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), wherein 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) and the heat quantity (Q) emitted from the electrolysis process is determined, and wherein the inlet temperature (TIN) is set as a function of the emitted heat quantity (Q). The invention also relates to an electrolysis plant (10) designed to carry out the method.

Description

[0001] 2024PF00351

[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] Hydrogen is currently produced, for example, using proton exchange membrane (PEM) electrolysis or alkaline electrolysis. These electrolyzers use electrical energy to produce hydrogen and oxygen from the supplied water.

[0007] An electrolyzer typically consists of numerous electrolysis cells arranged adjacent to one another. Water is split into hydrogen and oxygen in these cells via electrolysis. Various electrolysis technologies and electrolyzers are known. In a PEM electrolyzer, distilled water is typically supplied as the reactant on the anode side and split into hydrogen and oxygen across 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...The alkali in aqueous solution is oxidized to oxygen at the anode. The protons pass through the proton-permeable membrane. Hydrogen is produced on the cathode side. The water is typically pumped from one side into the anode compartment and / or cathode compartment. See also 2024PF00351.

[0008] 2

[0009] In alkaline electrolysis, a membrane is used, designed as a semipermeable membrane or diaphragm, which selectively allows the passage of certain ions. Potassium hydroxide solution (KOH) with a typical concentration of 20-40% serves as the electrolyte. The gas-tight membrane, the so-called diaphragm, allows the transport of OH⁻ ions but simultaneously prevents the mixing of the resulting product gases.

[0010] In terms of plant engineering, 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., phase separation of water and the respective gaseous product gas in the phase mixture. It is common practice to connect several electrolysis cells and, furthermore, several electrolysis units via piping, and to feed the exiting gas-water mixture to a central gas separator. It is possible for several electrolysis stacks or electrolysis modules to be connected in series to form an electrolysis series or electrolysis string.

[0011] 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 variety of sensors are implemented. These sensors are attached to the cells, stacks, modules, or strings and record physical parameters such as pressure, temperature, conductivity, process water flow rate, cell voltage, and current. This results in the following in an electrolysis plant: 2024PF00351

[0012] 3

[0013] This results in considerable manufacturing and operating costs, as well as potential maintenance expenses, solely due to the complexity of the sensors. On the other hand, certain sensors are essential for operation and safety, which must be taken into account. Therefore, particularly in large electrolysis plants, there is an urgent need to reduce the cost of sensors as much as possible while simultaneously cutting costs, without losing essential information on electrolysis plant operating data, critical operating conditions, and the resulting necessary control interventions for both economical and safe plant operation.

[0014] 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 for carrying out the method.

[0015] The problem directed towards a process 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 the supply temperature of the process water as the temperature setpoint and determining the amount of heat released from the electrolysis process, and wherein the supply temperature is adjusted as a function of the amount of heat released.

[0016] 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, ska- 2024PF00351

[0017] 4

[0018] Large-scale electrolysis plants are created by multiplying electrolysis cells, which are bundled into electrolysis stacks to form a single electrolyzer. The latter scales through multiplication. Thus, a large-scale electrolysis plant can have multiple electrolyzers. Typically, each electrolysis stack comprises multiple axially stacked electrolysis cells and incorporates a large number of temperature sensors to provide operational and fail-safe functions. In some sensor topologies, the temperature sensors are also placed on both sides of the electrolysis cells, i.e., on the anode and cathode sides. This allows for up to twelve temperature measurement points, each with its own temperature sensor, per electrolysis module or electrolysis stack.

[0019] For industrial temperature measurements, temperature sensor systems based on a thermocouple or a resistance temperature sensor are typically used, usually equipped with a transmitter and an input / output module (I0 module). Input / output (I0) modules are essential components in industrial automation systems because 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 I0 modules are available to meet different application requirements, such as analog input, digital output, analog output, safety, IO-Link, and fieldbus modules. Therefore, the deployment, installation, and operation of such a temperature measurement system can be quite costly.The operational requirement for temperature measurements is to optimize the temperature of the electrolysis stack, since while a high temperature is important for the efficiency of the electrochemical reaction, it also negatively affects cell aging. The error-proof measurements—provided 2024PF00351—

[0020] 5

[0021] They are designed to protect, in particular, the integrity of the electrolysis stacks and to prevent critical conditions to protect operating personnel. In industrial environments, the various forms of measurement are usually separate; technically, a combination of operational and fail-safe functions is also possible, e.g., transmitters that output 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 to the heat loss. The process water is circulated in a process water circuit, and its temperature is controlled by setting the inlet temperature as the target temperature and determining the amount of heat dissipated during the electrolysis process. The inlet temperature of the process water is then adjusted based on the amount of heat dissipated, i.e., the heat loss.Direct temperature measurement of the process water at the electrolysis stacks can be largely dispensed with and is advantageously replaced by calculations that rely on other existing measured variables such as cell voltage, current, and the quantity derived from the amount of heat dissipated (loss heat), such as the electrolysis efficiency.

[0023] This approach represents a fundamental departure from the previously established operating and sensor concept, in which either a plurality of appropriately equipped temperature sensors are located downstream of an electrolysis stack or electrolysis module 2024PF00351

[0024] 6

[0025] are integrated or directly integrated into the electrolysis stacks. Both approaches involve a significant number of temperature sensors, interfaces, wiring effort, and potentially galvanic isolation – the electrolysis stacks operate at electrical potential, and are often confined to a small space, poorly accessible, or require extensive wiring.

[0026] In a particularly 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 amount of heat removed is determined from the efficiency thus determined.

[0027] In electrolysis plants, the cell voltage, stack voltage, and / or string voltage (as a series connection of several electrolysis stacks), as well as the electrolysis current, are typically already being measured. Knowing these values ​​allows the efficiency of the electrolysis to be determined at the string level of each electrolysis cell, stack, or string, and potentially converted to the respective (averaged) other values. This allows the existing sensor system to be used for indirect temperature control of the electrolysis process. Advantageously, the efficiency can be determined from the cooling of the electrolysis stacks via the amount of heat dissipated by the process water, i.e., the heat loss.This takes into account, for example, loss mechanisms such as heat radiation, enthalpy of evaporation, heat capacity of the produced product gases hydrogen and oxygen and of the process water, as well as the efficiency of the electrolysis.

[0028] In a particularly preferred embodiment of the method, a cell voltage, a module voltage, and / or a string voltage are optionally measured. The string voltage results from the electrical series connection of several electrolysis stacks 2024PF00351

[0029] 7

[0030] 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 electrically connected in parallel.

[0031] Therefore, in a particularly preferred embodiment of the method, temperature control is carried out during the operation of the electrolysis plant, which selectively 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, the efficiency of the electrolysis process and from electrical measured variables optionally the cell voltage, the module voltage and / or the string voltage.

[0032] In a further preferred embodiment of the method, the temperature setpoint is derived from the indirectly determined values ​​of the process water temperature of the corresponding stage during temperature control.

[0033] The advantageous evaluation procedure eliminates the need for physical temperature measuring points and sensors in each stage of the electrolysis plant, or at most allows for a significantly reduced number of temperature sensors to be installed at selected measuring points. In the latter case, the values ​​for the operating temperature indirectly derived using the evaluation procedure can be validated, compared, and verified. This makes the method qualifiable and allows the evaluation procedure and the determination of the temperature setpoint to be adapted as needed, particularly during the operating life of the electrolysis plant, e.g., with regard to degradation effects of the electrolysis cells and preferred operating modes concerning the setting and specification of a lifetime-specific operating temperature. 2024PF00351

[0034] 8

[0035] In a particularly preferred embodiment of the method, the temperature setpoint is indirectly formed as a characteristic temperature quantity derived from the values, wherein a selection of the maximum, the minimum, the median, the mean value, or sorting and selection of the nth measured value of a series of measured values ​​is carried out after a quantity sorting.

[0036] In practice, several derived temperature measurements are typically determined continuously or periodically 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 setpoint for the flow temperature can be determined from the derived temperature measurements at each stage and read into the temperature control system for processing. In particular, this allows the flow temperature of the process water to be set to the temperature setpoint depending on the amount of heat dissipated and to be readjusted during operation.

[0037] 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 its operating time. The optimum can therefore be adjusted over time throughout the operating period.

[0038] 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.

[0039] If, in addition, the quantity of process water or cooling water supplied, i.e., the mass or volume flow rate, is increased in the process 2024PF00351

[0040] 9

[0041] If the water cycle is kept constant, a frequency-controlled pump can potentially be omitted, saving costs. Furthermore, temperature control is advantageously limited to regulating only the supply temperature of the process water or cooling water. Depending on the electrolysis plant's design, temperature control can be implemented at the electrolysis stack or electrolysis string level. Combinations are also possible. Additionally, temperature sensors can be installed at selected measuring points within an electrolysis cell, module, or string. This allows for calibration of the indirect temperature control and evaluation model, as well as periodic checks to detect excessively high deviations or changes over time.In any 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. This allows not only the supply temperature in the supply line of the electrolysis storage system but also the output temperature in the return line of the electrolysis plant to be measured and monitored.

[0042] 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 and furthermore a temperature control device which is designed to regulate the supply temperature of the process water to a temperature setpoint.

[0043] In a particularly preferred embodiment, the temperature setpoint is preset in the electrolyte temperature control device. 2024PF00351

[0044] 10

[0045] bar, wherein the temperature setpoint can be indirectly determined from measured variables and read into the temperature control device, and wherein the temperature setpoint for the flow temperature is adjustable depending on the amount of heat dissipated. In a further preferred embodiment of the electrolysis plant, a programmable control device is provided, into which the temperature control device is integrated.

[0046] This advantageously enables comprehensive operational management and control of the electrolysis plant.

[0047] The invention is advantageous and flexibly applicable to various types of electrolysis systems, such as alkaline water electrolysis, PEM electrolysis, or an ion exchange membrane water electrolysis (AEMWE), wherein a temperature control device is implemented in the electrolysis system.

[0048] 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

[0049] FIG 1 an electrolyzer with a plurality of axially stacked electrolysis cells;

[0050] FIG 2 shows a schematic representation of a process diagram of an electrolysis plant with a temperature control device.

[0051] 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 each arranged as a group between two pressure plates 7 and connected together to form an electrolysis module 3. Instead of pressure plates 7, an embodiment with so-called end plates is also possible. 2024 PF00351

[0052] 11

[0053] Ten, cell, or bipolar plates are possible. The design with pressure plates 7 is therefore only an example. 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, intimate, and precise manner. 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 to the electrolysis modules B, C, and D of the electrolyzer. The switching devices 11 are electrically arranged 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.

[0054] 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 with a constant power density. Advantageously, this means that electrolysis modules 3 or electrolysis cells 5 are not operated at partial load. It is particularly advantageous to use electrolysis modules 2024 PF00351.

[0055] 12

[0056] The three modules can be bridged 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.

[0057] 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 output. 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 the components of an electrolysis plant 100 comprising electrolyzer 1 (see FIG. 2 below), 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) and recovered, i.e., treated and returned to the cycle via a return line 23 and fed into the feed line 15. Thus, the hydraulic system is configured such that the process water (H2O) is circulated in a closed loop, as shown in the 2024 PF00351.

[0058] 13

[0059] The circuit comprises a supply line 23 and a return line 21, into which the electrolyzer 1 is connected. During the electrolysis process, process heat Q is generated and, 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. IN This is required, which is monitored via a temperature sensor 25 and on which the operation of the electrolyzer 1 is controlled. The return temperature T measured in the return line 21 by means of a temperature sensor 25 OUT is greater than the flow temperature T due to the absorption of process heat during electrolysis operation. IN . For temperature control on the flow temperature T INA higher-level programmable control unit 29 with I / O interfaces is provided, which implements various functions for plant operation. For example, a temperature control unit 27 is integrated into the programmable control unit 29, which receives sensor data from the temperature sensor 25 for the flow temperature T. IN The data can be read in. Furthermore, an input value for the amount of heat Q released from the electrolysis process, i.e., the heat loss, can be read in or entered. The program logic of the temperature control device 27 outputs a temperature setpoint T. SET on which the operational flow temperature T 2NThe flow rate is set or adjusted depending on the heat quantity Q. Further operating data of 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. SET is 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. 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. 2024 PF00351

[0060] 14

[0061] Figure 2 shows a 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 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 can be connected to a higher-level programmable control unit 29 of the electrolysis plant 10. This control unit is configured to process and exchange operating data as well as measurement and control signals, and in particular to determine derived or calculated control signals, such as the amount of heat Q produced or removed from the electrolysis process, and to transmit these values ​​to the temperature control device 27 as input values. For this purpose, the control unit 29 is equipped with a processor for data processing.However, it is also possible that the temperature control device 27 is already integrated within the programmable control device 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 measured. z , at the electrolysis module level 3 j respective module or stack voltages UM, and at the level of one or more electrolysis units 1a, 1b, 1c 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 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 solely responsible for the production of product gases 2024 PF00351

[0062] 15

[0063] The amount of oxygen (O2) and hydrogen (H2) used is therefore P ei = p - Po, where P ei = U - I - Q = Po - ( 1-g ) ' Po, where P0= U·I denotes the electrical power used for the operation of the electrolysis process.

[0064] The process water circuit 31 comprises a supply line 23 and a return line 21. The process water circuit 31 passes 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.

[0065] A supply of fully demineralized fresh water via a feed line into 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. 2. 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. The temperature T is maintained during this process. P The process water H2O is regulated by setting the temperature setpoint T 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. This is based on the control concept 2024 PF00351.

[0066] 16

[0067] the flow temperature T INThe temperature is set and regulated depending on the amount of heat Q released. This involves temperature control that selectively intervenes at the electrolysis cell stage (5), the electrolysis module stage (3), or the electrolysis units (1a, 1b, 1c), the so-called electrolysis string. The temperature T is thereby... P of the process water H2O at one of the stages indirectly from the current I, the efficiency g of the electrolysis process and from electrical measurements, optionally the cell voltage U z , the module voltage U M and / or the string voltage U s determined only indirectly. The temperature setpoint T SET In the present control concept, it is advantageously determined indirectly as a quantity derived from the aforementioned measured values, so that a characteristic setpoint for the temperature setpoint T is obtained. SETThis 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 the 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. INis adapted to the 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 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 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 also- 2024 PF00351

[0068] 17

[0069] In this case, temperature control is limited solely to the 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.

Claims

2024 PF00351 18 Patent claims 1. Method for operating an electrolysis plant (10) comprising an electrolyzer (1) with a plurality of electrically connected electrolysis cells (5) 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 the temperature setpoint (T). SET ) the flow temperature (T IN ) of the process water (H2O) is specified and the amount of heat (Q) released from the electrolysis process is determined, and where the flow temperature (T) IN ) is adjusted depending on the amount of heat (Q) released.

2. Method according to claim 1, 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 amount of heat (Q) released is determined from the efficiency (g) thus determined.

3. Method according to claim 2, wherein optionally a cell voltage (U) z ), a module voltage (U M ) and / or a string voltage (U s ) is measured.

4. Method according to claim 3, 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 (U M) and / or the string voltage (U s ) is determined. 2024 PF00351 19 5. Method according to claim 4, wherein the temperature setpoint (T) is used for temperature control. SET ) from the indirectly determined temperature measurements (T P ) of the process water (H2O) of the corresponding stage is derived.

6. Method according to claim 5, wherein the temperature setpoint (T SET ) is indirectly formed as a characteristic temperature quantity derived from the measured values, whereby a selection of the maximum, the minimum, the median, the mean, or sorting and selection of the nth measured value of a series of measured values ​​is carried out after a quantity sorting.

7. 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).

8. Electrolysis system (10) for carrying out the method according to one of the preceding claims, comprising a plurality of electrolysis cells (5) electrically connected in series and integrated into a process water circuit (31), and further comprising a temperature control device (27) which is designed to control the flow temperature (T IN ) of the process water (H2O) to a target temperature (T SET ) is designed.

9. Electrolysis system ( 10 ) according to claim 7, wherein the temperature setpoint (T ) is set to the temperature control device (27 ). SET ) can be specified, where the temperature setpoint (T SET ) can be indirectly determined from measured quantities and read into the temperature control device (27 ), wherein the temperature setpoint (T SET ) for the flow temperature (T IN ) is adjustable depending on the amount of heat (Q) released.

10. Electrolysis system ( 10 ) according to claim 7 or 8, wherein a programmable control and regulating device (29) 2024 PF00351 20 is provided into which the temperature control device (27) is integrated.

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