to the individual electrolysis cells 5 and the discharge of the product streams from the electrolysis cells 5 are typically carried out in parallel. Fully demineralized water H₂O is supplied to the electrolyzer 1 as process water via an reactant current line 15. A product stream line 19 for hydrogen H₂ and a separate product stream line 17 for oxygen O₂ are connected to the electrolyzer 1 at the outlet. The product stream comprises a phase mixture of water H₂O and the respective product gas, which is hydrogen H₂ at the cathode and oxygen O₂ at the anode.The phase mixture is separated and further processed in components of an electrolysis plant 10 comprising the electrolyzer 1 (see below for the description of FIG. 2), yielding gaseous hydrogen (H₂) and oxygen (O₂) as product gases. The water (H₂O) not decomposed into the product gases by the electrolysis process is collected as process water (H₂O), recovered, and returned to the cycle via a return line 21. The electrolysis process generates process heat (Q), which, among other things, heats the process water (H₂O), thus enabling heat removal or cooling of the reactant water (H₂O) to a predefined supply temperature (T). INThis is required, which is monitored by a temperature sensor 25 and on which the operation of the electrolyzer 1 is controlled. The return temperature TOUT measured in the return line 21 by means of a temperature sensor s 25 is higher than the supply temperature T due to the absorption of process heat Q by the electrolysis operation. IN . For temperature control on the flow temperature T IN A higher-level programmable control and regulation unit 29 with IO interfaces is provided, which performs various functions for plant operation 2024 PF00353

[0081] 19

[0082] and are implemented. Thus, a temperature control unit 27 is integrated into the programmable control and regulation device 29, into which sensor data from the temperature sensor s 25 for the flow temperature T are received. INare readable. Furthermore, an input value for the operational efficiency g or the operational efficiency loss Ag, relative to a starting value at the commissioning of the electrolyzer 1, is read or entered. The efficiency g or the operational efficiency loss Ag determines the waste heat Q produced from the electrolysis process and which must be discharged over the course of operation and is a measure of the degradation state of the electrolysis cells 5 and the electrolysis modules 3. The operating time t and the electrolysis load P(t) are recorded via an operating hours counter 41 over the course of the operating time t, so that a load curve is determined. A corresponding cooling capacity Q must be provided via the circulating process water H2O so that the corresponding process or waste heat Q is discharged from the electrolysis cells 5.The adjusted cooling capacity Q ensures a desired operating temperature for the electrolysis cells 5 and the electrolysis modules 3, for example 60 °C for PEM electrolysis. The program logic of the temperature control unit 27 outputs a temperature setpoint T. SET on which the operational flow temperature T IN The efficiency g or the operational efficiency loss Ag is set or adjusted. Further operating data of the electrolyzer 1, such as current values ​​for the volume or mass flow rate M of circulating process water H2O, can be processed, enabling mass flow rate control with a preferably constant predefined and set mass flow rate setpoint M. SETis implemented. For particularly reliable and precise operation of the temperature control device 27, a constant mass flow rate M is recommended. High operating pressures are possible in the hydraulic design of the electrolyzer 1. However, the temperature control device 27 is designed in such a way that it does not necessarily require a complex in-situ or periodic determination of the values ​​for the temperature control device 27.

[0083] 20

[0084] The system relies on the heat quantity Q released during the electrolysis process and other comprehensive measured values ​​to enable reliable electrolysis operation. Determining the heat quantity Q to be dissipated via the efficiency loss Ag over time is sometimes complicated and therefore costly. Instead, the temperature control device 27 incorporates and implements a control system for particularly robust and simple electrolysis operation, in which the temperature T PThe process water H2O is adjusted by solely relying on a constant flow temperature T. IN of the process water H2O with a predetermined temperature setpoint T SET The temperature is regulated according to a previously set value. Extensive and expensive temperature sensors are not required in this operating mode. Further sensor technology for operational control is also implemented optionally and additionally in the temperature control unit 27, as explained below with reference to FIGS. 2 and 4. The electrolyzer 1 shown in FIG. 1 can, for example, be designed as a pressure electrolyzer and be designed for a high operating pressure of up to 35 bar and beyond.

[0085] Figure 2 shows a simplified schematic process diagram of an electrolysis plant 10 with a temperature control device 27. The electrolysis plant 10 comprises an electrolyzer 1 with several electrolysis units a1a, 1b, 1c, which can be connected electrically in parallel and / or optionally in series. Each electrolysis unit a1a, 1b, 1c has a plurality of electrolysis cells 5 stacked in an axial direction, wherein an electrolysis unit a1a, 1b, 1c, for example, comprises four electrolysis modules A, B, C, D connected in series, forming an electrolysis series or a so-called electrolysis string. The temperature control device 27 in the electrolysis plant 10 can be connected to a higher-level programmable control unit 29 of the electrolysis plant 10. This extended control allows for greater operational flexibility and a wider selection of operating modes.The control and regulating device 29 is set up for operating data 2024 PF00353.

[0086] 21

[0087] as well as processing and exchanging measurement and control signals, and in particular determining derived or calculated control signals such as the amount of heat Q released or removed from the electrolysis process and passing them to the temperature control unit 27 as an input value. For this purpose, the control unit 29 is equipped with a processor for data processing. However, it is also possible that the temperature control unit 27 is already integrated within the programmable control unit 29 as a functional group with I / O interfaces. Thus, electrical measurement signals from the electrolyzer 1, such as the voltage U, the current I, and, at the electrolysis cell 5 stage, the respective cell voltages U, can be processed. z , at the electrolysis module stage, 3 respective module or stack voltages U Mas well as at the stage of one or more electrolysis units aa, b, c optionally string voltages U s The measured values ​​are measured during operation. They are read into the control unit 29 and processed there. From the measured voltage U and the current I, the efficiency g of the electrolysis process is determined, taking other parameters into account. The efficiency g allows the amount of heat Q to be dissipated by cooling the electrolysis stacks 3 to be determined. Factors such as heat radiation, enthalpy of vaporization, heat capacity of the produced gases and the process water, and the efficiency g of the electrolysis are considered. Thus, the amount of heat Q dissipated, i.e., the total heat losses Q from the electrolysis process, is determined from the calculated efficiency g. The electrolysis power P e i, which is used solely for the production of the product gases oxygen Oi and hydrogen H2, therefore amounts to P ei= p - Po, where P ei = U - I - Q = P o - ( 1-p ) ' Po, where P o = U - I denotes the electrical power used to operate the electrolysis process.

[0088] Furthermore, a process technology unit 33 is connected to the electrolyzer 1 in such a way that a process water circuit 31 is formed. For this purpose, the process water circuit 31 is routed through the process technology unit 33, which is connected to the 2024 PF00353

[0089] 22

[0090] Electrolyzer 1 is connected. In process technology unit 33, among other things, the fluid recycled from the electrolysis process and cooled to the return temperature T is processed. OUT process water H2O heated to a specific flow temperature T IN cooled down. Process technology unit 33 is equipped with a heat exchanger for this purpose, among other things. The temperature setpoint T SET , on which the flow temperature T INThe temperature is determined by the temperature control device 27 and provided via the temperature control device 27. The temperature control device 27 has a programmable memory 35 in which an efficiency curve 37 or an efficiency curve array 37 is stored. The efficiency curve 37 shows in a data set the efficiency g as a function of the operating hours t. The flow temperature T IN The efficiency is regulated in such a way that, according to the provided efficiency characteristic curve 37, an efficiency-dependent temperature setpoint T is determined. SET is specified.

[0091] The efficiency characteristic curve 37 gives a fixed relationship between the temperature setpoint T SET for setting or regulating the flow temperature T PThe efficiency loss Aq of electrolyzer 1 compared to a starting value at the beginning of operation is used as a basis for determining the required cooling capacity Q for the electrolysis process, and thus the flow temperature T. IN The efficiency loss Ag can be adjusted to account for age-related or operational efficiency losses. For this purpose, the operating hours t of electrolyzer 1 are recorded, and the resulting efficiency loss Ag is determined. The target temperature T SET for the flow temperature T IN The efficiency loss Ag is adjusted. The operating load P(t) of the electrolyzer is recorded as a function of the operating time t, from which equivalent operating hours (EOH), i.e., full-load hours, can be determined.

[0092] The efficiency characteristic curve 37 or a parameterized efficiency characteristic curve field 37 for setting a fixed pre- 2024 PF00353

[0093] 23

[0094] running temperature T 2N to the temperature setpoint T SET The value can be read into memory 35 via an input interface 39 using a data line or entered manually. The temperature control unit 27 can thus set a temperature setpoint T via the programmable memory 35. SET They are displayed and specified as an input signal to process engineering unit 33. Additionally, current operational measured values ​​for temperature T can be provided. P = T IN The process water H2O and its mass flow rate M are continuously measured and read into the temperature control device 27, so that a closed control loop for temperature control is formed.

[0095] During the operation of electrolysis plant 10, the process water H2O is circulated in the process water circuit 31. The temperature T is maintained. P The process water H2O is adjusted by simply focusing on the flow temperature T. IN The process water H2O is regulated, with a fixed temperature setpoint T. SET for the flow temperature T IN The process water H2O is specified. This operating mode of the electrolysis plant 10 with a fixed flow temperature T IN This is implemented by providing a predefined efficiency characteristic curve 37 in the storage unit 35, which shows the efficiency loss Ag as a function of the operating hours t, where the temperature setpoint T SET for the flow temperature T IN The required cooling capacity due to degradation is set depending on the efficiency loss Δη. Therefore, the temperature setpoint T is determined. SET for the flow temperature T INThe efficiency loss Ag of the electrolysis plant 10 is fixed and adjusted accordingly to the operating hours t during operation. The flow temperature T IN The efficiency is regulated or fixed in such a way that a temperature setpoint T is set according to the selected efficiency characteristic curve 37. SET The temperature setpoint T is specified. For a certain efficiency loss Ag or optionally also in an efficiency range or efficiency interval of the electrolysis plant 10, which ranges from a minimum efficiency value to a maximum efficiency value, the temperature setpoint T is set. SET and thus the set flow temperature T IN in the Be- 2024 PF00353

[0096] 24

[0097] The drive situation is constant and fixed predefined via a corresponding characteristic curve 37.

[0098] In this characteristic-curve-based operating mode, an in-si tu adjustment to current measurement data via a large number of expensive sensors, which would have to be specifically installed and maintained on the electrolysis cells 5 or the electrolysis modules A, B, C, D, is generally not necessary with the present temperature control. However, with this method, it is advisable to check the continued applicability of an existing efficiency characteristic curve 37 at least periodically via control measurements, e.g., during maintenance of the electrolysis system 10. If necessary, an adjustment of an existing efficiency characteristic curve 37 to the current operating or aging state of the electrolysis system 10 can then be carried out. Alternatively, a switch can be made to another efficiency characteristic curve 37 already stored in memory 35, whereby a selection is made from a stored parameterized efficiency characteristic curve field 37.The characteristic curve field 37 can, among other parameters, for example, also be provided and ordered with regard to different mass flows M with respect to the process water H2O.

[0099] The cooling capacity Q resulting from an evaluation of the efficiency characteristic curve 37 at an efficiency Ag or efficiency loss Ag, and thus the temperature setpoint T, SET At a specific mass flow rate M, the data is transferred to the process control unit 33 via an automated input interface 39a. Additionally, manual adjustment of the supply temperature T is possible. SET This is possible via a manual input interface 39b, so that this manual intervention bypasses or overwrites the automated input interface 39a, i.e., manual operation is carried out. In the process technology unit 33, the temperature T is maintained by means of a corresponding cooling capacity Q. O The process water H2O supplied to the UT is brought to the temperature setpoint T. SET = TIN cooled and fed into electrolyzer 1 or electrolysis units 1a, 1b, 1c in electrolysis plant 10. Measurement and monitoring of the current 2024 PF00353

[0100] 25

[0101] process water temperature T P The temperature measurement is taken at the inlet to electrolyzer 1 via a temperature measuring point. A characteristic of this operating mode of the electrolysis system 10 is that the operating temperature of the electrolysis cells 5 is determined solely by the inlet temperature T. IN is regulated, whereby an aging-based temperature control is carried out via the efficiency characteristic curve 37 which shows the efficiency loss Aq over the operating time t.

[0102] Figure 3 shows a simplified diagram of the efficiency curves 37 of an electrolysis plant 10, depicting their qualitative progression. The efficiency q of the electrolysis is plotted against the operating time t. In this diagram, the operating time t is normalized to equivalent full-load operating hours (EOH). The efficiency q = rp is highest when the plant starts at the beginning of life (BoL). In practical applications, PEM electrolysis achieves an electrical efficiency of approximately 80%, measured by the hydrogen production per unit of electricity used to carry out the reaction. The efficiency of PEM electrolysis is expected to reach 82–86% before 2030 and remain stable due to rapid advancements in this field. Over time, the efficiency q of an electrolysis plant decreases due to degradation effects. This decrease is highly dependent on the operating conditions of the electrolysis plant.Start-up and shut-down processes, as well as frequent load changes and alternating load operation, lead to faster degradation. Further effects can occur due to the quality of the reactant water H2O used. Figure 3 shows three exemplary efficiency curves 37, i.e., a field of curves that, while qualitatively similar over the operating time, exhibit different aging behavior. Towards the end of the operating time EoL, the efficiency q is significantly reduced compared to the initial value rp and may exhibit saturation behavior at the low level, i.e., a nearly constant or slightly decreasing efficiency q. Relative to the efficiency rp at initial commissioning BoL, the efficiency- 2024 PF00353.

[0103] 26

[0104] The efficiency loss Ar, i.e., the efficiency loss of the electrolysis system 10, increases continuously with the operating time t, resulting in an increased cooling requirement. Therefore, the electrolysis cells 5 must be cooled and the process heat Q dissipated so that the specified operating temperature of the electrolysis cells 5 is maintained and they do not overheat. Typically, PEM electrolysis is carried out at an operating temperature of 60 °C as the process temperature in the electrolysis cells 5. Therefore, the process heat Q must be dissipated via the circulating process water H2O, for which purpose the process water H2O is cooled accordingly in the process technology unit 33.

[0105] Figure 4 shows a schematic process diagram of an electrolysis plant 10 with a temperature control device 27 that is extended compared to Figure 2. The electrolysis plant 10 is configured here for two alternative operating modes, with the control set to a constant supply temperature T. INAs explained with reference to FIG. 2, this is implemented and selectable as a particularly advantageous operating mode in the present embodiment. This allows, for example, a temporary emergency or backup operation to be carried out in contrast to normal or controlled operation of the electrolysis system 10 with comprehensive temperature control of the electrolysis cells 5. Thus, continued operation of the electrolysis system 10 is possible during fault conditions of the control loop or the temperature control sensors. Therefore, an emergency or backup operation is implemented here if the first operating mode is faulty, disrupted, or temporarily interrupted due to maintenance work on the sensors.

[0106] The electrolysis plant 10 shown in FIG. 4 has for this purpose an electrolyzer 1 with several electrolysis units 1a, 1b, 1c, which can be connected electrically in parallel and / or optionally in series. The temperature control device 27 in the electrolysis plant 10 is connected to a higher-level programmable control unit. 2024 PF00353

[0107] 27

[0108] The control unit 29 of the electrolysis plant 10 is connected to the temperature control unit 27. It is configured to process and exchange operating data as well as measurement and control signals in-situ during normal or controlled operation, and in particular to determine derived or calculated control signals, such as the amount of heat Q released or dissipated from the electrolysis process, and to transmit these as input values ​​to the temperature control unit 27. For this purpose, the control unit 29 is equipped with a processor for data processing. However, it is also possible that the temperature control unit 27 is already integrated within the programmable control unit 29 as a functional group with I / O interfaces. Thus, during normal or controlled operation of the electrolysis plant 10, electrical measurement signals from the electrolyzer 1, such as the voltage U, the current I, and the respective cell voltages U at the electrolysis cell 5 stage, can be transmitted. z, at the electrolysis module stage, 3 respective module or stack voltages U M as well as at the stage of one or more electrolysis units aa, b, c optionally string voltages U sThe measured values ​​are measured during operation. They are read into the control unit 29 and processed there. From the measured voltage U and the current I, the efficiency g of the electrolysis process is determined, taking other parameters into account. The amount of heat Q to be dissipated by cooling the electrolysis stacks 3 can be determined from the efficiency g or the aging-related efficiency loss Ag. Factors such as heat radiation, enthalpy of vaporization, heat capacity of the produced gases and the process water, and the efficiency g of the electrolysis are considered. Thus, the amount of heat dissipated Q, i.e., the total heat losses Q from the electrolysis process, is also determined from the calculated efficiency g. The electrolysis power P ei , which is used solely for the production of the product gases oxygen O2 and hydrogen H2, therefore amounts to P ei = η·P0, where P ei= U·I − Q = P0− (1−η)·P0, where P0= U·I denotes the electrical power input for operating the electrolysis process. 2024 PF00353

[0109] 28

[0110] As described in FIG. 2, the process water circuit 31 is routed through a process technology unit 33, which is connected to the electrolyzer 1. In the process technology unit 33, among other things, the water returned from the electrolysis process is cooled to the return temperature T. OUT heated process water H2O to a flow temperature T IN cooled down. Process technology unit 33 is equipped with a heat exchanger for this purpose, among other things. The temperature setpoint T SET , on which the flow temperature T INThe temperature T is determined by the programmable control unit 29, provided and displayed via the temperature control unit 27, and is supplied to the process technology unit 33 as an input control signal. P = T IN The process water H2O and its mass flow rate M are continuously measured and read into the temperature control device 27, so that a closed control loop is formed.

[0111] A supply line of fully demineralized fresh water to the process water circuit 31 is provided to compensate for the water consumption by the electrolysis process. This is not shown in detail in FIG. 4. During operation of the electrolysis plant 10, process water H₂O is supplied to the electrolysis cells 5, and the electrolysis cells 5 are subjected to an electric current I, whereby hydrogen H₂ and oxygen O₂ are produced as product gases, and the process water H₂O is circulated in the process water circuit 31. In a first operating mode – a control mode – the temperature T P The process water H2O is regulated by setting the temperature T as the target value. SET the flow temperature T IN The process water H2O is specified and the amount of heat Q released from the electrolysis process is determined via the efficiency g or the operational efficiency loss Ag.

[0112] In the first operating mode, the underlying control concept is the flow temperature T. IN The system is set and continuously regulated depending on the efficiency loss Ag and the associated heat output Q. (Es 2024 PF00353)

[0113] 29

[0114] A temperature control system is implemented, which selectively intervenes at the level of the electrolysis cells 5, the electrolysis modules 3, or the electrolysis units 1a, 1b, 1c, the so-called electrolysis string. The temperature T is thereby controlled. P of the process water H2O on one of the stages indirectly from the current I, the efficiency g of the electrolysis process and from electrical measured quantities optionally the cell voltage Uz, the module voltage UM and / or the string voltage U s determined only indirectly. The temperature setpoint T SETIn the control concept of this first operating mode, the temperature setpoint T is advantageously determined indirectly as a quantity derived from the aforementioned measured values, so that a characteristic setpoint for the temperature setpoint T can be obtained. SET This eliminates the need for numerous and very expensive temperature sensors that would otherwise have to be installed locally in the electrolyzer. For example, in the indirect temperature control of electrolysis plant 10, the maximum, minimum, median, or mean value is selected, or the nth measured value of a series is sorted and selected according to a quantity sorting process, in order to determine a characteristic temperature value T. SET as temperature setpoint T SET To determine and define or specify for control purposes. The temperature of the electrolysis cells 5 is therefore only indirectly controlled by the flow temperature T. INThe system is adapted to the efficiency-related heat loss Q. As already mentioned, this eliminates the need for multiple temperature measurements and, if necessary, even mass flow or volume flow control of the process water H2O circulating in the process water circuit 31. A particularly simple and advantageous operation in the electrolysis plant 10 is achieved by keeping the mass flow M of process water H2O in the feed line of the process water circuit 31 constant, i.e., M SET = constant = M. If the supplied process water quantity, i.e., the mass flow rate M, is kept constant, a frequency-controlled pump can be dispensed with, which saves considerable costs, and the temperature control is limited solely to the 2024 PF00353

[0115] 30

[0116] Control of the flow temperature T INof the process water H2O. This leads to particularly advantageous operation and high reliability of the indirect temperature control.

[0117] In a second and particularly advantageous operating mode of the electrolysis plant 10, temperature control of the electrolysis can be omitted or bypassed to reduce complexity and improve availability while simultaneously saving costs. Instead, an algorithm-based control system with fixed, predefined supply temperatures T is used. IN of the process water H2O as a function of the operational efficiency g or the efficiency loss Ag according to the embodiments explained in FIGS. 2 and 3. To enable this second operating mode of the temperature control device 27, the temperature control device 27 follows an efficiency characteristic curve 37 stored in the memory 35. The temperature setpoint T SETThe required cooling capacity Q is thus derived from the efficiency loss Ag as a function of the operating time t. This function is stored in the programmable memory 35 in the form of a data set for an efficiency characteristic curve 37 or a characteristic curve array. The electrolysis system 10 includes a programmable control unit 29, into which the temperature control unit 27 is integrated. In this case, the temperature control unit 27 is connected to the programmable control unit 29 for the exchange of control and measurement data.

[0118] In normal operation of the electrolysis plant 10, the switch S is open and temperature control is carried out, which selectively intervenes at the stage of an electrolysis cell 5, an electrolysis module 3 or an electrolysis string 1a, 1b, 1c, whereby the temperature T Pof the process water H2O at one of the stages indirectly from the current I as well as the efficiency g of the electrolysis process and from electrical measured quantities optionally the cell voltage U z , the module voltage (U M ) and / or the string voltage U s is determined. In this first operating mode, which is, for example, a regular operation 2024 PF00353

[0119] 31

[0120] This shows that when switch S is open, temperature control is performed and the temperature setpoint T is set. SET from indirectly determined temperature measurements T P of the process water H2O of the corresponding stage determined.

[0121] To activate the second operating mode – such as emergency or backup operation – switch S is closed, meaning the system switches from a regular operation with indirect temperature control to the second operating mode – such as emergency or backup operation – particularly temporarily. In this mode, the in-situ measurement-based indirect temperature control is bypassed or deactivated, and the control of the flow temperature T is disabled. IN This is done by accessing a stored efficiency curve 37, from which a fixed temperature setpoint T is derived. SET for the flow temperature T INThe required cooling capacity Q is derived as a function of the operational efficiency g or the efficiency loss Ag in order to provide the required cooling capacity Q at the operating point. In the process water circuit 31, the mass flow rate M of process water (H2O) in the upstream of the process water circuit 31 is monitored and preferably kept constant, which significantly simplifies the control. However, it is possible that, depending on the mass flow rate M or other parameters – such as the operating temperature of the electrolysis cells 5 – corresponding efficiency curves 37 are stored in the programmable memory 35. Thus, the efficiency curve 37 can also be implemented as a field of curves with a plurality of efficiency curves 37 differentiated according to order parameters.

[0122] In this second operating mode, a certain loss of efficiency g is deliberately accepted in favor of a simple and robust temperature control to a fixed flow temperature T. INThis allows the complexity of the process engineering and measurement effort to be reduced and kept to a minimum, or temporarily bypassed. As described, the second operating mode can also serve as a fallback option for complex temperature control systems in the event of a control loop error (2024 PF00353).

[0123] 32

[0124] or in the event of a sensor error, in order to increase the availability of the electrolysis plant 10 and, for example, to enable emergency operation or a backup operation. In general, however, it is also conceivable to operate the electrolysis plant 10 permanently via an operation based on an efficiency characteristic curve 37 or, if necessary, via a manual adjustment of the flow temperature T. IN to a predetermined temperature setpoint T SETto operate. This largely eliminates the need for sensors and control elements for the first operating mode, enabling a simple, robust and cost-effective design and operation of an electrolysis plant 10.

Claims

2024 PF00353 33 Patent claims 1. Method for operating an electrolysis plant (10) comprising an electrolyzer (1) with a plurality of electrolysis cells (5) connected in series, wherein process water (H2O) is supplied to the electrolysis cells (5) and the electrolysis cells (5) are supplied with an electric current, wherein hydrogen (H2) and oxygen (O2) are produced as product gases, and wherein the process water (H2O) is circulated in a process water circuit (31), wherein the temperature (T P The temperature of the process water (H2O) is controlled by setting a temperature setpoint (T). SET ) for the flow temperature (T IN ) of the process water (H2O) is specified, wherein the operating hours (OH) of the electrolyzer ( 1 ) are recorded and an efficiency loss (Aq ) caused by operation is determined, and wherein the temperature setpoint (T ) SET ) for the flow temperature (T IN) is adjusted depending on the efficiency loss (Aq ).

2. Method according to claim 1, wherein the operational load (P) of the electrolyzer (1) is plotted as a function of time, and equivalent operating hours (EOH) are determined.

3. Method according to claim 1 or 2, wherein the cooling capacity (Q) required for the electrolysis process is determined, and the inlet temperature (T) is determined. IN ) is adjusted to the age-related loss of efficiency (Aq ).

4. The method of claim 3, wherein an efficiency characteristic curve (37) is provided which shows the efficiency (q) as a function of the operating hours (OH), and wherein the flow temperature (T) IN ) is regulated depending on the efficiency in such a way that, according to the efficiency characteristic curve (37 ), an efficiency-dependent temperature setpoint (T ) is set. SET ) is specified. 2024 PF00353 34 5. Method according to claim 3 or 4, wherein a voltage (U) and a current (I) are measured and the efficiency (g) of the electrolysis process is determined from this, and wherein the cooling power (Q) required for the electrolysis process is determined from the efficiency (g) thus determined.

6. Method according to claim 5, wherein optionally a cell voltage (U) z ), a module voltage (U M ) and / or a string voltage (U s ) is measured.

7. Method according to claim 6, wherein a temperature control is carried out which selectively acts at the stage of an electrolysis cell (5), an electrolysis module (3) or an electrolysis string (1a, 1b, 1c), wherein the temperature (T P ) of the process water (H2O) on one of the stages indirectly from the current (I) and the efficiency (g) of the electrolysis process and from electrical measurements optionally the cell voltage (U) z ), the module voltage (UM ) and / or the string voltage (U s ) is determined.

8. Method according to claim 7, wherein the temperature setpoint (T SET ) is formed indirectly as a result from characteristic temperature quantity derived from determined partial efficiencies of a stage, whereby a selection of the maximum, the minimum, the median, the mean, or sorting and selection of the nth result of a series of results or after a quantity sorting is carried out.

9. Method according to one of the preceding claims, wherein the mass flow rate (M) of process water (H2O) in the process water circuit (31) is kept constant in the upstream of the process water circuit (31).

10. Electrolysis system ( 10 ) for carrying out the method according to one of the preceding claims, comprising a 2024 PF00353 35 A large number of electrically connected electrolysis cells (5) integrated in series into a process water circuit (31), as well as a further comprising a temperature control device (27) which is responsible for controlling the flow temperature (T IN ) of the process water (H2O) to a temperature setpoint (T SET ) designed i st.

11. Electrolysis system ( 10 ) according to claim 11, in which the temperature setpoint ( T ) is set in the temperature control device ( 27 ). SET ) as a function of the operating hours (OH) can be determined using an efficiency curve (37), wherein the efficiency curve (37) shows the efficiency (η) as a function of the operating hours (OH) and is stored as a data set in a programmable memory (35) or can be read into the memory (35).

12. Electrolysis system ( 10 ) according to claim 11 or 12, in which a programmable control and regulating device (29) is provided, into which the temperature control device (27) is integrated.

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